A572 Grade 50 steel (K02303): properties, composition, equivalents
ASTM A572 Grade 50 (UNS K02303): HSLA structural steel with 345 MPa (50 ksi) minimum yield and 450 MPa (65 ksi) tensile, micro-alloyed with Nb/V. All five grades (42–65), thickness limits, A572 vs A36 / A992 / S355, Q355/SM490 equivalents.
What is A572 Grade 50?
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.
A572 Grade 50 chemical composition
| Element | Mass % | Note |
|---|---|---|
| C | ≤ 0.23 | Grade 50 plate/shapes; Grade 42: 0.21; Grades 60/65: 0.26 |
| Mn | ≤ 1.35 | Grade 50: 1.35 (1.65 for Grades 60/65); shapes may go to 1.60 with C ≤ 0.21 |
| P | ≤ 0.03 | |
| S | ≤ 0.03 | |
| Si | ≤ 0.4 | plate > 40 mm: 0.15–0.40 |
| Nb | 0.005 – 0.05 | Type 1 (Nb); Type 2 (V 0.01–0.15); Type 3 (Nb + V); Type 5 (N ≤ 0.015 with V) |
| V | 0.01 – 0.15 | Type 2 / Type 3 |
| Cu | ≥ 0.2 | when copper steel is specified |
ASTM A572/A572M-21 Tables 1 and 2. Micro-alloy 'Type' (1–5) is at the producer's option unless specified. Grade 50 shapes over 634 kg/m and plate over 40 mm: Mn ≤ 1.35, Si 0.15–0.40. Supplementary S90/S91 for CE limits, S5 for Charpy.
A572 Grade 50 mechanical properties
| Thickness / condition | Yield strength ReH / Rp0.2 MPa (ksi) | Tensile strength Rm MPa (ksi) | Elongation A % | Hardness |
|---|---|---|---|---|
| Grade 42 (290 MPa) — plate ≤ 150 mm, all shapes | 290 (42.1) | ≥ 415 (≥ 60.2) | 20 (L0 200 mm) / 24 (50 mm) | — |
| Grade 50 (345 MPa) — plate ≤ 100 mm, all shapes | 345 (50.0) | ≥ 450 (≥ 65.3) | 18 / 21 | ≈ 135–185 HB (typ.) |
| Grade 55 (380 MPa) — plate ≤ 50 mm, shapes | 380 (55.1) | ≥ 485 (≥ 70.3) | 17 / 20 | — |
| Grade 60 (415 MPa) — plate ≤ 32 mm, shapes ≤ 634 kg/m | 415 (60.2) | ≥ 520 (≥ 75.4) | 16 / 18 | — |
| Grade 65 (450 MPa) — plate ≤ 32 mm, shapes ≤ 634 kg/m | 450 (65.3) | ≥ 550 (≥ 79.8) | 15 / 17 | — |
| Grade 50 — typical mill certificate (plate 10–25 mm) | ≈ 370–420 (≈ 53.7–60.9) | ≈ 500–550 (≈ 72.5–79.8) | ≈ 25–30 (50 mm) | ≈ 150–170 HB |
ASTM A572/A572M-21 Table 3; yield minimum only (no maximum; A992 adds a 450 MPa cap and Fy/Fu ≤ 0.85 for seismic design). Elongation in 200 mm or 50 mm. No Charpy unless S5 ordered; bridge plate uses A709-50 with Charpy zones.
Impact toughness
A572 Grade 50 requires a minimum Charpy V-notch energy of 27 J at 20 °C (typical only; not required by A572). Fine-grained HSLA structure gives typical 27 J transition around −20 °C for plate ≤ 25 mm, but the specification guarantees nothing; order S5 or A709/A709-50W for impact-critical members.
