Effect of the initial austenitization temperature on the structural microheterogeneity during drawing of carbon steel with a pearlite structure

Abstract

During wire production, strain fields can be distributed inhomogeneously over the section during drawing and cause structural micro-inhomogeneity, which significantly affects the stability of the process. However, during plastic deformation of carbon steel with a pearlite structure, the interlamellar spacing in the ferrite-carbide mixture and the size of pearlite colonies, which determine the deformation behavior of steel, are of great importance. In addition, in the wire manufacturing technology, heat treatment operations are used with heating the steel to the austenitic state, the temperature of which significantly affects the formation of the structure and properties of the steel. The paper investigates the effect of the austenitization temperature on the structural microheterogeneity of a wire made of carbon steel with a pearlite structure after drawing. The results of studying the microstructure, determining the interlamellar spacing, the anisotropy coefficient of pearlite colonies, as well as the distribution of microhardness over the cross section of the sample during drawing after different temperatures of preliminary austenitization are presented. It is shown that after preliminary austenitization at temperatures of 900, 950 and 1000 °C in a wire made of carbon steel with a pearlite structure, microstructural inhomogeneity in the dispersion of the ferrite-pearlite mixture is observed. It manifests itself as a difference of the interlamellar spacing in pearlite at the surface and in the center of the sample cross section and is retained during subsequent drawing with a total reduction of 8 to 15%. It has been established that the temperature of preliminary austenitization has practically no effect on the anisotropy coeffi cient of pearlite colonies in the initial state after austenitization, and it does not change over the cross section of the sample. However, with subsequent drawing with an increase in the total reduction, the anisotropy coefficient increases, while it increases from the surface to the center of the sample. It is revealed that with an increase in the preliminary austenitization temperature from 900 to 1000 °C, the microstructural inhomogeneity in the drawn wire is manifested to a greater extent, which can be associated with an increase in the grain size of the initial austenite, the size of pearlite colonies, and the interlamellar spacing in pearlite. Microstructural inhomogeneity is confirmed by the nature of the distribution of microhardness over the cross section of the sample. The research was carried out with the financial support of the Russian Foundation for Basic Research and DNT within the framework of the scientific project No. 18-58-45008 IND_a.