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 conditio ns and on the dynamic fracture toughness of high chromium white cast i ron 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 a dded 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 w as also reduced, while the volume fraction of eutectic M(7)C(3) and V6 C5 carbides increased. The morphology of eutectic colonies also change d. In addition, the amount of very fine M(23)C(6) carbide particles pr ecipitated in austenite and the degree of martensitic transformation d epended on the content of vanadium in the alloy. Because this strong c arbide-forming element changed the microstructure characteristics of h igh chromium white iron, it was expected to influence wear resistance and fracture toughness. By adding 1.19% vanadium, toughness was expect ed to improve by approximately 20% and wear resistance by 10%. The hig her 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 austeni tic matrix. An Fe-C-Cr-V alloy containing 3.28% V showed the highest a brasion resistance, 27% higher than a basic Fe-C-Cr alloy. A higher ca rbide phase volume fraction, a finer and more uniform structure, a sma ller distance between M(7)C(3) carbide particles and a change in the m orphology of eutectic colonies were primarily responsible for improvin g wear resistance.