254 SMO (UNS S31254 / EN 1.4547) Open-Die Forgings: Rings, Flanges, Bars and Shafts
Grade summary
254 SMO is a 6% molybdenum, nitrogen-alloyed super austenitic stainless steel. Its 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. That chemistry gives a pitting resistance equivalent number (PREN) of at least 42.5, which is why the grade is specified for natural seawater and other strong chloride media.
Forgings in this grade are ordered to ASTM A182 Grade F44 for flanges, fittings and valve parts, or to ASTM A473 for general forged products. Both require solution annealing at 1150 to 1200 C followed by a water quench. Minimum properties are 94 ksi (650 MPa) tensile, 44 ksi (300 MPa) yield, 35% elongation and 50% reduction of area.
We forge UNS S31254 into seamless rolled rings, flanges, shafts, round bars, discs, sleeves, bushings, tube sheets and forged pipe, supplied with EN 10204 3.1 or 3.2 certification and ultrasonic testing to EN 10228-3, SEP 1921 or ASTM A388. Enquiries: sales@steelforgepieces.com or +86-189-2135-9659.
- UNS
- S31254
- EN
- 1.4547
- Forging spec
- A182 F44
- PREN
- 42.5 min
- Molybdenum
- 6.0 to 6.5%
- Yield, min
- 300 MPa
- Tensile, min
- 650 MPa
- Anneal
- 1150 to 1200 C
Designations and equivalent grades
The same alloy carries several designations. When you place a forging order, quote the UNS number together with the product specification rather than the trade name, since the trade name does not by itself fix the testing or heat treatment requirements.
| 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 material data sheets | NORSOK MDS R11 and 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) |
Trademark notice: 254 SMO is a registered trademark owned by Outokumpu OY. Jiangyin Jiangnan Metal Co., Ltd. manufactures forgings in the generically designated grade UNS S31254 / EN 1.4547 / ASTM A182 F44. The trade name appears on this page only to identify the grade.
Chemical composition of UNS S31254
The table gives the ASTM A182 Grade F44 limits that apply to forgings, next to the nominal mill analysis published for the grade. All figures are weight percent.
| Element | ASTM A182 F44 limits | Nominal analysis |
|---|---|---|
| Carbon, C | 0.020 max | 0.020 max |
| Chromium, Cr | 19.50 to 20.50 | 20 |
| Nickel, Ni | 17.50 to 18.50 | 18 |
| Molybdenum, Mo | 6.00 to 6.50 | 6.1 |
| Nitrogen, N | 0.18 to 0.25 | 0.20 |
| Copper, Cu | 0.50 to 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 |
The sulphur limit is shown as 0.010% max, in line with the published mill analysis. Some secondary sources print 0.10% max, which looks like a transcription error. Confirm against the current edition of ASTM A182 for your order. Melting route at our works is EAF plus VOD, with ESR remelting available where the purchaser asks for tighter cleanliness and segregation control.
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 values
Mill data for solution annealed product gives Rp0.2 of 310 MPa (45 ksi) minimum, Rp1.0 of 340 MPa (49 ksi) minimum, and a tensile band of 655 to 850 MPa for sections above 5 mm, or 675 to 850 MPa below 5 mm. Elongation is 35% minimum and hardness 96 HRB maximum. The structure is fully austenitic, so impact toughness stays high down to cryogenic temperature: the grade meets the 60 J at minus 196 C requirement in 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 |
Service temperature caution. Intermetallic phases precipitate between 600 C and 1000 C. UNS S31254 must not be held in that range for long periods, so it is not a creep service alloy even though proof strength at temperature is tabulated above.
Physical properties
| Density | 8.0 g/cm3 (0.29 lb/in3) |
|---|---|
| Modulus of elasticity at 20 C | 195 GPa (28.3 x 10³ ksi) |
| Modulus of elasticity at 300 C | 174 GPa |
| Thermal conductivity at 20 C | 10 W/m.C |
| Specific heat at 20 C | 485 J/kg.C |
| Mean thermal expansion, 30 to 100 C | 16 x 10⁻⁶ /C |
| Mean thermal expansion, 30 to 500 C | 17 x 10⁻⁶ /C |
| Magnetic response | Non-magnetic in the solution annealed condition |
Low thermal conductivity combined with high thermal expansion is the practical reason distortion control matters when welding this grade and when heat treating large rolled rings.
