Fatigue crack propagation behaviour of some low alloy steels in case carburised condition

摘要

Low alloy steels of case carburising grade are generally employed in the manufacture of various automotive components. These components have to work under fatigue loading during their service life, which occasionally results in fatigue failures. The present work is aimed at investigating the fatigue crack propagation behaviour of some commonly used low alloy steels in case carburised condition. The crack propagation mechanisms were investigated through fractographic observations on the fractured surfaces of standard fatigue test specimens failed under four-point rotating bending fatigue tests. Despite the presence of residual compressive stresses induced during case carburisation, majority of the fatigue cracks were found to initiate at the surface. Crack initiation was followed by transgranular mode of stable crack propagation for all the steels, while subsequent crack propagation behaviour was found to be dependent on the contents of alloying elements in a given steel. Steels containing higher amounts of chromium were found to exhibit greater tendency towards intergranular decohesion cracking.