Rolling Pass Research Articles

Insight to the Influence of Ti Addition on the Strain-Induced Martensitic Transformation in a High (about 7 wt.%) Mn Stainless Steel

The kinetics of strain-induced martensite (SIM) formation in a Ti-bearing 201L stainless steel were evaluated and compared to the existing results of two conventional stainless steel grades; i.e., 201L and 304L AISI. The effects of strain rate and rolling pass reduction on the kinetics of SIM formation during cold rolling were investigated. The Ti-microalloying was found to be intensifying the transformation due to lowering the stacking fault energy. It was seen that decreasing the rolling pass reduction strongly affected the variation of SIM volume fraction. Furthermore, a close correlation between the hardness and strain-induced transformation was found arising from microstructural evolution during the cold rolling process. Three stages in the hardening behavior were detected associated with lath-type martensite formation, transition stage of martensite laths break up and formation of dislocation-cell-type martensite.

Effects of hot-core heavy reduction rolling during continuous casting on microstructures and mechanical properties of hot-rolled plates

Abstract A slab’s internal defects that are associated with porosities significantly influence the qualities of hot-rolled plates, especially which are rolled with low reduction ratio. Hot-core heavy reduction rolling (HHR2) is an innovative technology to eliminate the porosity defects in casting steel through a single pass rolling, after the final solidification point. In this study, a Nb–Ti-microalloyed steel grade was investigated as the research object. The effects of the HHR2 process on the microstructures and mechanical properties of the final hot-rolled pates were systematically studied to evaluate the effectiveness of the process. Accordingly, the work pieces fabricated with and without the HHR2 process were reheated to 1250 °C, following which they were subjected to hot rolling, then plates with both similar thickness of 40 mm were obtained. Subsequently, the microstructures and mechanical properties of the plates manufactured using two different processes were compared. The experimental results showed that both the microstructure homogeneity and the uniformity of mechanical properties along the thickness of the plate manufactured using the HHR2 process were obviously improved. In addition, the microstructure-inheritance mechanisms of the HHR2 process at three different process stages: continuous casting, reheating, and multi-pass hot rolling, are discussed.

Effects of Vertical and Pinch Rolling on Residual Stress Distributions in Wire and Arc Additively Manufactured Components

Residual stresses are inherent in parts manufactured using the wire + arc additive manufacturing (WAAM) technique, resulting in unpredictable mechanical response and structural integrity (Colegrove et al.: J Mater Process Technol 213:1782-1791, 2013). An effective post-processing technique, which enhances the mechanical properties of WAAM parts, is rolling. This study investigates the vertical and pinch rolling effects on residual stress distribution in WAAM components. Initially, a WAAM model was created using a thermo-mechanical finite element modelling approach and validated against the experimental results. Subsequent to the validation of the model, the effect of the main parameters involved in vertical and pinch rolling processes, namely the rolling depth, the curvature depth of the roller, the roller shape, transversal displacement, rolling direction and roller thickness, was investigated. The results from this study show that the residual stress profile in the vertical rolling process applied on a WAAM wall can be enhanced by increasing the rolling depth and curvature depth of the roller. Moreover, it is shown that in the pinch rolling process, the residual stress profile is sensitive to the rolling direction and more compressive residual stresses can be induced into the wall by applying fewer passes of rolling using thicker rollers.

Influence of cathodic polarity during electrocleaning process on the brown stain defect formation after skin pass on cold‐rolled close annealed steel

AbstractSkin pass rolling is considered as the final forming stage in cold‐rolled close annealed steel. Surface properties and flatness are the key attributes for automotive customers. Efficient skin pass rolling overcomes surface defects that lead to material rejection. This study portrays a brown stain defect with higher defect severity. The brown stain defect is observed in a few coils that are processed through alkaline electrocleaning (ECL). Coils bypassing ECL do not show such defect. Defect characterization through scanning electron microscopy, Fourier transform infrared spectroscopy, and Raman spectroscopy shows initiation of oxidation of steel substrate. The presence of skin pass fluid residues in the defected area is the root cause for the stain formation. Techniques such as glow discharge optical emission spectroscopy, Kelvin probe, Raman spectroscopy, and electrochemical tests emphasize the role of final electrode polarity in ECL with the nature of passive oxide film formed when skin pass fluid is applied on the steel surface. This study reveals that skin pass fluid applied on anodically cleaned coils provides a uniform passive surface that restricts the defect formation.

