Fatigue Performance of PM Steels in as-sintered State
An overview of the plane bending fatigue performance of PM steels in as-sintered state is presented. Pre-alloyed Molybdenum and Chromium-Molybdenum materials, diffusion-bonded Ni-Cu-Mo and Fe-2%Cu pre-mixes are reviewed. The effect of varying density level and Carbon content upon fatigue performance is analyzed separately. Diffusion-bonded materials exhibit heterogeneous microstructures with high performance metallographic phases distributed along the sinter-necks and around the pores. Optimized carbon content in diffusion-alloyed materials is characterized by a well-distributed martensitic microstructure. Furthermore, fatigue crack initiation is found in the low yield stress phase in the base powder core. PM steels based on pre-alloyed powders exhibit one phase or random distribution of two or more phases with no systematic order in relation to the pores, hence fatigue crack initiation is related to sinter-neck failure. Influence of density is more pronounced for pre-alloyed materials than compared to diffusion-bonded materials.