Heat treatment of sintered porous steels

Heat-treatment features are considered for steels prepared from mechanical powder mixtures The rise in the temperature of the critical point Ac-1 and the fall in the point Ac-3 as the homogeneity of steel increases is described by a linear dependence on the coefficient of concentration variation. A chemically inhomogeneous low-alloy powder steel has the kinetics of the pearlite-austenite transformation limited by the diffusion growth of nuclei. In more homogeneous steels, the limiting stage is nucleation. Decrease in stability of the supercooled austenite and narrowing of a temperature difference between the pearlite and intermediate regions occur with reduction in homogeneity of a high-alloy powder steel. The porosity and chemical inhomogeneity activate the decomposition of martensite on low-temperature annealing and reduce the temperatures of the four transformations on tempering.