UNS S31008: Low-Carbon Austenitic Stainless Steel for High-Temperature Service

Overview of UNS S31008

UNS S31008 is the low-carbon member of the 310 family of high-chromium, high-nickel austenitic stainless steels, equivalent to AISI 310S, EN 1.4845 (X8CrNi25-21), JIS SUS310S and GB 06Cr25Ni20. With 24.00-26.00% chromium and 19.00-22.00% nickel it forms a stable, protective chromium oxide film that resists oxidation, carburization and sulfidation at elevated temperature. The 0.08% maximum carbon improves weldability and minimizes chromium carbide precipitation, while the austenitic structure remains essentially non-magnetic with good ductility.

Chemical Composition

Composition limits per ASTM A240/A240M and JIS G4303/G4304.

Element (wt %)	UNS S31008
Carbon, max	0.08
Manganese, max	2.00
Silicon, max	1.00
Phosphorus, max	0.045
Sulfur, max	0.030
Chromium	24.00-26.00
Nickel	19.00-22.00

Mechanical Properties

Minimum values for annealed plate, sheet and strip per ASTM A240/A240M.

Property	Requirement
Tensile strength (MPa / ksi), min	515 / 75
0.2% yield strength (MPa / ksi), min	205 / 30
Elongation in 2 in (50 mm), min (%)	40
Brinell hardness, max (HBW)	217
Rockwell hardness, max (HRB)	95

High-Temperature Service and Applications

The grade is designed for continuous high-temperature service in air, with a maximum continuous service temperature of 1150°C (2100°F) and a maximum intermittent service temperature of 1035°C (1895°F). It is used for high-temperature furnace linings, boiler superheater tubes, petrochemical cracking furnaces, incinerators, radiant tubes and thermal processing equipment. Because of the high chromium and nickel content it also resists carburizing and sulfur-containing atmospheres better than lower-alloyed austenitic grades, although chloride pitting resistance remains limited compared with molybdenum-bearing grades.

Fabrication Notes

The low carbon content allows welding by standard austenitic stainless steel processes without mandatory post-weld heat treatment for sensitization control. Forming is carried out in the annealed condition, and parts exposed to service above 425°C should be solution annealed before installation if they were cold worked during fabrication. The material is supplied in plate, sheet, strip, tube, bar and wire forms.

Frequently Asked Questions

Q1. What is UNS S31008?
The UNS designation of AISI 310S, a low-carbon 25Cr-20Ni austenitic stainless steel for high-temperature service, with 24.00-26.00% chromium and 19.00-22.00% nickel.

Q2. What is the equivalent EN designation?
EN 1.4845 (X8CrNi25-21); the JIS designation is SUS310S and the GB designation is 06Cr25Ni20.

Q3. What is the maximum service temperature?
1150°C (2100°F) continuous and 1035°C (1895°F) intermittent in air.

Q4. Why choose the low-carbon S31008 over 310?
The 0.08% max carbon reduces sensitization during welding and improves resistance to intergranular corrosion, while the chromium oxide film resists oxidation, carburization and sulfidation at elevated temperature.

Q5. Is S31008 magnetic?
The annealed austenitic structure is essentially non-magnetic with good ductility.

Q6. Which standard applies to plate?
ASTM A240/A240M for plate, sheet and strip; bar is covered per ASTM A276/A276M.