Stainless Steel S21904
UNS S21904 · AISI/SAE XM-11
S21904 (XM-11) is the low-carbon version of the 21Cr-6Ni-9Mn (S21900, Nitronic 40) nitrogen-strengthened austenitic stainless, with carbon held low to improve weldability.
Reference datasheet — S21904 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
S21904 tempers and conditions
S21904 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, rapid cool) | Standard stocked condition: maximum ductility and cryogenic toughness, best for welded fabrication and forming. | 415 | 745 | 48 | 200 HB | — |
Hot rolled | As-hot-worked heavy bar and plate for subsequent machining or annealing; properties vary with finishing temperature. | 480 | 800 | 40 | 21 HRC | 2.4 % IACS |
Cold drawn | Pick for machined shafts and fasteners needing ~690 MPa yield with better straightness and surface than annealed bar. | 690 | 900 | 25 | 28 HRC | — |
Quarter hard | Use where roughly double annealed yield strength is needed while keeping ~20% elongation for mild forming. | 760 | 965 | 20 | 30 HRC | — |
Half hard | Higher-strength strip/bar for springs, clamps and load-carrying panels with limited bending. | 895 | 1,105 | 15 | 35 HRC | — |
Three-quarter hard | For high-strength flat springs and thin high-load sections where only gentle radii are formed. | 1,035 | 1,240 | 12 | 38 HRC | — |
Full hard | Maximum strength strip/wire for spring clips and high-strength non-magnetic fasteners; essentially no formability. | 1,170 | 1,380 | 8 | 42 HRC | — |
What is S21904?
S21904 (XM-11) is the low-carbon version of the 21Cr-6Ni-9Mn (S21900, Nitronic 40) nitrogen-strengthened austenitic stainless, with carbon held low to improve weldability. Annealed properties are about 415 MPa yield, 745 MPa tensile, 48% elongation, 200 HB (95 HRB) and 200 GPa elastic modulus; it is used as welded plate, bar and fastener stock and retains toughness at cryogenic temperatures. Weldability rates 78, but machinability is only 30, formability 58 and corrosion resistance 56, below 316; service is limited to about 760 °C. S21900 is the choice when welding is not required. S21904 has a density of 7.83 g/cm³ (0.283 lb/in³), heavier than 58% of stainless steel grades. It melts at 1,370°C (2,498 °F). S21904 has a yield strength of 415 MPa (60.2 ksi) and a tensile strength of 745 MPa (108 ksi) — stronger than 62% of stainless steel grades. Elongation at break is 48% and the elastic modulus is 200 GPa (29 Msi).
What is S21904 used for?
- welded cryogenic tanks
- aerospace structures
- marine fasteners
Advantages
- Tough — resists crack growth — 200 MPa·√m (182 ksi·√in), better than 86% of stainless steel grades
- Ductile — tolerates forming and impact — 48%, better than 85% of stainless steel grades
S21904 properties
Typical room-temperature values for S21904-Annealed; bars are the position among stainless steel grades.
Physical3
S21904 has a density of 7.83 g/cm³ (0.283 lb/in³), heavier than 58% of stainless steel grades. It melts at 1,370°C (2,498 °F).
Mechanical16
S21904 has a yield strength of 415 MPa (60.2 ksi) and a tensile strength of 745 MPa (108 ksi) — stronger than 62% of stainless steel grades. Elongation at break is 48% and the elastic modulus is 200 GPa (29 Msi).
Thermal6
S21904 is rated for continuous service to 760°C (1,400 °F). It conducts heat at 14.5 W/m·K (8.38 BTU/hr·ft·°F), worse than 72% of stainless steel grades. Thermal expansion is 15.1 µm/m·K (8.39 µin/in·°F).
Electrical3
S21904 conducts electricity at 2.4 % IACS, better than 67% of stainless steel grades.
Chemical & Environmental3
Corrosion resistance is good (56/100), worse than 66% of stainless steel grades.
Sustainability4
Producing a kilogram of S21904 takes about 57 MJ of energy and emits 5.4 kg of CO₂ — more than 62% of stainless steel grades. Typical recycled content is 55%.
Manufacturability8
S21904's machinability is poor (30/100, worse than 70% of stainless steel grades); weldability very good (78/100); formability good (58/100).
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. S21904 is highlighted; hover a dot for its name, or open the interactive family chart.
