A36 vs A572 Grade 50: differences explained
A36 vs A572 Grade 50: yield 250 vs 345 MPa (36 vs 50 ksi), tensile 400–550 vs ≥ 450 MPa, price +3–8 %, weight saving 25–30 % in strength-governed members. Chemistry, weldability, forming and when each US structural steel is right.
Overview
A36 and A572 Grade 50 are the two structural steels an American fabricator quotes on almost every job. A36 is the plain carbon steel with 36 ksi (250 MPa) yield that has defined 'mild steel' since 1960; A572 Grade 50 is the high-strength low-alloy steel with 50 ksi (345 MPa) yield, micro-alloyed with niobium and vanadium so that the extra strength costs only a few percent per tonne and almost nothing in weldability. Since W-shapes moved to A992 (a 50 ksi grade) around 2000, the A36-vs-A572 question is mostly about plate, bar, angles and channels.
The arithmetic is simple: 39 % more yield for 3–8 % more money means A572-50 wins whenever strength governs the member size. A36 keeps its place where stiffness, buckling of slender elements, heavy cold forming or plain habit govern — and in bar and small-angle sizes where A572 is not stocked. The table gives the full comparison; A992's differences from A572-50 are noted for shapes.
A36 vs A572 Grade 50 side by side
| Property | A36 | A572 Grade 50 |
|---|---|---|
| Type | carbon structural steel | HSLA (Nb/V micro-alloyed) structural steel |
| UNS | K02600 | K02303 |
| Min. yield | 250 MPa (36 ksi); 220 MPa > 200 mm plate | 345 MPa (50 ksi), plate ≤ 100 mm |
| Tensile | 400–550 MPa (58–80 ksi) | ≥ 450 MPa (65 ksi), no max (A992: 450–620) |
| Elongation (200 mm / 50 mm) | ≥ 20 % / 23 % | ≥ 18 % / 21 % |
| Yield/tensile ratio (typ.) | ≈ 0.65–0.75 | ≈ 0.75–0.85 (A992 caps at 0.85) |
| Carbon max | 0.25–0.29 % (by product/thickness) | 0.23 % |
| Mn | 0.80–1.20 % (plate > 20 mm) | ≤ 1.35 % (1.65 % Gr 60/65) |
| Micro-alloy | none | Nb 0.005–0.05 and/or V 0.01–0.15 % |
| Carbon equivalent (typ.) | 0.30–0.40 | 0.35–0.45 |
| Impact toughness | not required (S5 optional) | not required (S5 optional; A709-50 has zones) |
| Plate thickness limit | none (yield drops > 200 mm) | 100 mm (Grade 50) |
| Preheat (AWS D1.1 Table 3.3) | category A/B: none ≤ 19 mm … 110 °C > 64 mm | category B: same schedule, low-hydrogen mandatory |
| Consumables | E70XX / ER70S-6 (over-matching) | E70XX / ER70S-6 (matching) |
| Cold-bend inside radius (transverse) | ≈ 1.5 t | ≈ 1.5–2 t |
| Hardness (typ.) | 119–159 HB | 135–185 HB |
| Fatigue (AISC/AASHTO categories) | same detail categories | same detail categories — no benefit from higher yield |
| Price (2026, plate) | 1.00 | ≈ 1.03–1.08 |
| Weight for equal strength | 1.00 | ≈ 0.72 |
| W-shapes | rare today | dual-certified A992/A572-50 |
| EN cross-reference | S235JR / S275JR | S355J2 / S355M |
Which should you choose?
A572 Grade 50 when strength sets the section: plate girders, columns, crane runways, lifting structures, truck and trailer frames, transmission towers, any design where a thinner plate or lighter section pays back the 3–8 % premium. For rolled beams simply specify A992.
A36 when it does not: deflection-limited floor beams and platforms (E is identical), slender compression members, gusset and base plates sized by geometry, heavy cold forming, small bar and angle sizes that stockists carry only in A36, and low-volume shops that want one steel in the yard.
Fatigue does not favour either — AISC detail categories are independent of grade — so fatigue-governed members gain nothing from Grade 50. And neither has an impact requirement: for cold-climate or dynamically loaded structures add supplementary S5 or move to A709.
- Deflection-governed beams, platforms, vibration-sensitive floors
- Slender members governed by buckling
- Base plates, gussets, stiffeners sized by geometry
- Heavily cold-formed parts, tight-radius bends
- Small bar, flat and angle sizes from stock
- Non-code fabrication, jigs, machine bases
- Plate girders, built-up columns, transfer beams
- Crane girders, runway beams, lifting frames
- Truck/trailer chassis, heavy equipment weldments
- Towers, masts, sign structures
- Any strength-governed member where weight or shipping cost matters
- Rolled W-shapes (order as A992)
Frequently asked questions
What is the difference between A36 and A572 Grade 50?
Yield strength: 250 MPa (36 ksi) vs 345 MPa (50 ksi). A572-50 is an HSLA steel with niobium/vanadium micro-alloying; A36 is plain carbon steel. Tensile is 400–550 vs ≥ 450 MPa. A572 saves 25–30 % weight in strength-governed members for 3–8 % more per tonne.
Is A572 harder to weld than A36?
Marginally: its carbon equivalent is a little higher, so AWS D1.1 puts it in preheat category B with low-hydrogen consumables mandatory, but the preheat schedule by thickness is the same as for A36 and both are prequalified with 70 ksi consumables.
Is A572 Grade 50 the same as A992?
Nearly. A992 is written for rolled W-shapes: same 50 ksi minimum yield plus a 65 ksi yield cap, a maximum yield/tensile ratio of 0.85 and a CE limit, for predictable seismic behaviour. W-shapes are dual-certified A992/A572-50; plate cannot be A992.
Does A572 deflect less than A36?
No. Both have E = 200 GPa (29 × 10⁶ psi); a member of the same size deflects identically. A572 only allows a smaller section when strength — not deflection — governs.
How much more does A572 cost?
Typically 3–8 % more per tonne for plate and about the same for shapes (where A992 is the default anyway). Per unit of capacity it is about 25 % cheaper.
Which has better fatigue performance?
Neither. AISC and AASHTO fatigue design uses detail categories that do not depend on grade; higher yield does not raise fatigue resistance of welded details.
Related comparisons
Verified against ASTM A36/A36M-19; ASTM A572/A572M-21. Last checked: September 2026.