SS 310 / 310S
Fasteners
Manufacturer India
SS 310 / 310S — Why 25%Cr and 20%Ni Changes the Temperature Ceiling
SS 310 (UNS S31000) and SS 310S (UNS S31008) are the highest-chromium, highest-nickel grades in the standard austenitic stainless steel family — 24–26% Cr and 19–22% Ni, compared with 316L’s 16–18% Cr and 10–14% Ni. This elevated alloy content transforms the service ceiling from SS 316L’s approximately 870°C (with 321’s Ti-stabilisation limit) to 310/310S’s 1040°C continuous oxidation resistance — well above any other standard austenitic SS grade.
The primary mechanism: at high temperature, stainless steels protect themselves by forming a Cr₂O₃ (chromia) scale on the surface. The rate at which this scale grows and ultimately fails (spalls off, exposing fresh metal, which re-oxidises and eventually causes section loss) is a function of chromium content. 310’s 25% Cr forms a denser, more adherent Cr₂O₃ scale that grows more slowly and survives thermal cycling better than 304 (18% Cr) or 321 (17–19% Cr). The 20% Ni simultaneously raises the alloy’s resistance to carburisation — the internal carbon absorption that embrittles stainless steel in reducing high-temperature atmospheres (furnace atmospheres, ethylene cracker environments).
310 vs 310S selection: The “S” designation indicates low carbon — SS 310S (S31008) has C ≤0.080% vs SS 310’s C ≤0.25%. For most fastener applications where the lower carbon prevents carbide precipitation at the weld HAZ, 310S is the preferred grade. Standard 310 (C ≤0.25%) is used only for non-welded applications in severely carburising atmospheres where higher carbon content is not a concern. The carbon limit difference between 310 and 310S is similar to the 321 vs 347 stabilisation discussion — specify 310S by default.
| Element | Min % | Max % |
|---|---|---|
| Iron (Fe) | Balance | — |
| Chromium (Cr) | 24.0 | 26.0 |
| Nickel (Ni) | 19.0 | 22.0 |
| Carbon (C) — 310S | — | 0.080 |
| Carbon (C) — 310 | — | 0.250 |
| Manganese (Mn) | — | 2.0 |
| Silicon (Si) | — | 1.50 |
| Phosphorus (P) | — | 0.045 |
310S Tops the Austenitic SS Temperature Ladder
SS 310/310S occupies the highest temperature range of all standard austenitic stainless steels. Above 1040°C, nickel alloys (Incoloy 800H, Inconel 600) are specified. The diagram shows each grade’s practical service zone.
<400°C
425–870°C
to 870°C
870–1040°C ✔
Inconel 600 / 601
SS 321 / 347 (425–870°C): Ti-stabilised or Nb-stabilised grades for welded stainless in the sensitisation temperature range. See SS 321 page.
SS 310 / 310S (870–1040°C): Specify when service temperature exceeds 870°C or when carburisation resistance in reducing atmospheres is required. 310S for welded service, 310 for non-welded carburising atmospheres.
>1040°C — Nickel alloys: Specify Incoloy 800H or Inconel 600/601.
Why SS 310 — The Top of the Austenitic SS Temperature Range
1040°C Continuous Oxidation Resistance
The highest temperature rating of any standard austenitic stainless steel. 310/310S forms a tenacious, slowly-growing Cr₂O₃ scale at high temperature that resists spalling under thermal cycling. For furnace doors, heat treatment basket hardware, incinerator internals, and fired heater structural bolts operating above 870°C where 321 or 347 would fail, 310/310S is the correct and well-proven specification. No other standard SS grade approaches this temperature ceiling.
Carburisation Resistance in Reducing Atmospheres
The 20% Ni content dramatically improves resistance to carburisation — the absorption of carbon into the metal at high temperature in reducing or carbon-containing atmospheres (furnace gases containing CO/CO₂, cracking furnaces, cement kiln hot zones). Carburisation embrittles stainless steel by precipitating chromium carbides throughout the bulk material, not just at grain boundaries. 310/310S resists carburisation better than 321 or 347 because of its higher Ni content, and is the standard specification for carburising atmosphere furnace hardware.
