Papers by Keyword: Hot Rolling

Abstract: Magnesium alloys are highly desirable for weight critical applications owing to their high weight to strangth ratio. However, their poor formability at room temperature limits their widespread use in industrial applications. In this study, we invstigate the hot deformation behaviour of AZ31 and AZ31-0.7% Ca magnesium alloys and explore their microstructural and thermal properties. Our findings reveal that dynamic recrystallization during hot deformation leads to successful grain refinement in the AZ31 alloy, resulting in a normal grain size distribution. In contrast, the AZ31-0.7% Ca alloy shows bimodal grain size distribution due to the addition of calcium. Additionally, the number and size of β-Mg₁₇Al₁₂ particles were found to increase with the addition of a small amount of calcium. These particles are responsible for the discontinuous precipitation phenomenon, which strongly influences microstructural changes during hot rolling. Our study provides valuable insights into the dynamic recrystallization and discontinuous precipitation phenomena of magnesium alloys, which can aid in the development of novel alloys with improved formability and mechanical properties.

Abstract: Numerical modelling tools provide valuable means to quantitatively control thermomechanical processing. Several modelling tools have been applied and developed at University of Oulu during previous years, such as finite element models for hot rolling, recrystallization models, heat transfer and conduction model, coupled with phase transformation, as well as cellular automata and phase field models for simulating phase transformation during cooling. This article describes the overall development and recent progress of the developed numerical modeling tools.

Abstract: The safety of basic parts of the rolling equipment is most at risk due to the complex geometrical shape and significant levels of nominal stresses. With a significant mass of such parts and a long production time, the replacement process is accompanied by the need to dismantle the old mill and install a new one. Currently, there are no specialized methods for assessing the risks of failures in relation to the rolling equipment, therefore, it is required to develop new methodological provisions and adapt the existing general methods of risk assessment to real production conditions. Based on the fundamentals of the regulatory document, a methodology for assessing the risks of failures in relation to the rolling equipment has been developed. The roughing stand of the “2000” hot rolling mill for titanium alloy sheet production was chosen as a practical object for assessing the risks of failure. The preliminary analysis of the dangers and their consequences had shown that for most of the elements of the working stand, which perceive the rolling force, as well as for the units and parts of the main drive loaded with the rolling torque, there are dangers that can lead to disruption of the deadlines for fulfilling orders for rolled products. For a numerical assessment of these risks, special calculations were performed.

Abstract: The purpose of this work is to evaluate the performance of several wear models, either with different mathematical formulation or different definition of the unknown wear coefficients, on the prediction of the work-roll wear amplitude in Hot Strip Mills (HSM). To achieve this goal, a classical model calibration approach based on inverse optimization has been developed to calibrate these several wear models. A large industrial hot rolling database composed by roll wear amplitude measurements for both later finishing mill stands (F6 and F7) from ArcelorMittal Dofasco HSM was considered and a least-square cost function was applied to minimize the differences between both numerical and experimental results during the optimization process. The averaged roll wear gap between measurements and optimized numerical predictions was then used as a quantitative indicator to compare the performance between the wear models and identify the most suitable one for roll wear prediction. In addition, an Artificial Neural Network (ANN) approach was developed based on the most suitable wear model. Thus, roll wear predictions obtained using the ANN were compared with the ones obtained using Classical calibration to evaluate the performance of both approaches.

Abstract: Grain-oriented electric steel is hot rolled at different hot rolling temperature, and subsequent thermal maintained. Precipitation features of MnS and Cu₂S were observed under different process conditions using thermal field emission scanning electron microscopy. The results show that Cu is precipitate out in the form of a composite precipitate with MnS during hot rolling, The hot rolling temperature and the postrolling maintain time had no obvious effect on the precipitation of MnS, The lower the hot rolling temperature, the faster the Cu₂S precipitation. And the insulation process after high temperature hot rolling can make a large number of the Cu₂S diffusion precipitation, There was no significant effect on the precipitation of Cu₂S after low temperature hot rolling, still remain in the precipitate state after hot rolling.

