Hot Rolling Production Research Articles

AUTOMATION OF CONTINUOUS BROADBAND HOT ROLLING MILL

The article deals with a continuous wide-field hot rolling mill for a foundry and rolling complex (LPC). The goal of automation of a continuous broadband hot rolling mill is to ensure the production of high - quality hot rolled products regardless of the working staff using a self-learning neural network and huge databases in the rolling industry. The collector was designed with an innovative shape and a new cooling liquid spray scheme in the COMPASS-3D CAD. The collector is equipped with infrared sensors that read the surface temperature of the rolling roll and actuators. An open microcontroller platform Arduino UNO was chosen to implement an automatic system for purposeful cooling of rolling mill rolls. The proposed scheme of an automatic system for purposeful cooling of rolls is a classic system with negative feedback. The whole system can be divided into two circuits: the first is to regulate the amount of water supplied based on the readings of temperature sensors, one for regulating the pressure of water supplied based on the pressure sensor. This approach is proposed for the first time to automate cooling of rolling mill rolls. Analysis of the results of modeling the operation of the automated collector showed the following results: 16 transshipments per month, 2 scheduled preventive repairs, and the average roll working rate of 87%. The proposed system allows efficient use of the coolant compared to the old system. Based on the analysis of the operating time of rolling rolls under various cooling modes, the system will allow you to track roll wear and inform the staff about the upcoming transshipment dates. An artificial neural network was developed and implemented in the cooling system of rolling rolls at the 1950 LPC mill in order to increase the stability of the working rolls and improve the quality of the resulting products.

ASSESSMENT OF THE INFLUENCE OF MANGANESE CONTENT ON THE CORROSION OF THERMALLY HARDENED METAL

In this work, we studied the corrosion behavior of hot-rolled and heat-hardened rolled products made of low-carbon steel with different manganese content in it in order to select the optimal conditions for its heat treatment to obtain a satisfactory combination of strength and corrosion resistance during the development of general corrosion processes with hydrogen polarization. A promising way to save metal in construction, mechanical engineering and transport, as well as to reduce the consumption of alloying elements and deoxidizers as a result of replacing, in some cases, low-alloy structural steels with simpler and less costly low-carbon ones, is the use of hardening heat treatment, especially using the heat of rolling heating. However, the widespread use of thermally hardened rolled products of thinner thickness in order to save metal in structures and structures exposed to the surrounding, as a rule, corrosive environments of various nature and intensity, comes across a completely insufficient study of the corrosion behavior of such a material as an energetically more unstable system than a conventional hot rolled steel products. It is the hot-rolled state that is attributed to the scientific data on the corrosion behavior of carbon and low-alloy structural steels, which are far from systematic and not unanimous in their assessments, and the data on the corrosion of heat-hardened rolled steel, as a metastable system with increased free energy, are limited and contradictory. Therefore, the study of the laws governing the behavior of thermally hardened rolled metal as a metastable metal system is of great practical importance for the choice of processing technology and materials that would provide a satisfactory combination of strength and ductility of thermally hardened rolled metal. The studies were carried out on samples of low-carbon steel of laboratory heats, having in their chemical composition approximately the same content of C, Si, S, P, Cu and different content of Mn (0,66, 1,00 and 1,68 % by mass) in hot-rolled and thermally hardened conditions (quenching from 880-900 oC, and then tempering was carried out in the temperature range 200-700 oC every 25-50 oC for 1 hour, followed by cooling in calm air). Corrosion tests were carried out on polished and degreased samples constantly immersed in 1 N H2SO4 solution at room temperature for 72 h. It was found that alloying low-carbon steel with manganese (up to 2 %) leads to an increase in the corrosivity of the metal in a thermally hardened state, shifts the peak of corrosivity during tempering towards a lower temperature (from 475 to 375 oC) and increases corrosion losses in the region of the peak in 1, 6 times. It is shown that after quenching and high tempering (at temperatures > 600 oC), on the contrary, in steel with an increased manganese content, corrosion losses, for example, in an acidic environment, are significantly reduced due to the fact that manganese accelerates the processes of coagulation of carbide particles. It is recommended to carry out heat hardening treatment of structural steel with an increased (1,5 %) manganese content while satisfying the technical requirements for a combination of strength and satisfactory corrosion durability; it is advisable to prescribe a tempering (self-tempering) of at least 600 oC for heat hardening. In this case, with a significant gain in strength (increase by 20-25 %), it is possible to achieve a higher corrosion resistance of the metal in comparison with the hot-rolled (unhardened) state.

