Microstructures and mechanical properties of creep resistant steel for application at elevated temperatures

The subject of this paper is the microstructural and mechanical characterisation of regions of the heat-affected zone (HAZ) in steels containing 9–12% Cr that are used for operation at elevated temperatures. Tests were performed on regions in the HAZ, which was created by physical simulation using a thermal welding simulator. Half of the simulated samples (SSs) were tested at room temperature (RT) and at an operating temperature (OT) of 600 °C immediately after simulation/welding, while the rest of the simulated samples were tested at RT and at the OT after heat treatment following the welding, i.e., post-weld heat treatment (PWHT). In addition to the results from mechanical testing, the results from microstructural analysis using light microscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) are also presented. The manner in which PWHT contributes to the creep resistance of the HAZ in P91 steel is demonstrated.

► The microstructural and mechanical characterisation of HAZ regions was analysed.
► The thermal welding simulation is used for simulation of HAZ microstructure.
► Testing of the effects of PWHT on microstructure of HAZ soft zone.
► Testing of the effects of PWHT on mechanical behaviour of HAZ soft zone.
► TEM micrographs show precipitates at the boundaries of martensitic laths after PWHT.