OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 26 No. 1 2024 the dumps [1, 2]. Storage of this solid waste requires many square kilometers of land. Waste is collected in the form of wet or dry powders [1–7]. It is estimated [1, 2, 6, 7] that more than 100,000 tons of waste are generated annually during the production of metallic silicon [7]. Despite signifi cant eff orts to reduce its harmful eff ects on the environment, there is no way to prevent contamination of soil and groundwater. Currently, work is being carried out in the Russian Federation on the use of industrial waste as modifying additives in various industries: construction [4–6], metallurgy [1, 2, 7]. Modifi cation is one of the most important metallurgical treatments applied to molten iron immediately before casting to promote solidifi cation without excessive eutectic undercooling, which promotes the formation of carbides, usually with undesirable graphite morphology. Gray iron (lamellar graphite) continues to be the most produced metal material in the global foundry industry, although its rate has slowed due to its replacement by higher-performing malleable irons or lighter-weight aluminum-based alloys. It is well known [8–21] that the crystallization of graphite is signifi cantly infl uenced by the presence of molten impurities in the melt in which it grows, even when these minor elements are present in quantities of less than 0.1 %. It can have a positive eff ect, promoting nucleation and spheroidization, or a negative eff ect, causing graphite degeneration. The main source of these elements is charge materials such as scrap steel, pig iron and pig iron return. A three-stage model of the nucleation of lamellar graphite in gray cast iron was proposed in 2,000 with the formation of oxide-sulfi de graphite [8–14]. A large series of research programs have defi ned the following model [8–21]: (1) Small oxide regions (0.1–3 μm, typically < 2 μm) are formed in the melt; (2) Complex compounds (Mn,X)S (from 1 to 10 μm, usually < 5 μm) nucleate on these microinclusions, where X = Ca, Ba, Sr, Zr, Mg, P, Ti, La, Ce, etc.; (3) Graphite nucleates on the sides of (Mn,X)S compounds due to the low crystallographic mismatch of graphite [8, 9]. The role of complex sulfi des (Mn,X)S in the formation of graphite in gray cast irons is confi rmed by other representative research works [10–15]. Recently [16, 17] it was discovered that oxygen is mainly present in the fi rst microcompound, which is visible as the core of the (Mn,X)S particle, and, in any case, also at the sulfi de-graphite interface, formed into a thin (nano-sized) layer and including O, Si, Al, Ca, Ba, Sr, La and Mg. The presence of this oxide-based layer is hypothesized to increase the ability of (Mn,X) S compounds to nucleate graphite due to their better crystallographic compatibility: this is illustrated by the use of a hexagonal system compared to a cubic system for sulfi de and the low mismatch found for the face (0001) graphite. The smaller the mismatch between two substances (δ), the stronger the nucleation potential between it: the highest nucleation capacity is achieved at δ < 6 % (LaS, CeS, SrMnS), the average nucleation capacity is achieved at δ = 6 % to 12 % (BaS , CaS), and weak nucleation ability is detected at δ > 12 % (MnS, MgS) [18, 19]. The results of research on the morphological characteristics of graphite lead to adjustments to national standards [22–25]. The works [1, 2, 7] show the possibility of using silicon production waste as modifi ers in the production of cast iron. Two modifi ers were developed [7], obtained after fl otation processing of waste in the form of silicon dioxide and nanotubes [1, 7]. The use of modifi ers obtained from silicon production waste not only improves the mechanical properties of gray cast iron, but also aff ects the morphology of graphite [26–34]. The morphology of graphite is a very important parameter aff ecting the properties of cast iron. The room temperature morphology of graphite in cast Fe-C-Si alloys is primarily the result of nucleation from a liquid melt and growth of graphite crystals followed by diff usive growth of carbon in the solid state. The chemical complexity of iron melts and the temporary nature of nucleation and local segregation caused by the chemical composition of the alloy, melt processing and casting conditions are the main determining factors. The interaction between these variables can result in a wide variety of graphite forms, including lamellar/ fl ake (LG), compacted/vermicular (CG), spheroidal/nodular (SG), and other graphite forms (TG) [9, 10, 14, 15, 26–9], as well as some degenerate morphologies such as pointed, blasted or massive graphite (CHG). Although nodular cast iron was discovered in the late 1930s [8–12], the mechanism, by which graphite changes its shape, remains unclear [8–21, 26–30]. Compacted graphite (CG) iron is a new engineering material containing graphite, worm-shaped (vermicular) with rounded edges in a (ferrite-pearlite) matrix.
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