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Duplex & Super Duplex Steel |
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Duplex alloys were originally created to combat corrosion problems caused by chloride-bearing cooling waters and other aggressive chemical process fluids.
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Called Duplex because of its mixed microstructure with about equal proportions of ferrite and austenite, duplex stainless steels are a family of grades, which range in corrosion performance depending on their alloy content. The chemical composition based on high contents of Cr and Mo, improves intergranular and pitting corrosion resistance, respectively. Additions of nitrogen can promote structural hardening by interstitial solid solution mechanism, which raises the yield strength and ultimate strength values without impairing toughness. Moreover, the two-phase microstructure guarantees higher resistance to pitting and stress corrosion cracking in comparison with conventional stainless steels. |
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| The various Alloys |
| The development of the Duplex stainless steels has continued, graded for their corrosion performance depending on their alloy content. Today, modern duplex stainless steel can be divided into four groups: |
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| Composition of Duplex Stainless Steels : |
| The table lists the duplex stainless steels covered in ASTM specifications for plate, sheet, and bar products. |
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UNS Number
Duplex Grades |
Typeb |
C |
Mn |
P |
S |
Si |
Cr |
Ni |
Mo |
N |
Cu |
S31200 |
- |
0.030 |
2.00 |
0.045 |
0.030 |
1.00 |
24.0-26.0 |
5.5-6.5 |
1.20-2.00 |
0.14-0.20 |
- |
S31260 |
- |
0.03 |
1.00 |
0.030 |
0.030 |
0.75 |
24.0-26.0 |
5.5-7.5 |
2.5-3.5 |
0.10-0.20 |
0.20-0.80 |
S31803 |
- |
0.030 |
2.00 |
0.030 |
0.020 |
1.00 |
21.0-23.0 |
4.5-6.5 |
2.5-3.5 |
0.08-0.20 |
- |
S32001 |
- |
0.030 |
4.0-6.0 |
0.040 |
0.030 |
1.00 |
22.0-23.0 |
1.00-3.00 |
0.60 |
0.05-0.17 |
1.00 |
S32205 |
2205 |
0.030 |
2.00 |
0.030 |
0.020 |
1.00 |
19.5-21.5 |
4.5-6.5 |
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0.14-0.20 |
- |
S32304 |
2304 |
0.030 |
2.50 |
2.50 |
0.030 |
1.00 |
21.5-24.5 |
3.0-5.5 |
0.05-0.60 |
0.05-0.20 |
0.05-0.60 |
S32520 |
- |
0.030 |
1.50 |
0.035 |
0.035 |
0.80 |
24.0-26.0 |
5.5-8.0 |
3.0-4.0 |
0.20-0.35 |
0.50-2.00 |
S32550 |
255 |
0.04 |
1.50 |
0.040 |
0.030 |
1.00 |
24.0-27.0 |
4.5-6.5 |
2.9-3.9 |
0.10-0.25 |
1.5-2.5 |
S32750 |
2507 |
0.030 |
1.20 |
0.035 |
0.020 |
0.80 |
24.0-26.0 |
6.0-8.0 |
3.0-5.0 |
0.24-0.32 |
0.50 |
S32760 |
- |
0.030 |
1.00 |
0.030 |
0.010 |
1.00 |
24.0-26.0 |
6.0-8.0 |
3.0-4.0 |
0.20-0.30 |
0.50-1.00 |
S32900 |
329 d |
0.06 |
1.00 |
0.040 |
0.030 |
0.75 |
23.0-28.0 |
2.5-5.0 |
1.0-2.0 |
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S32950 |
- |
0.03 |
2.00 |
0.035 |
- |
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- |
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- |
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- |
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| BENEFITS |
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High strength |
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High resistance to pitting, crevice corrosion resistance. |
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High resistance to stress corrosion cracking, corrosion fatigue and erosion, |
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Good sulfide stress corrosion resistance, |
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Low thermal expansion and higher heat conductivity than austenitic steels, |
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Good workability and weldability, |
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High energy absorption. |
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