Development of low-nickel austenitic stainless-steel wire for forming ...

Development of low-nickel
austenitic stainless-steel wire for
forming, grids, springs…
JM. Hauser 1 , E. Chauveau 1 , L. Antoni 1 ,B. Héritier 1 ,
A. Sage 2
1 - Ugine-Savoie Imphy
Avenue Paul-Girod F73400 Ugine
2 - Sprint-Métal Immeuble Pacific
13, Cours Valmy F-92070 La Défense Cedex
A new 16.2 % Cr- 7.5% Mn – 3 %Cu- 0.2%N –
1.9% Ni austenitic steel may substitute to 304. Its
metallurgical , magnetic, and mechanical
properties are presented here. It is oxidation
resistant up to 800°C. Its corrosion resistance is
equivalent to that of 304 for many applictions ,
including gratings, grids, springs,….
1. INTRODUCTION
Standard austenitic stainless steels, such as
304,are prone to large price variations in relation with
the economical cycles and with the nickel price .
Steadinox, also called 204Cu, a low-nickel austenitic
grade containing manganese, copper and nitrogen,
was designed to be able to replace 304 in most 304
wire applications. Its typical composition is (mass%) :
0.05 C - 0.8 Si- 7.5 Mn -1.9 Ni - 16.2 Cr- 0.3 Mo - 3
Cu-0.2 N - 0.0025 B - 0.001 S - 0.025 P ; it is in
accordance with UNS S20430 (204Cu) and under
european EN10088 standardisation procedure
(X8CrMnCuNB17-8-3 ) .
Similar stainless steels have been already studied
[1][2][3][4][5] , although this one is somehow
differently equilibrated, to be in ferritic solidification
mode ( weldable), without too much high
temperature ferrite ( hot-workable) and with
sufficiently low carbon to avoid ICS after most
operations. A small quantity of nickel contributes to
adequate phase equilibrium as well as to sufficient
resistance to crevice corrosion; the medium level of
silicon was designed to obtain fairly good oxidation
resistance despite of the high level of manganese.
Austenite stability was adapted to obtain the same
level of work-hardening coefficient as that of 304, and
therefore equivalent tensile ductility.
1- METALLURGICAL, MECHANICAL AND
PHYSICAL PROPERTIES
2.1 Phases
As-cast or as-welded structures exhibit a few %
remaining ferrite, mainly on dendritic axis; thus, it
solidifies in a ferritic mode, which is prefered to avoid
hot-cracking . After hot-rolling and quench-annealing
at 1050°C, a fully austenitic structure is obtained
(ferrite < 0.5% ).
2.2 Mechanical properties and cold-working ;
amagnetism
Tensile properties of the annealed material are
slightly higher than those of 304, due mainly to the
hardening effect of nitrogen ( table 1 ).
Table 1 -Tensile properties
( φ 5.5 mm rod-wire, annealed, typical)
Y.S. T.S. Elongation
Mpa MPa %(5d)
Steadinox 340 675 60
304 235 600 62
During cold-working, for instance by drawing, the
austenite of Steadinox partially transforms to α’quadratic
martensite, just as 304 does, but with a
lower transformation rate. This result in a colddrawing
curve parallel to that of 304 (figure 1) and in
lower values of magnetic permeabilty, depending of
the cold-reduction ratio (figure 2)
Y.S. and T.S. ( Mpa )
realtive permeability
1800
1600
1400
1200
1000
800
600
400
200
0
0 10 20 30 40 50 60 70
reduction ratio %
Figure 1 : cold work-hardening curve by cold-drawing
7
6
5
4
3
2
1
Steadinox
304
Polynomial (304)
Polynomial (Steadinox)
Figure 2 : magnetic permeability µr
steadinox Y.S.
304 Y.S.
steadinox T.S.
304 T.S.
Polynomial (steadinox T.S.)
Polynomial (304 T.S.)
Linéaire (304 Y.S.)
Linéaire (steadinox Y.S.)
0
0 10 20 30 40 50 60 70
reduction ratio ( % )

3. HIGH TEMPERATURE BEHAVIOUR
3.1 Mechanical behaviour
Annealed 204Cu wires exhibit high tensile strength,
at the same level as AISI 347 [6], up to 800°C
(figures 3 ), with secondary hardening in the range
500-800°C, due probably to chromium nitride
precipitation ( no sigma phase was observed in that
range ) .
Y.S., U.T.S. ( Mpa)
Y.S. ( Mpa )
800
700
600
500
400
300
200
100
400
300
200
100
STEADINOX
EL %
U.T.S.
Y.S.
