Mechanism of Spheroidization of Carbide in RE-Complex Modified Vanadium White Iron

The effects of RE-complex modification on morphology of the carbide in-vanadium white iron was studied.After modification both the cubic-shape hyper eutectic Vc and strip-like eutectic Vc change into perfectly spheroidal carbide and the toughness and abrasion resistance of vanadium white iron is pronouncedly improved.
The experimental results showed that to get spheroidal carbide a certain minimum content of vanadium in white iron is necessary.The sulphide and nitride with higher melting point formed during modification process are the substrate of heterogeneous nucleation of Vc and this is of great importance for carbide to grow in divorced eutectic.The desulphurizing and deoxidizing effects of rare earth elements raises the VC/melt interfacial tension and at the same time decreases the difference in the interfacial tension of advancing planes of different indices.Therefore the basal planes of growth pyramids advance at about equal speed, and finally the carbide grows as a spheroid.Furthermore,the higher interfacial tension makes the spheroidal surface of VC stable during growth process.