Duplex stainless steel

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Duplex stainless steels[1][2][3] are a family of stainless steels. These 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]

Grades of duplex stainless steels[edit]

Duplex stainless steels are usually divided into three groups:

- Standard Duplex, typically Grade EN 1.4462 (also called 2205) initially developed. and represents the "mid-range" of properties and is perhaps the most used today

- Super-duplex, Typically grade EN 1.4410 up to so-called Hyper duplex grades developed later to meet specific demands of the oil& gas as well as those of the chemical industries. They offer a superior corrosion resistance and strength but are more difficult to process because the higher contents of Cr, Ni, Mo, N and even W promote the formation of intermetallic phases, which reduce drastically the impact resistance of the steel. Faulty processing will result in poor performance and users are advised to deal with reputable suppliers/processors.[5] Applications include deepwater offshore oil production.

- 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[edit]

Chemicals composition of grades from EN 10088-1 (2014) Standard are given in the table below:[6]

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[edit]

Mechanical properties from European Standard EN 10088-3 (2014)[6] (for product thickness below 160mm):

Mechanical properties at room temperature of solution-annealed austenitic–ferritic stainless steels
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 temperature are important because they allow thinner sections.

Duplex Stainless Steel Temperature Limits [7][edit]

Grade Temperature
Duplex 2707 HD 1080-1120 °C / 1976-2048 °F
Duplex 2507 1050-1125 °C / 1922-2057 °F
Duplex 2205 1020-1100 °C / 1868-2012 °F
Duplex 2304 930-1050 °C / 1706-1922 °F


References[edit]

  1. ^ Peckner D, Bernstein I.M. (1977). Handbook of Stainless Steels. McGraw Hill. pp. Chapter 8. ISBN 0-07-049147-X.
  2. ^ P.Lacombe, B. Baroux, G. Beranger (1990). Les Aciers Inoxydables. Les Editions de Physique. pp. Chapter 18. ISBN 2-86883-142-7.CS1 maint: multiple names: authors list (link)
  3. ^ "Practical Guidelines for the fabrication of Duplex Stainless Steels" (PDF). 2014.
  4. ^ "NACE (National Association of Corrosion Engineers)". Archived from the original on 2018-12-22.
  5. ^ "Knowledge center — Sandvik Materials Technology". www.materials.sandvik. Retrieved 2019-03-25.
  6. ^ a b "The standard is available from BSI Shop".
  7. ^ "Duplex Stainless Steel". Retrieved July 12, 2019.