Study on the microstructure and properties of welded joint of 32 and 50 mm thick Q690 high strength bridge steel plates

The microstructure and properties of submerged arc welded joints of 32 mm and 50 mm thick steel plates prepared by thermo-mechanical control process (TMCP) and quenching and low-temperature tempering (QLT) were studied. The coarse grain heat affected zone (CGHAZ) in the welded joint was composed of granular bainite (GB) and lath bainite (LB), with the highest hardness and coarser prior austenite grains. The CGHAZ had a high content of large angle grain boundaries, which was conducive to its impact toughness. The base metal was composed of martensite and ferrite, and its microstructure was distributed along the rolling direction. The microstructure of the fine grain heat affected zone (FGHAZ) was ferrite and a small amount of GB, and the hardness of FGHAZ was the lowest.