Study of Methods for Increasing Ductility and Formability of Cold-Rolled Ti-Stabilized IF Steels

Abstract

Study of the influence of the chemical composition and parameters of the complex treatment technology on characteristics of the microstructure, phase precipitates, the solid solution state, and mechanical properties was carried out for hot-rolled and cold-rolled Ti-stabilized IF steels. Cold-rolled products were annealed according to the regime of continuous hot-dip galvanizing units. The following methods of investigation were used: light, scanning and transmission electron microscopy, mechanical properties testing, thermodynamic analysis of phase stability conditions, and determination of the interstitial impurities content in a solid solution by internal friction. The possibility and conditions of a significant increase in ductility, formability of cold-rolled steels are established. They are obtained not by the traditional way consisting in reducing the content of interstitial elements and impurities, but by giving them a favorable form of existence. This is achieved by optimizing the chemical composition, first of all, the sulfur content, and parameters of thermo-deformation treatment of steel, which ensure complete carbon binding in Ti4C2S2 as a result of TiS transformation already at the hot-rolling stage. To reduce the yield and tensile strength, it is necessary to decrease the content of interstitial elements and to increase the temperature of recrystallization annealing of cold-rolled steel.