Study on Decarburization and Mechanical Properties of Ultra-Low Carbon Steel by Enlarged Vacuum Chamber Volume

The increasing demand for ultra-low carbon steel (Interstitial free steel of Ti-Nb composite stabilized type) has underscored the importance of the RH degassing process, which is critical to achieving stringent quality standards and high productivity. This study aimed to boost decarburization efficiency by expanding the lower volume of the RH degasser and adjusting the circulation gas flow rates (190 Nm³/h, 230 Nm³/h, 250 Nm³/h). The effects of these variations on decarburization time, carbon content, and mechanical properties were systematically evaluated. The Enlarged RH degasser (ERH) achieved a higher decarburization rate than the conventional RH degasser (CRH) at the same gas flow rate of 190 Nm³/h, identifying 230 Nm³/h as the optimal rate for ERH. The experimental decarburization times to reach a carbon content of 0.003 wt% in ultra-low carbon steel were 12.4 min for CRH and 10.8 min for ERH, thus reducing the time by 1.6 min. Conversely, the calculated decarburization times were 13.11 min for CRH and 10.75 min for ERH, with ERH showing a reduction of 2.36 min. Consequently, calculated times were 0.76 min longer than experimental times. No significant differences in inclusions were observed between the CRH and ERH at circulation times of 3, 4, and 5 min; however, the mechanical properties of the ERH showed improvements at 4 and 5 min. Therefore, from an economic perspective, 4 min was established as the optimum time. Ultimately, enhancing the lower volume of the RH degasser has increased productivity and decreased production costs.