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The material behaviors of two types of bearing steels at hot working conditions are investigated. Stress-strain curves at various temperatures (900–1300°C) and strain rates (1–50/s) are obtained by compression tests with a computer controlled servo-hydraulic Gleeble 3800 testing machine. Elongation and reduction of the area are also obtained by tensile tests with the Gleeble 1500 testing machine. Flow stresses are calculated from the experiments and are used to predict the temperature distribution and the metal flow of a workpiece during a multistage hot forging process of a bearing race. A rigid-thermoviscoplastic finite element method is applied. The experimental and numerical results are summarized to reveal the reasons for internal crack formation.

In this paper, the stress-strain curves of bearing steels at hot working conditions are obtained by hot compression test with a computer controlled servo-hydraulic Gleeble 3800 testing machine and elongations and reductions of area of the bearing steels are also obtained by hot tensile test with a Gleeble 1500 testing machine. Experiments are conducted under the various strain-rates and temperatures and their results are used to obtain the flow stress information. A rigid thermo-viscoplastic finite element method is applied to the multi-stage hot forging process in order to predict temperature distribution of workpiece. The experimental results and the analysis results are used to obtain an optimal hot forging condition.