International Scientific Journals
of Scientific Technical Union of Mechanical Engineering "Industry 4.0"

This paper analyses the effect of different charge compositions for melt production, cooling rate (i.e. casting wall thickness) and inoculation on the gray iron microstructure. In this study, three gray iron melts were produced that had almost the same chemical composition. The proportions of steel scrap (SS), pig iron (PI), gray iron return (GIR) and SiC in charge were as follows: melt 1 (10 % SS, 39.4 % PI, 49.2 % GIR, 0.6 % SiC), melt 2 (38.8 % SS, 9.9 % PI, 47.9 % GIR, 1.6 % SiC) and melt 3 (0 % SS, 0 % PI, 99.2 % GIR, 0.06 % SiC). One uninoculated and one inoculated stepped test casting with walls thicknesses of 5, 10, 20, 45 and 65 mm was casted from each melt. The inoculant was added in the melt stream during pouring in the mould in an amount of 0.23 wt.%. The type, size and distribution of graphite flakes in the analysed walls did not significantly depend on the charge compositions. The structure of the metal matrix, carbides precipitation and type, size and distribution of graphite flakes were largely dependent on the wall thickness. As the wall thickness increased, the cooling rate decreased and the type of graphite flakes changed, from D and E through B to A type. Carbide formation has occurred in the edge region of the 5 mm thick walls. With the decrease of the cooling rate and increasing the proportion of D and E type graphite flakes, the ferrite content in the metal matrix increased. The carbide content in the edge region of the 5 mm thick walls was significantly reduced by inoculation. Inoculation increased the proportion of A type graphite flakes in the middle of 5 mm thick wall and in walls with a thickness from 10 to 65 mm. In addition, inoculation significantly reduced the proportion of B, D and E type graphite flakes or were completely eliminated. Wall thickness has affected this effect.

The possibility of high energy synthesis of Ti–Al–C system powder grain refiner by using high voltage electric discharges for treatment of powder mixtures of 75 % Ti + 25 % Al and 85 % Ti + 15 % Al composition in kerosene with subsequent briquetting by spark plasma sintering is shown in present work. It is found out that high voltage electric discharge treatment of powders leads to the increase of dispersity as well as to synthesis of new carbon containing phases during chemical interaction between system components and products of working hydrocarbon liquid destruction. The possibility of controlling this process by changing initial composition of powders, specific treatment energy and spatial distribution of plasma formations by changing electrode system type is shown. It is also shown that changing master alloy synthesis parameters allows controlling inoculation efficiency. Thereby it is possible to achieve surface or volumetric inoculation, so selective increasing of plastic or strength properties of Ni-based cast superalloys becomes possible. Introduction of 0.01 % of synthesized grain refiner during the casting of SM88U (СМ88У) superalloy allows decreasing mean grain size from 1…2 mm to 0.2…0.5 mm. Tensile strength of inoculated superalloy at the temperature of 900˚С was 68 MPa while their stress rupture strength increased by 20 % in average. Composition and properties of inoculated alloys comply with standard technical documentation, which allows their usage for the
production of gas turbines blades.