Evaluation and Repair of Wrought Iron and - Purdue e-Pubs ...
Evaluation and Repair of Wrought Iron and - Purdue e-Pubs ... Evaluation and Repair of Wrought Iron and - Purdue e-Pubs ...
78strength from the existence of pearlite is negligible. Carbon in wrought iron typicallyexists as fine precipitates of iron carbide, or cementite intermixed with the ferrite(Gordon,1988). This is because the wrought iron was never fully heated to a liquid formduring the manufacturing process, and so the carbon is not heated fully enough to formpearlite.The dark, elongated areas in the micrograph in Figure 4.1 are inclusions whichconsist of a variety of impurities like phosphorous, sulfur or silicon. The majority ofthese impurities are iron silicate and other oxides which are commonly grouped togetherand known as slag. The slag was intertwined into the microstructure of the wrought ironduring the manufacturing process where the molten slag was used to help heat the ironore. Most of the molten slag was squeezed out of the material during rolling of thewrought iron into the eyebar shape.The slag inclusions that remained in the material were typically elongated andextended along only one direction in the material. These inclusions were larger thaninclusions that are typically found in other metals such as steel. Some of these inclusionsare large enough to be seen with the naked eye. Figure 4.2 shows a typical largeinclusion found throughout the material.Figure 4.3 is a photograph of a micrograph taken of the scrap piece of steel. Thismicrograph was used to compare the microstructure of the historic wrought iron to that ofa common structural steel. The micrograph of the steel indicated that steel consisted of asmaller grain structure than wrought iron. It also shows a mixture of ferrite, pearlite andimpurities that create the microstructure of steel. The impurities, or inclusions in the steelwere much smaller and more distributed, unlike the inclusions in wrought iron.The addition of carbon in the form of pearlite increases the strength and ductilityof pure iron to form steel. Since the composition of wrought iron consists mainly offerrite with widely dispersed areas of cementite and impurities, the mechanical properties
79are not similar to that of steel and indicate the wrought iron has lower strength andductility.The non-uniform nature of the microstructure of the wrought iron caused by theamount and irregular distribution of impurities and inclusions in the material create pointsof higher stresses that initiate crack growth through out the material. This reduces thestrength and ductility of the material. The lack of uniformity also makes it difficult toaccurately determine a definite yield and ultimate strength, since the amount of inclusionsfound in wrought iron varies considerably. This variation in microstructure is the reasonwhy a significant variation in mechanical properties was observed in the historical datagathered for wrought iron.4.2 Chemical AnalysisA chemical analysis of the wrought iron test material was completed to determinethe elements present. Table 4.1 shows the results from this chemical analysis. Theelements that were found to be prevalent in Eyebars E1 and E2 included carbon,phosphorous, sulfur, and most importantly, silicon.The amount of silicon present in the wrought iron and was between 0.12 and 0.15percent by weight. In steel, silicon amounts exceeding 0.3% are sometimes used incertain heat-treatable alloy steels and electrical steels (Linnert, 1994). Silicon typicallypromotes the fluidity of the metal while it is being processed into shapes and it alsopromotes hardenability. In wrought iron, silicon can be found mainly in the slag that isdispersed in pockets through out the metal. This slag causes an overall decrease instrength, but also helps to prevent corrosion. Since slag is a major component in thedefinition of wrought iron, the presence of silicon in excess of what is typically found insteel would be a crucial step in identifying an unknown metal as wrought iron.
- Page 48 and 49: 28Table 2.1 Average Ultimate Streng
- Page 50 and 51: 30Figure 2.3 Wrought Iron “Sponge
- Page 52 and 53: 32Histogram of Kirkaldy Wrought Iro
- Page 54 and 55: 34Percent Occurance in Range - %45.
