Billet Continuous Casting Research Articles

Thermo-mechanical analysis of the flange in a Billet continuous casting machine based on limited temperature measurements

ABSTRACT This paper targets at the calculation of in-service deformation of a flange in a billet continuous casting machine due to thermal loading. In this regard, first, the thermal analyses of the mould will be thoroughly and accurately conducted. Henceforth, the heat flux profile from the melt to the mould is derived from the literature and, based on the limited temperature measurements, it is calibrated for the understudy mould. Moreover, for the upper part of the meniscus, the effect of radiation is considered as a heat flux profile with an exponential function. Subsequently, the thermo-mechanical analysis is conducted by applying the thermal load, as a temperature distribution, on the corresponding finite element (FE) model. The results of the analysis for the critical flange showed that the calculated deformation at the critical point, 1.08 mm, is close to the value reported by the manufacturer which is 1.25 mm.

Drawing fracture behavior and mechanism analysis of ER50-6G welding wire steel

In this paper, we investigated the drawing fracture behavior of ER50-6G welding wire steel and analyzed the factors affecting the fracture, such as continuous casting slag and inclusion, billet structure segregation, Ti inclusion, surface defect inheritance, metallographic structure type, fracture morphology, and so on. OLYMPUS GX53 optical microscope was used to observe and analyze the macrostructure of the cross-section and longitudinal section of the continuous casting billet and the original quality state of the wire rod surface. The continuous cooling transformation curve (CCT curve) of the steel was measured using a DIL805A thermal dilatometer and a Gleeble-3500 thermal simulation test machine. The microstructures of the non-fracture area and drawing fracture of wire rod samples were observed through a ZEISS-ULTRA scanning electron microscope. The results show that the austenite starting transformation temperature (Ac1) and the austenite finishing transformation temperature (Ac3) of ER50-6G welding wire steel are 732 °C and 865 °C, respectively. Under the actual cooling conditions of online production, the strip structure is composed of ferrite (F), pearlite (P), and a small amount of bainite (B). There is a small amount of slag and inclusion in the continuous casting billet; in addition, Al2O3 inclusions and TiC (or Ti(C,N)) inclusions can be observed in the wire rod. The scratch depth of the wire rod surface is 24∼62 μm and the width is 31∼50 μm. With the increase in drawing cumulative deformation, the Al2O3 and TiC (or Ti(C,N)) inclusions that are not easy to deform lead to drawing fracture and brittle fracture. In addition, a small amount of bainite in the wire rod microstructure causes the fracture of the wire with a fine diameter, whereas, the limited-depth scratches on the steel surface do not have an obvious effect on the drawing fracture.

Cracking Behavior and High-Temperature Thermoplastic Analysis of 09CrCuSb Steel Billets

This paper characterizes the surface crack morphology and elements of 09CrCuSb steel continuous casting slabs and studies the high-temperature thermo-plasticity of continuous casting slabs using a Gleeble 3500 thermal simulator. Combining the macro/micro fracture morphology and microstructure characteristics, the formation rules of slab cracks are discussed. The research results show that the increase in Ae3 temperature caused by changes in alloy elements results in the precipitation of a thin, film-like coexisting ferrite along the grain boundaries at a certain temperature, as well as the element segregation behavior of low-melting-point alloy elements at the original austenite grain boundaries, which are the main factors inducing cracks in 09CrCuSb steel continuous casting billets. The plasticity of 09CrCuSb steel at high temperatures is poor at 800~900 °C. In continuous casting process control, it is necessary to try to avoid long-term stay of the billet at this temperature range.

Analysis of the transformation of the microstructure of axial billets after rolling

