Pastukhova T. Increasing tribological properties and cost-effective alloying of white cast iron with spheroidal vanadium carbide

The object of research - processes of formation of structure and properties of alloy cast iron. The subject of research - Features of the effect of chemical composition and heat treatment on microstructure and tribological properties of complex-alloyed cast iron with spheroidal vanadium carbide. Research methods: optical and scanning electron microscopy, 3D-profilometry, energy dispersive spectroscopy, XRD, dilatometric methods; mechanical properties determination; erosive and abrasive wear test; methods of mathematical statistics and factorial experiment design. The thesis is devoted to solution of scientific and technical problem of improving tri-bological properties and effectiveness of alloyed white cast iron with spheroidal vanadium carbide (SCI-alloys). The influence of V and Cr in an amount of 5-10 % and up to 9% re-spectively on microstructure, phase chemical composition, temperature of transformation "pearlite-austenite" of V-Mn-Ni-Cr SCI-cast irons is studied. The effect of quenching temperature on the microstructure, hardness, abrasive and erosive wear resistance SCI-alloys is investigated. The ambiguous impact of chromium on the stability of austenite (cast, destabilized, retained) to phase transformations in the investigated cast irons is revealed. The impact of metastable austenite on abrasive wear resistance of SCI-alloys is shown. A differential approach for choosing the optimal structure of SCI-alloys' metal matrix depending on the mechanism of wear is described. The basic mechanisms of fracture surface after abrasive and erosive wear are found; the factors of increased wear resistance of new SCI-irons are explained. It is shown that the new cost-effective SCI-irons have increased in 1,5-3,0 times abrasive and erosive wear resistance as compared with the prototype and high-Cr cast iron at reduced by 4-5% the amount of vanadium. Bench tests on abrasive wear revealed that the use of iron Ф10Х4,5 instead of steel X12Ф1, cast iron 270Х21Г2 and hard alloy BK8 saves 5.44; 10.67 and 397.30 grvn. per 1 kg of alloy, respectively. A chemical composition of Ni-free SCI-iron (Ukraine patent # 98897) is designed, which is submitted for implementation to JSC "Dnieper Metallurgical Plant".