Quality improvement of calibrated steel by surface deformation. Part 1. Determination of the stressed state of cylinderical parts during orbital surface deformation

Cold drawn calibrated steel is an effective blank for the manufacture of low-rigid cylindrical parts such as shafts and axles. High accuracy of the diametric size along the length of the workpiece, low surface roughness, increased hardness and strength of the surface layer compared to hot rolled products allow us to produce a variety of parts with high metal utilization and high machining performance. The main disadvantage of calibrated metal is the residual stresses that occur during pressure treatment. To reduce or change the nature of the distribution over the cross section, it is proposed to use small plastic deformations in the surface layer of the hire. Known in practice methods of surface plastic deformation (PPD) usually lead to the curvature of non-rigid workpieces. To intensify the stress-strain state in the deformation zone, we propose a method of orbital surface deformation. Based on the finite element modeling, influence of the main parameters of orbital surface deformation on stress state in the deformation zone and residual stresses in the finished products is considered. Compared with the traditional PPD process, the stress intensity during orbital surface deformation will increase by 10 – 15 %. The residual compressive stresses that form in the surface layers reach 70 – 85 % of the material tensile strength. In the second part of the article, it is supposed to provide information on a more effective method of surface deformation and on the change in initial residual stresses that are formed during the calibration of cylindrical rods.

Development of a method and equipment for testing materials for alternating bending during piercing in screw rolling mills

Hot-rolled pipe production is complicated process of metal treatment by pressure and as a rule it has three operations of form charging: piercing, plugging, calibration or reduction. Each of them is characterized by complex schemes of stress-deformed state which promotes either formation or detection of various defects. Hot billet piercing at screw piercing rolling mill is widely used for pipe production for its high output and getting the shells of long length. But this operation of form charging of the metal is realized under the conditions of complicated stress-deformed state with cyclic alternating bending of all metal layers. Defects appearing on the outside surface of the shell such as captures and cracks is caused by plastic bending of shell wall, which is followed by alternating stress and deformation at the inlet and outlet cone of deformation zone in consequence of four times plastic bending of the wall. Shell wall is influenced by compression stress of the working rolls and guides. The less favorable scheme of stress state with tensile stress arises on the shell surface between the rolls and the guide. And as a results it generates and increases the defects on the outside surface. Theoretical and experimental research of deformation and speed conditions of billet piercing process for screw piercing rolling mill is presented in the work. Statistic data of production mills which operate in TRA 50-200 and TRA 159-426 lines were used for the research. All the calculations were done with use of applied software and test machine of original design with crank and connecting rod mechanism was constructed. The machine carries out the process of alternating plastic bending which is in maximum close to the conditions taking place in deformation zone of screw piercing rolling mill. Definition of rational configuration of sample shape was determined. Process plasticity of the metal of hot samples was analyzed as well. The samples were made from hot-rolled bars of different steel grades.

End-to-End Quality Evaluation of Continuous Cast Slabs and Hot-Rolled Sheet Products from Ship-Delivered Batches

The results of an end-to-end quality evaluation of continuous cast SS400 steel slabs, followed by its hot-rolled thick-sheet products in ship-delivered batches, are presented. The evaluation of the frequency distribution of defects for each of the continuous casting machines (CCMs) revealed the following: even during control fire cleaning, the surface quality of slabs from CCM No. 1 was slightly lower (1.1–2.0%) than from CCM No. 2; the finished sheets from slabs casted at CCM No. 1 have a better quality than from slabs casted at CCM No. 2. At the same time, on both machines, the quality of slabs from strand No. 2 is better than from strand No. 1. The unstable internal quality of the sheet with a thickness of 30–45 mm was due to restrictions imposed on the maximum thickness of the sheet which was 25.0 mm. During microstructural analysis of the causes of cracks and segregation nature, it was found that the presence of non-metallic inclusions in the sheet structure serves, in fact, as a source of crack development. Analysis using energy-dispersive x-ray spectroscopy (EDX) showed that nonmetallic inclusions in the dominant mass are manganese sulfides.

