High strength, low carbon, Cu containing steel plates with tailored microstructure and low yield ratio

A steel composition substantially leaner than that of HSLA-100 was proposed in an earlier work to produce thick plates with mechanical properties equivalent to that of HSLA-100. The present work was to improve the ratio of yield strength to ultimate tensile strength, which was higher than 0.95 in the previous studies. A low carbon MnCrMoNiCu 320 mm thick steel slab was rolled by thermomechanical control processing into a 50 mm mother plate. Daughter plates were subjected to two kinds of heat treatments, respectively, conventional reheating, water quenching and tempering (QT) and reheating and water quenching was followed by intercritical annealing, water quenching and tempering (QLT). The effect of tempering on microstructure and mechanical properties was investigated. The results indicate that QLT is effective to produce heavy plates with yield strength >690 MPa and secured Charpy V notch toughness more than 150 J at -08 degrees C and yield ratio lower than 0.83.