Hot Rolling Operation Research Articles

Modelling of Oxide Scale Evolution in Hot Rolling and Descaling

Oxide scale behaviour in thermomechanical processing has been the subject of intensive research for several years that allowed developing a finite element (FE) based model to simulate a range of events of relevance to the process and the surface quality of the hot rolled product. A range of experimental techniques have also been developed, each providing a partial insight. An overview of this research is presented in the sequence of rolling and finishing with descaling. The model has been extended to provide the basis for detailed numerical investigations of the roll/stock interface behaviour during multi-pass hot rolling operations. The modelling techniques have been used for providing design criteria for AISI430 ferritic stainless steel scale failure during bending. Modelling of near surface deformation during rolling of aluminium alloys is under consideration.

MULTI-MODAL SIMULATION FOR MICROSTRUCTURAL AND PROPERTY PREDICTION FOR AL ALLOY HOT ROLLING

This study presents the application of FE modelling and intelligent systems techniques to the prediction of microstructural mapping for aluminium alloys. Here, the material within each finite element is defined using a set of non-linear physically-based equations. These are then solved in real-time using a semi-physical grey-box model. This model is based on a neuro-fuzzy approach and it has been embedded within the FE technique. The model maps the evolution of the internal state variables (i.e. dislocation density, subgrain size and subgrain boundary misorientation) and their effect on the recrystallisation behaviour of the stock. This paper presents the model development, the integration between the numerical techniques, and the application of the technique to a hot rolling operation using an Aluminium, 1wt% Magnesium alloy. In addition, the developed model includes a CA (Cellular Automata) level to represent inhomogeneous nature of microstructural beheviour.

Influence of cold work and plate thickness on the gas-tungsten arc weldability of commercially pure aluminium

Abstract This body of work reveals the weldability of commercially pure aluminium after the base metal received different amounts of hot and cold work. This process included the continuous casting of molten aluminium Alloy 1235 directly into an endless coiled strip suitable for cold rolling. Following casting and hot rolling, the material was cold rolled (at room temperature) to different thicknesses and reduction ratios. Gas-tungsten arc welding (GTAW) was used to join the aluminium plats after both hot and cold rolling operations. The purpose of these studies was to determine the influence of the workpiece temper condition and thickness on weldability. This contribution summarises the main results of this investigation.

Thermomechanical modelling of hot slab rolling

A model is developed to evaluate strain and temperature fields as well as to predict microstructural changes within the metal during a hot rolling operation. For this purpose, the governing heat conduction and energy equations are solved with the aid of a two-dimensional finite element method and Galerkin and Petrov–Galerkin techniques. Also, to consider microstructural changes such as dynamic and static recrystallisation, the Bergstrom dislocation model and Avrami's equation are coupled with the finite element model. Verification of the modelling results is performed through hot rolling experiments and microstructural studies. The comparison between the experimental and the theoretical results shows the reliability of the simulation results.

Real-Time Prediction of Geometrical Distortions of Hot-Rolled Steel Rings during Cooling

The paper deals with the application of neural network modelling to the real-time prediction of the geometrical distortion of hot rolled steel rings during cooling from rolling to room temperature. The neural network model was designed and developed to be part of a new modular system for the in-line monitoring and real-time control of the geometrical quality of rings, even those with a complex profile, during hot and warm ring rolling operations. The data utilised to train the neural network were generated by numerical simulations of the cooling phase. In order to do these simulations, an FE model capable of coupling thermal, mechanical and metalllurgical events was accurately calibrated. The proposed model was then applied to an industrial case that is described in the paper.

Thermo-mechanical-metallurgical model to predict geometrical distortions of rings during cooling phase after ring rolling operations

The paper presents a validated numerical model able to predict geometrical distortions of rings during cooling phase after hot ring rolling operations. The model is capable to take into account the effects of all the phenomena resulting from the coupling of thermal, mechanical and metallurgical events. As simulation results strongly depend on the accuracy of input data, physical simulation experiments on real-material samples are developed and carried out to characterize material behaviour during phase transformation. The numerical model is then validated by an industrial case proving its effectiveness in predicting final ring distortions at room temperature.

