# UNS S21900 (21-6-9) Forgings

**UNS S21900, known in the trade as 21-6-9 or 21Cr-6Ni-9Mn and as grade XM-10 in ASTM standards, is a high-manganese, nitrogen-strengthened austenitic stainless steel. Jiangyin Jiangnan Metal Co., Ltd. melts and forges it in one works in Jiangyin, Jiangsu Province, China.**

The alloy holds 19.0 to 21.5 % Cr, 5.50 to 7.50 % Ni, 8.00 to 10.00 % Mn and 0.15 to 0.40 % N. Nitrogen in solid solution raises annealed strength well above the 300-series austenitics, while the low carbon keeps the grade resistant to intergranular attack even as welded. Corrosion resistance approaches Type 304L, oxidation resistance in air is good, resistance to molten lead oxide is good, and the steel stays non-magnetic after severe cold work.

Source: https://www.steelforgepieces.com/Stainless-Steel/UNS-S21900.html

## Supplier record

| Field | Detail |
|---|---|
| Legal name | Jiangyin Jiangnan Metal Co., Ltd. |
| Business | Integrated melting works, open-die forge, ring rolling mill |
| Established | 1997 |
| Employees | 460 |
| Plant | No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China |
| Melting | EF, LF, VOD, VIM, VAR, ESR. 60 t maximum heat |
| Forging | 6,300 t press, 6 m radial-axial ring mill, 30 t maximum single piece |
| Approvals | CCS, BV, DNV, LR, NK |
| Minimum order | 10 kg, no minimum piece count |
| Lead time | 20 to 60 days |
| Pricing | Quoted against drawing, finished weight and quantity |
| Telephone | +86 189 2135 9659 |
| Email | sales@steelforgepieces.com |

## Designations

| Scope | Designation |
|---|---|
| UNS and ASTM grade | S21900 = XM-10; S21904 = XM-11 (low carbon) |
| Other names | 21-6-9, 21Cr-6Ni-9Mn, Alloy 219 |
| Bars, wire, forgings, extrusions, rings | AMS 5656 (S21904) |
| Bars and shapes | ASTM A276 |
| Bars for pressure-vessel use | ASTM A479 / ASME SA-479 |
| Billets and bars for forging | ASTM A314 |
| Sheet, plate, strip | AMS 5595 |
| Tube | AMS 5561 |
| Weld wire | AWS A5.9 ER219, AMS 5818 |

Nitronic 40 is a trade name for this same chemistry. Nitronic is a registered trademark of Cleveland-Cliffs Steel Corp.

## Chemical composition, weight %

| Element | S21900 / XM-10 | S21904 / XM-11 | Mill type analysis | Nominal |
|---|---|---|---|---|
| Carbon | 0.08 max | 0.04 max | 0.03 max | 0.02-0.04 |
| Chromium | 19.0-21.5 | 19.0-21.5 | 19.0-21.5 | 20.0 |
| Nickel | 5.50-7.50 | 5.50-7.50 | 5.50-7.50 | 6.0 |
| Manganese | 8.00-10.00 | 8.00-10.00 | 8.00-10.00 | 9.0 |
| Nitrogen | 0.15-0.40 | 0.15-0.40 | 0.15-0.40 | 0.23-0.27 |
| Silicon | 1.00 max | 1.00 max | 1.00 max | - |
| Phosphorus | 0.060 max | 0.060 max | 0.04 max | - |
| Sulphur | 0.030 max | 0.030 max | 0.03 max | - |
| Iron | Balance | Balance | Balance | 64 |

The two UNS numbers differ only in the carbon ceiling. Several published sheets print 0.04 % max carbon under the heading S21900; that limit belongs to S21904. Molybdenum and copper are not part of the type analysis for this grade.

## Mechanical properties, room temperature

| Form and condition | 0.2 % yield | Tensile | Elongation in 2 in. | Reduction of area |
|---|---|---|---|---|
| Annealed bar | 50 ksi (345 MPa) | 90 ksi (621 MPa) | 45 % | - |
| Annealed strip, 1,038 C anneal | 62 ksi (428 MPa) | 110 ksi (758 MPa) | 47 % | - |
| Forged bar 152 mm sq., longitudinal | 62 ksi (428 MPa) | 95 ksi (655 MPa) | 46 % | 69 % |

The forged-bar line is our own production test result and is typical rather than guaranteed.