Cyclic Oxidation — Spalling Resistance
Equipment that experiences temperature cycling (start-up and shut-down cycles, batch heat treatment furnaces, intermittent operation) is harder on oxide scale than continuous service. The Cr₂O₃ scale formed by 310/310S has better thermal expansion compatibility with the base metal than lower-Cr grades, resisting spalling during thermal cycling. For batch-process heat treatment furnaces, waste incinerators with variable load, and petrochemical fired heaters with periodic decoking cycles, 310/310S’s spalling resistance is the decisive advantage.
10S — Low Carbon, Weld-Safe at Temperature
310S (C ≤0.080%) is the standard specification for welded 310 service — the lower carbon reduces sensitisation risk at the HAZ during welding. But unlike 321 (which addresses sensitisation by titanium stabilisation), 310S addresses it by limiting carbon so that less Cr₂₃C₆ can form. For high-temperature furnace piping, fired heater nozzles, and pressure vessel connections in the 870–1040°C range, 310S with matching 310S filler wire is the standard weld procedure. The higher carbon 310 is reserved for heavily carburising non-welded applications.
310 / 310S Fastener Types & Standards
310S is the primary stocking grade (low carbon, weld-safe). Standard 310 available on order. All forms from ASTM A193 certified S31008/S31000 bar stock, PMI-verified before machining. Matched heat available.
310S Stud Bolts
Fully threaded stud bolts for ASME B16.5 pressure flanges on furnace piping, fired heater connections, and petrochemical process vessels operating 870–1040°C. Class 150–600, M12–M100, lengths to 3,000mm. Matched ASTM A194 Grade 8 heavy hex nuts from same certified S31008 heat on request.
Hex Bolts
Full thread and partial thread hex bolts in 310S. M6–M100. Furnace door hinge bolts, heat treatment fixture bolts, incinerator structure connections, fired heater structural bolts, and all industrial high-temperature equipment connections operating above 870°C where standard 321 or 347 stainless steel hex bolts show scale spalling or structural failure.
Hex Nuts
Standard hex and heavy hex nuts in 310S. M6–M100. ASTM A194 Grade 8 covers 310S nuts for use with ASTM A193 B8 stud bolts in high-temperature flanged assemblies. Matched from same S31008 certified bar as stud bolts — single MTC for complete 310S stud bolt assembly documentation for furnace and fired heater service.
Washers
Plain flat washers in 310S. M5–M100. For complete 310S stud bolt assembly sets in high-temperature furnace and petrochemical service — same MTC covering stud bolt, nut, and washer from the same S31008 certified bar stock heat.
Threaded Rods
Full thread and end-thread in 310S. M6–M100, lengths to 3,000mm. Furnace tube hanger systems, fired heater structural tie-rods, heat treatment oven structural rods, and all applications where high-temperature structural threaded rod above 870°C is required and 321 or 347 threaded rod is at the edge of its service capability.
Socket Cap Screws
Hex socket cap screws in 310S. M4–M24. Furnace internal fixture screws, heat treatment basket hardware connections, fired heater internal baffle screws, and petrochemical furnace internal connections where confined-access high-temperature bolting is required.
Matched 310S Sets
310S stud bolts + ASTM A194 Grade 8 heavy hex nuts + 310S washers from the same S31008 certified heat. Single MTC, PMI, and COC for the complete assembly. For furnace and fired heater EPC projects specifying 310S as the standard high-temperature stainless stud bolt assembly — simplified TPI hold plan for high-temperature pressure vessel documentation.
Custom 310 / 310S
Non-standard dimensions, inch UNC/UNF thread, fine pitch, coupling nuts, and drawing-specific configurations in 310 or 310S. For proprietary furnace designs, kiln internals, and bespoke heat treatment equipment where standard DIN/ASME dimensions are insufficient. Contact sales@akbarfasteners.in with application temperature and drawing.
