# UNS S31008 (310S) Forgings

**UNS S31008 is grade 310S stainless steel, the low-carbon version of 25 % chromium, 20 % nickel grade 310, with carbon held to 0.08 % maximum.** It is used at up to 1150 °C in continuous service and 1035 °C in intermittent service, and resists oxidation, sulphidation and carburisation.

Jiangyin Jiangnan Metal Co., Ltd. forges this grade as seamless rolled rings, forged rings, flanges, round bars, discs, tube sheets, sleeves, bushings and shafts to ASTM A182. The steel is melted on site on the electric arc furnace, ladle furnace and vacuum oxygen decarburisation route, so the certificate traces a part back to its melt number rather than to a purchased billet.

| Field | Detail |
|---|---|
| UNS | S31008 |
| Other designations | AISI 310S, EN 1.4845, X8CrNi25-21, X12CrNi25-21, JIS SUS310S, Z8CN25-20, 310S16 |
| Type | Austenitic, heat resisting, not hardenable by heat treatment |
| Forging specification | ASTM A182, F310 or F310H on request |
| Delivery condition | Solution annealed 1040 to 1065 °C, water quenched |
| Product forms | Seamless rolled rings, forged rings, flanges, bars, discs, tube sheets, sleeves, bushings, shafts |
| Size limits | Rings to OD 6,000 mm, single piece to 30 t, shafts turned to 14,000 mm |
| Non-destructive testing | ASTM A388, EN 10228-3, SEP 1921, ASTM E709 |
| Certification | EN 10204 3.1 standard, EN 10204 3.2 witnessed on request |
| Minimum order | 10 kg, no minimum piece count |
| Lead time | 20 to 60 days |
| Telephone | +86 189 2135 9659 |
| Email | sales@steelforgepieces.com |
| Page | https://www.steelforgepieces.com/Stainless-Steel/UNS-S31008.html |

## Reading the designation

Three numbers circulate for the same 25Cr-20Ni steel and they are not interchangeable on an order. The difference is carbon.

| Grade | UNS | Forging spec | Carbon | Ordered for |
|---|---|---|---|---|
| 310 | S31000 | ASTM A182 F310 | 0.25 max | General high-temperature furnace work |
| 310S | S31008 | A182 F310, dual certified to 0.08 C | 0.08 max | Welded work, less risk of embrittlement and sensitisation |
| 310H | S31009 | ASTM A182 F310H | 0.04 to 0.10 | Creep strength in long-term high-temperature service |

If a drawing calls up S31008 but the purchase order says A182 F310, the two documents conflict on carbon: F310 permits 0.25 % while S31008 permits 0.08 %. State which ceiling governs and the melt will be aimed at it.

## Chemical composition

Weight percent, balance iron. Molybdenum and copper are not specified elements in this grade.

| Grade | C | Cr | Ni | Mn | Si | P | S |
|---|---|---|---|---|---|---|---|
| 310S (S31008) | 0.08 max | 24.00-26.00 | 19.00-22.00 | 2.00 max | 1.50 max | 0.045 max | 0.030 max |
| 310 (S31000) | 0.25 max | 24.00-26.00 | 19.00-22.00 | 2.00 max | 1.50 max | 0.045 max | 0.030 max |
| ASTM A182 F310 | 0.25 max | 24.00-26.00 | 19.00-22.00 | 2.00 max | 1.00 max | 0.045 max | 0.030 max |

The forging specification tightens silicon to 1.00 % max against the 1.50 % allowed by the general grade definition. Where both are invoked, the tighter figure is met.

