Abstract: Ultra-low-carbon P-added high-strength steel has IF steel characteristics and is characterized by adding a certain amount of alloying elements such as P, Mn and Nb to achieve solid solution strengthening and increasing the strength of the steel without affecting the plasticity of the steel, but the high P content of molten steel is likely to cause nozzle clogging. By investigating the direct key influence factors of the formation and removal of oxide inclusions (Al2O3 mainly) in steel, analyzing the internal mechanism, conducts relevant theoretical research and production test, optimizing the selection by process, controlling the high temperature and high P content of molten steel at converter end-point, optimizing RH refining microalloying process and full process time matching, reducing the formation of inclusions in steel, and promoting the accumulation of inclusions, the castability of molten steel was improved. The average value of T.O mass fraction leaving RH station is 2510-6, and the average value of T.O mass fraction in continuous casting tundish is 1910-6. Finally, the problem of castability of P-added high-strength ultra-low carbon steel has been solved, and large-scale stable production with100t LD→RH→CC process flow and stable 4 furnace sequence continuous casting have been realized.

Key words: P-added ultra low carbon high-strengt castability h steel, castability, inclusion, production process flow, process optimization