EL%
0
0
0 200 400 600 800 1000
Temperature °C
316L
steadinox
347
304
321
0
0 200 400 600 800
Temperature °C
1000
Figures 3 : high temperature tensile properties
100
3.2 Scaling
High temperature oxidation properties of Steadinox
has been compared with that of a classical AISI 304
(18.0 Cr 11.1Ni 1.3 Mn 0.5 Si 0.05 C 0.04 N bal.
Fe),using cylindrical samples (φ4x30 mm) from
industrial wires. Metal losses were measured after
descaling the samples by a chemical procedure [7].
The maximum operation temperature Tmax of these
grades has been determined following the definition
incorporated in the draft of EN 10295 [8], known as
the 5 x 24 h test. The results are presented in figure
4. It can be deduced that Tmax is almost the same
for both grades and equals 870°C.
90
80
70
60
50
40
30
20
10
Metal Loss (g/m²/h)
10
9
8
7
6
5
4
3
2
1
T max : Metal loss < 1 g/m²/h at T max
and Metal loss < 2 g/m²/h at T max+50°C
steadinox
304
0
650 750 850
Temperature (°C)
950 1050
Figure 4 : Metal loss vs. temperature plots for
the isothermal oxidation in still air of alloys
Steadinox and 304 after 5 x 24 h testing time.
The resistance to thermal cycling of these materials,
which can strongly influence their lifetime in service
conditions [9] has been characterized at 800°C up to
1200 cycles (or 400 h total dwell time) using a severe
thermal cycle described elsewhere [7]. Figure 5
indicates that both grades behave analogously.
Metal Loss (g/m²)
8
7
6
5
4
3
2
1
0
number of cycles
0 300 600 900 1200
steadinox
304
0 100 200 300 400
Total Dwell Time (h)
Figure 5 : Metal loss vs. total dwell time plots
for the cyclic oxidation in still air of alloys
Steadinox and 304 at 800°C (thermal cycle :
20 min dwell time, 5 min air forced cooling)

4 . CORROSION RESISTANCE : GENERAL
BEHAVIOUR
This part includes a comparison of Steadinox, 430
(1.4016) and 304 (1.4301) for different types of
corrosion in several chemical solutions.
4.1 CORROSION RESISTANCE IN A HIGHLY
CHLORINATED MEDIUM : CREVICE CORROSION
In some complicated confined areas, an acid solution
may exist, by the crevice corrosion mechanism,
which is studied by several electrochemical tests.
Electrochemical test for crevice corrosion :
measurement of depassivation pH : the lower this
pHd, the higher the corrosion resistance ; pHd is
evaluated using the dissolution current on a
polarisation curve at different pH values (1,5 à 3) in a
highly chlorinated ( 2M ) solution at 23°C : pHd is
obtained at 10 µA/cm².
Figure 6 shows the variation of the dissolution
current at several pH values for 304 , Steadinox and
430. .
i critical (µA/cm²)
1200
1000
800
600
400
200
CREVICE CORROSION TEST in NaCl 2M, 23°C
430
Steadinox
304
0
1,5 1,7 1,9 2,1 2,3 2,5 2,7 2,9 3,1
Figure 6 : electrochemical dissolution current
Steadinox appears to be equivalent to 304 :same
depassivation pH and same speed of crevice’s
growth ( represented by the slope of the curve ) .
4.2 STRESS CORROSION RESISTANCE
Stress corrosion resistance is studied by tensile
testing in a solution of MgCl2 boiling at 155°C : it is
defined as the critical deformation speed, under
which the tensile strength and the rupture elongation,
measured in corrosive solution, are lower than those
in an inert silicon oil ( or lower than at very high
speed of deformation in corrosive solution ) .
Steadinox and 304 both have a critical speed of
about 2.10 -3 s -1 , and are thus equivalent .
pH
4.3 PITTING CORROSION RESISTANCE IN A
WEAKLY CHLORINATED SOLUTION
4.3.1 Methods
Pitting corrosion was studied for NaCl 0,02M to 2M ;
pH 2 to 6,6 ; temperature 23°C to 50°C ; with or
without an oxidizing agent in the solution.
Using the OCP (Open Circuit Potential)
electrochemical test, the potential of the sample in a
corrosive solution was measured along 5 days
,leading to different kinds of behaviour :
*behaviour A : stable potential, no corrosion on the
sample,
*behaviour B : some variations of the potential; the
depth and the length of the variations are small :
unstable repassivating pits ; corrosion is not
dangerous in these conditions ;
*behaviour C : deep variations of potential (very
cathodic potential’s value for example) : pits are
growing ; there is pitting corrosion on the sample.
