RESEARCH OF THE BEHAVIOR OF MACROSTRUCTURE DEFECTS OF THE PRE-DEFORMED CONTINUOUS CAST BILLETS DURING ROLLING

Abstract

The most significant trend in recent decades in the field of continuous casting of steel billets is a partial transfer of the process of deformation of the exposure to the field of complete solidification (rolling mill) in the area of two-phase (solid-liquid)state (technological line of CCM). However, the implementation of such two-stage deformation of the continuous cast ingot leads to the need for changes to the methodology of physical simulation of the behavior of defects (surface and bulk) in the course of the subsequent rolling, first and foremost, in terms of the correct choice of their geometric shape and spatial orientation. The paper presents the results of a study of the influence of spatial orientation of the surface defects and continuity of the macrostructure of the metal axial region deformed in the line of the continuous casting machine using layered physical models. An experimental study performed in the conditions of deformation of reduced billets by two schemes with rolling simulation scale1:5: in smooth rolls, simulating the process of groоvelles rolling as applied to the first two stands of the crimp group of medium-section mill 300; in the first and second pairs of rectangular grooves of breakdown stand of the mill 500/370 of PJSC “Donetsk Metal Rolling Plant”. According to the multiplicity of the problem, the universal design of physical models was developed to simulate the spatial location of both surface and internal defects. Studies have shown that in case of rolling of physical models with extract ratio over 2.0 and an angle of misalignment defects imitators close to 60° their complete “healing” is possible. In turn, decrease in the angle to 30° contributes to greater extraction of the defect-simulator and only a small decrease in their width. In the case of total misalignment of defect-simulators (angle 90°) there is a broadening of the defects and their deposition to the initial length after tilting by 90°. The obtained experimental data allowed understanding of the mechanisms of “healing” defects integrity of metal depending on magnitude of the total extracts, the angle of misalignment of the longitudinal axis of the defect with the rolling direction and the distance of their occurrence from the longitudinal-transverse plane of symmetry.