Abstract: The effect of La treatment on the transformation of inclusions in H13 steel was investigated by subjecting H13 die steel to vacuum induction melting and subsequently treating the molten steel with La under an argon atmosphere protection.The results demonstrate that La has a beneficial effect on inclusions in H13 steel， the number of inclusions increases with the increase of La content， while the average size of inclusions initially decreases and then increases. The inclusions in H13 steel without the rare earth La additions are primarily Al₂O₃ and MnS. However， with a La content of 0.016% in H13 steel， the dominant inclusions shift to La₂O₂S. When the La content in H13 steel is 0.016%， the inclusions in the steel are mainly La₂O₂S；Furthermore， when the La content reaches 0.045% and 0.073%， the predominant inclusions in steel become LaP and La₂O₂S. Thermodynamic calculations show that the transformation process of La-treated inclusions is Al₂O₃→LaAlO₃→La₂O₂S in molten steel at 1 600 ℃. During the solidification process， La₂S₃ is initially precipitated in the molten steel. As the temperature continues to decline， LaP begins to precipitate on the surface of La₂S₃ and La₂O₂S， ultimately forming the composite inclusions La₂O₂S-LaP and La₂S₃-LaP.

Key words: H13 Hot Work Die Steel, La Treatment, Inclusions, Thermodynamic Calculation

摘要： 采用真空感应炉熔炼H13模具钢，在氩气保护下加入稀土镧处理钢液并浇铸成钢锭，研究了La处理对H13钢中夹杂物转变的影响。结果表明，La对H13钢中夹杂物具有很好的改性效果，随La含量的提高，夹杂物的数量呈上升趋势，夹杂物的平均尺寸先减小后增大。不添加稀土时，H13钢中夹杂物主要为Al₂O₃和MnS；当H13钢中w［La］为0.016%时，钢中夹杂物以La₂O₂S为主；当w［La］为0.045%和0.073%时，钢中夹杂物主要为LaP和La₂O₂S。热力学计算表明，在1 600 ℃下钢液中，La处理后夹杂物的转变过程为Al₂O₃→LaAlO₃→La₂O₂S。在凝固过程中，钢液中首先析出La₂S₃，当温度继续降低，LaP开始在La₂S₃和La₂O₂S表面析出，最终形成复合夹杂物La₂O₂S-LaP和La₂S₃-LaP。

关键词: H13热作模具钢, La处理, 夹杂物, 热力学计算