Microstructural evolution and mechanical properties of friction stir welded 12Cr-ODS steel

Abstract

Abstract 12Cr oxide dispersion strengthened (ODS) steel was welded by friction stir welding (FSW) method. The weld joint is composed of heat-affected zone (HAZ), advancing side thermo-mechanically affected zone (AS-TMAZ), retreating side thermo-mechanically affected zone (RS-TMAZ) and stir zone (SZ). Electron back scattering diffraction (EBSD) results reveal that dynamic recrystallization occurs in SZ and AS-TMAZ, and the size and orientation of the grains change drastically compared with base mental (BM). Structures transfer from elongated grains in BM towards equiaxed grains in SZ. The dynamic recrystallization process is accompanied by a transition from low angle boundaries (LAB) to high angle boundaries (HAB). In SZ, parts of oxide particles are found to agglomerate together. High compressive stress exists in all the FSW joint region, and two peaks are detected in AS-TMAZ and RS-TMAZ, respectively. Compared with the hardness of BM (295 HV), the hardness of SZ increases obviously, and the highest value is up to 350 HV.