Austenitic stainless steel, 3 to 4 % molybdenum
SUS 317L Forgings UNS S31703 / EN 1.4438 / ASTM A182 F317L
SUS 317L carries half again as much molybdenum as 316L. It is the grade specified when 316L starts to pit but a 6 % molybdenum or duplex alloy cannot be justified on price.
We forge it as rolled rings, flanges, shafts, discs, bars, sleeves and tube sheets, from steel melted in our own furnaces. Every piece is solution annealed, ultrasonically tested and certified before it ships.
- Type
- Low-carbon austenitic, Mo-bearing
- Equivalents
- 317L, SUS 317L, 1.4438, X2CrNiMo18-15-4, 317S12, Z3CND19-15-04, SS 2367
- Chemistry
- Cr 18-20 / Ni 11-15 / Mo 3-4
- Carbon
- 0.030 % max
- A182 F317L
- 485 MPa tensile min, 170 MPa yield min
- PREN
- About 29.7 (range 27.9 to 33.2)
- Density
- 7.89 g/cm³
- Hardenable
- No, cold work only
- Max piece
- 30 t forged, rings to 6,000 mm OD
What SUS 317L is
SUS 317L is the JIS name for the grade the rest of the world calls 317L, UNS S31703 or EN 1.4438. It sits one step above 316L: 18 to 20 % chromium, 11 to 15 % nickel and 3 to 4 % molybdenum, with carbon kept to 0.030 % maximum.
Two things follow from that chemistry. The extra molybdenum raises resistance to chloride pitting and crevice attack, which is why the grade turns up in flue gas scrubbers and pulp bleach plant. The low carbon stops chromium carbide forming at the grain boundaries during welding, so fabricated parts keep their corrosion resistance without a post-weld anneal.
It is also stronger than conventional austenitics at temperature, with better creep and stress-to-rupture figures than 304. What it will not do is harden by heat treatment. The structure stays austenitic and non-magnetic, and the only way to raise its strength is cold work.
Chemical composition
Two columns, because the forging specification and the plate specification are not identical. Order against the one named in your enquiry.
| Element | ASTM A182 F317L (forgings) | ASTM A240 / UNS S31703 |
|---|---|---|
| Chromium, Cr | 18.0 - 20.0 | 18.0 - 20.0 |
| Nickel, Ni | 11.0 - 15.0 | 11.0 - 15.0 |
| Molybdenum, Mo | 3.0 - 4.0 | 3.0 - 4.0 |
| Carbon, C | 0.030 max | 0.030 max |
| Manganese, Mn | 2.00 max | 2.00 max |
| Silicon, Si | 1.00 max | 0.75 max |
| Phosphorus, P | 0.045 max | 0.045 max |
| Sulphur, S | 0.030 max | 0.030 max |
| Nitrogen, N | not specified | 0.10 max |
| Iron, Fe | Balance | Balance |
Secondary datasheets sometimes quote 0.08 % carbon for F317L. That figure belongs to non-L grade 317. Check the carbon limit against the edition of ASTM A182 named on your order. We supply to 0.030 % maximum as standard.
Mechanical properties
Specified minimums and typical test values are different numbers and get confused often. Both are below. Quote against the minimums.
| Property | A182 F317L forgings, min | A240 plate, min | Typical annealed |
|---|---|---|---|
| Tensile strength | 485 MPa (70 ksi) | 515 MPa (75 ksi) | 595 MPa (86,300 psi) |
| Yield strength, 0.2 % offset | 170 MPa (25 ksi) | 205 MPa (30 ksi) | 260 MPa (37,700 psi) |
| Elongation, 50 mm or 4D | 30 % min | 40 % min | 55 % |
| Reduction of area | 50 % min | not specified | - |
| Hardness, Rockwell B | not specified | 95 max | 85 |
| Modulus of elasticity | 200 GPa (29,000 ksi) | ||
| Poisson's ratio | 0.27 to 0.30 | ||
Physical properties
| Property | Metric | Imperial |
|---|---|---|
| Density | 7.89 g/cm³ | 0.285 lb/in³ |
| Melting range | 1390 - 1440 °C | 2540 - 2630 °F |
| Specific heat, 0 to 100 °C | 502 J/kg·K | 0.12 Btu/lb·°F |
| Thermal conductivity at 20 °C | 14 W/m·K | 8.1 Btu/hr·ft·°F |
| Mean thermal expansion, 20 to 100 °C | 16.2 x 10-6/°C | 8.9 x 10-6/°F |
| Electrical resistivity at 20 °C | 85.1 µΩ·cm | 33.5 µΩ·in |
| Magnetic response | Non-magnetic when annealed | |
Corrosion resistance and PREN
317L outperforms 304L and 316L in most media. It resists sulphuric acid, acidic chloride and phosphoric acid, and copes with the hot organic and fatty acids found in food and pharmaceutical plant.
