Material number G41400: 4140
G41400 is the Unified Numbering System designation for 4140, chromium-molybdenum low-alloy steel (chromoly) specified in ASTM A29.
What G41400 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 G41400 appears in several ASTM specifications (plate, bar, pipe) with different mechanical requirements.
4140 at a glance
AISI 4140 is the definitive chromoly steel: 0.40 % carbon, 1 % chromium and 0.2 % molybdenum, UNS G41400. Chromium and molybdenum push hardenability deep enough that a 50 mm bar through-hardens in oil, and the steel tempers over a wide range to any strength from 900 to 1800 MPa — which is why it is the standard for shafts, axles, gears, bolts, tooling, drill collars and every 'machine steel' job that needs more than plain carbon steel can give. It is also the most-stocked alloy steel in North America, usually as pre-hardened bar (4140 HT / PH) at 28–32 HRC, ready to machine and use without further heat treatment.
As an AISI grade 4140 is defined by chemistry, not properties; the tables give typical values for annealed, normalized, pre-hard and quenched-and-tempered conditions at various tempers, and the ASTM A434 or customer specification supplies minimums when required. Weldability is poor (CE ≈ 0.8) — preheat and post-weld tempering are mandatory — and hydrogen embrittlement is a real risk above about 38 HRC, so plating and pickling of hardened parts must be followed by baking.
EN 42CrMo4 (1.7225), JIS SCM440, GB 42CrMo and BS 708M40 (EN19) are the same steel; 4142, 4145 and 4150 are the higher-carbon steps, 4130 the weldable low-carbon cousin, 4340 the nickel-bearing upgrade.
Full data sheet for 4140 → · Equivalent grades →