EBSD Characterization of Microstructure and Micro-texture in a Friction Stir-Welded DP600 Steel

Abstract

The microstructure and micro-texture in different areas of a friction stir (FS)-welded DP600 steel were investigated by means of electron backscatter diffraction. The volume fraction of martensite and non-polygonal ferrite was evaluated based on the image quality (IQ) parameter. Analysis of grain boundaries revealed that the fraction of sub-grain boundaries as well as that of low-angle grain boundaries in the heat-affected zone (HAZ) and stir zone (SZ) was more than doubled compared to those in the DP600 steel base metal (BM). The micro-texture examination of the BM showed strong {112} < 110 > and {111} < 112 > components with an intensity 4.6 times of that random texture. The texture showed a memory effect in the HAZ, with a reduced overall intensity. Within the SZ, D 1 , D 2 and E shear texture components together with a cube component were developed. Formation of these texture components of ferrite were attributed to the transformation of B and R texture components of prior austenite, which are evidences of continuous dynamic recrystallization mechanism in the SZ of the friction stir-welded DP600 steel.