Hot Strip Rolling Research Articles

A Study on Potential Strip Shape Control of High‐Strength Steel during Hot Pinch Rolling Process

Hot‐rolled high‐strength steel (HSS) strips always present side‐camber after they are cut into subsections along the rolling direction. To deal with the potential strip shape defect of hot‐rolled HSS, the nonlinear finite element (FE) software is applied to establish a 3D model of pinch roll and strips to simulate the pinch rolling process before the hot rolling coiler. The effects of temperature distribution, roll wear, friction coefficient, initial strip flatness defects, and tension on the strip longitudinal extension distribution are studied along the width direction. The results indicate that the pinch roll wear presents a great influence on both the tendency and quantitative value of the strip longitudinal extension distribution. The maximum unevenness value is 178%, and the maximum differences of longitudinal strain between the center and edge of the strips reach to 51.43%. A newly pinch roll contour is proposed to improve the potential strip shape defects. After the industrial application, the average pinch roll wear thickness decreases from 180 to 120 μm. The hot rolled strips are cut into substrips and the maximum side‐camber value decreases from 12 to 3 mm, which meets the requirement from the auto part manufacturers.

Adaptive feedforward thickness control in hot strip rolling with oil lubrication

The application of oil lubrication in hot strip rolling has many advantages for the process, i.e., reduced roll force, reduced energy consumption, better strip surface quality, and reduced roll wear. On the other hand, oil lubrication may also induce severe disturbances for several control loops in a tandem hot rolling mill, which can reduce the final strip quality or might even jeopardize a stable operation of the plant. For example, the widely used automatic gauge control (AGC) has a limited bandwidth to ensure stability in the whole operating range and thus cannot (dynamically) reject the thickness deviations caused by switching on and off the oil lubrication. For this reason, the effect of lubrication is analyzed in detail and mathematically modeled in this work. Based on this dynamic lubrication model together with a hydrodynamic roll gap model and a mill stand model, two feedforward control approaches for the strip thickness are presented. These controllers counteract the negative effects of varying lubrication. Moreover, the feedforward controllers are extended by a moving horizon estimator to track changes of uncertain parameters of the underlying models based on the measured roll force. The estimated parameters are instantly used by the feedforward controller. Simulation studies using an experimentally validated simulation model of a whole mill stand show that the proposed adaptive feedforward control approach provides a significant improvement of the strip exit thickness accuracy for strips with oil lubrication compared to conventional controllers.

Effect of carbon on isothermal reduction of high-strength steel oxide scale in 30%H2–N2 atmosphere

To replace the traditional pickling process, an environmentally friendly gaseous reduction method was used for the removal of the oxide scale of steel in this work. Isothermal hydrogen reduction of high-strength steel was investigated in the temperature range from 500 °C to 800 °C in 30%H2–N2 atmosphere. The obtained results revealed a clear relationship between the oxide phase composition and the holding temperature during the heating stage, prior to hydrogen reduction. With increasing temperatures, the Fe2O3 and Fe3O4 components of the oxide scale gradually transform into FeO. When the sample was reduced under H2–N2 atmosphere, the surface morphology of the high-strength steel was different from that of the traditional hot-rolled steel strip. It was observed that the surface pore size and porosity increased with increasing temperatures and internal and external oxidation occurred simultaneously in the reduction layer. The addition of carbon to the reduction system decreased the water pressure and clearly promoted the reduction at 800 °C. The surface of the sample was reduced to irregular but uniformly distributed small particles of pure iron. Defects in the oxide scale such as cracks and gaps and carbon reacting with water play a vital role in the reduction process. Since the use of hydrogen reduction of hot-rolled strip eliminates the need for the acid pickling pollution process and the pre-oxidation process in the annealing of cold-rolled strips, it can significantly reduce the energy consumption of steel production and improve the production line efficiency. Thus, this approach is a promising green production technology in hot-dip galvanizing.

Developing Energy Efficient Modes of Hot Rolling of Broad Strips with Strain Hardening

This article analyzes the known techniques of calculating the energy intensity of continuous hot rolling of broad steel strips. The analysis is used to propose new rolling modes to ensure better energy efficiency by considering the influence of the partial cold work of the strip’s material on the energy consumption. The proposed modes were tested and adopted in the continuous finishing train of rolling mill 2000.

Improving the Milling of Hot-Rolled Strip

A model is proposed for the formation of surface relief in strip milling. The recommended procedure is to select the milling conditions on the basis of a regression equation expressing the final surface relief as a function of those conditions. Regulation of the milling conditions in terms of tool wear improves the mill life and productivity.

Substantiation for the Implementation of Controlled Coil Cooling Technology after Hot Rolling of Strip Steel

The analysis of technology for the production of hot-rolled strip steel in coils has shown that the technological instructions for this metallurgical processing stage finishes at the stage of winding a finished hot strip into a coil. The development and implementation for technology to control the cooling of hot-rolled strip coils in accordance with the grade-and-size assortment, as well as with customer’s requirements, are necessary.