## Mechanical properties

| Property | 310 / 310S annealed | ASTM A182 F310 forgings |
|---|---|---|
| Tensile strength, min | 520 MPa | 515 MPa (75 ksi) |
| 0.2 % proof stress, min | 205 MPa | 205 MPa (30 ksi) |
| Elongation, min | 40 % | 30 % in 2 in. or 4D |
| Reduction of area, min | not specified | 50 % |
| Hardness, max | 225 HV | per specification |

## Physical properties

| Property | At | Value |
|---|---|---|
| Density | - | 8,000 kg/m3 |
| Melting range | - | 1400 to 1450 °C |
| Modulus of elasticity | 20 °C | 200 GPa |
| Shear modulus | 20 °C | 77 GPa |
| Poisson's ratio | 20 °C | 0.30 |
| Thermal conductivity | 100 °C | 14.2 W/m·°C |
| Specific heat | - | 500 J/kg·°C |
| Coefficient of expansion | 0-100 °C | 15.9 x10-6/°C |
| Coefficient of expansion | 0-315 °C | 16.2 x10-6/°C |
| Coefficient of expansion | 0-540 °C | 17.0 x10-6/°C |
| Electrical resistivity | 25 °C | 0.78 micro-ohm·m |
| Relative magnetic permeability | - | 1.02 |

## Equivalent grades

| USA | EN number | EN name | Japan | France | UK |
|---|---|---|---|---|---|
| S31008 / AISI 310S | 1.4845 | X8CrNi25-21, also X12CrNi25-21 | SUS310S | Z8CN25-20 | 310S16 |

## Forging, heat treatment, machining, welding

**Forging.** Grades 310 and 310S are forged in the range 975 to 1175 °C. Heavy reduction is carried out down to 1050 °C and light finishing passes are made at the bottom of the range. The grade should not be forged below 982 °C. Annealing after forging is recommended to relieve forging stresses.

**Heat treatment.** Solution anneal at 1040 to 1065 °C, hold until thoroughly soaked, water quench. The grade cannot be hardened by heat treatment, as is normal for austenitic stainless steels; strength is raised only by cold work. A request to solution treat and age this grade is a specification error carried over from precipitation-hardening steels such as 17-4 PH, because 310S has no ageing response.

**Machining.** Machinability is similar to type 304. Work hardening is the main difficulty. Cut beneath the work-hardened layer using slow speeds and heavy cuts, sharp tools, good lubrication and rigid, powerful machines.

**Welding.** Readily welded by SMAW, GMAW, GTAW and SAW with matching consumables: electrodes to AWS A5.4 E310-XX and AWS A5.22 E310T-X, filler metal to AWS A5.9 ER310, argon shielding. Preheat and post-heat are not required. For corrosive liquid service a full post-weld solution anneal is essential, followed by pickling and passivation. For high-temperature service that treatment is not needed, but welding slag must be removed completely.

## Service behaviour and limits

| Condition | Behaviour |
|---|---|
| Continuous service | Used to 1150 °C. Oxidation data for continuous service in air is also quoted as 1050 °C, so the design figure depends on atmosphere and acceptable scale loss |
| Intermittent service | Up to 1035 °C, limited by scale spalling under thermal cycling |
| Sulphur-bearing reducing atmospheres | Capable in reducing atmospheres containing H2S |
| Carburising atmospheres | Suited to moderately carburising conditions. For severe carburisation select another heat-resisting alloy |
| Cryogenic service | Used for its toughness and low magnetic permeability |
| 550 to 800 °C exposure | Sensitises to intergranular corrosion |
| Chloride-bearing liquids | Chloride stress corrosion cracking can occur above 100 °C |
| Pitting service | No molybdenum, pitting resistance is poor |
| Repeated liquid quenching | Not recommended, the grade suffers from thermal shock |

## Product forms forged in UNS S31008

- **Seamless rolled rings.** Radial-axial rolled from a punched preform, rectangular or contoured section, OD 50 mm to OD 6,000 mm.
- **Forged flanges and tube sheets.** Weld neck, blind, slip-on, lap joint and orifice flanges to ASME B16.5 and B16.47, plus tube sheets and covers proof-machined for volumetric inspection.
- **Round bars and blocks.** Round, flat and square bar for machined furnace hardware, thermowells, refractory anchor bolts and burner parts.
- **Discs, sleeves and bushings.** Solid discs, hollow sleeves, bushings and rolls bored to 1,600 mm dia by 10,000 mm.
- **Shafts and spindles.** Stepped shafts, spindles and eccentric shafts turned to 14,000 mm, quenched vertically in a 15 m well furnace.
- **Valve and process parts.** Valve bodies, bonnets, seat rings, stems, nozzles and manifolds for hot gas and petroleum refining duty.

