SUS 312L Forgings: UNS S31254, EN 1.4547, 254 SMO
Forged rings, seamless rolled rings, flanges, shafts, bars, discs, tube sheets and valve parts in 6% molybdenum super austenitic stainless steel, melted and forged in one works by Jiangyin Jiangnan Metal Co., Ltd.
- 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, see below)
- 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
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%, giving 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.
SUS 312L belongs to the group of highly alloyed austenitic stainless steels often called super stainless steels. The combination of about 20% chromium, 18% nickel, 6 to 7% molybdenum and 0.16 to 0.25% nitrogen gives corrosion resistance in chloride-bearing and acid service far beyond SUS 316L, while 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.
We forge SUS 312L on open dies and roll it into seamless rings, working to customer drawings. Usual items are rings, flanges, round bars, shafts, discs, blanks, sleeves, bushings, tube sheets, nozzles, valve bodies and valve seat rings.
SUS 312L 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 product standards |
| EN forgings | EN 10250-4 | Open steel die forgings for general engineering, 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 of SUS 312L
| 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: check this before you order
The two specifications describe the same alloy, but they are not interchangeable on paper. SUS 312L runs wider on four elements, which matters when a purchase order quotes one designation and the mill certificate carries the other.
| 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, tell us 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 already cast.
PREN calculation
Pitting resistance equivalent number is calculated as PREN = %Cr + 3.3 × %Mo + 16 × %N. At the SUS 312L minimum limits, 19.00% chromium, 6.00% molybdenum and 0.16% nitrogen, the result is about 41.4. On a typical analysis of 20% chromium, 6.1% molybdenum and 0.20% nitrogen it works out at about 43.3. Published data for the equivalent grade quotes a PREN of 42.5 or higher, which is the range normally associated with super duplex stainless steels rather than with conventional austenitics.
Nitrogen is the element most often left off supplier data sheets for this grade, and it is the one that matters most per unit of content. It appears on every mill certificate we issue.
Mechanical properties of SUS 312L
| 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 |
For comparison, 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 in the solution annealed condition. Hardness limits on any given order should be taken from the governing purchase specification, not from this page.
Elevated temperature proof strength
| 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 in the 600 to 1000 °C range 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 temperature and at 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 down to −60 °C; below that we place the test 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 × 10⁻⁶ /°C |
| Poisson's ratio | 0.30 |
| Magnetic response | Non-magnetic in the annealed condition |
Published physical data varies slightly between mill sources, so ranges are shown where sources disagree rather than a single figure.
Corrosion behaviour
Chloride stress corrosion cracking
Ordinary austenitic steels of the 304 and 316 type are prone to chloride stress corrosion cracking above about 60 °C. Resistance improves with nickel and molybdenum, and SUS 312L carries a great deal of both. Two published accelerated tests on the equivalent grade make the difference concrete.
| 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 |
| Grade | Time to failure |
|---|---|
| ASTM TP316 | 105 h |
| 904L | 225 h |
| 254 SMO / S31254 | 425 h |
Pitting and crevice corrosion
Pitting and crevice 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 as a supplementary requirement.
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 temperature band, but published work reports they do not create an intergranular corrosion risk in the environments the steel is intended for, 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 annealing
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 has to be fast through the intermetallic precipitation range. Slow cooling throws out sigma and chi phases and the corrosion resistance goes with them. Our 14 heat-treatment furnaces include three high-temperature car-bottom furnaces for this class of work, and two 15 m well-type furnaces so that long shafts can be quenched vertically without distortion.
Hot working
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 to restore corrosion resistance.
Hardening and cold work
SUS 312L 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
Machining is slow. The alloy work hardens fast and carries no free-machining sulphur. Rigid machines with power in reserve, tough inserts, sharp tools, positive feeds, markedly reduced cutting speeds and plenty of coolant. The approach is the same as for 300 series stainless, applied far more conservatively.
Welding
Weldability is good, with TIG/GTAW the first choice and MMA/SMAW also suitable. Use over-alloyed nickel-base consumables: 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, and use a stringer bead technique. Fully austenitic steels have low thermal conductivity and high thermal expansion, so plan the welding sequence in advance to control distortion. Avoid abrasion against copper or copper alloys, which can cause cracking during later welding or heat treatment.
SUS 312L against 316L, 904L and super duplex
Against SUS 316L, SUS 312L buys a large gain in chloride pitting, crevice and stress corrosion resistance together with roughly 1.5 times the proof strength, at a higher price. Against 904L it is the stronger performer in both of the 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. That means it remains non-magnetic, keeps good toughness down to cryogenic temperatures, and avoids the phase balance and section thickness problems that come with a duplex structure in a heavy forging. Super duplex still wins on yield strength. Which way to go depends on whether the governing requirement is strength per unit weight or simpler metallurgy in thick sections.
SUS 312L forged products we supply
Seamless rolled rings
Rolled and forged rings for seawater-cooled plant, offshore modules, bearings and rotating equipment. Up to OD 6000 mm.
Flanges
Weld neck, blind, slip-on, socket weld, lap joint and orifice flanges to ASME B16.5, B16.47 and API 6A.
Tube sheets and discs
Solid forged discs, tube sheets, covers and blanks for heat exchangers and separators, proof-machined for ultrasonic examination.
Shafts, spindles and bars
Forged shafts, eccentric shafts, spindles, crankshafts and round bars for pumps and compressors.
Valve and wellhead parts
Valve bodies, bonnets, stems, seat rings and blocks for ball, gate, globe, check and plug valves.
Forged pipe and cylinders
Hollow forged cylinders, sleeves, bushings, couplings, manifolds and heavy-wall pipe sections bored from solid.
