Bar Rolling Research Articles

Development of significantly hard hypereutectoid plain carbon steel through incomplete austenitization based cyclic quenching treatment

AbstractIn this investigation hot rolled steel bars of 1.24 weight % carbon steel are subjected to incomplete austenitization based cyclic quenching treatment. Each cycle consists of inserting the specimen in an electric resistance furnace at a temperature of 894 °C and holding for a short duration (6 minutes), followed by oil quenching to the room temperature. Such a typical thermal cycling results in the evolution of a novel microstructure that comprises of large clusters and blocks of cementite in a matrix of martensite after 3 and 4 cycles. Accordingly, a significantly high hardness (7.13 GPa) is achieved on execution of 3 cycles which envisages a new pathway of incomplete austenitization based cyclic quenching treatment for development of new‐generation plain carbon hypereutectoid tool steel.

Improving compositional homogeneity of CF53 steel products by modifying their solidification structure and F-EMS intensity

In this article, based on the mechanism of stirring induced solute washing, the solidification characteristics of CF53 steel for camshafts were systematically studied through industrial casting tests and numerical simulations, focusing on the impact of solidification structure and final electromagnetic stirring (F-EMS) on solute distribution homogeneity in the core area of the bloom casting. The results indicate that excessive columnar crystal development, coupled with inappropriate use of F-EMS, can lead to significant negative segregation in the bloom, resulting in the formation of “white bands” in the following rolling bar products. Compared with weak stirring, strong stirring can affect solutes at deeper levels between dendrites. By reducing superheat and casting speed, expanding the equiaxed crystal zone in the bloom's centre, and carefully controlling the stirring intensity of F-EMS to position the molten steel washing in the equiaxed crystal zone, along with maintaining a maximum tangential velocity of 0.0041 m/s, a substantial improvement in solute distribution homogeneity within the bloom's core area was achieved. The carbon range can be reduced from 0.093% to 0.032%. These findings offer a theoretical foundation and practical suggestions for enhancing the quality of CF53 steel bloom castings and their hot-rolled bar products used in camshaft manufacture.

Thermal stability of a newly developed Mn containing β-solidifying γ-TiAl intermetallic compound at 750 °C

A newly low-cost β-solidifying γ-TiAl alloy Ti-44Al-3Mn-0.4Mo-0.4W-0.1B-0.1C (in at. %, named as TMMW) was invented. The rolled bars with a diameter of 12 mm were successfully fabricated by conventional hot rolling process, directly carrying out from the ingot without the pre-forging or hot-packing. The heat-treated TMMW rolled bar, which had a fine-grained nearly lamellar (NL) microstructure, was then air-exposed at 750 °C for up to 3000 h. The changes of the microstructure during this exposure were characterized using electron probe X-ray micro-analyzer (EPMA), transmission electron microscope (TEM), electron backscattered diffraction (EBSD) and high-energy X-ray diffraction (HEXRD). The tensile properties of the samples before and after thermal exposure were also tested. The fine-grained NL microstructure is found to be thermodynamically stable during the exposure. Meanwhile, the combined addition of Mo and W shows a positive effect on the stabilization of βo phase at colony boundaries, with only slight precipitation of the nanometer βo phases with no other brittle phases, such as Laves, in the metastable α2 lamellae. It is found that the thickness of the α2 lamellae decreases after 500 h exposure, while remains basically unchanged from 500 h to 3000 h, which is contributed by the effective pinning effect of the precipitated βo phase in α2 lamellae. As a result, the exposure-induced embrittlement under room temperature and elevated temperature does not take place. Interestingly, the ductility tested at 800 °C improves significantly after exposure. As for the tensile strength, it is only reduced by less than 10 % after 500 h exposure, while it remains essentially unchanged when increasing the exposure time from 500 h to 3000 h. Finally, the mechanisms of the precipitation of βo phases in the α2 lamellae and the tensile properties evolution during the exposure were carefully discussed.

