Laser Welding of Boron and Bainitic Steels

This work was concerned with the development of welding procedures for joining of thinultra high strength sheets, using an ytterbium fiber laser with a power of 4KW. Sheet thicknesses of 4 and 5 mm were tested for boron steels and the bainitic steels had a thickness of 5 mm. The sheet materials have a tensile strength of 1500 MPa and an average hardness of 480HV0.5 . The softening and hardening behavior respectively and hot and cold cracks weredetermined. Influence of quenching and partitioning heat-treatment with induction-heater in Laser welding with constant parameters was discussed. The steel in this work had carboncontents of 0.22%, 0.24% and 0.3% and Boron content of 0.0032% for increase of strength and hardenability of the materials. The fusion zone shows hardness values up to 587HV0.5 with martensitic microstructures if it is welded without any pre-or post-weld heat treatments.Different post weld heat treatment will decrease the hardness values. The results show that the microstructure of HAZ and weld metal consists of low carbon martensite and bainite. Although the grain size of the heat affected zone and weld metal has increased but the steels still have excellent strength.Validerat; 20120620 (cani