Novel method on homogenized La treatment of GCr15 steel by the self-reaction of La2O3 containing slag and steel for vacuum electroslag remelting

The interaction between slag and GCr15 steel under argon and vacuum were investigated by laboratory ex-periments. The results show that the maximum and average size of inclusions, and the proportion of large in-clusions decrease after slag-steel interaction. Compared with the test under argon, inclusion size of the steel in the test under vacuum is smaller and more uniform, which is attributed to that vacuum promotes the reaction of C and O in molten steel to form CO. The La content increase from 0 to 0.0022 wt% in the steel processed by La2O3 containing slag after for 5 min holding at 1873 K under 0.5 kPa. Thermodynamic calculation reveals that the La2O3 in molten slag can be reduced by dissolved C in liquid steel to form dissolved La under vacuum due to the relatively higher carbon content of GCr15 steel and appropriate vacuum condition. The microstructure and primary carbides of the tested steel under vacuum are finer than that under argon. The present study provides a theoretical basis for the homogenized La treatment of GCr15 steel under vacuum, which shows a promising prospect in vacuum electroslag remelting of high-end bearing steel.