310S stainless steel – UNS S31008
Heat-resisting 25Cr-20Ni austenitic stainless steel
Heat-resisting stainless with 25% Cr and 20% Ni, for oxidation and carburization resistance up to ≈ 1,050 °C continuous. The 310S version (C ≤ 0.08%) is the usual one in bar and plate; 310 (C ≤ 0.25%) is now uncommon. Subject to sigma-phase embrittlement between 650 and 900 °C.
Designations and equivalents
| System | Designation |
|---|---|
| UNS | S31008 (310: S31000; 310H: S31009) |
| W.Nr./EN | 1.4845 (X8CrNi25-21) |
| DIN | X8CrNi25-21 |
| JIS | SUS310S |
| Trade names | AISI 310S |
| Others | 1.4841 (X15CrNiSi25-21) is a variant with Si, not equivalent |
Standards by product form
| Form | Standard |
|---|---|
| Bar | ASTM A479 / A276 |
| Forging/flange | ASTM A182 F310 |
| Plate | ASTM A240 |
| Tube | ASTM A312 / A213 TP310S |
Tolerances and HS codes
- Forged bars (round and square): machining allowance from 2 mm (Ø 6–16 mm) to 24 mm (Ø 400–500 mm) on the diameter. E.g. Ø 100–125 mm finished: +7 mm, tolerance +6 / −0 (length up to 3,500 mm).
- Forged discs: allowance of 4 to 9 mm on the diameter and 3 to 11 mm on the height, plus-only tolerance.
- Cutting and machining: band saw −0 / +5 to +15 mm on length; waterjet +10 % of thickness on the diameter (min. 2 mm); machined parts −0 / +2 to +5 mm on the diameter. See the full tables (INF 002 and INF 003, the same for every alloy).
| Form | NCM (Brazil, 8 digits) | HS (international, 6 digits) | HTS (USA, 10 digits)* | CN (European Union, 8 digits)* |
|---|---|---|---|---|
| Forged bar | 7222.30.00 | 7222.30 | 7222.30.0024 | 7222 30 51 |
| Hot-rolled bar | 7222.11.00 | 7222.11 | 7222.11.0059 | 7222 11 11 |
| Plate (> 10 mm, width ≥ 600 mm) | 7219.21.00 | 7219.21 | 7219.21.0020 | 7219 21 10 |
| Seamless pipe | 7304.41.90 | 7304.41 | 7304.41.6045 | 7304 41 00 |
| Welded pipe | 7306.40.00 | 7306.40 | 7306.40.5085 | 7306 40 80 |
| Flange and fitting | 7307.21.00 | 7307.21 | 7307.21.5000 | 7307 21 00 |
Tariff class: stainless steel (by chemical composition, under the Chapter 72 Notes and Section XV Note 5).
*: US and EU codes for reference. NCM per current legislation (General Rules of Interpretation, Notes to Chapters 72, 74 and 75 and Section XV Note 5). Confirm the final code with your customs broker according to the item size and finish. HS = first 6 digits of the NCM.
Chemical composition (%)
ASTM A479 / A240 (S31008)
| Element | Range (%) |
|---|---|
| C | ≤ 0.08 (310: ≤ 0.25) |
| Mn | ≤ 2.00 |
| P | ≤ 0.045 |
| S | ≤ 0.030 |
| Si | ≤ 1.50 |
| Cr | 24.0 – 26.0 |
| Ni | 19.0 – 22.0 |
| Fe | balance |
Mechanical properties
Solution annealed (ASTM A479; A240 in parentheses)
| Property | Value |
|---|---|
| Yield strength (0.2%) | ≥ 205 MPa |
| Tensile strength | ≥ 515 MPa |
| Elongation | ≥ 30% (A240: ≥ 40%) |
| Reduction of area | ≥ 40% |
| Hardness | ≤ 217 HB (A240) |
Typical physical properties
| Property | Value |
|---|---|
| Density | 7.9 g/cm³ |
| Melting range | ≈ 1,400 – 1,450 °C |
| Modulus of elasticity | 195 – 200 GPa |
| Thermal conductivity (20 °C) | ≈ 13 – 14 W/m·K |
| Thermal expansion (20–100 °C) | ≈ 15.9 µm/m·K (typical) |
Heat treatment, welding and machining
| Item | Usual practice |
|---|---|
| Service temperature | In air: ≈ 1,050 °C continuous, ≈ 1,100 °C peak (less in sulfurous atmospheres, ≈ 950 °C). Avoid long dwell at 650–900 °C under impact (sigma). |
| Heat treatment | Solution annealing 1,040 – 1,120 °C with rapid cooling. Not hardenable by quenching. |
| Welding | Good with care: the fully austenitic structure carries a risk of hot cracking. Consumable AWS ER310 / E310, low heat input, interpass ≤ 150 °C. |
| Machining | Machinability lower than carbon steel: it work hardens quickly; use sharp tools, positive rake, constant feed without 'rubbing' and abundant coolant. |
Filler metal for welding
The wire composition is usually not identical to the material: each page explains why.
