Structure/Property Relationships in Irons and ... - ASM International

Metals Handbook Desk Edition, Second Edition 

J.R. Davis, Editor, p 153-173 

Structure/Property 

Relationships in Irons and Steels 

THE PROPERTIES of irons and steels are 

linked to the chemical composition, processing 

path, and resulting microstructure of the material; 

this correspondence has been known since the 

early part of the twentieth century. For a particular 

iron and steel composition, most properties depend 

on microstructure. These properties are called 

Bruce L. Bramfitt, Homer Research Laboratories, Bethlehem Steel Corporation 

Basis of Material Selection ............................................... 153 

Role of Microstructure .................................................. 155 

Ferrite ............................................................. 156 

Pearlite ............................................................ 158 

Ferrite-Pearl ite ....................................................... 160 

Bainite ............................................................ 162 

Martensite .................................... ...................... 164 

Austenite ........................................................... 169 

Ferrite-Cementite ..................................................... 170 

Ferrite-Martensite .................................................... 171 

Ferrite-Austenite ..................................................... 171 

Graphite ........................................................... 172 

Cementite .......................................................... 172 

This Section was adapted from Materials 5election and Design, Volume 20, ASM Handbook, 1997, 

pages 357-382. Additional information can also be found in the Sections on cast irons and steels which 

immediately follow in this Handbook and by consulting the index. 

structure-sensitive properties, for example, yield 

strength and hardness. The structure-insensitive 

properties, for example, electrical conductivity, 

are not discussed in this Section. Processing is a 

means to develop and control microstructure, for 

example, hot rolling, quenching, and so forth. In 

this Section, the role of these factors is described 

Copyright © 1998 ASM International® 

All rights reserved. 

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in both theoretical and practical terms, with par- 

ticular focus on the role of microstructure. 

Basis of Material Selection 

In order to select a material for a particular 

component, the designer must have an intimate 

" "o" - grade 50). 2% nital + 4% picral etch. 200x Fig. :2 Microstructu 

repearlite interlamellar°f a typicalspacing.fUllY2%pearlitiCnital + 4%rail steelpicralShowingetch. 500xthe characteristic fine

154/Structure/Property Relationships in Irons and Steels 

knowledge of what properties are required. Con- 

sideration must be given to the environment 

(corrosive, high temperature, etc.) and how the 

component will be fabricated (welded, bolted, 

etc.). Once these property requirements are es- 

tablished the material selection process can be- 

gin. Some of the properties to be considered 

are: 

Mechanical properties Other properties/ 

Strength characteristics 

Tensile strength (ultimate Formability 

strength) Dmwability 

Yield strength Stretchability 

Compressive strength Bendability 

Hardness Wear resistance 

Toughness Abrasion resistance 

Notch toughness Galling resistance 

Fracture toughness Sliding wear resistance 

Ductility Adhesive wear resistance 

Total elongation Machinability 

Reduction in area Weldability 

Fatigue resistance 

Table 1 lists mechanical properties of selected steels 

in various heat-treated or cold-worked conditions. 

In the selection process, what is required for 

one application may be totally inappropriate for 

another application. For example, steel beams for 

a railway bridge require a totally different set of 

properties than the steel rails that are attached to 

the wooden ties on the bridge deck. In designing 

the bridge, the steel must have sufficient strength 

to withstand substantial applied loads. In fact, 

the designer will generally select a steel with 

higher strength than actually required. Also, the 

designer knows that the steel must have fracture 

toughness to resist the growth and propagation of 

cracks and must be capable of being welded so 

that structural members can be joined without 

sacrificing strength and toughness. The steel 

bridge must also be corrosion resistant. This can 

be provided by a protective layer of paint. If 

painting is not allowed, small amounts of certain 

alloying elements such as copper and chromium 

can be added to the steel to inhibit or reduce 

corrosion rates. Thus, the steel selected for the 

bridge would be a high-strength low-alloy 

(HSLA) structural steel such as ASTM A572, 

grade 50 or possibly a weathering steel such as 

ASTM A588. A t);pical HSLA steel has a ferrite- 

pearlite microstructure as seen in Fig. 1 and is 

microalloyed with vanadium and/or niobium for 

strengthening. (Microalloying is a term used to 

describe the process of using small additions of 

carbonitride forming elements--titanium, vana- 

dium, and niobium--to strengthen steels by grain 

refinement and precipitation hardening.) 

On the other hand, the steel rails must have 

high strength coupled with excellent wear resis- 

tance. Modem rail steels consist of a fully pearli- 

tic microstructure with a fine pearlite interlamel- 

lar spacing, as shown in Fig. 2. Pearlite is unique 

because it is a lamellar composite consisting of 

88% soft, ductile ferrite and 12% hard, brittle 

cementite (Fe3C). The hard cementite plates pro- 

vide excellent wear resistance, especially when 

embedded in soft ferrite. Pearlitic steels have 

high strength and are fully adequate to support 

heavy axle loads of modem locomotives and 

freight cars. Most of the load is applied in com- 

pression. Pearlitic steels also have relatively 

poor toughness and cannot generally withstand 

impact loads without failure. The rail steel could 

not meet the requirements of the bridge builder, 

Table I Mechanical properties of selected steels 

Tensile Yield 

strength strength 

Steel Condition MPa ksi MPa kd 

Elongation 

iaS0muma, Reduction Hardness, 

Carbon steel bar(a) 

1006 Hot rolled 295 43 165 24 30 55 86 

Colddrawn 330 48 285 41 20 45 95 

1008 Hot rolled 305 44 170 24.5 30 55 86 

Colddrawn 340 49 285 41.5 20 45 95 

1010 Hot rolled 325 47 180 26 28 50 95 

Cold drawn 365 53 305 44 20 40 105 

1012 Hot rolled 330 48 185 26.5 28 50 95 

Colddrawn 370 54 310 45 19 40 105 

1015 Hot rolled 345 50 190 27.5 28 50 101 

Cold drawn 385 56 325 47 18 40 111 

1016 Hot rolled 380 55 205 30 25 50 110 

Cold dmwn 420 61 350 51 18 40 121 

1017 Hot rolled 365 53 200 29 26 50 105 

Cold drawn 405 59 340 49 18 40 116 

1018 Hot rolled 400 58 220 32 25 50 116 

Cold drawn 440 64 370 54 15 40 126 

1019 Hot rolled 405 59 225 32.5 25 50 116 

Cold drawn 455 66 380 55 15 40 131 

1020 Hot rolled 380 55 205 30 25 50 l 1 l 

Cold drawn 420 61 350 51 15 40 121 

1021 Hot rolled 420 61 230 33 24 48 116 

Colddrawn 470 68 395 57 15 40 131 

1022 Hot rolled 425 62 235 34 23 47 121 

Colddrawn 475 69 400 58 15 40 137 

1023 Hot rolled 385 56 215 31 25 50 111 

Cold drawn 425 62 360 52.5 15 40 121 

1524 Hot rolled 510 74 285 41 20 42 149 

Cold drawn 565 82 475 69 12 35 163 

1025 Hot rolled 400 58 220 32 25 50 116 

Colddrawn 440 64 370 54 15 40 126 

1026 Hot rolled 440 64 240 35 24 49 126 

Colddrawn 490 71 415 60 15 40 143 

1527 Hot rolled 515 75 285 41 18 40 149 

Colddmwn 570 83 485 70 12 35 163 

1030 Hot rolled 470 68 260 37.5 20 42 137 

Cold drawn 525 76 440 64 12 35 149 

1035 Hot rolled 495 72 270 39.5 18 40 143 

Colddrawn 550 80 460 67 12 35 163 

1536 Hot rolled 570 83 315 45.5 16 40 163 

COld drawn 635 92 535 77.5 12 35 187 

1037 Hot rolled 510 74 280 40.5 18 40 143 

Cold drawn 565 82 475 69 12 35 167 

1038 Hot rolled 515 75 285 41 18 40 149 

Colddrawn 570 83 485 70 12 35 163 

1039 Hot rolled 545 79 300 43.5 16 40 156 

Cold drawn 605 88 510 74 12 35 179 

1040 Hot rolled 525 76 290 42 18 40 149 

Colddrawn 585 85 490 71 12 35 170 

1541 Hot rolled 635 92 350 51 15 40 187 

Cold drawn 705 102.5 600 87 10 30 207 

Annealed, cold drawn 650 94 550 80 10 45 184 

1042 Hot rolled 550 80 305 44 16 40 163 

Colddrawn 6!5 89 515 75 12 35 179 

Normalized, cold drawn 585 85 505 73 12 45 179 

1043 Hot rolled 565 82 310 45 16 40 163 

Cold drawn 625 91 530 77 12 35 179 

Normalized, cold drown 600 87 515 75 12 45 179 

1044 Hot rolled 550 80 305 44 16 40 163 

1045 Hot rolled 565 82 310 45 16 40 163 

Colddmwn 625 91 530 77 12 35 179 


1046 Hot rolled 585 85 325 47 15 40 170 

Cold drawn 650 94 545 79 12 35 187 


1547 Hot rolled 650 94 360 52 15 30 192 

Cold drawn 710 103 605 88 10 28 207 


1548 Hot rolled 660 96 365 53 14 33 197 

Colddrawn 735 106.5 615 89.5 10 28 217 

Annealed, cold drawn 645 93.5 540 78.5 10 35 192 

(continued) 

(a) All values are estimated minimum values; type 1100 series steels are rated on the basis of 0.10% max Si or coarse-grain melt- 

ing practice; the mechanical properties shown are expected minimums for the sizes ranging from 19 to 31.8 mm (0.75 to 1.25 

in.). (b) Most data are for 25 mm (1 in.) diam bar. Source: Ref 1

Table I (continued) 

Tensile Yield 


Steel Condition MPa ksi MPa ksi 

Structure/Property Relationships in Irons and Steels / 155 

Elongation 

in 50 ram, Reduction Hardness, 

% ~a area, % HB 

Carbon steel bar(a) (continued) 

1049 Hot rolled 600 87 330 48 15 35 179 

Cold drawn 670 97 560 81.5 10 30 197 


1050 Hot roned 620 90 340 49.5 15 35 179 

Cold da'awn 690 100 580 84 10 30 197 


1552 Hot rolled 745 108 410 59.5 12 30 217 


1055 Hot rolled 650 94 355 51.5 12 30 192 


1060 Hot rolled 675 98 370 54 12 30 201 

Spheroidized annealed, cold drawn 620 90 485 70 10 45 183 

1064 Hot rolled 670 97 370 53.5 12 30 201 


1065 Hot rolled 690 100 380 55 12 30 207 


1070 Hot rolled 705 102 385 56 12 30 212 


1074 Hot rolled 725 105 400 58 12 30 217 


1078 Hot rolled 690 1130 380 55 12 30 207 

Spheroidized annealed, cold drawn 650 94 500 72.5 10 40 192 

1080 Hot rolled 770 112 425 61.5 10 25 229 


1084 Hot rolled 820 119 450 65.5 10 25 241 


1085 Hot rolled 835 121 460 66.5 10 25 248 

Spheroidized annealed, cold drawn 695 100.5 540 78 10 40 192 

1086 Hot rolled 770 112 425 61.5 10 25 229 

Spheroidized aimealed, cold drawn 670 97 510 74 10 40 192 

1090 Hot rolled 840 122 460 67 10 25 248 


1095 Hot rolled 825 120 455 66 10 25 248 


1211 Hot rolled 380 55 230 33 25 45 121 

Colddrawn 515 75 400 58 10 35 163 

1212 Hot rolled 385 56 230 33.5 25 45 121 

Cold drawn 540 78 415 60 10 35 167 

1213 Hot rolled 385 56 230 33.5 25 45 121 

Cold drawn 540 78 415 60 10 35 167 

12L14 Hot rolled 395 57 235 34 22 45 121 

Cold drawn 540 78 415 60 10 35 163 

1108 Hot roUed 345 50 190 27.5 30 50 101 

Colddrawn 385 56 325 47 20 40 121 

1109 Hot rolled 345 50 190 27.5 30 50 101 

Cold drawn 385 56 325 47 20 40 121 

11i7 Hot roned 425 62 235 34 23 47 121 

Colddrawn 475 69 400 58 15 40 137 

1118 Hot rolled 450 65 250 36 23 47 131 

Colddrawn 495 72 420 61 15 40 143 

1119 Hot roned 425 62 235 34 23 47 121 

Colddrawn 475 69 400 58 15 40 137 

1132 Hot roUed 570 83 315 45.5 16 40 167 

Cold drawn 635 92 530 77 12 35 183 

~1137 Hot roiled 605 88 330 48 15 35 179 

Colddrawn 675 98 565 82 10 30 197 

1140 Hot rolled 545 79 300 43.5 16 40 156 

Colddrawn 605 88 510 74 12 35 170 

1141 Hot roned 650 94 355 51.5 15 35 187 

Colddrawn 725 105.1 605 88 10 30 212 

1144 Hot rolled 670 97 365 53 15 35 197 

Colddrawn 745 108 620 90 10 30 217 

1145 Hot rolled 585 85 325 47 15 40 170 

Colddrawn 650 94 550 80 12 35 187 

1146 Hot roUed 585 85 325 47 15 40 170 

Cold drawn 650 94 550 80 12 35 187 

1151 Hot rolled 635 92 350 50.5 15 35 187 

Colddrawn 705 102 595 86 10 30 207 




in.). (b) Most data are for 25 mm (1 in.) diam bar. Source: Ref 1 

and the HSLA structural steel could not meet the 

requirements of the civil engineer who designed 

the bridge or the rail system. 

