Effects of Dislocation Substructure on Creep Deformation Behavior in 0.2%C-9%Cr Steel

Abstract

In this paper, microstructural evolution under creep deformation was investigated by using a simple 0.2%C-9%Cr steel to reveal effects of dislocation substructure on creep strength in addition to creep deformation behavior in high Cr martensitic steels. Whereas strain versus creep rate curves are composed of simple primary and tertiary creep stages on the steel tested at higher applied stress condition, complicated variation in creep rate are found on the curves examined at lower stress levels under a temperature of 873 K. Formation of cellular dislocation network substructure is observed in the early periods of the primary creep stage on the steel tested at a lower stress. Such substructure is stable until onset of acceleration creep. The degradation of the substructure is due to coarsening and condensation of the carbides existing along the lath boundaries. An increase in yield stress at elevated temperature and internal back stress in the whole course of the transient creep region are provided by the cellular dislocation network substructure having highly dense dislocation walls where intralath dislocations move and integrate in the early periods after loading. The complicated variation in creep rate at the lower stress conditions is caused by accumulation and partial disappearance of dislocations at cell and lath boundaries. It can be concluded from above results that dislocations act a key role for strengthening against creep deformation.