# SUS 312L Forgings: UNS S31254, EN 1.4547, 254 SMO

Source: https://www.steelforgepieces.com/Stainless-Steel/SUS-312L.html
Supplier: Jiangyin Jiangnan Metal Co., Ltd., open-die forging factory, Jiangyin, Jiangsu, China
Contact: +86-189-2135-9659 | sales@steelforgepieces.com
Revised: October 2026

## Summary

SUS 312L is the JIS name for the 6% molybdenum, nitrogen-alloyed super austenitic stainless steel sold elsewhere as UNS S31254, EN 1.4547 and 254 SMO. It is specified at 19.00 to 21.00% chromium, 17.50 to 19.50% nickel, 6.00 to 7.00% molybdenum, 0.50 to 1.00% copper and 0.16 to 0.25% nitrogen, with carbon capped at 0.020%. That gives a pitting resistance equivalent number around 43 and a minimum proof stress of 300 MPa, roughly 1.5 times that of SUS 304. Jiangyin Jiangnan Metal Co., Ltd. melts and open-die forges this grade at Jiangyin, Jiangsu, China, producing rolled rings to 6000 mm outside diameter and single forgings to 30 tonnes, from a 10 kg minimum order, with EN 10204 3.1 or 3.2 certification.

## Key facts

| Item | Value |
| --- | --- |
| Grade | SUS 312L (JIS) |
| Other designations | UNS S31254, EN 1.4547, 254 SMO, 6Mo, NSSC 270 |
| EN steel name | X1CrNiMoCuN20-18-7 |
| ASTM forging grade | A182 Grade F44 (narrower limits) |
| Nominal composition | 20Cr-18Ni-6Mo-0.7Cu-0.2N, low carbon |
| Alloy family | Super austenitic, non-magnetic |
| PREN, calculated | about 41.4 at grade minimum, about 43 typical |
| Melting route | EAF + LF + VOD on site; ESR or VAR on request |
| Certification | EN 10204 3.1 standard, 3.2 third party on request |

SUS 312L belongs to the group of highly alloyed austenitic stainless steels often called super stainless steels. The low carbon content keeps the risk of carbide precipitation during welding very low. Japanese mill literature lists the grade under the characteristics "seawater resistant, acid resistant, high strength" for industrial plant equipment, offshore structures and architectural exterior cladding. Nippon Steel's proprietary NSSC 270 is supplied to this JIS grade.

## Equivalent grades and standards

| System | Designation | Notes |
| --- | --- | --- |
| JIS | SUS 312L | Composition and mechanical limits per JIS G 4303 / G 4305 |
| UNS | S31254 | Most widely quoted designation worldwide |
| EN number | 1.4547 | Listed in EN 10088-1 and related product standards |
| EN name | X1CrNiMoCuN20-18-7 | Steel name form of 1.4547 |
| Trade name | 254 SMO | Trademark owned by Outokumpu OY |
| ASTM forgings | A182 Grade F44 | Narrower chemistry window than SUS 312L |
| ASTM other forms | A240, A312, A249, A269, A276, A479, A813, A814 | Plate, pipe, tube and bar |
| EN forgings | EN 10250-4 | Open steel die forgings, stainless steels |
| EN bar | EN 10088-3 / EN 10272 | Bar, including bar for pressure purposes |
| Japanese proprietary | NSSC 270 | Nippon Steel grade supplied to SUS 312L |

EN 10088-2 is a sheet, plate and strip standard and is not the delivery document for a forging. For forged product the relevant EN document is EN 10250-4; for bar, EN 10088-3 or EN 10272; for flanges and fittings, ASTM A182 under the F44 designation.

## Chemical composition (weight percent, JIS limits)

| | C | Si | Mn | P | S | Ni | Cr | Mo | Cu | N |
| --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
| Min | - | - | - | - | - | 17.50 | 19.00 | 6.00 | 0.50 | 0.16 |
| Max | 0.020 | 0.80 | 1.00 | 0.030 | 0.015 | 19.50 | 21.00 | 7.00 | 1.00 | 0.25 |

### SUS 312L against ASTM A182 F44

The two specifications describe the same alloy but are not interchangeable on paper.

