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.
| Fe | 59.1 to 65.4 | |
| Cr | 16 to 18 | |
| Ni | 8.0 to 9.0 | |
| Mn | 7.0 to 9.0 | |
| Si | 3.5 to 4.5 | |
| N | 0.080 to 0.18 | |
| C | 0 to 0.1 | |
| P | 0 to 0.060 | |
| 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