Abstract: High speed production of rolled steel strip on continue casting direct rolling is prone to porosity defects during rolling. The main influencing processes and causes were analyzed through methods such as scanning electron microscopy, energy spectrum analysis, and process data statistics. The results show that the main cause of steel strip holes is the detachment of flocs from the stopper bowl mouth and SEN inner wall during non steady state casting due to changes in static pressure and flow rate of molten steel, which are not floating in the mould and adsorbed by protective slag. Finally, large particle inclusions are formed in the billet, and the main type is high melting point composite inclusions of CaO·2Al₂O₃＋CaO·5Al₂O₃. The sum of residual oxygen content and molten steel sulfur content after RH decarburization directly determines the primary inclusion content of molten steel in LF process. Although deep calcium treatment in LF process leads to an increase in the number of inclusions, it reduces the precipitation and enrichment of high melting point inclusions in the turbulent flow of molten steel from ladle to tundish to mould, which can reduce the generation of pore defects. With the same amount of steel flow, the cleanliness control of steel in continuous casting with large cross-section and low drawing speed is better than that with small cross-section and high drawing speed. 

Key words: continue casting direct rolling, holes, inclusion, refining