Effect of Ti and B on Microstructure of 780 MPa Class High Strength Steel Weld Metal

Abstract

The effect of Ti and B on the microstructure of 780 MPa class high strength steel weld metal was investigated. It was found that the morphology of bainitic ferrite of weld metal was changed from lath-like into acicular type by adding Ti. It was also revealed that the morphology of bainitic ferrite in the Ti bearing weld metal revested to lath-like by adding B. The change of microstructure by the Ti addition could be explained by the promotion of nucleation of acicular type bainitic ferrite, which was bainitic ferrite nucleated at Ti-oxides inside of austenite grains. It was supposed that segregation of free B around Ti-oxides restrained the nucleation of bainitic ferrite on Ti-oxides.