Effect of simulated cooling time on microstructure and toughness of CGHAZ in novel high-strength low-carbon construction steel

Abstract

Influences of cooling time (welding heat input) on microstructure, impact toughness and the fracture mechanism of the weakest CGHAZ (coarse-grained heat-affected zone) in a novel high-strength low-carbon microalloyed construction steel were studied for the purpose of laying a theoretical foundation for developing welding support technologies. When the cooling time (t8/5) was increased, the microstructure changed from dot shape M-A constituents and lath martensite/bainite to slender and blocky M-A constituents and coarse granular bainite. Accordingly, the impact toughness deteriorated. Large blocky M-A constituents seriously reduced the impact absorbed energy during crack initiation. For coarse bainite, the high-misorientation boundary almost disappeared. Therefore, crack initiation energy determines the cleavage fracture micromechanism of high heat input construction steel.