The grain boundary character distribution of a fully-orthorhombic Ti–25Al–24Nb(at.%) alloy

The grain boundary character distribution (GBCD) of a fully-orthorhombic (O) Ti–25Al–24Nb (at.%) microstructure was investigated using electron backscatter diffraction (EBSD). The fine-grained (GS=17 μm) equiaxed microstructure was processed by hot forging and hot-rolling operations performed below the body-centered cubic (bcc) phase transus temperature followed by heat treatment in the O-phase field at 875 °C. Nearly all the O/O grain boundaries were greater than 15 degrees misoriented and such boundaries exhibited the highest frequencies at misorientations of approximately 65° (∼26% of all grain boundaries) and 90° (∼10% of all grain boundaries). Twin-related O-phase variant interfacial (1 1 0) planes were identified and such boundaries represented 39% of all the O/O grain boundaries with 65° misorientation about [0 0 1].

A Comparative Finite-Element Study of Hot Rolling and Plane Strain Compression Testing of Aluminum AA1050

Abstract A comprehensive study on the comparison of hot rolling and plane strain compression testing (PSC) using the finite-element method (FEM) is reported in the present paper. The key physical variables during hot rolling and PSC testing of aluminum AA1050 are quantified and compared. The results show that the process variables, i.e., local stress, strain, strain rate, and temperature, vary from entry to exit and throughout the thickness of the work piece during hot rolling, while the evolution pattern of these parameters during PSC testing under a constant nominal strain rate is quite uniform. Therefore, for a given amount of nominal deformation (reduction), the loading history and the spatial distributions of these process variables are quite different in both cases. It is indicated that a further examination of the deformation history should be made when applying the relationships established from PSC testing to real industrial hot rolling operations.

Surface defects—evolution and behaviour from cast slab to coated strip

Surface defects can evolve in a number of ways during the hot rolling of strip products. Over the past few decades the causes of many defects have been determined and countermeasures introduced, but one issue still remains unresolved. This is sliver, which is usually observed after the galvannealing (GA) process as thin white lines. A proposal is made to determine the likely causes of this defect, using backward material tracking to determine the source location. Material tracking is a recent innovation that relies on FE based models to provide a framework for calculating material movement during hot rolling operations.

Metallurgical aspects relating to the production of ferritically hot-rolled interstitial-free steel

Although ferritic hot rolling was introduced to avoid the temperature control problems that can be encountered during traditional hot rolling of thin strip in the austenite condition, numerous advantages are offered by finishing the hot rolling operations with a fully ferritic microstructure. Laboratory hot rolling facilities and procedures were therefore developed to establish the influence of variations in the reheating, finishing and coiling temperatures on the microstructure and mechanical properties of interstitial-free (IF) steels. Processing schedules suitable for both recrystallized and strained ferritically hot-rolled IF steels are identified and discussed in relation to the feasibility of manufacturing these products using conventional hot mills.

Hot-Roll Bonding of Al-Pb Bearing Alloy Strips and Hot Dip Aluminized Steel Sheets

In this paper, the basic bonding mechanism between two materials of practical importance is identified. One of the materials is carbon steel, which has been aluminized on its surface by immersion in molten aluminum. This step produced a Fe-Al intermetallic compound layer. The other material is an Al-Pb alloy (a bearing material). The two materials were hot roll bonded together. It was found that the Fe-Al intermetallic compound broke into discontinuous blocks during the hot rolling operation. The block of intermetallic compound remained bonded to the steel. The overall bond between the Al-Pb strip and the steel strip resulted from two different bonds. The Al-Pb strip and the Fe-Al intermetallic compound (this is called the “block bond” in this paper) and the Al-Pb strip and the bare steel surface in the area where the block separated from the steel substrate (this is called the “blank bond” in this paper).