Abstract: Recently much interest has been attracted in replacing heavy metals with light metals such as aluminum to reduce weight to improve fuel efficiency of automobiles. However, weight reduction by light metals often leads to decrease in strength, which causes problems in terms of safety and sustainability. This study aims to produce carbon nanotube (CNT) reinforced aluminum (Al) matrix composites with high performance using a combination of spark plasma sintering (SPS) and hot rolling techniques. Dry ball milling and SPS followed by hot rolling were conducted to uniformly disperse CNT in Al matrix. The microstructures of the composites including dispersibility of CNT were observed using a scanning electron microscope (SEM) and transmission electron microscope (TEM). Anisotropic mechanical behavior was investigated through Vickers hardness and tensile tests. The experimental results demonstrated that the post-sintering hot rolling can highly enhance the tensile strength of the composites.

Abstract: Pipe steel sheet is manufactured by hot rolling technological process. Technological regimes of every technological operation can vary in a wide range affecting pipe steel sheet properties. It is shown that system analysis provides the effective way for searching out the basics for mathematical modeling of multi-variant technological processes. The detailed scheme of steel sheet hot rolling process is presented, determining its input and output parameters. Flows of material, energy, and information are presented for each technological operation. Metallurgical concept of pipe steel manufacturing is shown as the basics for competitive product manufacturing. It is proposed to analyze the hot rolling process as a set of target functions, which will make it possible to achieve the pipe steel sheet with the desired level of mechanical properties. The proposed approach based on system analysis allows to find tendencies for further development of hot rolling.

Abstract: The aim of this work is to investigate the dissolution behavior of Nb in hot charging hot rolling configurations. To do so, an indirect experimental procedure is used to quantify the amount of Nb present in solution before rolling. The method is based on the effect of dissolved Nb on static recrystallization kinetics due to its solute drag effect. After different thermal cycles, simulating cold and hot charging conditions, double hit torsion tests have been performed with a 0.23%C steel microalloyed with 0.03% Nb. By means of these tests, the static softening behavior has been determined. Comparison of the recrystallization times allows indirect evaluation of the amount of Nb in solid solution after each treatment. The results have been correlated with the precipitation state of the samples.

Abstract: While the role of Nb in flat rolling of low carbon steels has been investigated in many works, the information about the use of Nb in rebar rolling of higher carbon grades is more limited. Rebar rolling presents differences relative to flat rolling that can affect the role of Nb, such as the application of higher number of rolling passes, higher strain rates, lower interpass times, and, consequently, enhanced adiabatic heating. Increasing the number of passes can contribute to austenite grain refinement. However, the high finishing temperatures in rebar rolling can lead also to significant austenite grain growth and microstructural heterogeneity development before phase transformation. This phenomenon will directly influence the final grain size and can also lead to the appearance of second hard phases in the final product. One of the options to avoid austenite grain growth is to add microalloying elements that retard grain growth kinetics, either in solid solution or as precipitates. This can open new roles for the application of Nb in rebar rolling. To analyze this, in this work laboratory torsion tests were performed with two 0.2%C steels microalloyed with two different Nb contents (0.029% and 0.015%). Soaking temperatures from 1100°C to 1250°C were applied to obtain different amounts of Nb in solid solution before grain growth study. The study shows that not only finish rolling temperature and cooling time, but also reheating temperature and the amount of Nb remaining in the form of undissolved precipitates are important factors controlling austenite grain growth.

Abstract: The technology has been developed for the production of low-carbon and microalloyed steel for the production of strips in order to manufacture small and medium-diameter pipes for the extraction and transportation of petroleum products. The developed technology allows to obtain stable corrosion properties, according to the NACE Standard TM 0284 technique, in a hot-rolled condition from slab with thickness more than 200 mm and with a content of more than 0.03% of carbon, which is very difficult in terms of ensuring the availability of inclusions and heterogeneity in the structure - as the main reasons for the reduced fracture toughness of steels working in acid media (in environments saturated with H2S). The obtained results allowed, with minimum costs, to prepare the previously developed integrated computer model (STAN 2000) for calculating the structure and mechanical properties. Calculations using the model made it possible to select such temperature-deformation regimes, which would be the minimum structural inhomogeneity over the section of the thickness of the hot-rolled strip. The results obtained: corrosion resistance repeatedly confirmed by the absence of cracks at the beginning after testing in accordance with the procedure Standard TM 0284.