Corrosion performance and PREN
Resistance to pitting and crevice attack in chloride media depends mainly on chromium, molybdenum and nitrogen. The usual index is the pitting resistance equivalent number:
PREN = %Cr + 3.3 x %Mo + 16 x %N, giving PREN of 42.5 minimum for UNS S31254
Pitting and crevice corrosion
In natural seawater at 60 C the grade has been exposed for long periods without crevice corrosion. Crevice attack under gaskets, deposits and biofouling is the failure mode that normally limits conventional stainless steels in seawater, so this is the property that puts S31254 into seawater cooling and firewater systems.
Stress corrosion cracking
Standard austenitic steels of the TP304 and TP316 type are liable to chloride stress corrosion cracking above roughly 60 C. Higher nickel and molybdenum raise that resistance, and UNS S31254 performs well in accelerated testing. Figures are in the comparison table below.
Intergranular corrosion
Carbon is held to 0.020% max, so carbide precipitation during welding is not a practical problem. The grade passes the Strauss test, ASTM A262 practice E, even after a one hour sensitising treatment anywhere in the 600 to 1000 C range. The intermetallic phases that can form in that range do not cause intergranular corrosion in the environments the grade is used for.
Acid service
In pure sulphuric acid the grade is considerably more resistant than ASTM TP316. In naturally aerated sulphuric acid that contains chloride ions it is more resistant than 904L.
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 in under 150 h by pitting | 105 h |
| 904L | No failure at 1000 h, but crevice corrosion | 225 h |
| UNS S31254 (254 SMO) | No failure at 1000 h, no attack | 425 h |
For duties beyond this grade, such as hot concentrated chlorides, reducing acids or wet chlorine, the usual step up is a nickel-base alloy: Hastelloy C-276, Alloy 59 or Alloy 31. Where higher strength is wanted at a similar PREN, super duplex A182 F55 (S32760) and A182 F53 (S32750) are the common alternatives, but they do not offer the cryogenic toughness of a fully austenitic grade.
Forging and heat treatment of UNS S31254
Solution annealing
Anneal at 1150 to 1200 C (2100 to 2190 F) and quench in water. Thin sections can be annealed from 1130 C minimum with air or water quenching. Quench rate is the point to watch: slow cooling through 1000 to 600 C lets intermetallic phases form at grain boundaries, which costs toughness and corrosion resistance.
ASTM A182 sequence requirement
After hot working, forgings have to be cooled below 1000 F (538 C) before the specified heat treatment is carried out. We control and record this step, and the chart goes out with the material certificate.
Shop notes
The grade is stiff under the hammer and its hot working window is narrower than 304 or 316, so reheats are planned rather than improvised and finish temperature is controlled to keep the work out of the precipitation range. Contact with copper and copper alloys is avoided all the way through handling, because metallic copper pick-up can cause cracking during 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
Welding
Weldability is good. TIG is the first choice and SMAW is also suitable. Molybdenum segregates in as-cast weld metal, so an over-alloyed nickel-base filler is needed to hold corrosion resistance in the as-welded condition.
| Process | Filler metal classification |
|---|---|
| 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) |
Keep heat input below 1.5 kJ/mm and interpass temperature below 100 C (210 F), and run stringer beads. Set the welding sequence before starting to limit distortion. Where residual stress matters, solution anneal after welding.
Machining
As a highly alloyed austenitic grade it work-hardens quickly and needs tougher insert grades and much lower cutting speeds than 304/304L or 316/316L. Rigid setups, positive rake geometry, plenty of coolant and no dwelling are the essentials. We can supply forgings rough-machined with an agreed allowance, or finished to drawing, if you would rather leave the difficult metal removal with us.
UNS S31254 forged products we supply
The following configurations are produced in UNS S31254 to ASTM A182 F44 or ASTM A473, to customer drawing.
| 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. Send a drawing, a sketch with dimensions, or simply OD x ID x height, and we will come back with weight, lead time and price.
Applications by industry
Seawater handling and desalination
Seawater cooling systems, cooling water pipes, ballast water systems, firefighting systems, desalination plants, high pressure reverse osmosis plant and seawater piping. Crevice corrosion resistance in natural seawater is what decides the grade choice here.
Offshore oil and gas
Subsea and deepwater production systems, risers, manifolds, pressure vessels, valves and heat exchangers, along with topside seawater and firewater pipework. The grade is listed under NACE MR0175 for sulphide stress cracking resistance in oilfield equipment.
Chemical and petrochemical processing
Tanks and pipelines for chemicals with high halide content, sulphuric acid duties, and mixed or organic acids containing chloride ions at raised pressure and temperature.
Pulp and paper
Equipment in pulp bleaching plants, where hot chloride-bearing bleach liquors defeat ordinary stainless steels.