Working with S21904
Is S21904 easy to machine?
Machine like a high-nitrogen austenitic: rigid setups, sharp positive-rake carbide, heavy feed with slow speed (~30% of 1212), flood coolant, and never dwell — it work-hardens instantly.
Can S21904 be welded?
Readily welded by GTAW/GMAW/SMAW without preheat or PWHT; use matching 21-6-9 or 209/240 filler (or ER308L for lower-strength joints), keep heat input low and avoid nitrogen loss from excessive arc exposure.
Can S21904 be formed, bent or molded?
Cold forms well but needs roughly twice the press force of 304 and generous bend radii; hot work at 1040–1200 °C then water quench, and re-anneal after severe cold work to restore ductility.
S21904 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 |
|---|---|---|
| Clow-carbon version of S21900 | ≤ 0.04 | 0.03 |
| Mn | 8 – 10 | 9 |
| Si | ≤ 1 | 0.5 |
| P | ≤ 0.06 | 0.02 |
| S | ≤ 0.03 | 0.01 |
| Cr | 19 – 21.5 | 20.3 |
| Ni | 5.5 – 7.5 | 6.5 |
| Nprincipal strengthener | 0.15 – 0.4 | 0.3 |
| Fe | balance |
What surface finishes work on S21904?
Passivate per ASTM A967 or electropolish; takes a bright mechanical polish, but do not anodize — pickling of high-Mn scale requires stronger acid mixes than 304.
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 S21904 in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
- AISI / SAE
- XM-11
- Similar grades
- S21900
How much does S21904 cost?
S21904 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.
S21904 — frequently asked
What is S21904 used for?
S21904 is typically used for welded cryogenic tanks, aerospace structures and marine fasteners. In short: weldable Nitronic 40; best weldability in family; cryogenic toughness retained.
What is the yield strength of S21904?
S21904 has a typical yield strength of 415 MPa (60.2 ksi) and a tensile strength of 745 MPa (108 ksi) — stronger than 62% of stainless steel grades. Strength varies by condition: see the 7 listed tempers.
Is S21904 easy to machine?
Not especially — machinability is rated poor (30/100, worse than 70% of stainless steel grades). Machine like a high-nitrogen austenitic: rigid setups, sharp positive-rake carbide, heavy feed with slow speed (~30% of 1212), flood coolant, and never dwell — it work-hardens instantly.
Can S21904 be welded?
Yes — weldability is rated very good (78/100). Readily welded by GTAW/GMAW/SMAW without preheat or PWHT; use matching 21-6-9 or 209/240 filler (or ER308L for lower-strength joints), keep heat input low and avoid nitrogen loss from excessive arc exposure.
What surface finishes work on S21904?
Passivate per ASTM A967 or electropolish; takes a bright mechanical polish, but do not anodize — pickling of high-Mn scale requires stronger acid mixes than 304.
Can S21904 be formed, bent or molded?
Cold forms well but needs roughly twice the press force of 304 and generous bend radii; hot work at 1040–1200 °C then water quench, and re-anneal after severe cold work to restore ductility.
What is the maximum service temperature of S21904?
S21904 is rated for continuous use to about 760°C (1,400 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between S21904 Annealed and S21904-FH?
Annealed is the default condition — standard stocked condition: maximum ductility and cryogenic toughness, best for welded fabrication and forming. FH: maximum strength strip/wire for spring clips and high-strength non-magnetic fasteners; essentially no formability. Yield strength is 415 MPa in Annealed versus 1,170 MPa in FH.
How much does S21904 cost?
S21904 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 A240/A240M — Chromium and Chromium-Nickel Stainless Steel Plate, Sheet and Strip — ASTM International (2023)
- ASTM A276/A276M — Stainless Steel Bars and Shapes — ASTM International (2023)
- ASTM A479/A479M — Stainless Steel Bars and Shapes for Boilers and Pressure Vessels — ASTM International (2021)
- SAE/AMS 5561 & AMS 5656 (21Cr-6Ni-9Mn tube and bar) — SAE International (2019)
- ASM Handbook Vol. 1: Properties and Selection — Irons, Steels and High-Performance Alloys — ASM International (1990)
- Nitronic 40 (21-6-9) alloy datasheet — Specialty metals producer (2020)
- MMPDS-type typical/design allowables for 21-6-9 stainless — Battelle/FAA (2021)
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.