Mechanism of lateral metal flow on residual stress distribution during hot strip rolling

During hot strip rolling, the lateral metal flow can change the longitudinal residual stress to reduce the risk of buckling deformation of the strip. The mechanism of lateral metal flow on residual stress was studied by combining a residual stress model with experimentation. A buckling risk coefficient was proposed to quantify the risk of buckling deformation. The calculated results show that the lateral metal flow has a self-correcting effect on the residual stress caused by the change in unit crown, this is, metals preferentially flow towards the direction helping reduce the maximum residual compressive stress. Changes in width and thickness of the strip induce a large difference in the attenuation of the maximum residual compressive stress even if the unit crown has the same change. For instance, under a large reduction rate the mode of residual stress may change from the edge-waves to the W-waves mode. A novel rolling experiment was developed, in which the grid method was employed to capture the tiny metal flow along the width. The measured lateral metal flow law is consistent with the description of the self-correcting effect of the lateral metal flow.

Prediction model for mechanical properties of hot-rolled strips by deep learning

The prediction of the mechanical properties of hot-rolled strips is a very complex, highly dimensional and nonlinear problem, and the published models might lack reliability, practicability and generalization. Thus, a new model was proposed for predicting the mechanical properties of hot-rolled strips by deep learning. First, the one-dimensional numerical data were transformed into two-dimensional data for expressing the complex interaction between the influencing factors. Subsequently, a new convolutional network was proposed to establish the prediction model of tensile strength of hot-rolled strips, and an improved inception module was introduced into this network to abstract features from different scales. Many comparative experiments were carried out to find the optimal network structure and its hyperparameters. Finally, the prediction experiments were carried out on different models to evaluate the performance of the new convolutional network, which includes the stepwise regression, ridge regression, support vector machine, random forest, shallow neural network, Bayesian neural network, deep feed-forward network and improved LeNet-5 convolutional neural network. The results show that the proposed convolutional network has better prediction accuracy of the mechanical properties of hot-rolled strips compared with other models.

Nonlinear fault detection for batch processes via improved chordal kernel tensor locality preserving projections

The quality and stability of products are seriously influenced by the process conditions. A large number of modern production processes can be considered as batch processes, with nonlinear relationships between the process variables. How to troubleshoot batch processes has attracted considerable attention in the literature. The research object of batch processes is expressed as the third-order tensor data of batch × variable × time. The traditional methods convert the tensors into second-order forms through matrix expansion. A novel method named improved chordal kernel tensor locality preserving projections (ICK-TLPP) is proposed for fault detection of batch processes. First, the chordal distance is introduced as a measurement of the similarity of matrix, and an improved method is proposed for describing the variation of time series data. Then, the chordal kernel function is introduced to preserve the spatial structure of the tensor data without the information loss caused by vectorization, and describe the nonlinear correlation during the multivariate control system. Next, the locality preserving projections algorithm is applied to detect the intrinsic manifold structure. Parallel analysis is applied to optimize the hyper-parameters in the model. Finally, Granger causality analysis is performed to locate the root cause of the process fault. The proposed method is validated on two datasets, penicillin fermentation process and the hot strip rolling process. The best results of false alarm rate and fault detection rate are 16% and 94% respectively. The proposed method performs better compared with the traditional algorithms.

A Comparative Assessment of Six Machine Learning Models for Prediction of Bending Force in Hot Strip Rolling Process

In the hot strip rolling (HSR) process, accurate prediction of bending force can improve the control accuracy of the strip crown and flatness, and further improve the strip shape quality. In this paper, six machine learning models, including Artificial Neural Network (ANN), Support Vector Machine (SVR), Classification and Regression Tree (CART), Bagging Regression Tree (BRT), Least Absolute Shrinkage and Selection operator (LASSO), and Gaussian Process Regression (GPR), were applied to predict the bending force in the HSR process. A comparative experiment was carried out based on a real-life dataset, and the prediction performance of the six models was analyzed from prediction accuracy, stability, and computational cost. The prediction performance of the six models was assessed using three evaluation metrics of root mean square error (RMSE), mean absolute error (MAE), and coefficient of determination (R2). The results show that the GPR model is considered as the optimal model for bending force prediction with the best prediction accuracy, better stability, and acceptable computational cost. The prediction accuracy and stability of CART and ANN are slightly lower than that of GPR. Although BRT also shows a good combination of prediction accuracy and computational cost, the stability of BRT is the worst in the six models. SVM not only has poor prediction accuracy, but also has the highest computational cost while LASSO showed the worst prediction accuracy.

