A review on heat affected zone softening of dual-phase steels during laser welding

The usage of dual-phase (DP) steels in the production of laser-welded blanks in the automotive industry is of critical importance to the progression of passenger safety and crashworthiness of modern vehicles while at the same time pushing for weight savings to improve the fuel efficiency of these cars. DP steels have been in use for over four decades. During their first introduction into the automotive industry, the steels had limited use for wheel rim applications. Since then, their usage in the automotive industry has grown exponentially, with DP steels now being used for a multitude of crash critical applications as part of the overall material mix used for automotive design. However, as we strive towards continuous improvement ideologies and lean manufacturing philosophies, it has become critical to fine-tune existing processes to the finest degree. To accomplish these goals, the present work provides a critical review of one of the most impotant problems associated with the laser welding of DP steels – an issue that is commonly known as the heat-affected zone softening phenomenon, which is a consequence of the in-situ tempering of the steel's martensite-containing microstructure during laser welding. This review provides a survey of the literature on HAZ softening during laser welding and summarizes the major findings on this subject to identify several significant solutions to this issue while identifying potential areas of interest that should be investigated further to help minimize or mitigate this issue.