Study on the hot ductility evolution mechanism of high-sulfur peritectic steel

Abstract

In this study, the hot ductility of as-cast peritectic steel (w_C = 0.12 wt%) with S contents of 0.005 and 0.027 wt% was evaluated in the temperature range of 650 to 1000 °C using a Gleeble-3500 thermal-mechanical simulator. The tensile fracture morphology within this temperature range was examined using a field emission scanning electron microscope, while the proeutectoid ferrite morphology was analysed using an optical microscope. The results indicate that as the S content increases from 0.005 to 0.027 wt%, the dynamic recrystallisation (DRX) starting temperature decreases from 1000 to 950°C. Consequently, the reduction of area (RA) for high-sulfur peritectic steel (w_S = 0.027 wt%) is greater than that for low-sulfur peritectic steel (w_S = 0.005 wt%) at temperature between 950 and 1000 °C. Furthermore, the amount of MnS precipitation increases from 0.0135% to 0.0678% as the S content rises. Concurrently, the Mn content surrounding the MnS decreases from 1.3 to 0.35 wt%, resulting in an increase in the ferrite precipitation temperature from 688.2 to 726.8 °C and an increase in the ferrite precipitation amount from 44.9% to 60.1%. Therefore, at 750 °C, the thickness of the proeutectoid ferrite film increases from 12.8 to 16.6 μm, while the RA decreases from 43.5 to 35.1, leading to the formation of a brittle zone in the high-sulfur peritectic steel.