Sinter hardening of low-alloy steels: influence of part geometry and physical properties of the material

Assuming that the cooling rate of parts depends on thermal conductivity of the material and on the surface/volume ratio, a two-ways study has been carried out. Firstly, the isothermal surfaces have been calculated by a numerical method on parallelepipeds of constant cross section and varying height and weight. Microstructures, depending on isothermal surfaces predicted by the numerical model, agree with microhardness and mechanical properties. A maximum weight of about 200 grams has been observed to be apt to a full sinter-hardening process and the surface/volume ratio seems to be the critical driving factor. Numerical analysis and experimental tests show that the thermal diffusivity of sintered steels increases as porosity increases.