Impact of Post-Weld Heat Treatment on the Microstructural and Mechanical Behavior of API X70 Steel

The global advancement in scientific research within the petroleum sector, particularly in transportation methods, has driven interest in understanding the welding characteristics of petroleum pipelines. This study provides an experimental evaluation of the effects of heat treatments on the mechanical and microstructural properties of welded API X70 steel. Specifically, it investigates the influence of varying heat treatment conditions on the fusion zone (FZ) of API X70 steel welds. The heat treatment process was carried out at temperatures ranging from 450℃ to 650℃, in increments of 50℃, with each temperature maintained isothermally for 2 hours. Comprehensive characterization techniques, including optical microscopy, scanning electron microscopy (SEM), and X-ray diffraction (XRD), were employed to analyze the microstructural evolution. Additionally, Vickers hardness testing was conducted to evaluate the mechanical response. The results demonstrated that increasing the heat treatment temperature promoted grain coarsening and growth within the fusion zone, accompanied by a progressive decline in the hardness of the weld joints. These findings highlight the critical role of heat treatment parameters in tailoring the performance of welded pipelines.