a study of mechanical properties and fracture mechanisms of powder metallurgy parts prepared using semi pre-alloyed steels

in the present study, the mechanical properties and fracture mechanisms of two powder metallurgy low alloy steels, i.e. distaloy dh and distaloy hp, were investigated. all samples were sintered at 1120 ºc for 30 min in n2/h2 atmosphere. for evaluation of the effect of cooling rate on final properties, samples were cooled from sintering temperature with two different cooling rates. in addition, density, hardness, and tensile and fatigue strengths of the samples were measured and microstructure and fractured surfaces were examined using standard methods. the results showed that pores characterizations, i.e. pores shape and distribution, have strong effects on the mechanical properties of sintered steels. for example, an increase in the density by 4.5% resulted in an increase in the tensile strength by 44% and fatigue strength by 55% for distaloy dh steel containing 0.2% carbon. these values for distaloy hp steel were measured to be 26% and 47%, respectively. the results of experiments as well as those obtained from microstructural examinations for two investigated materials indicated that the type of microstructure and distribution of metallurgical phases affect the mechanical and fatigue behaviour of samples. distalloy hp steel sample with 0.5%c and 7.2 g/cm3 density after being cooled at 1.2 ºc/sec showed the best mechanical properties among all the samples investigated. study of fractured surfaces indicated that the major mechanisms in crack growth region of the samples are ductile fracture, brittle fracture and formation of fatigue striations.