# ALLOY 40 Forgings, 21Cr-6Ni-9Mn / UNS S21900 Seamless rolled rings, forged rings, flanges, shafts, discs, sleeves and bars in 21-6-9 nitrogen-strengthened stainless steel. Manufacturer: Jiangyin Jiangnan Metal Co., Ltd., No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province 214423, China Telephone: +86 189 2135 9659 | Email: sales@steelforgepieces.com Canonical page: https://www.steelforgepieces.com/Stainless-Steel/ALLOY-40.html Category: https://www.steelforgepieces.com/Stainless-Steel/ Reviewed: 2 October 2026 ## Summary ALLOY 40 is a designation for 21Cr-6Ni-9Mn, a high-manganese nitrogen-strengthened austenitic stainless steel, widely sold as 21-6-9 and covered by UNS S21900 (XM-10) and the lower-carbon UNS S21904 (XM-11). Nominal chemistry is 19.0 to 21.5 percent Cr, 5.5 to 7.5 percent Ni, 8.0 to 10.0 percent Mn and 0.15 to 0.40 percent N. Published data give it about twice the yield strength of Types 304, 321 and 347 in the annealed condition, corrosion resistance approaching 304L, good oxidation resistance at high temperature and good resistance to molten lead oxide. It stays non-magnetic after severe cold work and cannot be hardened by heat treatment, since strength comes from nitrogen in solid solution plus cold or hot-cold work. Jiangyin Jiangnan Metal melts and forges this grade in one works. Rings roll to 6,000 mm outside diameter, single pieces run to 30 t, minimum order is 10 kg, and material is released against EN 10204 3.1 or witnessed 3.2 certification. ## The grade ALLOY 40 sits in the nitrogen-strengthened austenitic family. Rather than relying on nickel alone to hold austenite stable, it substitutes manganese and nitrogen, which is why nickel runs at only 5.5 to 7.5 percent while manganese sits at 8 to 10 percent. Nitrogen in solid solution lifts strength without a hardening heat treatment, and the low carbon of the S21904 variant keeps the steel resistant to intergranular attack even as welded. Producer datasheets describe it as combining high strength in the annealed condition with good resistance to oxidation at high temperature, good resistance to lead oxide, and a high level of corrosion resistance at ambient temperature. It forms and fabricates much like Type 304 and 316, welds readily, and stays non-magnetic after heavy cold work. ## Designations and specifications | System | Designation | | --- | --- | | Common names | ALLOY 40, 21-6-9, 21Cr-6Ni-9Mn | | UNS | S21900 (ASTM XM-10), S21904 (ASTM XM-11, lower carbon), S21906 also cited | | Billets and bars for forging | ASTM A314 | | Bars and shapes | ASTM A276 / ASME SA-276, ASTM A580 wire | | Tube and pipe | ASTM A412 / SA-412, ASTM A269 (XM-10), AMS 5561 welded, AMS 5562 seamless, MIL-T-9821 | | Aerospace | AMS 5656 bar, wire, rings, extrusions; AMS 5595 sheet, plate, strip | | Welding consumables | AWS E/ER219 matching strength; AWS E/ER309 lower strength | Most material sold as 21-6-9 is now made to UNS S21904 (XM-11), a tighter and lower-carbon chemistry than the original S21900 (XM-10). The two differ mainly in carbon, so state the UNS number on the enquiry rather than the trade name alone. ## Chemical composition Weight percent, balance iron. | Element | Min | Max | | --- | --- | --- | | Chromium | 19.0 | 21.5 | | Nickel | 5.50 | 7.50 | | Manganese | 8.00 | 10.0 | | Nitrogen | 0.15 | 0.40 | | Carbon | - | 0.04 | | Silicon | - | 1.00 | | Phosphorus | - | 0.060 | | Sulphur | - | 0.030 | | Molybdenum | - | 0.75 | | Copper | - | 0.75 | Carbon separates the variants. Datasheets quote 0.04 percent maximum and 0.03 percent maximum depending on variant, with the original S21900 (XM-10) permitting more. Check against the current revision of the governing specification. Melting route: electric arc furnace, ladle furnace and vacuum oxygen decarburisation, with electroslag remelting under protective atmosphere available where tighter cleanliness applies. ## Mechanical properties at room temperature, annealed Typical values, not guaranteed minima. | Section | Direction | 0.2% YS ksi | 0.2% YS MPa | UTS ksi | UTS MPa | Elongation % | Reduction of area % | | --- | --- | --- | --- | --- | --- | --- | --- | | 152 mm square | Longitudinal | 62 | 428 | 95 | 655 | 46 | 69 | | 152 mm square | Transverse | 52 | 358 | 93 | 641 | 30 | 45 | | 102 mm square | Longitudinal | 56 | 386 | 97 | 668 | 53 | 73 | | 25.4 mm square | Longitudinal | 52 | 358 | 101 | 696 | 53 | 73 | The transverse ductility drop in heavy sections is the figure to watch: 30 percent elongation and 45 percent reduction of area against 46 and 69 percent longitudinal in the same 152 mm square. State the required test direction and sampling position at enquiry stage. Annealing temperature moves these figures. On strip, 982 C leaves roughly 483 MPa yield and 793 MPa tensile at 44 percent elongation and HRB 95, while 1066 C gives about 421 MPa and 738 MPa at 48 percent elongation and HRB 90. Minima such as 620 MPa tensile, 330 MPa