Material number K02303: A572 Grade 50
K02303 is the Unified Numbering System designation for A572 Grade 50, high-strength low-alloy (HSLA) columbium-vanadium structural steel specified in ASTM A572.
What K02303 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 K02303 appears in several ASTM specifications (plate, bar, pipe) with different mechanical requirements.
A572 Grade 50 at a glance
ASTM A572 is the American high-strength low-alloy (HSLA) structural steel: carbon-manganese steel micro-alloyed with niobium (columbium) and/or vanadium so that fine grain and precipitation strengthening lift the yield from A36's 250 MPa to 290, 345, 380, 415 or 450 MPa (Grades 42, 50, 55, 60, 65) without hurting weldability. Grade 50 — 345 MPa (50 ksi) yield, 450 MPa (65 ksi) tensile — is by far the most used and is what engineers mean by '50 ksi steel' or 'Grade 50'. UNS K02303.
Because the alloying is measured in hundredths of a percent, A572-50 costs only a few percent more than A36 while saving 25–30 % weight in strength-governed members; it is the standard for plate girders, columns, crane rails and runways, transmission towers, heavy equipment, truck frames and trailer chassis. W-shapes are rolled to the closely related A992 (which adds a yield cap for seismic design) and are dual-certified A992/A572-50; bridges use A709 Grade 50, which adds Charpy zones. A572 itself has no impact requirement unless supplementary S5 is ordered.
European S355J2 (non-alloy) and S355M/N (fine-grain HSLA) are the practical substitutes; JIS SM490, GB Q355B, GOST 09G2S and IS 2062 E350 are the Asian near matches.
Full data sheet for A572 Grade 50 → · Equivalent grades →