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UNS S21904 (XM-11) Stainless Steel

S21904 stainless steel is an austenitic stainless steel formulated for primary forming into wrought products. XM-11 is the ASTM designation for this material. S21904 is the UNS number.

This material is well established: the Further Reading section below cites a number of published standards, and that list is not necessarily exhaustive.

It has a moderately high electrical conductivity and can have a moderately high tensile strength among wrought austenitic stainless steels.

The properties of S21904 stainless steel include two common variations. This page shows summary ranges across both of them. For more specific values, follow the links immediately below. The graph bars on the material properties cards further below compare S21904 stainless steel to: wrought austenitic stainless steels (top), all iron alloys (middle), and the entire database (bottom). A full bar means this is the highest value in the relevant set. A half-full bar means it's 50% of the highest, and so on.

Mechanical Properties

Brinell Hardness

210 to 300

Elastic (Young's, Tensile) Modulus

200 GPa 29 x 106 psi

Elongation at Break

17 to 51 %

Fatigue Strength

380 to 550 MPa 55 to 80 x 103 psi

Poisson's Ratio


Shear Modulus

78 GPa 11 x 106 psi

Shear Strength

510 to 620 MPa 73 to 89 x 103 psi

Tensile Strength: Ultimate (UTS)

700 to 1000 MPa 100 to 150 x 103 psi

Tensile Strength: Yield (Proof)

390 to 910 MPa 56 to 130 x 103 psi

Thermal Properties

Latent Heat of Fusion

290 J/g

Maximum Temperature: Corrosion

430 °C 800 °F

Maximum Temperature: Mechanical

980 °C 1800 °F

Melting Completion (Liquidus)

1400 °C 2550 °F

Melting Onset (Solidus)

1350 °C 2470 °F

Specific Heat Capacity

480 J/kg-K 0.12 BTU/lb-°F

Thermal Conductivity

14 W/m-K 8.1 BTU/h-ft-°F

Thermal Expansion

17 µm/m-K

Electrical Properties

Electrical Conductivity: Equal Volume

2.5 % IACS

Electrical Conductivity: Equal Weight (Specific)

2.9 % IACS

Otherwise Unclassified Properties

Base Metal Price

15 % relative


7.7 g/cm3 480 lb/ft3

Embodied Carbon

3.0 kg CO2/kg material

Embodied Energy

43 MJ/kg 19 x 103 BTU/lb

Embodied Water

160 L/kg 19 gal/lb

Common Calculations

PREN (Pitting Resistance)


Resilience: Ultimate (Unit Rupture Work)

160 to 310 MJ/m3

Resilience: Unit (Modulus of Resilience)

380 to 2070 kJ/m3

Stiffness to Weight: Axial

14 points

Stiffness to Weight: Bending

25 points

Strength to Weight: Axial

25 to 36 points

Strength to Weight: Bending

23 to 29 points

Thermal Diffusivity

3.8 mm2/s

Thermal Shock Resistance

15 to 21 points

Alloy Composition

Among wrought stainless steels, the composition of S21904 stainless steel is notable for containing a comparatively high amount of manganese (Mn). Manganese is used to improve ductility at elevated temperatures. It also permits a higher nitrogen content than would otherwise be possible.

Iron (Fe) 59.5 to 67.4
Chromium (Cr) 19 to 21.5
Manganese (Mn) 8.0 to 10
Nickel (Ni) 5.5 to 7.5
Silicon (Si) 0 to 1.0
Nitrogen (N) 0.15 to 0.4
Phosphorus (P) 0 to 0.045
Carbon (C) 0 to 0.040
Sulfur (S) 0 to 0.030

All values are % weight. Ranges represent what is permitted under applicable standards.

Followup Questions

Similar Alloys

Further Reading

ASTM A473: Standard Specification for Stainless Steel Forgings

ASTM A479: Standard Specification for Stainless Steel Bars and Shapes for Use in Boilers and Other Pressure Vessels

ASTM A666: Standard Specification for Annealed or Cold-Worked Austenitic Stainless Steel Sheet, Strip, Plate, and Flat Bar

ASTM A182: Standard Specification for Forged or Rolled Alloy and Stainless Steel Pipe Flanges, Forged Fittings, and Valves and Parts for High-Temperature Service

ASTM A240: Standard Specification for Chromium and Chromium-Nickel Stainless Steel Plate, Sheet, and Strip for Pressure Vessels and for General Applications

Welding Metallurgy of Stainless Steels, Erich Folkhard et al., 2012

ASTM A959: Standard Guide for Specifying Harmonized Standard Grade Compositions for Wrought Stainless Steels

Corrosion of Austenitic Stainless Steels: Mechanism, Mitigation and Monitoring, H. S. Khatak and B. Raj (editors), 2002

Pressure Vessels: External Pressure Technology, 2nd ed., Carl T. F. Ross, 2011

Austenitic Stainless Steels: Microstructure and Mechanical Properties, P. Marshall, 1984