EBSD Study of the Effect of Post-weld Intercritical Annealing on the Microstructure and Micro-texture of a Friction Stir Welded DP600 Steel

In the present study, effect of a post-weld intercritical annealing (PWIA) on the microstructure and micro-texture of a friction stir-welded DP600 steel was investigated by means of optical microscopy and electron backscatter diffraction. For this purpose, DP600 steel sheets were butt-welded together using friction stir welding. The weldment was then annealed at the intercritical temperature of 720 °C for 120 s followed by water quenching. Results showed that despite differences in the microstructure in the as-weld condition, a dual phase microstructure of ferrite and martensite was developed in all regions after PWIA. Formation of bainite and Widmanstatten ferrite in the heat affected zone (HAZ) and stir zone (SZ) of the as-weld sample resulted in the increase in the kernel average misorientation (KAM) value. The KAM value remained high after PWIA despite the transformation of microstructure to ferrite and martensite. Strong α and γ components were observed in the texture of the HAZ in the as-weld condition, while the SZ showed shear texture components of D, E and cube. The texture components remained the same after PWIA, but the overall texture intensity decreased.