Fatigue Behavior and Inclusion‐Based Lifetime Prediction of 42CrMo4 Steel

Three variants of 42CrMo4 steel were investigated regarding the fatigue life at two test frequencies of 90 Hz and 20 kHz and temperatures up to 500°C. The materials varied in different levels of sulfur and oxygen content and steel cleanliness in terms of nonmetallic inclusions. The steels had a tempered martensitic microstructure with a hardness of 300 HV. A frequency dependence was observed only for the medium‐sulfur steel, whereas for low‐ and high‐sulfur levels, both test frequencies yielded in a common S‐N curve. The fracture surface analysis of the fatigue specimens was compared with the inclusion rating done on unloaded samples. A correlation of both methods was observed by introducing a size factor. Based on the distribution functions and by using Murakami's approach of a projected area of an inclusion, a method was developed to predict the S‐N curve. This offers the opportunity for an inclusion‐based lifetime prediction.