Variations in mechanical properties of RAFM steel under vacuum diffusion welding with pre-deformation and subsequent heat treatment

Vacuum diffusion welding (VDW) experiments have been carried out for reduced activation ferritic/martensitic (RAFM) steel at different conditions. Both as-recieved and pre-deformed samples are used for investigating the influence of pre-welding deformation on the mechanical properties of VDW joint and related microstructure evolution. The results show that preferable metallurgical bond is realized and the microstructure is mainly composed of lath martensite and small amount of retained-austenite. The mechanical properties of the joint before and after the post welding heat treatment (PWHT) are measured by tensile test and Charpy impact test. The results show that the tensile strength increases with the increase of temperature, time, and pressure before PWHT. Within the tested range, the tensile strength of the un-deformed sample increases significantly with the increase of pressure, time and temperature during VDW, while the impact fracture toughness is only sensitive to the welding temperature and time. Parameter match of 1050 degrees C,120 min, 15 MPa is considered as the best one considering comprehensive mechanical properties. The tensile strength of the joint increases with the increase of pre-welding deformation when the deformation temperature is above 800 degrees C, but gradually decreases with the increase of the deformation temperature. A combination of 900 degrees C and 0.4 straining is regarded as the optimal.