Microstructure as a Criterion for the Selection of Hot Working Process Parameters for Plain Medium Carbon Steel

Abstract

Cylindrical compression specimens of 0.42 carbon steel were deformed at temperatures from 816 to 982°C (1500–1800°F) and at average strain rates of 0.5 to 3.0 s−1, to a true strain of 0.47. This testing was performed at the lower bound of the dynamic recrystallization region, where dynamic recovery can predominate. After deformation, the insulated specimens were allowed to slowly cool to room temperature under near equilibrium conditions. The resulting microstructures were examined by optical microscopy to determine whether there were significant variations, and if any observed variations could be related to the processing parameters. In the overall range of these temperatures and strain rates, there were changes in grain size and distribution. A large number of the tests produced similar structures in the middle range of temperatures. However, substantial differences were observed at the higher temperatures, with strain rate effects being particularly noticeable. At the lowest temperatures, interesting features of the microstructure were attributed to the proximity of the testing temperature to the transformation temperature.