Cleanliness of Ti-bearing Al-killed ultra-low-carbon steel during different heating processes

During the production of Ti-bearing Al-killed ultra-low-carbon（ULC） steel, two different heating processes were used when the converter tapping temperature or the molten steel temperature in the Ruhrstahl–Heraeus（RH） process was low: heating by Al addition during the RH decarburization process and final deoxidation at the end of the RH decarburization process（process-Ⅰ）, and increasing the oxygen content at the end of RH decarburization, heating and final deoxidation by one-time Al addition（process-Ⅱ）. Temperature increases of 10°C by different processes were studied; the results showed that the two heating processes could achieve the same heating effect. The T.[O] content in the slab and the refining process was better controlled by process-Ⅰ than by process-Ⅱ. Statistical analysis of inclusions showed that the numbers of inclusions in the slab obtained by process-Ⅰ were substantially less than those in the slab obtained by process-Ⅱ. For process-Ⅰ, the Al;O;inclusions produced by Al added to induce heating were substantially removed at the end of decarburization. The amounts of inclusions were substantially greater for process-Ⅱ than for process-Ⅰ at different refining stages because of the higher dissolved oxygen concentration in process-Ⅱ. Industrial test results showed that process-Ⅰ was more beneficial for improving the cleanliness of molten steel.