Dynamic materials modelling concepts applied to analysis of hot rolling of commercial aluminium alloys

A typical industrial hot rolling operation applied to a commercial Al–1%Mg alloy has been analysed in terms of some concepts from dynamic materials modelling (DMM), particularly the so called dissipator co-content J and the efficiency of power dissipation through microstructural changes η. The calculation of the parameter η for every deformation condition of the hot rolling schedule has been conducted assuming that this variable depends not only on the mean deformation temperature and strain rate but also on the strain applied to the material. All the analysis has been conducted on the basis of a constitutive equation previously determined for this material on a rational basis, which is capable of describing the strain, strain rate, and temperature dependence of the flow stress. It has been determined that, for this material, η can be significantly dependent on strain under certain deformation conditions, particularly low deformation temperatures and relatively high strain rates. It has also been shown that for the materials analysed, η is much more dependent on deformation temperature than on strain rate. A comparative analysis carried out with aluminium of various purities indicates that η is much lower for the alloy when it is deformed under similar conditions. In this sense, it has been suggested that such results could be interpreted in terms of the impurity content of the material and the interaction of the alloying atoms with the dislocation structure developed during high temperature deformation. However, this is only possible if the hypothesis advanced by Prasad and co-workers, that the power dissipation efficiency is associated with the dynamic microstructural processes that occur during deformation, is considered valid. The present results indicate that, contrary to previous findings, in terms of DMM concepts there are no specific conditions of temperature and strain rate for the optimum processing of the materials investigated.

Finite element analysis of the temperature profile of rolls

The thermal conditions during hot rolling operations can adversely affect the rolls’ service life and the quality of the rolled product. Analysis of the temperature profile of the rolls is an essential step towards the development of precise cooling systems to minimise their surface deterioration and thermal bending or camber. This paper makes an attempt at developing a finite element model for analysing the steady state temperature profile of rolls of varying dimensions. Rolls of large surface area exhibit greater differences in temperature between the surface and the interior as compared to those having smaller surface area and therefore make greater demands on the cooling system. Die Temperaturverhältnisse beim Warmwalzen können die Standzeit der Walzen und die Qualität des gewalzten Produktes nachteilig beeinflussen. Die Analyse des Temperaturprofils der Walzen ist ein bedeutender Schritt im Hinblick auf die Entwicklung eines präzisen Kühlsystems, um Oberflächenschädigungen, Biegung infolge thermischer Einflüsse oder Durchbiegung zu minimieren. In der vorliegenden Arbeit wird der Versuch gemacht, ein FE-Modell zur Analyse des stationären Temperaturprofils der Walzen unterschiedlicher Abmessungen zu entwickeln. Walzen mit großer Oberfläche weisen größere Temperaturunterschiede zwischen Oberfläche und dem Walzeninneren auf als solche mit kleineren Oberflächen. Folglich stellen sie größere Anforderungen an das Kühlsystem.

Mathematical and physical modelling of steel flow and solidification in twin-roll/horizontal belt thin-strip casting machines

