1000MPa급 DP강의 Nd:YAG 레이저 용접부의 미세 조직 및 경도에 미치는 용접 속도의 영향

Effect of Welding Speed on Microstructures and Hardness in Nd:YAG Laser Welding of 1000MPa Grade DP Steel

DP(Dual Phase)steels which consist of ferrite and martensite have not only high strength but also good ductility. So DP steels were used for automotive parts such as bumper or member widely. Application of laser heating-sources in process of automobile assembly is used for many ways because it has safe heating sources, less heating deformation and high speedy welding. In this study, the characteristics of Nd:YAG laser welded 1000MPa grade DP steels with respect to hardness, microstructures were investigated. A shielding gas was not used, and bead-on-plate welding was performed using various welding speeds at a power of 3.5kW. Defects of inner and surface bead were not observed in all conditions of welding speed. Increasing welding speed. bead shape was changed from the trapezoid having wider bottom bead, through X type finally to V type in partial penetration range of welding speed. The characteristic of hardness distribution was investigated. The hardness of laser welded region showed the higher value than base metal, and the maximum hardness was obtained at the HAZ near the WM regardless of welding speed.