The Significance of Central Segregation of Continuously Cast Billet on Banded Microstructure and Mechanical Properties of Section Steel

Abstract

The solidification structure and segregation of continuously cast billets produced by different continuous casting processes are investigated to elucidate their effect on segregated bands in hot-rolled section steel. It suggested that segregated spots are mainly observed in the equiaxed crystal zone of a billet. The solidification structure is directly related to superheating and the intensities of secondary cooling. To a certain extent, the ratio of the columnar crystal increases with the increase of superheating and secondary cooling. Moreover, the number of spot segregations decreases with the decrease of the equiaxed crystal ratio. After hot rolling, the segregation spots are deformed to form segregated bands in steels. The severe segregation of Mn in segregated bands corresponds with that in the segregation spots. The elongation ratio and low temperature toughness deteriorate significantly by a high fraction of degenerate pearlite caused by central segregation. With a decrease of central segregation, the total elongation is increased by 10% and the ductile–brittle transition temperature (DBTT) is also reduced from −10 to −40 °C. According to the experimental results, columnar crystal in billets is preferred to effectively reduce the degree of central segregation and further improve low temperature toughness and the elongation ratio.

High-Strength Low-Alloy Steels

“…Regarding the processing techniques and the evaluation of mechanical properties, different research lines were followed. Guo et al [5] evaluated the casting process conditions on the mechanical properties of hot-rolled steel and studied the billet quality by developing and optimisation method. Khosravani et al [6] tackled the microstructural changes that occur during the processing of dual-phase steels by using multiresolution spherical indentation stress-strain tests.…”

Effect of magnetic alternate stirring on solidification structure of the round billet

“…For example, the failure of the axle pipe used for vehicle transportation will cause serious traffic accidents and endanger the safety of life and property. Most of the reasons for the failure of the pipe come from the internal quality of the product, such as the banded structure and uneven distribution of elements [3][4][5][6]. These defects were mainly inherited from the spot segregation inside the continuous casting billet, so optimizing the internal quality of the billet is one of the effective ways to fundamentally solve the internal defects of the pipe [7][8][9].…”

Study on the effect of mould alternate stirring on the internal quality of the round billet

“…The failure of oil pipe is mainly related to the internal banded structure, and the spot segregation defect in the central equiaxed crystal zone of the billet is one of the main reasons for the banded structure [8][9][10]. Some studies have shown that with the decrease of the intensity of electromagnetic stirring in the mould or secondary cooling zone, the proportion of the central equiaxed crystal zone decreases, thereby reducing the number of spot segregation in the billet, and finally controlling the banded structure defect in the finished product [11][12][13].…”