Fatigue crack growth behavior of hybrid and prealloyed sintered steels: Part I. Microstructure characterization

Powder metallurgy (P/M) steels have been widely employed due to the cost-savings associated with near-net shape manufacturing. The microstructure of P/M steels, especially the porosity, has a significant effect on the mechanical behavior. In this paper, the microstructure of hybrid and prealloy Ni–Mo P/M steels was studied. Porosity, pore size, shape, interpore spacing, as well as phase fraction of steel matrix have been quantified. The quantification of pore clustering was also investigated. The mechanical behavior of each phase in steel matrix was investigated using Vickers microhardness. Significant difference in pore morphology and steel matrix microstructure between hybrid and prealloy steels, at the similar densities, were observed. The microstructure characterization presented in this paper is linked to the companion paper on fatigue crack growth behavior of these steels.