Herein, the 3D characterization of internal defects in medium carbon steel with different soft reduction (SR) parameters is investigated, as regards its spatial morphology and size distribution using X‐ray computed tomography. The size of defects and their shape complexity increase from the equiaxed toward the center of the ingot, and the total number of defects is larger at the equiaxed region, which exhibits the aggregation and growth of small spherical pores into the large defects from equiaxed toward the center region. The two types of shrinkage defects, including island and net shrinkage, are identified. With the minimum reduction amount of 2 and 4 mm, the number and size of defects along with the carbon macrosegregation in the equiaxed region and center of the ingot are less as compared to the high reduction amount of 6 mm and without SR technology. The size of gas pores with sphericity >0.6 is <70 um with different reduction amounts and exceeds up to 150 um without SR. Therefore, minimum reduction amounts can easily regulate the internal defects in medium carbon steel.
Continuous casting is a dominant steelmaking process due to its steady-state nature, enhanced yield of steel production, and low consumption of energy and manpower. However, the production of defect-free cast products is still a big challenge, as the internal defects, including macro-segregation of alloying elements, cracks, and pores, can be easily formed during the solidification process, which seriously deteriorates the microstructure and mechanical properties of the cast products. Therefore, this paper puts forward the common solutions to overcome these problematic issues. The reduction technology can effectively improve the center segregation of the billet, bloom, and slab. The history of the development of the reduction technology is summarized and classified according to the variations in research trend. Furthermore, the basic principles and parameters of reduction technology are described to implement them in the actual production process. This paper compares the similarities and differences between soft reduction (SR) and heavy reduction (HR) technologies with a particular focus on the theoretical research of HR technology and further elaborates the key parameter and equipment problems during implementation of HR. Moreover, this paper also considers the HR technology adopted by Baosteel as a case study, which helped to put forward some viewpoints for the future development of reduction technology.
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