Material number S31000: 310
S31000 is the Unified Numbering System designation for 310, austenitic heat-resisting stainless steel (25 % Cr, 20 % Ni) specified in ASTM A240.
What S31000 means
UNS numbers (ASTM E527 / SAE J1086) use a letter for the alloy family and five digits: G = AISI/SAE carbon and alloy steels (G41400 = 4140), S = stainless and heat-resisting steels (S30400 = 304), K = miscellaneous steels (K02600 = A36), T = tool steels, N = nickel alloys. The UNS number identifies a composition, not a product form or property level, so S31000 appears in several ASTM specifications (plate, bar, pipe) with different mechanical requirements.
310 at a glance
Type 310 is the heat-resisting austenitic stainless steel: 25 % chromium and 20 % nickel give a scale that stays adherent in air to about 1100 °C (2000 °F) continuous and 1150 °C intermittent — roughly 250 °C beyond 304 or 321. It also resists carburizing, nitriding and sulphur-bearing atmospheres better than the 18-8 grades, and its high nickel keeps the structure fully austenitic and ductile through repeated heating and cooling. That combination puts it in furnace muffles, radiant tubes, kiln linings, heat-treatment baskets, burner parts, thermowells and fluidized-bed components. UNS S31000; the low-carbon 310S (S31008, C ≤ 0.08 %) is the grade actually stocked as plate and pipe, and 310H (S31009) is the creep-rated version for ASME pressure parts.
Room-temperature minimums are the familiar 205/515 MPa; at 800 °C the alloy still holds about 120 MPa yield. The main service limitation is sigma-phase formation after long exposure at 650–900 °C, which embrittles the steel at room temperature — parts that cycle through that range should be inspected for cracking on cooling. Corrosion resistance in aqueous service is moderate (PREN ≈ 25) and rarely the reason for choosing 310.
EN 1.4845, JIS SUS310S, GB 06Cr25Ni20 and BS 310S24 are the same grade; the higher-silicon EN 1.4841 and the cast HK-40 are near relatives for furnace work.
Full data sheet for 310 → · Equivalent grades →