Stainless steel grade data · Sheet 21-6-9
UNS S21900 Forgings 21-6-9 / 21Cr-6Ni-9Mn / XM-10. Nitrogen-strengthened austenitic stainless steel, melted and forged in one works.
UNS S21900 is a high-manganese, nitrogen-strengthened austenitic stainless steel holding 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 the 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, and the steel stays non-magnetic after severe cold work.
Jiangyin Jiangnan Metal Co., Ltd. melts this grade on site, under vacuum where the nitrogen window demands it, then forges it on a 6,300 t press and a 6 m radial-axial ring mill. Rings to OD 6,000 mm, shafts to 14,000 mm turned length, single pieces to 30 t. Minimum order 10 kg.
- UNS
- S21900, ASTM grade XM-10
- Low-C variant
- S21904, XM-11 (AMS 5656)
- Other names
- 21-6-9, 21Cr-6Ni-9Mn, Alloy 219
- Structure
- Austenitic, non-magnetic
- Density
- 7,830 kg/m³ (0.283 lb/in³)
- Modulus E
- 196.5 GPa (28.5 × 10³ ksi)
- Forge from
- 1,150–1,205 °C (2,100–2,200 °F)
- Anneal
- 982–1,177 °C, air cool
- Stress relieve
- 482–760 °C (900–1,400 °F)
- Service limit
- 871 °C (1,600 °F)
- Ring capacity
- OD 50 mm to OD 6,000 mm
- Lead time
- 20 to 60 days
Chemical composition
The two UNS numbers in this family share one chemistry and differ only in the carbon ceiling. Check which number your drawing invokes before the enquiry goes out, because an AMS 5656 order is an S21904 order.
| 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 |
Limits per Hightemp Metals 21Cr-6Ni-9Mn type analysis and AZoM grade 21-6-9; carbon-ceiling split between XM-10 and XM-11 per Michlin Metals. Molybdenum and copper are not part of the type analysis for this grade. Where a drawing imposes residual limits on Mo, Cu or Co, state them on the order and we will aim and certify to them.
Mechanical properties
Room temperature
| Form and condition | 0.2 % yield | Tensile | Elong. in 2 in. | Red. 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 % |
Annealed-bar line per Electralloy data published by HP Alloys; strip line per Hightemp Metals; the forged-bar line is our own production test result and is typical rather than guaranteed. Section size, test direction and anneal temperature all move these numbers, so the acceptance values are those of the specification on the order.
Effect of annealing temperature
| Anneal | 0.2 % yield | Tensile | Elong. in 2 in. | 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 |
Hightemp Metals. Grain coarsening sets in toward the top of the annealing range, so a ring with a grain-size restriction is annealed low in the band, and one needing maximum formability high in it.
Elevated temperature
| Test temperature | 0.2 % yield | Tensile | Elong. in 2 in. |
|---|---|---|---|
| 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 % |
Hightemp Metals. The MPa figures printed in that source against the 75 °F and 200 °F tensile values are transcription errors, so only the ksi values are reproduced on those two lines. The alloy is not recommended for service above 871 °C (1,600 °F). Between 704 and 871 °C the annealed condition gives the best stress-rupture life, which is why hot-side rings leave here annealed rather than stress relieved.
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 × 10³ 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 at 93 °C | 14 W/m·K | 96 Btu·in/ft²·h·°F |
| Thermal conductivity at 538 °C | 23 W/m·K | 156 Btu·in/ft²·h·°F |
| Thermal conductivity at 871 °C | 29 W/m·K | 200 Btu·in/ft²·h·°F |
| Mean expansion, 27–93 °C | 16.7 × 10⁻⁶/K | 9.3 × 10⁻⁶/°F |
| Mean expansion, 27–538 °C | 19.1 × 10⁻⁶/K | 10.6 × 10⁻⁶/°F |
| Mean expansion, 27–871 °C | 20.2 × 10⁻⁶/K | 11.2 × 10⁻⁶/°F |
| Magnetic permeability, annealed | 1.004 to 1.005 at 50 to 200 oersteds | |
| Magnetic permeability, 60 % cold reduced | 1.010 to 1.012, below 1.020 at 500 oersteds | |
Hightemp Metals. The permeability figures are the reason this grade turns up in instrument housings, non-magnetic clamps and sensor hardware: cold work does not drive it magnetic the way it does in 301 or 304.
