Influence of inclusion on stress and strain fields in ultra-high strength steel

The influence of non-metallic inclusion on the performance of steels is closely related to the characteristic parameters. The in-situ scanning electron microscope (SEM) observation results of the crack initiation induced by TiN inclusion under tensile and fatigue loads in the ultra-high strength steel were analyzed. The stress fields of the inclusions and nearby matrix were then calculated using the MSC Marc finite element analysis software. Subsequently, the stress and strain fields of the TiN inclusions with different characteristic parameters and the nearby matrix were simulated. The results show that the mechanical behavior of the inclusions and the nearby matrix can be explained and predicted by finite element method. The maximum stress concentration is located around the sharp angle of a triangle inclusion. The position of the high-stress region in a rectangle inclusion is affected by the angle between the inclusion and the load direction. The position of the maximum stress in the matrix changes from the outer-inclusion region to the inter-inclusion region with the increase of the inter-inclusion distance. The high-stress region near the free surface results from the sub-surface inclusions, and the position of the maximum stress is affected by the distance from the inclusion to the free surface and the inclusion size.