Application of Singular Perturbation Control Technology in the Control of Hot Strip Rolling

Application of Singular Perturbation Control Technology in the Control of Hot Strip Rolling

Pickling behavior of 2205 duplex stainless steel hot-rolled strips in mixed solutions of HNO3-HF

The pickling behaviour of 2205 DSS hot-rolled strips after annealing and sand blasting was studied in the mixed solutions of HNO3-HF using weight loss rate, surface analysis, corrosion potential, and electrochemical impedance spectroscopy measurements. The pickling rate decreased as the concentration of HNO3 increased in the mixed solutions of x HNO3 + 25 g l−1 HF (x = 40 ∼ 200 g l−1) at 50 °C due to passivation. The passivating effect of HNO3 became weak as its concentration was less than 80 g l−1. The pickling rate increased noticeably when the concentration of HF in the mixed solutions of 120 g l−1 HNO3 + y HF (y = 5 ∼ 80 g l−1) at 50 °C was increased. The dissolution of the metal under the oxide scale may have changed from the passive state to the active state as the HF concentration was higher than 25 g l−1. The pickling dissolution accelerated noticeably as the temperature rose from 40 to 60 °C. With the optimised pickling process, 2205 DSS hot-rolled strips can be pickled industrially with good efficiency and surface topography.

New economically effective steel strips production technologies (based on materials of international conferences)

Production of steel rolled products by using traditional metallurgical technologies are rather material- and energyintensive and its concentration at gigantic steel plants resulted in the increased expenses for transportation of raw materials and finished products. To solve the problems, a practice of comparatively small metallurgical plants (mini-mills) construction is becoming widespread in the world steel industry. The mini-mills include modern electric arc furnaces, ladle steel treatment facilities and steel continuous casters combined with continuous rolling mills. The review complied from materials of international conferences, taken place in 2015–2019. In the review achievements in equipment and technology of metal products at mini-mills development considered, as well as analysis of modern economical methods of steel coils presented. It was shown, that the methods of strips endless rolling, widely used already at industrial scale in several countries, enable producing rather thin hot-rolled strips from liquid steel. Universal casting-rolling aggregates (CRA) developed, by which high quality strips of rather wide assortment can be produced. For a mass production of rather thin (down to 0.8 mm) hot-rolled strips, which can in many applications substitute more expensive coldrolled ones, compact aggregates of endless casting-rolling are recommended, which provide the yield of up to 98%. Concepts of the CRA elaborated for production of steel strips of wide assortment, from ultrathin strips to thick (25 mm) ones. The concepts include application of thermomechanical treatment to increase the mechanical properties of the rolled products from various steels, including low-alloyed ones.

The Effects of High-Speed Steel Roll and Lubrication on Work Roll Wear and Fatigue During Electrical Steel Strip Hot Rolling

Work rolls in the hot strip mill withstand extreme service conditions, especially when electrical steels are rolled, resulting in severe roll wear and fatigue. High-speed steel (HSS) work rolls and rolling lubrication are applied to the mill to improve roll wear and fatigue. Tests show that HSS work rolls manifest good performance in wear, fatigue and oxidation resistance during electrical steel hot rolling. The wear loss of HSS work rolls decreases remarkably, but the heat dispersion deteriorates. The service period of HSS work rolls can be increased significantly, but the fatigue failure risk increases as well. In addition, rolling lubrication is proven to be effective in alleviating roll wear and fatigue, but high temperature reduces the positive effects of rolling lubrication. Roll wear and fatigue are considered to be parallel and mutual effective processes. The applications of HSS rolls together with rolling lubrication contribute the most to the improvement of work roll wear and fatigue during electrical steel hot rolling.

Numerical Simulation of Strip Shape of High-Strength Steel during Hot Rolling Process

High-strength steel is widely applied due to its excellent mechanical properties. However, its high strength in turn brings great difficulties to production and processing such as hot strip rolling owing to the high rolling force, which results in large elastic deformation of roll stack and poses a huge challenge to the control of strip crown and flatness. In this paper, A three-dimensional (3D) elastic-plastic coupled thermo-mechanical finite element (FE) model for hot strip rolling of high-strength steel is developed and then verified experimentally. This model not only calculates the elastic deformation of rolls and plastic deformation of strip simultaneously, but also considers the effect of temperature variation during hot strip rolling. Based on this valid model, the effects of bending force and shifting value of work roll (WR), back-up roll (BR) size, entrance strip crown and rolling force on strip crown have been investigated quantitatively. The results obtained provide valuable guidelines for industrial strip production.