| Element | SUS 312L (JIS) | A182 F44 (UNS S31254) | Consequence |
| --- | --- | --- | --- |
| Nickel | 17.50 to 19.50 | 17.50 to 18.50 | SUS 312L heat may exceed the F44 ceiling |
| Chromium | 19.00 to 21.00 | 19.50 to 20.50 | Wider band both ways |
| Molybdenum | 6.00 to 7.00 | 6.00 to 6.50 | Higher Mo lifts PREN but can fail an F44 check |
| Nitrogen | 0.16 to 0.25 | 0.18 to 0.25 | Lower N floor under JIS |
| Sulphur | 0.015 max | 0.010 max | JIS limit is looser |

If the end user audits to ASTM A182 F44 while the drawing says SUS 312L, state it at enquiry stage. Because the steel is melted in our own shop rather than bought in as billet, the aim chemistry can be set inside the intersection of both windows and the certificate issued as dual-certified. That option disappears once the heat is cast.

### PREN

PREN = %Cr + 3.3 x %Mo + 16 x %N. At the SUS 312L minimum limits (19.00% Cr, 6.00% Mo, 0.16% N) the result is about 41.4. On a typical analysis (20% Cr, 6.1% Mo, 0.20% N) it is about 43.3. Published data for the equivalent grade quotes 42.5 or higher, the range normally associated with super duplex stainless steels.

## Mechanical properties, solution annealed, room temperature

| Property | Metric | Imperial |
| --- | --- | --- |
| 0.2% proof stress, min | 300 N/mm2 | 43.5 ksi |
| Tensile strength, min | 650 N/mm2 | 94 ksi |
| Elongation, min | 35% | 35% |
| Reduction of area, min | 40% | 40% |
| Hardness, max | 223 HBW | 96 HRB / 230 HV |

SUS 304 is specified at 205 MPa minimum proof stress, so SUS 312L is roughly 1.5 times stronger in proof terms. Suppliers of the equivalent grade commonly report an actual tensile range of 650 to 850 MPa solution annealed.

### Proof strength at temperature (published data, equivalent grade)

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

Prolonged exposure between 600 and 1000 C precipitates intermetallic phases and is to be avoided in service, not only during heat treatment.

### Impact toughness

The microstructure is fully austenitic, so impact strength stays high at room and cryogenic temperatures. Published testing on the equivalent grade shows the material meeting the 60 J requirement at -196 C set by EN 13445-2 and EN 10216-5. Our in-house pendulum machine with low-temperature bath covers Charpy testing to -60 C; below that the test is placed with an accredited third-party laboratory.

### Typical physical properties

| Property | Value |
| --- | --- |
| Density | 8.0 g/cm3 (0.289 lb/in3) |
| Modulus of elasticity at 20 C | 195 GPa |
| Thermal conductivity at 20 C | 10 to 14 W/m.K |
| Specific heat capacity at 20 C | 485 J/kg.K |
| Thermal expansion, 30 to 100 C | 16 x 10-6 /C |
| Poisson's ratio | 0.30 |
| Magnetic response | Non-magnetic in the annealed condition |

## Corrosion behaviour

### Chloride stress corrosion cracking

U-bend specimens, boiling 25% NaCl, pH 1.5:

| Grade | Time to failure | Observation |
| --- | --- | --- |
| ASTM TP316 | under 150 h | Pitting |
| 904L | No failure at 1000 h | Crevice corrosion |
| 254 SMO / S31254 | No failure at 1000 h | No attack |

Drop evaporation method, 0.1 M NaCl at 300 C, stress 0.9 x Rp0.2:

| Grade | Time to failure |
| --- | --- |
| ASTM TP316 | 105 h |
| 904L | 225 h |
| 254 SMO / S31254 | 425 h |

### Pitting and crevice corrosion

Resistance is governed by chromium, molybdenum and nitrogen, and by how the part was made and fabricated. Tests in natural seawater at 60 C have shown the equivalent grade can be exposed for prolonged periods without crevice attack, which is why it is specified for seawater cooling, ballast water and firewater systems where 316L fails under gaskets, deposits and fouling. Critical pitting temperature testing to ASTM G48 can be arranged through an accredited laboratory.

### Intergranular corrosion and acid service

Carbon is held to 0.020% maximum, so there is very little risk of carbide precipitation on heating, and the equivalent grade passes the Strauss test (ASTM A262 practice E) even after sensitising for one hour between 600 and 1000 C. Intermetallic phases can precipitate at grain boundaries in that band, but published work reports they do not create an intergranular corrosion risk in the intended environments, so welding can be carried out without that concern. In pure sulphuric acid the grade is far more resistant than TP316, and in naturally aerated sulphuric acid containing chloride ions it outperforms 904L.

