超深冲汽车板“砂眼”缺陷成因分析及工艺优化

Process optimization and causes analysis on"sand hole"defect of automobile sheet with ultra-deep drawing

伴随着汽车工业的快速发展,国内外各大主机厂对汽车板表面质量要求日益苛刻,特别是超深冲大减薄量复杂成形汽车板在冲压过程中基板表面“砂眼”现象,成为限制汽车板高质量发展的制约因素。针对超深冲大减薄量汽车板冲压“砂眼”缺陷,借助扫描电镜(SEM)及能谱(EDS)等分析手段,明确了浸入式水口富集的Al_(2)O_(3)夹杂物脱落是导致汽车板冲压“砂眼”缺陷的根本原因。通过炼钢关键工艺与“砂眼”缺陷对应性影响分析,表明转炉终点氧、RH出站顶渣TFe含量、结晶器液面波动、连铸炉次交接坯等是诱发基板表面“砂眼”缺陷的主要原因。采取降低钢液氧含量、优化RH渣中TFe含量降低渣/金界面传氧、保护浇注防止钢水二次氧化、优化结晶器流场减少液面波动以及中间包液位稳态控制等措施可提高钢水洁净度,有效改善超深冲大减薄量汽车板“砂眼”缺陷,缺陷发生率由0.086%降低至0.026%。研究结果为超低碳钢高洁净度冶炼提供了技术支撑,可为超深冲大减薄量汽车板表面质量提升提供参考。

With the rapid development of the automobile industry,the surface quality of the automobile sheet is becoming more and more severe in the main machine factories at home and abroad,especially the"sand hole"phenomenon of the substrate surface in the stamping process of the ultra-deep drawing and large reduction complex forming automobile sheet,becomes the restriction factor which limits the automobile board high quality development.In view of the"sand hole"defect in the stamping of automobile sheet with ultra-deep drawing and large reduction,by means of scanning electron microscopy(SEM)and energy dispersive spectroscopy(EDS),it was clear that the removal of Al_(2)O_(3) inclusions enriched by submerged nozzle was the fundamental cause of"sand hole"defect in sheet metal stamping.Through the analysis of the correspondence between the key steelmaking process and the"sand hole"defect,it was shown that the main causes of the"sand hole"defect were the end-point oxygen of the converter,the top slag TFe of the RH outlet,the fluctuation of the mold level,and the continuous casting of transition blank were the main causes of"sand hole"on the substrate surface.The cleanliness of molten steel can be improved by reducing oxygen content in molten steel,optimizing TFe content in RH slag,reducing oxygen transfer at slag/gold interface,protecting casting to prevent secondary oxidation of molten steel,optimizing flow field of mold to reduce fluctuation of liquid level and steady state control of liquid level in tundish.The"sand hole"defect of the ultra-deep drawing and large thinning volume automobile sheet is effectively improved,and the defect incidence is reduced from 0.086%to 0.026%.The research results provide technical support for high cleanliness smelting of ultra-low carbon steel,and provide reference for improving the surface quality of ultra-deep drawing and large reduction automobile sheet.