Engineering Guide · 4 min read
310S Stainless Steel Fasteners: What to Specify for High-Temperature Service
310S is widely supplied for heat-resistant equipment. Loaded fasteners also need suitable creep strength, atmosphere resistance and mating parts.
The short answer: 310S is a heat-resistant austenitic stainless steel and a mainstream grade within the 310 family, identified as UNS S31008. For fasteners, its resistance to oxidation is only part of the choice: a bolt must also retain its clamping force during hot service.[1][2][3][7]
Explore the stainless steel guide series
Start with the material basics and the earlier grade introductions:
- What Is Austenitic Stainless Steel? A Fastener Buyer's Guide — material structure, cold work and grade selection.
- 304 Stainless Steel Fasteners: When to Use Them and What to Specify — the starting grade for general-purpose assemblies.
- 316 Stainless Steel Fasteners: Applications, Grades and Service Limits — chloride exposure, 316L and finished strength.
310S and the 310 family
310S contains nominally 25% chromium and 20% nickel. Chromium supports a protective oxide scale at high temperature. The carbon limit distinguishes it from plain Type 310:[1][4][5]
| Grade | Carbon and selection |
|---|---|
| 310 / UNS S31000 | 0.25% maximum carbon. |
| 310S / UNS S31008 | 0.08% maximum carbon; the lower-carbon version of 310. |
| 310H / UNS S31009 | 0.04–0.10% carbon; the controlled minimum supports high-temperature strength. |
Lower carbon helps limit welding-related sensitization, in which carbide precipitation leaves grain boundaries vulnerable to corrosion. 310S can still develop this condition after thermal exposure.[4][5]
Oxidation resistance and clamping force
A furnace attachment can remain visibly intact while its joint loses clamping force. At elevated temperature, time-dependent deformation—creep—can relax the bolt’s preload during a long hot dwell.[7]
Outokumpu gives 1,050 °C as air-service guidance for 310S/4845, not as a working-temperature rating for a loaded bolt. The connection designer needs the fastener’s metal temperature, load and required life to assess strength, creep and retained preload.[6][7]
Unequal thermal expansion of the bolt and clamped parts can also raise or lower preload during a heating and cooling cycle. Include the materials and temperatures of the nuts and washers in this assessment.[7][8]
The conditions at the furnace joint
310-family alloys are used in burner components, furnace supports and heat-treatment fixtures. Hot air, sulfur-bearing combustion gas and a carburizing atmosphere can call for different material choices at the same temperature.[4][6]
| At the joint | Information to provide |
|---|---|
| Hot oxidizing air | Normal and maximum fastener metal temperatures, dwell time and required life. |
| Repeated heating and cooling | Cycle range, frequency and the materials being clamped. |
| Sulfur-bearing, reducing, carburizing or deposit-forming service | Gas chemistry, oxygen conditions and deposits. |
| Long service followed by cool-down or wet shutdown | Thermal history, condensate chemistry and any plan to remove or reuse the fasteners. |
Prolonged thermal exposure can cause carbide precipitation and sigma-phase formation, reducing corrosion resistance or toughness. The loss of toughness is particularly relevant during maintenance after cooling.[5][6]
Material, finished fastener and assembly
A quotation labeled only “310” leaves the exact grade unclear. Confirm the certified grade and available sizes with the supplier.[1][2][3]
For a fastener machined from bar, ASTM A276/A276M-25 may cover the starting material; finished-fastener mechanical requirements need a separate specification. ASTM F593-24 does not list 310S among its alloy groups. Agree on the specification and tests for the actual 310S product.[9][10]
Use a lubricant or anti-seize suited to the temperature and atmosphere, with tightening data for that supplied condition. The thread galling guide covers seizure during assembly.[11]
Match the heat or batch number to the chemical and finished-fastener test reports. Where carbon verification is required, use a carbon-capable method: handheld X-ray fluorescence (XRF) cannot measure carbon.[12]
What to send with a 310S fastener RFQ
- Part: dimensional standard or drawing, head, thread system and fit, diameter and length.
- Material: 310S / S31008, material specification, supply condition and finished-fastener mechanical requirements.
- Temperature history: metal temperatures, dwell, cycles and target life.
- Joint and atmosphere: load, clamped materials, mating-part requirements, gas chemistry, deposits and shutdown conditions.
- Delivery: quantity, traceability, agreed test reports, lubricant and tightening procedure.
References
- ATI. ATI 310S — UNS S31008. Current offering, composition limits and flat-product forms.
- Outokumpu. Therma range. Current commercial listing of Therma 310S/4845 and heat-resistant applications.
- Aperam. 310S–1.4845. Current commercial grade offering and product forms.
- ATI. ATI 309/309S/310/310S technical data sheet, version 1, February 17, 2014. Grade chemistry, furnace applications, protective oxide formation and material behavior.
- Atlas Steels. Stainless Steel 310, 310S, 310H Grade Data Sheet, revised April 23, 2021. Carbon distinctions, sensitization and dual certification.
- Outokumpu. Therma range datasheet. Air-temperature guidance, hot-gas environments, structural stability and time-dependent strength.
- NASA. NASA-STD-5020B — Requirements for Threaded Fastening Systems in Spaceflight Hardware, August 6, 2021; revalidated January 5, 2026. Joint preload calculations, creep and temperature, Section 4.3.1 and Table 1.
- Richard T. Barrett, NASA. Fastener Design Manual, NASA-RP-1228, March 1990, “Thermal Cyclic Loading of Bolts,” printed page 15. Differential thermal expansion and joint loading.
- ASTM International. ASTM A276/A276M-25 — Stainless Steel Bars and Shapes. Public scope for starting-product forms and supply conditions.
- ASTM International. ASTM F593-24 — Stainless Steel Bolts, Hex Cap Screws, and Studs. Public scope and alloy groups; 310S is not a listed alloy.
- Australian Stainless Steel Development Association. Technical FAQ 5: Galling and its Control. Thread condition, lubrication and tightening considerations.
- Thermo Fisher Scientific. Analysis of Stainless Steel Testing Using the Niton Apollo Handheld LIBS Analyzer. Carbon measurement and the limitations of XRF for distinguishing carbon-controlled stainless grades.