4.3.2 Corrosion resistance in a neutral solution
Hooks out of Steadinox, 430 and 304 were tested in
NaCl 5% ( 0.86 M ), pH 6,6 at 35°C ( figure 7 ) . This
medium is equivalent to that of the salt spray test
(French standard NFX41002 )
On Steadinox, the number of variations of potential
were small ( behaviour B , close to behaviour A ) ;
there was no corrosion neither on Steadinox nor on
304 (430 exhibits stable pits with corrosion ,
behaviour C).
304 behaviour A
Steadinox
behaviour A
430 behaviour C
Figure 7 : Hooks in a neutral solution : OCP test

4.3.3 Corrosion resistance in a highly chlorinated
warm solution NaCl 2M , pH 6,6 , 50°C, with oxygen
bubbling
430 exhibits stable pits ( behaviour C), whereas for
Steadinox, the formation of pits is limited and they
are not growing ( behaviour B ) : Steadinox
behaviour is better than 430 , in these pitting
corrosion conditions .
4.3.4 Corrosion resistance in a weakly chlorinated
solution with oxidizing agent
After a first 24 h step in NaCl 0,02M, pH 6,6 ,
23°C ,the solution is changed to : NaCl 0,02M or
0,5M , pH 6,6 , 23°C , together with an oxidizer
(FeCl3 , 2.10-4 M or 5.10-3M ), which is added to
obtain a very anodic potential.
Such an oxidizer produces, on Steadinox, unstable
pits which don’t grow ( repassivation mechanism ); on
430, numerous unstable pits, with deep potential
variations : the pitting corrosion is more sever on 430.
So, it is possible to use Steadinox in solutions with
an oxidizer, but the use in warm highly-chlorinated
solutions containing an oxidizing agent will need a
more complete study .
4.4 UNIFORM CORROSION RESISTANCE IN ACID
SOLUTIONS
Using an electrochemical test in H2SO4 2M at 23°C ,
dissolution current in microamp/cm2
600
500
400
300
200
100
0
204 Cu very similar to 304
UNIFORM CORROSION H2SO4 2M 23°C
13.7 mA/cm2
304 (1.4301) UGI 204 Cu 430 (1.4016)
Figure 8 : activity current for uniform corrosion
a current of dissolution (or activity, in opposition to
the passivity current), representing the speed of
corrosion, was measured on a polarization curve .
In this mechanism, Steadinox behaves as 304 ;
their corrosion speed ( 80 to 90 µA/cm² ) are far
slower than that of 430 (13.7 mA/cm² ).
4.5 USE FOR FOOD STORAGE : dissolution in
drinking water and in acetic acid :
The elemental quantities of Cu , Ni , Fe, Cr et Mn
dissolving from Steadinox in drinking water (distilled
water with 506 mg/l MgSO4 , 95 mg/l K2SO4 , and
330 mg/l NaCl ; pH = 6.6. ) at 23°C or 70°C are
entirely consistent with the recommanded values of
World Health Organisation .
In µg/l Cu Ni Mn Fe Cr
Drinking water 23°C
Steadinox
7 2,6 23 90 2,6
Drinking water 70°C
Steadinox
1,7 1,7 100 235 4,4
WHO values
( max )
2000 20 100 300 50
In acetic acid (3 %, 70°C), dissolved elemental
quantities are equivalent for Steadinox and 304 (in
µg/dm² ) :
period Cu Ni Mn Fe Cr
Steadinox 0 - 30 mn 2,8 0,4 7,1 106 15,8
30 - 60 mn 0,1 0,1 1,2 5 2
60 - 90 mn 0 0,3 1 1,3 1,2
304 0 – 30 mn -

T2 : 650°C / 10 mn / WQ T1 : 700°C / 30 mn/ WQ
Mas Crack Test Mass Crack Test
loss depth Validatio loss Depth Validation
In mg In µm n in mg in µm
Steadinox 3,7 0 Yes 5 30 Yes
304 nr1 0,5 0 Yes 0,9 0 Yes
304 nr2 2,5 0 Yes 3,4 0 Yes
5 . STUDY OF SOME APPLICATIONS
5.1 PIGSTY GRATINGS
The Steadinox resistance in the synthetic solutions
(50°C ; pH 6,5 ; 0,1M NaCl ; 10ml/l NH4OH ; 25 mg/l
KOH ; 5 mg/l H3PO4) of pigsty medium is equivalent
to that of 304 ;potential variations in OCP test remain
very limited (figure 9 ).