Near-net-shape casting technology is one of the most important research areas in the iron and steel industry today. Driving forces for the development of this technology include a reduction in the number of operations needed for conventionally produced strip. This is especially true of hot rolling operations. The consequent reduction in investment cost when considering new industrial facilities, makes near-net-shape casting operations extremely attractive from a commercial standpoint. Various processes for near-net-shape casting of steel are currently being developed around the world. Of these processes, twin-roll casting machines represent a major area of concentration. We believe that one of the main issues concerning the design of twin-roll casters is the metal delivery system and its effect on the homogeneity of solid shell formation, segregation and surface quality. In the present work, computational fluid dynamics has been used to study different metal delivery systems for twin-roll casting (TRC) and horizontal belt casting (HBC) operations. The METFLO code has been adapted to simulate three-dimensional turbulent fluid flows, heat transfer and solidification in these types of machines. The enthalpy–porosity technique was used to couple fluid flow and solidification phenomena. Two configurations for metal delivery system have been studied to date for TRC: one is a conventional tubular nozzle with horizontal outlets in the directions of the side dams; the other is a slot nozzle with a vertical inlet stream. These simulations have been applied to a pilot caster being studied in Canada, with a roll radius of 0.30 m, producing steel strips with thicknesses ranging from 4 to 7 mm, at relatively low roll speeds ranging between 4 and 12 m/min. Different positions and penetrations of the nozzles in the liquid pool have also been analysed. It has been shown that a tubular nozzle leads to the formation of a non-uniform solid shell along the roll width. In both configurations, a thicker solid shell is formed close to the roll edges, due to the presence of the side dams. In the case of HBC, computations have been made for an extended nozzle metal delivery system, and preliminary water modelling tests carried out to confirm the flow delivery concepts proposed. In addition, instantaneous heat flux measurements to simulated belt substrates have been performed for the horizontal casting of aluminum strip that show somewhat similar characteristics to those measured for steel in the pilot TRC, in terms of transient peaks and decays.

Computational Fluid Dynamics Applied to Twin-Roll Casting

Abstract Near-net-shape casting technology is one of the most important research areas in the iron and steel industry today. Driving forces for the development of this technology include a reduction in the number of operations needed for conventionally produced strip. This is especially true of hot rolling operations. The consequent reduction in investment costs, when considering new industrial facilities, makes near-net-shape casting operations extremely attractive from a commercial standpoint. Various processes for near-net-shape casting of steel are currently being developed around the world. Of these processes, the twin-roll casting machines represent a major area of concentration. We believe that one of the main issues concerning the design of twin-roll casters is the metal delivery system and its effects on the homogeneity of solid shell formation, segregation and surface quality. In the present work, computational fluid dynamics has been used to study different metal delivery systems for twin-roll casting. The METFLO code has been adapted to simulate three dimensional turbulent fluid flow, heat transfer and solidification in this type of machine. The enthalpy-porosity technique was used to couple fluid flow and solidification phenomena. Two configurations for metal delivery system have been studied to date, one is a conventional tubular nozzle with horizontal outlets in the directions of the side dams. The other is a slot nozzle with a vertical inlet stream. These simulations have been applied to a pilot caster being studied in Canada, with a roll radius of 0.30 m, producing steel strips with thicknesses ranging from 4 to 7 mm, at relatively low roll speeds ranging between 4 and 12 m⧹min. Different positions and penetrations of the nozzles in the liquid pool have also been analysed. It has been shown that the tubular nozzle leads to the formation of a solid shell that is thicker at the centre of the caster. The slot nozzle gives a more uniform thickness of the solid shell along the roll width. In both configurations, a thicker solid shell is formed close to the roll edges, due to the presence of the side dams. It has also been demonstrated that the slot nozzle gives lower levels of turbulence at the free surface, which can have positive effects on the product quality.

Computational fluid dynamics applied to twin-roll casting

Near-net-shape casting technology is one of the most important research areas in the iron and steel industry today. Driving forces for the development of this technology include a reduction in the number of operations needed for conventionally produced strip. This is especially true of hot rolling operations. The consequent reduction in investment costs, when considering new industrial facilities, makes near-net-shape casting operations extremely attractive from a commercial standpoint. Various processes for near-net-shape casting of steel are currently being developed around the world. Of these processes, the twin-roll casting machines represent a major area of concentration. We believe that one of the main issues concerning the design of twin-roll casters is the metal delivery system and its effects on the homogeneity of solid shell formation, segregation and surface quality. In the present work, computational fluid dynamics has been used to study different metal delivery systems for twin-roll casting. The METFLO code has been adapted to simulate three dimensional turbulent fluid flow, heat transfer and solidification in this type of machine. The enthalpy-porosity technique was used to couple fluid flow and solidification phenomena. Two configurations for metal delivery system have been studied to date, one is a conventional tubular nozzle with horizontal outlets in the directions of the side dams. The other is a slot nozzle with a vertical inlet stream. These simulations have been applied to a pilot caster being studied in Canada, with a roll radius of 0.30 m, producing steel strips with thicknesses ranging from 4 to 7 mm, at relatively low roll speeds ranging between 4 and 12 m⧹min. Different positions and penetrations of the nozzles in the liquid pool have also been analysed. It has been shown that the tubular nozzle leads to the formation of a solid shell that is thicker at the centre of the caster. The slot nozzle gives a more uniform thickness of the solid shell along the roll width. In both configurations, a thicker solid shell is formed close to the roll edges, due to the presence of the side dams. It has also been demonstrated that the slot nozzle gives lower levels of turbulence at the free surface, which can have positive effects on the product quality.

