Influence of post-weld heat treatment on microstructure and properties in heat-affected zone of KMN steel joint

The influence of temperature during post-weld heat treatment on the microstructure and properties of KMN steel joints was investigated. The results reveal that after heat treatment, the martensite transformed to tempered sorbite, causing the softening of the resultant joints. XRD test shows that the residual austenite content decreased obviously when the joint was heat-treated at 550 ℃ and 580 ℃, which degraded the impact toughness of heat-affected zone (HAZ). When the heat treatment temperature increased further, the dispersion strengthening from the precipitation of alloying elements improved the impact toughness of HAZ. The aggregation and coarsening of carbide also contributed to the improvement of impact toughness of HAZ.