Influence of the Cross-Sectional Shape of Hot Semifinished Rolled Products on the Formation of the Plot of Specific Tension in Cold-Rolled Strips

In view of the increasing competition in the market of rolled products, the problem of evaluation of the quality of strips in various stages of the process of rolling seems to be quite urgent. As the main geometric criteria of the quality of rolled strips, we can mention the cross-sectional profile of hot-rolled semifinished products and the plot of specific tension in the strips after cold rolling. We discuss the problems of formalization of measurements of the cross-sectional profiles, classification of hot-rolled profiles into characteristic types, and the influence of these criteria on the formation of the plots of specific tension in cold-rolled strips.

Improvement of Calibrated Steel Quality by Surface Deformation. Part 1: Determination of the Stress State of Cylindrical Parts during Orbital Surface Deformation

Cold-drawn calibrated steel is an effective workpiece for the manufacturing of low-stiff cylindrical parts such as shafts and axles. A high accuracy of the diametric size along the workpiece length, low surface roughness, and increased hardness and strength of the surface layer compared to hot rolled products allow the production of a variety of parts with high metal utilization and high machining performance. The main disadvantage of calibrated metal is the residual stresses that occur during pressure processing. To reduce or change the nature of the distribution over the cross section, we propose to use small plastic deformations in the product’s surface layer. Surface plastic deformation (SPD) methods known in practice usually lead to the curvature of non-rigid workpieces. To intensify the stress-strain state in the deformation zone, a method of orbital surface deformation is proposed. The orbital deformation scheme is a rod indenter (tool), one end of which is equipped with a ball tip that is in contact with the surface to be treated. The second end of the rod indenter rotates about the vertical axis, forming a conical surface in space with a certain angle at the apex. A deforming force acts along the rod axis. Based on the finite element modeling, we consider the effect of the main parameters of orbital surface deformation on the stress state in the deformation zone and residual stresses in the finished products. Compared with the traditional SPD process, the stress intensity during orbital surface deformation will increase by 10–15%. The residual compressive stresses formed in the surface layers reach 70–85% of the material tensile strength. The relative radius of the orbital rotation and the radius of the operating tool, at which the formation of maximal temporary and residual stresses is ensured, were established. At an increase in the frequency of the orbital rotation of the operating tool, the temporary and residual compressive stresses increase. In the second part of the paper, we provide information on a more effective method of surface deformation and on the change in initial residual stresses that are formed during the calibration of cylindrical rods.

The Effects of Reduction and Thermal Treatment on the Recrystallization and Crystallographic Texture Evolution of 5182 Aluminum Alloy

During forming, thickness reduction and thermal treatment affect the recrystallization and evolution of the crystallographic texture of metallic materials. The present study focuses on the consequences of rolling reduction of a widespread aluminum alloy with numerous automotive, marine and general-purpose applications, namely Al 5182. Emphasis is laid on the crystallographic texture and mechanical properties on both hot and cold-rolled semi-final products. In particular, a 2.8 mm-thick hot-rolled product was examined in the as-received condition, while two cold-rolled sheets, one 1.33 mm and the other 0.214 mm thick, both originating from the 2.8 mm material, were examined in both as-received and annealed (350 °C for 1 h) conditions. Electron back-scatter diffraction indicated the presence of a large percentage of random texture as well as a weak recrystallization texture for the hot-rolled product, whereas in the case of cold rolling the evolution of β-fiber texture was noted. In addition, tensile tests showed that both the anisotropy as well as the mechanical properties of the cold-rolled properties improved after annealing, being comparable to hot-rolled ones.

