Reverse ageing in hot-rolled high-carbon steel wire rod

Abstract

Effects of ageing time on area reduction of hot-rolled high-carbon steel wire rods were studied. Tensile testing and X-ray study of as-rolled wire rods were carried out. Gleeble simulation and hydrogen content determination were also conducted. The results show that the reduction of area increases with ageing time at room temperature and the UTS remain unchanged which are contrary to normal ageing or strain ageing. In normal ageing, the ductility drops and the yield strength increases. In this study, the Gleeble simulation and X-ray data support that the transformation from pearlite to austenite is normal and there is no evidence of retained austenite or martensitic transformation in the steel. The hydrogen content drops as the time passes. The drop is rapid in first few days and this drop increases the ductility in rolled high-carbon wire rod. Hydrogen reduces the cohesive strength and the pressure generated due to transformation of atomic hydrogen-to-molecular state combines with tensile stress and causes cleavage or mixed type of fracture.