Applied temperature analysis for designing technology of composite materials: parameter determination of aluminium alloys rolling

The solution of the problems for designing new materials by methods of applied temperature analysis of ATA provides the conversion of experimental data to a digitized form. Their application in the development of mass compositions of a new series of products with an aluminosilicate matrix, dispersion-hardened composites and conglomerates, in all cases it turned out to be useful and effective, the optimization of composition and structure was greatly simplified. In the presented work, ATA is used to determine the parameters of rolling sheet blanks of layered composites to a thickness providing the necessary strength of work in the composition. The correspondence to the principle of periodicity of temperature analysis - T m A of the number of passes of rolling the alloy of the {Al – Mg – Li} system, changes in sheet thickness, strain resistance and microhardness is established. A linear correlation of the parameters of the deformation process with a decrease in elasticity due to local contact integration of volume particles characteristic of Li compounds with respect to temperature is noted. Structural transformations by T m A microhardness are precisely limited by stationary temperatures of 171°C and 514°C mesh isothermal discrete scanning IDS. The obtained T m A diagrams were used to determine the parameters of the technology for overcoming the known limit of plastic deformation. It is experimentally proved that the optimum deformation range belongs to this temperature range by characteristic bends of the lines in the microhardness-temperature diagram at various penetration rates and hardening times.

Technical Feasibility Assessment for Roll Pass Designs in Three-High Shape-Mill Stands in Modern Mini-Mills

Construction and commissioning of a network of mini-mills of various maximum production volumes requires installation of equipment. Several plants have developed mills in which continuous-reduction stands have been replaced by three-high stands. Despite prior experience in using continuous-cast billets for production of a variety of rolled shapes in modern continuous mills, use of this approach in shape mills with three-high reduction stands requires an technical feasibility assessment of the new forming modes and pass designs used for these modes. Comparative analysis indicated that the newly developed billet forming modes and pass designs did not fully achieve the requisite technical feasibility. The stress-strain behavior in the early passes facilitates not only formation of end cracks, but also increases the likelihood of discontinuity defects in the metal over the entire free surface of the billet not in contact with the bottom or corners of the pass due to development of tensile stresses. Absence of reduction in the initial box passes during rolling of continuous-cast billets therefore will lead to rhombicity defects. Using excessively high reductions in individual passes makes clamping of the process cross section less stable, increases the likelihood of overfilling the pass, and increases the peak rolling load in certain passes Collectively this suggests that these process characteristics indicate that a better-validated approach is needed for determination of continuous-cast billet rolling schedules for three-high reduction stands.

Microstructure and mechanical properties of caliber rolled Mg–Y–Zn alloys

The microstructural evolution and mechanical properties were investigated using a caliber rolled Mg–5Y-2.5Zn (in at.%) alloy. Deformation kink bands could be induced by the caliber rolling process, which is the same as that of conventional wrought processed (extruded or rolled) Mg–Y–Zn alloys. The number of rolling passes was an influential factor for the microstructure, i.e., the bending angle of the long periodic stacking ordered (LPSO) phase associated with deformation kink bands. The mechanical properties of strength and hardness also depended on the number of rolling passes. These properties were improved with increased number of rolling passes (up to 6 passes). The yield strength and hardness before the rolling process were 260 MPa and ~90 Hv. On the other hands, after caliber rolling, these properties showed over 500 MPa and 129 Hv, respectively, for the alloy with 6 rolling passes. Microstructural observations revealed that such good properties resulted from the existence of deformation kink bands and dense dislocations induced by caliber rolling. Controlling the morphology of the LPSO phase associated with deformation kink bands was found to be an effective strategy; the bending angle of this phase of more than 20° is outstanding for further improving the mechanical properties.

Experimental and numerical investigation of cold roll forming process

This research work is focused on the cold roll forming process to produce U-channel from the flat sheet. The mechanical properties of aluminum alloy was obtained from the tensile test and subsequently, the properties were incorporated into LS-DYNA to define the material plastic region. The forming process involves the progressive sheet deformation by passing it through a roll pass at constant roll speed. Each sets are designed at different bending angle to increase the deformation until the final geometry is achieved and here, the forming machine with four roll stands were used to manufacture the parts. As a sheet is going into different passes at the same time, the sheet plastic deformation is so complex and highly non-linear because of various stress and strain developments. From experimental results, at low roll speed (RS) the longitudinal bow was observed in the formed parts and to investigate, numerical simulation was modeled at various roll speed and found that as roll speed increasing the longitudinal bow noticed to be decreasing. To confirm the finite element results, one more experiment at high speed was performed and the obtained results showed better agreement with the simulation results. Before confirming the accuracy, many issues were encountered and modified such as mesh size at roller and blank, contact mechanism, choosing element formulation and friction coefficient. Furthermore, the adaptive meshing procedure was adopted to efficiently remesh the sheet at contact locations. The research procedures presented can be utilized to perform the forming process for any existed or new material to form a desired shape for a specific applications in the automobile and aerospace industries.

