Cold-rolled Sheet Research Articles

Wrinkling Defect in Sheet Metal Process using Finite Element Analysis

Abstract: Deep drawing is popular sheet metal forming process. Deep drawing process is the most common metal forming process frequently used in automobile industry, the packaging industry and the house hold appliances industry to manufacture products with more complicated shapes and curvatures. Any metal that can be processed into sheet form by a rolling process should be sufficiently ductile to be capable of deep drawing. Both hot and cold rolled sheet products are used in deep drawing processes. The basic theories governing the deep drawing are based on application of theory of plasticity to the deep drawing process. It is very difficult to apply these theories and arrive at a general solution which can handle any arbitrary geometry. The idea of finite element analysis is to find the solution of complicated problem in relatively easy way. The finite element analysis has been a powerful tool for the numerical solution of a wide range of engineering problem. There are some possible failures likely occur during the process, like wrinkling, necking, scratching and surface defects. As thinner materials tend to be used in automotive industry, wrinkling has become the most important problem among the other defects. The study also aims to investigate wrinkling and its prevention. For this purpose, the commercial finite element analysis code Explicit Dynamic FEM model will be used

Influence of the Laser Deposited 316L Single Layers on Corrosion in Physiological Media

A multilayer laser-deposited lining of AISI 316L stainless steel makes a regular structural steel surface corrosion resistant in physiological media. Despite the application of single-layer stainless-steel linings being economically beneficial and allowing thinner surface modifications, dilution effects that modify the pitting resistance of the coating must be accounted for. In order to study the feasibility of employing single-layer coatings instead of multilayer coatings for corrosion protection in physiological media, a polarization testing back-to-back comparison was performed between laser-deposited AISI 316L monolayers on 42CrMo4 quenched and tempered steel and cold-rolled AISI 316L sheet in Dulbecco’s Phosphate Buffer Solution at 36 °C. A higher dispersion in pitting resistance, ranging from 800 mV to 1200 mV, was found on the coated samples, whereas the cold-rolled material was more stable in the 1200 mV range. The resulting differences in corrosion rates and pitting potentials open the discussion on whether the chemical composition deviations on AISI 316L dilution layers are acceptable in terms of surface functionality in medical devices.

New shapemeter roll technology based on Fiber Bragg Grating technology for on-line flatness monitoring of thin cold rolled metal sheets

The shape of laminated products is a crucial parameter in high-speed and high-volume finishing lines where they must fulfill tight tolerances. Latent defects are detected by flatness rolls (or shapemeter rolls) inserted in the manufacturing line for online flatness control. A prototype of flatness roll has been developed with high spatial resolution (5 mm) and measurement capability over a thickness range of 0.1–1 mm to evaluate flatness and residual stresses of flat metal strip products manufactured by continuous cold rolling (ultra-thin sheets for packaging and automotive markets). The flatness roll prototype relies on pressure-induced strain sensing on segmented blades using Fiber Bragg Grating technology. Synchronous measurement of the flatness profile across strip width rejects disturbances of strip tension during rolling. We provide a proof-of-concept on pilot lines in both static and dynamic conditions (e.g., roll in rotation and in contact with a strip under tension) and the sensing mechanism shows a capability above 3. This combination of performances remains unique up to now. Interblade crosstalk appears to be an important issue. We propose a crosstalk model that agrees with experimental coupling coefficients. A crosstalk matrix inversion yields the distribution in contact pressure from strain data measured on the reverse side. Additional work will be required to use the flatness roll in industrial conditions.

Nonlinear biaxial tensile stress path experiment without intermediate elastic unloading for validation of material model

A linear stress path (LSP) experiment was performed using uniaxial and biaxial tensile tests with a cold-rolled mild steel sheet (SPCD; nominal thickness: 0.8 mm) as the test material. In the LSP experiment, the contours of plastic work and the directions of the plastic strain rates, β, for a plastic strain range of 0.002 ≤ ε0p≤0.234 were measured. Then, the Yld2000-2d yield function was used to identify a material model that accurately reproduces the experimental data. Stepped nonlinear stress path (NLSP) experiments were also performed; the NLSPs consisted of several linear stress paths without intermediate elastic unloading. The measured work hardening behavior and β values were compared with those calculated using the yield functions identified from the LSP experiment, namely the von Mises, Hill’s quadratic, and Yld2000-2d yield functions. For the Yld200-2d yield function, both isotropic and differential hardening models were investigated. It was found that the data measured in the NLSP experiment are consistent with calculation results obtained using the Yld2000-2d yield function identified from the LSP experiment. Thus, it can be concluded that within the range of stress paths adopted in the NLSP experiment, the deformation behavior of a test sample can be accurately predicted using the material model identified from an LSP experiment.

