Dry sliding and contact fatigue behavior of different high density Ni-Cu-Mo PM Steels

The usage of PM steels in industry, claims for continuous efforts in research and development. For this purpose, the world biggest part manufacturer, GKN Sinter Metals and the Department of Industrial Engineering of University of Trento started a cooperation to investigate the wear and contact fatigue properties of PM steels. Wear is one of the most important factors that limit the life of engineering components in different ways. In this research two very common phenomena, dry sliding and contact fatigue behavior of PM parts have been investigated. In the first part of the work dry sliding behavior of Fe-Mo-Cu-C and Fe-Mo-Cu-Ni-C steels were investigated. This study was done to investigate the influence of Ni on dry sliding behavior of PM steels. Ni-rich constituent is expected to decrease wear resistance, due to a localized plastic deformation which reduces the load bearing capacity of the surface. Once the effect of the presence of Ni has been assessed, in the second part of the work dry sliding wear resistance of two Ni-alloyed sintered steels, differing for Ni content, was investigated to highlight any effect due to the amount of this alloying element. Based on experimental results, a procedure for the design of dry sliding wear resistant parts was proposed as well. In the second part of the work the contact fatigue behavior of three different steels was investigated. The aim was the proposal of a conservative approach to predict the contact fatigue behavior of different sintered and heat treated steels, based on the nucleation of the fatigue crack. The model is developed by calculating the maximum local stress from the theory of the elastic contact and the matrix yield strength from the microhardness of the steels, under different mean Hertzian pressures. Effect of shot peening on contact fatigue behavior was also investigated. Two different types of shot peening, ceramic or steel+ceramic, were considered. Stress and strength calculations were made based on the local approach on contact fatigue, which was validated in the second part of the work.