Numerical analysis of the effect of nonmetallic inclusionslocation in carburized layer of 16MNCR5 steel on initiation of fatigue cracking

This paper presents the results of a numerical analysis of the effect of the position of non-metallic inclusions in a hardened top layer in 16MnCr5 steel on the mechanism of fatigue destruction. An analysis of a hardened layer formed by thermo-chemical treatment using FineCarb® technology was conducted.Non-metallic inclusions formed by deoxidation of steel were studied; they are usually made of calcium and aluminum. Four positions of inclusions in the hardened layer were tested: under the layer, in the middle part of the layer, under the surface and on the border of two sublayers. The results of the FEM analysis were treated as a qualitative analysis. A map of plastic strains around the inclusion under study was observed. The appearance of plastic strains in the area under analysis signaledthe initiation of a fatigue crack. It was observed that the mechanism of destruction depends largely on the distribution of stress in the top layer and on the place where the inclusion is anchored in the layer. Inclusions under the layer were found to be the main cause of the loss of the structural continuity, which explains the most frequent cases of the initiation of fatigue cracks.