Study On The Control Technology Of Oxide Scale Of Hot-rolled High Strength Steel

Surface quality of iron and steel products has been one of the important indicators that iron and steel manufacturers and users pursue. It has become a research hotspot of steel manufacturers and scholars that how to reduce the oxide scale defects and control oxide scale structure. At present, there are few studies on oxide scale of hot rolled high strength steel. The object of this study is the high strength steel DP590 and the formation and evolution of its oxide scale on surface during hot rolling processes were studied. It provides a theoretical and experimental evidence for controlling of hot rolled high strength steel oxide scale.This paper, based on thermodynamics and dynamics of oxidation, analyzed the effects of temperature and time of oxidation on the oxide scale. It deduced the oxidation kinetics model of early oxide stage and mid-late oxide stage and established early and mid-late oxide equation of the high strength steel DP590.Impacts of initial rolling temperature, finish rolling temperature, coiling temperature and cooling rate after coiling on the thickness and structure of oxide scales were investigated in this paper, which adopted Gleeble 3800 thermal simulated test machine and scanning electron microscopy(SEM). The experimental result show that with the increase of initial rolling temperature and finish rolling temperature, a significant increase in the total thickness of the oxide scale experiments steel. The thickness fraction of Fe O gradually increased while the thickness fraction of Fe2O3 and Fe3O4 decreased. Coiling temperature has a great impact on the microstructure of the experimental steel oxide scale. When the coiling temperature is 650℃, the oxide scale does not contain Fe3O4 which is transformed by proeutectoid reaction, so it is easy to picking. However, once the coiling temperature decreased to 600 ℃ or below, the oxide scale contains more Fe3O4 transformed by proeutectoid reaction, which is difficult to pickling. Fast cooling rate after coiling can inhibit proeutectoid reactions and eutectoid reactions. In order to improve the oxide scale pickling rate, a control method is proposed, which can reduce Fe O proeutectoid reaction by increasing the coiling temperature and the rate of post-roll appropriately. In addition, the paper also deduced a model to calculate the thickness of the oxide scale under variable temperature conditions. Finally, the impact of the microstructure of high strength steel oxide scale, acid concentration and acid temperature on the pickling rate were investigated by pickling experiments, which provide a reference for the development of high-strength steel pickling process.