ASTM A572 is a high-strength low-alloy (HSLA) structural steel specification covering five grades-42, 50, 55, 60, and 65-with grade numbers representing minimum yield strength in ksi . Both Gr.42 and Gr.55 are columbium-vanadium microalloyed steels, fully killed, fine-grain treated, and intended for riveted, bolted, or welded structures such as bridges, buildings, and construction equipment .
Key Differences:
Strength: Gr.55 provides approximately 31% higher yield strength (55 vs 42 ksi) and 17% higher tensile strength (70 vs 60 ksi) .
Ductility: Gr.42 offers superior elongation (20% vs 17% in 8"), better formability for cold bending operations .
Carbon Content: Gr.55 permits higher carbon (0.25% max vs 0.21% max), increasing strength but slightly reducing weldability margin .
Weldability: Both are weldable with E7018 electrodes for thicknesses under 1.5"; Gr.55's higher carbon may require marginally more preheat control in thick sections .
Applications & Cost: Gr.42 suits light-load, cost-sensitive structures; Gr.55 is specified for moderate to high-stress applications where enhanced strength justifies premium pricing.
ASTM A572 Gr.42 Chemical Composition
|
Element |
Composition (%) |
|---|---|
|
Carbon (C) |
≤ 0.21 |
|
Manganese (Mn) |
≤ 1.35 |
|
Phosphorus (P) |
≤ 0.04 |
|
Sulfur (S) |
≤ 0.05 |
|
Silicon (Si) |
≤ 0.40 |
|
Vanadium (V) |
≤ 0.01-0.15 |
|
Columbium (Nb) |
≤ 0.005-0.05 |
|
Copper (Cu) (optional) |
≥ 0.20 |
ASTM A572 Gr.55 Chemical Composition
|
Element |
Composition (%) |
|---|---|
|
Carbon (C) |
≤ 0.25 |
|
Manganese (Mn) |
≤ 1.35 |
|
Phosphorus (P) |
≤ 0.04 |
|
Sulfur (S) |
≤ 0.05 |
|
Silicon (Si) |
≤ 0.40 |
|
Vanadium (V) |
0.01-0.15 |
|
Columbium (Nb) |
0.005-0.05 |
|
Copper (Cu) (when specified) |
≥ 0.20 |
ASTM A572 Gr.42 Mechanical Properties
|
Property |
Value |
|---|---|
|
Yield Strength (Min) |
290 MPa (42 ksi) |
|
Tensile Strength |
415 MPa (60 ksi) min |
|
Elongation (in 200mm) |
≥ 20% |
|
Elongation (in 50mm) |
≥ 24% |
|
Charpy Impact (at 0°C, optional) |
≥ 27 J |
ASTM A572 Gr.55 Mechanical Properties
|
Property |
Value |
|---|---|
|
Yield Strength (Min) |
380 MPa (55 ksi) |
|
Tensile Strength |
485 MPa (70 ksi) min |
|
Elongation (in 200mm) |
≥ 17% |
|
Elongation (in 50mm) |
≥ 20% |
|
Charpy Impact Toughness (at 0°C, optional) |
≥ 27 J |
