Relationship between creep behavior and microstructure in martensitic heatresistant 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 trans mission electron microscopy. Applied stress assists the recovery of martens ite at high temperature: Dislocation density is markedly decreased and Ostw ald growth of M23C6 type carbide is promoted. Creep deformation behavior st rongly depends on these microstructural changes in lath martensitic structu re. In the early stage of creep test, M23C6 type carbide particles precipit ate along lath boundary and form rod-like carbide. Such a carbide effective ly suppresses the movement of dislocations and contributes to the holding o f creep strength. But once the rod-like carbide is separated through Ostwal d growth of carbide particles during creep deformation, dislocations become easy to move and the recovery of martensite proceeds rapidly. This leads t o an acceleration of the creep deformation.