- Page 56 and 57: 3660Combined Wrought Iron BarsTensi
- Page 58 and 59: 38The Bell Ford Bridge consisted of
- Page 60 and 61: 40Two. These samples were taken fro
- Page 62 and 63: 42specimens were of constant cross
- Page 64 and 65: 44Along with rectangular tensile co
- Page 66 and 67: 46After the initial test loading wa
- Page 68 and 69: 483.6 Fatigue TestingTo develop a b
- Page 70 and 71: 50The final specimen category consi
- Page 72 and 73: 52This analysis was completed using
- Page 74 and 75: 54After the initial test was comple
- Page 76 and 77: 56completed, but before the surface
- Page 78 and 79: 58readings, load cell readings and
- Page 80 and 81: 60Figure 3.3 Donated Eyebars 4 and
- Page 82 and 83: 62Figure 3.7 Heated Areas in Blue o
- Page 84 and 85: 64Figure 3.11 Detail Used in Groove
- Page 86 and 87: 66900080007000y = 27.153xR 2 = 0.99
- Page 88 and 89: 68Figure 3.19 Charpy Impact Testing
- Page 90 and 91: 70Figure 3.23 Eyebar Connection in
- Page 92 and 93: 72Figure 3.27 Eyebar A After Filler
- Page 94 and 95: 74Figure 3.31 Side View of Finished
- Page 96 and 97: 76Figure 3.35 Front View of Eyebar
- Page 100 and 101: 80The carbon content present in the
- Page 102 and 103: 82value may not be very accurate bu
- Page 104 and 105: 84strengths was found to be 29,940
- Page 106 and 107: 86wrought iron bars were investigat
- Page 108 and 109: 88stresses are induced. These perma
- Page 110 and 111: 90toughness the material. The test
- Page 112 and 113: 92From the finite element analysis,
- Page 114 and 115: 94Table 4.1 Chemical Analysis of Ey
- Page 116 and 117: 96Table 4.3 Tensile Coupon Test Res
- Page 118 and 119: 98Table 4.5 Charpy Impact Test Resu
- Page 120 and 121: 100Table 4.7 Comparison of Strain G
- Page 122 and 123: 102Figure 4.1 Typical Micrograph of
- Page 124 and 125: 104Figure 4.5 Fracture Surface of D
- Page 126 and 127: 106Comparison of Tensile Strengthfo
- Page 128 and 129: 108Combined Wrought Iron Bar Histor
- Page 130 and 131: 110Figure 4.17 Macrograph of Weld u
- Page 132 and 133: 112Figure 4.21 Cleavage Fracture of
- Page 134 and 135: Figure 4.25 Elongation of Hole in E
- Page 136 and 137: 116signs on or near the bridge that
- Page 138 and 139: 118testing of historic wrought iron
- Page 140 and 141: 120so that they would act in symmet
- Page 142 and 143: 122The reasons for the differences
- Page 144 and 145: 124The second corrosion pattern mod
- Page 146 and 147: 126Keating (1984) stated that the s
78strength from the existence <strong>of</strong> pearlite is negligible. Carbon in wrought iron typicallyexists as fine precipitates <strong>of</strong> iron carbide, or cementite intermixed with the ferrite(Gordon,1988). This is because the wrought iron was never fully heated to a liquid formduring the manufacturing process, <strong>and</strong> so the carbon is not heated fully enough to formpearlite.The dark, elongated areas in the micrograph in Figure 4.1 are inclusions whichconsist <strong>of</strong> a variety <strong>of</strong> impurities like phosphorous, sulfur or silicon. The majority <strong>of</strong>these impurities are iron silicate <strong>and</strong> other oxides which are commonly grouped together<strong>and</strong> known as slag. The slag was intertwined into the microstructure <strong>of</strong> the wrought ironduring the manufacturing process where the molten slag was used to help heat the ironore. Most <strong>of</strong> the molten slag was squeezed out <strong>of</strong> the material during rolling <strong>of</strong> thewrought iron into the eyebar shape.The slag inclusions that remained in the material were typically elongated <strong>and</strong>extended along only one direction in the material. These inclusions were larger thaninclusions that are typically found in other metals such as steel. Some <strong>of</strong> these inclusionsare large enough to be seen with the naked eye. Figure 4.2 shows a typical largeinclusion found throughout the material.Figure 4.3 is a photograph <strong>of</strong> a micrograph taken <strong>of</strong> the scrap piece <strong>of</strong> steel. Thismicrograph was used to compare the microstructure <strong>of</strong> the historic wrought iron to that <strong>of</strong>a common structural steel. The micrograph <strong>of</strong> the steel indicated that steel consisted <strong>of</strong> asmaller grain structure than wrought iron. It also shows a mixture <strong>of</strong> ferrite, pearlite <strong>and</strong>impurities that create the microstructure <strong>of</strong> steel. The impurities, or inclusions in the steelwere much smaller <strong>and</strong> more distributed, unlike the inclusions in wrought iron.The addition <strong>of</strong> carbon in the form <strong>of</strong> pearlite increases the strength <strong>and</strong> ductility<strong>of</strong> pure iron to form steel. Since the composition <strong>of</strong> wrought iron consists mainly <strong>of</strong>ferrite with widely dispersed areas <strong>of</strong> cementite <strong>and</strong> impurities, the mechanical properties
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