Typical applications of 310 and 310S: fluidised bed combustors, kilns, radiant tubes, tube hangers for petroleum refining and steam boilers, coal gasifier internals, lead pots, thermowells, refractory anchor bolts, burners and combustion chambers, retorts, muffles, annealing covers, saggers, food processing equipment, cryogenic structures.

## Melting, testing and certification

| Stage | Carried out on | Reference |
|---|---|---|
| Melting and refining | 25 t electric arc furnace, 25 t and 50 t ladle furnaces, 30 t and 60 t vacuum oxygen decarburisation | Melt analysis by optical emission spectrometry |
| Forging or ring rolling | 6,300 t, 4,000 t and 2,000 t presses; 6 m, 3 m and 1 m radial-axial ring mills | Forged 975 to 1175 °C |
| Heat treatment | 14 furnaces, including three high-temperature car-bottom units and two 15 m well furnaces | Solution anneal 1040 to 1065 °C, water quench |
| Mechanical testing | 600 kN and 300 kN universal testing machines, pendulum impact machine with low-temperature bath | ASTM A370, ISO 6892 |
| Chemical verification | Optical emission spectrometer, infrared carbon and sulphur analyser, handheld PMI analyser | ASTM E415, ASTM E1019 |
| Non-destructive testing | Digital ultrasonic flaw detectors, magnetic particle equipment, bore endoscope | ASTM A388, EN 10228-3, SEP 1921, ASTM E709 |
| Metallography | Microscope, mounting press, pre-grinder, polisher | ASTM E112 grain size |
| Certification | In-house laboratory, or witnessed by BV, DNV, LR, SGS, TUV or the customer's inspector | EN 10204 3.1 standard, 3.2 on request |

Intergranular corrosion testing to ASTM A262 and other tests outside the in-house scope are placed with an accredited third-party laboratory and reported alongside the mill certificate. The works holds CCS, BV, DNV, LR and NK approvals.

## Questions we are asked about this grade

**Is UNS S31008 the same as 310H?**
No. S31008 is 310S, carbon 0.08 % maximum. 310H is UNS S31009, ordered as ASTM A182 F310H, carbon 0.04 to 0.10 % for creep strength. Both share the 24 to 26 Cr, 19 to 22 Ni base.

**What is the difference between 310, 310S and 310H?**
Carbon, and nothing else in the base chemistry. 310 allows up to 0.25 %, 310S caps at 0.08 %, 310H holds 0.04 to 0.10 %.

**What is the maximum service temperature?**
Up to 1150 °C continuous and 1035 °C intermittent. The intermittent figure is lower because scale spalls under thermal cycling. Oxidation data for continuous service in air is also quoted as 1050 °C.

**Can 310S be hardened by heat treatment?**
No. It is austenitic and cannot be hardened by heat treatment. Cold work is the only route to higher strength.

**What mechanical minima apply to A182 F310 forgings?**
Tensile 515 MPa, yield 205 MPa, elongation 30 %, reduction of area 50 %.

**What is the European equivalent?**
EN 1.4845, X8CrNi25-21, also listed as X12CrNi25-21.

**Is 310S suitable for corrosive liquids?**
It is a high-temperature grade. There is no molybdenum, so pitting resistance is poor, and chloride stress corrosion cracking can occur above 100 °C. For wet corrosion consider 904L, Alloy 20 or duplex.

**How large a ring can you roll?**
OD 6,000 mm on the 6 m radial-axial mill. Heaviest single forging 30 tonnes.

**What is the minimum order?**
10 kg, no minimum piece count. Lead time 20 to 60 days.

**What certification is supplied?**
EN 10204 3.1 as standard, EN 10204 3.2 witnessed by BV, DNV, LR, SGS or TUV on request.

---

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

Last reviewed 5 October 2026. Data is compiled from published grade data and ASTM A182 requirements and is given for guidance. The governing documents for any order are the purchase specification and the mill certificate.