ASTM A572 Grade 50 and Grade 55 are High-Strength Low-Alloy (HSLA) steel plates for structural uses, differing mainly in strength; Grade 50 has a minimum yield strength of 50 ksi (345 MPa), while Grade 55 offers higher strength with a minimum yield of 55 ksi (380 MPa), both providing good strength-to-weight, formability, and weldability for applications like bridges, towers, and construction equipment, with Grade 50 being the most common.
Chemical Composition of A572 Grade 50
| Chemical | Composition |
|
Carbon max |
0.23% |
|
Manganese max |
1.35% |
|
Phosphorus max |
0.030% |
|
Sulfur max |
0.030% |
|
Silicon to 1 1/2" thick. max |
0.40% |
|
Silicon over 1 1/2" thick |
0.15-0.40% |
Chemical Composition of A572 Grade 55
|
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 |
Mechanical Properties of A572 Grade 50
|
Grade |
Thickness |
Yield strength |
Tensile strength |
Elongation in 2" 1) |
Elongation in 8" 1) |
|---|---|---|---|---|---|
|
ASTM A572 Grade 50 |
0.100 - 4.00 |
50 |
65 |
21 |
18 |
Mechanical Properties of A572 Grade 55
|
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 |
Key Features
Good Weldability: Suitable for welded, bolted, or riveted structures.
Formability: Can be cold-formed but may require pre-testing due to alloying.
Corrosion Resistance: Offers standard atmospheric corrosion resistance; coatings (paint, galvanizing) are recommended for harsh environments.
