Microstructure and properties of the interlayer heat-affected zone in X80 pipeline girth welds

The heat-affected zone between the layers of a weld metal is a sensitive and important component of girth welds in X80 pipelines. However, only a few studies have focused on the interlayer heat-affected zone (IHAZ). In this work, thermal simulation was conducted to investigate the relationship between IHAZ microstructure and properties. Results showed that the toughness of the weld metal improved after a single welding thermal cycle but decreased after double welding thermal cycles, particularly when the weld metal was subjected to unaltered coarse grains of IHAZ. The relationship between the microstructure and properties of IHAZ was established to present the correlation of toughness with granular bainite content, grain size, and high-angle grain boundary content.