Creep behavior and structure evolution of an advanced 9Cr-1.5Mo-1Co-VNbBN heat-resistant steel at elevated temperature

The creep behavior and structure evolution of an advanced ultra-supercritical 9Cr-1.5Mo-1Co-VNbBN martensitic steel were investigated at temperatures of 620 degrees C and 650 degrees C. The microstructure before and after creep was observed by optical microscopy and transmission electron microscopy. It was shown that high temperature and high stress promoted the recovery of the laths and the growth of the secondary phases. The spheroidal precipitation of M23C6 within the sample which crept at 620 degrees C for 1994 h/5075 h and 650 degrees C for 942 h, grows continuously with increasing creep time and temperature, as results of atom diffusion at high temperature and plastic flow, while MX particles maintained high stability. Laves phase of Fe2Mo precipitated and grew rapidly into large size of samples after the creep and aging exposure at 620 degrees C for 1994 h and more, resulting in a negative effect on the creep resistance of the steel.