Effect of test temperature on tensile behavior of Fe-6.5wt.%Si alloy as-cast strip

The non-oriented Fe-6.5wt.%Si alloy as-cast strip is prepared by the top side-pouring twin-roll casting (TSTRC) process and the solidification structure of the as-cast strip is a uniform fine equiaxed grain structure. This paper studied the mechanical properties, fracture morphology, ordered phase morphology, and types of Fe-6.5wt.%Si alloy as-cast strips at different temperatures. The results show that the yield and tensile strength of the as-cast strip decreased gradually with the increase of tensile temperature, and the elongation after fracture increased gradually. The temperature rise prevented the formation of cleavage cracks, and the temperature rise is an effective method to improve the plasticity of Fe-6.5wt.%Si alloys. Concurrently, the ambient temperature is the main factor determining the tensile mechanical properties of Fe-6.5wt.%Si alloy at medium temperature. When the stretching temperature exceeds 500 °C, the Fe-6.5wt.%Si alloy has apparent plastic deformation ability. The Fe-6.5wt.%Si alloy exhibits excellent elongation when the stretching temperature is 700 °C. The serration fluctuations that appear on the 400 °C stretch curve should be attributed to the Portevin-Le Chatelier (PLC) effect caused by the reordering of the antiphase domains and the deformation-induced disorder. The Fe-6.5wt.%Si alloy as-cast strip is directly subjected to warm-rolling without the hot-rolling. When the warm-rolling is performed at the temperature of 700 °C, there are almost no cracks at the edge of the plate, the edge cracks are effectively controlled, and the surface quality of the warm-rolled sheet is fine. The obtained 700 °C warm-rolled sheets were cold-rolled at room temperature, and after recrystallization annealing, the sample had good comprehensive magnetic properties. Suppose the TSTRC-warm rolling-cold rolling-annealing process prepares the Fe-6.5wt.%Si alloy cold-rolled sheet. In that case, the production efficiency will be significantly improved, the process flow will be shortened, and the goal of energy-saving and emission reduction will be achieved.

STRUCTURE AND PROPERTIES OF THIN SHEET STEEL 08ПС AFTER SKIN-ROLLING

The requirements of standards for quality indicators of rolled products are increasing. Relevant is the saving of operating costs in the manufacture of a thin sheet. Skin rolling is one of the key operations in the technological process of production of hot-rolled sheets for cold stamping. In order to improve the quality of thin-sheet rolled products, it is important to develop an effective skin rolling technology. In this work, the structure and properties of hot-rolled thin-sheet low-carbon steel 08пс after skin pass at a separately located mill are studied. It is shown that as a result of processing, the plasticity of the metal increases and a uniform structure is formed over the sheet section. It has been established that hot-rolled sheet metal in terms of quality meets the requirements for cold-rolled products in accordance with ДСТУ 2834-94. It is possible to replace an expensive cold-rolled sheet with a cheaper, but of the same quality, hot-rolled sheet. As a result, an increase in labor productivity, a decrease in the metal consumption coefficient, and savings in electricity and natural gas are achieved.

Effect of Prior Cold Reduction of C–Si–Mn Hot-Rolled Sheet on Microstructures and Mechanical Properties after Quenching and Partitioning Treatment

This paper studies the microstructures and mechanical properties of quenching and partitioning (Q&P) samples prepared with 35% and 75% cold reduction sheets at an annealing temperature of 810 °C (intercritical temperature). The results indicate that prior cold reduction could significantly influence the ferrite recovery and recrystallization during intercritical annealing, which changes the size and distribution of the ferrite and retained austenite in the Q&P samples. Compared with the 75%—Q&P sample, the 35%—Q&P sample had smaller recrystallized ferrite and retained austenite grains, a higher volume fraction of retained austenite, and a more uneven size distribution of retained austenite. The 35%—Q&P sample presented better total elongation and a higher product of strength and elongation (PSE) than the 75%—Q&P sample. The higher total elongation was related to the higher content and uneven size distribution of retained austenite for they strengthened the TRIP effect and improved the uniform elongation of the sample. The results proved that Q&P steel prepared with a cold-rolled sheet with lower reduction exhibits a better combination of strength and plasticity due to the fact that lower reduction can delay the growth rate of austenite and recrystallized ferrite grains during the intercritical annealing stage.