The task of improving the quality of metal products of large cross-sections pro-duced from continuous cast billets (CBS) is associated with a number of difficulties. These include the presence of internal defects in the macrostructure of the workpiece (axial looseness, porosity, liquation, crystallization cracks, etc.). Processing from the point of view of deformation of cast workpieces is necessary first of all to eliminate cast defects. An increase in working out contributes not only to the welding of existing mi-crodiscontinuities and, in this connection, to an increase in the density of the metal, but also to the extraction, crushing and reduction of the cross-section of the existing non-metallic inclusions. However, the dimensions of the elements of the primary structure, which are presented on the graphs, are also of the greatest importance. The smallest level of liquation is formed in the surface areas during crystallization. At the same time, as a rule, it is necessary to obtain a homogeneous structure in terms of grain size on the cross-section of large-sized metal products. A study of the features of the structure of axle blanks made of steel grade F (AAR M-101-2017 Axles, carbon steel, heat-treated) after longitudinal rolling on a TPA 5-12" pipe rolling unit with pilgrim mills in three crimping modes (1 mode: Ø 470 → Ø 380 → Ø 260 mm; 2nd mode: Ø 470 → Ø 420 → Ø 260 mm; 3rd mode: Ø 470 →Ø 260 mm). Determination of the features of the distri-bution of deformation work and the formation of the final structure after deformation according to the experimental modes of BLZ Ø470 mm per circle Ø260 mm is the pur-pose of the research. Samples for the structure study were taken both from the original BLZ and the finished draft axle along the entire cross-section. The greatest unevenness of the liquation background, which is observed in the axial blank manufactured using mode No. 1, is also manifested during the study of the microstructure of railway of the axes obtained by the indicated modes. It was determined that the uniformity of the grain structure is the highest after using mode No. 3 (Ø 470 →Ø 260 mm).

Influence of mechanical reduction amount on internal quality of continuous casting billets by thermal and numerical simulation

Influence of mechanical reduction amount on internal quality of continuous casting billets by thermal and numerical simulation

Numerical modelling of macrosegregation in three-dimensional continuous casting of steel billets

Macrosegregation presents a considerable defect in the continuous casting of billets and can critically affect the final properties of the product. The numerical modelling can help to predict and better understand the segregation and flow patterns inside the mould. The process is modelled with a physical model described by a set of conservation equations describing the t heat transfer, turbulence, fluid flow, solidification and segregation. A two-equation low-Re k-epsilon model and Abe-Kondoh-Nagano closures are used to close governing equations in this incompressible fluid flow example. The Boussinesq approximation is applied to account for the thermo-solutal buoyancy effects, and the Darcy approximation is applied for the description of the flow through the porous mushy zone. On a microscale, a lever rule solidification model is used to couple liquid fraction, temperature and concentration. The three-dimensional model is solved with the method based on local collocation with multiquadric radial basis functions on seven-nodded subdomains. The aim of this contribution is to explore the three-dimensional macrosegregation patterns of 0.51 wt% carbon steel in the solidified shell of the steel in the mould.

The Effect of Mold Structure and Cooling Parameters on Heat Transfer during Billet High-Speed Continuous Casting.

Mold structure and cooling parameters are significant factors that affect the heat transfer capacity of high-speed continuous casting molds of billets. Therefore, a three-dimensional fluid flow and heat transfer model of a 160 mm × 160 mm billet mold was established, and its accuracy was verified. Thereby, the characteristics of heat transfer and influences of mold structure and cooling parameters on heat transfer in the high-speed continuous casting billet mold region were revealed. It was found that extending the effective length of a mold is the most valuable method to improve its heat transfer capability and achieve high-speed continuous casting. The total heat and the shell thickness at a mold outlet increased by 19% and 9.21% on average with every 100 mm extension. Enlarging the fillet radius could enhance the uniformity of heat transfer in the mold. Considering the loss of material, the optimal fillet radius of the mold was determined to be R = 10 mm.

Modern approaches ensuring rational conditions for continuously cast billet formation in a billet CCM mold.

The development of technology and technology of continuous steel casting actualizes the improvement of the control system of casting processes and diagnostics of the formation of continuously cast billets. The conditions determining the stability of continuous cast billet forming process in billet CCM mold are considered: the correspondence of liquid steel mass entering the mold and the outgoing billet mass; ensuring the specified intensity and uniformity of billet cooling in the mold sleeve; ensuring a rational level of friction in the crystallizer. It is shown that, on the one hand, heat transfer in the mold is largely determined by the correspondence of the billet shrinkage and the internal profile of the mold, but, on the other hand, it is noted that it is impossible to obtain a universal profile that creates optimal conditions for the formation of billets from all grades of steel with arbitrary temperature-speed parameters. Therefore, the concept of a universal crystallizer assumes that rational conditions of heat removal are achieved due to additional influences. The basics of diagnosing of heat exchange processes in the crystallizer are presented, based on the computational processing of the current ACS signals about the cooling water temperature drop in the crystallizer and its flow rate. It is noted that this system, unfortunately, does not guarantee the detection of local unevenness of the heat removal in the crystallizer and needs to be improved by providing the possibility of assessing the billet faces cooling uniformity. Modern approaches to optimize internal profile of crystallizer sleeves, choice of materials for coating inner surface of sleeves, choice of parameters of mold swinging system and diagnostics of parameters of force interaction between crust of forming billet and mold sleeve are briefly considered on issue of friction rational level establishing. The creation of a “universal” crystallizer with an increased number of control systems and the creation of a system for optimization of casting processes for specific conditions are identified as possible directions for the development of approaches to ensure rational conditions for the formation of continuous cast billets in the crystallizer of a billet caster.