## Heat treatment, forging and fabrication

Solution anneal at 1150 to 1200 C, then water quench. Thin sections may be annealed from a minimum of about 1130 C with air or water cooling. Cooling must be fast through the intermetallic precipitation range; slow cooling throws out sigma and chi phases and the corrosion resistance goes with them.

Forge and upset at roughly 982 to 1149 C. Above that range the material scales heavily and workability drops. Every hot-worked part is re-solution annealed and quenched afterwards.

The alloy does not respond to hardening heat treatment. Higher strength comes only from cold reduction, and the high work hardening rate makes that heavy going. Formability is good and cold bending to tight radii is possible; re-annealing after cold bending is not normally necessary.

Machining is slow. The alloy work hardens fast and carries no free-machining sulphur. Use rigid machines with power in reserve, tough inserts, sharp tools, positive feeds, markedly reduced cutting speeds and plenty of coolant.

Welding: use over-alloyed nickel-base consumables, because matching filler leaves the weld metal short of molybdenum and the weld corrodes before the parent material does. Normal choices are AWS A5.14 ERNiCrMo-3 (alloy 625 type) or ERNiCrMo-13 wire, and AWS A5.11 ENiCrMo-3, ENiCrMo-12 or ENiCrMo-13 type electrodes. Keep heat input below 1.5 kJ/mm and interpass temperature below 100 C, with a stringer bead technique. Avoid abrasion against copper or copper alloys, which can cause cracking during later welding or heat treatment.

## Against 316L, 904L and super duplex

Against SUS 316L, SUS 312L buys a large gain in chloride pitting, crevice and stress corrosion resistance plus roughly 1.5 times the proof strength, at a higher price. Against 904L it is the stronger performer in both published stress corrosion tests above and in chloride-bearing sulphuric acid. Against high-nickel alloys and titanium it has been reported as a cost-effective substitute in seawater and chemical service.

Against super duplex forging grades such as F53 and F55 the PREN figures are close, but SUS 312L stays austenitic: non-magnetic, good toughness to cryogenic temperatures, and free of the phase balance and section thickness problems a duplex structure brings in a heavy forging. Super duplex still wins on yield strength.

## Forged products supplied in SUS 312L

Seamless rolled rings, forged rings, weld neck and blind and slip-on and socket weld and lap joint and orifice flanges to ASME B16.5 / B16.47 / API 6A, round bars, shafts, eccentric shafts, spindles, crankshafts, discs, blanks, tube sheets, covers, sleeves, bushings, couplings, nozzles, manifolds, hollow cylinders, heavy-wall forged pipe, valve bodies, bonnets, stems, seat rings and valve blocks.

## Typical applications

Seawater handling and desalination (seawater cooling, cooling water pipes, ballast water, firefighting systems, condensers, coolers, high pressure reverse osmosis plant). Offshore and subsea oil production (firewater and seawater systems, risers, manifolds, deepwater production hardware). Flue gas desulphurisation and power plant scrubbers, marine exhaust gas cleaning. Chemical plant handling sulphuric acid, organic acids, mixed acids and chloride-bearing media at raised pressure and temperature. Pulp bleaching plant and tall oil distillation columns. Food processing tanks and equipment. Architectural exterior components in coastal and salt-damage areas, and stainless lining of marine structures. Heat exchangers, waste water, demineralised water and polycarbonate production.

## Manufacturing capability

Most forging suppliers in China buy billet. Jiangyin Jiangnan Metal melts its own steel. Carbon, alloy, stainless and duplex grades run through a 25 t electric arc furnace, are refined in 25 t and 50 t ladle furnaces and decarburised under vacuum in 30 t and 60 t VOD units, which is the route that delivers the 0.020% carbon ceiling and the controlled 0.16 to 0.25% nitrogen window SUS 312L depends on. Electroslag and vacuum arc remelting are available in house. Maximum heat size is 60 tonnes. The works has operated since 1997, employs 460 people and exports to North America, Europe, the Middle East and Asia-Pacific.

