Vol 47, No 2 (2017)

The development of the alloying and modification of steel by oxides, including natural materials, is very promising. Potential materials include barium–strontium carbonate ores, nickel concentrates, and vanadium converter slag, which may be used to produce steel with improved properties, without the expensive process of producing ferroalloys and intermediate alloys. Considerable research is required to improve steel-making processes. Thermodynamic modeling may be used for that purpose. In the present work, thermodynamic modeling is used for elementary systems involved in the extraction of barium, strontium, vanadium, and nickel from their oxides by means of different reducing agents. The results indicate that microalloying and modification of steel by inexpensive materials is possible; and permit the determination of the type of reducing agent and the optimal quantities employed. The Terra software used in thermodynamic modeling permits the determination of the equilibrium composition of the multicomponent heterogeneous system for high-temperature conditions, on the basis of the maximum-entropy principle. The reducing agents considered are carbon, silicon, and aluminum. The influence of the temperature and reducing-agent consumption on the reduction processes is investigated. The results regarding the reduction of barium and strontium show that silicon or aluminum is the best reducing agent when barium-bearing oxide materials are employed. The optimal reducing-agent consumption corresponding to maximum reduction of the barium and strontium is determined. The possibility of reducing nickel by carbon is confirmed. It is found that vanadium may be reduced by silicon or carbon or a complex process in which carbon is the predominant reducing agent. The results permit the development of a resource-saving technology based on oxides for the alloying, microalloying, and modification of Fe–C systems.

The micro- and nanostructure of 40Kh13 stainless steel is studied by optical, scanning electron, and atomic-force microscopy. The images of the steel’s structure and phase composition in three different states (after annealing, quenching, and high-temperature tempering) are compared. The optical images of the ferrite–pearlite structure with considerable content of (Cr, Fe)₂₃C₆ globular carbides obtained after annealing are compared with the results of scanning electron and atomic-force microscopy. It is found that the qualitative conclusions regarding the microstructure of the steel obtained by atomic-force and scanning electron microscopy not only agree with the results of optical microscopy but also provide greater detail. Data from the scanning electron microscope indicate that large carbides are located at the boundaries of ferrite grains. Some quantity of carbides may be found within the small ferrite grains. The size of the inclusions may be determined. The structure formed after quenching consists of coarse acicular martensite. Images from the atomic-force microscope show the acicular structure with greater clarity; three-dimensional images may be constructed. The undissolved carbides are also globular. The size of the martensite plates may be determined. The structure of the steel after high-temperature tempering (tempering sorbite) is formed as a result of the decomposition of martensite to ferrite–carbide mixture, with the deposition of regular rounded carbides. As confirmed by spectral analysis, the individual and row carbides (Cr, Fe)₂₃C₆ that appear contain chromium, which rapidly forms carbides. This structure is stronger than martensite. Data from uniaxial tensile tests are presented for all the states; the hardness HB is determined.

Silicon carbide may be produced from fine-grain batch consisting of two main components: microsilica waste; and semicoke obtained from Berezovsk lignite (Kansko-Achinsk Basin). The physicochemical properties of the silicon carbide are certified in the present work. Two forms of microsilica are considered: (1) microsilica formed in the production of silicon (containing 93.41–95.33% SiO₂; 1.96–3.28% C_free; 0.30–0.34% Si_free; and 1.25–1.45% CaO + Fe₂O₃ + MnO); (2) microsilica formed in the production of high-silica ferrosilicon: (containing 91.72–93.63% SiO₂; 0.56–1.18% C_free; 0.18–0.20% Si_free; and 1.38–2.32% CaO + Fe₂O₃ + MnO). Its specific surface is 21000–24000 m²/kg. The microsilica is inclined to form spherical aggregates measuring 200–800 nm. The aggregates consist of spherical particles ranging in size from 30 to 100 nm. The lignite semicoke contains 94.05% carbon, 9.2% ash, 0.2% sulfur, and 0.007% phosphorus; its specific surface is 264000 m²/kg. The composition of the silicon carbide is investigated, along with its specific surface; the size and shape of the carbide particles are determined. In both cases, the predominant phase is cubic silicon carbide (β-SiC), with an accompanying glassy phase consisting of silicates of calcium, magnesium, and iron. When the batch containing microsilica from ferrosilicon production, the silicon carbide is accompanied by α iron. In synthesis at 1923 and 1973 K for 50 and 90 min, respectively, polymorphic conversion of β-SiC to α-SiC_p is observed. The content of silicon carbide in the products is 82.52–84.90%. Chemical enrichment of silicon carbide proves expedient. The optimal enrichment conditions are as follows: the action of hydrochloric acid (concentration no less than 35%) at 353 K for 3 h, with a 1:2 solid/liquid ratio. The enrichment characteristics are as follows: the content of silicon carbide in the products is 90.42–91.10%; and 87–95% of the impurities (metal oxides and iron) are removed. The silicon carbide is obtained as micropowder consisting of irregular particles (size 0.2–1.0 μm) with specific surface 8000–9000 m²/kg.

Reductive blast-furnace smelting consists of multifactorial oxidative, heat-transfer, smelting, and reducing processes that involve solid carbon and are associated with carburization of the metal. Analysis yields functional relations of the zonal process with controllable parameters of the hot blast. The ore load on the coke, the batch and coke consumption, the reduction rate of iron, and the rate of slag formation may be regulated as a function of the blast flow rate. If the degree of reduction of iron declines from 0.998 to 0.96–0.98, the oxidation of the slag with respect to iron (the FeO content) may be increased to 2–10%, with slowing of the carburization of iron as the melt flows through the coke bed. Slag oxidation may be increased by the injection of powdered iron oxide into the hot blast through tuyeres. As a result, the carbon content in the metal will be 1.5–2.0%, which corresponds to the composition of austenitic steel.

The development of steel-ball production within the Commonwealth of Independent States over the last 50 years is analyzed. Three periods are identified and characterized. The factors responsible for poor ball quality are discussed. The requirements for the production of high-quality balls with hardness up to HRC 65 are outlined, in terms of the chemical composition of the steel, the equipment required, and the production technology. Significant increase in ball quality requires the creation of specialized rolling systems. The fundamental principles to be adopted in creating such systems are reviewed.

The influence of titanium, which readily forms nitrides, on the structure and the long- and short-term mechanical properties of Cr–Mo–V steel is investigated. Increase in the Ti content to 0.075% increases the thermal stability of the steel. With increase in Ti content to 0.13%, the thermal stability of the steel declines sharply, on account of structural changes.