A572 Grade 50 equivalent grades
| Grade | System | Match | Why / differences |
|---|---|---|---|
| A992 | ASTM / ASME | Identical | Same 345 MPa yield for W-shapes with added yield cap and Fy/Fu limit; shapes are dual-certified. |
| A709 Gr. 50 | ASTM / ASME | Identical | A572-50 chemistry and strength plus Charpy zone requirements for bridges. |
| A588 / A709-50W | ASTM / ASME | Near | Weathering HSLA with 345 MPa yield and Cu-Cr-Ni for unpainted service. |
| S355JR / S355J2 | EN (European) | Near | Yield 355 MPa (≤ 16 mm), Rm 470–630 MPa, guaranteed Charpy (+20 / −20 °C); non-alloy rather than HSLA chemistry. S355J2 is the standard European substitute for A572-50 plate. |
| S355M / S355N | EN (European) | Near | EN 10025-4 / -3 thermomechanical or normalized fine-grain HSLA — the closest metallurgical match (Nb/V micro-alloyed, 355 MPa). |
| Q355B / Q345B | GB/T (China) | Near | GB/T 1591 Q355B: yield 355 MPa, Rm 470–630 MPa, 34 J at +20 °C (formerly Q345B: 345 MPa). |
| 09G2S / S345 | GOST (Russia/CIS) | Near | GOST 19281 09G2S (C345): yield 325–345 MPa; GOST 27772 S345 structural class. |
| IS 2062 E350 | IS (India) | Near | Yield 350 MPa, Rm 490 MPa min (quality A/BR/B0/C by impact). |
| SM490A / SM490YB | JIS (Japan) | Near | JIS G3106 SM490A: yield 325 MPa (≤ 16 mm), Rm 490–610 MPa; SM490YB: yield 365 MPa, 27 J at 0 °C. |
| A36 | ASTM / ASME | Functional | 250 MPa carbon steel — the grade A572-50 replaces when weight matters. |
| S355MC | EN (European) | Functional | Same yield class (345 MPa) as plate/sections, but not thermomechanically rolled and without the guaranteed bend radii. |
Identical = same composition and mechanical limits within rounding. Near = one limit differs (e.g. carbon max or impact temperature). Functional = interchangeable for most uses after an engineering check. Full cross-reference for A572 Grade 50 →
Old and superseded designations
| Old name | Standard | Note |
|---|---|---|
| K02303 (Gr 50), K02703 (Gr 42), K02003 (Gr 60/65) | UNS | |
| A441 | ASTM A441 (withdrawn 1989) | Predecessor Mn-V HSLA (50 ksi) replaced by A572. |
| A709 Grade 50 | ASTM A709 / AASHTO M270 | Bridge version with Charpy zones; 50W is the weathering variant (A588 chemistry). |
| A992 | ASTM A992 | W-shape grade (50–65 ksi yield, Fy/Fu ≤ 0.85); most W-shapes are dual-certified A992/A572-50. |
| CSA G40.21 350W | Canada | Canadian 350 MPa structural equivalent. |
Product forms and tolerance standards
Product forms: plate up to 100 mm (Grade 50), 150 mm (Grade 42), shapes: W, S, M, C, L, HP (W-shapes usually dual-certified A992/A572-50), bar and merchant sections, sheet piling (as A572-50 or A690), bridge plate (as A709-50).
Dimensional tolerances: plate, shapes, bar: ASTM A6/A6M; surface: A6 (mill scale); blast-cleaned to SSPC on request.
Key property values
A572 Grade 50 yield strength
Minimum 345 MPa (50 ksi) for plate up to 100 mm and all shapes; typical 370–420 MPa. Other grades: 42 → 290 MPa, 55 → 380 MPa, 60 → 415 MPa, 65 → 450 MPa.
A572 Grade 50 tensile strength
Minimum 450 MPa (65 ksi), no maximum (A992 caps W-shapes at 450–620 MPa); typical 500–550 MPa. Grade 42: ≥ 415; 55: ≥ 485; 60: ≥ 520; 65: ≥ 550 MPa.
A572 elongation and hardness
Grade 50: ≥ 18 % in 200 mm / ≥ 21 % in 50 mm (typical 25–30 %). Hardness not specified; typical 135–185 HB.
Thickness limits
Grade 42: plate to 150 mm; Grade 50: plate to 100 mm; Grade 55: 50 mm; Grades 60/65: 32 mm and shapes ≤ 634 kg/m. Yield does not step down with thickness inside these limits (unlike EN 10025).
