Definition
ASTM A36 is the historical American carbon structural steel grade, with a minimum yield of 250 MPa (36 ksi) and a tensile range of 400-550 MPa. ASTM A572 is the High-Strength Low-Alloy (HSLA) structural steel standard, covering Grades 42, 50, 55, 60 and 65; Grade 50 (yield 345 MPa, 50 ksi) is by far the most-used. A572 achieves its higher yield through controlled microalloying, small additions of columbium (niobium), vanadium and/or titanium, without the cost or weldability penalty of older HSLA chemistries.
Mechanical and chemical comparison
Property | A36 | A572 Gr 50 Minimum yield | 250 MPa (36 ksi) | 345 MPa (50 ksi) Tensile strength | 400-550 MPa | minimum 450 MPa Minimum elongation (200mm) | 20% | 18% Carbon (max, plate ≤20mm) | 0.26% | 0.23% Manganese | 0.80-1.20% | 1.35% max Microalloying | none | Cb, V, Ti as required Weldability | Excellent | Very good EN nearest equivalent | S235/S275 | S355 US use today | mostly secondary steel | primary frames, beams, columns
Weldability
Both grades weld with standard E7018 SMAW, ER70S-6 GMAW and E71T-1 FCAW consumables. A36's lower carbon equivalent (typically 0.35-0.40 CEV) means it rarely needs preheat for plate up to 50mm. A572 Gr 50 (typical CEV 0.42-0.45) tolerates the same conditions but earns preheat above ~30mm thickness or in high-restraint joints. Low-hydrogen consumables are recommended for both grades on critical members.
Where each grade wins
A36 remains the right call for: ancillary structural steel, base plates, gussets, anchor plates, low-stress secondary members, and any application where formability and unrestricted welding dominate. It is also the de-facto choice on retrofit work that must match existing structures.
A572 Grade 50 wins on: primary building frames, long-span beams, transfer girders, bridge members, crane runways and any structure where section weight saving offsets the premium. Most modern US-specification building tenders default to A572 Gr 50 (or A992 for W-shapes) for primary framing.
A572 vs A992
A992 was introduced in 1998 specifically for wide-flange (W-shape) sections, with tightened chemistry and a yield range (345-450 MPa) rather than just a minimum. A992 is now the default US W-shape grade, when an American engineer specifies "W14x68", the mill ships A992. A572 Gr 50 remains the dominant grade for plate, angles, channels and HSLA-specific orders.
Cost and availability
A572 Gr 50 typically prices 4-10% above A36 on a per-tonne FOB basis from American, Korean, Indian and Far Eastern mills. The economics flip favourable for A572 once design weight savings (typically 15-22% on primary frames) are included. Both grades are mill-direct available from most major structural steel producers serving the GCC, often dual-certified with EN 10025 S275 (for A36) or S355 (for A572 Gr 50) on the same MTC.
GCC context
Aramco, ADNOC and major US-spec EPC contractors regularly call A36 and A572 Gr 50 in their structural steel masterspecs. On dual-spec projects (an EN tender with American engineering review), TIC Dubai issues dual-certified MTCs so contractors do not need to source twice. For UAE infrastructure and building projects following Eurocode, A572 Gr 50 is routinely accepted as an equivalent to S355 with no design change.