Seamless rolled rings
Ring-rolled from a punched preform on a radial-axial mill, rectangular or contoured section, from OD 50 mm up to OD 6,000 mm.
Kilns, retorts, annealing covers, furnace ringsHeat-resistant austenitic stainless steel, 25Cr-20Ni
UNS S31008 Forgings Seamless rolled rings, forged rings, flanges, bars, discs, tube sheets, sleeves and shafts in 310S, melted and forged in one works.
UNS S31008 is grade 310S, the low-carbon version of 25 per cent chromium, 20 per cent nickel grade 310. Carbon is held to 0.08 per cent maximum, which makes the steel less prone to embrittlement and sensitisation in service than plain 310. 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 melts this grade in-house on the electric arc furnace, ladle furnace and vacuum oxygen decarburisation route, then forges, heat treats, machines and tests it on the same site. The certificate traces a part back to its melt number rather than to a purchased billet.
01
Reading the designation
Three numbers circulate for the same 25Cr-20Ni steel and they are not interchangeable on an order. The difference is carbon, and carbon decides whether the part is bought for creep strength or for freedom from sensitisation.
| 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 per cent while S31008 permits 0.08 per cent. State which ceiling governs and the melt will be aimed at it. All three grades are forged here.
02
Chemical composition
Composition limits in weight per cent, balance iron. Molybdenum and copper are not specified elements in this grade; residual limits can be controlled at the melt if your specification sets them.
| 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 |
| 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 per cent max against the 1.50 per cent allowed by the general grade definition. Where both are invoked, the tighter figure is met.
03
Mechanical and physical properties
Two sets of numbers matter on a purchase order: the minima the specification enforces, and the physical constants used for design. Both are below. Acceptance is always against the ordered specification and the test certificate issued with the heat.
| Property | 310 / 310S, annealed | ASTM A182 F310 forgings |
|---|---|---|
| Tensile strength, min | 520 MPa | 515 MPa (75 ksi) |
| 0.2 per cent proof stress, min | 205 MPa | 205 MPa (30 ksi) |
| Elongation, min | 40 per cent | 30 per cent in 2 in. or 4D |
| Reduction of area, min | not specified | 50 per cent |
| Hardness, max | 225 HV | per specification |
| Property | At | Value |
|---|---|---|
| Density | - | 8,000 kg/m3 |
| Melting range | - | 1400-1450 °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 x 10-6/°C |
| Coefficient of expansion | 0-315 °C | 16.2 x 10-6/°C |
| Coefficient of expansion | 0-540 °C | 17.0 x 10-6/°C |
| Electrical resistivity | 25 °C | 0.78 micro-ohm·m |
| Relative magnetic permeability | - | 1.02 |
04
Equivalent grades
Cross-references accepted on enquiry. Quote whichever designation appears on your drawing and the order will be written against it.
| USA | EN number | EN name | Japan | France | UK |
|---|---|---|---|---|---|
| S31008 / AISI 310S | 1.4845 | X8CrNi25-21, also X12CrNi25-21 | SUS310S | Z8CN25-20 | 310S16 |
05
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 the 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 the stresses left by the forging process.
Heat treatment
Solution annealing is carried out at 1040 to 1065 °C, held until the section is thoroughly soaked, then water quenched. The quench matters: slow cooling through the carbide precipitation range undoes the treatment. The alloy cannot be hardened by heat treatment, as is normal for austenitic stainless steels, and strength is raised only by cold work, which is rarely applied to forgings.
A request to solution treat and age this grade is a specification error carried over from precipitation-hardening steels such as 17-4 PH. 310S has no ageing response. If age-hardened strength is needed at temperature, look at A286, Incoloy 901 or Inconel 718 instead.
Machining
Machinability is similar to type 304. Work hardening is the main difficulty, and the usual practice is to cut beneath the work-hardened layer with slow speeds and heavy cuts, sharp tools, good lubrication and rigid, powerful machines.
Welding
The grade is 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 to remove high-temperature oxide and restore aqueous corrosion resistance. For high-temperature service that treatment is not needed, but welding slag must be removed completely.
06
Service behaviour and limits
The 25 per cent chromium and 20 per cent nickel content is what buys the temperature capability, and it also sets the boundaries of where the grade should not be used.
| Condition | Behaviour |
|---|---|
| Continuous service | Used to 1150 °C. Published 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. The lower figure reflects scale spalling under thermal cycling rather than loss of base strength. |
| Sulphur-bearing reducing atmospheres | Capable in reducing atmospheres containing H2S, helped by the high chromium and medium nickel. |
| Carburising atmospheres | Widely used in moderately carburising conditions of the kind met in petrochemical plant. For severe carburisation select a different heat-resisting alloy. |
| Cryogenic service | Used at low temperature for its toughness and low magnetic permeability. |
| 550 to 800 °C exposure | Sensitises to intergranular corrosion after service in this band. |
| Chloride-bearing liquids | Chloride stress corrosion cracking can occur above 100 °C. |
| Pitting service | No molybdenum, so pitting resistance is poor. Consider 904L, Alloy 20 or duplex for wet corrosion duty. |
| Repeated liquid quenching | Not recommended, because the grade suffers from thermal shock. |
07
What we forge in UNS S31008
Every item is forged from a single piece of steel melted on site. No welding, no casting, no purchased billet of unknown origin.
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 supplied proof-machined for volumetric inspection.
Heat exchangers, pressure vessels, boilersRound bars and blocks
Forged round, flat and square bar for machined furnace hardware, thermowells, refractory anchor bolts and burner components.
Machining stock, valve bodies, fittingsDiscs, sleeves and bushings
Solid forged discs, hollow sleeves, bushings and rolls bored from forged blanks on a deep-hole drilling machine to 1,600 mm diameter by 10,000 mm.
