Features of formation of the structure of thin slabs cast at different speeds, their influence on the structure and properties of hot-rolled steel

Abstract

For the first time, a complete comprehensive study of the internal quality of metal products with a carbon content of 0.3 % produced in a combined process of thin-slab casting and rolling was carried out. A feature of the combined process is the absence of a cooling and heating cycle before rolling and the small thickness of the initial slab. The zonal chemical heterogeneity of continuously cast "thin" slabs poured at different speeds has been studied. The research methods were metallographic analysis of the macrostructure and spectral method for determining the content of elements by the thickness of slabs. The results of calculations of the segregation coefficients of basic and impurity chemical elements in slabs poured at different speeds are presented. As a result of the study, it was found that an increase in the casting rate by ~ 1.2 times does not lead to a significant increase in the zonal chemical heterogeneity of the continuously cast metal produced in the process of thin-slab casting. Of particular interest was the measurement of quantitative parameters of the initial dendritic structure of "thin" slabs depending on the casting speed. The segregations formed as a result of dendritic liquation were measured. It is shown that with an increase in the casting rate, the dispersion of the dendritic structure increases and the dendritic segregation decreases by 20 %. In the course of simulation rolling, the regularity in changing the parameters of the dendritic structure during deformation of "thin" slabs into the final microstructure of rolled products is considered. When the slabs are compressed by 65 %, the distance between the primary dendrite arm spacing decreases by an average of 65 %. The comparison of the microstructure and mechanical characteristics of rolled products produced in industrial conditions from slabs poured at different speeds using thin-slab casting technology is carried out. The results of the study indicate that an increase in the casting rate increases the dispersion of the initial dendritic structure and, as a result, favorably affects the formation of the final microstructure. It is shown that hot-rolled products made from a slab with a 1.2-fold increased casting speed have a homogeneous microstructure and demonstrate an increase in the values of impact strength by an average of 30 J/cm2.