Abstract
In this study, neutron diffraction mapping was performed on linear friction welded joints of a 12 mm thick high-phosphorus weathering steel (SPA-H) to evaluate the distribution of residual stress, dislocation density and crystallographic orientation. Linear friction welding (LFW) was conducted under two applied pressures (100 MPa and 250 MPa). The welded interface primarily consisted of refined ferrite with minor retained austenite and martensite, suggesting that peak temperatures during welding exceeded the A1 point (the eutectoid transformation temperature) and induced reverse transformation to austenite. However, the joint produced at 250 MPa exhibited a lower welding temperature. At the weld region, grains near the specimen surface were elongated along the oscillation direction (OD), whereas equiaxed grains appeared at the center in both thickness and width directions. Inhomogeneous microstructural distributions were observed near the interface along OD. Both joints exhibited high tensile residual stresses in all directions at the weld center, while compressive residual stresses developed near the surface in the direction perpendicular to the weld interface. The applied pressure had minimal influence on the overall residual stress distribution trend within the tested welding conditions. Dislocation density at the weld interface was higher than that in the base metal, and the increase was more pronounced under higher applied pressure. This is attributed to suppressed dynamic recovery caused by the lower welding temperature at higher pressure. Finally, strong texture formation was observed at the weld interface due to plastic flow during welding. The applied pressure had only a limited effect on texture development.