310S Grade Selection Matrix — High-Temperature Service
310S fills the temperature gap between Ti-stabilised 321 (870°C max) and nickel alloys (Incoloy 800H, Inconel 601). This matrix identifies when 310S is the cost-effective and technically correct choice.
| Criterion | SS 310S This Page | SS 321 | SS 316L | Incoloy 800H |
|---|---|---|---|---|
| TEMPERATURE & OXIDATION | ||||
| Max continuous service | 1040°C | 870°C | ~300°C (sensitises) | 982°C |
| Chromium content | 24–26% | 17–19% | 16–18% | 19–23% |
| Scaling resistance at 1000°C | ✔ Excellent | Fails above 870°C | Fails | Good |
| Carburisation resistance | ✔ Good (20% Ni) | Moderate (9–12% Ni) | Moderate | ✔ Excellent |
| Cyclic oxidation / spalling | ✔ Good | Borderline >870°C | Fails | ✔ Good |
| SENSITISATION & WELDING | ||||
| Weld HAZ sensitisation (310S) | 310S ≤0.080% C | ✔ Ti-stabilised | ✔ 316L ≤0.030% C | Low C + stabilised |
| Carburising HAZ (high C) | 310 ≤0.25% C option | Not for carburising | Not for HT | Stable |
| COST POSITION | ||||
| Relative cost vs 316L | 2.5–3.5× 316L | 1.3–1.6× 316L | Baseline 1× | 5–7× 316L |
| Position | 870–1040°C SS choice | 425–870°C SS choice | Standard corrosion | When 310S fails |
Above 1040°C: Incoloy 800H / 800HT · Inconel 600 / 601
310 / 310S Application Areas
High-temperature furnace, incinerator, heat treatment, and petrochemical fired heater service above 870°C — the temperature zone where 321 and 347 reach their limit and 310/310S takes over.
Industrial Furnaces
heat treat basket hardware
Petrochemical
reformer tube hanger bolts
Incinerators
waste-to-energy bolts
Cement & Lime Kilns
high-temp structural
Power Generation
high-temp steam duct bolts
Chemical Processing
pyrolysis furnace flanges
Aerospace / Defence
gas turbine fixture bolts
Heat Treatment
hardening furnace bolts
310 / 310S Standards Coverage
Same ISO 9001:2015 quality system as our complete stainless steel fastener range. PMI XRF confirms Cr 24–26% and Ni 19–22% before machining — the critical verification that distinguishes 310S from lower-alloy SS grades.
Complete Documentation Package
S31008 UNS Stated
Conformance
19–22% Ni Confirmed
Tensile · Hardness
TÜV · BV · Lloyds
Related High-Temperature Fastener Grades
321 below 870°C. 310S for 870–1040°C. Incoloy 800H and Inconel 600/601 above 1040°C.
SS 321 Fasteners
The temperature zone below 310S — Ti-stabilised 321 handles the 425–870°C sensitisation range. When service temperature is between 425°C and 870°C and welded connections are involved, specify 321 rather than 310S. 321 is the correct lower-cost choice below 870°C.
View SS 321 Page →Incoloy 800H / 800HT
The grade above 310S — when service temperature exceeds 1040°C or when carburisation resistance in very severe reducing atmospheres is beyond 310S’s capability, Incoloy 800H (to 982°C) or 800HT provide the necessary upgrade. The next step for steam reformers and ethylene crackers.
View Incoloy Range →Inconel 600 / 601
For oxidising service above 1040°C — furnace fixtures to 1175°C (Inconel 600) and to 1250°C (Inconel 601). Combustion hardware, calcining kilns, and high-temperature aerospace structural connections above 310S’s service ceiling.
View Inconel Range →SS 316L Fasteners
When service temperature is below 300°C — 316L is the standard corrosion-resistant choice. 310S adds significant alloy cost (approximately 2.5–3.5× 316L per kg) for the high-temperature capability that is not needed below the sensitisation onset temperature of ~425°C.
View SS Range →Need SS 310 or
310S Fasteners?
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