Effect of Density on the Microstructure and Mechanical Behavior of Powder Metallurgy Fe-mo-ni Steels

The microstructure and mechanical properties of Fe-0.85Mo-Ni powder metallurgy (P/M) steels were investigated as a function of sintered density. A quantitative analysis of microstructure was correlated with tensile and fatigue behavior to understand the influence of pore size, shape, and distribution on mechanical behavior. Tensile strength, Young’s modulus, strain-to-failure, and fatigue strength all increased with a decrease in porosity. The decrease in Young’s modulus with increasing porosity was predicted by analytical modeling. Two-dimensional microstructurebased finite element modeling showed that the enhanced tensile and fatigue behavior of the denser steels could be attributed to smaller, more homogeneous, and more spherical porosity which resulted in more homogeneous deformation and decreased strain localization in the material. The implications of pore size, morphology, and distribution on the mechanical behavior and fracture of P/M steels is discussed.