The influence of long-term thermal exposure on microstructural stabilization and mechanical properties in 9Cr-0.5Mo-1.8 W-VNb heat-resistant steel

A series of long-term thermal aging experiments on P92 steel were carried out at 650 °C from 200 h up to 1.1×10⁴ h. Microstructural evolution of the samples during long-term aging exposure was investigated using OM observations, SEM examinations and TEM investigations. Additionally, variations of mechanical properties, including tensile properties, Charpy impact toughness and Vickers micro-hardness were also exhibited. Experimental results indicate that martensitic lath structure, M₂₃C₆ carbides as well as MX carboniterides all exhibit a high stability during short-term aging exposure, whereas Laves phase grows rapidly in this period. After the long-term aging treatment, the recovery of martensitic lath structure occurs after an incubation period, which is resulted from the continuous growth and coarsening of M₂₃C₆ and Laves phase. Based on the correlations between the microstructural evolution and the variations of mechanical properties during long-term aging exposure, the degradation mechanism of P92 steel was discussed.