Effect of post-weld heat treatment on microstructure, hardness and low-temperature impact toughness of electron beam welds of NIFS-HEAT-2 and CEA-J57 heats of V-4Ti-4Cr alloy

Bead-on-plate electron beam welding in high vacuum atmosphere was applied to the plates of NIFS-HEAT-2 and CEA-J57 heats of V-4Ti-4Cr alloy. Effect of post-weld heat treatment (PWHT) in the temperature range 673-1273 K on the hardness, impact toughness at 77 K and microstructure of weld metal was investigated. After PWHT at 773 K, hardness of weld metal slightly decreases from 180 HV100 (as-welded state) to ∼170 HV100 while absorbed energy increases up to ∼10 J showing ductile fracture mode. PWHT at 973 K results in re-hardening of weld metal up to ∼180 HV100 caused by re-precipitation of Ti-C,O,N precipitates and corresponding decreasing absorbed energy to ∼2 J with brittle fracture mode. PWHT in-between 1073-1273 K results in gradual recovery of hardness towards values comparable with those of base metal. Impact toughness (77 K) of weld metal after PWHT at 1073K is not recovered nether to the value in as-welded state nor to that one of base metal.