Research on Edge Surface Warping Defect Diagnosis Based on Fusion Dimension Reduction Layer DBN and Contribution Plot Method

ABSTRACTThe edge surface warping defect seriously affect the surface quality of strips. In this paper, a technology for diagnosis of warping defects in hot-rolled strip based on data-driven methods is studied. Based on the mechanism analysis of the warping defects, the process parameters affecting the warping defects were sorted out and used as the original input parameters of the defect diagnosis model. Firstly, a diagnostic model that combines the deep belief network and contribution plots of each dimensionality reduction layer is proposed. The deep belief network that integrates each dimensionality reduction layer can predict product defects more accurately and stably than the traditional deep belief network. Meanwhile, on the basis of the pre-judgment model, the method of contribution plot is further introduced to trace the defects, and the comprehensive diagnosis function of model pre-judgment and traceability is realized. Finally, collected the production data from a hot rolling production line for a period of time. Tested the model and predicted a hit rate of 85%. The main influencing factors of edge surface warping defects were determined that the rate of defect decrease with the increase of furnace temperature. When the heating temperature of the second stage of the heating furnace is higher than 1160°C, the incidence of defects is significantly reduced. Defect rate is relatively low within 240min of total furnace time. With the first and third pass phosphorus removal equipment turned on, the incidence of defects was relatively low.

Dynamic rolling model based on uniform deformation

Abstract Accurate prediction of rolling force is a core point during the hot-rolled strip production. In-depth research on static rolling processes has been carried out in the past. Most models, however, can only be used under static conditions. Therefore, it is challenging to research the dynamic rolling process. This paper presents a dynamic rolling model for hot rolling. Firstly, the strip dynamic velocity model and the dynamic boundary condition model are established, and then the total power equation of the dynamic rolling process is solved based on the energy method. Furthermore, by minimizing the total power function, the dynamic rolling force equation can be obtained. Finally, the effectiveness of the proposed dynamic model is verified by hot strip rolling plant experiments and finite element simulations. The results show that the dynamic model of this paper has higher prediction accuracy and can be applied to the research on the dynamic hot rolling process. Besides, the influence of the vertical velocity of the rolls on the dynamic rolling force and influencing factors of dynamic rolling force are discussed.

Steel Strip Surface Defect Identification using Multiresolution Binarized Image Features

The shaped steel strip, in the hot rolling process, may exhibit some surface flaws. Their origin could be the internal discontinuities in the input product or the thermomechanical transformation of the material, during the shaping process. Such defects are of a random occurrence and may lead to costly rework operations or to a downgrading of the final product. So, they should be detected and identified as soon as possible, to allow a timely decision-making. For such a quality monitoring, the used vision systems are mainly based on an image description and a reliable classification. In this paper, we explore pre-defined image filters and work on a procedure to extract a discriminant image feature, while realizing the best trade-off between the improved recognition rate of the surface defects and the computing time. The proposed method is a multiresolution approach, based on the Binarized Statistical Image Features method, employed to date in biometrics. The filters, pre-learnt from natural images, are applied to steel defect images as a new surface structure indicator. They provide a quite discriminating image description. A relevant data reduction is used together with a classifier to allow an efficient recognition rate of the defective hot rolled products.

Temperature and deformation conditions of gas bubbles welding at hot rolling

At production of hot-rolled product from middle-carbon and low-carbon steel, a surface defect “rolled-out bubble” is formed sometimes. To decrease rejections by surface defects like this one, it is necessary to know the mechanism of their origination. The comprehensive study by methods of micro-X-ray-spectral and X-ray-phase analysis on internal surface of the rolled-out bubbles and areas, located in the direct vicinity of the defects mentioned, allowed to determine the content of isolations, localized at the internal surface of the defects. The content was as follows (%, mas.): quartz - 24, tridymite - 28, magnetite - 48. By the method of differential scanning calorimetry the melting temperature of isolations on the internal surface of the rolled-out bubbles determined, amounted to 1178 dC, which corresponds to melting temperature of iron-silicon eutectic Fe 3 O 4 -SiO 2 . A mechanism of the defect “rolled-out bubble” formation proposed. According to the mechanism proposed, the inclusions of silicates, localized at the internal surface of the bubbles and complex inclusions based on silicon and iron oxides, form the low-melting eutectic of Fe 3 O 4 -SiO 2 type when interacting with oxygen of air during the heating before rolling. As a result of expanding forces during the rolling, in the surface metal layer, which has a liquid eutectic at the rolling temperatures, discontinuity flaws are formed. To avoid the defects it was proposed to keep the reheating and rolling temperature lower the melting temperature of the eutectic of Fe 3 O 4 -SiO 2 type. The corrected rolling regime allowed to exclude practically completely the rejections by defect “rolled-out bubble” and to decrease the metal consumption coefficient at production of rolled products from S355J2G3 and C45R steels.