Control of texture and earing in aluminium alloy AA 8011A-H14 closure stock

The development of crystallographic texture during the thermo-mechanical processing of aluminium sheet results in the formation of pronounced plastic anisotropy, including the well-known earing phenomenon. In the present study we track the evolution of texture, microstructure and the resulting earing profiles in Al alloy AA 8011A during down-stream processing to final-gauge sheet in temper H14. This processing, which includes two interannealings, followed by a mild final temper rolling pass, was designed for providing minimum earing for earing-critical packaging applications. Besides the experimental characterization of microstructure, texture and earing along the standard process chain, means to optimize the earing behaviour are addressed. This includes changes in the homogenization practice, possible omission of one of the two interannealings and variation of the interannealing gauge. The resulting earing properties are discussed in the light of the interplay of deformation and recrystallization with the resultant texture changes along the process chain.

Optimal control of plate motion and camber in a reversing rolling mill

In plate rolling, reversing roughing mills are commonly used as a first processing step after casting. They are typically equipped with edger rolls for width reduction. During a rolling pass, lateral asymmetries like temperature gradients or thickness inhomogeneities can cause two major problems. The plate may rotate in the rolling gap and thus move in lateral direction. Another problem is that the plate may leave the mill stand with a cambered shape. In the worst case, these problems entail collisions with the mill stand or other equipment along the roller table. It is an essential control task to avoid such problems. In general, the exit thickness profile and the motion of the plate are controlled by adjusting the roll gap height. The latter has also an influence on the contour shape but, for active control of the plate width and contour shape, the use of edger rolls is more common. This is especially true if the roll gap adjustment is self-retaining, meaning that it cannot be adjusted during a rolling pass. In this work, such a roughing mill and its edger rolls are considered. A mathematical model for the motion and the camber of the plate is derived. Based on this model, a linear quadratic regulator (LQR) for both the plate motion and the resulting camber is developed. It uses the lateral forces of the edgers as control inputs. In a cascaded control structure, these forces are regulated by a subordinate admittance controller. The developed control system is validated in simulation studies.

Prediction for Manufacturing Factors in a Steel Plate Rolling Smart Factory Using Data Clustering-Based Machine Learning

A Steel Plate Rolling Mill (SPM) is a milling machine that uses rollers to press hot slab inputs to produce ferrous or non-ferrous metal plates. To produce high-quality steel plates, it is important to precisely detect and sense values of manufacturing factors including plate thickness and roll force in each rolling pass. For example, the estimation or prediction of the in-process thickness is utilized to select the control values (e.g., roll gap) in the next pass of rolling. However, adverse manufacturing conditions can interfere with accurate detection for such manufacturing factors. Although the state-of-the-art gamma-ray camera can be used for measuring the thickness, the outputs from it are influenced by adverse manufacturing conditions such as the high temperature of plates, followed by the evaporation of lubricant water. Thus, it is inevitable that there is noise in the thickness estimation. Furthermore, installing such thickness measurements for each passing step is costly. The precision of the thickness estimation, therefore, significantly affects the cost and quality of the final product. In this paper, we present machine learning (ML) technologies and models that can be used to predict the in-process thickness in the SPM operation, so that the measurement cost for the in-process thickness can be significantly reduced and high-quality steel plate production can be possible. To do so, we investigate most-known technologies in this application. In particular, Data Clustering based Machine Learning (DC-ML), combining clustering algorithms and supervised learning algorithms, is introduced. To evaluate DC-ML, two experiments are conducted and show that DC-ML is well suited to the prediction problems in the SPM operation. In addition, the source code of DC-ML is provided for the future study of machine learning researchers.

Roll Pass design, numerical model and processing procedure of a 3rd generation dual phase sheet steel

A dual phase steel have been developed, where it contains 0.13% carbon in addition to different Si & Cr contents.Allotropic and polymorphic transformation temperatures of investigated steel were calculated by using JMatPro7 software. The designed rolling passes considered the phase transformation temperatures.Two stages hot flat deformation were used for thickness reduction. 1st stage was carried out by forging for a thickness reduction from 36 to 8 mm. 2nd stage was finish hot flat rolling to reduce the thickness from 8.0 to 3.0 mm through 5-consecutive passes.A numerical model was constructed and built based on the Z- parameter calculations for expecting of the austenite grain size. The numerical model was verified by using the data of the designed rolling passes. The model expect austenite grain size is 0.24 micron after the last pass.After finish hot rolling, the strips were then subjected to austentizing at 900oC and holding for 30 min., followed by a double quenching process. First quenching is done in a salt bath at 450oC for 7, 14 and 21 min. Finally the strips were then water quenched to the room temperature. It was found that created martensite colonies are executing with the bainite aggregates in a ferrite matrix.Tensile testing possesses continuous yielding phenomena even at the hot- rolled strips as a result of martensite creation, while elongation decreases. Ductility still reasonable for sheet metal forming in the range of 12-16%. The optimum time of salt bath treatment was concluded as 7 min.

