Duplex stainless steel
Duplex stainless steels[1][2][3] is the most recent family of stainless steels.
They are called duplex (or austenitic-ferritic) grades because their metallurgical structure consists of two phases, austenite (face-centered cubic lattice) and ferrite (body centered cubic lattice) in roughly equal proportions.
They are used for their good mechanical properties in the as-cast (and therefore as-welded condition) and/or their excellent corrosion resistance properties (particularly to stress corrosion cracking).[4]
They tend to be divided in three sub groups:
Grade 1.4462 which has been the grade initially developed. and reperesents the "mid-range" of properties and is perhaps the most used today
Super-duplex grades which were developed later to meet specific demands of the oil& gas as well as those of the chemical industries. They offer a superior corrosion resistance but are more difficult to process. Faulty processing will result in poor performance and users are advised to deal with reputable suppliers/processors
Lean Duplex grades, typically grade EN 1.4362, have been developed more recently for less demanding applications, particularly in the building & construction industry. Their corrosion resistance is closer to that of the standard austenitic grade EN 1.4401 (with a plus on resistance to stress corrosion cracking) and their mechanical properties are higher. This can be a great advantage when strength is important. This is the case in bridges, pressure vessels or tie bars.
Chemical compositions
Chemicals composition of grades from EN 10088-1 (2014) Standard are given in the table below:[5]
| Steel
Designation |
Number | C
Max |
Si | Mn | P
Max |
S
Max |
N | Cr | Cu | Mo | Ni | Other |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| X2CrNiN22-2 | 1.4062 | 0.03 | ≤1.00 | ≤2.00 | 0.04 | 0.010 | 0.16 to 0.28 | 21.5 to 24.0 | - | ≤0.45 | 1.00 to 2.90 | - |
| X2CrCuNiN23-2-2 | 1.4669 | 0.045 | ≤1.00 | 1.00 to 3.00 | 0.04 | 0.030 | 0.12 to 0.20 | 21.5 to 24.0 | 1.60 to 3.00 | ≤0.50 | 1.00 to 3.00 | - |
| X2CrNiMoSi18-5-3 | 1.4424 | 0.03 | 1.40 to 2.00 | 1.20 to 2.00 | 0.035 | 0.015 | 0.05 to 0.10 | 18.0 to 19.0 | - | 2.5 to 3.0 | 4.5 to 5.2 | - |
| X2CrNiN23-4 | 1.4362 | 0.03 | ≤1.00 | ≤2.00 | 0.035 | 0.015 | 0.05 to 0.20 | 22.0 to 24.5 | 0.10 to 0.60 | 0.10 to 0.60 | 3.5 to 5.5 | - |
| X2CrMnNiN21-5-1 | 1.4162 | 0.04 | ≤1.00 | 4.0 to 6.0 | 0.040 | 0.015 | 0.20 to 0.25 | 21.0 to 22.0 | 0.10 to 0.80 | 0.10 to 0.80 | 1.35 to 1.90 | - |
| X2CrMnNiMoN21-5-3 | 1.4482 | 0.03 | ≤1.00 | 4.0 to 6.0 | 0.035 | 0.030 | 0.05 to 0.20 | 19.5 to 21.5 | ≤1.00 | 0.10 to 0.60 | 1.50 to 3.50 | - |
| X2CrNiMoN22-5-3 | 1.4462 | 0.03 | ≤1.00 | ≤2.00 | 0.035 | 0.015 | 0.10 to 0.22 | 21.0 to 23.0 | - | 2.50 to 3.50 | 4.5 to 6.5 | - |