Analysis Model of Molten Crystallization of Mold Flux based on Image Segmentation Recognition

In this paper, through the research and analysis of the melting and crystallization process of mold flux, the characteristics of steel are improved. In the process of casting billet, the solidification characteristics of continuous casting billet are closely related to the physical and chemical properties of mold flux. The hot wire recognition image caused a great waste of manpower and material resources. Therefore, it is particularly important to develop automatic feature extraction and mathematical modeling techniques for sequence images. In this paper, correlation analysis, image segmentation and extraction technology, time series, discrete wavelet and other related models are used to study the images in the melting and crystallization process of mold flux, and analyze the differences of mold flux in the melting and crystallization process, so as to solve the kinetic relationship between the melting and crystallization process of mold flux.

Automatic recognition and intelligent analysis of central shrinkage defects of continuous casting billets based on deep learning

Automatic recognition and intelligent analysis of central shrinkage defects of continuous casting billets based on deep learning

Numerical Simulation of Solidification Structures Influenced by Cooling Spraying and Process Parameters Based on Cellular Automaton Finite‐Element Model

A cellular automaton finite‐element coupling model is developed to investigate the influences of the solidification structure of a continuous casting slab by the state of the cooling spray and process conditions. The model is validated. The solidification structure is simulated for different cooling spray schemes, superheat degrees, and casting speeds. The grain growth and distribution of the continuous casting slab near the corner area are sensitive to the cooling spray. As the distance of the nozzle from the surface of the continuous casting slab increases, the radii of the columnar and equiaxed grains tend to increase near the corners. The distribution of a columnar‐to‐equiaxed grain transition near the corner area gradually moves toward the core of the slab as the distance of the nozzle from the continuous casting slab decreases. At a casting speed of 1.2 m min−1 and superheat degree of 20 °C, the best nozzle height from the surface of the continuous casting billet is 234.5 mm. The casting speed and superheat significantly affect the grain radius. With the increase in the casting speed and decrease in the degree of superheat, the average grain radius decreases, while the equiaxed grain area increases.

Numerical analysis of the comprehensive effect of continuous casting process parameters on the continuous casting billet remelting

In the present study, a coupled 3-D model of flow, solidification, and heat transfer was established to apply to gain new insights into the effects of casting speed and nozzle diameter on the remelting of continuous casting billets. The effects of nozzle diameters and casting speeds on the remelting of continuous casting billet were analyzed separately. Nozzle diameters vary from 20 mm to 50 mm, and casting speed varies from 1 m/min to 4 m/min. The flow behavior and velocity distribution, which are at different casting speeds, were calculated, and the reasons for shell remelting at high casting speeds were analyzed. The remelting of the billet shell, which is at different combinations of different nozzle diameters and casting speeds, was calculated. Then, the comprehensive effects of nozzle diameters and casting speeds on the remelting of the billet shell are analyzed. Finally, the remelting degree maps of different continuous casting process parameters were presented. By the simulation, it is found that the casting speed has more obvious effects on whether the remelting phenomenon occurs, while the diameter of the nozzle has more obvious effects on the degree of remelting. When the casting speed is lower than 2 m/min, remelting does not appear. When the casting speed is higher than 3 m/min, remelting will occur. When the casting speed is 3 m/min, as the nozzle diameter increases, the remelting degree continues to decrease, and the range of remelting first remains stable, then gradually decreases. It can be observed that when the casting speed is increased to 3–4 m/min, the nozzle diameter should be in the range of 30–40 mm.