Analytical approximation and evaluation of roll separating force in bar rolling process

Analytical approximation and evaluation of roll separating force in bar rolling process

Electropolishing study of metastable austenitic steel AISI 347 for EBSD analyses

Abstract For the metastable austenitic steel AISI 347 (X6CrNiNb18-10), various electropolishing parameters were evaluated by means of hardness testing, electron backscatter diffraction (EBSD), and atomic force microscopy. Depending on the chosen parameters, different surface characteristics could be achieved simply by only varying voltage, flow rate, and polishing time, although EBSD indexing was always possible. Differences in hardness of up to 20 HV0.5 and in microscopic roughness could be detected on otherwise comparable samples. Finally, the microstructure distribution of a hot rolled bar material with a diameter of 153 mm made from AISI 347 was characterized over the cross section using the previously determined parameter set. Here, insights about recrystallization during forming were concluded and δ-ferrite was differentiated from α’-martensite by kernel average misorientation and morphology.

Optimization of Billet Cooling after Continuous Casting Using Genetic Programming—Industrial Study

ŠTORE STEEL Ltd. is one of the three steel plants in Slovenia. Continuous cast 180 mm × 180 mm billets can undergo cooling to room temperature using a turnover cooling bed. They can also be cooled down under hoods or heat treated to reduce residual stresses. Additional operations of heat treatment from 36 h up to 72 h and cooling of the billets for 24 h, with limited capacities (with only two heat treatment furnaces and only six hoods), drastically influence productivity. Accordingly, the casting must be carefully planned (i.e., the main thing is casting in sequences), while the internal quality of the billets (i.e., the occurrence of inner defects) may be compromised. Also, the stock of billets can increase dramatically. As a result, it was necessary to consider the abandoning of cooling under hoods and heat treatment of billets. Based on the collected scrap data after ultrasonic examination of rolled bars, linear regression and genetic programming were used for prediction of the occurrence of inner defects. Based on modeling results, cooling under hoods and heat treatment of billets were abandoned at the casting of several steel grades. Accordingly, the casting sequences increased, and the stock of billets decreased drastically while the internal quality of the rolled bars remained the same.

Homogenization Path Based on 250 mm × 280 mm Bloom under Mixed Light and Heavy Presses: Simulation and Industrial Studies

This study proposed a new method for homogenizing continuous casting blooms based on solidification simulation calculations and industrial tests. The text describes a theoretical analysis of the solidification route of a cast billet of high-carbon alloy steel (B300A) under different process conditions. It summarizes the changing law of different under-pressure process parameters and under-pressure efficiency. The text also presents a solution to the seriousness of center shrinkage defects in the continuous casting of a large square billet of high-carbon alloy steel with the synergistic control technology of mixed light and heavy mixing under pressure. The study indicates that the center carbon segregation index of a high carbon steel continuous casting billet is 1.05, with a carbon extreme difference of not more than 0.08% and a proportion of 98.4%. Additionally, the center shrinkage is not more than a 0.5 level with a proportion of 99.5%. Meanwhile, the internal quality of cast billets has been improved, allowing for the rolling of large-size bars with a low consolidation ratio. The pass rate for internal ultrasonic flaw detection using the GB/T4162A grade is now higher than 99.95%, significantly reducing process costs and improving production efficiency for continuous casting and rolling.

ВИЗНАЧЕННЯ АДЕКВАТНОСТІ КОМП’ЮТЕРНИХ МОДЕЛЕЙ СКЛАДНИХ БАГАТОЗВ’ЯЗНИХ ОБ’ЄКТІВ

Proving the adequacy of models of complex, multi-connected objects such as continuous rolling mills poses a problem due to the impossibility of accurately reproducing the conditions of an industrial experiment during modeling. Most of the input and output variables in the given continius bar rolling mill computer model are not experimentally measurable and therefore cannot be compared with simulation results. It is proposed to determine the adequacy of such models by comparing the qualitative and quantitative effects of the mutual influence of various modeled parameters with similar effects, the presence of which has been clearly established in practice. The application of the specified method made it possible to test a new method of interstand tention regulation based on the data on armature currents of rolling mill motors.