Analysis of interconnections between technical systems on hierarchically connected technological levels of steel sheet production by hot rolling

Complexity of modern metallurgical plants, presence of great number of horizontal and vertical interactions between their various structural subdivisions makes it necessary to apply a systems analysis to elaborate effective measures for stable development of a plant operation. Among such measures, digitalization of a plant is widespread at present. To implement the digitalization it is necessary to have clear vision about links at all the levels of the technological system of a plant. A terminology quoted, accepted in the existing regulatory documents for defining of conceptions, comprising the technological system. It was shown, that the following four hierarchical levels of technological systems are distinguished: technological systems of operations, technological systems of processes, technological systems of production subdivisions and technological systems of plants. A hierarchical scheme of technological systems of hot-rolled sheet production at an integrated steel plant presented. Existing horizontal and vertical links between the basic plant’s shops shown. Peculiarities of flows of material, energy and information at the operation “rolling” of the technological system “hot rolling of a steel sheet” considered. As a technical system of the technological process of the hot rolling, the hot rolling mill was chosen. A structural diagram of the hot rolling mill was elaborated, the mill being consisted of reheating furnaces, roughing and finishing stand groups, with an intermediate roll-table between them, and down-coilers section. Since the rolling stands are the basic structural elements of the hot rolling mill, structural diagrams of a roughing and a finishing stands were elaborated. Results of the systems analysis of the technological and technical systems, hierarchically linked in the process of steel sheet hot rolling, can be applied for perfection of organization structure of the whole plant, as well as for elaboration mathematical models of a system separate elements functioning, which is a necessary condition for a plant digitalization.

Analyzing the production and economic indicators of Russia's largest iron and steel works

Subject. We investigate trends in the development of the largest steel companies in the Russian Federation. Objectives. The aim of the study is to conduct an industry-wide analysis of the production and economic activities of the largest domestic enterprises operating in the iron and steel industry. Methods. The study employs methods of comparative and system analysis, graphical and statistical methods for data processing. Results. We present the analysis of main production and economic indicators of the leading steel producers of the Russian Federation, i.e. NLMK, Severstal, MMK, and EVRAZ. The paper reveals their current status and key development trends. Conclusions. The largest Russian steel companies face serious challenges in both the domestic and foreign market. Competitive interactions in the domestic market as to the sale price of rolled metal and the share of presence are particularly sensitive. The threat of reduced supplies to export markets is also significant for Russian steel producers. It may entail insufficient utilization of capacities and potential loss of added value. The companies mainly export semi–finished goods and hot-rolled flat products, i.e. low-added value products. Products with high added value are usually delivered to the domestic market.

Effect of Heat Treatment in Pipe Processing Stage on Corrosion Resistance of Micro-Alloyed Steel Hot-Rolled Products

The effect of heat treatment on corrosion resistance of low-alloy pipe steels is investigated in relation to oilfield pipeline operating conditions. It is established that after pipe bulk heat treatment at 720 °C metal corrosion resistance increases, but at a lower temperature of 680 °C no significant change is detected. Analysis of the corresponding structural changes is performed and the main factors facilitating an increase in corrosion resistance are determined: cementite component spheroidization in the areas of pearlite or degenerated pearlite, and a reduction in dislocation density. The role of nanoscale precipitate type on pipe corrosion resistance is noted. It is established that at a higher processing temperature there is a larger fraction of ferritic precipitates. In contrast to interphase precipitates these particles do not adversely affect steel corrosion resistance.

Optimization of the Schedule for the Whole Process in Hot Strip Manufacturing

Optimization of the schedule is an effective way to reduce energy consumption in hot strip manufacturing. The heating energy and the rolling energy contribute the vast majority of the energy consumption. In order to reduce the energy consumption for the whole process, an optimization method based on the multi-objective function was applied, and the heating energy and rolling energy were both taken into consideration during the function modeling. Meanwhile, process constraints and equipment limitations were taken as objective function boundary conditions, and the tapping temperature in the furnace exit and thickness of each pass were decision variables. Further, to obtain the optimal solution of the objective function, the differential evolution algorithm was used, finally, the optimal tapping temperature and the thickness were obtained successfully. Meanwhile, the validity of the calculated results was verified by comparing with the actual process in a hot rolling production line in Hebei province, the results indicated that with the proposed method, a more reasonable schedule were obtained; compared with the existing actual schedule of typical specification, the energy consumption can be reduced by about 1.5%.

