Effect of thermo-mechanical treatment on microstructure and mechanical properties of P92 heat resistant steel

The effect of thermo-mechanical treatment on the microstructure and mechanical properties of commercial P92 steel was investigated. The steels were warm-rolled in metastable austenitic state with reductions of 75 and 93%, respectively. Tempering in a certain temperature range from 650 to 765 °C for 1 h was subsequently used to optimize the size of precipitates and form a homogeneous steady-state dislocation structure through recovery process. The results showed that the microstructure was obviously refined and a great amount of nano-scale precipitates were increased significantly compared to the as-received material. The tensile strengths and microhardness were significantly improved by increasing plastic deformation and tempering at 650 and 700 °C, but were decreased dramatically after tempering at 765 °C. The creep tests were carried out at 600 °C under 210 MPa and at 650 °C under 160 MPa. The results demonstrated that the creep rupture life of the thermo-mechanical treated P92 steel was improved significantly. High density of homogeneously distributed precipitates reduced creep rates by pinning the grain boundaries and blocking the motion of dislocation.