卷 47, 编号 5 (2017)

The expediency of producing and using complex ferroalloys in steelmaking is analyzed in terms the manufacturing technology, the raw materials employed, and the interactions of the ferroalloys with the molten steel. The need to produce complex ferroalloys with boron is established. The fundamental principles for determining the best composition of such alloys are presented. The basic compositions of complex ferroalloys with boron (ferrosilicomanganese with boron, ferrosilicon with boron, ferrosilicomanganese with boron and chromium) are established by studying the physicochemical properties of alloys and their interactions with the steel melt. If the characteristics (melting point, density, melting time of the ferroalloy in liquid steel, etc.) of complex ferroalloys with boron are compared with those of ferroboron, which is widely used, the complex alloys have clear benefits. The composition of the complex ferroalloys with boron includes active elements (Si, Al, Ti) facilitating the binding of oxygen and nitrogen from the steel melt in strong compounds and hence preventing their reaction with boron. The recommended boron content in the ferroalloy is 0.7–2%. That permits increase in the quantity of complex ferroalloys with boron in the steel and hence increase in the reliability and stability of boron assimilation. At elevated temperatures (1430–1570°C), the oxidation of ferrosilicoboron is 4–7 times less than that of ferroboron. Data are presented regarding the industrial production and use of ferrosilicoboron in the steel-smelting shop. The boron assimilation from complex alloys in microalloying of the steel is studied. The use of ferrosilicoboron does not require significant changes in the existing system for reduction by ferrosilicon; the boron assimilation is 77.8–96.3% (mean 86.6%). With a boron concentration of 0.0021–0.0027% in the steel during ladle treatment, its content in the cast metal will be no less than 0.0020%. If boron is introduced in steel by means of ferrosilicomanganese with boron, the boron assimilation is increased by a factor of 1.6 (from 48 to 77%, on average) in comparison with the use of ferroboron.

The structure and mechanical properties of 35Kh12G3MVFDR steel are investigated. After normalization or quenching, the steel contains up to 35 vol % austenite and may be assigned to the martensitic–austenitic class. On heat treatment—tempering, isothermal holding, or isothermal quenching—the austenite is converted to martensite within 2 h. The martensite in 35Kh12G3MVFDR steel is more thermally stable: the first signs of its conversion to sorbitic structure are observed after 25-h isothermal quenching at 640°C, and its complete decomposition requires 50 h. The breakdown of martensite is accompanied by decrease in the high-temperature strength and hardness. Aging of the quenched and tempered 35Kh12G3MVFDR steel at 670–720°C lowers the hardness from 61–65 HRA to 55–60 HRA after 1600–3200 h and the yield point at 20°C from 1350 MPa to 750–850 MPa. Likewise, the yield point at 720°C declines from 310 MPa to 160–230 MPa after 600 h and then stops. The state of the martensitic structure of 35Kh12G3MVFDR steel determines its creep resistance at 700°C. For example, the martensite remains in the steel structure after relatively brief isothermal quenching (up to 24 h at 640°C), and consequently the creep limit σ^700°C_0.1%/h is no lower than after simple quenching with subsequent high tempering: 86.2 ± 9.4 MPa and 89.3 ± 8.8 MPa, respectively. At the same time, in response to the decomposition of martensitic structure as a result of prolonged aging (1600 h at 670°C), σ^700°C_0.1%/h declines to 63.9 ± 7.1 MPa. In contrast to martensite, the austenite in 35Kh12G3MVFDR steel is thermally unstable and is converted to martensite after only 1–2 h of heating, depending on the temperature.

The reindustrialization of production is considered. As an example, a working model is developed for the heat-treatment equipment used in the production of dies made from special steels. In reindustrialization, productive capacity that has been lost or has grown outdated during deindustrialization must be restored or modernized. Heat treatment is of particular importance since it is part of the manufacture and restoration of most tools. Modern Russian equipment permits high-quality heat treatment of many special steels so as to ensure the required mechanical properties. All the basic groups of die steels are considered in terms of their performance: steel of increased wear resistance; secondary-hardening crumple-resistant steel; steel with elevated impact strength; steel of moderate thermostability and high ductility; steel of elevated thermostability and ductility; and steel of high thermostability. The requirements on the properties of these groups are analyzed, and possible means of attaining those properties by heat treatment are identified. By comparing the specific purpose of die steels, their required properties, and the possible means of attaining those properties by heat treatment, the appropriate equipment is chosen. Modern Russian equipment permits high-quality heat treatment of die steels so as to ensure the required mechanical properties. At present, it is important to create production systems that incorporate the vast wealth of Russian specialists’ accumulated experience and the best available technologies. This is a very complex problem, in both engineering and economic terms.

The influence of the structure of the tundish on the hydrodynamics of the melt flux is investigated on physical models and in industrial conditions. The influence of design modifications in the tundish on the refining of the steel is analyzed. Factors that affect tundish operation include the injection conditions, the tundish capacity, and the melt level.

The screw piercing of blanks on a two-roller mill with mushroom-shaped rollers is modeled by the finite-element method. That permits calculation of the piercing forces and analysis of its dimensional precision. The models are verified by comparing the calculated and experimental rolling parameters and sleeve dimensions. On that basis, stable rolling of thin-walled 328 × 20.5 and 433 × 26.9 mm sleeves is possible.

The production of microalloyed steel coils (thickness 8 mm) of strength category K60 (X70) with requirements on the low-temperature strength is studied in industrial trials. Microalloying of the steel with 0.10% V and 0.020% N and controlled rolling in the casting and rolling system, with a final deformation temperature of 800°C, results in the production of metal with high strength (σ_B ≥ 600 N/mm², σ_y ≥ 520 N/mm²) and plasticity (δ₅ = 28%) with satisfactory strength at –40°C according to impact-flexure and drop tests.

The formation of the phase-transformation front in complex iron alloys during decarburization is studied. The influence of the main alloying element (tungsten) on the morphology of the recrystallization front in γ + Me₆C → α transformation is analyzed; this transformation is responsible for diffusional change in composition in isothermal conditions.