Relationship between creep behavior and microstructure in martensitic heat resistant steel

Relationship between creep deformation behavior and microstructural change has been investigated in a 12%Cr-0.12%C steel by means of optical and transmission electron microscopy. Applied stress assists the recovery of martensite at high temperature: Dislocation density is markedly decreased and Ostwald growth of M₂₃C₆ type carbide is promoted. Creep deformation behavior strongly depends on these microstructural changes in lath martensitic structure. In the early stage of creep test, M₂₃C₆ type carbide particles precipitate along lath boundary and form rod-like carbide. Such a carbide effectively suppresses the movement of dislocations and contributes to the holding of creep strength. But once the rod-like carbide is separated through Ostwald growth of carbide particles during creep deformation, dislocations become easy to move and the recovery of martensite proceeds rapidly. This leads to an acceleration of the creep deformation.