| X2CrNiMnMoCuN24-4-3-2 | 1.4662 | 0.03 | ≤0.70 | 2.5 to 4.0 | 0.035 | 0.005 | 0.20 to 0.30 | 23.0 to 25.0 | 0.10 to 0.80 | 1.00 to 2.00 | 3.0 to 4.5 | |
| X2CrNiMoCuN25-6-3 | 1.4507 | 0.03 | ≤0.70 | ≤2.00 | 0.035 | 0.015 | 0.20 to 0.30 | 24.0 to 26.0 | 1.00 to 2.50 | 3.0 to 4.0 | 6.0 to 8.0 | - |
| X3CrNiMoN27-5-2 | 1.4460 | 0.05 | ≤1.00 | ≤2.00 | 0.035 | 0.015 | 0.05 to 0.20 | 25.0 to 28.0 | - | 1.30 to 2.00 | 4.5 to 6.5 | - |
| X2CrNiMoN25-7-4 | 1.4410 | 0.03 | ≤1.00 | ≤2.00 | 0.035 | 0.015 | 0.24 to 0.35 | 24.0 to 26.0 | - | 3.0 to 4.5 | 6.0 to 8.0 | - |
| X2CrNiMoCuWN25-7-4 | 1.4501 | 0.03 | ≤1.00 | ≤1.00 | 0.035 | 0.015 | 0.20 to 0.30 | 24.0 to 26.0 | 0.50 to 1.00 | 3.0 to 4.0 | 6.0 to 8.0 | W 0.50 to 1.00 |
| X2CrNiMoN29-7-2 | 1.4477 | 0.03 | ≤0.50 | 0.80 to 1.50 | 0.030 | 0.015 | 0.30 to 0.40 | 28.0 to 30.0 | ≤0.80 | 1.50 to 2.60 | 5.8 to 7.5 | - |
| X2CrNiMoCoN28-8-5-1 | 1.4658 | 0.03 | ≤0.50 | ≤1.50 | 0.035 | 0.010 | 0.30 to 0.50 | 26.0 to 29.0 | ≤1.00 | 4.0 to 5.0 | 5.5 to 9.5 | Co 0.50 to 2.00 |
| X2CrNiCuN23-4 | 1.4655 | 0.03 | ≤1.00 | ≤2.00 | 0.035 | 0.015 | 0.05 to 0.20 | 22.0 to 24.0 | 1.00 to 3.00 | 0.10 to 0.60 | 3.5 to 5.5 | - |
Mechanical properties
Mechanical properties from European Standard EN 10088-3 (2014)[5] (for product thickness below 160mm):
| 0.2% proof Stress (MPa)
Min. |
Ultimate Tensile strength (MPa) | Elongation (%)
Min. | ||
|---|---|---|---|---|
| X2CrNiN23-4 | 1.4362 | 400 | 600 to 830 | 25 |
| X2CrNiMoN22-5-3 | 1.4462 | 450 | 650 to 880 | 25 |
| X3CrNiMoN27-5-2 | 1.4460 | 450 | 620 to 680 | 20 |
| X2CrNiN22-2 | 1.4062 | 380 | 650 to 900 | 30 |
| X2CrCuNiN23-2-2 | 1.4669 | 400 | 650 to 900 | 25 |
| X2CrNiMoSi18-5-3 | 1.4424 | 400 | 680 to 900 | 25 |
| X2CrMnNiN21-5-1 | 1.4162 | 400 | 650 to 900 | 25 |
| X2CrMnNiMoN21-5-3 | 1.4482 | 400 | 650 to 900 | 25 |
| X2CrNiMnMoCuN24-4-3-2 | 1.4662 | 450 | 650 to 900 | 25 |
| X2CrNiMoCuN25-6-3 | 1.4507 | 500 | 700 to 900 | 25 |
| X2CrNiMoN25-7-4 | 1.4410 | 530 | 730 to 930 | 25 |
| X2CrNiMoCuWN25-7-4 | 1.4501 | 530 | 730 to 930 | 25 |
| X2CrNiMoN29-7-2 | 1.4477 | 550 | 750 to 1000 | 25 |
| X2CrNiMoCoN28-8-5-1* | 1.4658 | 650 | 800 to 1000 | 25 |
*for thickess ≤ 5 mm
The minimum yield stress values are about twice as high as those of austenitic stainless steels.
Duplex grades are therefore attractive when mechanical properties at room tempearature are important because they allow thinner sections.
- Typical applications
References
- ↑ Peckner D, Bernstein I.M. (1977). Handbook of Stainless Steels. McGraw Hill. pp. Chapter 8. ISBN 0-07-049147-X.
- ↑ P.Lacombe, B. Baroux, G. Beranger (1990). Les Aciers Inoxydables. Les Editions de Physique. pp. Chapter 18. ISBN 2-86883-142-7.
- ↑ "Practical Guidelines dor the fabrication of Duplex Stainless Steels" (PDF). 2014.
- ↑ "NACE (National Association of Corrosion Engineers)".
- 1 2 "The standard is available from BSI Shop".