Steel Billets Research Articles

Features of diffusion-controlled processes of regulated volumetric synthesis from powder mixtures Ti-Al-Fe-Fe2O3

Experimentally and theoretically analyzed processes occurring in mixtures of powders Ti-Al-Fe-Fe2O3 during reactive sintering (sintering from chemically interacting components) under controlled heating. As one of the components wastes of steel billets were used. This makes the study relevant. The heating rate was varied. Possible physical and chemical stages, their sequence and the assumed phase composition of the synthesis products were analyzed. Although reactive sintering has attracted considerable interest for the production of composite materials, the regularities established for binary systems cannot be purely transferred to sintering powders of more than two kinds. It is shown that the multistage process results in the formation of sets of nonequilibrium phases of variable composition based on α-titanium solid solution. The structures obtained from powder compositions «Ti+Al+Fe» and «Ti+Al+metal chips» do not differ much from each other, despite the presence of an appreciable share of oxides in the latter. The examples of particular problem solutions which correspond to the possible variants of diffusion interaction in a heterogeneous system are presented. Analytical solutions are obtained in the quasi-stationary approximation. The diffusive nature of changes in the position of interfaces is the same for constant and variable diffusion coefficients. The shape of the refractory reagent particle has little effect on the dynamics of the process. An example of calculating the stresses and strains in a conditional reaction cell when the phases are separated by moving boundaries is given. In the quasi-static approximation, the time for the mechanical part of the problem is a parameter. It is shown that the driving forces of diffusion transfer may be related to local stresses, which, in turn, may be related to changes in composition.

ТЕХНОЛОГІЧНІ ОСОБЛИВОСТІ КОМБІНОВАНОГО ЛИВАРНО-ІНДУКЦІЙНОГО МЕТОДУ ОДЕРЖАННЯ ТРИШАРОВИХ ВИЛИВКІВ

The technological features of developed casting-induction method for obtaining threelayer «cast iron-steel-cast iron» castings were studied. The specified method consists in the use of induction heating of a steel billet with a high-frequency electromagnetic field in the casting process for obtaining three-layer products. The paper represents mathematical modeling results of temperature fields distribution under the action of electromagnetic fields on a steel workpiece. The main regularities of steel billet temperature changes depending from the current level and heating time have been established. As a result of simulation modeling, the technological parameters of the steel workpiece heating and cooling process were determined, as well as the pouring of the melt during the production of three-layer castings. Obtained dependences between temperature of the poured melt and temperature of the workpiece are necessary to ensure a high-quality connection between the steel inner part and working layer made of cast iron. The results of the experimental testing confirmed the adequacy of the mathematical modeling of the thermal state of the workpiece, as well as the effectiveness of using the developed combined casting-induction method for obtaining three-layer castings. Keywords: induction casting method, induction heating, simulation modeling, three-layer casting, electromagnetic field, melt.

PREDICTION OF THE TENSILE STRENGTH OF STEEL FORGINGS

Great attention is paid to the issues of improving the methods of product quality prediction, in particular, a comprehensive approach to its evaluation is being developed based on the principles of qualimetry. The example of experimental approach is provided to predict one of the mechanical properties ‒ tensile strength which is an important indicator of the steel forgings quality. The investigation has been carried out to estimate the accumulated strain degree, chemical composition, friction conditions at contact surface influencing on temporal resistance distribution in the forging volume. The accumulation of strain degree was carried out by crimping of cubic billets in three mutually perpendicular directions with different number of crimping cycles according to cube‒cube scheme. The distribution of strain degree over the volume of a deformed billet was experimentally determined for lead samples by coordinate grid technique. The lead cubic billets were cut in half. A square grid was applied to one of the halves, and then the halves were fused with a fusible Wood alloy and subjected to the first upsetting. After upsetting the sample was unsoldered and the Λ value in each cell was calculated from the curvature of the coordinate grid. The forging of steel billets was carried out in a similar way. After forging the steel billets, the specimens were cut out for mechanical testing. As a result of experimental data processing, the equation of regression has been received, which enables to predict the level of forgings’ tensile strength at the known technological parameters. Significance of the coefficients of the obtained equation was validated by the Student's criterion and the adequacy by the Fisher's criterion. The developed technique can be applied for selection of rational mode of deformation during forging for maintenance of the given level of mechanical properties.