Saggers, rollers, oven linings, fan hubsShafts and spindles
Stepped shafts, spindles and eccentric shafts, turned to 14,000 mm and quenched vertically in a 15 m well-type furnace to control distortion.
Furnace drives, conveyors, gearboxesValve and process parts
Valve bodies, bonnets, seat rings, stems, nozzles and manifolds for hot gas and petroleum refining duty, including tube hangers and lead pot components.
Refining, gasification, combustionTypical applications of 310 and 310S
Fluidised bed combustors, kilns, radiant tubes, tube hangers for petroleum refining and steam boilers, coal gasifier internal components, lead pots, thermowells, refractory anchor bolts, burners and combustion chambers, retorts, muffles, annealing covers, saggers, food processing equipment and cryogenic structures.
08
Melting, testing and certification
Stainless grades such as S31008 run through the electric arc furnace, are refined in a ladle furnace and are decarburised under vacuum where low carbon and tight nitrogen control are needed. Maximum heat size is 60 tonnes. Chemistry is verified at the furnace rather than taken from a supplier certificate, because the steel is melted here.
| 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 | Full-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 your own inspector | EN 10204 3.1 standard, 3.2 on request |
Intergranular corrosion testing to ASTM A262, and other order-specific tests outside the in-house scope, are placed with an accredited third-party laboratory and the report is issued alongside the mill certificate. State the requirement at enquiry stage so it is scheduled before shipment rather than added afterwards. The works holds CCS, BV, DNV, LR and NK approvals.
09
Questions we are asked about this grade
Is UNS S31008 the same as 310H?
No. UNS S31008 is grade 310S, the low-carbon version of 310 with carbon held to 0.08 per cent maximum. 310H is UNS S31009, ordered as ASTM A182 F310H, with carbon controlled to 0.04 to 0.10 per cent so that creep strength is retained at high temperature. All three share the same 24 to 26 per cent chromium and 19 to 22 per cent nickel base, and all three are forged here.
What is the difference between 310, 310S and 310H?
Carbon, and nothing else in the base chemistry. Grade 310 allows up to 0.25 per cent carbon. Grade 310S caps it at 0.08 per cent and is therefore less prone to embrittlement and sensitisation in service. Grade 310H holds it between 0.04 and 0.10 per cent for creep strength. Pick 310S for welded fabrications and 310H where a code case requires creep data.
What is the maximum service temperature?
Up to 1150 °C in continuous service and 1035 °C in intermittent service. The intermittent figure is lower because oxide scale spalls under thermal cycling. Published oxidation data for continuous service in air is also quoted as 1050 °C, so the figure a designer should use depends on the atmosphere and on how much scale loss the part can tolerate over its life.
Can 310S forgings be hardened by heat treatment?
No. Like other austenitic stainless steels it cannot be hardened by heat treatment. It can be hardened by cold work, which is rarely practised on forgings. The delivery condition is solution annealed at 1040 to 1065 °C, soaked through and water quenched.
What mechanical minima apply to A182 F310 forgings?
Tensile strength 515 MPa (75 ksi) minimum, 0.2 per cent offset yield 205 MPa (30 ksi) minimum, elongation 30 per cent minimum in 2 in. or 4D, and reduction of area 50 per cent minimum. The general 310 and 310S grade definition quotes a 520 MPa tensile minimum, 205 MPa proof stress, 40 per cent elongation and 225 HV maximum hardness in the annealed condition.
Is 310S suitable for corrosive liquids?
It is a high-temperature grade rather than a wet-corrosion grade. The high chromium and nickel put its corrosion resistance above 304, but there is no molybdenum, so pitting resistance is poor. It sensitises after service between 550 and 800 °C, and chloride stress corrosion cracking can occur in chloride-bearing liquids above 100 °C. For wet corrosive duty look at 904L, Alloy 20 or a duplex grade such as A182 F51.
How large a ring or forging can you produce in this grade?
Seamless rings roll to 6,000 mm outside diameter on the 6 m radial-axial mill, with 3 m and 1 m mills for smaller sizes and an upset-and-punch route from OD 50 mm. The heaviest single forging is 30 tonnes, worked on 6,300 t, 4,000 t and 2,000 t hydraulic presses. Downstream, shafts turn to 14,000 mm, discs to 5,000 mm machined diameter, and bores to 1,600 mm by 10,000 mm.
What is the minimum order, and the lead time?
10 kg, with no minimum piece count, because the limit is weight rather than quantity. A single small part is quotable and so is a one-off large ring. Lead time runs 20 to 60 days from order confirmation. Standard stainless grades such as S31008 sit at the lower end of that range, since no remelting step is involved.
What certification is supplied?
EN 10204 3.1 mill test certificates as standard, and EN 10204 3.2 witnessed by a classification society or an inspection body such as BV, DNV, LR, SGS or TUV on request. Supporting records cover heat-treatment charts, NDT reports, dimensional reports and PMI records. Traceability runs from the melt number through forging, heat treatment and machining to shipment.
Can you supply rough forgings as well as finish-machined parts?
Both. Parts are supplied as-forged with machining allowance, proof-machined for ultrasonic testing, or finish-machined to drawing. Heat treatment, machining and testing are all carried out on site before shipment.
11
Request a price for UNS S31008
Send the grade or specification, the dimensions or a drawing in PDF, DWG, DXF or STEP, the quantity, the delivery condition, the heat treatment and testing requirements, and the destination port. Six lines in the first email usually gets a price back within two working days.
For rings, outside diameter by inside diameter by height plus machining allowance is enough to quote. For shafts and bars, diameter by length.
Jiangyin Jiangnan Metal Co., Ltd.
No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China
+86 189 2135 9659 sales@steelforgepieces.com