High cycle fatigue behavior of a low carbon alloy steel: The influence of vacuum carburizing treatment

The present investigation attempts to explore the influence of vacuum carburizing treatment on the high cycle fatigue behavior of a low carbon alloy steel 20Cr2Ni4 by using rotating bending fatigue test. The same heat steel subjected to conventional quenched & tempered (QT) treatment was used for comparison. It was found that the vacuum carburizing treatment significantly promoted the formation of a particular area of granular bright facet in the vicinity of non-metallic inclusion in the fatigue crack initiation region with fatigue life beyond ~106 cycles and thus caused mainly an interior inclusion-induced failure mode compared with the QT treatment. Both the high cycle fatigue strength and the threshold value of stress intensity factor range controlling macroscopic crack growth were significantly enhanced on condition that the crack initiation site was still within the carburized case layer. These beneficial enhancements are mainly ascribed to the introduction of a case layer with much higher hardness and compressive residual stress.