An Improved Particle-Swarm-Optimization Algorithm for a Prediction Model of Steel Slab Temperature

Aiming at the problem of the low accuracy of temperature prediction, a mathematical model for predicting the temperature of a steel billet is developed. For the process of temperature prediction, an improved particle-swarm-optimization algorithm (called XPSO) is developed. XPSO was designed based on a multiple swarm scheme to improve the global search capability and robustness; thus, it can improve the low accuracy of prediction and overcome the problem of easy entrapment into local optima. In the XPSO, the multiple swarm scheme comprises four modified components: (1) the strategy of improving the positional initialization; (2) the mutation strategy for particle swarms; (3) the adjustment strategy of inertia weights; (4) the strategy of jumping out local optima. Based on widely used unimodal, multimodal and composite benchmark functions, the effectiveness of the XPSO algorithm was verified by comparing it with some popular variant PSO algorithms (PSO, IPSO, IPSO2, HPSO, CPSO). Then, the XPSO was applied to predict the temperatures of steel billets based on simulation data sets and measured data sets. Finally, the obtained results show that the XPSO is more accurate than other PSO algorithms and other optimization approaches (WOA, IA, GWO, DE, ABC) for temperature prediction of steel billets.

AC-MFL testing of orthogonal cracks detection of square billet based on the flexible-printed parallel cable magnetizer

Longitudinal and transverse cracks that appear in the manufacturing and processing of square steel billets are a critical safety hazard. An integrated alternating current magnetic flux leakage (ACMFL) detection probe is composed of parallel cables (PC) magnetizer and pick-up coils manufactured by flexible printed circuit (FPC). Experiments verified the probe could detect longitudinal and transverse cracks in a unidirectional scan. It was proven that when the probe scans the cracks parallel to the direction of the magnetic flux line, the signal at the end of the crack mainly originates from the local magnetic flux leakage (LMFL) field. With an increase in the frequency, the LMFL characteristics become more obvious. Experiments show that the probe can effectively detect longitudinal cracks with a width of 0.4 mm or more when the depth is 0.4 mm, and cracks with a depth of more than 0.3 mm when the width is 1.0 mm in the axial scanning.

Development of Three-Dimensional LES Based Meshless Model of Continuous Casting of Steel

A large-eddy simulation (LES) based meshless model is developed for the three-dimensional (3D) problem of continuous casting (CC) of steel billet. The local collocation meshless method based on radial basis functions (RBF) is applied in 3D. The method applies scaled multiquadric (MQ) RBF with a shape parameter on seven nodded local sub-domains. The incompressible turbulent fluid flow is described using mass, energy, and momentum conservation equations and the LES turbulence model. The solidification system is solved with the mixture continuum model. The Boussinesq approximation for buoyancy and the Darcy approximation for porous media are used. Chorin’s fractional step method is used to couple velocity and pressure. The microscopic model is closed with the lever rule model. The LES model is compared to the two-equation Low Re k−ε turbulence Reynolds Averaged Navier–Stokes (RANS) model in terms of temperature, velocity and computational times. The LES model resolves transient character of vortices which RANS-type turbulence models are unable to tackle. The computational cost of LES models is considerably higher than in RANS. On the other hand, it results in a much lower computational cost than the direct numerical simulation (DNS). The paper demonstrates the ability of the method to solve realistic industrial 3D examples. Trivial adjustment of nodal densities, high accuracy, and low numerical diffusivity are the main advantages of this meshless method.

Solidification structure and central segregation of 6Cr13Mo stainless steel under simulated continuous casting conditions

Central macrosegregation and coarse microstructure are the main defects in ingot castings of high alloy steels. Rapid cooling associated with continuous casting could be beneficial in improving the internal quality of ingot castings. This work evaluated the effects of superheat and cooling intensity on the solidification structure and macrosegregation in 6Cr13Mo stainless steel billet. Numerical modeling was performed to determine the cooling conditions of a continuous casting billet. The simulated cooling conditions were used to solidify 6Cr13Mo steel samples in a thermal simulator. Experimental results suggest that low superheat of the melt combined with an increased cooling intensity reduce central segregation and form refine microstructure. Relationships between the macrosegregation index, (Km_i), of solute elements in the final solidification zone and secondary dendritic arm spacing (λ2), which inversely proportional to cooling rates, conform to simple monotonic equations. Such monotonic relationships indicate that increasing cooling rates is an effective way of reducing central macrosegregation and refining microstructure of 6Cr13Mo steel billet.