A similar case can be made for the selection of 

cast irons. A cast machine housing on a large 

lathe requires a material with adequate strength, 

rigidity, and durability to support the applied 

load and a certain degree of damping capacity in 

order to rapidly attenuate (dampen) vibrations 

from the rotating parts of the lathe. The cast iron 

jaws of a crusher require a material with substan- 

tial wear resistance. For this application, a cast- 

ing is required because wear-resistant steels are 

very difficult to machine. For the machine hous- 

ing, gray cast iron is selected because it is rela- 

tively inexpensive, can be easily cast, and has the 

ability to dampen vibrations as a result of the 

graphite flakes present in its microstructure. 

These flakes are dispersed throughout the ferrite 

and pearlite matrix (Fig. 3). The graphite, being a 

major nonmetallic constituent in the gray iron, 

provides a tortuous path for sound to travel 

through the material. With so many flakes, sound 

waves are easily reflected and the sound damp- 

ened over a relatively short distance. However, 

for the jaw crusher, damping capacity is not a 

requirement. In this case, an alloy white cast iron 

is selected because of its high hardness and wear 

resistance. The white cast iron microstructure 

shown in Fig. 4 is graphite free and consists of 

martensite in a matrix of cementite. Both of these 

constituents are very hard and thus provide the 

required wear resistance. Thus, in this example 

the gray cast iron would not meet the require- 

ments for the jaws of a crusher and the white cast 

iron would not meet the requirements for the 

lathe housing. 

Role of Microstructure 

In steels and cast irons, the microstructural 

constituents have the names ferrite, pearlite, 

bainite, martensite, cementite, and austenite. In 

most all other metallic systems, the constituents 

are not named, but are simply referred to by a 

Greek letter (ct, 13, Y, etc.) derived from the loca- 

tion of the constituent on a phase diagram. Fer- 

rous alloy constituents, on the other hand, have 

been widely studied for more than 100 years. In 

the early days, many of the investigators were 

petrographers, mining engineers, and geologists. 

Because minerals have long been named after 

their discoverer or place of origin, it was natural 

to similarly name the constituents in steels and 

cast irons. 

It can be seen that the four examples described 

above have very different microstructures: the 

structural steel has a ferrite plus pearlite micro- 

structure; the rail steel has a fully pearlitic mi- 

crostructure; the machine housing (lathe) has a 

ferrite plus pearlite matrix with graphite flakes; 

and the jaw crusher microstructure contains 

martensite and cementite. In each case, the mi- 

crostructure plays the primary role in providing 

the properties desired for each application. From 

these examples, one can see how material proper- 

ties can be tailored by microstructural manipula- 

tion or alteration. Knowledge about microstruc- 

ture is thus paramount in component design and 

alloy development. In the paragraphs that follow, 

each microstructural constituent is described 

with particular reference to the properties that 

can be developed by appropriate manipulation of 

the microstructure through deformation (e.g., hot 

and cold rolling) and heat treatment. Further de-

156 / Structure/Property Relationships in Irons and Steels 

tails about these microstructural constituents can 

be found in Ref 2 to 6. 

Ferrite 

A wide variety of steels and cast irons fully 

exploit the properties of ferrite. However, only a 

few commercial steels are completely ferritic. An 

example of the microstructure of a fully ferritic, 

ultralow carbon steel is shown in Fig. 5. 

Ferrite is essentially a solid solution of iron 

containing carbon or one or more alloying ele- 

ments such as silicon, chromium, manganese, 

and nickel. There are two types of solid solu- 

tions: interstitial and substitutional. In an inter- 

stitial solid solution, elements with small atomic 

diameter, for example, carbon and nitrogen, oc- 

cupy specific interstitial sites in the body-cen- 

tered cubic (bcc) iron crystalline lattice. These 

sites are essentially the open spaces between the 

larger iron atoms. In a substitutional solid solu- 

tion, elements of similar atomic diameter replace 

or substitute for iron atoms. The two types of 

solid solutions impart different characteristics to 

ferrite. For example, interstitial elements like 

carbon and nitrogen can easily diffuse through 

the open bcc lattice, whereas substitutional ele- 

ments like manganese and nickel diffuse with 

great difficulty. Therefore, an interstitial solid 

solution of iron and carbon responds quickly dur- 

ing heat treatment, whereas substitutional solid 

solutions behave sluggishly during heat treat- 

ment, such as in homogenization. 

According to the iron-carbon phase diagram 

(Fig. 6a), very little carbon (0.022% C) can dis- 

solve in ferrite (ctFe), even at the eutectoid tem- 

perature of 727 °C (1330 °F). (The iron-carbon 

phase diagram indicates the phase regions that 

exist over a wide carbon and temperature range. 

The diagram represents equilibrium conditions. 

Figure 6(b) shows an expanded iron-carbon dia- 

gram with both the euteetoid and eutectic re- 

gions.) At room temperature, the solubility is an 

order of magnitude less (below 0.005% C). How- 

ever, even at these small amounts, the addition of 

carbon to pure iron increases the room-tempera- 

ture yield strength of iron by more than five 

times, as seen in Fig. 7. If the carbon content 

exceeds the solubility limit of 0.022%, the car- 

bon forms another phase called cementite (Fig. 

8). Cementite is also a constituent of pearlite, as 

seen in Fig. 9. The role of cementite and pearlite 

on the mechanical properties of steel is discussed 

below. 

The influence of solid-solution elements on the 

yield strength of ferrite is shown in Fig. 10. Here 

one can clearly see the strong effect of carbon on 

increasing the strength of ferrite. Nitrogen, also 

an interstitial element, has a similar effect. Phos- 

phorus is also a ferrite strengthener. In fact, there 

are commercially available steels containing 

phosphorus (up to 0.12% P) for strengthening. 

These steels are the rephosphorized steels (type 

1211 to 1215 series). Mechanical property data 

for these steels can be found in Table 1. 

In Fig. 10, the substitutional solid solution ele- 

ments of silicon, copper, manganese, molybde- 

num, nickel, aluminum, and chromium are shown 

to have far less effect as ferrite strengtheners 

than the interstitial elements. In fact, chromium, 

nickel, and aluminum in solid solution have very 

little influence on the strength of ferrite. 

In addition to carbon (and other solid-solution 

elements), the strength of a ferritic steel is also 

]'able 1 (continued) 

Steel Condition 

Low-alloy steels(b) 

1340 Normalized at 870 °C (1600 °F) 834 

Annealed at 800 °C (1475 °F) 703 

3140 Normalized at 870 °C (1600 oF) 889 

Annealed at 815 °C (1500 °F) 690 


Annealed at 865 °C (1585 °F) 560 

Water quenched from 855 °C (1575 °F) 1040 

and tempered at 540 °C (1000 °F) 


Annealed at 815 °C (1500 °F) 655 

Water quenched from 845 °C ( 1550 °F) 1075 


4150 Normalized at 870 °C ( 1600 °F) 1160 

Annealed at 830 °C (1525 °F) 731 

oil quenched from 830 °C (1525 °F) 1310 



Annealed at 850 °C (1560 °F) 580 


Annealed at 810 °C (1490 oF) 745 

Oil quenched from 800 °C (1475 °F) 1207 



Annealed at 915 °C (1675 °F) 450 




Annealed at 815 °C (1500 °F) 685 


Annealed at 830 °C (1525 °F) 570 










and tempered at 540 °C (1000 oF) 





8620 Normalized at 915 °C 0675 °F) 635 



Annealed at 845 °C (1550 °F) 565 

Water quenched from 845 °C (1550 °F) 931 


8650 Normalized at 870 °C (1600) 1025 

Annealed at 795 °C ( 1465 °F) 715 

oil quenched from 800 °C (1475 °F) 1185 

and tempered at 540 °C ( 1000 °F) 



Oil quenched from 830 °C ( 1525 °F) 1225 


9255 Normalized at 900 °C ( 1650 oF) 931 



and tempered at 540 °C ( 1000 oF) 



Ferritie stainless steels(b) 

405 Annealed bar 

Cold draw n bar 



Tensile Yield 


MPa ksi MPa ksi 

Elongatba 

inSOnma, l~lt~tion Hardm~ 

% ~a area, % lib 

121 558 81 22.0 63 248 

102 434 63 25.5 57 207 

129 600 87 19.7 57 262 

100 420 61 24.5 51 197 

97 435 63 25.5 59.5 197 

81 460 67 21.5 59.6 217 

151 979 142 18.1 63.9 302 

148 655 95 17.7 46.8 302 

95 915 60 25.7 56,9 197 

156 986 143 15.5 56,9 311 

168 731 106 11.7 30,8 321 

106 380 55 20.2 40,2 197 

190 1215 176 13.5 47.2 375 

115 460 67 20.8 51 235 

84 425 62 29.0 58 163 

186 862 125 12.2 36.3 363 

108 470 68 22.0 50.0 217 

175 1145 166 14.2 45.9 352 

75 350 51 32.5 69.4 143 

65 330 48 31.2 62.8 121 

83 365 53 29.0 66.7 174 

74 370 54 31.3 60.3 149 

110 485 70 24.0 59.2 229 

99 460 67 22.3 58.8 197 

115 470 68 22.7 59.2 229 

83 290 42 28.6 57.3 167 

141 841 122 18.5 58.9 293 

126 530 77 20.7 58.7 255 

98 360 52 22.0 43.7 197 

159 1000 145 16.4 52.9 311 

149 650 94 18.2 50.7 285 

105 275 40 17.2 30.6 197 

166 1005 146 14.5 45.7 341 

136 615 89 21.8 61.0 269 

97 415 60 23.0 48.4 197 

174 1160 168 14.5 48.2 352 

92 360 52 26.3 59.7 183 

78 385 56 31.3 62.1 149 

94 425 62 23.5 53.5 187 

82 370 54 29.0 58.9 156 

135 850 123 18.7 59.6 269 

149 690 100 14 45.0 302 

104 385 56 22.5 46.0 212 

172 1105 160 14.5 49.1 352 

135 605 88 16.0 47.9 269 

101 415 60 22.2 46.4 201 

178 1130 164 16.0 53.0 352 

135 580 84 19.7 43.4 269 

113 485 70 21.7 41.1 229 

164 924 134 16.7 38.3 321 

132 570 83 18.8 58.1 269HRB 

119 450 65 17.3 42.1 241HRB 

483 70 276 40 30 60 150 

586 85 483 70 20 60 185 

450 65 240 35 25 75HRB 

517 75 310 45 30 --65" 155 

(confnued) 



in.). (b) Most data are for 25 mm (1 in.) diam bar. Source: Ref I

Table 1 (continued) 

Tensile 

strength 

Steel Ccmdition MPa ksi 

Ferritic stainless steels(b) (continued) 

430 (cont'd) Annealed and cold drawn 586 85 

442 Annealed bar 515 75 

Annealed at 815 °C (1500 °F) and cold 545 79 

worked 


Annealed at 815 °C (1500 °F) and cold 607 88 

drawn 

Martensilic stainless steels(b) 


Tempered bar 765 111 

410 Oil quenched from 980 °C ( 1800 °F); 1085 158 

tempered at 540 °C (1000 °F);.16 nun 

(0.625 in.) bar 

Oil quenched from 980 °C (1800 °F); 1525 221 

tempered at 40 °C (104 °F); 16 mm 

(0.625 in.) bar 


Cold drawn bar 895 130 


tempered at 650 °C (1200 oF) 


Annealed and cold drawn 760 110 




tempered at 650 °C (1200 oF) 


tempered at 40 °C (104 °F) 

440C Annealed bar 760 110 

Annealed and cold drawn bar 860 125 

Hardened and tempered at 315 °C 1970 285 

(6OO °F) 

Austenitle stainless steels(b) 

201 Annealed 760 110 

50% hard 1035 150 

Full hard 1275 185 

Extra hard 1550 225 


Annealed sheet 655 95 

50% hard sheet 1030 150 

301 Annealed 725 105 

50% hard 1035 150 

Full hard 1415 205 

302 Annealed strip 620 90 

25% hard strip 860 125 

Annealed bar 585 85 


Colddrawn 690 100 



Cold-drawn high tensile 860 125 

305 Annealed sheet 585 85 








Annealed and cold-drawn bar 620 90 





Annealed and cold-drawn bar 655 95 






Yield 

strength 

MPa ksi 

Elongation 

in 50ram, 

% 

483 70 20 65 185 

310 45 30 50 160 

427 62 35.5 79 92HRC 

345 50 25 45 86HRB 

462 67 26 64 96HRB 

275 40 35 70 82HRB 

585 85 23 67 97HRB 

1005 146 13 70 ... 

