Effect of oxidizing slag on the decarburization of ultra-low-carbon steel during the ruhrstahl-heraeus vacuum process

In this study, the effect of oxidizing slag on the decarburization of ultra-low carbon steel during the RH vacuum process was investigated. Based on the experimental results under different operating conditions, it was concluded that high oxidazibility in the top slag could enhance the decarburization rate, particularly in the rapid decarburization stage during the first 4 min of the vacuum process. The highly efficient decarburization for liquid steel depends on two parts of oxygen source. Internal oxygen source is the free oxygen in the liquid steel, and the external oxygen source is the FeO that existed in the RH slag or formed due to the re-oxidation of the splashed scrap and steel skull on the wall of the vacuum chamber. The external oxygen sources participated in decarburization reaction, and promoted the mass transfer of oxygen from the slag to molten steel in the early stage of the vacuum process to further improve the decarburization rate. The decarburization mechanism considering the influence of the oxidizing slag was proposed to explain the reaction sites at different stages of RH decarburization. •The external oxygen source and vacuum decarburization behavior have been studied.•The relationship between the oxidizability of slag and vacuum decarburization rate has been investigated.•Vacuum decarburization reaction mechanism during RH process with oxidizing slag.