Abstract
In the electric steelmaking shop of PJSC "Magnitogorsk Iron and Steel Works" steel casting is carried out on longitudinal CCMs by two methods: closed and open casting. Estimated daily productivity of the machine at casting by open jet is 3.3-5.7 % (relative) higher than at casting by closed jet because of the possibility to cast metal in longer series. However, the quality of metal cast by open jet is lower than that of closed jet casting. The purpose of this paper is to compare the quality of billets cast by different methods. Reinforcing steel of A500C grade, intended for reinforcing reinforced concrete structures, manufacturing of foundation blocks, heavy reinforcement meshes and frames, road construction, is cast by both open and closed jet casting. The paper analyzes an array of production data from 144 melts. Metal from 118 melts (82 %) was cast by open casting, and 26 melts (18 %) - by closed casting. A comparison of the macrostructure quality of a 150×150 mm section billet cast by different methods showed that all defects of internal structure without exception have a higher degree of development in open jet casting than in closed jet casting. The greatest difference (by 1.28 points) is characteristic for edge point contamination. An increasing linear dependence of the degree of development of this defect on the sulfur content in the metal poured by open jet was established. This indicates that at this method of casting a significant contribution to the total contamination of metal is made by sulfide and oxysulfide inclusions. To reduce the contamination of steel by inclusions, it is recommended to have a sulfur content of less than 0.010 % in the metal.
Keywords:
steel, longitudinal CCM, casting methods, continuous cast billet, macrostructure, quality.