1225 178 15 64 45HRB 

620 90 20 60 235 

795 115 15 58 270 

800 116 19 58 ... 

345 50 25 55 195 

690 100 14 40 228 

655 95 20 55 260 

760 110 15 35 270 

738 107 20 64 ... 

1140 166 17 59 45HRC 

450 65 14 25 97HRB 

690 100 7 20 260 

1900 275 2 10 580 

380 55 52 ... 87HRB 

760 ll0 12 ... 32HRC 

965 140 8 ... 41HRC 

1480 215 1 ... 43HRC 

275 40 40 ...... 

310 45 40 ...... 

760 110 10 _ ... 

275 40 60 70' ... 

655 95 54 61 ... 

1330 193 6 ... 

275 40 55 ... 80HRB 

515 75 12 _ 25HRC 

240 35 60 70" 80HRB 

240 35 50 55 160 

415 60 40 53 228 

235 34 60 70 149 

415 60 45 ... 212 

655 95 25 ... 275 

260 38 50 _ 80HRB 

205 30 55 65' 150 

275 40 45 65 83HRB 

310 45 45 _ 85HRB 

275 40 45 65' 160 

345 50 45 60 180 

290 42 50 _ 79HRB 

240 35 60 70" 149 

415 60 45 65 190 

275 40 45 ... 85HRB 

275 40 50 ... 160 

240 35 45 _ 80HRB 

240 35 55 65' 150 

415 60 40 60 185 

260 38 40 ... ... 

290 42 45 ... 80HRB 

275 40 45 _ 85HRB 

240 35 50 65" 160 



in.). (b) Most data are for 25 mm (1 in.) diam bar. Source: Ref 1 


determined by its grain size according to the 

Hall-Petch relationship: 

Reduction Hardness, Gy = Go + kyd -1/2 (Eq 1) 

in area, % HB 

where Oy is the yield strength (in MPa), ~o is a 

constant, ky is a constant, and d is the grain diame- 

ter (in mm). 

The grain diameter is a measurement of size of 

the ferrite grains in the microstructure, for exam- 

ple, note the grains in the ultralow carbon steel in 

Fig. 5. Figure 11 shows the Hall-Petch relation- 

ship for a low-carbon fully ferritic steel. This 

relationship is extremely important for under- 

standing structure-property relationships in 

steels. Control of grain size through ther- 

momechanical treatment, heat treatment, and/or 

microalloying is vital to the control of strength 

and toughness of most steels. The role of grain 

size is discussed in more detail below. 

There is a simple way to stabilize ferrite, 

thereby expanding the region of ferrite in the 

iron-carbon phase diagram, namely by the addi- 

tion of alloying elements such as silicon, chro- 

mium, and molybdenum. These elements are 

called ferrite stabilizers because they stabilize 

ferrite at room temperature through reducing the 

amount of y solid solution (austenite) with the 

formation of what is called a y-loop as seen at the 

far left in Fig. 12. This iron-chromium phase dia- 

gram shows that ferrite exists up above 12% Cr 

and is stable up to the melting point (liquidus 

temperature). An important fully ferritic family 

of steels is the iron-chromium ferritic stainless 

steels. These steels are resistant to corrosion, and 

are classified as type 405, 409, 429, 430, 434, 

436, 439, 442, 444, and 446 stainless steels. 

These steels range in chromium content from 11 

to 30%. Additions of molybdenum, silicon, nio- 

bium, aluminum, and titanium provide specific 

properties. Ferritic stainless steels have good 

ductility (up to 30% total elongation and 60% 

reduction in area) and formability, but lack 

strength at elevated temperatures compared with 

austenitic stainless steels. Room-temperature 

yield strengths range from 170 to about 440 MPa 

(25 to 64 ksi), and room-temperature tensile 

strengths range from 380 to about 550 MPa (55 

to 80 ksi). Table 1 lists the mechanical properties 

of some of the ferritic stainless steels. Type 409 

stainless steel is widely used for automotive ex- 

haust systems. Type 430 free-machining stainless 

steel has the best machinability of all stainless 

steels other than that of a low-carbon, free-ma- 

chining martensitic stainless steel (type 41.6). 

Another family of steels utilizing a ferrite sta- 

bilizer (y-loop) are the iron-silicon ferritic alloys 

containing up to about 6.5% Si (carbon-free). 

These steels are of commercial importance be- 

cause they have excellent magnetic permeability 

and low core loss. High-efficiency motors and 

transformers are produced from these iron-sili- 

con electrical steels (aluminum can also substi- 

tute for silicon in them). 

Over the past 20 years or so, a new breed of 

very-low-carbon fully ferritic sheet steels has 

emerged for applications requiring exceptional 

formability (see Fig. 5). These are the intersti- 

tial-free (IF) steels for which carbon and nitro- 

gen are reduced in the steelmaking process to 

very low levels, and any remaining interstitial 

carbon or nitrogen is tied up with small amounts 

of alloying elements (e.g., titanium or niobium) 

that form preferentially carbides and nitrides.


Table I (continued) 

qI~mBe Yield 

st~ngth strength 

Sted Cand~laa MPa k~ MPa I~ 

Austenilic stainless steels(b) (continued) 

347 (eont'd) Annealedandcolddrawnbar 690 

384 Annealed wire 1040 °C (1900 °F) 515 

Maraging steels(b) 

18Ni(250) Annealed 965 

Aged bar 32 mm (1.25 in.) 1844 

Aged sheet 6 mm (0.25 in.) 1874 


Aged bar 32 mm (1.25 in.) 2041 



Aged bar 32 mm (l.25 in.) 2391 


Elongation 

inS0mm, Reduction Hardness, 

% in area, % liB 

100 450 65 40 60 212 

75 240 35 55 72 70HRB 

140 655 95 17 75 30 HRC 

269 1784 259 11 56.5 51.8 HRC 

272 1832 266 8 40.8 50.6HRC 

150 758 110 18 72 32HRC 

296 2020 293 11.6 55.8 54.7 HRC 

315 2135 310 7.7 35 55.1HRC 

165 827 120 18 70 35 HRC 

347 2348 341 7.6 33.8 58.4 HRC 

356 2395 347 3 15.4 57.7 HRC 

(a) All values are estimated minimum values; type 1100 series steels ate rated on the basis of 0.10% max Si or coarse-grain melt- 


in.). (b) Most data are for 25 mm (1 in.) diam bar. Some: Ref 1 

These steels have very low strength, but are used 

to produce components that are difficult or im- 

possible to form from other steels. Very-low-car- 

bon, fully ferritic steels (0.001% C) are now be- 

ing manufactured for automotive components 

that harden during the paint-curing cycle. These 

steels are called bake-hardening steels and have 

controlled amounts of carbon and nitrogen that 

combine with other elements, such as titanium 

and niobium, during the baking cycle (175 °C, or 

350 °F, for 30 min). The process is called aging, 

and the strength derives from the precipitation of 

titanium/niobium carbonitrides at the elevated 

temperature. 

Another form of very-low-carbon, fully ferritic 

steel is motor lamination steel. The carbon is re- 

moved from these steels by a process known as 

decarburization. The decarburized (carbon-free) 

ferritic steel has good permeability and suffi- 

ciently low core loss (not as low as the iron-sili- 

con alloys) to be used for electric motor lamina- 

tions, that is, the stacked steel layers in the rotor 

and stator of the motor. 

As noted previously, a number of properties 

are exploited in fully ferritic steels: 

• Iron-silicon steels: Exceptional electrical 

properties 

• Iron-chromium steels: Good corrosion resis- 

tance 

• Interstitial-free steels: Exceptional forma- 

bility 

• Bake-hardening steels: Strengthens during 

paint cure cycle 

• Lamination steels: Good electrical properties 

PearlRe 

As the carbon content of steel is increased be- 

yond the solubility limit (0.02% C) on the iron- 

carbon binary phase diagram, a constituent called 

pearlite forms. Pearlite is formed by cooling the 

steel through the eutectoid temperature (the tem- 

perature of 727 °C in Fig. 6) by the following 

reaction: 

Austenite ~ cementite + ferrite ffXl2) 

The cementite and ferrite form as parallel plates 

called lamellae (Fig. 13). This is essentially a 

composite microstructure consisting of a very 

hard carbide phase, cementite, and a very soft and 

ductile ferrite phase. A fully pearlitic microstruc- 

ture is formed at the eutectoid composition of 

0.78% C. As can be seen in Fig. 2 and 13, pearlite 

forms as colonies where the lamellae are aligned 

in the same orientation. The properties of fully 

pearlitic steels are determined by the spacing be- 

tween the ferrite-cementite lamellae, a dimension 

called the interlamellar spacing, X, and the colony 

size. A simple relationship for yield strength has 

been developed by Heller (Ref 10) as follows: 

fly = -85.9 + 8.3 (X -t/2) (Eq 3) 

where fly is the 0.2% offset yield strength (in 

MPa) and X is the interlamellar spacing (in mm). 

Figure 14 shows Heller's plot of strength versus 

interlamellar spacing for fully pearlitic eutectoid 

steels. 

It has also been shown by Hyzak and Bernstein 

(Ref 11) that strength is related to interlamellar 

spacing, pearlite colony size, and prior-austenite 

grain size, according to the following relation- 

ship: 

YS = 52.3 + 2.18 (~-1/2) -0.4 (de -L'2) -2.88 (d-1/2)(Eq 4) 

where YS is the yield strength (in MPa), d e is the 

pearlite colony size (in mm), and d is the prior- 

austenite grain size (in mm). From Eq 3 and 4, it 

can be seen that the steel composition does not 

have a major influence on the yield strength of a 

fully pearlitic eutectoid steel. There is some solid- 

Fig, 3 Microstructure of a gray cast iron with a ferrite-pearlite matrix. Note the graphite Fig. 4 Microstructure of an alloy white cast iron. White constituent is cementite and the 

flakes dispersed throughout the matrix. 4% picral etch. 320x. Courtesy of A.O. darker constituent is martensite with some retained austenite. 4% picral etch. 

Benscoter, Lehigh University 250x. Courtesy ofA.O. Benscoter, Lehigh University

Fig. 5 Microstructure of a fully ferritic, ultralow carbon 

steel. Marshalls etch + HF, 300x. Courtesy of 

A.O. Benscoter, Lehigh University 

solution strengthening of the ferrite in the lamel- 

lar structure (see Fig. 10). 

The thickness of the cementite lamellae can 

also influence the properties of pearlite. Fine ce- 

mentite lamellae can be deformed, compared 

with coarse lamellae, which tend to crack during 

deformation. 

Although fully pearlitic steels have high 

strength, high hardness, and good wear resis- 

tance, they also have poor ductility and tough- 

ness. For example, a low-carbon, fully ferritic 

¢D 

O. 

E 

1180 

1140 

1100 

1060 

1020 

980 

940 

900 

86O 

820 

780 

740 

700 / 

66O 

Fe 

steel will typically have a total elongation of 

more than 50%, whereas a fully pearlitic steel 

(e.g., type 1080) will typically have a total elon- 

gation of about 10% (see Table 1). A low-carbon 

fully ferritic steel will have a room-temperature 

Charpy V-notch impact energy of about 200 J 

(150 ft. lbf), whereas a fully pearlitic steel will 

have room-temperature impact energy of under 

10 J (7 ft. lbf). The transition temperature (i.e., 

the temperature at which a material changes from 

ductile fracture to brittle fracture) for a fully 

pearlitic steel can be approximated from the fol- 

lowing relationship (Ref 11): 

TT = 217.84 - 0.83 (de -1/2) - 2.98(d -1"~) (Eq5) 

where TT is the transition temperature (in °C). 

From Eq 5, one can see that both the prior- 

austenite grain size and pearlite colony size con- 

trol the transition temperature of a pearlitic steel. 

Unfortunately, the transition temperature of a 

fully pearlitic steel is always well above room 

temperature. This means that at room tempera- 

ture the general fracture mode is cleavage, which 

is associated with brittle fracture. Therefore, 

fully pearlitic steels should not be used in appli- 

cations where toughness is important. Also, pear- 

litic steels with carbon contents slightly or mod- 

erately higher than the eutectoid composition 

(called hypereutectoid steels) have even poorer 

toughness. 

