Cleanliness improvement and microstructure refinement of ingot processed by vacuum electroslag remelting

The composition analysis, inclusion and microstructure characterizations for two ingots processed by Ar gas protective electroslag remelting (ESR) and vacuum ESR as well as thermodynamic calculation were carried out to explore mechanisms of cleanliness improvement and microstructure refinement of ingot processed by vacuum ESR. The results show that compared with the ingot processed by Ar gas protective ESR, the Al pickup in ingot processed by vacuum ESR is less due to the lower Al2O3 activity in molten slag resulted by fluoride vaporization from molten slag. During Ar gas protective ESR, only Al deoxidation occurs in molten steel. But, the new equilibriums among liquid steel, inclusions and gas phase are established, and C deoxidation could occur upon 1635 °C during vacuum ESR. The inclusions size in vacuum ESR ingot is finer because the time for Al2O3 inclusion growth is shorter. The C deoxidation and less steel reoxidation resulted by slag-steel interaction during vacuum ESR contributes to the lower oxygen content in vacuum ESR ingot. Furthermore, because of more uniform temperature distribution in molten slag pool, the smaller SDAS is acquired in vacuum ESR ingot. The higher cleanliness, microstructure refinement and smaller size of carbides contribute to the performance improvement in vacuum ESR ingot.