FATIGUE RESISTANCE AND MACHINABILITY OF A HIGH-STRENGTH SINTERED STEEL IN DEPENDENCE ON TEMPERING TEMPERATURE

Unnotched and notched specimens with a density of 7.1 g/cm3 and made of diffusion-alloyed Distaloy AB(Fe-1.75Ni-1.5Cu-0.5Mo) powder admixed with 0.5 % C and 0.5 % MnS in the quenched and tempered state were subjected to fatigue tests under axial loading and different stress ratios and to the hole drilling test for the evaluation of the machinability. Three tempering temperatures (250, 300 and 350-degrees-C) were investigated in order to find the optimal tempering temperature with respect to fatigue strength and machinability. The results indicate that 300-degrees-C is the optimum tempering temperature. The material selected had an acceptable machinability coupled with a noticeable fatigue strength and low notch sensitivity which makes it particularly suitable for the production of notched components. In comparison to alternating loading, the presence of a tensile mean stress induces a significant decrease in the endurable stress amplitude due to the high mean stress sensitivity of the as-treated materials. On the other hand, in the presence of a compressive mean stress a noticeable increase in the endurable fatigue strength can be obtained. This must be taken into account when designing with regard to the acting mean stresses.