МІНІМІЗАЦІЯ МІЖКЛІТЬОВОГО НАТЯГУ НА БЕЗПЕРЕРВНИХ СТАНАХ ЗА ЯКІРНИМИ СТРУМАМИ ЕЛЕКТРОПРИВОДІВ ПРОКАТНИХ КЛІТЕЙ

In the conditions of continuous rolling of graded profiles with no or too little metal deflection between adjacent rolling cages, the most promising is tension regulation based on information about the armature currents of the main electric drives. The effectiveness of the method of minimizing the tension of graded rolled products based on information about the armature currents of the main electric drives was investigated. The method is based on the hypothesis of the constant ratio of the armature current of the drive of the next cage to the armature current of the drive of the previous cage in the free rolling mode. The method involves predicting the free-rolling current in rolling electric drives based on information about the free-rolling current in the electric drives of previous cages. The study is based on a complex model of the process of continuous bar rolling in four finishing cages of a small-grade mill with individual electric drives equipped with subordinate speed control systems. Given the fundamental impossibility of approbation of the proposed method by the methods of an industrial experiment, verification of its operability requires computer simulation modeling. The created computer model allows for adequate simulation of the operation of the control system in the conditions of rolling in a continuous group of cages with an accuracy that is sufficient for conclusions about the effectiveness of its operation. According to the results of the study of the control system by means of computer simulation, the effectiveness of its work was proven, in particular, the reduction of the specific tension in all intercell spaces of the finishing group of roll stands to an acceptable level of 10 N/mm2 and a significant narrowing of the range of changes in the width of the finished rolled product.

OBTAINING THE NECESSARY MECHANICAL PROPERTIES OF BLANKS OF PARTS MADE OF ALUMINUM ALLOY 7075 BY PHYSICAL MODELING

The article considers physical modeling for aluminum alloy 7075, widely used in mechanical engineering, in particular for elements of aircraft structures. This alloy differs from other rolled aluminum-based alloys not only by high values of strength properties, but also by the presence of a large number of intermetallic compounds of alloying elements. The workpiece for the parts is a round rolled product with regulated mechanical properties. Thus, the purpose of this work was to determine the effect of the deformation pattern that occurs in metal during bar rolling on the mechanical properties of blanks of parts made of aluminum alloy 7075. The present study draws attention to the importance of physical modeling in determining the characteristics of materials necessary for effective management of plastic processing processes. Analyzing the results of physical modeling, we identify the optimal parameters of material processing, such as microstructure, mechanical properties and chemical composition. The results obtained allow a deeper understanding of the physical mechanisms underlying the production of blanks (rods) from aluminum rods of alloy 7075 by rolling, as well as optimizing it to achieve the required technical characteristics of products. Thus, as a result of physical modeling of the rolling process of bars made of aluminum alloy 7075, it was found that when the samples are deformed at a temperature of 250 ° C, the value of the plasticizing stress decreases by about 18%, and a more uniform distribution of microhardness over the transverse and longitudinal sections was obtained compared with deformation at a temperature of 200 °C. The research is of practical importance for the metalworking industry, and can also be used for educational purposes to train specialists in the field of materials science and metalworking. Keywords: workpiece parts, physical modeling, aluminum alloy 7075, metalworking, aluminum alloy microstructure, deformation of samples.

