Mechanism of Hot Ductility Improvement of a Peritectic Steel Containing Vanadium Using Very-High-Temperature Compression

摘要

The loss of hot ductility in the temperature range 700 °C to 1100 °C in carbon and low-alloy steels has been the subject of many investigations. Microalloyed steels with compositions near the peritectic have a coarse as-cast structure and large columnar grains that encourage grain boundary sliding, and also increase the crack aspect ratio and the density of the intergranular precipitates, resulting in loss of hot ductility and cracking during continuous casting. Recent work has shown that thermomechanical processing could improve the hot ductility of a hypoperitectic steel. In this study, a peritectic vanadium steel and also carbon steel as a reference were used to evaluate the hot ductility when the specimens were subjected to very high-temperature deformation. The tensile specimens were melted and solidified in situ on a 20 KN servohydraulic testing machine. Once the solidification was completed, compressive deformation was performed on the specimens in the temperature range 1400 °C to 1300 °C during cooling. The hot ductility was then evaluated using conventional isothermal testing at temperatures ranging from 700 °C to 1100 °C. It was found that applying such a deformation can refine the as-cast, dendritic structure, and consequently clean grain boundaries as a result of grain boundary migration, the latter being observed by Auger electron spectroscopy.