Effects of Cu-rich phases on microstructure evolution and creep deformation behavior of a novel martensitic heat-resistant steel G115

In this work, effects of Cu-rich phases on the microstructure evolution and creep deformation behavior of G115 steels with 1 (1Cu steel) and 2 wt% Cu (2Cu steel) were systematically investigated under 160–220 MPa at 650 °C. The results showed that dispersedly distributed Cu-rich phases played a vital role in retarding the microstructural degeneration and improving the creep strength. The Cu-rich phases inside grains could induce dislocation tangle and prohibit dislocation annihilation during creep, but they could be dissolved into the matrix due to the cutting effect of mobile dislocation lines. The Cu-rich phases at grain boundaries could hinder the migration of martensitic lath boundaries and thus delayed the creep failure behavior. Moreover, the independent Cu-rich phases at grain boundaries could provide heterogeneous nucleation sites for Laves phases, which strengthening pinning effect. As a result, compared with the 1Cu steel, the creep threshold stress of the 2Cu steel was enhanced from 103.36 to 117.93 MPa, and the creep lifetime was also prolonged markedly.