From Eq 4 and 5, one can see that for pearlite, 

strength is controlled by interlamellar spacing, 

colony size, and prior-austenite grain size, and 

toughness is controlled by colony size and prior- 

Carbon, at.% 

1 2 3 4 5 6 

I I I I I I 

Fe-C equilibrium (experimental) 

- - Fe-Fe3C equilibrium (experimental) 

(~Fe) 

auatenite 

~912 °C , / " 

~ ~0¢F.) ferrite . ,-~ 

%~ 770 °C (Curie temperature) -*°~ 

.../ 

.................. ~- - -'-~ 0.68 7 

I ~ 0.0206 ~ ~, .'°" 

0.0218 I 

I Ferrite + cementite 

I I I I 

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 

Carbon, wt% 

Structure/Property Relationships in Irons and Steels/159 

austenite grain size. Unfortunately, these three 

factors are rather difficult to measure. To deter- 

mine interlamellar spacing, a scanning electron 

microscope (SEM), or a transmission electron 

microscope (TEM) is needed in order to resolve 

the spacing, Generally, a magnification of 

10,000x is adequate, as seen in Fig. 13. Special 

statistical procedures have been developed to de- 

termine an accurate measurement of the spacing 

(Ref 12). The colony size and especially the 

prior-austenite grain size are very difficult to 

measure and require a skilled metallographer us- 

ing the light microscope or SEM and special 

etching procedures. 

Because of poor ductility/toughness, there are 

only a few applications for fully pearlitic steels, 

including railroad rails and wheels and high- 

strength wire. By far, the largest tonnage applica- 

tion is for rails. A fully pearlitic rail steel pro- 

vides excellent wear resistance for railroad 

wheel/rail contact. Rail life is measured in mil- 

lions of gross tons (MGT) of travel and current 

rail life easily exceeds 250 MGT. The wear resis- 

tance of pearlite arises from the unique morphol- 

ogy of the ferrite-cementite lamellar composite 

where a hard constituent is embedded into a soft- 

ductile constituent. This means that the hard ce- 

mentite plates do not abrade away as easily as the 

rounded cementite particles found in other steel 

microstructures, that is, tempered martensite and 

bainite, which is discussed later. Wear resistance 

of a rail steel is directly proportional to hardness. 

This is shown in Fig. 15, which indicates less 

weight loss as hardness increases. Also, wear re- 

sistance (less weight loss) increases as inter- 

lamellar spacing decreases, as shown in Fig. 16. 

7 8 9 

1154°C - ~...~ 2125 

2.08 I ~ J., "'" ~1,,/ 8 °C-'~ 2050 

.o"Y 211 -- 1975 

• *' Y 

• .~ -- 1900 

-- 1825 

-- 1750 

AUS tenite + cementite -- 1700 

-- 1625 

-- 1550 

-- 1475 

738 °C - 1400 

I -- 

727 °C 

1325 

I - 1250 

1.5 1.6 1.7 1.8 1.9 2.0 2.1 2.2 

Fig. 6(a) Iron-carbon phase diagram showing the austenite (y Fe) and ferrite (ocFe) phase regions and eutectoid composition and temperature. Dotted lines represent iron-graphite equi- 

librium conditions and solid lines represent iron-cementite equilibrium conditions. Only the solid lines are important with respect to steels. Source: Ref 2 

u- o 

E


Thus, the most important microstructural pa- 

rameter for controlling hardness and wear resis- 

tance is the pearlite interlamellar spacing. Fortu- 

nately, interlamellar spacing is easy to control 

and is dependent solely on transformation tem- 

perature. 

Figure 17 shows a continuous cooling transfor- 

mation (CCT) diagram for a typical rail steel. A 

CCT diagram is a time versus temperature plot 

showing the regions at which various constitu- 

cnts--ferdte, pearlite, bainite, and martensite-- 

form during the continuous cooling of a steel 

component. Usually several cooling curves are 

shown with the associated start and finish trans- 

formation temperatures of each constituent. 

These diagrams should not be confused with iso- 

thermal transformation (IT or TTT) diagrams, 

which are derived by rapidly quenching very thin 

specimens to various temperatures, and maintain- 

ing that temperature (isothermal) until the speci- 

mens begin to transform, partially transform, and 

fully transform, at which time they are quenched 

to room temperature. An IT diagram does not 

represent the transformation behavior in most 

processes where steel parts are continuously 

cooled, that is, air cooled, and so forth. 

As shown in Fig. 17, the peadite transforma- 

tion temperature (indicated by the pearlite-start 

curve, Ps) decreases with increasing cooling rate. 

The hardness of peaflite increases with decreas- 

ing transformation temperature. Thus, in order to 

provide a rail steel with the highest hardness and 

wear resistance, one must cool the rail from the 

austenite at the fastest rate possible to obtain the 

lowest transformation temperature. This is done 

in practice by a process known as head harden- 

ing, which is simply an accelerated cooling proc- 

ess using forced air or water sprays to achieve 

the desired cooling rate (Ref 15). Because only 

the head of the rail contacts the wheel of the 

railway car and locomotive, only the head re- 

quires the higher hardness and wear resistance. 

Another application for a fully pearlitic steel is 

high-strength wire (e.g., piano wire). Again, the 

composite morphology of lamellar ferrite and ce- 

mentite is exploited, this time during wire draw- 

ing. A fully pearlitic steel rod is heat treated by a 

process known as patenting. During patenting, 

1~ M 3270 

1~ 3090 

1 ! 2730 

GFe 

1~ 2550 

11 2010 

lC 1830 ~ 

E 

i ~ E 1470 

7 1290 

-~ 930 

4 750 

3 570 

I P_~ 

30 

Fe 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 

Carbon, wt% 

Fig. 6(b) Expanded iron-carbon phase diagram showing both the eutectoid (shown in Fig. 6a) and eutectic regions. 

Dotted lines represent iron-graphite equilibrium conditions and solid lines represent iron-cementite equilib- 

rium conditions. The solid lines at the eutectic are important to white cast irons and the dotted lines are important to gray 

cast irons. Source: Ref 2 

2910 

2370 

2190 

rILE[ 

the rod is transformed at a temperature of about 

540 °C (1000 °F) by passing it through a lead or 

salt bath at this temperature. This develops a 

microstructure with a very fine pearlite inter- 

lamellar spacing because the transformation 

takes place at the nose of the CCT diagram, that 

is, at the lowest possible pearlite transformation 

temperature (see Fig. 17). The rod is then cold 

drawn to wire. Because of the very fine inter- 

lamellar spacing, the ferrite and cementite lamel- 

lae become aligned along the wire axis during 

the deformation process. Also, the fine ccmentite 

lamella tend to bend and deform as the wire is 

elongated during drawing. The resulting wire is 

one of the strongest commercial products avail- 

able; for example, a commercial 0.1 mm (0.004 

in.) diam wire can have a tensile strength in the 

range of 3.0 to 3.3 GPa (439 to 485 ksi), and in 

special cases a tensile strength as high as 4.8 

GPa (696 ksi) can be obtained. These wires are 

used in musical instruments because of the sound 

quality developed from the high tensile stresses 

applied in stringing a piano and violin and are 

also used in wire rope cables for suspension 

bridges. 

Ferrite-Pearlite 

The most common structural steels produced 

have a mixed ferrite-pearlite microstructure. 

Their applications include beams for bridges and 

high-rise buildings, plates for ships, and rein- 

forcing bars for roadways. These steels are rela- 

tively inexpensive and are produced in large ton- 

nages. They also have the advantage of being 

able to be produced with a wide range of proper- 

ties. The microstructure of typical ferrite-pearlite 

steels is shown in Fig. 18. 

In most ferrite-pearlite steels, the carbon con- 

tent and the grain size determine the micro- 

structure and resulting properties. For example, 

Fig. 19 shows the effect of carbon on tensile and 

impact properties. The ultimate tensile strength 

steadily increases with increasing carbon con- 

tent. This is caused by the increase in the volume 

fraction of pearlite in the microstructure, which 

has a strength much higher than that of ferrite. 

Thus, increasing the volume fraction of pearlite 

has a profound effect on increasing tensile 

strength. 

However, as seen in Fig. 19, the yield strength 

is relatively unaffected by carbon content, rising 

from about 275 MPa (40 ksi) to about 415 MPa 

(60 ksi) over the range of carbon content shown. 

This is because yielding in a ferrite-pearlite steel 

is controlled by the fcrrite matrix, which is gen- 

erally considered to be the continuous phase (ma- 

"~ 35 241 ~: 

-'~ 25 ~' ..... 172 

"N, 

/ 103= 

0 

o~ 10 ~ 

o. 

o 

0 0.001 0.002 0.003 

Carbon, wt% 

0.004 0.005 o 

6 

Fig, 7 Increase in room-temperature yield strength of 

iron with small additions of carbon. Source: Ref 7 

O3

Fig. 8 Photomic.rograph of an annealed low-carbon sheet steel with grain-boundary ce- 

mentite. 2% nital + 4% picral etch. 1000x 

trix) in the microstructure. Therefore, pearlite 

plays only a minor role in yielding behavior. 

From Fig. 19, one can also see that ductility, as 

represented by reduction in area, steadily de- 

creases with increasing carbon content. A steel 

with 0.10% C has a reduction in area of about 

75%, whereas a steel with 0.70% C has a reduc- 

tion in area of only 25%. Percent total elongation 

would show a similar trend, however, with values 

much less than percent reduction in area. 

Much work has been done to develop empirical 

equations for ferrite-pearlite steels that relate 

strength and toughness to microstructural fea- 

tures, for example, grain size and percent of 

pearlite as well as composition. One such equa- 

tion for ferrite-pearlitc steels under 0.25% C is as 

follows (Ref 16): 

YS = 53.9 + 32.34 (Mn) + 83.2(Si) 

+ 354.2(Nf) + 17.4(d-U2) (Eq 6) 

where Mn is the manganese content (%), Si is the 

silicon content (%), Nf is the free nitrogen content 

(%), and d is the ferrite grain size (in mm). Equa- 

tion 6 shows that carbon content (percent pearlite) 

4-375 

+225 

.--~_m+150 

"~ +75 

o 0 

-75 

I 

C and N 

/ 

y -- Ni and AI 

0 0.5 1.0 1.5 2.0 2.5 3.0 

Alloy content, wt% 

Fig, 10 Influence of solid-solution elements on the 

changes in yield stress of low-carbon ferritic 

steels. Source: Ref 5 

Si 

has no effect on yield strength, whereas the yield 

strength in Fig. 19 increases somewhat with car- 

bon content. According to Eq 6, manganese, sili- 

con, and nitrogen have a pronounced effect on 

yield strength, as does grain size. However, in 

most ferrite-pearlite steels nitrogen is quite low 

(under 0.010%) and thus has minimal effect on 

yield strength. In addition, as discussed below, 

nitrogen has a detrimental effect on impact prop- 

erties. 

The regression equation for tensile strength for 

the same steels is as follows (Ref 16): 

TS = 294,1 + 27.7(Mn) + 83.2(Si) 

+ 3.9(P) + 7.7(d -lt2) (F-4 7) 

where TS is the tensile strength (in MPa) and P is 

pearlite content (%). Thus, in distinction to yield 

strength, the percentage of pearlite in the micro- 

structure has an important effect on tensile 

strength. 

Toughness of ferrite-pearlite steels is also an 

important consideration in their use. It has long 

been known that the absorbed energy in a Charpy 

V-notch test is decreased by increasing carbon 

content, as seen in Fig. 20. In this graph of im- 

Fig. 11 

& 

600 

500 

400 

~ 300 

200 

100 


Fig. 9 Photomicrograph of pearlite (dark constituent) in a low-carbon steel sheet. 2% ni- 

tal + 4% picral etch. 1000x 

pact energy versus test temperature, the shelf en- 

ergy decreases from about 200 J (150 ft • lbf) for 

a 0.11% C steel to about 35 J (25 ft. lbf) for a 

0.80% C steel. Also, the transition temperature 

increases from about -50 to 150 °C (-60 to 300 

°F) over this same range of carbon content. The 

effect of carbon is due mainly to its effect on the 

percentage of pearlite in the microstructurc. This 

is reflected in the regression equation for transi- 

tion temperature below (Ref 16): 

TT = -19 + 44(Si) + 700(N~/2) 

+ 2.2(P) - 11.5 (d -1/2) (F_.q 8) 

It can be seen in all these relationships that 

ferrite grain size is an important parameter in 

improving both strength and toughness. It can 

also be seen that while pearlite is beneficial for 

increasing tensile strength and nitrogen is benefi- 

cial for increasing yield strength, both are harm- 

ful to toughness. Therefore, methods to control 

the grain size of ferrite-pearlite steels have rap- 

idly evolved over the past 25 years. The two most 

important methods to control grain size are con- 

trolled rolling and microalloying. In fact, these 

I I I I I I I I I I I I 

0 1 2 3 4 5 6 7 8 9 10 11 12 

Grain diameter (d-l~), mm -1~ 

Hall-Petch relationship in low-carbon ~mtic steels, souse: Ref 8 

80 

80 

"N. 

20 |


Fig. 12 

oo 

(9 

¢:L 

E 

Chromium, at.% 

0 10 20 30 40 50 60 70 

20OO 

1800 

1600 

1400 - 1394 °C 

I I 

1538 °C 1516 °: ~ ...... 

1200 - ~ (~Fe,Cr) 

1000 _(~Fe)//_12. 7 

oc/I 

21 

8001:-- -.7 

I -/ ( o I 

~nn I Magnetic "~ • "---- ..... I , "* ". 

oc 

80 90 100 

Itransformabon.- 

/ 

o.'. .................. 