Corrosion and oxidation
Corrosion resistance approaches that of Type 304L, and the low carbon holds off intergranular attack even in the welded condition. For best performance the surface must be free of scale and embedded particles, and finished parts should be passivated. Resistance to high-temperature oxidation in air is good, as is resistance to molten lead oxide.
| 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 |
Hightemp Metals, five test periods of 48 hours each.
Forging, heat treatment, fabrication
Hot working
Initial forging temperature 1,150 to 1,205 °C, no intermediate preheat needed. Can be forged, hot rolled, hot headed and upset, and hot worked down to about 650 °C. Not susceptible to hot shortness across the working range, and forgings can be cooled rapidly without danger of cracking. Anneal after forging for best corrosion resistance.
Annealing
Generally 982 to 1,177 °C, air cool. Used for best stress-rupture life and for service between 704 and 871 °C, and to soften for maximum formability. Temperatures as low as 900 °C can be used where grain size is restricted. After annealing, strength can only be raised again by cold or hot and cold working.
Stress relieving
Range 482 to 760 °C, used for best all-round properties and service below 704 °C. From 482 to 677 °C there is little effect on the mechanical properties of cold-reduced material unless the reduction was heavy. Above 677 °C properties change faster, and 816 °C starts to cause rapid softening.
Strengthening
A solution-strengthened alloy that cannot be strengthened by heat treatment. Hot and cold working is normally done at 650 to 815 °C with reductions of 10 to 14 % depending on the strength wanted, followed by a 482 to 760 °C stress relief.
Machining
Machined by normal austenitic stainless practice, but the high work-hardening rate and higher initial yield mean a rigid setup and ample coolant flow. Our shop allows extra for tool wear when quoting proof-machined rings and tube sheets in this grade.
Welding
Suited to shielded fusion and resistance welding. Oxyacetylene welding is not recommended because of carbon pickup in the weld. AWS E/ER219 gives weld strength approaching the base metal; E/ER309 where high weld strength is not needed. A post-weld anneal restores intergranular corrosion resistance.
Specifications and designations
| Scope | Designation |
|---|---|
| UNS and ASTM grade | S21900 = XM-10; S21904 = XM-11 |
| Trade and common 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 |
Compiled from HP Alloys, Techsteel, Aircraft Materials and AMS Resources listings for this grade. If your enquiry names a specification not shown here, send it across; the mill either works to it already or will tell you plainly that it does not.
What we forge in this grade
Everything is forged from a single piece of steel melted on site. No casting, no welded fabrication, no purchased billet of unknown origin. Each part is made to drawing or to a dimensional sheet, heat treated, machined to the agreed allowance and tested.
| 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, proof-machined for inspection | To 5,000 mm machined diameter |
| Cylinders, sleeves, bushings | Hollow forged cylinders, couplings, heavy-wall sections bored from solid | To 1,600 mm dia × 10,000 mm bored |
| Valve and wellhead parts | Bodies, bonnets, blocks, stems, seat rings, spools, nozzles, manifolds | Per drawing |
Limits are set by plant equipment: a 6 m radial-axial ring mill, a 6,300 t open-die press, a 5,000 mm vertical lathe, a C61160 horizontal lathe and a CNC deep-hole drilling machine. Single-piece weight tops out at 30 t against a 60 t maximum heat. Price is quoted against drawing, finished weight and quantity; minimum order 10 kg with no minimum piece count.
Where 21-6-9 is used
Published mill and distributor data puts this grade in chemical process and pollution-control equipment, steam and autoclave service, aircraft and aero-engine components, food and chemical processing plant, and aircraft hydraulic tubing. The high annealed strength and the cryogenic toughness also carry it into low-temperature hardware, while the oxidation resistance and lead-oxide resistance suit parts near hot gas up to 871 °C.
In forged form that usually means autoclave closures and rings, scrubber and pollution-control 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 where a designer wants 304L-level corrosion behaviour at a much higher yield.