yield and 35 percent elongation are widely quoted, but minima are fixed by the governing specification, product form and section size, and differ between ASTM A276, AMS 5656 and customer specifications. ## Elevated temperature properties Typical short-time tensile properties, annealed. | Temperature | 0.2% YS ksi | 0.2% YS MPa | UTS ksi | UTS MPa | Elongation % | | --- | --- | --- | --- | --- | --- | | 204 C / 400 F | 41 | 283 | 89 | 614 | 40 | | 316 C / 600 F | 38 | 262 | 86 | 593 | 33 | | 427 C / 800 F | 32 | 221 | 79 | 545 | 33 | | 538 C / 1000 F | 29 | 200 | 71 | 490 | 35 | | 649 C / 1200 F | 26 | 179 | 60 | 414 | 26 | | 704 C / 1300 F | 26 | 179 | 51 | 352 | 24 | Stress-rupture strength annealed is about 221 MPa for rupture in 100 hours at 649 C, falling to roughly 40 MPa for 100 hours and 21 MPa for 1,000 hours at 816 C. ## Physical properties | Property | Metric | Imperial | | --- | --- | --- | | Density | 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 to 100 C | 0.12 Btu/lb.F | | Electrical resistivity | 730 micro-ohm.mm | 439 ohm.cmil/ft | | Thermal conductivity | 14 W/m.K at 93 C to 29 W/m.K at 871 C | 96 to 200 Btu.in/ft2.h.F | | Mean thermal expansion | 16.7 x 10^-6/K (27-93 C) to 20.5 x 10^-6/K (27-982 C) | 9.3 to 11.4 x 10^-6/F | | Magnetic permeability | 1.005 annealed at 50 Oe, under 1.020 after 60 percent cold reduction | | ## Corrosion and oxidation resistance Corrosion resistance approaches Type 304L, and the low carbon gives resistance to intergranular corrosion in the welded condition. Surfaces must be free of scale and embedded particles, and finished parts should be passivated. | Environment | Condition | Average rate | | --- | --- | --- | | 65% nitric acid, boiling | Annealed | 7 mpy | | 65% nitric acid, boiling | Annealed, sensitised at 677 C | 9 mpy | | 5% sulphuric acid, 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 | The grade also resists high temperature oxidation in air and attack by molten lead oxide. Where this grade is the wrong choice: ALLOY 40 is a high-strength, oxidation-resistant austenitic, not a chloride-pitting or strong-acid alloy. For seawater, subsea, desalination and flue-gas desulphurisation duty, specify a duplex or super-duplex such as F51, F53 or F55, a 6 percent molybdenum grade such as F44, or a nickel alloy such as Hastelloy C-276. ## Forging, hot working and heat treatment Forging: start temperature 1150 to 1205 C. Preheating to an intermediate temperature is not required. The grade is not susceptible to hot shortness in its working range, can be hot worked down to about 650 C, and forgings can be cooled rapidly without danger of cracking. Anneal after forging for best corrosion resistance. Solution annealing: 982 to 1177 C, air cool. Grain coarsening occurs toward the top of the band, so where a grain-size limit applies the lower end or around 900 C is used. The annealed condition gives the best stress-rupture life and is used for service between 704 and 871 C and for maximum formability. After annealing, strength can only be raised by cold work or hot-cold work. Stress relieving: 482 to 760 C, giving the best all-round properties below 704 C. From 482 to 677 C there is little effect on the properties of cold-reduced material unless cold reduction was heavy. Above 677 C properties change more rapidly, and 816 C starts to cause rapid softening. Hot-cold working: normally 649 to 816 C with reductions of about 10 to 14 percent, followed by a 482 to 760 C stress relief. ## Machining, cold forming and welding Machining: machines with the techniques used on austenitic stainless steels. A rigid setup and ample coolant flow are what matter. The high work-hardening rate rewards sharp tooling and positive feeds and punishes light rubbing cuts and dwell. Cold working: works by conventional methods, but the high work-hardening rate and higher starting yield strength mean more forming force than the same part in Type 301, 302, 304 or 316. Welding: satisfactory by shielded fusion and resistance processes. Oxyacetylene welding is not recommended because of carbon pickup. AWS E/ER219 filler gives welds approaching base-metal strength; E/ER309 serves where high weld strength is not required. A post-weld anneal restores intergranular corrosion resistance. ## Forged shapes supplied in ALLOY 40 - Seamless rolled rings, ring rolled on 1 m, 3 m and 6 m radial-axial mills to 6,000 mm outside diameter, rectangular or contoured section - Forged rings from OD 50 mm, upset and punched, for sizes outside the ring-mill envelope - Forged flanges: weld neck, blind, slip-on, socket weld, lap joint, orifice, anchor, girth, swivel, long weld neck and non-standard hubs - Shafts and spindles, straight, stepped and eccentric, turned to 14,000 mm between centres and quenched vertically in 15 m well furnaces - Discs, tube sheets and covers machined to 5,000 mm, supplied proof-machined for volumetric inspection - Hollow cylinders, sleeves