,, : 

475 o C 

=.." ........................... 

"-.. 

".,.. 

400 i r'1 °° I I I I I I I t "'~ 

0 10 20 30 40 50 60 70 80 90 

Fe Chromium, wt% 

Iron-chromium phase diagram. Source: Ref 9 

methods are used in conjunction to produce 

strong, tough ferrite-pearlite steels. 

Controlled rolling is a thermomechanical 

treatment in which steel plates are rolled below 

the recrystailization temperature of aastcnite. 

This process results in elongation of the austenite 

grains. Upon further rolling and subsequent cool- 

ing to room temperature, the austenite-to-ferrite 

transformation takes place. The ferrite grains are 

restricted in their growth because of the "pan- 

cake" austeaite grain morphology. This produces 

the fine ferrite grain size required for higher 

strength and toughness. 

Microalloying is the term applied to the addi- 

tion of small amounts of special alloying ele- 

ments (vanadium, niobium, or titanium) that aid 

I i I I I I I 

1863 °C 

100 

Cr 

in retarding austenite recrystallization, thus al- 

lowing a wide window of rolling temperatures 

for controlled rolling. Without retarding recrys- 

tallization, as in normal hot rolling, the pancake- 

type grains do not form and a fine grain size 

cannot be developed. Microalloyed steels are 

used in a wide variety of high tonnage applica- 

tions including structural steels for the construc- 

tion industry (bridges, multistory buildings, 

etc.), reinforcing bar, pipe for gas transmission, 

and numerous forging applications. 

Bainite 

Like pearlite, bainitc is a composite of ferrite 

and cementitc. Unlike pearlite, the ferritc has an 

Fig, 13 SEM micrograph of pearlite showing ferrile and cementite lamellae. 4% picral etch. 10, O00x 

acicular morphology and the carbides are dis- 

crete particles. Because of these morphological 

differences, bainite has much different property 

characteristics than pearlite. In general, bainitic 

steels have high strength coupled with good 

toughness, whereas pearlitic steels have high 

strength with poor toughness. 

Another difference between baiaite and pearl- 

ite is the complexity of the bainite morphologies 

compared with the simple lamellar morphology 

of pearlite. The morphologies of bainite are still 

being debated in the literature. For years, since 

the classic work of Bain and Davenport in the 

1930s (Ref 18), there were two classifications of 

bainite: upper and lower bainite. This nomencla- 

ture was derived from the temperature regions at 

which bainite formed during isothermal (constant 

temperature) transformation. Upper bainite 

formed isothermally in the temperature range of 

400 to 550 °C (750 to 1020 °F), and lower 

bainite formed isothermally in the temperature 

range of 250 to 400 °C (480 to 750 °F). Exam- 

ples of the microstructure of upper and lower 

bainite are shown in Fig. 21. One can see that 

both types of bainite have an acicular morphol- 

ogy, with upper bainite being coarser than lower 

bainite. The true morphological differences be- 

tween the microstructures can only be deter- 

mined by electron microscopy. Transmission 

electron micrographs of upper and lower baiaite 

are shown in Fig. 22. In upper bainitc, the iron 

carbide phase forms at the lath boundaries, 

whereas in lower bainite, the carbide phase forms 

on particular crystallographic habit planes within 

the laths. Because of these differences in mor- 

phology, upper and lower bainite have different 

mechanical properties. Lower bainite, with a fine 

acicular structure and carbides within the laths, 

has higher strength and higher toughness than up- 

per bainite with its coarser structure. 

Because during manufacture most steels un- 

dergo continuous cooling rather than isothermal 

holding, the terms upper and lower baiaite can 

become confusing because "upper" and "lower" 

are no longer an adequate description of mor- 

phology. Bainite has recently been reclassified 

by its morphology, not by the temperature range 

in which it forms (Ref 19). For example, a recent 

classification of bainite yields three distinct 

types of morphology. 

O. 

Class 1 (B1): Acicular ferrite associated with 

intralath (plate) iron carbide, that is, cemcn- 

tite (replaces the term "lower bainite") 

900 

8O0 

~ 7oo 

.~>6OO 

~.500 

0 

400 

Interlamellar spacing (Sp), nm 

300 200 100 80 60 

I I f I 

S 

.j¢ ,- 

60 80 100 120 140 

Reciprocal root of 

Interlamellar spacing (Sp-1/2), mm -1/2 

Fig. 14 Relationship behveen peadite interlamellar 

spacing and yield strength for eutectoid steels. 

Source: Ref I0

o~ 

o 

J~ 

o 

Fig. 15 

1.6 

1.2 

0.8 

0.4 

0 

2OO 225 250 275 300 325 350 375 

Brinell hardness, HB 

Relationship between hardness and wear resistance (weight loss) for rail steels. 

Source: Ref 13 

• Class 2 (B2): Acicular ferrite associated with 

interlath (plate) particles or films of cementite 

and/or austenite (replaces the term "upper 

bainite") 

• Class 3 (B3): Acicular ferrite associated with a 

constituent consisting of discrete islands of 

austenite and/or martensite 

The bainitic steels have a wide range of me- 

chanical properties depending on the micro- 

structural morphology and composition; for ex- 

ample, yield strength can range from 450 to 950 

MPa (65 to 140 ksi), and tensile strength from 

530 to 1200 MPa (75 to 175 ksi). Another aspect 

of a bainitic steel is that a single composition, 

I/2Mo-B steel for example, can yield a bainitic 

microstructure over a wide range of transforma- 

tion temperatures. The CCT diagram for this 

steel is shown in Fig. 23. Note that for this steel 

the bainite start (Bs) temperature is almost con- 

stant at 600 °C (1110 °F). This flat transforma- 

tion region is important because transformation 

temperature plays an important role in the devel- 

opment of microstructure. A constant transforma- 

tion temperature permits the development of a 

similar microstructure and properties over a wide 

range of cooling rates. This has many advantages 

in the manufacturing of bainitic steels and is par- 

ticularly advantageous in thick sections where a 

wide range in cooling rates is found from the 

surface to the center of the part. 

In designing a bainitic steel with a wide trans- 

formation region, it becomes critical that the 

pearlite and ferrite regions are pushed as far to 

the right as possible on the CCT diagram; that is, 

pearlite and ferrite form only at slow cooling 

rates. Alloying elements such as nickel, chro- 

mium, and molybdenum (and manganese) are se- 

lected for this purpose. 

For low-carbon bainitic steels, the relationship 

between transformation temperature and tensile 

strength is shown in Fig. 24 (martensite is dis- 

cussed in the next section). Note the rapid in- 

crease in tensile strength as the transformation 

temperature decreases. For these steels, a regres- 

sion equation for tensile strength has been devel- 

oped as follows (Ref 21): 

TS = 246.4 + 1925(C) + 231(Mn + Cr) + 185(Mo) 

+ 92(W) + 123(Ni) + 62(Cu) + 385(V + 11) (Eq9) 

In addition to the elements carbon, nickel, 

chromium, molybdenum, vanadium, and so forth, 

it is well known that boron in very small quanti- 

Structure/Property Relationships in Irons and Steels/163 

1.6 

1,2 

o= j 

z 0.8 /~ 

Fig. 16 

0.4 

ties (for example, 0.003%) has a pronounced ef- 

fect on retarding the ferrite transformation. Thus, 

in a boron-containing steel (e.g., l/2Mo + B), the 

ferrite nose in the CCT diagram is pushed to 

slower cooling rates. Boron retards the nuclea- 

tion of ferrite on the austenite grain boundaries 

and, in doing so, permits bainite to be formed 

(Fig. 23). Whenever boron is added to steel, it 

must be prevented from combining with other 

elements such as oxygen and nitrogen. Generally, 

aluminum and titanium are added first in order to 

lower the oxygen and nitrogen levels of the steel. 

Even when adequately protected, the effective- 

ness of boron decreases with increasing carbon 

content and austenite grain size. 

Attempts have been made to quantitatively re- 

late the microstructural features of bainite to me- 

chanical properties. One such relationship is (Ref 

22): 

YS = -194 + 17.4(d -1/2) + 15(nl/4) (Eq 10) 

where YS is the 0.2% offset yield strength (in 

MPa), d is the bainite lath size (mean linear inter- 

? 

9oo 

700 

600 

¢ 500 

tz 

E 

400 

300 

200 

100 

0 10 

i< 

0 

0.06 0.08 0.10 0.12 0.14 0.16 0.18 0.20 0.22 0.24 0.26 

Pearlite spacing, pm 

Relationship between pearlite interlamellar spacing and wear resistance 

(weight loss) for rail steels. Source: Ref 13 

cept) (in ram), and n is the number of carbides per 

mm 2 in the plane of section. 

With bainitic steels, the lath width of the 

bainite obeys a Hall-Petch relationship as shown 

in Fig. 25. The lath size is directly related to the 

austenite grain size and decreases with decreas- 

ing bainite transformation temperature. Because 

of the fine microstructure of bainite, the meas- 

urement of lath size and carbide density can only 

be done by SEM or TEM. 

In low-carbon bainitic steels, type B 2 (upper) 

bainite has inferior toughness to type B 1 (lower) 

bainite. In both cases, strength increases as the 

transition temperature decreases. In type B 2 (up- 

per) bainite, the carbides are much coarser than 

in type B 1 (lower) bainite and have a tendency to 

crack and initiate cleavage (brittle) fracture. In 

type B l bainite, the small carbides have less ten- 

dency to fracture. One can lower the transition 

temperature in type B l bainitic steels by provid- 

ing a finer austenite grain size through lower- 

temperature thermomechanical treatment and 

grain refinement. 

Bainitic steels are used in many applications 

including pressure vessels, backup rolls, turbine 

_I o.n,r .e 

°Clmln ~ ~s 

~_ 1 -643 \\1 ~ ~ 

2 - 600 

0-545_ ( % ~ . 'Bf 

4 - 500 

5 - 450 

6 400 

7 - 352 M s \ "~ 

8 - 300 

9 - 253 

10 - 225 Martensite 

11 -189 

12 - 50 

I I I I I I 

lO0 

Time, s 

Fig. 17 ^ ccT diagram of a typical rail steel (composition: 0.77% C, 0.95% Mn, 0.22% Si, 0.014% P, 0.017% S, 0.10% 

Cr). Source: Ref 14 

/ 

1000


(a) (h) 

Fig. 18 Microstructure of typical ferrite-pearlite structural steels at two different carbon contents. (a) 0.10% C. (b) 0.25% C. 2% nital + 4% picral etch. 200x 

rotors, die blocks, die-casting molds, nuclear re- 

actor components, and earthmoving equipment. 

One major advantage of a bainitic steel is that an 

optimal strength/toughness combination can be 

produced without expensive heat treatment, for 

example, quenching and tempering as in marten- 

sitic steels. 

Martensite 

Martensite is essentially a supersaturated solid 

solution of carbon in iron. The amount of carbon 

in martensite far exceeds that found in solid solu- 

tion in ferrite. Because of this, the normal body- 

centered cubic (bcc) lattice is distorted in order 

to accommodate the carbon atoms. The distorted 

lattice becomes body-centered tetragonal (bet). 

In plain-carbon and low-alloy steels, this super- 

saturation is generally produced through very 

rapid cooling from the austenite phase region 

(quenching in water, iced-water, brine, iced- 

brine, oil or aqueous polymer solutions) to avoid 

forming ferrite, pearlite, and bainite. Some 

highly alloyed steels can form martensite upon 

air cooling (see the discussion of maraging steels 

later in this section). Depending on carbon con- 

tent, martensite in its quenched state can be very 

hard and brittle, and, because of this brittleness, 

martensitic steels are usually tempered to restore 

some ductility and increase toughness. 

Reference to a CCT diagram shows that 

martensite only forms at high cooling rates in 

plain-carbon and low-alloy steels. A CCT dia- 

gram for type 4340 is shown in Fig. 26, which 

indicates that martensite forms at cooling rates 

exceeding about 1000 °C/rain. Most commercial 

martensitic steels contain deliberate alloying ad- 

ditions intended to suppress the formation of 

other constituents--that is ferrite, peariite, and 

bainite--during continuous cooling. This means 

that these constituents form at slower cooling 

rates, allowing martensite to form at the faster 

cooling rates, for example, during oil and water 

quenching. This concept is called hardenability 

and is essentially the capacity of a steel to harden 

by rapid quenching. Most all the conventional 

alloying elements in steel promote hardenability. 

For example, type 4340 steel shown in Fig. 26 

has significant levels of carbon, manganese, 

nickel, copper, and molybdenum to promote har- 

denability. More details about hardenability can 

be found in Ref 2. 

