连铸连轧产线生产压延钢带钢孔洞的成因分析及控制

Causes analysis and control of holes in rolled steel strip produced by continue casting direct rolling production line

ESP产线高拉速生产压延钢易在轧制时出现孔洞缺陷,通过扫描电镜、能谱分析、工艺数据统计等方法,分析其主要影响工序及成因。结果表明:引起带钢孔洞的原因主要为非稳态浇铸时塞棒碗口以及SEN内壁的絮流物因钢水静压力、钢水流速的变化脱落,未在结晶器上浮被保护渣吸附,最终在铸坯内形成大颗粒夹杂,其主要类型为CaO·2Al_(2)O_(3)+CaO·5Al_(2)O_(3)的高熔点复合型夹杂物。RH脱碳后剩余氧含量与钢水硫含量之和直接决定了钢水在LF工序初生夹杂物含量;LF深钙处理虽然导致了夹杂物数量增多,但减少了高熔点夹杂物在钢水由“钢包→中间包→结晶器”发生紊流时的析出与富集,可减少孔洞缺陷的产生;同样的通钢量,连铸大断面低拉速的钢水洁净度控制优于小断面高拉速。

High speed production of rolled steel strip on continue casting direct rolling is prone to porosity defects during rolling.The main influencing processes and causes were analyzed through methods such as scanning electron microscopy,energy spectrum analysis,and process data statistics.The results show that the main cause of steel strip holes is the detachment of flocs from the stopper bowl mouth and SEN inner wall during non steady state casting due to changes in static pressure and flow rate of molten steel,which are not floating in the mould and adsorbed by protective slag.Finally,large particle inclusions are formed in the billet,and the main type is high melting point composite inclusions of CaO·2Al_(2)O_(3)+CaO·5Al_(2)O_(3).The sum of residual oxygen content and molten steel sulfur content after RH decarburization directly determines the primary inclusion content of molten steel in LF process.Although deep calcium treatment in LF process leads to an increase in the number of inclusions,it reduces the precipitation and enrichment of high melting point inclusions in the turbulent flow of molten steel from ladle to tundish to mould,which can reduce the generation of pore defects.With the same amount of steel flow,the cleanliness control of steel in continuous casting with large cross-section and low drawing speed is better than that with small cross-section and high drawing speed.