Abstract: The effects of La-Ce rare earth treatment on inclusions， continuous casting castability and steel properties of Q345D structural steel were analyzed by field test. The results showed that the alloy yield of RE in Q345D structural steel was 21. 5%. Compared with the heats without RE addition， the desulfurization rate increased by 37. 5%， and the unit inclusion density decreased from 80. 16/mm²  to 60. 78/mm² . The inclusions in molten steel before La-Ce rare earth treat ment were mainly MgO-Al₂O₃-CaO composite inclusions. The modification effect of La-Ce rare earth treatment on small size （ D≤5 μm ） inclusions was more obvious. Small size inclusions were modified into （La-Ce-S） and （La-Ce-Al-S-O） rare earth inclusions. La-Ce rare earth treatment can significantly reduce the aspect ratio of MnS inclusions in steel， so that the morphology of MnS inclusions after rolling was closer to ellipse without long linear， which was the main reason for the increase of transverse impact energy of Q345D structural steel by 20%.

Key words: La-Ce Rare Earth Treatment, Q345D Structural Steel, Transverse Impact Energy, Inclusion Modification, Refine, Cleanliness

摘要： 通过现场试验，分析了La-Ce稀土处理对Q345D结构钢夹杂物、连铸可浇性和钢种性能的影响。结果表明， RE在Q345D结构钢中的合金收得率为21. 5%；与未添加RE的炉次相比，脱硫率提高了37. 5%，单位夹杂物密度从 80. 16个/mm²，降低至60. 78个/mm²；La-Ce稀土处理前钢液中夹杂物主要是MgO-Al₂O₃-CaO复合夹杂，La-Ce稀土处 理对小尺寸（D≤5 μm）夹杂物的改性作用较为明显，小尺寸夹杂物改性为（La-Ce-S）和（La-Ce-Al-S-O）稀土类夹杂 物；La-Ce稀土处理可以明显降低钢中MnS类夹杂物的纵横比，使MnS类夹杂物在轧制后的形貌更接近椭圆形，而 没有长线形，这是Q345D结构钢横向冲击功提高20%的主要原因。

关键词: La-Ce稀土处理, Q345D结构钢, 横向冲击功, 夹杂物改性, 精炼, 洁净度