Industry-Fit AI Usage for Crack Detection in Ground Steel

We investigated optimal implementation strategies for industrial inspection systems aiming to detect cracks on ground steel billets’ surfaces by combining state-of-the-art AI-based methods and classical computational imaging techniques. In 2D texture images, the interesting patterns of surface irregularities are often surrounded by visual clutter, which is to be ignored, e.g., grinding patterns. Even neural networks struggle to reliably distinguish between actual surface disruptions and irrelevant background patterns. Consequently, the image acquisition procedure already has to be optimised to the specific application. In our case, we use photometric stereo (PS) imaging to generate 3D surface models of steel billets using multiple illumination units. However, we demonstrate that the neural networks, especially in high-speed scenarios, still suffer from recognition deficiencies when using raw photometric stereo camera data, and are unable to generalise to new billets and image acquisition conditions. Only the additional application of adequate state-of-the-art image processing algorithms guarantees the best results in both aspects. The neural networks benefit when appropriate image acquisition methods together with image processing algorithms emphasise relevant surface structures and reduce overall pattern variation. Our proposed combined strategy shows a 9.25% better detection rate on validation data and is 14.7% better on test data, displaying the best generalisation.

Investigation on bonding interfaces of an SA508 steel billet manufactured by additive forging

Investigation on bonding interfaces of an SA508 steel billet manufactured by additive forging

Influence of hot-core heavy reduction rolling on microstructure uniformity of casting billet

ABSTRACT The hot-core heavy reduction rolling (HHR2) technology is a solidification end reduction technique to enhance the quality of steel. In the current study, the Cellular Automata (CA) calculation is applied to investigate the casting process before HHR2 and the HHR2 dynamic recrystallization (DRX) process. The experimental data and calculation data are compared to verify the accuracy of the method and models. Afterward, based on the actual casting process, the solidification structure in the thickness direction of a billet is calculated, and the influence on the HHR2 grain size of various conditions, such as rolling speed, deformation temperature, and reduction strain, is simulated. Furthermore, based on the fixed HHR2 process, the influence of different superheats, casting speeds, and cooling conditions on the core-surface temperature schedule and the grain size before and after HHR2 deformation is calculated. Finally, the process optimization trend to produce high-carbon bearing steel billet is obtained.

Genetic relationship of microstructure and mechanical properties between ferrite/pearlite steel plate and billet

This paper proposed the double-pass compression thermal/force simulation experiment to in situ analyze the phase transformation of continuous casting billet during the controlled rolling and controlled cooling process. The genetic relationship between the central segregation of the billet and solute element distribution of the steel plate, and also the genetic relationship of microstructure and mechanical properties between them were experimentally studied. The results show that the microstructure and mechanical properties between the billet and corresponding batch of steel plate have the genetic relationship, and the link of the relationship is central segregation. The phase transformation of supercooling austenite will be affected by the central segregation of Mn and C elements, and the granular bainite abnormal segregation band is the transformation product of Mn and C element segregation region.

Canola oil as an alternative quenchant for the AISI 8640 steel

AISI 8640 is one of the most used steel in the manufacturing industry due its wide range of applicability and properties. The quenching process is commonly applied in parts made of this steel in order to enhance some properties, such as strength and hardness. Petroleum derived oils are the most common quenchants, however this kind of quenchant is considered to be non-biodegradable, toxic to the health and environment, as well as, not renewable. In the present study, canola oil presented the same efficiency than a conventional petroleum derived oil in the quenching process of AISI 8640 steel billets with diameter of 25.4mm.

Experimental investigation on the oxidation process and mechanism of steel billet under oxygen-enriched combustion atmosphere

ABSTRACT Oxygen-enriched combustion is a promising next-generation combustion technology for the metallurgy industry, allowing net efficiency improvement compared to traditional combustion technology. In this paper, an experimental investigation of the Q235 billet oxidation process for oxygen-enriched combustion, based on a thermogravimetric furnace, is carried out to comprehend the scaling kinetic reheat by oxygen-enriched combustion. The formation of iron oxide scale under different temperatures (800–1200°C) and atmospheric combustion conditions was investigated by an isothermal kinetic experiment to simulate an oxygen-enriched combustion atmosphere (21–40%O2). This experiment observed the effects of heating time, surface temperature, combustion oxygen content, and oxidizing gas composition in the flue gas (H2O, CO2) on weight gain of billet oxidation. Conducted investigations demonstrate that the surface temperature of the billet and the oxygen content of the combustion is positively related to the oxidation rate. Temperature is the primary factor affecting the oxidation of billet. The oxide scales gaining weight in the component of oxygen-enriched combustion flue gas, O2, H2O, and CO2 are 26, 62, and 39 (mg/cm2), respectively. Although oxygen oxidation is the most vital factor among the flue gas, the water vapor is the dominant factor in the oxidation degree of the billet as its highest content. Moreover, the dynamic curve under different atmosphere and temperature conditions was investigated. Kinetic analysis shows that the billet oxidation process with oxygen-enriched combustion is closer to the SCM model.