Numerical simulation of shrinkage porosity defect in billet continuous casting

Abstract Shrinkage porosity is a typical internal defect in the continuous casting billet, which occurs frequently and is difficult to solve. To explore the influence factors of central shrinkage porosity, a novel unsteady thermomechanical coupling analysis algorithm is developed based on the billet solidification characteristics, and the central shrinkage behavior during the ending solidification process is simulated. Results show that when the casting speed increases from 1.6 to 2.8 m·min−1 and the center outward displacement is reduced from 9.20 × 10−2 mm to 5.8 × 10−2 mm, it means casting speed has a significant effect on the formation of shrinkage porosity, and for this caster, the higher casting speed is more suitable for the secondary cooling zone. Without the changes in the solidification structure, when the superheat degree of molten steel increases from 10 to 40°C, the center outward displacement value decreases from 7.12 × 10−2 mm to 6.91 × 10−2 mm. In that case, the superheat degree has no obvious effect on the center displacement value.

Development of a Novel Strand Reduction Technology for the Continuous Casting of Homogeneous High‐Carbon Steel Billet

Internal quality issues concerning center segregation, porosity, and internal crack are the major problems with respect to the production of high‐carbon steels billet with a continuous casting process. Herein, a heat transfer calculation model is developed, verified, and applied to calculate the appropriate casting speed and secondary cooling intensity of the continuous casting billet with a section size of 160 mm square during mechanical reduction processes. The mechanical reduction on the homogeneity of the billet is investigated by several field trails to improve the internal quality of the high‐carbon 82 A steel billet. Consequently, a superoptimum crack‐free high‐carbon steel billet with high homogeneity both in segregation and in compactness is successfully achieved through a novel strand reduction pattern, combined with consecutive multiroll soft reduction and single‐roll heavy reduction.

Study on the positive segregation in columnar-to-equiaxed transition zone

Laboratory experiments of steel ingots under three cooling modes and industrial trials of continuous casting (CC) blooms and billets were conducted, respectively. Corresponding results of the macrosegregation and the solidification structure were investigated. The mechanism of the positive segregation in the columnar-to-equiaxed transition (CET) zone was proposed. For laboratory experiments of ingots under three cooling modes, including water cooling, water cooling for 15 s followed by air cooling, and air cooling, obvious positive segregation was generated in the CET zone, and the degree of segregation was 1.024, 1.025, and 1.015, respectively. For industrial trials of three kinds of steel, CC bloom, round bloom, and billet, positive segregation was formed in the CET zone, and the degree of segregation was 1.06, 1.04, and 1.06, respectively. With the growth of columnar dendrites, solute elements were rejected on the liquid–solid interface. The downward flow near the columnar tip region and the upward flow in the center melt can carry the solute-rich melt to the molten pool. When the CET occurred, equiaxed grains accumulated around the columnar dendrite tips, and the solid network became less permeable. The liquid flow in the network was significantly suppressed, and thereby the solute-enriched liquid was ‘arrested’ locally. Solute-enrich liquid would be further sucked into the interdendritic region owing to the solidification shrinkage. As the sample was fully solidified, the obvious positive segregation was found at the CET zone.

Optimization of the rhomboidity of continuously cast billets using linear regression and genetic programming: A real industrial study

During the continuous casting of steel billets, several geometrical, inner and surface defects can occur due to the thermomechanical behavior during solidification. One of them is rhombic distortion (i.e. rhomboidity), which can lead to the occurrence of off-corner cracks and twisting of cast billets during further plastic deformation (i.e. rolling). Based on data of 2088 cast batches (64 different hypoeutectoid steel grades), 109,514 billets, produced from January 2022 to September 2022 in Štore Steel Ltd. (Slovenia), chemical composition (content of C, Si, Mn, S, Cr, Mo, Ni and V), casting parameters (average casting temperature, average difference between input and output cooling water, melt level, average cooling water flow and pressure in the first and second zone of secondary cooling) the linear regression and genetic programming were used in order to predict rhomboidity of continuously cast billets. The rhomboidity, in our case defined as relative diagonal difference, was determined using in-house developed computer vision system for measuring of rhomboidity. Based on the modelling results 9 batches (419 billets) of 42CrMos4 were cast in September 2022 with a 10 % higher water pressure in the first zone of secondary cooling (from 2.41 bar to 2.67 bar). The rhomboidity of continuously cast billets improved by 18.18 % (from 1.43 % to 1.21).