Design of Caliber Rolls Incorporating Load Path Dependent Damage Evolution

Caliber rolling is an important forming process to produce semi-finished parts. In caliber rolling, the process route can be varied with respect to the caliber geometry at intermediate passes without changing the initial and end geometry. Usually these intermediate passes are optimized with regard to the filling degree, which depends on the axis ratio of the oval caliber and on the area reduction in each pass. In order to improve the service life of products, this paper considers the damage evolution additionally. For a roll-sequence round-oval-round two rolling routes are found with adequate filling degree in each roll pass. The variation of the process route leads to a significantly different loading path, which is defined as the strain-dependent development of stress triaxiality and Lode parameter. In this study, the influence of the loading path variation on the damage evolution is investigated. Meanwhile, damage criteria, e.g. Oyane criterion, are applied to predict the progressive damage level. The results indicate a remarkable difference in damage at the end of the process due to the loading path variation and higher damage always occurs near the symmetric axis of the workpiece according to FE simulations.

Effect of Rolling Processing on Mechanical Properties of Material Cr12

The rolling process changes the mechanical properties of the specimen’s surface material, and it also directly affect the fatigue strength and service life of the workpiece. The effects of rolling parameters on surface residual stress, microhardness, surface roughness and surface microstructure are studied by rolling test of Cr12 specimens. After rolling, the residual stress on the surface of Cr12 specimens changes from tensile stress to compressive stress, and the maximum compressive stress is -216MPa. With the increase of contact stress and rolling passes, the residual compressive stress increases at first and then remains stable. Rolling processing can effectively improve the surface hardness of specimens up to 30%, and the surface roughness can be reduced by 25%-67%. The fine grains aligned with the rolling direction, and the 50-60 μm grain refinement layers were observed, which resulted in the changes in the surface mechanical properties of the specimens.

FEM simulation of fabrication of Al-steel layered composites with mechanical bonding through the interfacial concavo-convex lock effect

Development of advanced cold pressure welding technique is needed for fabrication of Al-Steel layered composites with improved bonding strength between the stacked layers. Obtaining of elevated strain at the interface of the composite in combination with mechanical bonding through the interfacial concavo-convex lock effect can provide superior bonding strength. This paper presents the results of the finite element simulation of a special cold roll bonding technique. This technique consisted of two rolling passes. During the first pass the cold roll bonding was performed by work rolls with microscopic sine profile of the surface. During the second pass the cold roll bonding was performed by smooth work rolls. As a result, the Al-Steel layered composite with wavy interface was developed. Simulations of the process of fabrication of composites, consisted of aluminium alloy 6082 and DC04 steel were carried out using the commercial FEM code QForm. Effect of the sine profile of work roll on the composite layers behavior was analyzed. It was numerically shown that special cold roll bonding technique is able to introduce an additional mechanical clinching and elevated plastic strain to the interface of the composite in comparison with conventional roll bonding process. The FEM results of investigation of interface bond behavior can be useful for the development of the improved cold pressure welding technique for manufacturing of Al/Steel composites with high bond strength.

Influence of snake rolling on metal flow in hot rolling of aluminum alloy thick plate

Most asymmetrical rolling conditions should not appear in regular rolling processes, but for obtaining large deformations inside aluminium alloy thick plates, the asymmetrical rolling process is the most effective method. Snake rolling is adopted for promoting more deformation inside the plates. For exploring the deformation inside an aluminium alloy thick plate, a finite element model for simulating the process of snake rolling is established and the key influence factors are set as initial thickness, speed ratio and offset distance. The results show that deformation inside of the plate increases obviously while the thickness of plate is less than 300 mm after snake rolling. The speed ratio has a positive effect on promoting deformation partly inside of the plate. On the contrary, the offset distance has a negative influence by affecting the exit thickness. A formula for calculating the exit thickness after snake rolling is proposed and validated by data from the finite element models. Thus, snake rolling is suggested to be used in the downstream pass of hot rough rolling considering that the influence of thickness and the offset distance should be controlled in a reasonable range.