Вплив швидкості охолодження та перегріву вище лінії ліквідусу на формування структурних складових

In the paper, the comparative analysis of the process of forming a cast structure of carbon steel after termination of its crystallization in continuous cast steel billet with diameter of 450 mm and overheating of steel to 50° C and 150° C above the liquidus line, and further pouring into wedge-shaped molds, is performed. The microstructure of the skin zone after continuous casting of steel with maximum cooling rate of 106 °С/min consists of dendrites, which have branches of the first and second order, indicating their formation from the melt. When etching the surface of the specimens with solution of nitric acid, the microstructure of the skin zone was represented by ferrite, perlite with separate areas of martensite. The formation of ferrite, perlite and bainite areas was observed at a distance of 0.5 ingot radius and in the central part of the samples, and separate areas of bainite and perlite were observed in the central part of the ingot. Upon further cooling of steels below the temperature of Ar3, the formation of excess ferrite along the boundaries of austenitic grains occurs. Overheating of steels to 50° C and 150° C above the liquidus line gives rise to the formation of a more homogeneous structure. Non-metallic inclusions formed in steel do not exceed 1 point according to DSTU 4967:2015and are not the centres of crystallization – they are observed in perlite grains. There is the formation of separate inclusions of phases located in the perlite grain, which contributes to the finely dispersed hardening of steel. Increasing the overheating temperature leads to the formation of more finely divided inclusions and to the formation of a more homogeneous structure. After overheating to 50° C in the middle part of the wedge (cooling rate of 102-103 ° C/min) no ferrite formation is observed. At all overheating temperatures, perlite has a fine differentiation, but increasing in the overheating temperature above the liquidus line enhances the dispersion of both individual inclusions and perlite. Keywords: carbon steel, continuous cast steel billet, hardening, cooling rate, overheating of steels above the liquidus line.

THE RESULTS OF THE STUDY ON THE CYCLIC STRENGTH OF THE DEVELOPED CUTTING CERAMICS

The paper presents the results of a study on the cyclic strength of cutting ceramics: a replaceable polyhedral plate developed at NSTU and VOK-60 cutting ceramics when processing a hardened steel billet made of HVG steel (45 HRC) with two opposite grooves. Turning was performed until the cutting edge of the plates was destroyed. Using the HITACHI S3400N electron microscope, the structure of the destroyed surface layer was investigated and the mechanism of destruction of the cutting edge of tool plates made of cutting ceramics was determined. It has been established that the developed cutting ceramics have a greater resistance to fracture under conditions of intermittent turning of hardened steel compared to the VOK-60 brand. The low operability of the cutting plates made of the developed ceramics under conditions of intermittent turning is mainly caused by the chipping of the cutting edge due to the formation of microcracks at the grain boundaries. A characteristic feature of the mechanism of brittle fracture of cutting ceramics is intergrain tearing and chipping of large Al2O3 grains.

Technology for manufacturing of reference calibration simulators of fuel pellets of pressurized water reactors

The work is devoted to the development of technology for the manufacture of reference calibration simulators of fuel pellets of pressurized water reactors. Reference calibration simulators of fuel pellets are necessary in the development of optoelectronic systems for monitoring the appearance and geometric dimensions of fuel pellets used in the production of uranium pellets. The article describes the developed technology for the manufacture of simulators, based on the manufacture of steel billets and subsequent multi-stage mechanochemical surface treatment based on blackening by the acid method.