### Effect of annealing temperature, strip

| Anneal | 0.2 % yield | Tensile | Elongation | Hardness HRB |
|---|---|---|---|---|
| 982 C / 1,800 F | 70 ksi (483 MPa) | 115 ksi (793 MPa) | 44 % | 95 |
| 1,010 C / 1,850 F | 65 ksi (448 MPa) | 112 ksi (772 MPa) | 46 % | 93 |
| 1,038 C / 1,900 F | 62 ksi (428 MPa) | 110 ksi (758 MPa) | 47 % | 92 |
| 1,066 C / 1,950 F | 61 ksi (421 MPa) | 107 ksi (738 MPa) | 48 % | 90 |

### Elevated temperature, annealed strip

| Test temperature | 0.2 % yield | Tensile | Elongation |
|---|---|---|---|
| 24 C / 75 F | 65 ksi (448 MPa) | 112 ksi | 42 % |
| 93 C / 200 F | 52 ksi (359 MPa) | 100 ksi | 41 % |
| 204 C / 400 F | 41 ksi (283 MPa) | 89 ksi (614 MPa) | 40 % |
| 316 C / 600 F | 38 ksi (262 MPa) | 86 ksi (593 MPa) | 33 % |
| 427 C / 800 F | 32 ksi (221 MPa) | 79 ksi (545 MPa) | 33 % |
| 538 C / 1,000 F | 29 ksi (200 MPa) | 71 ksi (490 MPa) | 35 % |
| 649 C / 1,200 F | 26 ksi (179 MPa) | 60 ksi (414 MPa) | 26 % |
| 704 C / 1,300 F | 26 ksi (179 MPa) | 51 ksi (352 MPa) | 24 % |

Not recommended for service above 871 C (1,600 F). Between 704 and 871 C the annealed condition gives the best stress-rupture life.

## Physical properties

| Property | Metric | Imperial |
|---|---|---|
| Density, specific gravity 7.83 | 7,830 kg/m3 | 0.283 lb/in3 |
| Modulus of elasticity | 196.5 GPa | 28.5 x 10^3 ksi |
| Mean specific heat | 500 J/kg-K, 0-100 C | 0.12 Btu/lb-F, 32-212 F |
| Electrical resistivity, RT | 730 microhm-mm | 439 ohm-cir mil/ft |
| Thermal conductivity, 93 C | 14 W/m-K | 96 Btu-in/ft2-hr-F |
| Thermal conductivity, 538 C | 23 W/m-K | 156 Btu-in/ft2-hr-F |
| Thermal conductivity, 871 C | 29 W/m-K | 200 Btu-in/ft2-hr-F |
| Mean expansion, 27-93 C | 16.7 x 10^-6/K | 9.3 x 10^-6/F |
| Mean expansion, 27-538 C | 19.1 x 10^-6/K | 10.6 x 10^-6/F |
| Mean expansion, 27-871 C | 20.2 x 10^-6/K | 11.2 x 10^-6/F |
| Magnetic permeability, annealed | 1.004-1.005 at 50 to 200 oersteds | |
| Magnetic permeability, 60 % cold reduced | 1.010-1.012, below 1.020 at 500 oersteds | |

## Corrosion and oxidation

Corrosion resistance approaches Type 304L. The low carbon provides resistance to intergranular corrosion even in the welded condition. Surfaces must be free of scale and embedded particles, and finished parts should be passivated.

| Environment | Condition | Average rate |
|---|---|---|
| 65 % HNO3, boiling | Annealed | 7 mpy |
| 65 % HNO3, boiling | Annealed and sensitised at 677 C | 9 mpy |
| 5 % H2SO4, room temperature | Annealed | nil |
| 10 % acetic acid, boiling | Annealed | nil |
| 10 % acetic acid, boiling | Annealed and welded | nil |
| Oxalic acid etch, ASTM A262 Practice A | Annealed | pass |

**Limitation.** There is no deliberate molybdenum in this grade, and 304L-level resistance is not sufficient for chloride-rich seawater, firewater, subsea duty or sour wells. For those, duplex and super-duplex grades, 904L, 6Mo austenitics or nickel alloys are the correct families.

