连铸非稳态430不锈钢铸坯大型夹杂物分析

Analysis of large inclusions in 430 stainless steel continuous casting slabs under unsteady state

为探究连铸非稳态对不锈钢大型夹杂物的影响,采用热轧超声探伤法研究了结晶器液面波动下430不锈钢连铸坯中大型夹杂物类型、来源、尺寸、数量、在铸坯中分布以及对冷轧板表面质量的影响等。结果表明,大型夹杂物主要包括4种类型,其中41.3%来源于结晶器水口结瘤物,38.7%为保护渣卷渣物,13.3%为精炼渣卷渣物,6.7%为内生夹杂物。水口结瘤物型夹杂物、精炼渣卷渣物和内生夹杂物一般在钢液出结晶器水口之前就已产生,主要集中在铸坯厚度方向距内弧面1/3到1/4处以及靠近窄面附近,保护渣卷渣物在结晶器内产生,存在某一区域聚集的情况。水口结瘤物型夹杂物属于脆性夹杂,且尺寸大,对冷轧板表面质量危害最大,因此应关注和减少连浇过程[Al]、[Mg]、[Ti]、[Ca]等残余活泼元素含量和钢水温度的波动,避免水口结瘤物结构变化产生大型夹杂物。通过热轧探伤法可获取连铸坯中大型夹杂物类型、尺寸、分布等信息,根据夹杂物变形特征可直观判断其危害性,但其准确度易受其他因素影响。

In order to investigate the effect of unsteady state continuous casting on large inclusions in stainless steel,the hot rolling and ultrasonic flaw detection method was used to study the types,sources,sizes,quantities,distribution in the 430 stainless steel continuous casting slab under the fluctuation of mold liquid level,as well as the influence on the surface quality of the cold-rolled plate.The results show that there are mainly four types of large inclusions,41.3%of them originate from the nodule at the mold nozzle,38.7%of them are caused by the entrapment of mold protective slag,13.3%of them are caused by the entrapment of refined slag,and 6.7%of them are endogenous inclusions.The inclusion of nozzle nodules,refining slag entrapment,and endogenous inclusions are generally generated before the molten steel exits the crystallizer nozzle,and their distribution is mainly concentrated at the distance of 1/3 to 1/4 from the inner arc surface in the thickness direction of the casting slab and near the narrow surface.The slag entrapment of protective slag is generated within the mold,and there is a certain area of aggregation.The nozzle nodule type inclusions which belong to brittle inclusions with large dimensions,have the greatest harm to the surface quality of the cold plate.Accordingly,attention should be paid to the fluctuation of residual active elements such as[Al],[Mg],[Ti],[Ca],and the temperature of molten steel during the continuous casting process,and these fluctuations should be reduced to avoid large inclusions caused by the structural changes in nozzle nodules.Using the hot rolling and flaw detection method can obtain information on the type,size,distribution,and other characteristics of large inclusions in continuous casting slabs.Based on the deformation characteristics of inclusions,their harmfulness can be intuitively judged,but the accuracy is easily affected by other factors.