Power and environmental plant
Flue gas desulphurisation systems, gas cleaning components, waste water and demineralised water production, and parts for industrial air, nitrogen and gas compressors.
Testing, inspection and certification
| Material certificate | EN 10204 3.1 mill certificate, or EN 10204 3.2 witnessed by third party such as TUV, BV, SGS, DNV, Lloyd's or ABS |
|---|---|
| Ultrasonic testing | EN 10228-3, SEP 1921 or ASTM A388, acceptance class to customer specification |
| Chemical analysis | Spectrometer analysis, ladle and product analysis |
| Mechanical testing | Tensile, Charpy V-notch including cryogenic, hardness |
| Corrosion testing | ASTM A262 practice E, and ASTM G48 pitting or crevice tests on request |
| Other NDT | Liquid penetrant to ASTM E165, dimensional inspection report, positive material identification |
| Traceability | Heat number hard stamped, heat treatment charts supplied |
Frequently asked questions
What is 254 SMO material?
254 SMO is the trade name for a 6% molybdenum, nitrogen-alloyed super austenitic stainless steel designated UNS S31254 and EN 1.4547 (X1CrNiMoCuN20-18-7). Nominal composition is about 20% Cr, 18% Ni, 6.1% Mo, 0.20% N and 0.7% Cu, which gives a PREN of at least 42.5. It was developed for seawater and other aggressive chloride-bearing media. The name is a trademark owned by Outokumpu OY; the generic designations are UNS S31254 and ASTM A182 Grade F44.
Is 254 SMO a duplex stainless steel?
No. UNS S31254 is fully austenitic. Nickel at 17.5 to 18.5% stabilises a single austenitic phase, while duplex grades such as S31803 and S32750 have a mixed ferritic-austenitic structure. Being fully austenitic, S31254 keeps good impact toughness at cryogenic temperature and is non-magnetic in the solution annealed condition.
What is the ASTM specification for 254 SMO forgings?
Forged flanges and fittings go to ASTM A182 Grade F44, general forged products to ASTM A473, and bar to ASTM A276, ASTM A479 or EN 10088-3.
What is the yield strength of ASTM A182 F44?
Minimum 0.2% offset yield strength is 44 ksi (300 MPa), with 94 ksi (650 MPa) minimum tensile, 35% minimum elongation and 50% minimum reduction of area.
What heat treatment is applied to UNS S31254 forgings?
Solution anneal at 1150 to 1200 C and quench rapidly in water. Under ASTM A182 the forging is first cooled below 1000 F (538 C) after hot working, then heat treated. Rapid quenching prevents intermetallic precipitation in the 600 to 1000 C range.
How does 254 SMO compare with 316L and 904L?
It outperforms both in the published tests. In drop evaporation testing at 0.9 times Rp0.2, time to failure was 105 h for TP316, 225 h for 904L and 425 h for 254 SMO. In boiling 25% NaCl U-bend tests, TP316 failed in under 150 h by pitting, 904L lasted 1000 h but suffered crevice corrosion, and 254 SMO lasted 1000 h with no attack.
What filler metal should be used to weld UNS S31254?
An over-alloyed nickel-base filler: AWS A5.14 ERNiCrMo-3 or ERNiCrMo-13 for TIG and MIG, AWS A5.11 ENiCrMo-3 or ENiCrMo-13 for SMAW. Heat input below 1.5 kJ/mm, interpass below 100 C, stringer beads.
Can Jiangyin Jiangnan Metal supply UNS S31254 forgings with third-party certification?
Yes. EN 10204 3.1 mill certificates, or EN 10204 3.2 certificates witnessed by TUV, BV, SGS, DNV or Lloyd's, with ultrasonic testing to EN 10228-3, SEP 1921 or ASTM A388. Write to sales@steelforgepieces.com or call +86-189-2135-9659.
Request a quotation for UNS S31254 forgings
Jiangyin Jiangnan Metal Co., Ltd., open-die forging factory
No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China
Telephone, WhatsApp and WeChat: +86-189-2135-9659
Email: sales@steelforgepieces.com
Website: www.steelforgepieces.com
Send the drawing or the dimensions of the UNS S31254 forging you need, with quantity, specification (A182 F44 or A473), NDT requirement and certificate level.
Capability summary: open-die forging, seamless ring rolling, in-house solution annealing, rough and finish machining, UT, PT and PMI, EN 10204 3.1 and 3.2 certification. Grades cover super austenitic and duplex stainless steels, nickel alloys, tool steels, alloy steels and carbon steels.
Data sources
Composition, corrosion test results, physical properties, heat treatment and welding recommendations on this page are 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 and your project specification before design or purchase.