Abstract: Through the study of LF+RH process and chemical composition of high strength steel, in view of the key problems of C,Mn ,S content and slag composition ,based on the analysis of the reasons for the failure of narrow composition control, the theory and practical operation mode of narrow composition control were put forward. Through practical operation, the qualified rate of C, Mn, S content in the narrow range of composition can reach more than 95 %, and can be stably controlled. After controlling the narrow composition of C,Mn and S elements, the fluctuation range of tensile strength of high-strength steel can be reduced by 30-70 MPa, and the strength, toughness and mechanical propeities of highstrength steel can be improved.

Key words: high strength steel, narrow composition control； LF+RH, tensile strength