Plasticity and deformation resistance of the alloyed rail steels in rolling temperature interval

Abstract

On the basis of conducted experimental studies, regularities of the influence of temperature-speed rolling conditions on the plasticity and deformation resistance in the zones of continuously cast billets of alloy rail steels of E76KhF, E76KhSF grades are determined and scientifically substantiated. The results indicate the complex nature of dependence of rail steel E76KhF plasticity on deformation temperature. In particular, for near-surface layers of continuously cast billets, a noticeable decrease in plasticity in the temperature range of 1025 – 1075 °Cwas recorded, which is absent for the layers located in central zone of that billets. Generalization of the results of plasticity studies of various layers of continuously cast rail E76KhF steel billets has shown that absolute values of the plasticity criterion are significantly reduced with the distance from the surface to the central zone. This fact can be explained by a coarse-grained structure and increased concentration of non-metallic inclusions in the central zone of continuously cast billets relative to their surface layers; it was confirmed by the results of metallographic studies. In particular, it was found that the average grains diameter in the surface layer of deformed continuously cast billets is in 1.3 – 2.1 times less compared to the central zone. There was confirmed the presence of significant concentrations of non-deformable inclusions of the silicate type (Al2O3· SiO2; FeO·SiO2; MnO·SiO2), which have most negative influence on steel plasticity while in the surface area such inclusions are absent. On the basis of conducted researches it was established that with increase in deformation temperature of rail steel E76KhSF there is a decrease in resistance to plastic deformation according to the exponential law. In this case, absolute values of the steel deformation resistance are reduced with the distance from the surface to the central zone of continuously cast billets, which is associated with the above illustrated increase in grain size and localization of non-metallic inclusions. The revealed tendency to reduce the deformation resistance from the surface layers to the center of continuously cast billets is maintained regardless to deformation rate, while the absolute values of the deformation resistance increase significantly with the growth of deformation rate from 1 to 10 s–1. Mathematical processing of the obtained experimental data allowed to obtain regression equations that help to predict plastic and deformation properties of alloyed rail steels of E76KhF and E76KhSF grades with a sufficient degree of reliability under the specified rolling conditions and are complex theoretical basis for the development and improvement of new heating modes of billets for rolling and rail rolling schemes. Adequacy of the obtained experimental dependences is confirmed by results of pilot industrial testing of the new mode of railway rails production on the universal rail mill of “EVRAZ ZSMK”.