Creep behavior, microstructure evolution and fracture mechanism of a novel martensite heat resistance steel G115 affected by prior cold deformation

In this paper, the influences of prior cold deformation on creep behavior, microstructure evolution, and fracture mechanism of the novel G115 steel were systematically investigated. It was found that the creep rupture life of the G115 steel could be significantly prolonged by moderate deformation reduction, which was a synergetic effect of deformation-induced dislocations and dispersed strengthening particles. The optimal deformation reduction was approximately 20%, at which the precipitation of Laves phases could be obviously promoted, and then restricted the coarsening of M23C6 carbides due to the competitive growth relationship. Besides, more nano-sized Cu-rich particles precipitated within lath interior, and obstructed the free dislocation motions. As a feedback, the dislocation recovery and the subgrain formation could be impeded, thus extending the creep rupture life. With the further increase of deformation reduction to 30% or higher, the coarsening of precipitates and the recovery of dislocations were intense, which could facilitate the formation of subgrains and then shorten the creep life. For the G115 steel with a deformation reduction within 30%, the creep damage was identified as microstructural degradation with limited contribution from necking. And, for the steel with a deformation reduction of 45%, the creep damage was cavity growth controlled by power law and diffusion creep.