Effect of Annealing Temperature on Microstructure Evolution, Tensile Property and Deformation Behavior of Electron Beam Welded S32101 Joints

In this paper, the effect of post-weld heat treatment (PWHT) on the microstructure and mechanical properties of the electron beam welding (EBW) joints was studied. The deformation behavior and fracture mechanism of the annealed joint was analyzed by the in-situ EBSD technology. The results demonstrated that the tensile properties of the EBW joints could be greatly improved by PWHT, especially the elongation increased from 8.0% without PWHT to 25.3% after annealing at 1080 ℃, and the tensile strength (TS) increased from 683 MPa to 727 MPa. After annealing, the texture of the ferrite was weakened. During in-situ tensile, a phase boundary was formed at the sharp corner of Widmanstätten austenite (WA) and the surrounding ferrite in accordance with the Nishiyama-Wassermann (N-W) orientation relationship, and the KAM value of ferrite near the phase boundary increased, with obvious stress concentration. Moreover, cracks nucleated and propagated at the interface between grain boundary austenite (GBA) and ferrite, and obvious necking occurred in the heat affected zone (HAZ) of the joint. Meanwhile, the original Kurdjumov-Sachs (K-S) boundaries changed into N-W boundaries with the increase of strain in the WA. The improvement of tensile properties could be attributed to the effects of an increase in austenite’s content and the twinning induced plasticity (TWIP) effect generated by austenite.