| Product | Size limit | Set by |
| --- | --- | --- |
| Seamless rolled rings | OD 50 mm to OD 6000 mm | 6 m radial-axial ring mill, plus 3 m and 1 m mills |
| Forged shafts | up to 14,000 mm turned length | C61160 horizontal lathe; 15 m well furnace for vertical quench |
| Discs, tube sheets, blocks | up to 5000 mm machined | 5000 mm vertical turning lathe |
| Bored cylinders, hollow shafts | up to 1600 x 10,000 mm | CNC deep-hole drilling machine |
| Single-piece weight | up to 30,000 kg | 60 t heat size; 6300 t hydraulic press |
| Minimum order | 10 kg, no minimum piece count | Limit is weight, not quantity |
| Lead time | 20 to 60 days from order confirmation | Standard stainless route at the lower end |

## Testing, certification and traceability

The works holds CCS, BV, DNV, LR and NK classification society approvals and runs its own laboratory. Chemistry is verified at the furnace by optical emission spectrometry and infrared carbon-sulphur analysis, with handheld positive material identification available. Mechanical testing runs on 600 kN and 300 kN universal machines with Charpy impact to -60 C. Ultrasonic examination is carried out to ASTM A388, EN 10228-3 or SEP 1921 as required, with magnetic particle, endoscope bore inspection and grain size determination to ASTM E112 in house.

Testing outside that scope is placed with an accredited third-party laboratory and reported alongside the mill certificate: typically ASTM A262 or ASTM G28 intergranular corrosion, ASTM G48 pitting, bench hardness where a portable instrument is not accepted, and impact testing below -60 C.

Standard documentation is an EN 10204 3.1 inspection certificate. EN 10204 3.2 witnessed by BV, DNV, LR, SGS, TUV, ABS or the customer's own inspector is available on request. Traceability runs from the melt number through forging, heat treatment and machining to shipment.

## Requesting a quotation

Send: 1) material grade and governing standard, stating whether SUS 312L alone or dual certification to ASTM A182 F44 is needed; 2) dimensions or a drawing in PDF, DWG, DXF or STEP; 3) quantity and expected repeat volume; 4) delivery condition, as-forged, proof-machined or finish-machined; 5) heat treatment and testing requirements; 6) EN 10204 certification level and destination port. Quotations normally returned within two working days.

Jiangyin Jiangnan Metal Co., Ltd.
No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China
Tel +86-189-2135-9659 | Email sales@steelforgepieces.com

## FAQ

**What is SUS 312L steel?** The JIS designation for a 6% molybdenum, nitrogen-alloyed, low-carbon super austenitic stainless steel of nominal composition 20Cr-18Ni-6Mo-0.7Cu-0.2N. Equivalent to UNS S31254, EN 1.4547 and 254 SMO.

**Is SUS 312L the same as 254 SMO and ASTM A182 F44?** Same alloy, different acceptance windows. SUS 312L allows Ni 17.50 to 19.50%, Cr 19.00 to 21.00%, Mo 6.00 to 7.00% and S up to 0.015%; A182 F44 narrows those to 17.50 to 18.50%, 19.50 to 20.50%, 6.00 to 6.50% and 0.010%. A SUS 312L heat will not automatically satisfy an F44 order.

**Is SUS 312L duplex or austenitic?** Fully austenitic and non-magnetic. Its PREN of roughly 41 to 43 matches super duplex levels, but the microstructure is not duplex.

**What is the PREN of SUS 312L?** About 41.4 at the grade minimum, about 43.3 on a typical analysis.

**At what temperature is SUS 312L solution annealed?** 1150 to 1200 C followed by a water quench. It cannot be hardened by heat treatment.

**Can SUS 312L be used in sulphuric acid service?** Yes. More resistant than TP316 in pure sulphuric acid, and better than 904L in naturally aerated sulphuric acid containing chloride ions. Limits depend on concentration, temperature and other species present.

**What size SUS 312L forgings can you make?** Rings to 6000 mm OD, single forgings to 30 tonnes, shafts to 14 m, discs and tube sheets to 5000 mm, bores to 1600 x 10,000 mm. Minimum order 10 kg.

**What is the lead time?** 20 to 60 days from order confirmation.

## Related grades

ASTM A182 F44, 904L, 654 SMO, UNS S32654, 317LMN, Sanicro 28, A182 F51, A182 F55, A182 F61, Alloy 20, Alloy 31, Incoloy 825.

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Technical data compiled from the JIS chemical and mechanical limits for SUS 312L and from published mill data for UNS S31254, EN 1.4547 and 254 SMO. Where sources differ, ranges are shown. 254 SMO is a trademark of Outokumpu OY, referenced for identification only. Figures are for guidance; the purchase specification governs.