Stainless Steel 310S
Stainless Steel 310S (UNS S31008) is the low-carbon version of Grade 310, with carbon limited to a maximum of 0.08%. It keeps the same high chromium (24-26%) and nickel (19-22%) levels as standard 310, which gives it excellent resistance to oxidation and scaling during continuous service in air up to 1050°C (2100°F). The lower carbon content improves weldability by reducing the risk of chromium carbide precipitation in the heat-affected zone, making 310S the preferred grade for welded components used at high temperatures.
1. Chemical Composition
The table below lists the elemental composition ranges for Stainless Steel 310S. The high chromium and nickel content provides its heat-resistant properties, while the reduced carbon ceiling (=0.08%) compared to standard 310 (=0.25%) improves weld-zone integrity and reduces sensitisation risk during fabrication.
| Grade | C | Mn | P | S | Si | Cr | Ni | Mo | Other |
| TP310S | = 0.080 | = 2.00 | = 0.045 | = 0.030 | = 1.00 | 24.00–26.00 | 19.00–22.00 | — | — |
2. Mechanical Properties
The following table gives minimum mechanical properties for Stainless Steel 310S in the annealed condition. These apply to seamless and welded pipe and tube product forms per ASTM specifications. The high alloy content helps maintain useful strength at elevated operating temperatures where lower-alloy austenitic grades lose load-bearing capacity.
| Grade | Condition | Tensile Strength Min, MPa (ksi) | Yield Strength Min, MPa (ksi) | Elongation Min, % | Heat Treatment Temp |
| TP310S | Annealed | 515 (75) | 205 (30) | 35 | 1040°C (1900°F) min |
3. Equivalent Grade
The table given below covers the various equivalent designations of the grade 310S, including UNS, European, Japanese, Chinese, and Russian equivalents.
| GRADE | UNS | GB | JIS | ISO | DIN/EN | GOST | |
| ISC | NEW | ||||||
| 310S | S31008 | S31008 | 06Cr25Ni20 | SUS310S | X8CrNi25-21 | 1.4845 | - |
3. Key Technical Advantages
- Improved Weldability Over Standard 310: The reduced carbon ceiling (=0.08% vs =0.25% in 310) lowers the volume of chromium carbides that can precipitate during welding. This means 310S can be welded in heavier sections with less risk of sensitisation and intergranular corrosion in the heat-affected zone, without requiring mandatory post-weld solution annealing in most applications.
- High-Temperature Oxidation and Scaling Resistance: With 24-26% Cr and 19-22% Ni, 310S forms a dense, adherent chromium oxide scale that resists spalling through repeated thermal cycling. It is rated for continuous service up to 1050°C (2100°F) in air and up to 1035°C (1900°F) under intermittent heating conditions.
- Stability in Carburising and Sulfur-Bearing Atmospheres: The elevated nickel content reduces carbon and sulfur diffusion into the alloy matrix, making 310S suitable for furnace retorts, radiant tubes, and heat-treating equipment operating in moderate carburising, nitriding, and mildly sulfidising atmospheres.
- Thermal Cycling Capability: The fully austenitic structure of 310S does not embrittle during repeated heating and cooling cycles between ambient and operating temperature. Unlike many ferritic heat-resistant grades, it retains toughness after thermal cycling, which is critical for furnace components that experience regular shutdowns.
Technical Note: 310S shares the same sigma phase susceptibility as standard 310. Prolonged exposure in the 650-900°C range can cause sigma phase precipitation, which reduces impact toughness at room temperature. For applications requiring sustained service in this temperature range, thermal processing schedules should account for sigma phase formation. 310S is not intended for aqueous corrosion service in chloride environments; for such applications, molybdenum-bearing grades (316L, 317L, or super-austenitic grades) should be specified.
4. Common Manufacturing Standards
- ASTM A312: Standard Specification for Seamless, Welded, and Heavily Cold Worked Austenitic Stainless Steel Pipes - TP310S designation.
- ASTM A213: Standard Specification for Seamless Ferritic and Austenitic Alloy-Steel Boiler, Superheater, and Heat-Exchanger Tubes - TP310S designation.
- ASTM A269: Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubing for General Service - applicable to 310S.
- ASTM A249: Standard Specification for Welded Austenitic Steel Boiler, Superheater, Heat-Exchanger, and Condenser Tubes.
- ASTM A358: Standard Specification for Electric-Fusion-Welded Austenitic Chromium-Nickel Stainless Steel Pipe for High-Temperature and General Corrosive Service.
- DIN EN 10216-5: Seamless steel tubes for pressure purposes - stainless steel (1.4845).
- DIN EN 10217-7: Welded steel tubes for pressure purposes - stainless steel (1.4845).
- DIN EN 10095: Heat-resisting steels and nickel alloys (1.4845).
- JIS G3459: Stainless Steel Pipes (SUS310S).
- JIS G3463: Stainless Steel Boiler and Heat Exchanger Tubes (SUS310S).
- GB/T 14976: Seamless stainless steel tubes for fluid transport (06Cr25Ni20).
- GB/T 13296: Seamless stainless steel tubes for boiler and heat exchanger (06Cr25Ni20).
- GOST 5632: High-alloy steels and alloys (20Kh23N18).
- GOST 9941: Seamless cold- and warm-deformed pipes from corrosion-resistant steel.
5. Primary Applications
- Heat Treatment Furnaces: Radiant tubes, muffles, retort liners, and conveyor belts in continuous annealing, carburising, and sintering furnaces operating at temperatures above 900°C where thermal cycling and carburising atmospheres are both present.
- Petrochemical Cracker and Reformer Furnaces: Convection and radiation section tubing, tube supports, and guide hangers in ethylene cracker and steam reformer furnaces where high skin temperatures and carburising or oxidising gas mixtures are the primary degradation mechanisms.
- Power Generation Boiler Components: Superheater shields, tube hangers, and refractory anchors in coal- and biomass-fired boilers where ash deposits create corrosive, high-temperature conditions and thermal cycling from load changes is routine.
- Cement and Lime Kiln Internals: Heat-resistant components, inlet housing liners, nose rings, and clinker cooler grate supports in oxidising kiln atmospheres at elevated temperatures where scaling resistance and structural retention are needed.
- Thermal Processing and Brazing Equipment: Fixtures, baskets, and retorts in vacuum and controlled-atmosphere brazing furnaces where repeated heating to 1000°C+ and subsequent cooling demands both oxidation resistance and weld integrity in fabricated assemblies.