Effect of post weld heat treatment on microstructural and mechanical properties of martensitic heat-resistant steel weldments

Martensitic heat-resistant steel (MHRS) serves as an important structural material for manufacturing ultra-supercritical unit due to its excellent fatigue resistance and corrosion resistance. Post weld heat treatment (PWHT) is a common method for regulating the microstructure and properties of MHRS welded parts. In this work, we investigated the influence of different PWHT methods on the microstructure, mechanical properties, and room temperature creep properties of Co3W2 welded joints. The results showed that post-weld direct tempering (PWDT) or post-weld re-automatizing and tempering (PWNT) treatment significantly reduces the differences in microstructure and local mechanical properties of as-welded joints. Compared to the as-welded specimens, the PWDT and PWNT welds show lower strength and hardness, but better impact resistance. The PWNT treated welds show more homogeneous microstructure and local mechanical performance, and better tensile property and impact resistance than PWDT welds. Furthermore, the fine grain heat affected zone in PWNT welds shows the smallest strain rate sensitivity value, which implies the PWNT method may alleviate type IV brittle fracture in martensitic heat-resistant steel weldments.