Evaluation of residual stress distribution in linear friction welded steel joint neutron diffraction mapping measurement

Yamashita, Takayuki*; Nagira, Tomoya*; Gong, W.   ; Kawasaki, Takuro   ; Harjo, S.   ; Ushioda, Kosaku*; Fujii, Hidetoshi*

In this study, neutron diffraction mapping was performed on linear friction welded (LFW) joints of 12 mm thick high-phosphorus weathering steel (SPA-H) to evaluate residual stress, dislocation density, and crystallographic orientation. Welding was conducted under applied pressures of 100 and 250 MPa. The weld interface mainly consisted of refined ferrite with minor retained austenite and martensite, indicating reverse transformation to austenite during welding. The 250 MPa condition resulted in a lower welding temperature. Elongated grains were observed near the surface along the oscillation direction, while equiaxed grains appeared at the center. Both joints showed high tensile residual stresses at the weld center and compressive stresses near the surface. Higher applied pressure increased dislocation density because of suppressed dynamic recovery. Strong texture formation due to plastic flow was observed, while the effect of applied pressure on texture development was limited.