A soft sensing method of billet surface temperature based on ILGSSA-LSSVM

It is difficult to measure the surface temperature of continuous casting billet, which results in the lack of important feedback parameters for further scientific control of the billet quality. This paper proposes a sparrow search algorithm to optimize the Least Square Support Vector Machine (LSSVM) model for surface temperature prediction of the billet, which is further improved by Logistic Chaotic Mapping and Golden Sine Algorithm (Improve Logistic Golden Sine Sparrow Search Algorithm LSSVM, short name ILGSSA-LSSVM). Using the Improved Logistic Chaos Mapping and Golden Sine Algorithm to find the optimal initial sparrow population, the value of penalty factor gamma and kernel parameter sigma for LSSVM are calculated. Global optimization method is adopted to find the optimal parameter combination, so that the negative influence of randomly initializing parameters on the prediction accuracy would be reduced. Our proposed ILGSSA-LSSVM soft sensing model is compared respectively with traditional Least Square Support Vector Machine, BP neural network and Gray Wolf optimized Least Square Support Vector Machine, results show that proposed model outperformed the others. Experiments show that the maximum error of ILGSA-LSSVM soft sensing model is 3.85733 °C, minimum error is 0.0174 °C, average error is 0.05805 °C, and generally outperformed other comparison models.

Study on high temperature mechanical properties of niobium microalloyed cold heading steel

In recent years, high-strength micro-alloyed cold heading steel has developed rapidly, mainly by adding Nb, V, Ti and other micro-alloying elements to the steel for grain refinement and precipitation strengthening, it is widely used in automobiles, bridges, construction machinery and other fields due to its excellent strength and toughness, fatigue resistance and corrosion resistance. However, the common quality defects in the process of continuous casting and hot rolling of such steels - transverse cracks on the surface and corners, are still one of the technical difficulties in the production of the world’s iron and steel enterprises. Therefore, it is of great scientific and engineering significance to deeply explore the evolution law of high temperature mechanical properties of niobium microalloyed cold heading steel, to analyze the common generation mechanism of surface transverse cracks and to propose general improvement measures. In this work, the high temperature thermoplastic properties of niobium microalloyed cold heading steel was studied by using Gleeble-3500 thermal simulator, combined with optical microscope (OM) and scanning electron microscope (SEM), the tensile fracture morphology and nearby microstructure were observed, and its high temperature plasticity mechanism was analyzed. The results show that the niobium microalloyed cold heading steel has two brittle temperature ranges: the first brittle zone is from the melting point to 1200°C, the temperature range of the third brittle zone is below 700°C, and the optimum plasticity zone is 700-1200°C. At 650°C, the fracture mode is ductile fracture and cleavage fracture; at 800°C, it is a typical cleavage-brittle fracture type; at 950°C, the fracture mode is dimple fracture, with good plasticity; at 1100°C, the particles become finer and the plastic deformation is more uniform. In order to avoid the occurrence of cracks in the continuous casting billet, the straightening temperature of the continuous casting billet should be higher than 700°C, it should be heated slowly in the early stage of heating, and the hot rolling temperature should be controlled at 700-1100°C.

Effect of solidification end impact vibration on the internal quality of a continuous casting billet

ABSTRACT Application of vibration impact at the outer arc side of a billet with a central linear liquid fraction of 25% -35% at 9.5 m from the meniscus. The results show that the impact vibration with low frequency and high impact energy can not only reduce the central porosity degree of the billet from 1.532 to 1.169, but also compact the liquid core, improve the central porosity and promote the heterogeneous nucleation of the molten pool. High frequency and low impact energy can not only increase the proportion of mixed crystal zone by about 8 %, but also reduce the central carbon segregation index from 1.08 to 1.04. Meanwhile, the two kinds of impact vibrations increase the area ratio of the central carbon segregation index in the range of 0.95-1.05 from 56.32% to 70.26% and 80.17%, respectively, and uniform the central carbon distribution of the billet.

Research on solidification behavior of a high Mn steel during continuous casting based on solidification characteristic unit analysis

A novel research route combining numerical simulation and physical simulation was used to study the solidification behavior of high Mn steel continuous casting billet under different superheats in this work. The results indicated that higher super heat degree will lead to lower equiaxed crystals content and severer element segregation. Moreover, the Mn element segregation was lighter than that of the C element, and it was caused by the higher value of solute partition coefficient of Mn. Finally, the superheat degree suitable for continuous casting of high Mn steel was modified to be 10 ℃.