The Microstructure and Toughness of HAZ in Low Carbon Ti-Nb Series Steels after Welding

Effects of cooling rate (t_8/5) during simulated welding thermal cycle on the microstructures and toughness of HAZ in two series Ti-Nb steels were studied. The morphology, numbers and distribution of ferrite and granular bainite, especially M-A constituent in HAZ at different cooling rate (t_8/5) were observed by optical and electron microscopes. The relation between microstructures and impact toughness in different cooling rates was analysised. The actions of added microalloying elements Ti, Nb and N on improving microstructures and toughness of HAZ in specimens was discussed.