Effect of Hot Rolling Regimes on Solid Solution Structure, State and Properties of Titanium-Stabilized if-Steel Hot-Rolled and Cold-Rolled Product

Using contemporary physicochemical approaches for predicting phase precipitate stability conditions for laboratory melted metal by optical, scanning, and transmission electron microscopy, local X-ray spectral analysis, testing mechanical characteristics, and determining the content of interstitial elements in solid metal a detailed study is made of the structural state and properties of titanium stabilized IF steels of three compositions. Based on the results obtained, the main requirements for hot-rolled steels are formulated, and the principles and conditions for obtaining good ductility and formability indices are determined for cold-rolled product subjected to recrystallization annealing by a continuous hot-dip galvanizing unit (HDGU) regime.

Structure and characteristics of boron-containing steels for fasteners

According to TU 14-1-4486-88 and TU 14-1-5490-2004, in accordance with international standards DIN EN 10263-4, OJSC «BSW – Management Company of the Holding «BMC» produces hot-rolled products of the following grades of steel: 20Г2Р, 30Г1Р, 20MnB4, 30MnB4 and 32CrB4 microalloyed with boron. They are used for the manufacture of fasteners instead of previously used steels 35X, 38X and 40X. The use of boron-containing steels reduces the surface defects of hardware; to increase the stability of the mechanical properties of bolts, screws, studs, strength class 8.8 and 10.9 by GOST 1759.4-87; to achieve a high level of toughness at negative temperatures. It is shown that steel 20Г2Р provides stable mechanical properties of products up to M27 (in contrast to steel grades 35X, which are designed exclusively for bolts of class M16 8.8). The boron-containing steels in the delivery state with the structure of granular perlite have high technological plasticity – in the cold, the bolt head is formed and the thread is rolled without tearing in the thread hollows, as is the case with chromium steels of type 40X. It was found that their ductility increases due to the low content of carbon and chromium, as well as the formation of dispersed carbonitride-boride phases of a globular form.

Robust Scheduling of Hot Rolling Production by Local Search Enhanced Ant Colony Optimization Algorithm

Scheduling of a hot strip mill is an important decision problem in the steel manufacturing industry. Previous studies on the hot strip mill scheduling problem have mostly neglected the random factors in production. However, random variations in processing times are inevitable due to unpredictable delays and disturbances. In this article, we adopt a robust optimization approach to deal with the uncertainty in processing times. The advantage is that no assumption has to be made regarding the distribution of random data, and the obtained schedule will remain strictly feasible when the variations have not exceeded a predefined uncertainty set. First, a mixed-integer linear programming model is presented to formulate the robust scheduling problem. Then, a hybrid metaheuristic algorithm, which combines ant colony system (ACS) and enhanced local search, is proposed to provide an efficient solution to the problem. Finally, extensive computational experiments involving both randomly generated and real-world instances have been conducted to verify the effectiveness of the proposed algorithm. It is shown that the algorithm achieves optimality for small instances and outperforms two state-of-the-art metaheuristics when used to solve large instances.

Effect of the Production Conditions of Continuously Cast Steels on the Degree of Hot Rolled Product Downgrading

Abstract Nowadays, quality development is a growing challenge, which places a heavy burden on economic operators, especially on smaller companies. ISD Dunaferr Zrt is the largest steel company in Hungary with its annual steel production of about 2 million tons, but it is small on a global scale. Taking advantage of the opportunities, locating the hidden problems, qualitative development and productivity enhancement can be realized without major investment. This study points out the steel production and casting parameters that have the greatest impact on the quality of the hot rolled product (sheet and coil) and touches upon the effect of rolled product final thickness on the ratio of downgrading. As a result the examination of overheating shows correlation with the ratio of downgrading, but the age of the mould does not. Regarding the thickness of the rolled product, it can be stated that in the case of thicker products (above 9 mm) the ratio of downgrading increases.