Effect of La Treatment on Inclusions in H13 Hot Work Die Steel

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.

Keywords

• h13 hot work die steel； la treatment； inclusions； thermodynamic calculation