310 & 310S Stainless Steel Fasteners: Understanding This High‑Temperature Alloy, Its Chemistry, and Properties

When temperatures rise beyond the practical limits of 304 and 316 stainless steel—where oxidation, scaling, and creep begin to compromise standard fasteners—310 stainless steel enters the picture. With its high chromium and nickel content, this fully austenitic alloy resists oxidation up to 1100°C and retains good strength at elevated temperatures. At RAYCHIN LIMITED, a specialist global manufacturer and supplier of high‑temperature alloy fasteners with decades of in‑house experience, we produce the complete range of 310 and 310S fasteners—hex bolts, studs, nuts, and custom parts—for furnace, chemical, and power generation applications. This guide explains what these alloys are, their chemical compositions, key properties, and how we deliver certified bolting solutions.

1. What Is 310 Stainless Steel?

What is 310 stainless steel? Alloy 310 (UNS S31000) is a high‑chromium (25%), high‑nickel (20%) austenitic stainless steel designed for elevated‑temperature service. Its high chromium content forms a dense, adherent chromium‑oxide (Cr₂O₃) scale that resists oxidation and sulfidation up to approximately 1100°C (2010°F) in continuous service. The high nickel content stabilizes the austenitic structure, providing good creep resistance and preventing sigma‑phase embrittlement at intermediate temperatures.

310 is primarily used in furnace hardware, heat‑treat baskets, radiant tubes, and chemical plant equipment where high‑temperature oxidation and carburization resistance are the dominant selection criteria. It is not designed for aqueous corrosion resistance at ambient temperatures, where 316 or duplex alloys are superior.

2. 310 vs 310S Fasteners: The Low‑Carbon Variant

The 310 vs 310S fasteners distinction is important. 310S (UNS S31008) is the low‑carbon version of 310, with carbon content restricted to a maximum of 0.08% (compared to 0.25% for standard 310). This lower carbon level prevents chromium‑carbide precipitation at grain boundaries during welding or prolonged exposure in the sensitization temperature range (450–850°C). In practice, 310S is preferred for welded fabrications, heavier sections, and applications where the fastener may be exposed to slow cooling through the sensitization range. Both grades are fully austenitic and non‑magnetic. RAYCHIN stocks both variants and can advise on the appropriate choice for your application.

3. Chemical Compositions

The following tables present the 310 stainless steel chemical composition and 310S chemical composition as specified by ASTM A276 / A479.

4. 310 Stainless Steel Properties

310 stainless steel properties are defined by its fully austenitic microstructure and high alloy content. Key room‑temperature mechanical properties per ASTM A276 (annealed condition) include:

• Tensile Strength: 515 MPa (75 ksi) min
• Yield Strength (0.2% offset): 205 MPa (30 ksi) min
• Elongation: 40% min
• Hardness: ≤ 95 HRB

While the room‑temperature strength of 310 is moderate, its defining capability is 310 stainless steel high temperature performance. At 800°C, 310 retains approximately 50% of its room‑temperature yield strength, and its oxidation resistance remains excellent to 1100°C. Key physical properties include:

• Density: 8.03 g/cm³
• Melting Range: 1400–1455°C (2550–2650°F)
• Thermal Conductivity: 14.2 W/m·K at 100°C
• Mean Coefficient of Thermal Expansion (20–1000°C): 19.3 µm/m·°C

310 is non‑magnetic in the annealed condition, though slight magnetism may develop after cold working or prolonged high‑temperature exposure due to sigma‑phase formation.

5. RAYCHIN's 310 and 310S Fastener Product Range

RAYCHIN LIMITED supplies the complete line of UNS S31000 fasteners and UNS S31008 fasteners for global high‑temperature applications:

• Hex bolts – ASME B18.2.1, DIN 931/933, ISO 4014, sizes 1/4″–2″ and M6–M48
• Double‑end studs and fully threaded rods – ASME B16.5, DIN 976
• Socket head cap screws – ASME B18.3
• Heavy hex nuts – ASME B18.2.2, DIN 934
• Flat and spring lock washers
• Custom parts – per your drawings; stepped studs, special head forms, furnace hardware

All 310/310S fasteners are supplied with full material traceability, OES‑PMI reports, and mechanical testing per ASTM A193 (Grade B8N for 304, adapted for 310) or ASTM A276. EN 10204 Type 3.1 is standard; Type 3.2 is available on request.