Microstructural evolution and creep-rupture life estimation of high-Cr martensitic heat-resistant steels

The creep behavior of high-Cr martensitic heat-resistant steels was investigated to discuss the dominant factors determining the creep-rupture life in the temperature range from 839 to 894 K. Variation in the content of Nb, a carbide former, induced a difference in creep-degradation at the long-term creep condition, which was attributed to the formation of a Z-phase at the expense of M2N precipitates. Due to the continuous evolution of the microstructure during creep service, a simple form of the Monkman-Grant equation could not properly describe the creep-rupture life of the alloys; however, the modified Monkman-Grant equation, which incorporates the creep rate at the tertiary creep region, resulted in a reasonable estimation of creep-rupture life.