# 254 SMO (UNS S31254 / EN 1.4547) Open-Die Forgings: Rings, Flanges, Bars and Shafts

Supplier: Jiangyin Jiangnan Metal Co., Ltd., open-die forging factory, Jiangyin, Jiangsu, China
Address: No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China
Telephone / WhatsApp / WeChat: +86-189-2135-9659
Email: sales@steelforgepieces.com
Web: https://www.steelforgepieces.com/Stainless-Steel/254SMO.html
Updated: 2026-09-27

## Grade summary

254 SMO is a 6% molybdenum, nitrogen-alloyed super austenitic stainless steel. Generic designations are UNS S31254 and EN 1.4547 (X1CrNiMoCuN20-18-7). Nominal analysis is about 20% Cr, 18% Ni, 6.1% Mo, 0.20% N and 0.7% Cu, giving a pitting resistance equivalent number (PREN) of at least 42.5. The grade is specified for natural seawater and other strong chloride media.

Forgings are ordered to ASTM A182 Grade F44 for flanges, fittings and valve parts, or ASTM A473 for general forged products. Both require solution annealing at 1150-1200 C followed by a water quench. Minimum properties: 94 ksi (650 MPa) tensile, 44 ksi (300 MPa) yield, 35% elongation, 50% reduction of area.

Jiangyin Jiangnan Metal Co., Ltd. forges UNS S31254 into seamless rolled rings, flanges, shafts, round bars, discs, sleeves, bushings, tube sheets and forged pipe, with EN 10204 3.1 or 3.2 certification and ultrasonic testing to EN 10228-3, SEP 1921 or ASTM A388.

Trademark notice: 254 SMO is a registered trademark owned by Outokumpu OY. We manufacture forgings in the generically designated grade UNS S31254 / EN 1.4547 / ASTM A182 F44.

## Designations and equivalent grades

| Item | Designation |
|---|---|
| UNS number | S31254 |
| EN number | 1.4547 |
| EN name | X1CrNiMoCuN20-18-7 |
| AFNOR (obsolete) | Z1 CNDU 20.18.06AZ |
| Forged flanges, fittings, valve parts | ASTM A182 Grade F44 |
| Forged products, general | ASTM A473 |
| Bar | ASTM A276, ASTM A479, EN 10088-3 |
| Seamless pipe | ASTM A312, ASTM A213, EN 10216-5 |
| Offshore MDS | NORSOK MDS R11 / R18; IOGP S-563 MDS IR111, IR111S, IR118, IR118S |
| Sour service | Listed under NACE MR0175 for sulphide stress cracking resistance |
| Nearest higher-alloy grade | 1.4529 (UNS N08926, Alloy 926) |

## Chemical composition, weight percent

| Element | ASTM A182 F44 limits | Nominal analysis |
|---|---|---|
| Carbon, C | 0.020 max | 0.020 max |
| Chromium, Cr | 19.50-20.50 | 20 |
| Nickel, Ni | 17.50-18.50 | 18 |
| Molybdenum, Mo | 6.00-6.50 | 6.1 |
| Nitrogen, N | 0.18-0.25 | 0.20 |
| Copper, Cu | 0.50-1.00 | 0.7 |
| Manganese, Mn | 1.00 max | 1.00 max |
| Silicon, Si | 0.80 max | 0.80 max |
| Phosphorus, P | 0.030 max | 0.030 max |
| Sulphur, S | 0.010 max | 0.010 max |
| Iron, Fe | Balance | Balance |

Sulphur is shown as 0.010% max per the published mill analysis; some secondary sources print 0.10% max, which appears to be a transcription error. Melting route at our works: EAF + VOD, with ESR available on request.

## Mechanical properties

ASTM A182 Grade F44 minimum requirements, solution annealed:

| Property | Requirement |
|---|---|
| Tensile strength, min | 94 ksi [650 MPa] |
| Yield strength, 0.2% offset, min | 44 ksi [300 MPa] |
| Elongation in 2 in. [50 mm] or 4D, min | 35% |
| Reduction of area, min | 50% |

Typical annealed product: Rp0.2 310 MPa (45 ksi) min, Rp1.0 340 MPa (49 ksi) min, tensile 655-850 MPa above 5 mm section (675-850 MPa below 5 mm), elongation 35% min, hardness 96 HRB max. Fully austenitic structure, so the grade meets the 60 J at -196 C requirement of EN 13445-2 and EN 10216-5.