Typical applications for SUS 312L
Seawater handling and desalination, covering seawater cooling systems, cooling water pipes, ballast water and firefighting systems, condensers, coolers and high pressure reverse osmosis plant. Offshore and subsea oil production, covering firewater and seawater systems, risers, manifolds and deepwater production hardware. Flue gas desulphurisation and power plant scrubber systems, and 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 to extend life-cycle. Also heat exchangers, waste water, demineralised water and polycarbonate production.
Why buy SUS 312L forgings from the melt shop
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 are 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 that SUS 312L depends on. Where a specification or end user calls for it, electroslag or vacuum arc remelting is 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 up 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 and hollow shafts | up to 1600 × 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 sits 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. Because the steel is melted here, chemistry is verified at the furnace by optical emission spectrometry and infrared carbon-sulphur analysis rather than taken from a supplier certificate, and positive material identification is available by handheld analyser. 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 metallographic grain size determination to ASTM E112 also in house.
Order-specific corrosion testing that falls outside our laboratory scope is placed with an accredited third-party laboratory and the report issued alongside the mill certificate. For this grade that typically means intergranular corrosion testing to ASTM A262 or ASTM G28, pitting resistance to ASTM G48, bench Brinell or Rockwell hardness where a portable instrument is not accepted, and impact testing below −60 °C. State the requirement on the enquiry so it is scheduled before shipment rather than discovered afterwards.
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, supported by heat-treatment charts, non-destructive testing reports, dimensional reports and material identification records.
Request a quotation for SUS 312L forgings
Quotations are prepared from a drawing or a written specification, normally returned within two working days. Sending these six items in the first email removes a round trip:
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, for example solution annealed, ultrasonic to ASTM A388, ASTM G48. 6. Certification level under EN 10204 and destination port.
Jiangyin Jiangnan Metal Co., Ltd., open-die forging factory
No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China
Tel +86-189-2135-9659 | Email sales@steelforgepieces.com
Frequently asked questions about SUS 312L
What is SUS 312L steel?
SUS 312L is 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. It is the Japanese equivalent of UNS S31254, EN 1.4547 and the trade name 254 SMO, and is used for seawater equipment, sulphuric acid plant, flue gas desulphurisation, food tanks and offshore structures.
Is SUS 312L the same as 254 SMO and ASTM A182 F44?
Same alloy, different acceptance windows. SUS 312L allows nickel 17.50 to 19.50%, chromium 19.00 to 21.00%, molybdenum 6.00 to 7.00% and sulphur up to 0.015%. ASTM A182 F44 narrows those to 17.50 to 18.50%, 19.50 to 20.50%, 6.00 to 6.50% and 0.010% respectively. A heat certified to SUS 312L will not automatically satisfy an F44 order. Because we melt our own steel, the aim analysis can be placed inside both windows if dual certification is agreed before the heat is cast.
Is SUS 312L duplex or austenitic?
Fully austenitic and non-magnetic. Its calculated PREN of roughly 41 to 43 matches super duplex levels, but the microstructure is not duplex. The duplex and super duplex forging grades we supply are F51, F55 and F61.
What is the PREN of SUS 312L?
Using PREN = %Cr + 3.3 × %Mo + 16 × %N: about 41.4 at the grade minimum of 19.00% Cr, 6.00% Mo and 0.16% N, and about 43.3 on a typical analysis of 20% Cr, 6.1% Mo and 0.20% N. Published figures for the equivalent grade quote 42.5 or higher.
At what temperature is SUS 312L solution annealed?
1150 to 1200 °C followed by a water quench, with thin sections annealed from a minimum of about 1130 °C and cooled in air or water. Cooling must be rapid through the 600 to 1000 °C band where intermetallic phases precipitate. The alloy cannot be hardened by heat treatment.
Can SUS 312L be used in sulphuric acid service?
Yes, and it is specified for exactly that. In pure sulphuric acid the equivalent grade is far more resistant than TP316, and in naturally aerated sulphuric acid containing chloride ions it outperforms 904L. Japanese mill literature lists sulphuric acid plant among its applications. Actual limits depend on concentration, temperature and what else is in the stream, so each case needs reviewing on its own figures.
What size SUS 312L forgings can you make?
Seamless rings up to 6000 mm outside diameter, single forgings up to 30 tonnes, shafts turned to 14 m, discs and tube sheets machined to 5000 mm, and bores drilled to 1600 × 10,000 mm. Minimum order is 10 kg with no minimum piece count. Send the drawing or the finished dimensions with the governing standard and we will confirm feasibility, forging ratio and weight with the quotation.
What is the lead time?
20 to 60 days from order confirmation. SUS 312L melted through the electric arc furnace, ladle furnace and vacuum oxygen decarburisation route sits towards the lower end. Orders requiring an electroslag or vacuum arc remelting step, third-party witnessed inspection to EN 10204 3.2, or corrosion testing at an outside laboratory sit towards the upper end, so flag those at enquiry stage and they are built into the quoted date rather than added to it.
Related grades we forge
ASTM A182 F44 (the ASTM forging designation for this same alloy), 904L, 654 SMO, UNS S32654, 317LMN, Sanicro 28, A182 F51, A182 F55, A182 F61, Alloy 20, Alloy 31, Incoloy 825
Technical data compiled from the JIS chemical and mechanical limits for SUS 312L and from published mill data for the equivalent grades UNS S31254, EN 1.4547 and 254 SMO. Where published sources differ, ranges are shown rather than single values. 254 SMO is a trademark of Outokumpu OY; the grade is referenced here for identification only. Figures are for guidance; the purchase specification governs. Revised October 2026.