Choosing between neighbouring grades
| Grade | UNS | What sets it apart | Pick it when |
|---|---|---|---|
| 21-6-9 | S21900 / S21904 | Nitrogen plus 9 % Mn, high annealed strength, no deliberate Mo, stays non-magnetic after cold work | Strength, weldability and cryogenic toughness matter more than chloride resistance |
| Nitronic 50 | S20910 | Nitrogen strengthened with molybdenum added | You need the strength and better corrosion performance together, as on marine shafting |
| Nitronic 60 | S21800 | High strength plus galling resistance | Metal-to-metal sliding contact where surfaces tend to seize |
| Nitronic 40 | S21900 / S21904 | Trade name for this same chemistry | Your specification names the brand; tell us, because branded and generic material are not always interchangeable on a purchase spec |
| Type 304L | S30403 | The corrosion benchmark this grade is measured against, much lower strength | Corrosion duty is routine and strength does not govern the design |
| Duplex 2205 | S32205 | Austenite plus ferrite, high strength, chloride stress-corrosion resistance, magnetic response | Chloride-bearing or petrochemical service governs |
Grade positions follow Michlin Metals' summary of the nitrogen-strengthened austenitics and the Hightemp Metals data above. Nitronic is a registered trademark of Cleveland-Cliffs Steel Corp. Final grade selection stays with the design authority and the applicable code.
Melting, testing, certification
This grade carries a 0.15 to 0.40 % nitrogen window and a low carbon ceiling, which is a refining problem before it is a forging problem. Heats run through the electric arc furnace and ladle furnace, then through vacuum oxygen decarburisation to pull carbon down while holding nitrogen, which is the same route used here for the duplex and low-carbon stainless grades. Where a specification calls for a remelted product, the 3 t and 6 t protective-atmosphere electroslag furnaces take nitrogen-alloyed grades. Maximum heat size is 60 t.
Forgings are ultrasonically tested to EN 10228-3, SEP 1921 or ASTM A388, as nominated. Documentation is issued 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 can be added to the inspection plan. The works holds CCS, BV, DNV, LR and NK approvals, and traceability runs from the melt number through to the shipped part because no step leaves the site.
Questions we get on this grade
What is UNS S21900?
A high-manganese, nitrogen-strengthened austenitic stainless steel, known as 21-6-9 or 21Cr-6Ni-9Mn and as grade XM-10 in ASTM standards. It 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. It combines high strength in the annealed condition with resistance to oxidation at high temperature, resistance to molten lead oxide and corrosion resistance approaching Type 304L, and it remains non-magnetic after severe cold work.
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 for bars, forgings and rings, so an AMS 5656 order is an S21904 order even if the enquiry says S21900.
Is 21-6-9 magnetic?
No. Permeability is about 1.004 to 1.005 annealed and stays below 1.020 after 60 % cold reduction, so cold work does not drive it magnetic the way it does in 301 or 304.
Can it be hardened by heat treatment?
No. It is solution strengthened. Strength comes from cold working, or from hot and cold working at 650 to 815 °C with 10 to 14 % reduction followed by a 482 to 760 °C stress relief.
At what temperature do you forge it?
From 1,150 to 1,205 °C, with no intermediate preheat. It works down to about 650 °C, shows no hot shortness across that range and can be cooled rapidly without cracking. We anneal after forging unless the order specifies otherwise, because that is what restores the corrosion resistance.
Is it suitable for seawater or sour service?
Generally not. There is no deliberate molybdenum and the resistance only approaches 304L. For chloride-rich seawater, subsea or sour wells, duplex, super-duplex, 904L, 6Mo austenitics or nickel alloys are the right families. Send the medium, temperature and chloride level and we will say which grade we would actually quote.
What is the smallest order you will take?
10 kg, with no minimum piece count. Lead time runs 20 to 60 days depending on size, heat-treatment route and inspection scope.
How large can you go?
Rings to OD 6,000 mm on the 6 m radial-axial mill, shafts to 14,000 mm turned length, discs and tube sheets to 5,000 mm machined diameter, bored cylinders to 1,600 mm diameter by 10,000 mm, and 30 t as a single piece against a 60 t maximum heat.
Sheet prepared by the technical sales department, Jiangyin Jiangnan Metal Co., Ltd., from published alloy data (Hightemp Metals 21Cr-6Ni-9Mn, AZoM grade 21-6-9, Electralloy data via HP Alloys, Michlin Metals, Techsteel, Aircraft Materials, AMS Resources) together with our own production test results. Published figures are typical and are not a guarantee of properties for any particular heat or part. Acceptance is governed by the specification named on the order and the agreed inspection plan. Machine-readable version: UNS-S21900.md. Last reviewed .