Abstract
It is well known that the refractory elements (Mo, W, Re) play an important role in increasing the creep strength of heat resistant ferritic steels. However, the long-term creep strength of the ferritic steels depends on a number of factors, e.g., phase stability of the martensite, the diffusivity of alloying elements, the coarsening rate of precipitates in the steels, etc. Therefore, it is important for the future alloy design to make it clear the main factor influenced by the refractory elements. The purpose of this study is to examine the effect of the refractory elements only on the phase stability of martensite itself. For this purpose, the microstructure evolution was investigated using quaternary martensitic steels: Fe-Cr-C-X (X: Mo, W, Re). It was found that the microstructure evolution was retarded by the Re addition, since Re worked to increase the phase of the martensite and also to suppress the carbide (M 2 3 C 6 ) agglomeration during tempering. On the other hand, it was suggested that W could suppress the recovery of defects such as dislocations in the martensite phase.
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