Minimum proof strength at temperature:

| Temperature | Rp0.2, MPa | Rp1.0, MPa |
|---|---|---|
| 100 C | 230 | 270 |
| 200 C | 190 | 225 |
| 300 C | 170 | 200 |
| 400 C | 160 | 190 |
| 500 C | 148 | 180 |

Caution: intermetallic phases precipitate between 600 C and 1000 C, so the grade is not for prolonged service in that range and is not a creep service alloy.

## Physical properties

| Property | Value |
|---|---|
| Density | 8.0 g/cm3 (0.29 lb/in3) |
| Modulus of elasticity, 20 C | 195 GPa (28.3 x 10^3 ksi) |
| Modulus of elasticity, 300 C | 174 GPa |
| Thermal conductivity, 20 C | 10 W/m.C |
| Specific heat, 20 C | 485 J/kg.C |
| Mean thermal expansion, 30-100 C | 16 x 10^-6 /C |
| Mean thermal expansion, 30-500 C | 17 x 10^-6 /C |
| Magnetic response | Non-magnetic in solution annealed condition |

## Corrosion performance

PREN = %Cr + 3.3 x %Mo + 16 x %N, giving PREN 42.5 minimum for UNS S31254.

Pitting and crevice corrosion: exposed for long periods in natural seawater at 60 C without crevice corrosion, which is the failure mode that normally limits conventional stainless steels under gaskets, deposits and biofouling.

Stress corrosion cracking: TP304 and TP316 type steels are liable to chloride SCC above roughly 60 C; higher nickel and molybdenum raise resistance, and S31254 performs well in accelerated tests.

Intergranular corrosion: with carbon at 0.020% max the grade passes the Strauss test (ASTM A262 practice E) even after one hour sensitising anywhere in the 600-1000 C range.

Acid service: considerably more resistant than ASTM TP316 in pure sulphuric acid, and more resistant than 904L in naturally aerated sulphuric acid containing chloride ions.

## Comparison with 316L and 904L

| Grade | Boiling 25% NaCl, pH 1.5, U-bend | Drop evaporation at 0.9 x Rp0.2, time to failure |
|---|---|---|
| ASTM TP316 | Failed under 150 h by pitting | 105 h |
| 904L | No failure at 1000 h, crevice corrosion | 225 h |
| UNS S31254 (254 SMO) | No failure at 1000 h, no attack | 425 h |

## Forging and heat treatment

Solution anneal 1150-1200 C (2100-2190 F), water quench. Thin sections from 1130 C minimum, air or water quench. Slow cooling through 1000-600 C forms intermetallic phases at grain boundaries and costs toughness and corrosion resistance.

Under ASTM A182, forgings are cooled below 1000 F (538 C) after hot working before heat treatment. Charts are supplied with the certificate.

Shop notes: narrower hot working window than 304 or 316, so reheats are planned and finish temperature controlled. Contact with copper and copper alloys is avoided throughout handling, since copper pick-up can cause cracking in later welding, hot working or heat treatment. Cold bending is well tolerated and re-annealing after cold bending is not normally needed.

## Welding and machining

| Process | Filler metal |
|---|---|
| TIG / GTAW and MIG / GMAW | AWS A5.14 ERNiCrMo-3 (ISO 18274 S Ni 6625) or ERNiCrMo-13 (S Ni 6059) |
| MMA / SMAW | AWS A5.11 ENiCrMo-3 (ISO 14172 E Ni 6625) or ENiCrMo-13 (E Ni 6059) |

Heat input below 1.5 kJ/mm, interpass below 100 C (210 F), stringer bead technique. Solution anneal after welding where residual stress matters.

Machining: work-hardens quickly, needs tougher insert grades and much lower cutting speeds than 304/304L or 316/316L. Rigid setup, positive rake, plenty of coolant, no dwelling. Rough-machined or finish-machined forgings available.

