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UNS S21800 (Alloy 218) Stainless Steel

S21800 stainless steel is an austenitic stainless steel formulated for primary forming into wrought products. Cited properties are appropriate for the annealed condition. S21800 is the UNS number for this material. Alloy 218 is the common industry name.

It has a moderately high tensile strength among the wrought austenitic stainless steels in the database.

The graph bars on the material properties cards below compare S21800 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

Elastic (Young's, Tensile) Modulus

190 GPa 28 x 106 psi

Elongation at Break

40 %

Fatigue Strength

330 MPa 48 x 103 psi

Poisson's Ratio

0.28

Reduction in Area

62 %

Rockwell B Hardness

88

Shear Modulus

75 GPa 11 x 106 psi

Shear Strength

510 MPa 73 x 103 psi

Tensile Strength: Ultimate (UTS)

740 MPa 110 x 103 psi

Tensile Strength: Yield (Proof)

390 MPa 57 x 103 psi

Thermal Properties

Latent Heat of Fusion

340 J/g

Maximum Temperature: Corrosion

410 °C 770 °F

Maximum Temperature: Mechanical

900 °C 1650 °F

Melting Completion (Liquidus)

1360 °C 2470 °F

Melting Onset (Solidus)

1310 °C 2400 °F

Specific Heat Capacity

500 J/kg-K 0.12 BTU/lb-°F

Thermal Expansion

16 µm/m-K

Otherwise Unclassified Properties

Base Metal Price

15 % relative

Density

7.5 g/cm3 470 lb/ft3

Embodied Carbon

3.1 kg CO2/kg material

Embodied Energy

45 MJ/kg 19 x 103 BTU/lb

Embodied Water

150 L/kg 18 gal/lb

Common Calculations

PREN (Pitting Resistance)

19

Resilience: Ultimate (Unit Rupture Work)

250 MJ/m3

Resilience: Unit (Modulus of Resilience)

390 kJ/m3

Stiffness to Weight: Axial

14 points

Stiffness to Weight: Bending

26 points

Strength to Weight: Axial

27 points

Strength to Weight: Bending

24 points

Thermal Shock Resistance

17 points

Alloy Composition

Among wrought stainless steels, the composition of S21800 stainless steel is notable for containing comparatively high amounts of silicon (Si) and manganese (Mn). Silicon content is typically governed by metallurgical processing concerns, but it can also be added for the purpose of improving oxidation resistance. Manganese is used to improve ductility at elevated temperatures. It also permits a higher nitrogen content than would otherwise be possible.

Iron (Fe) 59.1 to 65.4
Chromium (Cr) 16 to 18
Nickel (Ni) 8.0 to 9.0
Manganese (Mn) 7.0 to 9.0
Silicon (Si) 3.5 to 4.5
Nitrogen (N) 0.080 to 0.18
Carbon (C) 0 to 0.1
Phosphorus (P) 0 to 0.060
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 A479: Standard Specification for Stainless Steel Bars and Shapes for Use in Boilers and Other Pressure Vessels

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

Properties and Selection: Irons, Steels and High Performance Alloys, ASM Handbook vol. 1, ASM International, 1993

ASM Specialty Handbook: Stainless Steels, J. R. Davis (editor), 1994

Advances in Stainless Steels, Baldev Raj et al. (editors), 2010