ASTM A572 - High-Strength Low-Alloy Steel

Available Grades & Properties

A572 is available in multiple grades designated by minimum yield strength in ksi:

• Grade 42: 290 MPa (42 ksi) yield strength
• Grade 50: 345 MPa (50 ksi) yield strength - Most common
• Grade 55: 380 MPa (55 ksi) yield strength
• Grade 60: 415 MPa (60 ksi) yield strength
• Grade 65: 450 MPa (65 ksi) yield strength

Tensile Strength (Grade 50): 450-620 MPa

Key Characteristics

• Higher strength than A36 - ~40% increase in yield strength (Gr 50)
• Better atmospheric corrosion resistance - Due to alloying elements
• Good weldability - Suitable for all common welding processes
• Reduced weight - Higher strength allows thinner sections
• Cost-effective - Good balance of strength and economy

Applications

• Bridge structures and components
• High-load beams and columns
• Crane booms and heavy lifting equipment
• Heavy buildings and industrial structures
• Transmission towers
• Railway cars and wagons
• Offshore structures
• Mining equipment frames

Chemical Composition (Grade 50, Typical)

Carbon (C): ≤0.23%

Manganese (Mn): ≤1.35%

Phosphorus (P): ≤0.04%

Sulfur (S): ≤0.05%

Silicon (Si): ≤0.40%

Vanadium (V): 0.01-0.15% (for grain refinement)

Niobium (Nb): 0.005-0.05% (optional, for strength)

Advantages

• Weight savings - Higher strength allows reduced material thickness
• Improved corrosion resistance - Better than plain carbon steel
• Excellent weldability - No special procedures required
• Good formability - Can be bent and formed with proper equipment
• Wide availability - Commonly stocked grade

Processing Characteristics

Cutting: Can be cut using all standard methods. Plasma and laser cutting recommended for precision work.

Forming: Good formability, though slightly more difficult than A36 due to higher strength. Cold forming possible with appropriate equipment.

Welding: Excellent weldability with SMAW, GMAW, FCAW, and SAW processes. Preheat may be required for thick sections (>40mm) or low temperatures.

Machining: Moderate machinability. Carbide tooling recommended for production work.

Grade Selection Guide

Grade 42: Light structural applications, similar strength to A36 but with better corrosion resistance.

Grade 50: Most popular grade. Ideal for general high-strength structural work, bridges, and buildings.

Grades 55-65: Specialized high-strength applications where maximum weight reduction is needed.

Comparison with Other Grades

vs. A36: A572 Gr 50 offers ~40% higher yield strength, better corrosion resistance, but slightly higher cost and lower formability.

vs. A992: A992 is optimized for W-shapes (I-beams) with controlled chemistry for better weldability. A572 is more versatile for plates and shapes.

vs. S355 (EN): A572 Gr 50 and S355 are roughly equivalent in strength and applications.

Best for: Bridges, high-load structural members, and applications requiring higher strength than A36 with good weldability and atmospheric corrosion resistance.

Design Considerations

Temperature Service: Suitable for service down to -45°C with proper material selection and impact testing.

Thickness Range: Commonly available from 6mm to 200mm depending on grade.

Corrosion Protection: While more resistant than A36, still requires painting or coating for long-term outdoor exposure.