On the influence of heavy warm reduction on the microstructure and mechanical properties of a medium-carbon ferritic-pearlitic steel

The current study on a medium-carbon steel (0.36% C) with deformation-induced spheroidized cementite produced by heavy warm deformation (HWD) was carried out in order to investigate an alternative microstructural route when compared to conventional quenching and tempering (QT) or soft annealing (SA) processes. After austenite deformation, the HWD samples were cooled and heavily deformed at temperatures below the gamma-alpha transformation followed by a simulated coiling treatment. In particular, the study addresses the influence of adiabatic heating due to the heavy deformation on the microstructure and properties. The mechanical properties after the various treatments show that the strength-ductility relation after HWD and QT are superior to those after continuous cooling (CC) or soft annealing (SA). In the microstructures obtained from the CC and SA treatments we observed lamellar pearlite which deteriorated the mechanical properties. A similar effect was observed after the adiabatic HWD treatment, which also entails some lamellar pearlite. HWD at 670 degreesC with subsequent coiling produced a microstructure with dispersed spheroidized cementite distributed homogeneously in the fine-grained ferrite matrix. The mechanical properties of the HWD samples are well comparable to those observed after the QT process owing to the resemblance in microstructure.