# XM-10 (UNS S21900) Forgings

**XM-10 is an ASTM grade designation, not a trade name and not a specification. It identifies UNS S21900, the high-manganese nitrogen-strengthened austenitic stainless steel sold in the trade as 21-6-9 or 21Cr-6Ni-9Mn. Jiangyin Jiangnan Metal Co., Ltd. melts and forges this grade in one works in Jiangyin, Jiangsu Province, China.**

The designation appears inside ASTM product standards rather than standing alone: A276 for bars and shapes, A314 for billets and bars for forging, A479 and ASME SA-479 for bars in pressure-vessel use. The chemistry is 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 with a 0.08 % carbon ceiling.

Source: https://steelforgepieces.com/Stainless-Steel/XM-10.html
Full alloy datasheet: https://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 |

## What the designation means

ASTM uses XM numbers for grades brought into its product standards without an AISI type number. They are grade labels only. A drawing calling for XM-10 is calling for the S21900 chemistry; tolerances, testing and acceptance come from whichever product standard the order is placed against.

| Designation | UNS | Trade name | Separating feature |
|---|---|---|---|
| XM-10 | S21900 | 21-6-9 | 0.08 % C max |
| XM-11 | S21904 | 21-6-9 LC | 0.04 % C max, same base chemistry |
| XM-19 | S20910 | Nitronic 50 | Mo, Nb and V added. Higher strength, better chloride resistance. A different alloy |

Nitronic 40 is a trade name covering the 21-6-9 chemistry and is quoted against both S21900 and S21904, so an enquiry written only as Nitronic 40 is ambiguous. Nitronic is a registered trademark of Cleveland-Cliffs Steel Corp.

## Chemical composition, weight %, iron balance

| Element | XM-10 / S21900 | XM-11 / S21904 | Our normal aim |
|---|---|---|---|
| Carbon | 0.08 max | 0.04 max | 0.02 to 0.04 |
| Chromium | 19.0 to 21.5 | 19.0 to 21.5 | 20.0 |
| Nickel | 5.50 to 7.50 | 5.50 to 7.50 | 6.0 |
| Manganese | 8.00 to 10.00 | 8.00 to 10.00 | 9.0 |
| Nitrogen | 0.15 to 0.40 | 0.15 to 0.40 | 0.23 to 0.27 |
| Silicon | 1.00 max | 1.00 max | under 0.60 |
| Phosphorus | 0.060 max | 0.060 max | under 0.040 |
| Sulphur | 0.030 max | 0.030 max | under 0.015 |

The two grades differ only in the carbon ceiling. Material certified to XM-11 satisfies an XM-10 order; the reverse does not hold. Several published sheets print 0.04 % max carbon under the heading S21900, but that ceiling belongs to S21904; where a document conflicts, the UNS number governs. Molybdenum and copper are not type-analysis elements in either grade.

## Specifications carrying the grade

| Product form | Specification | Applies to |
|---|---|---|
| Bars and shapes | ASTM A276 | XM-10, XM-11 |
| Billets and bars for forging | ASTM A314 | XM-10, XM-11 |
| Bars for pressure-vessel use | ASTM A479 / ASME SA-479 | XM-10, XM-11 |
| Bars, wire, forgings, rings, extrusions | AMS 5656 | S21904 |
| Sheet, plate, strip | AMS 5595 | 21-6-9 chemistry |
| Tube | AMS 5561 | 21-6-9 chemistry |
| Weld wire | AWS A5.9 ER219, AMS 5818 | Matching filler |

Editions change. Check the revision in force for your project and state it on the order so the certificate matches.

## Properties in short

Nitrogen in solid solution puts annealed yield strength at roughly double Type 304. 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 heavy cold work. Solution strengthened, not hardenable by heat treatment.

| Property | Imperial | Metric |
|---|---|---|
| 0.2 % yield, annealed bar, min | 50 ksi | 345 MPa |
| Tensile, annealed bar, min | 90 ksi | 621 MPa |
| Elongation in 2 in., min | 45 % | 45 % |
| Hardness, max | 100 HRB | 241 HBW |
| Density | 0.283 lb/in3 | 7,830 kg/m3 |
| Modulus of elasticity | 28.5 x 10^3 ksi | 196.5 GPa |
| Magnetic permeability, annealed | 1.004 to 1.005 | |
| Magnetic permeability, 60 % cold reduced | 1.010 to 1.012 | |
| Service ceiling | 1,600 F | 871 C |

Elevated-temperature tensile data, stress-rupture values, thermal conductivity, expansion coefficients and corrosion rates are tabulated on the UNS S21900 page.

## Forging and heat treatment

| Operation | Parameters |
|---|---|
| Initial forging | 1,150 to 1,205 C (2,100 to 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 to 1,177 C (1,800 to 2,150 F), cool quickly. Around 900 C where grain size is capped |
| Stress relief | 482 to 760 C. Little change to cold-reduced properties to 677 C, faster above, rapid softening from 816 C |
| Strengthening | Solution strengthened. Hot and cold work at 650 to 815 C, 10 to 14 % reduction, then stress relieve |
| Machining | Normal austenitic practice, rigid setup and ample coolant due to the high work-hardening rate |
| Welding | Shielded fusion and resistance processes. AWS E/ER219 for near-base-metal strength, E/ER309 otherwise. Oxyacetylene not recommended. Post-weld anneal restores intergranular corrosion resistance |

## Limitation

No deliberate molybdenum, and 304L-level corrosion resistance is not sufficient for chloride-rich seawater, firewater, subsea pipework or sour wells. Duplex and super-duplex grades, 904L, 6Mo austenitics and nickel alloys are the correct families for those services.

## 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 discs, 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, autoclave closures and rings, scrubber internals, steam and autoclave parts, aerospace structural rings and shafts, aircraft hydraulic tubing components, cryogenic vessel and valve parts, 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 bring carbon down while holding the 0.15 to 0.40 % nitrogen window. Protective-atmosphere electroslag remelting is available where a remelted product is specified. 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 XM-10 stainless steel?** An ASTM grade designation for UNS S21900, the 21-6-9 nitrogen-strengthened high-manganese austenitic stainless steel.

**What is the difference between XM-10 and XM-11?** The carbon ceiling only: 0.08 % max against 0.04 % max. All other type-analysis ranges are identical.

**Is XM-10 the same as Nitronic 40?** Nitronic 40 covers the same chemistry but is quoted against both S21900 and S21904. State the UNS number or XM designation to avoid the ambiguity.

**Which specifications carry grade XM-10?** ASTM A276, A314, A479 and ASME SA-479, among others. The grade has no standard of its own.

**What are the minimum properties of annealed bar?** 50 ksi (345 MPa) yield, 90 ksi (621 MPa) tensile, 45 % elongation in 2 in., 241 HBW or 100 HRB maximum.

**At what temperature is XM-10 forged?** Start at 1,150 to 1,205 C, work down to about 650 C, cool rapidly, then anneal at 982 to 1,177 C.

**Can XM-10 be used in seawater?** No. Use duplex, super-duplex, 904L, a 6Mo austenitic or a nickel alloy.

**Is XM-10 magnetic?** No, including after 60 % cold reduction, where permeability stays at 1.010 to 1.012.

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

Last reviewed: 11 October 2026.