Comparison of transmission electron microscopy and optical microstructures in Al–1% Mg after plane strain compression

Modelling the microstructural evolution of aluminium alloys during hot rolling operations is becoming increasingly dependent on accurate measurements of the deformed microstructure using transmission electron microscopy, scanning electron microscopy and light microscopy. In this paper, an experimental technique which directly compares the microstructure observed in thin foils with that observed using light microscopy is described.

Origin of cube texture during hot rolling of commercial AlMnMg alloys

Investigation of samples taken at different gauges during multi-pass hot rolling has been made with emphasis on characterisation of the through-thickness variation in microstructure and texture. The evolution of the cube texture ((001),(100)), which is a major cause of anisotropy after hot rolling is of particular interest. In the present study a detailed investigation of the origin of the cube texture component during hot rolling has been performed. Information on the characteristics of this special crystallographic orientation during the hot rolling operation has been obtained by applying the electron back scattering pattern (EBSP) technique in SEM. The results show that the cube orientation is metastable during hot deformation in the sense that large fractions of the cube are able to survive through heavy reductions without rotating towards the stable texture components. Cube grains, which during a few hot rolling passes get flattened to a critical thickness, subsequently serve as sites for the nucleation of second generation cube grains.

High-Temperature deformation of B2 NiAl-base alloys

The high-temperature deformation behavior of three rapidly solidified and processed NiAl-base alloys-NiAl, NiAl containing 2 pct TiB2, and NiAl containing 4 pct HfC—have been studied and their microstructural and textural changes during deformation characterized. Compression tests were conducted at 1300 and 1447 K at strain rates ranging from 10-6 to 10-2 s-1. HfC-containing material showed dispersion strengthening as well as some degree of grain refinement over NiAl, while TiB-2 dispersoid-containing material showed grain refinement as well as secondary recrystallization and did not improve high-temperature strength. Hot-pack rolling was also performed to develop thin sheet materials (1.27-mm thick) from these alloys. Without dispersoids, NiAl rolled easily at 1223 K and showed low flow stress and good ductility during-the hot-rolling operation. Rolling of dispersoid-containing alloys was difficult due to strain localization and edge-cracking effects, resulting partly from the high flow stress at the higher strain rate during the rolling operation. Sheet rolling initially produced a (111)< 112) texture, which eventually broke into multiple-texture components with severe deformation.

Determination of Recrystallization Stop Temperature from Rolling Mill Logs and Comparison with Laboratory Simulation Results.

The tempreature of no-recrystallization, Tnr, was measured by means of laboratory torsion rests for three low carbon steels. The Tnr values for these steels were also established from rolling mill log data obtained from the Algoma plate mill; these were found to be virtually identical to those from torsion tests. The mill log calculations were carried out by organizing the Sims roll force equations into a spreadsheet software for desktop personal computers. The results of both the torsion testing and mill log calculations compare well with previously developed correlations between Tnr and the chemical composition, and between Ar3 and the composition. It was also found that the overall levels of the mean flow stresses calculated from the mill logs are close to those determined from torsion testing. This excellent agreement confirms that laboratory torsion testing can provide a convenient and very effective simulation of industrial hot rolling operations.