Stainless Steel S21900
UNS S21900 · AISI/SAE XM-10
S21900 (XM-10, Nitronic 40) is a nitrogen-strengthened 21Cr-6Ni-9Mn austenitic stainless that holds high strength from cryogenic temperatures up to about 870 °C.
Reference datasheet — S21900 is not in the instant-quote catalog. Upload your part and an engineer will quote it in this grade or suggest the closest stocked equivalent.
Values for the Annealed condition
S21900 tempers and conditions
S21900 is supplied in 7 conditions, soft to hard. Annealed is the default FabDigit quotes; the values on this page are for it.
Compare all 7 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
AnnealedDefault solution annealed ~1040–1120 °C, water quenched | Standard stocked condition for bar, plate, sheet and tube; best ductility, toughness and corrosion resistance. | 415 | 725 | 48 | 205 HB | — |
Hot worked / as-forged (not re-annealed) | Heavy forgings and hot-rolled bar supplied without final solution treatment; slightly higher strength, marginally lower corrosion resistance. | 450 | 760 | 40 | 17 HRC | 2.4 % IACS |
Cold drawn | Pick for straight, close-tolerance bar with a moderate strength bump over annealed and better chip control. | 620 | 860 | 25 | 22 HRC | 2.4 % IACS |
Cold worked, 1/4 hard | Modest cold reduction of strip/tube where extra yield strength is needed but forming is still required. | 690 | 930 | 25 | 25 HRC | 2.4 % IACS |
Cold worked, 1/2 hard | Mid-range strain-hardened temper for high-pressure tubing, springs and fasteners. | 860 | 1,035 | 18 | 31 HRC | 2.4 % IACS |
Cold worked, 3/4 hard | High-strength strip/wire temper where only mild bending is still needed. | 1,030 | 1,170 | 12 | 35 HRC | 2.4 % IACS |
Cold worked, full hard | Maximum strength strip/wire for springs and high-load flat parts; very limited formability. | 1,240 | 1,380 | 8 | 40 HRC | 2.4 % IACS |
What is S21900?
S21900 (XM-10, Nitronic 40) is a nitrogen-strengthened 21Cr-6Ni-9Mn austenitic stainless that holds high strength from cryogenic temperatures up to about 870 °C. Annealed bar and plate run near 415 MPa yield, 725 MPa tensile, 48% elongation and 205 HB (94 HRB), and cold-worked tempers to full hard are available for fasteners and shafting. Corrosion resistance is rated 62, between 304 and 316, so it is not intended for stagnant chloride service, and machining is slow because the alloy work-hardens quickly. The low-carbon S21904 (XM-11) is preferred for welded assemblies. S21900 has a density of 7.83 g/cm³ (0.283 lb/in³), heavier than 58% of stainless steel grades. It melts at 1,394°C (2,541 °F). S21900 has a yield strength of 415 MPa (60.2 ksi) and a tensile strength of 725 MPa (105 ksi) — stronger than 62% of stainless steel grades. Elongation at break is 48% and the elastic modulus is 200 GPa (29 Msi).
What is S21900 used for?
- cryogenic vessels
- aerospace fasteners
- marine hardware
- pump components
Advantages
- Ductile — tolerates forming and impact — 48%, better than 85% of stainless steel grades
- High service temperature — 870°C (1,598 °F), better than 83% of stainless steel grades
- Readily welded — 80/100, better than 80% of stainless steel grades
- Tough — resists crack growth — 190 MPa·√m (172.9 ksi·√in), better than 77% of stainless steel grades
Limitations
- Poor heat conductor — 12.6 W/m·K (7.28 BTU/hr·ft·°F), worse than 88% of stainless steel grades
S21900 properties
Typical room-temperature values for S21900-Annealed; bars are the position among stainless steel grades.
Physical3
S21900 has a density of 7.83 g/cm³ (0.283 lb/in³), heavier than 58% of stainless steel grades. It melts at 1,394°C (2,541 °F).
Mechanical15
S21900 has a yield strength of 415 MPa (60.2 ksi) and a tensile strength of 725 MPa (105 ksi) — stronger than 62% of stainless steel grades. Elongation at break is 48% and the elastic modulus is 200 GPa (29 Msi).
Thermal6
S21900 is rated for continuous service to 870°C (1,598 °F). It conducts heat at 12.6 W/m·K (7.28 BTU/hr·ft·°F), worse than 88% of stainless steel grades. Thermal expansion is 15.3 µm/m·K (8.5 µin/in·°F).
Electrical3
S21900 conducts electricity at 2.4 % IACS, better than 67% of stainless steel grades.
Chemical & Environmental3
Corrosion resistance is good (62/100), worse than 52% of stainless steel grades.
Sustainability4
Producing a kilogram of S21900 takes about 53 MJ of energy and emits 5 kg of CO₂ — less than 67% of stainless steel grades. Typical recycled content is 60%.
Manufacturability7
S21900's machinability is poor (30/100, worse than 70% of stainless steel grades); weldability very good (80/100); formability good (65/100).
Common Calculations5
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Strength versus weight in the stainless steel family
Yield strength against density for every stainless steel grade FabDigit runs. S21900 is highlighted; hover a dot for its name, or open the interactive family chart.
