Evolution of microstructure and crystallographic texture of high-frequency electric-resistance welded X65 pipeline steel

Abstract

The microstructure and texture evolution in X65 steel pipe high-frequency electric-resistance welding (HF-ERW) zones under as-welded and heat-treated conditions were investigated in this study. Dynamic recrystallization occurs in austenite within the bondline and coarse-grained heat-affected zone (CGHAZ), but in ferrite within the fine-grained heat-affected zone (FGHAZ). The CGHAZ exhibits higher residual stress than the FGHAZ. The thermomechanical-affected zone (TMAZ) exhibits only dynamic recovery and deformation. The grain orientations in the weld zone and matrix were similar under compressive stress direction (weld zone-TD, matrix-ND). Along TD, the bondline, CGHAZ and FGHAZ develop {111} recrystallization textures, whereas TMAZ forms {100}<011> and {111} deformation textures. After heat treatment, the weld zone retains the texture characteristics of the as-welded condition. Conventional heat treatment increases harmful <100>//TD and <110>//TD texture components in the CGHAZ, whereas optimized treatment reduces these components, enhances high-angle grain boundaries, and refines grains. These texture components originate from {110}<001>, {100}<011>, and {110}<110> orientations formed during welding thermo-mechanical processes. They intensify in the CGHAZ after conventional treatment due to residual stresses but weaken after optimized treatment through phase transformation effects. This provides valuable insights into texture development during welding.