Weldability
Good: CE typically 0.35–0.45 (S90/S91 supplementary requirements cap CE for critical work). AWS D1.1 prequalified with E70XX/ER70S-6 (matching) — preheat per Table 3.3 category B: none ≤ 19 mm, 10 °C to 38 mm, 65 °C to 64 mm, 110 °C above; low-hydrogen consumables mandatory.
Physical properties
Density 7.85 g/cm³, E = 200 GPa (29 × 10⁶ psi), expansion 11.7 × 10⁻⁶/K, conductivity ≈ 47 W/m·K. AISC design: Fy = 50 ksi, Fu = 65 ksi.
Weldability
Readily weldable by SMAW (E7018), GMAW (ER70S-6), FCAW (E71T-1) and SAW (F7A2) under AWS D1.1 prequalified procedures; matching-strength 70 ksi consumables suffice for Grade 50 (80 ksi for Grades 60/65). Preheat by thickness per AWS D1.1 Table 3.3 (category B); low-hydrogen practice required. No PWHT for structural work. For seismic connections use A992 shapes with demand-critical weld consumables (Charpy-rated).
Machining, forming and heat treatment
Machinability ≈ 65–70 % of B1112 (slightly harder than A36). Flame, plasma, laser and waterjet cutting routine; shearing to ~20 mm; punching to 16 mm. Cold bending: inside radius ≥ 1.5–2 t transverse (AISC/producer guidance), 2.5 t for Grades 60/65; hot forming 900–1100 °C followed by air cooling (do not quench). Galvanizes and paints as A36.
Typical applications
- Plate girders, columns and trusses in buildings and industrial structures
- W-shapes (as A992/A572-50), HP piles, channels and angles for heavy framing
- Crane runway girders, crane booms and lifting-equipment structures
- Transmission and telecom towers, wind-tower internals, substation structures
- Truck frames, trailer chassis, dump bodies, heavy-equipment weldments
- Bridge girders (as A709-50 / 50W), sign structures, culverts
- Pressure-free tanks, bins and hoppers where thinner walls save weight
A572 Grade 50 compared with related grades
Frequently asked questions
What is the difference between A572 Grade 50 and A36?
Yield 345 vs 250 MPa (50 vs 36 ksi) and tensile ≥ 450 vs 400–550 MPa. A572-50 is micro-alloyed HSLA steel; it lets members be 25–30 % lighter for a few percent more per tonne. A36 is more ductile and remains common for plate, bar, angle and channel; A572-50 (or A992) dominates beams, columns and girders.
What is the difference between A572 Grade 50 and A992?
A992 is written specifically for rolled W-shapes: same 345 MPa (50 ksi) minimum yield but with a 450 MPa (65 ksi) yield cap, Fy/Fu ≤ 0.85 and a carbon-equivalent limit for predictable seismic behaviour. Most W-shapes are dual-certified A992/A572-50; plate cannot be A992.
What is the European equivalent of A572 Grade 50?
S355J2 (EN 10025-2) for general plate and sections — 355 MPa yield with guaranteed −20 °C impact — or S355M/S355N (EN 10025-4/-3) for a true fine-grain HSLA match. Both are graded 'near' because chemistry and thickness rules differ.
Does A572 have an impact (Charpy) requirement?
Not by default. Order supplementary requirement S5 with the temperature and energy needed, or specify A709 Grade 50 (bridges) which includes Charpy zones 1–3.
What are the A572 grades?
Grade 42 (290 MPa / 42 ksi), Grade 50 (345 MPa / 50 ksi), Grade 55 (380 MPa / 55 ksi), Grade 60 (415 MPa / 60 ksi) and Grade 65 (450 MPa / 65 ksi). Grade 50 is the standard; 60/65 are limited to 32 mm plate and lighter shapes.
Is A572 Grade 50 weldable without preheat?
Yes up to 19 mm under AWS D1.1 (category B) with low-hydrogen consumables; 10 °C preheat to 38 mm, 65 °C to 64 mm, 110 °C above 64 mm.
Related grades
Verified against ASTM A572/A572M-21; ASTM A572/A572M-21 Tables 1–3; ASTM A992/A992M-22; ASTM A709/A709M-23; AWS D1.1:2020 Table 3.3. Last checked: September 2026.