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ASTM A913
Quenched and Self-Tempered (QST) High-Strength Low-Alloy Structural Steel Shapes
Overview
ASTM A913 covers a revolutionary category of structural steel called Quenched and Self-Tempered (QST) sections. Unlike conventional steel that requires controlled rolling or post-production heat treatment, QST steel achieves exceptional strength and toughness through an in-line heat treatment process during production. This results in 50 ksi, 65 ksi, or 70 ksi minimum yield strength with superior toughness properties throughout the entire cross-section, not just at the flanges.
Key Requirements
- Minimum yield strengths: Grade 50 (345 MPa), Grade 65 (450 MPa), Grade 70 (485 MPa)
- Charpy V-notch toughness: 40 ft·lbf at 70°F for seismic applications
- Through-thickness properties uniform across entire cross-section
- Maximum carbon equivalent for excellent weldability
- Available in W-shapes up to W14×550
Primary Building Applications
- Seismic moment frames in high seismic zones
- Blast-resistant structures requiring high toughness
- Column base plates and connections in cold climates
- Long-span trusses where weight reduction is critical
- Architecturally exposed structural steel (AESS) applications
Advantages Over Conventional Steel
The QST process creates uniform properties through the entire thickness, eliminating the "k-area" weakness found in conventional rolled sections where the web-to-flange junction has lower strength. This makes ASTM A913 particularly valuable for seismic design where plastic hinge formation must be predictable and reliable. The steel's high toughness at service temperatures also eliminates concerns about brittle fracture, even in extreme cold or under impact loading.
Design Considerations
While A913 costs more than conventional A992 steel, it enables smaller member sizes and reduced tonnage for the same strength requirements. This can offset material costs through savings in shipping, handling, and connection fabrication. For seismic applications, A913 Grade 65 or 70 can eliminate the need for doubler plates and continuity plates in moment connections, significantly reducing fabrication costs.