Investigation of 60SPb20 steel flow stress changes in high-temperature compression tests

The aim of this study was to investigate the behavior of 60SPb20 free-cutting steel at high-temperature compression tests and to find the relationships of flow stress with strain rate and temperature based on the Arrhenius model. For this purpose, compression tests were performed on standard samples of the alloy in the temperature range of 800 to 1050 °C and at a strain rate of 0.001 to 1 s-1. In addition to the use of high-temperature lubricant, the effect of friction on flow stress was eliminated by a modification model and obtained flow curves were applied for further calculations. The compression curves and microstructural studies showed that the dynamic recrystallization mechanism was responsible for softening of the alloys at high temperatures. Moreover, the constitutive equations of hot deformation were determined using the Zener-Hollomon parameter for this steel. The results of changing the flow stress versus temperature at different strain rates showed that the activation energy of hot deformation of 60SPb20 free-cutting steel was about 434 kJ/mol. The difference between this value and values of other steels such as low and medium carbon steels, tool steels, etc. was discussed. Finally, after calculating the required constants for the alloy, the relation of flow stress versus the Zener-Hollomon parameter was determined which can be used to predict hot deformation behavior at higher strain rates.