Effects of Chemical Composition and Heat Treatment on Mechanical Properties of Carburized Steels

Abstract

The tensile, Charpy impact bending, rotating bending fatigue, and impact bending fatigue tests on some carburized steels were performed in order to investigate the effect of chemical composition in steel and of heat treatment after carburizing on mechanical properties.
The results obtained are summarized as follows:
(1) The steel with re-quenching after direct quenching (specimen B) had superior properties of strength and ductility to the steel with direct quenching only (specimen A) in both tensile and Charpy impact tests. On the other hand, the fatigue strength of specimen A was higher than that of specimen B under both impact bending fatigue and rotating bending fatigue.
(2) For these fatigue tests, the highest fatigue strength was obtained in the steel containing about 0.25% carbon. It was also found that these strength were improved by addition of Cr, Mo, and Ni.
(3) In the impact fatigue tests, there was no clear difference in the number of blows to crack initiation for both specimen A and B. For each carburized steels, the crack propagation rate was decreased with the growth of crack at first, and then the rate was increased gradually with increasing number of blows and, finally, the specimen was led to the rupture with higher propagation rate of crack, that is, the three different stages were distinguished in the process of crack propagation. The crack propagation rate of specimen A was lower than that of specimen B for every stage to the rupture.