Experimental study on the surface defects of materials in bar rolling with a processing map applicable to billet-to-oval groove rolling

This paper proposes a systematic method for detecting surface defects (SDs) on specimens by performing a pilot hot (850°C–950°C) bar rolling test and suggests a processing map for billet-to-oval groove pass in bar rolling mills. Unlike previous studies, the specimens for the rolling test were prepared such that the billet surface became the surface of the specimens. A series of the rolling tests were performed at different temperature and area reduction ratios. Physical-chemical nondestructive testing was employed to detect SDs in the specimens before and after the rolling test. The depth of the SDs of the rolled specimens was measured using an optical microscope. The results revealed that the SDs depended both on the rolling parameters (temperature and reduction ratios) and the contact condition between the specimen and the roll groove during rolling, which is one of the characteristics of bar rolling that distinguishes it from flat rolling. The decrease in temperature caused an increase in the defect depth above the appropriate reduction ratio of 24.61% when the part of the specimen was in contact with the roll shoulder curve and the relief line of the oval roll groove. The proposed processing map presents a guiding path for operators in actual bar rolling mills to quickly determine a rolling condition (combination of temperature and reduction ratio), avoid SDs, and minimize defect depth within an acceptable range.

Environmental impact assessment of steel reinforcing bar manufacturing process from scrap materials using life cycle assessment method: a case study on the Ethiopian metal industries

A clear understanding of the major environmental impacts of steelmaking from scraps, as well as potential solutions involving a circular economy paradigm, is essential. This study is conducted to pave the way for using life cycle assessment (LCA) to have sustainable development and effective resource management by evaluating the environmental impacts of the steel rebar manufacturing process using secondary resources. It is a cradle-to-gate LCA that includes scrap collection and sorting, transportation, melting, continuous casting, billet reheating, and reinforcing bar rolling. Inventory data were acquired as primary data from the factory and secondary data from ecoinvent v3.8, 2021 version integrated with SimaPro 9.4.0.2 faculty version. All of the analyses in this LCA were conducted using the Recipe 2016 Midpoint (H)V1.00 and Endpoint (I)V1.00 impact assessment techniques taking one-ton reinforcing bar production as reference flow. This LCA study shows that using renewable energy and bulk transport systems has a significant advantage in reducing the environmental impact created during steel production processes. Because of this, the global warming potential created during the rebar manufacturing process is 467 kgCO2 eq as taken from the environmental impact calculation report. By charging hot billet from the continuous casting machine (CCM) to the rolling mill and using an efficient transportation system, the environmental impact of GWP can be reduced by 50%.

Investigation of the Temperature Field during Radial-Shear Rolling of Technical Copper

Radial-shear rolling is one of the most promising methods of metal forming, allowing to develop a level of strain in the rolled bar sufficient to obtain an ultrafine-grained structure. At the same time, it has already been theoretically and experimentally confirmed that after metal processing by this method, a gradient distribution of grain size is observed in the cross section of the rod, which is a consequence of the laminar-turbulent flow of metal in the deformation zone. This work, carried out within the framework of grant №AP14869128, funded by the Science Committee of the Ministry of Science and Higher Education of the Republic of Kazakhstan, is devoted to the study of the temperature field during radial-shear rolling of M1 technical copper at an initial workpiece temperature of 20°C. To study the temperature distribution over the bar cross section, finite element modeling of radial-shear rolling of M1 technical copper was performed in the Deform program. A rod with a diameter of 30 mm and a length of 150 mm was set as the initial workpiece. It was decided to conduct three passes of radial-shear rolling with compression of 3 mm per pass. In addition to studying the temperature fields on the workpiece, the temperature distribution on the rolls was also considered. Analysis of the simulation results showed that the temperature distribution over the cross-section of the rod has a gradient character.

Reduction of surface defects by optimization of casting speed using genetic programming: An industrial case study