and bushings bored to 1,600 mm by 10,000 mm - Round, flat and square bars and blocks from ASTM A314 billet - Valve bodies, bonnets, blocks, stems, seat rings, spools and nozzles Presses run to 6,300 t with 4,000 t and 2,000 t presses and hammers from 750 kg to 5 t. Maximum heat size 60 t, heaviest single forging 30 t. Minimum order 10 kg with no minimum piece count. Lead time 20 to 60 days. ## Applications Aircraft and aero-engine parts: engine components and hydraulic and fuel line systems, where the strength-to-weight ratio allows thinner walls. AMS 5656 and AMS 5595 exist for this market. Chemical process and pollution control equipment: casings, housings, shafts, flanges and rings where 304L-class corrosion resistance has to arrive with roughly double the yield strength, and where as-welded intergranular resistance avoids a post-weld solution anneal on a large assembly. Steam and autoclave service: closures, retaining rings, covers and fasteners working hot and under pressure, using retained strength through 540 to 650 C. High temperature oxidising and lead oxide environments: furnace and heat-treatment fixtures, hangers and structural parts up to the 871 C ceiling. Parts that must remain magnetically transparent after forming, since the grade stays non-magnetic after heavy cold work. ## Testing and certification Steel is melted on site, so chemistry is verified at the furnace rather than taken from a billet supplier's certificate, and the melt number follows the part through forging, heat treatment, machining and shipment. The works holds CCS, BV, DNV, LR and NK approvals. In-house: optical emission spectrometry to ASTM E415, infrared carbon and sulphur to ASTM E1019, positive material identification, tensile to ASTM A370 and ISO 6892 on 600 kN and 300 kN machines, Charpy V-notch impact to minus 60 C, ultrasonic examination to ASTM A388 and EN 10228-3, magnetic particle to ASTM E709, hardness, grain size to ASTM E112. Through accredited third-party laboratories: intergranular corrosion to ASTM A262, impact below minus 60 C, bench Brinell or Rockwell hardness where the specification requires it. Certification: EN 10204 3.1 as standard; EN 10204 3.2 witnessed by BV, DNV, LR, SGS, TUV or the customer's inspector on request, with heat treatment charts, NDT reports, dimensional reports and PMI records. ## Requesting a quotation Send the grade and UNS variant, the dimensions or a drawing in PDF, DWG, DXF or STEP, the quantity, the delivery condition, the heat treatment and testing requirements, and the destination port. With those six items a price normally comes back within two working days. Email sales@steelforgepieces.com or call +86 189 2135 9659. ## Questions **What is ALLOY 40?** A designation for 21Cr-6Ni-9Mn, a high-manganese nitrogen-strengthened austenitic stainless steel, also sold as 21-6-9 and covered by UNS S21900 (XM-10) and the lower-carbon UNS S21904 (XM-11). **Is ALLOY 40 the same as 21-6-9?** Yes. Most material supplied now is made to UNS S21904 (XM-11), a tighter and lower-carbon chemistry than the original UNS S21900 (XM-10), so put the UNS number on the order. **How strong is it compared with 304?** About twice the yield strength of Types 304, 321 and 347. Typical annealed bar is 358 to 428 MPa yield and 655 to 696 MPa tensile at 46 to 53 percent elongation longitudinally. **At what temperature is ALLOY 40 forged?** Start at 1150 to 1205 C. No intermediate preheat needed, no hot shortness in the working range, hot working down to about 650 C, rapid cooling without cracking. **How is it heat treated?** Solution strengthened, so it cannot be hardened thermally. Solution anneal 982 to 1177 C and air cool. Stress relieve 482 to 760 C. **What is the maximum service temperature?** Not recommended above 871 C. Annealed condition from 704 to 871 C for best stress-rupture life; stress-relieved below 704 C for best all-round properties. **Can it be welded?** Yes, by shielded fusion and resistance processes. AWS E/ER219 for near base-metal strength, E/ER309 where high weld strength is not needed. Avoid oxyacetylene welding. **What is the minimum order and lead time?** Minimum order 10 kg with no minimum piece count. Lead time 20 to 60 days from order confirmation. ## Related grades Nitronic 50, Nitronic 60, Nitronic 30 and Nitronic 32 in the nitrogen-strengthened family; A182 F51, F53, F55 and F44 for chloride service; A286, 17-4 PH, 15-5 PH and PH13-8Mo for higher strength. Full list at https://www.steelforgepieces.com/Stainless-Steel/ ## Data sources Composition, mechanical, physical, corrosion, heat treatment and fabrication data are compiled from published 21Cr-6Ni-9Mn producer datasheets and from the scope of ASTM A314, ASTM A276 and the AMS specifications cited. Values are typical and given for guidance, not as a warranty. Properties of a given forging depend on section size, orientation, delivery condition and the specification revision in force.