2O0 

(271) 

Notched impact tests / 

The martensite start temperature (Ms) for type 

4340 is 300 °C (570 °F). Carbon lowers the M s 

temperature, as shown in Fig. 27, and alloying 

elements such as carbon, manganese, chromium, 

nickel, and molybdenum also lower M s tempera- 

ture. Many empirical equations have been devel- 

oped over the past 50 years relating M s tempera- 

"~ (217) 

,~ 

~ e 

If energy 

>:, 120 

(163) 

j ~ ," Transition temperature 

= 80 

(106) 

~ 40 

0 (54) ~ ~ '------ 

0 

~ 100 

.cg ~ 80 ~ ~'~UItimate: ~'~ strength I t ~ 

= Yield strength 

0= 

.¢ 60 ~ 

=m Reduction in area 

20 -- Smooth tensile testa I 

03 

0 0 0.1 0.2 0:3 0.4 0.5 0.6 0.7 0.8 0.9 

Carbon, wt% 

Fig. 19 Mechanical properties of ferrite-pearlite steels as a function of carbon content. Source: Ref 2 

160 

120 

80 

40 

-4O 

oo 

E 

e 

8 

,== 

CO 

== 

o

Fig. 20 

Temperature, °F 

-1 O0 0 100 200 300 400 

250 I I I F I 

200 

¢= 

• 150 

t~ 

¢x 

_E 

f 

0.11%C 

100 / 0.20% C .." ....................... 0.31 Yo C - 75 

__ 0.41%C 060%C- 

~ " ........ ~0.49%C 2 50 

50 ~~........~ ."" .""" • .- s ~ , • 

,'°1 ,, .-" "'.t..-" --.-'.'. .......... 

oO." • 

,.: ... s .o.° "~ .." .. " ~'~ 0.80%C 25 

0 • 0 

-100 -50 0 50 100 150 200 250 

Temperature, °C 


175 

150 

125 a= 

>~ 

Effect Of carbon content in ferrite-peadite steels on Charpy V-notch transition temperature and shelf energy. 

Sou rce: Ref 17 

ture to composition. One recent equation by An- 

drews (Ref 24) is: 

M s (°C) = 539 - 423(C) - 30.4(Mn) - 12.1(Cr) 

- 17.7(Ni) - 7_5(Mo) (Eq 11) 

With sufficient alloy content, the M s tempera- 

ture can be below room temperature, which 

means that the transformation is incomplete and 

retained austenite can be present in the steel. 

The microstructure of martensitic steels can be 

generally classed as either lath martensite, plate 

martensite, or mixed lath and plate martensite. In 

plain carbon steels, this classification is related 

100 

to carbon content, as shown in Fig. 27. Lath 

martensite forms at carbon contents up to about 

0.6%, plate martensite is found at carbon con- 

tents greater than 1.0%, and a mixed martensite 

microstructure forms for carbon contents be- 

tween 0.6 and 1.0%. An example of lath marten- 

site is shown in Fig. 28 and plate martensite in 

Fig. 29. Generally, plate martensite can be distin- 

guished from lath martensite by its plate mor- 

phology with a central mid-fib. Also, plate 

martensite may contain numerous microcracks, 

as shown in Fig. 30. These form during transfor- 

mation when a growing plate impinges on an ex- 

isting plate. Because of these microcracks, plate 

martensite is generally avoided in most applica- 

(a) (b) 

Fig. 21 Microstructure of (a) upper bainite and (b) lower bainite in a Cr-Mo-V rotor steel. 2% nital + 4% picral etch. 500x 

g 

tions. The important microstructural units meas- 

ured in lath martensite are lath width and packet 

size. A packet is a grouping of laths having a 

common orientation. 

Plain-carbon and low-alloy martensitic steels 

are rarely used in the as-quenched state because 

of poor ductility. To increase ductility, these 

martensitic steels are tempered (reheated) to a 

temperature below 650 °C (1200 °F). During 

tempering, the carbon that is in supersaturated 

solid solution precipitates on preferred crystal- 

lographic planes (usually the octahedral {111} 

planes) of the martensitic lattice. Because of the 

preferred orientation, the carbides in a tempered 

martensite have a characteristic arrangement as 

seen in Fig. 31. 

Tempered martensite has similar morphologi- 

cal features to type B) (lower) bainite. However, 

a distinction can be made in terms of the orienta- 

tion differences of the carbide precipitates. This 

can be seen by comparing type B l bainite in Fig. 

22 with tempered martensite in Fig. 31. However, 

unless the carbide morphology is observed it is 

very difficult to distinguish between B] bainite 

and tempered martensite. 

The hardness of martensite is determined by its 

carbon content, as shown in Fig. 32. Martensite 

attains a maximum hardness of 66 HRC at carbon 

contents of 0.8 to 1.0%. The reason that the hard- 

ness does not monotonically increase with carbon 

is that retained austenite is found when the car- 

bon content is above about 0.4% (austenite is 

much softer than martensite). Figure 33 shows 

the increase in volume percent retained austenite 

with increasing carbon content. Yield strength 

also increases with increasing carbon content as 

seen in Fig. 34. This empirical relationship be- 

tween the yield strength and carbon content for 

untempered low-carbon martensite is (Ref 25): 

YS (MPa) = 413 + 17.2 x 10P(C 1/2) (Eq 12) 

Lath martensite packet size also has an influence 

on the yield strength, as shown in Fig. 35. The


(a) (b) 

Fig, 22 TEM micmgraphs of (a) upper bainite and (b) lower bainite in a Cr-Mo-V rotor steel 

linear behavior follows a Hall-Petch type rela- 

tionship of (d-l/2). 

Most martcnsitic steels are used in the tem- 

pered condition where the steel is reheated after 

quenching to a temperature less than the lower 

critical temperature (Act). Figure 36 shows the 

decrease in hardness with tempering temperature 

for a number of carbon levels. Plain-carbon or 

low-alloy martensitic steels can be tempered in 

lower or higher temperature ranges, depending 

on the balance of properties required. Tempering 

between 150 and 200 °C (300 and 390 °F) will 

maintain much of the hardness and strength of 

the quenched martensite and provide a small im- 

provement in ductility and toughness (Ref 26). 

This treatment can be used for bearings and gears 

that are subjected to compression loading. Tem- 

pering above 425 °C (796 °F) significantly im- 

proves ductility and toughness but at the expense 

of hardness and strength. The effect of tempering 

temperature on the tensile properties of a typical 

oil-quenched low-alloy steel (type 4340) is 

shown in Fig. 37. These data are for a 13.5 mm 

(0.53 in.) diam rod quenched in oil. The as- 

1 0 0 0 ~ 1800 

Ac 3 = 930 °C 

900 Fs 1 ! 0 1600 

.0o 

,oo ?-- 

° o 6oo " 

500 - . . . . -- + 

~'E ~ l I I "l\ ~ \1 I I \ ~l~""r I I I ~ ~ I I I X I I I II -1800 

200 ~ ~ 400 

100 200 

0 32 

10 102 103 104 105 

Seconds I ' ' ' ' I ' ' ' ' I ~ ' ' ~ I 

1 10 102 103 

Minutes I ' I ' ' I ' I 

1 4 10 30 

Time Hours 

Fig. 23 A CCT diagram of a I/2Mo-B steel. Composition: 0.093% C, 0.70% Mn, 0.36% Si, 0.51% Mo, 0.0054% B. 

Austenitized at Ac 3 + 30 °C for 12 rain. Bs, bainite start; B o bainite finish; Fs, ferrite start; F o ferrite finish. Num- 

bers in circles indicate hardness (HV) after cooling to room temperature. Source: Ref 20 

quenched rod has a hardness of 601 HB. Note 

that by tempering at 650 °C (1200 °F), the hard- 

ness (see x-axis) decreased to 293 HB; or to less 

than half the as-quenched hardness. The tensile 

strength has decreased from 1960 MPa (285 ksi) 

at a 200 °C (400 °F) tempering temperature to 

965 MPa (141 ksi) at a 650 °C (1200 °F) temper- 

ing temperature. However, the ductility, repre- 

sented by total elongation and reduction in area, 

increases dramatically. The tempering process 

can be retarded by the addition of certain alloy- 

ing elements such as vanadium, molybdenum, 

manganese, chromium, and silicon. Also, for 

tempering, temperature is much more important 

than time at temperature. 

Temper embrittlement is possible during the 

tempering of alloy and low-alloy steels. This em- 

brittlement occurs when quenched-and-tempered 

steels are heated in, or slow cooled through the 

340 to 565 °C (650 to 1050 °F) temperature 

range. Embrittlement occurs when the embrit- 

tling elements, antimony, tin, and phosphorus, 

concentrate at the austenite grain boundaries and 

create intergranular segregation that leads to in- 

tergranular fracture. The element molybdenum 

1200 "'"q'e 

~-. 1050 ~ ' ~ 

" 900 

.== 

¢/) 

750 

i.~ 600 ~1 

eel==, 

Ferrite + 

peadite 

450 Martensites Bainites ~'~ ', ~* "/45 

I I I I ~-'- i i 1- 

3OO 4OO 500 600 7OO 8O0 

Transformation temperature, °C 

Fig. 24 Relationship between transformation tempera- 

ture and tensile strength of ferrite-pearlite, bain- 

itic, and martensitic steels. Source: Ref 5

t~ 

IL 

900 / 

to 

750 

~ QII) • 

" 600 • 

° 

450 

15 20 25 

Grain size (d-1/2), mm -1/2 

Fig. 25 Relationship between bainite lath width (grain 

size) and yield strength. Source: Ref 5 

has been shown to be beneficial in preventing 

temper embrittlement. 

The large variation in mechanical properties of 

quenched-and-tempered martensitic steels pro- 

vides the structural designer with a large number 

of property combinations• Data, like that shown 

in Fig. 37, are available in the Section "Carbon 

and Alloy Steels" in this Handbook as well as 

Volume 1 of the ASM Handbook and the ASM 

Specialty Handbook: Carbon and Alloy Steels. 

Hardnesses of quenched-and-tempered steels can 

be estimated by a method established by Grange 

et al. (Ref 27). The general equation for hardness 

is: 

HV = HV C + AHVMn + AHVp + AHVsi + AHVNi 

+ AHVcr + AHVMo + AHV v (Eq 13) 

where HV is the estimated hardness value (Vick- 

ers). 

In order to use this relationship, one must de- 

termine the hardness value of carbon (HVc) from 

Fig. 38. For example, if one assumes that a tem- 

pering temperature of 540 °C (1000 °F) is used 

and the carbon content of the steel is 0.2% C, the 

HV c value after tempering will be 180 HV. Sec- 

ond, the effect of each alloying element must be 

determined from a figure such as Fig. 39. This 

graph represents a tempering temperature of 540 

°C (1000 °F). Graphs representing other temper- 

ing temperatures can be found in Ref 27. 

To illustrate the use of the Grange et al. 

method, the same type 4340 steel shown in Fig. 

37 is used. The composition of the steel is 0.41% 

C, 0.67% Mn, 0.023% P, 0.018% S, 0.26% Si, 

1.77% Ni, 0.78% Cr, and 0.26% Mo. Assuming a 

540 °C (1000 °F) tempering temperature, the es- 

timated hardness value for carbon is 210 HV. 

From Fig. 38, the hardness values for each of the 

other alloying elements are: 

Element Ccetent, % Hardaess, HV 

Carbon 0.41 210 

Manganese 0.67 38 

Phosphorus 0.023 7 

Silicon 0.26 15 

Nickel 1.77 12 

Chromium 0.78 43 

Molybdenum 0.26 55 

Total hardness 380 

According to Fig. 37, the hardness value after 

tempering at 540 °C (1000 °F) was 363 HB (see 

Brinell hardness values along x-axis). From the 

ASTM E 140 conversion table (included in the 

g 

1600 

1400 

1200 

1000 

E 800 

600 

400 


200 1 2 5 10 20 50 100 200 

Cooling timel s 

Fig, 26 The CCT diagram for type 4340 steel austenitized at 845 °C (I 550 °F). Source: Ref 23 

examples of hardness conversion tables for 

steels, which can be found in the Section "Glossary 

of Terms and Engineering Data" in this 

Handbook), a Brinell hardness of 363 HB equates 

to a Vickers hardness of 383 HV. The calculated 

value of 380 HV (in the table above) is very 

close to the actual measured value of 383 HV. 

Thus, this method can be used to estimate a specific 

hardness value after a quenching-and-tempering 

heat treatment for a low-alloy steel. Also, 

as a rough approximation, the derived Brinell 

hardness value can be used to estimate tensile 

strength by the following equation (calculated 

from ASTM 

.8o 

E 140 conversion table): 

870 

760 

650 

540 o ~ 

425 E 

315 

205 

95 

500 1000 

TS (MPa) =- 42.3 +3.6 HB (Eq 14) 

For the above example, a type 4340 quenched- 

and-tempered (540 °C, or 1000 °F) steel with a 

calculated hardness of 363 HB would have an 

estimated tensile strength from Eq 14 of 1265 

MPa (183 ksi). From Table 1, this measured ten- 

sile strength of a type 4340 quenched-and-tem- 

pered (540 °C, or 1000 °F) steel is 1255 MPa 

(182 ksi). 

It is seen that quenched-and-tempered marten- 

sitic steels provide a wide range of properties. 

