Evaluation of strength of stainless steel bolt without heat treatment considering Bauschinger effect during manufacturing process

Isotropic hardening models for elastic-plastic materials are often used to simulate cold forging processes, although it cannot represent the Bauschinger effect. However, the Bauschinger effect must be considered for precise simulation of the strength in service of cold-forged components without heat treatment, as well as their geometry. A cold-forged bolt made of stainless steel is a typical example. In this report, finite element analysis of the forming process and the strength was performed for two multi-stage cold forging processes of non-heat-treated stainless steel bolts. The Yoshida-Uemori model was used as a kinematic hardening model that takes into consideration the Bauschinger effect of a material. The Yoshida-Uemori model was modified so that they can represent the strain hardening behavior in a large strain region appropriately for applying the model to cold forging process. As a result, it was possible to account for the Bauschinger effect during the forming process. Moreover, it was possible to estimate the difference in strength between the isotropic and kinematic hardening models by analysis of the tensile test results. Furthermore, the impact of the forming process on the strength of the cold-forged bolt was also evaluated.