The Effect of Temperature, Cooling Rate and Casting Speed on Quality of Continuous Cast Steel Billets

In continuous casting, the cooling rate, casting speed, and molten metal temperature significantly affect the quality of cast steel billets. Appropriate casting parameters can minimize quality problems such as surface, subsurface and interior crack, rhomboidity, oscillation mark depth, and central porosity. This research determines the relationship between defects and three significant factors temperature, cooling rate, and casting speed. The work has been performed on the two-strand continuous casting machine to investigate the billet (BS-4449 steel grade) cross-section of 150 x 150 cm2. The defects analysis through macro examination at different tundish temperatures (1510 °C to 1560 °C), varying cooling rates, and casting speeds (0.9 to 1.6 m/min). The present study provides detailed insight into the three parameters mentioned earlier, which directly affect the quality of cast steel billets.

Development of Production of Continuous Cast Billets of Grade 08Kh18N10T Steel for Fabricating Hot-Rolled and Pressed Pipes

Development of Production of Continuous Cast Billets of Grade 08Kh18N10T Steel for Fabricating Hot-Rolled and Pressed Pipes

Особливості формування неоднорідних структур у вуглецевих сталях

Obtaining a homogeneous structure and uniform-phase distribution is critical to a high set of mechanical and operational properties of rolled metal. However, in practice it is not always possible to create metal products with the specified characteristics. In order to determine the morphological features of the structure of rolled carbon steel, a comparative study of carbon steel samples with a carbon content of 0.49 % C and 0.2 % C selected from hot-rolled billets was carried out. The billets of each group were produced under the conditions of the same enterprise, with close temperature-time modes of deformation processing. The main difference was in manufacturing processes of the output continuous cast steel billets. This research shows that with identical normalized chemical composition of steel and the same thermomechanical treatment, the formation of the morphological structure features of hot-rolled steel occurs in a different way. Therefore, we can assume that the liquation, the diffusive mobility of elements is particularly influenced by the content of impurity elements and gases in steel, which leads to a different type of structures in the finished rolled metal. At the same time, these differences are observed in carbon steels with different carbon content. A sample of non-vacuumed OC grade axle steel (0.49 % C) from converter steelmaking has a more homogeneous structure without local areas of pearlite or ferrite accumulation. It was shown that the formation of ferrite rim in the microsegregation areas occurs not only in manganous sulfides, but also arises on the background of the smallest oxide inclusions. There is significant structural heterogeneity in the samples of electric steel, despite the lower sulfur content and gassiness of steel; at the same time, a dense perlite layer is formed around the sulfides. There is also a difference in steel grade 20 (0.2 % C) of different manufacturing processes. The structure is more homogeneous in qualitatively deoxidized vacuum degassed steel; no local areas with different dimensional characteristics were detected. The size of the structural elements is much larger and the structure has mostly large sections of the Widmanstatten ferrite. Since a large number of non-metallic inclusions and gassiness of steel is not a positive factor for providing a high set of properties of metal products, the modes of thermomechanical treatment used today require adjustments depending on the characteristics of steel melting. Keywords: microstructural heterogeneity, ferritic-pearlitic banding, mechanical properties, manganous sulfides.

Complex analysis of the influence of impurity and alloying elements on the toughness of steels for the manufacture of railway axles

The paper presents and summarizes the results of statistical analysis of industrial data on chemical composition and mechanical properties of more than 1,500 samples taken from rough railway axles made of steel grades OS and EA1N with different degrees of deformation. The analysis was performed using the parametric Student's t-test, which allows to assess the statistical significance of differences between the compared values, namely, the greater the value of the t-test, the more statistically significant differences between the compared values. A significant reserve for improving the structure and properties of axial steel is the adjustment of the chemical composition, even within the vintage composition, which will minimize the cost of additional heat treatment of steel in the manufacture of railway axles. The difference between the chemical composition of steel for railway axles and the level of impact strength, in particular manganese and sulfur, has been determined. Manganese, although a strengthening element, promotes the growth of austenite grains and enhances carbon sequestration, which leads to uneven distribution of structural components of ferrite and perlite, especially with increasing its amount and insufficient deformation. This is due to the positive effect of sulfur on toughness. Although sulfur is an element that significantly reduces the properties of steel, but in this case, its content is likely to reduce the liquation of manganese. As the temperature in the austenitic region decreases, Mn is concentrated more in the nonmetallic MnS inclusion, thereby reducing its concentration around the inclusion. The necessity of applying a greater degree of deformation of the original continuously cast steel billets of EA1N grade and the implementation of measures that will have a positive effect on the reduction of dendritic segregation is shown. The significant influence of steel production technology for railway axles of close chemical composition is emphasized.