Analysis Of Formation Cause For Billet Defect Of Lue Yang Steel And Measures Of Prevention

The quality of continuous casting billet which is 150mm×150mm in LueYang Iron&Steel Co.Ltd was studied. According to the result, the measures of prevention were brought.By the studies on quality of continuous casting billet, the main defect was discovered which are off-square, non-metallic inclusions and subsurface air bubble.The results show that uneven cooling is the main cause of forming off-square defect. Water slot of cooler-crystallizer is beyond the limit, taper copper-tube is too small, Inner taper of copper-tube don't consist with shrink rule of continuous casting billet," distribution of cooling water isn't uniform, quality of cooling water is beyond the limit, content of alloying agent is different and thickness of billet continuous casting shell is over the mark. The facts made continuous casting billet cooled unevenly. Off-square defect of continuous casting billet is generated.By chemical analysis, machine capability examination, mechanical test and scanning lens analysis, the sample of billet was examined. The research indicated as follow:(1) The main reason which made the billet bended and fractional was that the content of non-metallic inclusions was overrun badly, especially the inclusions which stretched towards the center of the billet; the main reason which made the billet don't reach the mark was that the content of non-metallic inclusions was overrun which reduced the steel's tensile strength. Non-metallic inclusion in billet mostly came from products of deoxidization, inner lining and slag.(2) Subsurface air bubble was directly connected with oxygen content in steel. Oxygen content was high in steel and refractory was affected with damp would increase the oxygen content. These factors made subsurface air bubble form. Subsurface air bubble was directly connected with hydrogen and nitrogen content in steel, but the increase of hydrogen and oxygen content in steel improved the rate to form subsurface air bubble.According to the analytic result of the formation of the billet defect, combination the fact, root of defect formation was studied. Main effect factors were confirmed and analyzed one by one. Measures of prevention were put forward in order to improve quality of billet.Main defect effecting on quality of billet was analyzed and studied in paper. Measures of prevention were put forward. Important advices were brought forward on smelting, refining and improvement of continuous casting technology. At the same time, it distinctly pointed out the direction of further improving on quality of billet.