E (mV/ECS)
Figure 9 : OCP on Steadinox in pigsty medium
5.2 GRIDS FOR FOOD STORAGE
U (en mV/ECS)
100
0
-100
-200
-300
-400
0
-50
-100
-150
-200
-250
-300
-350
0 24 48 72 96 120
exposure( h)
Steadinox
Steadinox: behaviour B
0 10 20 30 40 50 60 70
Temps (en h)
.
Figure 10 : OCP on a Steadinox grid sample
Figure10 represents the OCP result of a Steadinox
grid sample in NaCl 5% 35°C pH 6.6, exhibiting a B
behaviour , with some metastable pits ; no corrosion
is visible at the end of the test.
5.3 TILE HOOKS FOR ROOFS
Steadinox tile hooks show a good corrosion
resistance in salt environment (salt spray test , 1000
hours, french standard NFX41002 NaCl 5% 35°C pH
6.6 ) and in an industrial environment (test with
sulphur dioxide and dampness condensation over
500 hours) , in spite a very small pitting corrosion .
6 . APPLICATION TO SPRING WIRES
6.1 Mechanical behaviour
Compression springs were made using Steadinox
and 302 cold-drawn wires,at eqivalent U.T.S. levels :
T.S. Y.S. Martensite
MPa Mpa %
Steadinox As-drawn 2090 1750 10
304
180°C
3 mn
2140 10
300°C
3 mn
2290 1920 11
As-drawn 2080 1830 52
180°C
3 mn
2130 1890 52
A short stabilizing treatment ( 3 mn at 180°C or
300°C ) was made on springs. Resistance to sagging
was evaluated by successive limited compressions or
by one full compression .
The sagging resistance (measured by shortening)
of Steadinox springs was equivalent to that of 304
springs :
SAGGING %
0,12
0,10
0,08
0,06
0,04
0,02
0,00
Steadinox springs,HT300°C
Steadinox springs, HT 180°C
302 springs, HT 180°C
1 full compression
0 2 4 6
Number of limited compressions

6.2 Corrosion resistance
The Steadinox and AISI302 spring samples were
tested by Open Circuit Potential in NaCl 5% , 35°C
pH 6.6 after the following treatments :
- stabilizing treatment
- pickling, and passivation , in HNO3 solution.
Both kinds of springs behave correctly the OCP test
(A-behaviour).
7. CONCLUSION
Steadinox is similar to 304 in respect to workhardening
and tensile ductility, although being less
magnetic after cold-working. It may be used up to
800°C without excessive oxidation. Steadinox springs
exhibit as low sagging as 304 springs
Its corrosion resistance is equivalent to that of 304 in
weakly chlorinated mediums ; it was proved by OCP
or exposure tests that it may be used as formed
wires or welded assemblies, grids,… in lot of usual
mediums, and in body-, food- or water-contact.
Finally, Steadinox may replace 304 in most wire
applications .
REFERENCES
[1] J.H.MAGEE Development of type 204 CU
stainless, a low cost alternate to type 304
Interwire Conf., 2001-05-14,Atlanta, ed .Wire Ass.Int.
[2) M.G.MECOZZI et al. Un acciao inossidable
austenitico con nichel inferiore al 2 %
La Metallurgia Italiana 10/99 pp 49-55
[3] R.SANCHEZ et al. Properties of an austenitic
stainless with less than 2% nickel
Innovation in Stainless Steel Conf, Florence,It.,
11-14/10/1993 pp 2-231-2.236,
ed.Ass.Ital.Metallurgia 1993
[4] M.B.CORTIE et al.
Experimental austenitic stainless steels containing
7% Mn, 2%Ni and up to 4% Cu ,
High manganese high Nitrogen Austenitic Steels
Conf.Proc. ed R.A.LULA / ASM (1992) pp177-185
[5] K.. HOSHINO et al. The various characteristics of
Ni-free austenitic Stainless Steels, type NHS104
Tool & Alloy Steels vol 8 (1974 ) n°1 pp 84-94
Steel Furnace Monthly,1974 (9), 5, pp325-340
[6] J.H.HOKE Mechanical properties of Stainless
Steels at elevated temperatures,
in D.PECKNER et al. Handbook of Stainless steels
ed McGraw Hill 1977, pp 21-121-2
[7] ANTONI L. Comparison of the cyclic
oxidation behaviour between AISI 304 and lownickel
austenitic stainless steels,
Mater. Sci. Forum 369-372 (2001) 345-352
[8] “Heating resistant steel castings” pr EN
10295, draft for European Standard, issued May
1998, chapter 7.2.3.1
[9]. Cyclic oxidation of high temperature
materials, EFC n°27, M. Schütze , W.J.
Quaddakkers Eds., (The Institute of Materials,
London 1999) 496pp.