The exception worth knowing is strongly oxidising acid. In nitric acid, molybdenum-bearing grades generally do worse than molybdenum-free ones, so 317L is not the right answer there.
| Alloy | Cr % | Mo % | N % | PREN |
|---|---|---|---|---|
| 304 | 18.0 | - | 0.06 | 19.0 |
| 316 | 16.5 | 2.1 | 0.05 | 24.2 |
| 317L | 18.5 | 3.1 | 0.06 | 29.7 |
| 6 % Mo super austenitic | 20.5 | 6.2 | 0.22 | 44.5 |
Where 317L is the wrong choice. A PREN near 32 is the figure usually quoted as the minimum for seawater pitting resistance. 317L typically sits at 29.7, below that line, and it still cracks under chloride stress corrosion given enough temperature and stress. For seawater, produced water or deepwater service we would rather sell you ASTM A182 F44, the 6 % molybdenum grade, or 904L. Both cost more and both will outlast 317L in that duty.
Equivalent designations
| Standard or country | Designation |
|---|---|
| Japan, JIS | SUS 317L |
| USA, AISI and UNS | 317L, S31703 |
| Europe, EN | 1.4438, X2CrNiMo18-15-4 |
| England, BS | 317S12 |
| France, AFNOR | Z3CND19-15-04 |
| Sweden, SS | 2367 |
| Finland, SFS | 770 |
| Product standards | ASTM A182 forgings, A240 and ASME SA240 plate, A213, A249, A312, A774, A778, A813, A814 |
Cross-reference tables show nearest known equivalents. For a contractual order, work from the source standard.
Forging, heat treatment and fabrication
Published guidance on hot working ranges differs between mill datasheets. Both sets are given rather than averaged into one misleading figure.
| Operation | Published range A | Published range B |
|---|---|---|
| Hot working | 1149 - 1260 °C | 900 - 1150 °C |
| Minimum finishing temperature | 927 °C | 950 °C |
| Solution anneal | 1010 - 1121 °C | 1080 - 1180 °C |
| Cooling | Rapid cool or quench, in every case | |
| Hardening | Not possible by heat treatment. Cold work only. | |
Machining
317L work hardens, so cut at low speed with a constant positive feed and never let the tool dwell. The chip comes off long and stringy, so chip breakers earn their keep. It is harder going than 304 and much harder going than 410. Carbide tooling runs at roughly 70 to 110 m/min depending on depth of cut, high speed steel at roughly 11 to 30 m/min with cutting oil.
Welding
Weldable by the normal fusion and resistance processes with no post-weld heat treatment. Use AWS E317L or ER317L filler. Do not use oxyacetylene.
SUS 317L forged products
Everything below is forged from a single piece of steel melted on site. No casting, no welded fabrication, no bought-in billet of unknown origin.
Seamless rolled rings
Radial-axial rolled from a punched preform. Rectangular or contoured section, bearing races, gear ring blanks, slewing rings.
Forged rings
Upset and punched for sections outside the ring mill envelope, retaining rings and valve seat rings.
Flanges
Weld neck, blind, slip-on, socket weld, lap joint and orifice to ASME B16.5 and B16.47, or to drawing.
Shafts and bars
Stepped shafts, pinion shafts, eccentric shafts, spindles, round and flat bar.
Discs and tube sheets
Solid discs, heat exchanger tube sheets and covers, supplied proof machined for volumetric inspection.
Sleeves and hollows
Trepanned or mandrel forged hollow bar, sleeves, bushings and liners for slurry and process duty.
Valve parts
Bodies, bonnets, stems, blocks and seat rings for ball, gate, globe, check and plug valves.
Open-die to drawing
Nozzles, manifolds, rolls and wheels, and non-standard profiles made to your print and inspection plan.
Working envelope
| Item | Limit | Set by |
|---|---|---|
| Rolled ring outside diameter | 50 to 6,000 mm | 6 m radial-axial ring mill, upset and punch below range |
| Single piece weight | up to 30 t | 6,300 t press, 60 t maximum heat |
| Shaft turned length | up to 14,000 mm | C61160 horizontal lathe, 15 m well furnace for vertical quench |
| Disc and tube sheet diameter | up to 5,000 mm | 5,000 mm vertical turning lathe |
| Bored cylinders | 1,600 mm dia x 10,000 mm | CNC deep-hole drilling machine |
| Minimum order | 10 kg | No minimum piece count |
| Lead time | 20 to 60 days | Depends on size, heat treatment and machining |
Melting, testing and certification
317L is melted in the electric arc furnace, refined in the ladle furnace and decarburised under vacuum to hold carbon at 0.030 % maximum. Electroslag remelting is available where a cleaner structure is specified.