Štore Steel Ltd. produces more than 200 different types of steel with a continuous caster installed in 2016. Several defects, mostly related to thermomechanical behaviour in the mould, originate from the continuous casting process. The same casting speed of 1.6 m/min was used for all steel grades. In May 2023, a project was launched to adjust the casting speed according to the casting temperature. This adjustment included the steel grades with the highest number of surface defects and different carbon content: 16MnCrS5, C22, 30MnVS5, and 46MnVS5. For every 10 °C deviation from the prescribed casting temperature, the speed was changed by 0.02 m/min. During the 2-month period, the ratio of rolled bars with detected surface defects (inspected by an automatic control line) decreased for the mentioned steel grades. The decreases were from 11.27 % to 7.93 %, from 12.73 % to 4.11 %, from 16.28 % to 13.40 %, and from 25.52 % to 16.99 % for 16MnCrS5, C22, 30MnVS5, and 46MnVS5, respectively. Based on the collected chemical composition and casting parameters from these two months, models were obtained using linear regression and genetic programming. These models predict the ratio of rolled bars with detected surface defects and the length of detected surface defects. According to the modelling results, the ratio of rolled bars with detected surface defects and the length of detected surface defects could be minimally reduced by 14 % and 189 %, respectively, using casting speed adjustments. A similar result was achieved from July to November 2023 by adjusting the casting speed for the other 27 types of steel. The same was predicted with the already obtained models. Genetic programming outperformed linear regression.

Sub-zero temperature flexural and flexural fatigue behaviour of glass fabric /epoxy composite tubular anti roll bars

Flexural and flexural fatigue reliability of glass fabric/epoxy composites used in anti-roll bars in room and sub-zero temperature regions at +25 °C, +10 °C, 0 °C, −10 °C, −20 °C, −30 °C, and −40 °C are investigated. The mean flexural strength of anti-roll bars substantially varies and improves in the sub-zero flexural property assessment (+25 °C to −40 °C). The fixed amplitude pulsating mode fatigue test was carried out at temperature points, i.e., 25 °C and −40 °C. The improvement in fatigue strength was observed 3.5 times at a sub-zero temperature of −40 °C. The fatigue durability of glass/epoxy composite anti-roll bars is observed to be longer at sub-zero temperatures due to residual stresses building up, an increase in glass transition temperature, and a lack of molecular mobility leading to higher chain stiffness in the epoxy matrix. The structural properties like flexural rigidity and modulus were calculated with reference to the shape factor and test temperatures for better correlations. These lifetime prediction studies under unpredictable operating conditions for automotive are crucial in the development of robust designs. Automotive performance under service conditions and environmental extremes will become increasingly important as lighter weight, longer life, and higher structural performance continue to evolve.

Semi-macrosegregation and carbide banding in high-carbon chromium bearing steels: Characteristics, evolution, and control

Semi-macrosegregation in continuously cast blooms and its associated carbide banding defects in hot-rolled bars were investigated to explore the characteristics, evolution, and control methods in high-carbon chromium bearing steel. It was found that the semi-macrosegregation exists only in the central equiaxed crystal zone of the blooms, and C, Cr solute elements inside show typical spot-like positive segregation. Carbide banding appears as white bright bands along the rolling direction, composed of high number density M3C carbide particles, with a significant effect on the mechanical properties of the rolled products. The hereditary evolution from semi-macrosegregation to carbide banding was established by means of banded segregation. Morphologically, normal semi-macrosegregation and carbide-typed semi-macrosegregation are formed based on whether Cr-rich primary carbides are generated. These two types of semi-macrosegregation evolved into two kinds of carbide banding respectively, that is, dark bands and bright bands defined according to the ability to reflect light under OM. To alleviate the carbide banding defect in rolling products of high-carbon chromium bearing steel, the morphology and area ratio of equiaxed crystals in continuous cast blooms should be modified. It is observed that the equiaxed crystal ratio in the bloom can be decreased from 62.5 % to 28 % by increasing liquid steel superheat and inhibiting superheat dissipation in the mold through casting practices. Additionally, the morphology of equiaxed crystals is related to the as-cast solidification structure, and when the equiaxed crystal ratio is large, the equiaxed crystals turn out to be coarser ones with only cellular primary dendrite; when the columnar crystals are longer, however, the equiaxed crystals appear as a dendrite structure with fine secondary dendrites. As a result, semi-macrosegregation was improved obviously with the fine dendrite structure splitting the local residual liquid phase, leading to the decrease of the maximum width of carbide banding from 268.41 μm to 73.72 μm, and the increase of mechanical properties in the rolled bar of high-carbon chromium bearing steel.

