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*

Neutron diffraction mapping was conducted on linear friction welded joints of 12 mm thick high-phosphorus weathering steel (SPA-H) to evaluate residual stress, dislocation density, and crystallographic orientation. Welding was performed at 100 MPa and 250 MPa. The weld interface mainly comprised refined ferrite with retained austenite and martensite, indicating temperatures exceeded A1 and induced reverse transformation. The 250 MPa joint showed a lower welding temperature. Elongated grains formed near the surface along the oscillation direction (OD), while equiaxed grains appeared at the center. High tensile residual stresses were found at the weld center, with compressive stress near the surface perpendicular to the weld. Pressure had little effect on overall stress trends. Dislocation density increased with pressure due to suppressed dynamic recovery. Strong texture developed at the interface, with limited pressure dependence.