【摘要】 700L高强大梁钢作为承载车身质量和外部载荷的关键部件，须具备优良的产品性能，对钢水洁净度要求较高。钢中存在的Al₂O₃、Ca-（Mg）-Al-O等硬质夹杂物在轧制过程中不易变形，控制不当会造成钢板冲压、折弯开裂。以铈为代表的稀土元素活性高，能将钢中夹杂物变性为稀土夹杂物，减轻大尺寸球类夹杂物危害，且稀土夹杂物在钢中具有较低错配度，可作为异质形核核心细化铸坯凝固组织。结果表明，钢中稀土铈质量分数为0.001 3%时，球类夹杂物得到细化，单位面积数量由22个降低到11个，最大尺寸由11μm降低到6μm;TiN类夹杂物数量、尺寸变化不大。稀土铈将钢中Al₂O₃、Ca-（Mg）-Al-O类夹杂物变性为Ce-Al-O，变性程度取决于局部铈含量，变性后的Ce-Al-O继承钢中原始夹杂物的形貌特征；TiN析出形态发生改变，呈现易碎裂结构，有利于缓解应力集中。根据FactSage热力学计算可知，未添加稀土铈时钢液成分位于非理想相区（liquid+slag+CaAl₄O₇），添加稀土铈后钢液进入liquid+slag+AlCeO₃相区，稀土将脱氧产物类和钙铝酸盐类夹杂物变性为Ce-Al-O夹杂物，这与扫描电镜（scanning electron microscopy,SEM）观测结果吻合。Ce-Al-O在铁素体钢中错配度小于8%，对钢的凝固形核有促进作用，铸坯等轴晶区扩大，枝晶得到细化，一次枝晶间距由426μm缩小到280μm。更多还原

【Abstract】 The 700L high-strength large beam steel, which is a key component for bearing the weight of vehicle body and external loads, must has excellent product performance and requires a high level of cleanliness for molten steel.The hard inclusions such as Al₂O₃, Ca-（Mg）-Al-O present in the steel are difficult to deform during the rolling process and their improper control can cause cracking during stamping and bending of the steel plate.The rare earth element, represented by Ce, has high reactivity and can transform the inclusions in the steel into rare earth inclusions, reducing the harm caused by large-sized spherical inclusions.Moreover, the rare earth inclusions in the steel have a lower degree of misfit and can serve as hetero nucleation cores to refine the solidification structure of casting billet.The results show that when the mass fraction of rare earth Ce in the steel is 0.001 3%, the spherical inclusions are refined, with the number per unit area decreasing from 22 to 11 and the maximum size reducing from 11 μm to 6 μm.The number and size of TiN-like inclusions remain unchanged.The rare earth Ce transforms Al₂O₃, Ca-（Mg）-Al-O inclusions in the steel into Ce-Al-O inclusions, and the degree of transformation depends on the local Ce content.The transformed Ce-Al-O inherits the morphological characteristics of original inclusions in the steel.The morphology of TiN changes, presenting a brittle structure, which is conducive to alleviating stress concentration.Based on FactSage thermodynamic calculations, when no rare earth Ce is added, the steel liquid composition is in the non-ideal phase region（liquid+slag+CaAl₄O₇）, and after adding rare earth Ce, the steel liquid enters the liquid+slag+AlCeO₃ phase region.The rare earth transforms the deoxidation products and calciumaluminate inclusions into Ce-Al-O inclusions, which is consistent with the SEM（scanning electron microscopy） observation results.The mismatch degree of Ce-Al-O in ferrite steel is less than 8%, which promotes the solidification nucleation of the steel.The equiaxed grain zone of slab is expanded, the dendrite is refined, and the primary dendrite spacing is reduced from 426 μm to 280 μm.更多还原