低合金钢铸坯中NbC析出行为的二次冷却调控  

Secondary cooling control of NbC precipitation behavior in low alloy steel slabs

作　　者：康惠柄 郑万[1] 叶飞[2] KANG Huibing;ZHENG Wan;YE Fei(Key Laboratory for Ferrous Metallurgy and Resources Utilization of Ministry of Education,Wuhan University of Science and Technology,Wuhan 430081,China;Wuhan Iron and Steel Co.,Ltd.,Baoshan Iron&Steel Co.,Ltd.,Wuhan 430083,China)

机构地区：[1]武汉科技大学钢铁冶金及资源利用省部共建教育部重点实验室,湖北武汉430081 [2]宝山钢铁股份有限公司武汉钢铁有限公司,湖北武汉430083

出　　处：《炼钢》2023年第4期62-69,共8页Steelmaking

基　　金：国家自然科学基金资助项目(52174323);武汉科技大学科技创新团队项目(2018TDX08)。

摘　　要：针对含铌低合金钢中大颗粒NbC晶界析出及先共析铁素体膜诱导连铸坯裂纹的问题,利用Matlab建立凝固传热模型和优化二冷各段目标设定温度,反算改进连铸二次冷却水量,有效提高了NbC析出温度区间内的铸坯边部冷却速率及矫直前铸坯温度,增强了铸坯窄边在矫直区前的热塑性。研究表明:Q345钢中NbC在A_(e3)上温度区间(1108~905℃)基本完全析出,在原有连铸二次冷却制度下,NbC析出区间的铸坯冷却速率低(4.33℃/s),难以避免大颗粒NbC在奥氏体晶界析出,而且连铸坯矫直前窄边温度低于相变A_(e3)温度,导致奥氏体晶界先共析铁素体膜的形成,二者共同诱导铸坯窄边裂纹的形成;通过二次冷却3~7段的目标温度及边部水量的调整计算,实现了铸坯窄边冷却速率达到5.92℃/s,有助于NbC细小弥散析出,同时铸坯窄边矫直前温度高于A_(e3)温度,避免了先共析铁素体膜的形成,可显著提高含铌低合金钢的热塑性,对控制CSP工艺下含铌低合金钢边部缺陷提供了理论参考。In view of the problem of large grain NbC grain boundary precipitation and proeutectoid ferrite film induced continuous casting slab cracks in Nb containing low alloy steel,the solidification heat transfer model was established by using Matlab and the target temperature of each secondary cooling section was optimized.The secondary cooling water volume of continuous casting was improved by back calculation,which effectively increased the cooling rate of slab edges within the NbC precipitation temperature range and the slab temperature before straightening,and enhanced the hot plasticity of narrow edges of the slab before straightening.The research shows that the NbC in Q345 steel is basically completely precipitated in the upper temperature range of A_(e3)(1108~905℃).Under the original secondary cooling system of continuous casting,the cooling rate of the slab in the NbC precipitation range is low(4.33℃/s),which makes it difficult to avoid the precipitation of large particles of NbC at the austenite grain boundary.In addition,the temperature of the narrow edge of the continuous casting slab before straightening is lower than the temperature of the transformation A_(e3),resulting in the formation of proeutectoid ferrite film at the austenite grain boundary,both of them can induce the formation of narrow edge cracks.Through the adjustment and calculation of the target temperature of the secondary cooling section 3-7 and the edge water volume,the narrow edge cooling rate of the slab is achieved to 5.92℃/s,which is conducive to the fine dispersion and precipitation of NbC.At the same time,the temperature before the narrow edge straightening of the slab is higher than A_(e3)temperature,which avoids the formation of the proeutectoid ferrite film,can significantly improve the thermoplasticity of the Nb containing low alloy steel,and provides a theoretical reference for controlling the edge defects of the Nb containing low alloy steel under the CSP process.

关 键 词：含铌低合金钢 薄板坯连铸 窄边裂纹 二次冷却优化 NbC析出调控 

分 类 号：TF777[冶金工程—钢铁冶金]