Typical applications
- Furnace parts, muffles and belts
- Baskets and fixtures for heat treatment
- Burners and refractory supports
- High-temperature heat exchangers
- Tube hangers and supports in furnaces
- Furnace fans, belts and conveyors
Alternatives: 309S up to ≈ 1,000 °C (cheaper); 253 MA (S30815) or Ni alloys (600/601, 800H) for higher creep and carburization resistance.
310S stainless steel: complete guide
What 310S stainless steel is
310S belongs to the family of austenitic stainless steels, in the heat-resisting group. The high chromium forms a stable, adherent oxide layer in air up to about 1,100 °C, and the high nickel keeps the austenitic structure stable and tough in that range, without the embrittlement that affects high-chromium ferritics. Silicon, up to 1.50%, reinforces oxidation resistance.
310, 310S and 310H
The usual commercial grade is 310S, with carbon up to 0.08%. The original 310 allows up to 0.25% carbon, and 310H controls carbon between 0.04 and 0.10% to guarantee creep resistance: it is 310H, not 310S, that must be specified when the part works under load at temperature and the design is based on creep.
Temperature limits
Oxidation resistance in air goes up to about 1,100 °C in continuous service and 1,050 °C in intermittent service (heating and cooling cycles spall the scale). Between 650 and 900 °C, however, prolonged exposure forms sigma phase, which embrittles the material when it returns to room temperature; this risk must be considered in equipment that stops and starts frequently. The high nickel makes 310S sensitive to sulfur in reducing atmospheres and gives it only moderate carburization resistance, which is why it is not the material for carburizing and nitriding furnaces.
Heat treatment and welding
Supplied solution annealed at 1,040 – 1,120 °C and rapidly cooled. Weldable with ER310 consumable, without preheating or post-weld heat treatment, with low heat input to avoid hot cracking in the fully austenitic structure. Dustre performs solution annealing in its own furnaces as part of its heat treatment service.
Applications
Burners and nozzles, supports, belts and baskets of heat treatment furnaces in oxidizing atmospheres, stacks and hot gas ducts, recuperators and heat exchangers, boiler and incinerator components. For severe creep, alloys such as Incoloy 800HT.
Supply forms and Dustre services
Round bars and blocks forged in open die, cut to size on a band saw, with rough or finish machining, solution annealing in our own furnaces and hardness, tensile and impact testing. All material is supplied with a 3.1 inspection certificate and heat traceability.
Frequently asked questions
What is the chemical composition of 310S stainless steel?
Per ASTM A479 / A240 (S31008): C ≤ 0.08 (310: ≤ 0.25); Mn ≤ 2.00; P ≤ 0.045; S ≤ 0.030; Si ≤ 1.50; Cr 24.0 – 26.0.
Which standards cover 310S stainless steel?
Bar: ASTM A479 / A276. Forging/flange: ASTM A182 F310. Plate: ASTM A240. Tube: ASTM A312 / A213 TP310S.
Up to what temperature can 310S stainless steel be used?
In air: ≈ 1,050 °C continuous, ≈ 1,100 °C peak (less in sulfurous atmospheres, ≈ 950 °C). Avoid long dwell at 650–900 °C under impact (sigma).
Which materials can replace 310S stainless steel?
309S up to ≈ 1,000 °C (cheaper); 253 MA (S30815) or Ni alloys (600/601, 800H) for higher creep and carburization resistance.
Is 310 stainless suitable for carburizing or nitriding furnaces?
It is not the best choice. 310S has only moderate carburization resistance and is sensitive to sulfur in reducing atmospheres. For carburizing, nitriding and carburizing atmospheres, prefer nickel alloys such as Incoloy 800HT or Inconel 600/601.
What is the difference between 310 and 310S stainless?
The carbon: up to 0.25% in 310 and up to 0.08% in 310S, which is the usual grade in bar and plate. For parts under load at temperature (creep design), specify 310H, with C of 0.04 to 0.10%.