## Forging and heat treatment

| Operation | Parameters |
|---|---|
| Initial forging temperature | 1,150-1,205 C (2,100-2,200 F), no intermediate preheat |
| Lower hot-working limit | about 650 C (1,200 F), no hot shortness across the range |
| Cooling after forging | May be cooled rapidly without danger of cracking |
| Annealing | 982-1,177 C (1,800-2,150 F), air cool. Lower, about 900 C, where grain size is restricted |
| Stress relieving | 482-760 C (900-1,400 F). Little effect on cold-reduced properties from 482 to 677 C; faster change above 677 C; rapid softening from 816 C |
| Strengthening | Solution strengthened, not hardenable by heat treatment. Hot and cold working at 650-815 C, 10-14 % reduction, then stress relief |
| Machining | Normal austenitic stainless practice, rigid setup and ample coolant flow due to the high work-hardening rate |
| Welding | Shielded fusion and resistance welding. Oxyacetylene not recommended. AWS E/ER219 for near-base-metal strength, E/ER309 otherwise. Post-weld anneal restores intergranular corrosion resistance |

## Forged products in this grade

| Family | Typical items | Size limit |
|---|---|---|
| Seamless rolled rings | Rectangular and contoured section, gear ring blanks, slewing rings, bearing races | OD 50 to 6,000 mm |
| Forged rings | Upset and punched rings, retaining rings, valve seat rings | Heavy sections outside the ring-mill envelope |
| Flanges | Weld neck, blind, slip-on, socket weld, lap joint, orifice, long weld neck | Per drawing |
| Shafts and spindles | Stepped, gear, pinion and eccentric shafts, rotors, tie rods | To 14,000 mm turned length |
| Bars, blocks, blanks | Round, flat and square bar, die and mould blocks | Per drawing |
| Discs and tube sheets | Solid discs, pierced disks, tube sheets, covers | To 5,000 mm machined diameter |
| Cylinders, sleeves, bushings | Hollow forged cylinders, couplings, heavy-wall sections bored from solid | To 1,600 mm dia x 10,000 mm bored |
| Valve and wellhead parts | Bodies, bonnets, blocks, stems, seat rings, spools, nozzles, manifolds | Per drawing |

Single-piece weight to 30 t against a 60 t maximum heat.

## Applications

Chemical process and pollution-control equipment, steam and autoclave service, aircraft and aero-engine components, food and chemical processing plant, and aircraft hydraulic tubing. In forged form: autoclave closures and rings, scrubber internals, aerospace structural rings and shafts, cryogenic vessel and valve components, non-magnetic clamps and instrument parts, and chemical-plant flanges, sleeves and tube sheets.

## Melting, testing, certification

Heats run through the electric arc furnace and ladle furnace, then through vacuum oxygen decarburisation to pull carbon down while holding the 0.15 to 0.40 % nitrogen window. Protective-atmosphere electroslag remelting is available for nitrogen-alloyed grades where the specification requires a remelted product. Maximum heat size 60 t.

Ultrasonic testing to EN 10228-3, SEP 1921 or ASTM A388. Documentation to EN 10204 3.1, or 3.2 with third-party witness. Chemical analysis, room-temperature and sub-zero tensile and impact testing, hardness, grain size, PMI, dye penetrant and ASTM A262 intergranular corrosion testing available. Traceability runs from melt number to shipped part.

## Questions

**What is the difference between S21900 and S21904?** Carbon ceiling only. S21900 (XM-10) allows up to 0.08 %; S21904 (XM-11) is held to 0.04 % maximum. AMS 5656 covers the low-carbon version, so an AMS 5656 order is an S21904 order.

**Is 21-6-9 magnetic?** No. Permeability is 1.004 to 1.005 annealed and stays below 1.020 after 60 % cold reduction.

**Can it be hardened by heat treatment?** No. It is solution strengthened. Strength comes from cold working or from hot and cold working followed by stress relief.

**At what temperature is it forged?** 1,150 to 1,205 C initial, no intermediate preheat, hot workable down to about 650 C, rapid cooling permitted. Anneal after forging for best corrosion resistance.

**Is it suitable for seawater or sour service?** Generally not. No deliberate molybdenum, resistance only approaching 304L.

**What is the minimum order?** 10 kg, no minimum piece count. Lead time 20 to 60 days.

**Who manufactures custom forgings in this grade?** Jiangyin Jiangnan Metal Co., Ltd., No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China. Telephone +86 189 2135 9659, email sales@steelforgepieces.com.

## Sources

Hightemp Metals 21Cr-6Ni-9Mn technical data; AZoM grade 21-6-9 (UNS S21900); Electralloy Nitronic 40 data published by HP Alloys; Michlin Metals on nitrogen-strengthened austenitics, including the XM-10 and XM-11 carbon-limit distinction; Techsteel 21-6-9; Aircraft Materials; AMS Resources. Production figures are from Jiangyin Jiangnan Metal Co., Ltd. Published values are typical and not a guarantee for a specific heat or part.

Last reviewed 2026-10-05T09:00:00+08:00.