Recent Topics in Steelmaking Research and Development
摘要
In steelmaking R & D, developing a process with less emissions and creating quality steel are essential for a sustainable future. There are two methods of reducing emissions from refining slag: Firstly , the slag composition can be optimized in order to increase the dephosphorization efficiency. For example, since 3CaO·P2O5 forms a solid solution with 2CaO·SiO2, the usage of this solid phase as well as liquid slag is expected to improve the dephosphorization efficiency. Secondly, the reuse or recycling of slag reduces emissions.In the MURC (Multi-Refining Converter in Nippon Steel) process dephosphorization is conducted at the first blow in a converter and the dephosphorization slag is discharged while hot metal stays in the converter. Decarburization is then conducted by adding decarburization slag at the second blow in the same converter.After that,the refined steel is tapped and the carburization slag is hot recycled to the dephosphorization of the next charge. By this process, counter flow of the slag and the hot metal is realized and the usage of refining slag is much reduced. In the continuous casting process, the application of electromagnetic casting removes the formation of oscillation marks, subsurface entrapment of nonmetallic inclusions and surface depressions. As a result, surface treatment of continuously cast slab becomes unnecessary and yield is improved, which results in significant energy saving. Secondly, the control of nonmetallic inclusions, including the reduction of their total amount, their elimination from the subsurface and surface of slabs and their chemical compositions control, used to be to mediate their harmfulness on steel qualities, but, it is now utilized to obtain steel properties, which realize the reduction of steel consumption per unit performance of the steel products through increase of strength, elongation of life time with improved corrosion resistance, etc., and energy saving through improved performance of products using improved steel properties. These efforts are indispensable for a sustainable future.