The design engineer can choose from a large 

number of plain-carbon and low-alloy steels. In 

870 1600 

650 

~ o 

cff 540 

425 ~""~.,,~ 

315 

205 

95 l% ~: ~ ......... 

Lath .... ?~ Mixea / ,~ ~:,: 

D20 

0 0.2 0.4 0.6 0.6 

Carbon, wt% 

Fig. 27 Effect of carbon content on M s temperature in steels. Source: Ref 6 

Plate 

0 

1.0 1.2 1.4 1.6 

1400 

1200 

ii 

o 

lOOO =d 

800 

Q_ 

E 

~o ff 

400


Fig. 28 Microstructure of a typical lath martensite. 4% picral + HCI. 200x Fig. 29 Microstructure of a typical plate martensite. 4% picral + HCI. 1000x 

addition to this large list of steels, there are two 

other commercially important categories of fully 

martensitic steels, namely, martensitic stainless 

steels and maraging steels. 

Like the ferritic stainless steels, martensitic 

stainless steels (e.g., type 403, 410, 414, 416, 

420, 422, 431, and 440) are high-chromium iron 

alloys (12 to 18% Cr), but with deliberate addi- 

tions of carbon (0.12 to 1.2% C). These steels 

use carbon in order to stabilize austenite in iron- 

chromium alloys (Fig. 12). The expanded region 

of austenite is called the y-loop. In the Fe-Cr 

phase diagram (without C), the y-loop extends to 

about 12% Cr (see Fig. 12). With carbon addi- 

tions, austenite can exist up to 25% Cr. These 

steels can be heat treated much like those of the 

low-alloy steels. However, martensitic stainless 

steels, with such high chromium contents, can 

form martensite on air cooling, even in thick sec- 

tions. Martensitic stainless steels are considered 

high-strength stainless steels because they can be 

treated to achieve a yield strength between 550 

MPa (80 ksi) and 1725 MPa (250 ksi), as seen in 

Table 1. On the other hand, ferritic stainless 

steels, which do not contain carbon, are not con- 

sidered high-strength steels because their yield 

strength range is only 170 to 450 MPa (25 to 64 

ksi). Because of their high strength and hardness, 

coupled with corrosion resistance, martensitic 

stainless steels are used for knives and other ap- 

plications requiring a cutting edge as well as 

some tool steel applications (for example, molds 

for producing plastic parts). 

Maraging steels are a separate class of marten- 

sitic steels and are considered ultrahigh-strength 

steels with yield strength levels as high as 2500 

MPa (360 ksi), as seen in Table 1. In addition to 

extremely high strength, the maraging steels 

have excellent ductility and toughness. These 

very-low carbon steels contain 17.5 to 18% Ni, 

8.5 to 12.5% Co, 4 to 5% Mo, 0.20 to 1.8% Ti, 

and 0,10 to 0.15% A1. Because of the high alloy 

content, especially the cobalt addition, they are 

very expensive. Their high strength is developed 

by austenitizing at 850 °C (1560 °F), followed by 

air cooling to room temperature to form lath 

martensite. However, the martensitic constituent 

in maraging steels is relatively soft--28 to 35 

HRC--which is an advantage because the com- 

ponent can be machined to final form directly 

upon cooling. The final stage of strengthening is 

through an aging process, carried out at 480 °C 

(900 °F) for 3 h. During aging, the hardness in- 

creases to about 51 to 58 HRC depending on the 

grade of maraging steel. The aging treatment pro- 

motes the precipitation of a rodlike intermetallic 

compound Ni3Mo. These precipitates can only be 

observed at high magnification (e.g., by TEM). 

The precipitates strengthen the surrounding ma- 

trix as they form during aging. Full hardening 

Fig. 30 Microcracks formed in plate martensite. 4% picral + HCl/sodium metabisulfite Fig. 31 Ttransmission electron micrograph showing carbide morphology in tempered 

etch. 1000x martensite

"I- 

¢= 

t~ 

"1- 

900 

800 

700 

600 

500 

400 

300 

200 

100 

0 

J I I I I I 

0.2 0.4 0.6 0.8 1.0 1.2 

Carbon, wt% 

65 

6o 

o 

t~ 

-.r 

of 

so ~ 

40 

30 

20 

1o 

0 

Fig. 32 Effect of carbon content on the hardness of 

martensite. Source: Ref 4 

can be developed, even in very thick sections. 

Maraging steels are used for die-casting molds 

and aluminum hot-forging dies as well as numer- 

ous aircraft and missile components. 

Austenite 

Austenite does not exist at room temperature 

in plain-carbon and low-alloy steels, other than 

as small amounts of retained austenite that did 

not transform during rapid cooling. However, in 

certain high-alloy steels, such as the austenitic 

stainless steels and Hadfield austenitic manga- 

nese steel, austenite is the microstructure. In 

these steels, sufficient quantifies of alloying ele- 

ments that stabilize austenite at room tempera- 

ture are present (e.g., manganese and nickel). 

The crystal structure of austenite is face-centered 

cubic (fee) as compared to ferrite, which has a 

(bcc) lattice. A fcc alloy has certain desirable 

characteristics; for example, it has low-tempera- 

ture toughness, excellent weldability, and is non- 

magnetic. Because of their high alloy content, 

austenitic steels are usually corrosion resistant. 

Disadvantages are their expense (because of the 

260 

- 220 

J~ 

"o 

180 

"~ 140 

~. 100 

o 

60 

o o -~,~1 1700 

t300 

-lltOO 

o,° "o 

so "~ 

Y t oo 

I I I I 

0 0.10 0.20 0.30 0.40 

Carbon content, wt% 

Fig. 34 Relationship between carbon content and the 

yield strength of martensite. Source: Ref 4 

>o 

• ->¢ 100 

=o 

"~ 75 

8 

t~ 

03 

E 

25 

L ] M s temperature 


Lath marten 'lite,'~~ ~"~1..........~ -- 

relative volh°/° ---~ ~ ~ / 

Retained 7, vol% 

.t ~ I I I 

0.4 0.8 1.2 1.6 

Carbon, wt% 

Fig. 33 Effect of carbon content on the volume percent of retained austenite (7) in as-quenched martensite. Source: 

Ref 4 

alloying elements), their susceptibility to stress- 

corrosion cracking (certain austenitic steels), 

their relatively low yield strength, and the fact 

that they cannot be strengthened other than by 

cold working, interstitial solid-solution strength- 

ening, or precipitation hardening. 

The austenitic stainless steels (e.g., type 301, 

302, 303, 304, 305,308, 309, 310, 314, 316, 317, 

321, 330, 347, 348, and 384) generally contain 

from 6 to 22% Ni to stabilize the austenite at 

room temperature. They also contain other alloy- 

ing elements, such as chromium (16 to 26%) for 

corrosion resistance, and smaller amounts of 

manganese and molybdenum. The widely used 

type 304 stainless steel contains 18 to 20% Cr 

and 8 to 10.5% Ni and is also called 18-8 stain- 

less steel. From Table 1, the yield strength of 

annealed type 304 stainless steel is 290 MPa (40 

ksi), with a tensile strength of about 580 MPa (84 

ksi). However, both yield and tensile strength can 

be substantially increased by cold working as 

shown in Fig. 40 (see Table 1). However, the 

increase in strength is offset by a substantial de- 

crease in ductility, for example, from about 55% 

< 

700 

500 

3OO 

100 

elongation in the annealed condition to about 

25% elongation after cold working. 

Some austenitic stainless steels (type 200, 201, 

202, and 205) employ interstitial solid-solution 

strengthening with nitrogen addition. Austenite, 

like ferrite, can be strengthened by interstitial 

elements such as carbon and nitrogen. However, 

carbon is usually excluded because of the delete- 

rious effect associated with precipitation of chro- 

mium carbides on austenite grain boundaries (a 

process called sensitization). These chromium 

carbides deplete the grain-boundary regions of 

chromium, and the denuded boundaries are ex- 

tremely susceptible to corrosion. Such steels can 

be desensitized by heating to high temperature to 

dissolve the carbides and place the chromium 

back into solution in the austenite. Nitrogen, on 

the other hand, is soluble in austenite and is 

added for strengthening. To prevent nitrogen 

from forming deleterious nitrides, manganese is 

added to lower the activity of nitrogen in the 

austenite, as well as to stabilize the austenite. 

For example, type 201 stainless steel has compo- 

sition ranges of 5.5 to 7.5% Mn, 16 to 18% Cr, 

ASTM grain size 

2 4 6 8 10 12 

1200 i i = i i = 

a. E 

,50 

"~ 800 o-o~ 80 

600 ~ ~ -r., 

400 ~.~ 40 o 

0 2 4 6 8 10 12 14 16 

Lath martensite packet size (d-1/2), mm -1/2 

Fig. 35 Relationship between lath martensite packet size (dl and yield strength of Fe-0.2%C (upper line) and Fe-Mn 

(lower line) martensites. Source: Ref 2 

40 

20 

120 

o 

E 

o 

p-


70 

60 

Tempering temperature,°F 

200 400 600 800 1000 1200 1400 

0 ,0,,o 

~-o.~c % 

n-° 50 ~ ~ ~ ~ o ~ 

= 0=00=0; 

"l- ~ = m 40 ~ ~ 0.10"0.20 ~ ~/o C~ ~ 

30 

20 

\ 

10 I I I I I I 

As- 100 200 300 400 500 600 700 

quenched Tempering temperature, °C 

Fig. 36 Decrease in the hardness of martensite with tempering temperature for various carbon contents. Source: Ref 2 

3.5 to 5.5% Ni, and 0.25% N. The other type 2xx 

series of steels contain from 0.25 to 0.40% N. 

Another important austenitic steel is austenitic 

manganese steel. Developed by Sir Robert Had- 

field in the late 1890s, these steels remain 

austenitic after water quenching and have consid- 

erable strength and toughness. A typical Hadfield 

manganese steel will contain 10 to 14% Mn, 0.95 

to 1.4% C, and 0.3 to 1% Si. Solution annealing 

is necessary to suppress the formation of iron 

carbides. The carbon must be in solid solution to 

stabilize the austenite. When completely austeni- 

900 

As-quenched 

800 65 

'= 

As-quenched / 

hardiness "~-//I 

/ 

~0~°F I 

400°F 

°° 

0= ], / ..,° 

" /b'/'' = 

"f" 600 °F..,@ n- 

,6 z~"l"- ~.c. 50 =" 

"O il 

45 

400 800 °F"°" 40 ~ 

• -. ~,,,,, ~o- I 

300 ; ; ~ o ~ ~.,,,~ ~,-, 1000 OF .o" 30 

200 ~....,~ 1200 °F=o= 

1300 °F 

100 I 

0.2 0.4 0.6 0.8 1.0 

Carbon, % 

Fig. 38 Relationship between hardness of tempered 

martensite with carbon content at various tem- 

pering temperatures. Source: Ref 2 

tic, these steels can be work hardened to provide 

higher hardness and wear resistance. A work- 

hardened Hadfield manganese steel has excellent 

resistance to abrasive wear under heavy loading. 

Because of this characteristic, these steels are 

ideal for jaw crushers and other crushing and 

grinding components in the mining industry. 

Also, Hadfield manganese steels have long been 

used for railway frogs (components used at the 

junction point of two railroad lines). 

Ferrite-Cementite 

When plain-carbon steels are heated to temperatures 

just below the lower critical tempera- 

8O 

70 

> 60 

"1- 

~ 50 

~ 4o 

.E 

~ 3o 

o 

20 

I1. 

J:: 

o} 

Hardness, HB 

555 

300 

(2070) 

477 415 363 

250 

(172o) 

200 

(13oo) 

150 

(1030) 

100 

(690) 

\ \ 

N Tensile strength 

' ' '\ N 

-- Yield point - N N 

NiX 

-- Reduction in area --~ 

293 

Elongation 

' i ~ ' 

400 600 800 1000 1200 

(200) (320) (430) (540) (650) 

Tempering temperature, °F(°C) 

70 

6O 

¢5 

t~ 

4O 

!i 

5 ILl 

Fig. 37 Effect of tempering temperature on the me- 

chanical properties of type 4340 steel. Source: 

Ref 2 

ture (Ac]), the process of spheroidization takes 

place. Figure 41 shows a fully spheroidized steel 

microstructure. The microstructure before sphe- 

roidization is pearlite. During spheroidization, 

the cementite lamellae of the pearlite must 

change morphology to form spheroids. The proc- 

ess is controlled by the diffusion rate of carbon 

and portions of the lamellae must "pinch-off" 

(dissolve) and that dissolved carbon must diffuse 

to form a spheroid from the remaining portions 

of lamellae. This process takes several hours. 

Spheroidization takes place in less time when the 

starting microstructure is martensite or tempered 

martensite. In this process, the spheroidized car- 

bides are formed by growth of carbides formed 

during tempering. 