## Forged products supplied in UNS S31254

| Product form | Typical use |
|---|---|
| Seamless rolled rings, forged rings, retaining rings | Flange faces, bearing housings, valve seat rings |
| Forged flanges: weld neck, slip-on, blind, orifice, long weld neck | Seawater, firewater and subsea pipework |
| Forged round bars, blocks, rectangles, step shafts | Valve stems, pump shafts, fastener stock |
| Forged discs, disks, tube sheets, blanks | Heat exchangers, separators, pressure vessels |
| Forged sleeves, bushings, hollow bars | Pump wear parts, subsea connectors |
| Forged pipe and forged tubes | High pressure chloride-bearing service |
| Forged shafts, eccentric shafts, spindles, crankshafts | Compressors, gearboxes, power transmission |
| Forged valve bodies, bonnets, balls, gates, blocks | Ball, gate, globe, check and plug valves, strainers |
| Forged nozzles, manifolds, wheels, rolls, gears | Process plant and rotating equipment |

Open-die forging, ring rolling, upsetting and free forging are done in house.

## Applications by industry

Seawater handling and desalination: seawater cooling, cooling water pipes, ballast water systems, firefighting systems, desalination plants, high pressure reverse osmosis plant, seawater piping.

Offshore oil and gas: subsea and deepwater production systems, risers, manifolds, pressure vessels, valves, heat exchangers, topside seawater and firewater pipework. Listed under NACE MR0175.

Chemical and petrochemical: tanks and pipelines for high halide chemicals, sulphuric acid duties, mixed and organic acids containing chloride ions at raised pressure and temperature.

Pulp and paper: pulp bleaching plant equipment.

Power and environmental: flue gas desulphurisation systems, gas cleaning components, waste water and demineralised water production, industrial air, nitrogen and gas compressor parts.

## Testing and certification

| Item | Scope |
|---|---|
| Material certificate | EN 10204 3.1, or EN 10204 3.2 witnessed by TUV, BV, SGS, DNV, Lloyd's or ABS |
| Ultrasonic testing | EN 10228-3, SEP 1921, ASTM A388 |
| Chemical analysis | Spectrometer, ladle and product analysis |
| Mechanical testing | Tensile, Charpy V-notch including cryogenic, hardness |
| Corrosion testing | ASTM A262 practice E; ASTM G48 on request |
| Other NDT | Liquid penetrant to ASTM E165, dimensional report, PMI |
| Traceability | Heat number hard stamped, heat treatment charts supplied |

## FAQ

**What is 254 SMO material?** A 6% molybdenum, nitrogen-alloyed super austenitic stainless steel designated UNS S31254 and EN 1.4547, about 20% Cr, 18% Ni, 6.1% Mo, 0.20% N, 0.7% Cu, PREN 42.5 minimum, developed for seawater and other aggressive chloride media. The name is an Outokumpu OY trademark.

**Is 254 SMO duplex?** No, it is fully austenitic. Nickel at 17.5-18.5% stabilises a single austenitic phase, unlike duplex grades S31803 or S32750.

**Which ASTM specification covers 254 SMO forgings?** ASTM A182 Grade F44 for flanges and fittings, ASTM A473 for general forged products, ASTM A276 / A479 or EN 10088-3 for bar.

**Yield strength of A182 F44?** 44 ksi (300 MPa) minimum, with 94 ksi (650 MPa) tensile, 35% elongation, 50% reduction of area.

**Heat treatment?** Solution anneal 1150-1200 C, rapid water quench, after cooling below 1000 F (538 C) post hot working.

**Versus 316L and 904L?** Drop evaporation time to failure 105 h for TP316, 225 h for 904L, 425 h for 254 SMO. Boiling 25% NaCl U-bend: TP316 failed under 150 h, 904L 1000 h with crevice corrosion, 254 SMO 1000 h with no attack.

**Welding filler?** AWS A5.14 ERNiCrMo-3 or ERNiCrMo-13 for TIG and MIG; AWS A5.11 ENiCrMo-3 or ENiCrMo-13 for SMAW.

**Third-party certification?** Yes, EN 10204 3.1 or 3.2 with TUV, BV, SGS, DNV or Lloyd's.

## Contact

Jiangyin Jiangnan Metal Co., Ltd., open-die forging factory
No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China
Telephone / WhatsApp / WeChat: +86-189-2135-9659
Email: sales@steelforgepieces.com

Send a drawing, a sketch with dimensions, or OD x ID x height, with quantity, specification, NDT requirement and certificate level.

## Data sources

Compiled from the published mill data sheet for the grade and from ASTM A182/A182M Grade F44 requirements. Figures are for engineering guidance; confirm against the current edition of the governing standard before design or purchase.