THE INFLUENCE OF VANADIUM ON FRACTURE-TOUGHNESS AND ABRASION RESISTANCE IN HIGH CHROMIUM WHITE CAST IRONS

The influence of vanadium on wear resistance under low-stress conditions and on the dynamic fracture toughness of high chromium white cast iron was examined in both the ascast condition and after heat treatment at 500 degrees C. A vanadium content varying from 0.12 to 4.73% was added to a basic Fe-C-Cr alloy containing 2.9 or 19% Cr. By increasing the content of vanadium in the alloy, the structure became finer, i.e. the spacing between austenite dendrite arms and the size of massive M(7)C(3) carbides was reduced. The distance between carbide particles was also reduced, while the volume fraction of eutectic M(7)C(3) and V6C5 carbides increased. The morphology of eutectic colonies also changed. In addition, the amount of very fine M(23)C(6) carbide particles precipitated in austenite and the degree of martensitic transformation depended on the content of vanadium in the alloy. Because this strong carbide-forming element changed the microstructure characteristics of high chromium white iron, it was expected to influence wear resistance and fracture toughness. By adding 1.19% vanadium, toughness was expected to improve by approximately 20% and wear resistance by 10%. The higher fracture toughness was attributed to strain-induced strengthening during fracture, and thereby an additional increment of energy, since very fine secondary carbide particles were present in a mainly austenitic matrix. An Fe-C-Cr-V alloy containing 3.28% V showed the highest abrasion resistance, 27% higher than a basic Fe-C-Cr alloy. A higher carbide phase volume fraction, a finer and more uniform structure, a smaller distance between M(7)C(3) carbide particles and a change in the morphology of eutectic colonies were primarily responsible for improving wear resistance.