A fully spheroidized structure leads to im- 

proved machinability. A steel in its fully sphe- 

/ e • 

• Mo 

j 

• tw p 

.S/ !° Cr 

o Si 

lO 

j 

f 

0 

0.02 0.04 o.o6 0.1 0.2 

Element content, % 

0.4 0.6 1 2 

Fig. 39 E~ of alloying elements on the retardation or softening during tempering at 540 °C (1 000 °F) relative to iron- 

carbon alloys. Source: Ref 2

1200 

100o / f 

-- Tensile/~stStrength -- / 

~ mo 

I rength 

= 600 / / ' (0.2*/. offset) 

~- 40 =m 

o 

200 ~- [] 

~ 20 

0 ~ 

0 10 20 30 40 50 60 

Cold work. % 

Fig. 40 Influence of cold work on mechanical proper- 

ties of type 304 stainless steel. Source: Ref 4 

roidized state is in its softest possible condition. 

Some steels, such as type 1020, are spheroidized 

before cold forming into tubing because 

spheroidized steels have excellent formability. 

Ordinary low-carbon, cold-rolled, and an- 

nealed sheet steels have ferritic microstructures 

with a small amount of grain-boundary cemen- 

tite, as shown in Fig. 8. These carbides nucleate 

and grow on the ferrite grain boundaries during 

the annealing process, which takes place in the 

lower portion of the intercritieal temperature re- 

gion (i.e,, the region between the A 3 and A 1 tem- 

peratures shown in the iron-carbon diagram, Fig. 

6). Many modern-day automotive sheet steels are 

produced with very low carbon levels to avoid 

these grain-boundary carbides because they de- 

grade formability. 

Ferrite-Martensite 

A relatively new family of steels called dual- 

phase steels consists of a microstracture of about 

Fig. 42 Microstructure of a typical dual-phase steel. 2% nital etch. 250x 

/ 

Strudure/Property Relationships in Irons and Steels / 171 

0 ~+, ,+,.. + .,yff/S+~ ++ z9 O,o,:" Q ~ - * o " 

s ~t" ~ utz , o v # = = o © 

"x ~, o+ DO . ",-,~', . o o ~ o 

• ~, .o0. °%0 :':,~, - ,,~. o- ~ 

• . " ," ~. t) • 

OC~ 06 o o " +' (/ )1 (7 * .,~ ,,,,. ~ ====, I=, ¢'~'~ .',,a 

0 o o oo v . ,0 I= ~F' = ,~,=p " % 

O . .++ o,,o 0+,o+ .~l..~,,o.: .o ~, .= . . . . ~ + 

• ~ o +° "o. o ~>/2 + .~.,o,'-." • , ."1 ". ~ == ~+)1 ^+L 

~:~ ,e-~a ~, ~" 0,//~,,.. ,,- .. oOo..~:" 0~"o o:.- "'+,~" +o~"~'~ ~o'+


The duplex structure results in improved stress- 

corrosion cracking resistance, compared with 

austenitic stainless steels, and improved tough- 

ness and ductility, compared with the ferritic 

stainless steels. Duplex stainless steels are capa- 

ble of tensile yield strengths ranging from 400 to 

550 MPa (60 to 80 ksi) in the annealed condition, 

which is approximately twice the strength of 

either phase alone. 

The principal alloying elements in duplex 

stainless steels are chromium and nickel, but ni- 

trogen, molybdenum, copper, silicon, and tung- 

sten may be added to control structural balance 

and to impart certain corrosion-resistance char- 

acteristics. Four commercial groups of duplex 

stainless steels, listed in order of increasing cor- 

rosion resistance, are: 

Fe-23Cr-4Ni-0.1N 

• Fe-22Cr-5.5Ni-3Mo-0.15N 

• Fe-25Cr-5Ni-2.5Mo-0.17N-Cu 

• Fe-25Cr-7Ni-3.5Mo-0.25N-W-Cu 

Because of their excellent corrosion resistance, 

ferrite-austenite duplex stainless steels have 

found widespread use in a range of industries, 

particularly the oil and gas, petrochemical, pulp 

and paper, and pollution control industries. They 

are commonly used in aqueous, chloride-contain- 

ing environments and as replacements for 

austenitic stainless steels that have suffered 

stress-corrosion cracking or pitting during ser- 

vice. 

Graphite 

When carbon contents of iron-carbon alloys 

exceed about 2%, there is a tendency for graphite 

to form (see Fe-C diagram in Fig. 6b). This is 

especially true in gray cast iron in which graph- 

ite flakes are a predominant microstructural fea- 

ture (Fig. 3). Gray cast iron has been used for 

centuries because it melts at a lower temperature 

than steel and is easy to cast into various shapes. 

Also, the graphite flakes impart good ma- 

chinability, acting as chip breakers, and they also 

provide excellent damping capacity. Damping ca- 

pacity is important in machines that are subject 

to vibration. However, gray cast iron is limited to 

applications that do not require toughness or duc- 

tility, for example, total elongation of less than 

1%. The flake morphology of the graphite pro- 

vides for easy crack propagation under applied 

stress. 

Gray cast irons usually contain 2.5 to 4% C, 1 

to 3% Si, and 0.1 to 1.2% Mn. The graphite 

flakes can be present in five different morpholo- 

Type A Type B 

./T.¢,i! 

,/ I/ / ; [_,~'~" 

72,: • / ,'~..,,~, ,, ,,. --'~,1 '~. ' • 

Uniform distribution, Rosette grouping, 

random orientation random orientation 

Fig. 45 Classification of different graphite flake morphology 

Fig. 44 Microstructure of a typical mill-annealed duplex stainless steel plate showing elongated austenite islands in the 

ferrite matrix. Etched in 15 mL HCI in 100 mL ethyl alcohol. 200x 

gies as seen in Fig. 45. Type A, because of its 

random orientation and distribution, is preferred 

in many applications, for example, cylinders of 

internal combustion engines. The matrix of a 

typical gray cast iron is usually pearlite. How- 

ever, ferrite-pearlite or martensitic micro- 

structures can be developed by special heat treat- 

ments. As a structural material, gray cast iron is 

selected for its high compressive strength, which 

ranges from 572 to 1293 MPa (83 to 188 ksi), 

although tensile strengths of gray iron range only 

from 152 to 431 MPa (22 to 63 ksi). Gray cast 

irons are used in a wide variety of applications, 

including automotive cylinder blocks, cylinder 

heads and brake drums, ingot molds, machine 

housings, pipe, pipe fittings, manifolds, compres- 

sors, and pumps. 

Another form of graphite in cast iron is 

spheroidal graphite found in ductile cast irons 

(also called nodular cast irons). The micro- 

structure of a typical ductile cast iron is shown in 

Fig. 46. This form of graphite is produced by a 

process called inoculation, in which a magne- 

sium or cerium alloy is thrust into molten cast 

iron immediately prior to the casting operation. 

These elements form intermetallic compounds 

that act as a nucleating surface for graphite. With 

a spherical morphology, the graphite no longer 

renders the cast iron brittle as do graphite flakes 

in gray cast iron. Ductile irons have much higher 

ductility and toughness than gray iron and thus 

expand the use of this type of ferrous alloy. Most 

ductile iron castings are used in the as-cast form. 

However, heat treatment can be employed to al- 

Type C 

Superimposed flake size, 

random orientation 

• i:t" 

Type D 

ter the matrix microstructure to obtain desired 

properties. The matrix can be fully ferritic, fully 

pearlitic, fully martensitic, or fully bainitie, de- 

pending on composition and heat treatment. The 

yield strength of typical ductile cast irons ranges 

from 276 to 621 MPa (46 to 76 ksi), and their 

tensile strengths range from 414 to 827 MPa (60 

to 120 ksi). Total elongation ranges from about 3 

to 18%. Heat treated, austempered ductile irons 

have yield strengths ranging from 505 to 950 

MPa (80 to 138 ksi), tensile strengths ranging 

from 860 to 1200 MPa (125 to 174 ksi), and total 

elongations ranging from 1 to 10%. Uses for due- 

tile iron include gears, crankshafts, paper-mill 

dryer rolls, valve and pump bodies, steering 

knuckles, rocker arms, and various machine com- 

ponents. 

Cementite 

A major microstructural constituent in white 

cast iron is cementite. The microstructure of a 

typical white cast iron is shown in Fig. 47. The 

cementite forms by a eutectic reaction during so- 

lidification: 

Liquid ~-~ Cementite + Austeuite (Eq 15) 

The eutectic constituent in white cast iron is 

called ledeburite and has a two-phase morphology 

shown as the smaller particles in the white matrix 

in Fig. 48. The eutectic is shown in the Fe-C 

.~>..' 

~,~.

Fig, 46 Microstructure of a typical ductile (nodular) cast 

iron showing graphite in the form of spheroids. 

2% nital etch. 200x. Courtesy of A.O. Benscoter, Lehigh 

University 

binary diagram in Fig. 6(b). The austenite in the 

eutectic (as well as the austenite in the primary 

phase) transforms to pearlite, ferrite-pearlite, or 

martensite, depending on cooling rate and compo- 

sition. Because of the high percentages of cemen- 

tite, white cast irons are used in applications 

requiring excellent wear and abrasion resistance. 

These irons contain high levels of silicon, chro- 

mium, nickel, and molybdenum and are termed 

alloy cast irons. Such applications include steel 

mill rolls, grinding mills, and jaw crushers for the 

mining industry. Hardness is the primary me- 

chanical property of white cast iron and ranges 

from 321 to 400 HB for pearlitic white iron and 

400 to 800 HB for alloy (martensitic) white irons. 

REFERENCES 

1. P.D. Harvey, Ed., Engineering Properties of Steel, 

American Society for Metals, 1982 

2. G. Krauss, Principles of the Heat Treatment of Steel, 

American Society for Metals, 1980 

3. R.W.K. Honeycombe, Steels--Microstructure and 

Properties, American Society for Metals, 1982 

4. W.C. Leslie, The Physical Metallurgy of Steels, 

McGraw-Hill, 1981 

5. F.B. Picketing, Physical Metallurgy and the Design of 

Steels, Applied Science, 1978 

6. G. Krauss, Microstruetures, Processing, and Properties 

of Steels, Properties and Selection: Irons, Steels, and 

High-Performance Alloys, Vol 1, ASM Handbook, 

1990, p 126 

7. E.C. Bain and H.W. Paxton, Alloying Elements in Steel, 

2nd ed., American Society for Metals, 1961, p 62 

8. Microalloying 75, Conference Proceedings (Washing- 

ton, D.C., Oct 1975), Union Carbide Corp., 1977, p 5 

9. T.B. Massalski, J.L. Murray, L.H. Bennett, and H. 

Baker, Ed., Binary Alloy Phase Diagrams, Vol 1, 

American Society for Metals, 1986, p 822 

10. W. Haller, 1L Schweitzer, and L. Weber, Can. Metall. 

Q., Vol 21 (No. 1), 1982, p 3 

11. J.M. Hyzak and I.M. Bernstein, Metall. Trans. A, Vol 

7A, 1976, p 1217 


Fig, 47 Microstructure of a typical white cast iron. 4% picral etch. 100x. Courtesy of A.O. Benscoter, Lehigh University 

Fig. 48 Microstructure of the eutectic constituent ledebutite in a typical white cast iron. 4% picral etch. 500x. Courtesy 

of A.O. Benscoter, Lehigh University 

12. G.E Vander Voort and A. Ro6sz, Metallography, Vo117 

(No. 1), 1984, p 1 

13. H. Iehinose et al., paper 1.3, Proc. First Int. Heavy 

Hauls Railway Conf., Association of American Rail- 

roads, 1978, p 1 

14. G.E Vander Voort, Ed.,Atlas of Time-Temperature Dia- 

grams for Irons and Steels, ASM International, 1991, p 

570 

15. B.L. Bramfitt, Proc. 32nd Mechanical Working and 

Steel Processing Conference, Vol 28, ISS-AIME, 1990, 

p 485 

16. F.B. Picketing, Towards Improved Toughness and Duc- 

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17. G.J. Roe and B.L. Bramfitt, Notch Toughness of Steels, 

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18. E.C. Bain, The Sorby Centennial Symposium on the 

History of Metallurgy, TMS-AIME, 1963, p 121 

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21A, 1990, p 817 

20. G.E Vander Voort, Ed., Atlas of Time-Temperature Dia- 

grams for Irons and Steels, ASM International, 1991, p 

249 

21. W. Steven and A.G. Haynes, J. Iron Steel Inst., Vol 183, 

1956, p 349 

22. R.W.K. Honeycombe and F.B. Pickering, Metall. 

Trans. A, Vol 3A, 1972, p 1099 

23. G.E Vander Voort, Ed., Atlas of~me-Temperature Dia- 

grams for Irons and Steels, ASM Intgrantional, 1991, p 

544 

24. K.W. Andrews, J. Iron Steel Inst., Vol 203, 1965, p 271 

25. G.R. Speich and H. Warlimont, J. Iron Steel Inst., Vol 

206, 1968, p 385 

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27. R.A. Grange, C.R. Hrihal, and C.F. Porter, Metall. 

Trans. A, Vol 8A, 1977, p 1775

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