Precipitation behavior in a nitride-strengthened martensitic heat resistant steel during hot deformation

The stress relaxation curves for three different hot deformation processes in the temperature range of 750-1000 °C were studied to develop an understanding of the precipitation behavior in a nitride-strengthened martensitic heat resistant steel. The first sharp jump in the stress relaxation plots was assumed to be indicative of the commencement of precipitation in this paper, according to the abrupt change in ∂σ/∂t curve and the microstructure observation of the samples. The precipitation revealed by the stress jumps in the stress relaxation plots was further studied by transmission electron microscopy (TEM), X-ray diffraction (XRD) analysis, and energy dispersive X-ray analysis (EDAX). The results confirmed that, under the deformation situation of “Group C”, almost all the Nb atoms would precipitate as Nb(C,N) particles at its optimum precipitation temperature of 940 °C; Nearly all the C+N atoms would be consumed in forming M23C6 particle at its nose precipitation temperature of 800 °C; only 60% V atoms would deposit as V(C,N) particles at its fastest nucleation temperature of 750 °C.