Because the steel is melted in the same works that forges it, the certificate traces a finished part back to its melt number rather than stopping at a purchased billet.
Forgings are supplied solution annealed, then pickled or machined as agreed. Ultrasonic testing follows ASTM A388, EN 10228-3 or SEP 1921 to the acceptance class you nominate. Certificates are issued to EN 10204 3.1, or 3.2 with a third-party witness such as TUV, BV, DNV or Lloyd's Register. Intergranular corrosion testing to ASTM A262 Practice E, PMI, ferrite measurement, impact testing, grain size, hardness survey and dimensional reports are available on request. The works holds CCS, BV, DNV, LR and NK approvals.
Typical applications
317L gets specified where 316L is marginal on corrosion but a super austenitic or duplex grade cannot be justified on cost.
Common duties include flue gas desulphurisation and other air pollution control equipment, chemical and petrochemical process plant, petroleum refining including catalytic recovery systems and recuperators, pulp and paper mill equipment, condensers in fossil-fired and nuclear stations, food, beverage and pharmaceutical plant handling hot organic and fatty acids, and slurry tanks, stack liners, tanks and valve internals.
Questions we get asked
What is SUS 317L?
The JIS designation for a molybdenum-bearing low-carbon austenitic stainless steel, the same material as UNS S31703, AISI 317L and EN 1.4438. Chromium 18 to 20 %, nickel 11 to 15 %, molybdenum 3 to 4 %, carbon 0.030 % maximum. The molybdenum is what buys the extra pitting resistance over 304L and 316L.
What is the difference between 316L and 317L?
Molybdenum, mainly. 317L runs 3 to 4 % against roughly 2 % in 316L, with more chromium and nickel on top. Typical PREN rises from about 24.2 to about 29.7, which shows up as better resistance to pitting and crevice corrosion in chloride, sulphurous and halide service. 317L also holds more strength at temperature.
What are the mechanical minimums for A182 F317L forgings?
Tensile 485 MPa (70 ksi) minimum, 0.2 % yield 170 MPa (25 ksi) minimum, elongation 30 % minimum in 50 mm or 4D, reduction of area 50 % minimum. Typical annealed test values come out higher, near 595 MPa tensile and 260 MPa yield, but those are not what the standard guarantees.
Can SUS 317L be hardened by heat treatment?
No. It stays austenitic. Solution anneal and quench is the supply condition, and cold work is the only route to higher strength.
Is 317L good enough for seawater?
Usually not. Typical PREN is 29.7 against the figure of about 32 normally cited for seawater, and the grade is still open to chloride stress corrosion cracking. Specify F44 or 904L instead.
Does it need post-weld heat treatment?
No. The 0.030 % carbon ceiling keeps chromium carbides from forming at the grain boundaries, so the material serves as welded. Use E317L or ER317L filler and keep oxyacetylene away from it.
How big a piece can you forge?
Up to 30 tonnes as a single piece, from a maximum heat of 60 tonnes, on a 6,300 t open-die press. Rings roll to 6,000 mm outside diameter and down to 50 mm. Shafts turn to 14,000 mm, discs to 5,000 mm diameter. Minimum order is 10 kg with no minimum piece count.
What paperwork comes with the order?
EN 10204 3.1 as standard, 3.2 with third-party witness on request. Ultrasonic testing to ASTM A388, EN 10228-3 or SEP 1921. ASTM A262 Practice E intergranular testing, PMI, hardness, grain size and dimensional reports if you ask for them at enquiry stage.
Ask for a price
What to send
A drawing or a sketch with dimensions, the specification, quantity, delivery condition, NDT class and certification level, plus your destination port. With that in hand a price normally comes back within two working days. Without it, we have to ask questions first, which is the usual reason a quotation runs late.
Jiangyin Jiangnan Metal Co., Ltd.
No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China, 214423
Telephone, WhatsApp and WeChat: +86 189 2135 9659
Email: sales@steelforgepieces.com
Office hours: Monday to Saturday, 08:00 to 17:30 China Standard Time, UTC+8
Where the data comes from
Composition, mechanical and physical figures on this page are taken from published grade datasheets and standards summaries, chiefly the Sandmeyer Steel specification sheet for Alloy 317L and 317 (UNS S31703, W.Nr. 1.4438), the AZoM datasheet for stainless steel grade 317L, published summaries of ASTM A182 / A182M grade F317L, and the SteelNumber cross-reference entry for JIS SUS317L. Figures are for guidance. The governing document is the standard named on your purchase order.
Page reviewed 4 October 2026. A plain text version of this page is available at SUS-317L.md.