A Multi-Body Numerical Modeling Approach to Investigate the Role of Inclusions in the Fracture Toughness of Bearing Steels

Abstract

Abstract Antifriction bearings often fail from inclusion initiated surface and/or subsurface cracks that propagate in a hard tempered-martensite matrix that contains a certain amount of retained austenite, especially for case carburized surfaces. The primary inclusions present are carbides, sulfides, nitrides, and oxides that are characterized by distinct morphology, frequency, and constitutive behavior. Consequently, the fracture toughness of the inclusion-matrix system depends on the interactions between the inclusions themselves and their surrounding matrix. This paper presents a numerical framework for investigating the fracture response of the inclusions and the multiphase tempered martensite matrix. In this multibody approach, the inclusions are modeled as discrete bodies embedded in a plastic matrix with their distinct constitutive behavior. The plastic response of the polycrystalline matrix is modeled using a micromechanics approach for heterogeneous materials based on the original works of Eshelby and Hill. Finally, the mechanics of inclusion-matrix interface is included in the sliding surface description for the contacting bodies. This fracture model used in this study is based on the energy adsorption in the initiation of cracks and their subsequent propagation during tensile loading. The multibody model is calibrated and validated by comparison to experimental results reported in literature. Subsequently, the effect of phases surrounding the inclusion and the composition of the matrix are evaluated using the model. The constitutive behavior of the transition layer surrounding the inclusion is found to have a profound impact on the fracture toughness properties. The volume fraction of retained austenite in the matrix is also found to influence the fracture toughness of the material and cracking instability. Key results of this investigation are included in this paper.