Research On Slab Quality Control Of SPHC Steel For Continuous Casting

Tangshan Guofeng Iron and Steel Co.,Ltd.is the largest manufacturer and supplier of SPHC hot-rolled coils in China.With the improvement of product quality standards and economic benefits,the current production process cannot satisfy the demand for efficient production of SPHC steel due to the increasingly prominent defect problem of Slab.It is therefore imminent to control and improve the quality of SPHC steel slabs.In this paper,the SPHC steel slab producted by the No.1 steelmaking plant was chosen as research objects.The optimized measures were proposed on the basis of analysis of the parameters of LF refining and continuous casting process.The production condition of slab and the cause of defects were also discussed.Finally,the proposed measures were applied in industrial production and the follow-up evalutation were made.Under the experimental conditions of this paper,the following conculsions could be summarized.(1)Decrease of sulfur content in steel can effectively reduce the proportion of defects in slabs.The optimized measures for the LF refining process include the replacement of medium-carbon ferromanganese by the high-carbon ferromanganese for deoxdation alloying,and raising the Mn/S value to 15 or more.Besides,the top slag process,argon blowing parameters were adjusted to improve the desulfurization rate,so that the sulfure contont of steel liquid were decreased and the incidence of cracks in the slab decreased correspondingly.(2)The optimized measures for the continuous casting process mainly include:the minimus casting speed is strictly limited higher than 0.9 m/min;to ensure the uniform flow field of the crystallizer,the contering control of the nozzle is within±5 mm of the inside and outside arc and outside arc and±10 mm between the east and west.Additionally,the nozzle maintenance and cleaning system were improved,and the quality of secondary cold water were optimized to reduce the risk of clogging of the spray nozzle or blocking of the secondary cold water filter.Real-time monitoring of the crystallizer liquid level fluctuation were conducted to control the liquid wave within±3 mm.The actual water inlet immersion depth was 110?170 mm.The composition of mold powder were optimized and the slag consumption was controlled to 0.5?0.6 kg/t.The implementation of forced cooling system was employed,while taking secondary water distribution to replace the first-class water distribution.(3)After the optizmiation of LF refining process,the proportion of heats with an average Mn/S value less than 15 decreased from 48.9%to 15.3%.The production time of the soft blowing time adjusted to more than 7 minutes can reach 95.23%.The desulphurization rate effectively increased from 67.55%to 71.59%,which effectively inhibited the cracking of slabs.(4)After the optimization of the continuous casting process,the constant rate of the continuous casting process of SPHC steel increased from 75.34%to 85.57%,and the condition of the outlet went well.The quality of the second cold water was significantly improved,and nozzle clogging was significantly allivated.The proportion of the crystallizer with liquid level fluctuation greater than ±3 mm decreased to 0.44%,and the liquid surface stability was well controlled.The immersion depth of the nozzle was controlled at 110?170 mm,and the stability of the immersion depth of the nozzle was effectively improved.The slag consumption can be controlled within the range of 0.5-0.6 kg/t.The thickness of the liquid slag layer was maintained within the range of 10?15 mm,and the crack rate of the cast billet was significantly reduced.(5)The statistical analysis of 2256 heats showed that the defect rate of the SPHC steel slab decreased from 10.18%3.7%after optimization,and the strand quality was significantly improved.The research results of this thesis have important guidance for the improvement of the quality of SPHC steel billet of Tangshan Guofeng Steel Co.,Ltd.