PRECIPITATION BEHAVIOR OF MN(M=V,NB) PHASE IN THE 7CR-1.5MO FERRITIC HEAT RESISTANT STEELS

The relationship between precipitation behavior of MX(M=V, Nb) nitrides and mechanical property during aging in 7Cr-1.5Mo ferritic heat resistant steels were investigated in this study. Artificial aging was carried out at 700 degrees C for different time from 100 to 10000 hours to simulate the environment of fossil power plant. The Ostwald ripening equation is related to the containing elements can explain the accelerated coarsening of MX in the model alloys. The Ostwald ripening equation was modified by introducing the effective diffusion coefficient as a sum of the lattice diffusion coefficient and dislocation diffusion coefficient, based on an assumption that V, Nb and Ti might diffuse not only by the lattice diffusion mechanism but also by the dislocation diffusion mechanism.