Effect of directional solidification of electroslag remelting on the microstructure and primary carbides in an austenitic hot-work die steel

The microstructure of as-cast ingot and three-dimensional microstructure of carbides were analyzed by optical microscope and scanning electron microscope. The types of carbides were identified by X-ray diffraction. Directional solidification of electroslag remelting effectively reduced the segregation of alloying elements in as-cast ingot. The growing direction of dendrites in as-cast ingot refined by directional solidification of electroslag remelting was paralleled to <001> crystallographic orientation. The solidification microstructure of austenitic hot-work die steel was composed of austenite and primary carbides (V8C7-type and Mo2C-type) which distributed along grain boundaries. Compared with conventional electroslag remelting, the directional solidification of electroslag remelting process reduced the size of primary carbides and improved dispersed distribution of carbides, but not changed the types and compositions of carbides. The direction of driving force for carbides growth was irregular in conventional electroslag remelting, while that was nearly parallel to crystal <001> in directional solidification of electroslag remelting.