Vol 49, No 10 (2019)

The study of molten metal flow to the mold of a continuous casting machine (CCM) is still considered to be a complex and imperfect process. This paper is one of the author’s publication series that focuses on the theoretical possibility on the motion kinetics of a liquid metal and heat fluxes in a mold under traditional casting based on: hydrodynamic theory, mathematical physics equations, and an approved numerical approach. This well-known calculation methodology makes it possible to calculate the fluxes of liquid metal motions and their temperature in the mold for the proposed method and for other methods of supplying the metal, as well as to compare the results between each other. The formulation and solution of a three-dimensional problem for determining the velocity and temperature fields in a metal supplied to a CCM mold from a submerged nozzle to a round deflector is discussed. This calculation methodology is based on a system of constitutive equations, a numerical method, a numerical scheme, and an algorithm for solving the problem. According to calculations, the hardened metal crust growing on the faces of the mold has been neglected. If traditional and proposed methods are used to objectively analyze the results and solve the problem, the same theoretical (the velocity of drawing from the mold) and the geometric parameters of a rectangular mold are taken. A patent for describing this alternative method of liquid metal supplying to a rectangular mold has been registered (No. 2018108974/02 (013808)). Some results of the numerical solution of the problem are presented, namely, schemes of liquid metal flows and the temperature thereof in various sections of the mold.

The simplex lattice method has been applied to studying the chemical composition influence of CaO–SiO₂–B₂O₃ oxide system containing 15% Al₂O₃ and 8% MgO on viscosity and solidification point (hereinafter wt % are used). The addition of boron oxide to slags of the considered oxide system expands the range of slag composition with low solidification point and viscosity. The slags with basicity of 2.0–3.0 containing 1– 3% B₂O₃ are characterized by low (1400–1450°C) solidification point and high viscosity. Viscosity of such slags upon their heating to 1550 and 1600°C does not exceed 0.20 and 0.15 Pa s, respectively. An increase in B₂O₃ content to 4–6% in slags with basicity of 2.0–3.0 is accompanied by a decrease in solidification point to 1350–1425°C with retention of low (not higher than 0.15 Pa s) viscosity at heating temperature of 1550 and 1600°C. Generated slag displacement containing 1–6% B₂O₃ to the basicity regions increasing to 3.0–5.0 retains a sufficiently high fluidity. Herewith, it can be observed that the considered oxide system is displaced to a low solidification point region with an increase in boron oxide concentration. A slag solidification point with basicity of 3.0–4.0 containing 6% B₂O₃ reaches 1400°C and actually does not exceed 1475°C for the slags with basicity of 4.0–5.0 containing 1–2% B₂O₃. At 1600°C, the slag viscosity varies from 0.15 Pa s at basicity of 3.0 and B₂O₃ content of 5– 6% to 0.25 Pa s at basicity of 4.0–5.0 and B₂O₃ content of 1–3%. A temperature decrease of the considered oxide system by 50°C is accompanied by an insignificant (not more than 0.05 Pa s) increase in viscosity.

Fatigue strength of widely used engineering structural steels was studied at various loading frequencies according to the cantilever bending scheme of rotating cylindrical samples. The inclination angle tangent of the fatigue curve to the axis of durability was taken as the fatigue resistance index. It has been established that 40 and 45 grade steels (UNS G10400/G10420 and G1044/G1045) belong to the group of materials in which a decrease in the loading frequency leads to cyclic softening and a decrease in the fatigue resistance, which is numerically expressed by the increase in the slope of the fatigue curve. Test samples made of 40Cr grade steel (UNS G51400) have shown that the increase in the frequency of loading cycles leads to a noticeable decrease in the fatigue curve slope parameter, i.e., leading to an increase in the fatigue resistance. The decrease in the fatigue resistance parameter is associated with the enhanced hardening of the material of the samples’ surface layers, which reduces the fatigue damage to the surface itself. The tangent dependence of the fatigue curve slope is shown on the surface damage rate when the loading cycles change frequency. Regardless of the frequency, the damage rate of the material’s surface layers increases along the fatigue curve slope. For each of these groups, mathematical relations have been defined. A correlation coefficient that shows the degree of convergence of experimental results and the constructed fatigue curve is adopted as a criterion of the cyclic behavior stability of steels. An increase in the behavior stability of 40Cr steel is observed with the increasing cyclic deformation rate. 45 grade steel tests have shown that a decrease in the cyclic strength with an increasing loading frequency does not affect the material’s fatigue stability. Experimental results showed increased dispersion for 40 grade steel at a low loading frequency despite high values of the cyclic strength at a given loading frequency. Based on the experiments, the behavior dynamics of real machine parts and structures subjected to cyclic loads within the studied loading spectrum has been established.

The paper presents a prediction model for steel temperature in a specified time interval during its overheating over a liquidus point in the tundish of a continuous casting machine (CCM). This depends on the last temperature measurement in a ladle prior to casting with consideration to the ladle’s history and treatment during secondary metallurgical processes in an casting and rolling complex (CRC). The prediction of steel superheat temperature at CRC is based on two modeling stages: the first stage integrates two approaches—a machine-learning algorithm and a probabilistic-graphical model (PGM and Bayesian networks); and the second stage uses a method for evaluating probability distributions. The first approach gives a point estimate of the intermediate and final temperatures of specific heat. The PGM-approach is useful for scenarios with uncertain input data, which is often the case for metallurgical enterprises. The accuracy level in predicting the temperature of the metal in the tundish at the first stage reached 6.0°C. At the second stage, the model integration into the process control system improved prediction accuracy, as well as provided technological parameter control in real time. The model is used as an advisor (master) for the technical team of the ladle furnace and vacuum degasser.

Based on studies, the technological process results of the production of a complex calcium-containing ferrous alloy of waste blast-furnace slag using high-ash coal from the Saryadyr coal field and coal slurry from the Karaganda coal basin are presented. The study was conducted on the experimental site of the Abishev Chemical Metallurgical Institute using an ore-smelting furnace equipped with a 200-kV A transformer. The main task of the study was ensuring the complete reduction of all oxides of the charge comprised of blast-furnace slag, high-ash coal, and coal slurry in a continuous, stable, and easy-to-control slagless process.

This study includes the screw rolling of several blank parts of 12Kh18N10T steel on a two- and a three-roll mill, followed by modeling test rollings in the DEFORM FEM software. The test rolling results were used to evaluate changes in the dispersion of average grain size and hardness in the nonstationary and stationary phases of screw rolling. The computer-aided modeling results were used to evaluate variations in strain effective. The studies allowed identifying the changes in the average grain size and hardness in the different rolling phases and defined the compliance with the kind of changes in the average grain size, hardness, and strain effective across the blank part volume. The computer-aided modeling and test evaluation showed the differences in the kind of strain effective variations in the nonstationary phase at two- and three-high rolling.

The influence of manufacturing material methods based on Fe₃₀Cu₇₀ on their microstructure and inclusion size, which is determined by the cooling rate of the melt during crystallization, is investigated. The line structure of the solid phase microstructure enriched in iron in the early stages of cooling can be traced with all the technologies for producing the Fe₃₀Cu₇₀ alloy. It was found that the higher the cooling rate, the less manifested was the network nature of the structure. An elemental analysis of the structure showed that the content of iron and copper in all structural components is greater than the maximum possible mutual solubility of the elements.