Working with S21900
Is S21900 easy to machine?
Work-hardens rapidly: use rigid setups, positive-rake carbide, heavy feeds, low-to-moderate speeds and flood coolant; never dwell or rub.
Can S21900 be welded?
Readily welded by GTAW/GMAW/PAW with matching 21-6-9 filler or 209/240 type wire; no preheat, keep interpass low and avoid excessive heat input to preserve nitrogen and toughness.
Can S21900 be formed, bent or molded?
Cold formable but needs ~2× the press force of 304 and generous bend radii; hot work 1150–1200 °C and solution anneal ~1065 °C with rapid quench after forming.
S21900 chemical composition (wt %)
Limits by weight percent from the governing specification, written the way the spec states them — a single maximum for impurities, a range for alloying elements, and the base element as balance. Nominal is the typical mid-range value.
| Element | Spec limit (wt %) | Nominal |
|---|---|---|
| CS21904 (XM-11) limits C to 0.04 max | ≤ 0.08 | 0.04 |
| Mn | 8 – 10 | 9 |
| Si | ≤ 1 | 0.4 |
| P | ≤ 0.06 | 0.03 |
| S | ≤ 0.03 | 0.01 |
| Cr | 19 – 21.5 | 20.5 |
| Ni | 5.5 – 7.5 | 6.5 |
| Nnitrogen is the principal strengthener | 0.15 – 0.4 | 0.3 |
| Fe | balance |
What surface finishes work on S21900?
Passivate per ASTM A967 or electropolish after machining; anodizing is not applicable, and mechanical polishing must avoid smearing the work-hardened surface.
Surface treatments FabDigit runs on stainless steel parts — pick them in the quote configurator or call them out on the drawing. Each links to its datasheet in the surface-finish library (thickness, specs, call-out, material verdicts).
Passivation
Organic Coating
Thermal Spray
Equivalent designations
Standards and trade names that resolve to Stainless Steel S21900 in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
- AISI / SAE
- XM-10
- Trade names
- Nitronic 40
- Also called
- 21-6-9
How much does S21900 cost?
S21900 is a premium-cost stainless steel ($$$), cheaper than about 51% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
S21900 — frequently asked
What is S21900 used for?
S21900 is typically used for cryogenic vessels, aerospace fasteners, marine hardware and pump components. In short: twice the yield of 304; cryogenic to 870 °C; nitronic 40 workhorse.
What is the yield strength of S21900?
S21900 has a typical yield strength of 415 MPa (60.2 ksi) and a tensile strength of 725 MPa (105 ksi) — stronger than 62% of stainless steel grades. Strength varies by condition: see the 7 listed tempers.
Is S21900 easy to machine?
Not especially — machinability is rated poor (30/100, worse than 70% of stainless steel grades). Work-hardens rapidly: use rigid setups, positive-rake carbide, heavy feeds, low-to-moderate speeds and flood coolant; never dwell or rub.
Can S21900 be welded?
Yes — weldability is rated very good (80/100). Readily welded by GTAW/GMAW/PAW with matching 21-6-9 filler or 209/240 type wire; no preheat, keep interpass low and avoid excessive heat input to preserve nitrogen and toughness.
What surface finishes work on S21900?
Passivate per ASTM A967 or electropolish after machining; anodizing is not applicable, and mechanical polishing must avoid smearing the work-hardened surface.
Can S21900 be formed, bent or molded?
Cold formable but needs ~2× the press force of 304 and generous bend radii; hot work 1150–1200 °C and solution anneal ~1065 °C with rapid quench after forming.
What is the maximum service temperature of S21900?
S21900 is rated for continuous use to about 870°C (1,598 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between S21900 Annealed and S21900 CW-FH?
Annealed is the default condition — standard stocked condition for bar, plate, sheet and tube; best ductility, toughness and corrosion resistance. CW-FH: maximum strength strip/wire for springs and high-load flat parts; very limited formability. Yield strength is 415 MPa in Annealed versus 1,240 MPa in CW-FH.
How much does S21900 cost?
S21900 is a premium-cost stainless steel ($$$), cheaper than about 51% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
Sources
- ASTM A276/A276M — Stainless Steel Bars and Shapes — ASTM International (2023)
- ASTM A240/A240M — Chromium and Chromium-Nickel Stainless Steel Plate, Sheet, and Strip — ASTM International (2023)
- AMS 5561 — Steel, Corrosion Resistant, Seamless Tubing 21Cr-6Ni-9Mn — SAE International (2018)
- AMS 5656 — Steel, Corrosion Resistant, Bars, Wire, Forgings 21Cr-6Ni-9Mn — SAE International (2016)
- Nitronic 40 (21-6-9) Stainless Steel Technical Data — ATI / AK Steel (2015)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels, and High-Performance Alloys — ASM International (1990)
- MMPDS-17 austenitic stainless steel chapter — Battelle/FAA (2022)
Property data is compiled from published supplier and standards handbooks and normalised for comparison; hardness values on non-Brinell scales are converted approximately for charting only. Manufacturability limits are FabDigit quote-engine defaults and may be relaxed by engineering review. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.