Music as Magic

Music as Magic

Hot profiled rolling of C40 steel: production variable’s effect on rolling performance

ABSTRACT The usage of C40 steel bars is common in ships, mechanical, metallurgical, automobile, military hardware, and electrical construction fields. During manufacturing of these bars, roll force (RF), roll torque (RT), cropping loss (CL) and drive energy (DE) are important production variables that must be monitored for high-quality output, scrap reduction, and mill safety with minimum consumption of energy. Roll RPM, temperature of bloom, roll gap, bloom cross-section area, and diameter of roll are process characteristics that influence these response parameters. The impact of process variables on response variables during C40 steel rolling is probed in this research. To replicate the rolling procedure, FORGE® NxT 1.1 was employed. Following statistical testing, the simulated findings were validated utilizing data from experiments acquired in a bar rolling plant. The results of an analysis of variance were used to find significant model terms. There have been constructed regression models demonstrating the link between the response parameters and the process parameters.

Reserves for reducing energy consumption when rolling section bars on modern rolling mills

Metallurgical production is a highly energy-intensive process, and the search for solutions to reduce energy costs remains an urgent task for all stages. In this regard, the production of finished rolled products is considered as the most promising direction for the implementation of energy-saving technologies. There are two ways to reduce energy costs in hot rolling of section bars: saving energy for heating and improving the use of the main equipment to reduce intermediate energy costs. Due to the difference in silt conditions at the moment of capture and at the steady stage of the rolling process, a reserve of retracting friction forces arises, which can be used for additional shaping in non-drive devices and thereby increase the efficiency of the main equipment and reduce overall energy costs. For the practical implementation of the proposed concept, dependence was obtained that makes it possible to estimate the power potential that is not used at the steady stage of the rolling process. Using the obtained dependence, it was found that when rolling in smooth rolls, the potential of friction forces is used only by 50 – 60 %, and when rolling in calibers, by 35 – 40 %. It was experimentally established that during the rolling of shaped sections in passes with an elongation ratio of less than 1.10 – 1.15, more than 50 % of the energy is spent on idling. However, by replacing drive stands in these passes with non-drive cassettes (in continuous groups), it is possible to increase the efficiency of adjacent stands by 4 – 5 % and reduce energy costs.

AN APPLICATION OF COMPUTER SIMULATION OF AUSTENITE DECOMPOSITION IN OPTIMIZATION OF HOT ROLLING OF LOW ALLOYED STEEL BARS

Modern technologies need more and more precise computer design of manufacturing processes. Especially it is visible in thermal processing of steel, such as hot rolling, hot forging, casting, welding, 3D printing, and so on. An application of computer simulation of austenite decomposition in optimization of manufacturing of low alloyed steel bars by hot rolling was studied. For this purpose the mathematical model and computer software for very precise anticipation of TTT diagrams data was developed. The calculation of TTT diagrams data was based on chemical composition of low alloyed steels. The study started with definition mechanisms of austenite decomposition at constant subcritical temperatures. The mechanism of γ→α phase change in steel is not yet been adequately clarified. Methods for calibration of kinetic equations of austenite phase transition at constant subcritical temperatures were developed in this paper. Mathematical modeling of TTT diagrams data consists both, prediction of kinetic of phase transformations and anticipation of steel hardness. It was found out that the hardness of both, microstructural constituents and total hardness of steel mostly depends on the carbon content and temperature of γ→α phase transformation. The model of TTT diagrams data of low alloyed steel was verified in purpose to apply the model of isothermal decomposition of austenite in very precise method for prediction of microstructure composition and hardness of hot rolled steel bars. The verification of developed model was done by comparison of the calculated results of TTT diagrams data with experimentally estimated TTT diagrams data. By the simulation of hardness and microstructural composition of hot rolled steel bar the optimal cooling regime in cooling beds can be designed.