ASTM A514 Grade B steel is a high-strength, quenched & tempered Alloy steel plate primarily used in structural applications requiring exceptional strength-to-weight ratio:
High Strength (Primary Feature):
Minimum Yield Strength (Rp0.2): 100 ksi (690 MPa) - This is significantly higher than common structural steels like A36 (36 ksi) or A572 Grade 50 (50 ksi).
Minimum Tensile Strength (Rm): 110 - 130 ksi (760 - 895 MPa)
Typical Hardness: 235 - 293 HB (Brinell Hardness)
Ductility:
Minimum Elongation in 2 inches (A2): 16% (in longitudinal direction) / 14% (in transverse direction) - Good for a steel of its strength level.
Toughness:
Charpy V-Notch Impact Energy: Minimum 40 ft-lb (54 J) average at -50°F (-46°C) (test temperature varies slightly by thickness). This excellent low-temperature toughness is critical for demanding structural applications.
Chemical Composition (Typical Ranges - ASTM A514 specifies maximums):
Carbon (C): 0.12 - 0.21%
Manganese (Mn): 0.60 - 1.00%
Phosphorus (P): ≤ 0.035%
Sulfur (S): ≤ 0.030%
Silicon (Si): 0.15 - 0.35%
Chromium (Cr): 0.40 - 0.80%
Molybdenum (Mo): 0.15 - 0.25%
Boron (B): 0.0005 - 0.003% (Crucial for hardenability)
Vanadium (V): ≤ 0.03 - 0.08% (sometimes added)
Processing:
Thermal Treatment: Supplied in the Quenched and Tempered (Q&T) condition. This heat treatment process (rapid cooling followed by reheating to a specific temperature) is essential to achieve its high strength and toughness combination.
Weldability:
Moderate to Difficult. Due to its high carbon equivalent (CE) and hardenability:
Carbon Equivalent Formula (ASTM A514): CE = C + Mn/6 + (Cr + Mo + V)/5 + (Ni + Cu)/15
Typical CE: 0.50 - 0.65 (High)
Requires strict procedures: Preheating (often 300-400°F / 150-200°C depending on thickness), interpass temperature control, low-hydrogen electrodes (AWS E11018M or similar), and often Post Weld Heat Treatment (PWHT) for thicker sections or critical applications to prevent hydrogen-induced cracking (HIC) and reduce residual stresses.
Machinability:
Fair to Poor. Its high hardness makes it harder to machine than lower-strength steels, requiring slower speeds and feeds and robust tools/carbide inserts.
Corrosion Resistance:
Comparable to other low-alloy steels like AISI 4130. Not corrosion-resistant. Requires protective coatings (paint, galvanizing) for long-term service in most environments.
Key Applications (Driven by High Strength/Weight Ratio):
Crane Booms & Structural Components
Heavy Equipment Frames & Buckets (Excavators, Loaders)
Platform Structures
Mine Shoring and Support Systems
Bridge Components (Especially high-strength applications)
Mobile Equipment Frames & Chassis
Military Vehicle Components
Structural components where weight savings are critical
Advantages:
Excellent strength-to-weight ratio.
Good ductility for its strength level.
Excellent notch toughness at low temperatures.
Disadvantages/Cautions:
Higher cost than lower-strength carbon steels.
Complex welding procedures required.
Limited thickness availability (generally up to 6.25 inches / 160mm).
Requires corrosion protection.
Equivalents/Similar Steels (Note: Always check exact specifications):
Proprietary Equivalents: T-1 (Bethlehem Steel historical), ArcelorMittal's MARTIN 85, etc.
Similar International Grades: EN 10025-6 S690Q, JIS G3128 SHT690, ISO 4950 E690.
AISI/SAE: Compositionally similar to 4130/4140 but optimized and processed specifically for plate and structural performance.
Summary: ASTM A514 Grade B is a premium high-strength structural steel renowned for its 100 ksi minimum yield strength and excellent low-temperature toughness, achieved through quenching and tempering. Its use demands careful attention to fabrication, especially welding procedures, but offers significant weight-saving advantages over lower-strength steels.
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