The paper presents the results of abrasive wear resistance tests carried out on high-vanadium cast iron with spheroidal VC carbides. The cast iron of eutectic composition was subjected to spheroidising treatment using magnesium master alloy. The tribological properties were examined for the base cast iron (W), for the cast iron subjected to spheroidising treatment (S) and for the abrasion-resistant steel (SH). Studies have shown that high-vanadium cast iron with both eutectic carbides and spheroidal carbides has the abrasion resistance twice as high as the abrasion-resistant cast steel. The spheroidisation of VC carbides did not change the abrasion resistance compared to the base high-vanadium grade.
High-vanadium cast iron is the white cast iron in which the regular fibrous γ + VC eutectic with the volume fraction of vanadium carbide amounting to about 20% crystallises. This paper presents the results of studies on high-vanadium cast iron subjected to the inoculation treatment with magnesium master alloy. The aim of this operation is to change the morphology of the crystallising VC carbides from the fibrous shape into a spheroidal one. The study also examines the effect of the amount of the introduced inoculant on changes in the morphology of the crystallising VC carbides. To achieve the goals once set, metallographic studies were performed on high-vanadium cast iron of eutectic composition in base state and after the introduction of a variable content of the inoculant. The introduction of magnesium-based master alloy resulted in the expected changes of microstructure. The most beneficial effect was obtained with the introduction of 1.5% of magnesium master alloy, since nearly half of the crystallised vanadium carbides have acquired a spheroidal shape.
The paper presents the results of tests on the spheroidising treatment of vanadium carbides VC done with magnesium master alloy and mischmetal. It has been proved that the introduction of magnesium master alloy to an Fe-C-V system of eutectic composition made 34% of carbides crystallise in the form of spheroids. Adding mischmetal to the base alloy melt caused 28% of the vanadium carbides crystallise as dendrites. In base alloy without the microstructure-modifying additives, vanadium carbides crystallised in the form of a branched fibrous eutectic skeleton. Testing of mechanical properties has proved that the spheroidising treatment of VC carbides in high-vanadium cast iron increases the tensile strength by about 60% and elongation 14 - 21 times, depending on the type of the spheroidising agent used. Tribological studies have shown that high-vanadium cast iron with eutectic, dendritic and spheroidal carbides has the abrasive wear resistance more than twice as high as the abrasion-resistant cast steel.