Analysis of thin strip edge drop formation during cold rolling process

ABSTRACT In order to produce a thin non-oriental silicon steel strip with high surface quality, the hot rolled strip needs to undertake a large reduction by cold tandem rolling process. As a result of thin strip rolling, the rolling pressure is concentrated on a small area of the work roll surface causing a large elastic deformation. Because of the transverse thickness distribution of strip is strongly dependent of roll’s shape, it is imperative to consider work roll’s non-circular shape. By relaxing the Hitchcock assumption, vertical displacement of work roll surface is calculated in both rolling and transverse direction. By assuming the thickness of strip does not increase when rolled, a Slab method is implemented to calculate roll pressure due to work roll’s shape. Combined with Influence Function Method for loads distribution between stacked rolls, the proposed model can predict thin strip transverse thickness profile with a good accuracy compared with industrial data under varied conditions. Five-pass cold reversal rolling process is investigated by the validated model. It is revealed that the transverse thickness deviation can be effectively reduced by decreasing the entry thickness of strip.

Metallurgical Evaluation and Failure Analysis of Cracking in Wheel Rim SPFH590 Steel

Abstract Manufacturing wheel rims in the automobile industry demands high quality, high production, cost-effective and flawless wheels. At present, JIS G3138 SPFH 590 steel is widely used for manufacturing wheel rims for light and medium commercial vehicles. For high productivity, Flash butt welding is used for joining the edges of hot rolled strips. Cracking in wheel rims is a significant problem encountered in the production sectors. The present study is aimed at evaluating failure types in wheel rims by factors governing flash butt weld and subsequent cold forming processes. The microstructure of fractured specimens was examined by field emission scanning electron microscopy (FESEM) and an optical microscope. The mechanical characterization was analysed by tensile tests and crack tip opening displaced testing. The outcome of the results obtained was correlated with metallurgical concepts in order to find the cause of cracking failure.

Possibilities for Renovation of Functional Surfaces of Backup Rolls Used during Steel Making

The paper presents the results of the research aimed at possibilities of renovation of functional surfaces of back-up rolls that are part of the hot strip rolling mill operating line using new types of additive materials. Experimentally, four melts of alloyed steel were produced in laboratory conditions from which four types of filler materials in the form of wires were made. They were made by pulling through dies to a diameter of 2.4 mm. The renovation of functional surfaces was performed on the batch of rolls with the outer diameter of 1000 mm and length 3000 mm. Cladding technology submerged arc welding (SAW) was applied for cladding of four spirals with 40 mm oscillation onto the base material of the 31CrMoV9 (EN 10085) sub-roll. The base flux marked WLDC 17-AWS A5.17-89 EM13K with basicity index 3 was used for cladding. The four-layer weld deposition was made to eliminate the effect of mixing the surfacing layers with the base material. The refurbished rolls were annealed after welding. Surface quality was assessed by visual inspection (VT) according to EN ISO 17637. The presence of internal errors was determined by ultrasound control (UT) in accordance with EN ISO 11666 and EN ISO 17640. The quality of the clad layers was analysed on metallographic sections using light microscopy. The microhardness of the individual clad layers was evaluated according to Vickers according to EN ISO 9015-2. Based on realized experiments it can be stated that the selected cladding parameter was suitable, and the overlay layers showed no surface or internal defects. Mechanical and tribological tests were carried out, but they showed significant influence of chemical composition of additive materials on mechanical properties, or wear resistance of the layers.

Improvement of Methods of Calculation of Forces in Hot Strip Rolling

A new solution Karman’s equation with the Mises plasticity condition is proposed for determining contact stresses in the slip zones for hot strip rolling. Replacement of the precise plasticity condition by an approximate condition in terms of primary stress leads to a substantial decrease in the length of slip zones and to increase of the rolling force. It was shown that, even at high frictional coefficients, the length of slip zones forms a significant part of the length of deformation region. On the basis of the obtained solutions the techniques for plotting curves of the normal contact stresses, determining the length of the slip zones, the neutral position of the cross section and rolling force refined.

The experimental/numerical investigation of variations in strip speed, water shower pattern and water temperature on high-temperature strip cooling rate in hot strip mill

Hot-rolled strips are cooled on the run-out table to achieve the customer-required mechanical properties. Cooling reduces the oxidation, which can assist the coiling operation. The ability to obtain a range of mechanical properties from a single steel grade reduces the use of alloying elements (elements added to a metal or an alloy which are incorporated in the metallic structure and change in the properties of the basic alloy) and the size of the slab inventories. So in this paper, the high-temperature steel strip cooling pattern with the temperature of 870 °C and reaching the temperature of 630 °C using water and air is studied. Moreover, the numerical simulation of the high-temperature strip cooling and its cooling method is carried out. The results are compared with the similar sampler ones. The changes of three key parameters such as change in strip speed and its effect on cooling rate, change in pattern and arrangement of water showers and its effects and change in the cooling water temperature are investigated. It was found that the uniformity of the heat distribution inside the strip was increased, but the temperature of the strip was lower than the required temperature. The middle and up surface temperatures of the strip were performed at a speed of 3.48 (m s−1), which showed a very good match with the actual tested sample.