1. Why Quenching Alone Harms S355J0WP's Properties
Martensite raises the ductile-brittle transition temperature (DBTT) by 50–80°C, making the steel prone to brittle fracture even at room temperature (let alone the "J0" grade's required 0°C).
It drastically reduces impact toughness: Quenched S355J0WP may have 0°C impact energy <10 J (far below the 27 J minimum), failing basic performance standards.
2. Tempering Cannot Fully Rescue Toughness, and Risks Weather Resistance
Insufficient toughness recovery: Even after high-temperature tempering (550–650°C), the tempered martensite/bainite microstructure retains higher brittleness than the steel's original ferrite-pearlite structure. The 0°C impact energy typically only recovers to 15–20 J-still below the 27 J requirement.
Degraded weather resistance: S355J0WP relies on Cu and Cr to form a dense protective rust layer. High-temperature tempering (above 500°C) can cause Cu/Cr to precipitate as coarse carbides, breaking the continuity of the rust layer and reducing corrosion resistance by 30–40%.
3. Better Alternatives to Q&T for S355J0WP
These processes refine the ferrite-pearlite microstructure (no brittle martensite formation) and improve 0°C impact energy to 35–50 J (exceeding the J0 grade requirement) without harming weather resistance.
