Plasticity and Deformability of Alloy Rail Steels at Rolling Temperatures

摘要

Abstract—The influence of the rolling temperature and speed on the plasticity and deformability within continuous-cast billet of E76KhF and E76KhSF alloy rail steels is studied experimentally. The results indicate a complex dependence of the plasticity of E76KhF steel on the deformation temperature. In particular, for the surface layers of continuous-cast billet, the plasticity declines markedly in the range 1025–1075°C. That is not the case for the central region of the billet. The results for E76KhF steel indicate that the absolute plasticity declines considerably on moving away from the surface. This may be attributed to the larger grains in the steel and the higher concentration of nonmetallic impurities in the central zone, as confirmed by metallographic data. In particular, the mean grain size at the center of the deformed continuous-cast billet is 1.3–2.1 times greater than in the surface layer. The central zone is characterized by high concentrations of nondeforming silicate inclusions Al2O3 ? SiO2, FeO ? SiO2, and MnO ? SiO2, which greatly impair the billet plasticity. Such inclusions are absent from the surface zone of the billet. With increase in deformation temperature of E76KhSF rail steel, the resistance to plastic deformation declines exponentially. The absolute resistance to deformation declines on moving away from the billet surface, once again on account of the larger grains in the steel and the higher concentration of nonmetallic impurities in the central zone. Decrease in the resistance to deformation from the surface layers to the center of the billet is observed at any strain rate. However, the absolute resistance to deformation increases considerably with increase in the strain rate from 1 to 10 s–1. Mathematical analysis of the experimental data yields regression equations that may be used in practice to predict the plastic and deformational properties of E76KhF and E76KhSF alloy rail steels, in specified rolling conditions. Those equations provide the basis for the development of new billet-heating conditions in rolling and new systems for rail rolling. Their validity is confirmed by industrial trials of new production conditions for rails on the universal rail and beam mill at AO EVRAZ ZSMK.