Tensile properties of vacuum-sintered dual-phase steels

The cooling curves of Jominy specimens made from a powder metallurgy steel (0.65 w/o C) based on a hybrid powder (4 w/o Ni, 1.4 w/o Mo, 2.0 w/o Cu) have been obtained using still air or high-speed water as the cooling fluid. It has been observed that cooling rate increases as the density (6.8 g/cm 3 and 7.0 g/cm 3 ) decreases. This result agrees with recent literature data. Analysis of variables affecting cooling rate shows that thermal diffusivity decreases as the density decreases, while the amount of heat transferred to the cooling fluid, depends on the heat-transfer coefficient and is a function of material density and effective extension of the exchange surface, considering porosity. The influence of porosity on the cooling rate inside a porous body is discussed, and made explicit by a simple formula involving only the porosity. It is demonstrated that the effect of density on cooling rate is reversed with the hypothesis of an infinite heat-transfer coefficient.