Material number S30400: 304
S30400 is the Unified Numbering System designation for 304, austenitic chromium-nickel stainless steel specified in ASTM A240.
What S30400 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 S30400 appears in several ASTM specifications (plate, bar, pipe) with different mechanical requirements.
304 at a glance
Type 304 is the world's default stainless steel: an austenitic alloy of 18 % chromium and 8 % nickel (hence '18-8'), with carbon held at 0.08 % max, listed as UNS S30400 in ASTM A240 (plate), A276 (bar), A312 (pipe) and a dozen other product standards. It resists oxidizing acids, food media, most organic chemicals and ordinary atmospheres; it forms, draws and welds easily; it is non-magnetic, hygienic and tough to cryogenic temperatures. Roughly half of all stainless steel made is 304 or its low-carbon twin 304L.
Minimum properties are modest — 205 MPa (30 ksi) yield and 515 MPa (75 ksi) tensile — but the alloy work-hardens strongly, so cold-rolled tempers up to 1275 MPa are available, and typical annealed sheet actually tests at 260–300 MPa yield. Strength is retained to about 800 °C (oxidation limit ≈ 870 °C continuous), and there is no ductile-to-brittle transition.
Its limits are chloride pitting and stress-corrosion cracking above ~60 °C in chloride solutions — the reasons 316 exists — and sensitization when slowly cooled through 500–800 °C after welding thick sections, which is why 304L (C ≤ 0.03 %) is specified for heavy weldments. EN 1.4301, JIS SUS304, GB 06Cr19Ni10 and GOST 08Kh18N10 are identical for procurement.
Full data sheet for 304 → · Equivalent grades →