Effects of rolling-pass reduction on microstructural evolution and mechanical properties of SUS316LN stainless steel

Effects of rolling-pass reduction on microstructural evolution and mechanical properties of a SUS316LN austenitic stainless steel sheet were investigated. Pass reductions of 3%, 10% and 20% were employed and samples were cold rolled up to 92% reduction using a compact double-rolling mill. After rolling, mechanical properties were investigated by hardness and tensile tests, and microstructure was observed using SEM-BSE and TEM.Although some pass reductions were applied for cold rolling, the difference in reduction evidently appeared only just at the beginning of rolling process. During rolling, actual pass reduction achieved was rapidly reduced because of heavy work hardening. While the 92%-rolled samples exhibited quite high hardness, difference in the final hardness was not so distinct irrespective of the rolling pass reduction. The cold-rolled samples were followed by aging at 773 K. Clear peaks at around 5×103 s appeared and maximum hardness of about 5.0 GPa was achieved. Tensile property exhibited a large anisotropy and tensile strength along transverse direction was higher than that along rolling direction. The as-rolled sample possessed a good balance of tensile strength of 1.7 GPa, and ductility of 10%. Tensile strength gradually increased by the aging and maximum value around 2.0 GPa irrespective of rolling conditions was achieved. Even while high tensile strength was attained, plastic strain to failure was rather good and around 5%.When investigated the microstructure, a typical heterogeneous-nano structure, in which all the component structures were of deformation-induced ones as mechanical twins, shear bands and “eye-shaped” twin domains as well as low-angle lamellae, was observed in all the samples.

Hot workability of 420 J1 martensitic stainless steel

Steel grade 420 J1 is martensitic colonies embedded with ferritic phase stainless steel. The steel under investigation contains mainly 12.42 % chromium and 0.2% carbon.Hot workability of the 420 J1 steel grade became the most critical issue to suit the different application requirements. The present article is dealing with the parameters controlling successful hot workability of the steel grade 420 J1.4-conscutive hot rolling passes were designed for a thickness reduction from 7 to 3 mm. Hot deformation passes were designed to score two parallel goals. The first goal is to avoid instability regions, while the second one is to create dynamic softening.It was found that austenite is subjected to grain refinement to reach about 17 micron.The flow stress is calculated. Dynamic recovery is clearly noticed at the last two deformation passes. Microstructural investigation as well as mechanical properties for final hot rolled steel strips was executed.

Average austenite grain size evolution simulation during multi-pass shape metal hot rolling process

Constitutive equations describing the flow stress of Q235 steel undergoing hot plastic deformation have been developed by integrating the microstructure models and exponential flow stress models presented in literatures, in which the microstructure models parameters have been re-determined based on the related experiments carried out on cylindrical specimens of the Q235 steel. Therefore, the integrated constitutive equations are capable of calculating the evolution of austenite grain size and investigating the effects of average austenite grain size on the flow stress of Q235 steel during hot deformation. A three-dimensional thermo-mechanically coupled FEM simulation of an 11-pass H-shape metal roughing rolling process with the austenite grain size evolution taken into account have been carried out to verify the rationality of roll pass schedule. The accuracy of the integrated constitutive equations has been preliminary validated by the comparisons between measured and the calculated values of rolling force.

Dynamic recrystallization control in hot rolling

Recrystallization is important for steel processing because it modifies microstructure along the process route and thus determines the final properties of steel products. Loads in various deformation operations and consistency of dimensions and shape of deformed steels are also influenced by recrystallization and its homogeneity. These factors are especially important in hot rolling that aims at uniform refined hot rolled microstructure. This can be achieved by avoiding dynamic recrystallization (DRX) of austenite during hot rolling passes and static recrystallization between them and before cooling. Alternatively, microstructure can be refined by stimulating recrystallization. Experimental data and constitutive analysis show that for a given steel there exist two limiting values of Zener-Hollomon parameter Z that delineate three temperature – strain ranges for DRX: no-DRX range (high Z) where DRX cannot be initiated irrespective of the applied strain, full DRX range (low Z) and partial DRX range (intermediate Z). Avoiding DRX in finishing rolling sequence implies setting up rolling speeds and temperatures in no-DRX range of Z. Alternatively, for roughing sequence the mill settings should be such as to keep rolling speeds and temperatures in the full DRX range. In any case it is imperative to avoid partial DRX, i.e., to avoid rolling speeds and temperatures that correspond to intermediate Z range. This approach can be directly utilized to control DRX in hot strip mills and plate mills based on the experimental data.