In several metal forming processes, relation between stress and effective strain of the material must be known for obtaining important forming parameters such as forces and work, required for metal forming processes. Dependence of the flow stress on the effective strain is called the flow curve and is influenced by strain rate and temperature. In order to reach high quality and full functionality of the product, the characteristics of formed material must be determined as precisely as possible and flow stress is one of the main characteristic of the metal materials. In general, flow curves are determined by experiments such as tensile test, upsetting test and torsion test. The proper choice of testing method depends on the metal forming process to be simulated.
In this paper we present the experimental measurements of flow stress for stainless steel at elevated temperatures by using torsion test. In the experimental work a torque, temperature and number of twists of test pieces were measured. Also, the influence of forming parameters such as strain, strain rate and temperature on flow stress was analysed. Experimental results are presented in form of tables and diagrams. Finally, from experimental data the regression model was obtained for successful prediction of flow stress of stainless steel at elevated temperatures. The method of regression analysis allows with relatively small number of experiments the accurate information about the influence to mathematical model of the process.
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