1. College of Materials Science and Engineering, Chongqing University, Chongqing 400044, China; 2. Chongqing Key Laboratory of Vanadium-Titanium Metallurgy and New Materials, Chongqing University, Chongqing 400044, China
Abstract:The thermal acid etching test method is a common method for the quality inspection of continuous casting slabs,but the current test effect is not stable,and the phenomenon of over-corrosion or insufficient corrosion is prone to occur during the inspection process,and its reaction mechanism is also controversial. Taking high carbon steel as an example,a systematic research method of thermal acid etching inspection mechanism was explored. The purpose is to determine the specific reaction mechanism of thermal acid etching inspection and provide theoretical guidance for process optimization of thermal acid etching inspection. Firstly,the change law of the microstructure and morphology during the acid etching process was analyzed in situ,and then the phase change and the corrosion behavior corresponding to different phase were observed and analyzed,and the acid etching process was numerically simulated,polarization curve was measured and combining the electrochemical theory,the reaction mechanism of the thermal acid etching process was jointly analyzed,and the process optimization was carried out based on this mechanism. The results showed that the thermal acid corrosion test mechanism could be explained by the microbattery reaction between different phases,that is,the Fe3C phase in the slab could react with the surrounding matrix, and the segregation area with high C concentration had more Fe3C,and the distribution density of the microbattery was large,in the process of thermal acid etching,the corrosion rate was faster,and the difference in corrosion rate led to different corrosion morphology in different regions,and the solidification structure and defects of the slab were shown finally. According to the reaction mechanism,it was concluded that the acid etching effect has an inflection point with the increase of acid etching time and the optimum reaction time of the steel studied was 300 s. It is also found that an appropriate increase in temperature can increase the difference in the corrosion rate of different regions in the slab during the acid etching process,which is beneficial to improve the acid etching effect. It is of great significance for the quality optimization of continuous casting slabs and the improvement of the quality stability of high-quality steel. At the same time,the proposed research method also has reference value for process optimization of similar inspections.
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