Sheared edge formability characterization of cold-rolled advanced high strength steels for automotive applications

Edge cracking has become a limiting factor in the use of some advanced high strength steels (AHSS) for high-performance automotive applications. This fact has motivated the development of a multitude of experimental tests for edge formability prediction over the last years. In this sense, the Hole Expansion Test (HET) according to ISO16630 has been established in the automotive industry as a standard procedure for edge cracking sensitivity ranking. However, whereas it may be useful for rapid material screening, the results are often not accurate and reliable enough. Consequently, alternative methods based on Digital Image Correlation (DIC) have been proposed aimed at improving the prediction of edge cracking occurrence during forming and obtaining useful strain data that can be implemented in forming simulations. This paper explores the applicability of different DIC-based methods, such as Half-Specimen Dome Tests, Sheared Edge Tensile Tests, and KWI hole expansion tests with a flat nosed punch, for characterizing the edge formability of three cold-rolled AHSS sheets. The results obtained from the different testing methods are compared and validated with a laboratory-scale demonstrator. Finally, the limitations and advantages of the different methods are discussed.

Influence of work-roll grinding error and high-fidelity corrective grinding in cold sheet rolling

High-fidelity flatness defects in cold-rolled strip and sheet, arising from highly localized thickness strain variations, present an ongoing challenge to the metal industry. A primary cause of such defects, based on rolling practice, but for which the effects have not been rigorously investigated, is the transfer of localized work-roll diameter deviations due to roll grinding error. This study addresses high-fidelity work-roll diameter deviation transfer in the cold rolling of stainless steel, aluminum, and copper. Parametric studies are performed on a 4-high mill to examine the influences of roll diameter, reduction, strip width, and material on the transfer of high-fidelity work roll diameter deviations. Studies are conducted using an efficient 3D roll-stack model that predicts strip thickness profile deviations via the simplified-mixed finite element method. Reduction deviations on the outgoing strip, which correlate to strip flatness/shape defects, are quantified and analyzed to understand the transfer characteristics of work-roll grinding deviations relative to perfectly ground (smooth) work rolls. The results reveal that high-fidelity transfer depends not only on roll grinding deviation amplitudes and mill loading, but also on the specific locations of deviations along the roll face length due to 3D bulk roll-stack deformations as well as effective stiffness ratio between the work roll and the strip. Concluding the study is a novel approach to identify customized work roll grinding profiles tailored specifically to eliminate pre-existing high-fidelity strip flatness defect patterns, wherein “corrective” high-fidelity roll diameter profiles account for the predicted 3D mill deflections, contact force distributions, and coupled micro-/macro-scale deformation mechanics.

Microscale thermal characteristics of cold-rolled aluminum alloy using a thermoreflectance method

In this study, the microscale thermal propagation behavior of cold-rolled aluminum alloy sheets was characterized using a thermoreflectance (TR) method from the micro and macro perspectives, and the relationship between the crystallite sizes of cold-rolled aluminum sheets with different rolling reduction rates and their thermal propagation characteristics were described. The crystallite sizes were analyzed by X-ray diffraction using Scherrer’s equation. The microscale thermal propagation characteristics of these specimens were measured using a TR method with a high spatial resolution of several micrometers through a focused laser beam and by controlling the thermal diffusion length. The macroscale thermal propagation characteristics of these specimens were then measured using two methods: the spot periodic heating method and the electrical resistance measurement method with the Wiedemann–Franz law. Experimental results showed that the microscale thermal propagation correlated with a change in the crystallite size. However, the macroscale thermal conductivity decreased with an increase in the rolling reduction rate regardless of the crystallite size. It is expected that the thermal propagation characteristics at the microscale can be controlled by a change in the crystallite size.

Effect of Nanosized Precipitates on Corrosion Resistance of Nb-Microalloyed Steels

High-strength cold-rolled low-carbon microalloyed steels are widely used in the automotive industry. Preference is generally given to microalloying with niobium, since its effect on the mechanical properties of steel is most pronounced due to both precipitation hardening and a reduction in the ferrite grain size. For the operation of a car, the corrosion resistance of metal parts is an important factor, since, along with other properties of the material, it determines its service life. The study of the effect of the structural state of cold-rolled sheet low-carbon Nb-microalloyed steels, processed in continuous annealing units, on their corrosion resistance has been carried out. Methods of optical, scanning and transmission electron microscopy, mechanical and corrosion tests were used. It is shown that one of the main structural factors that determine the corrosion resistance of rolled products is the size of nanosized NbC precipitates. The influence of the temperature parameters of hot rolling and annealing on their formation has been established. An increase in the temperatures of the hot rolling end and coiling, as well as annealing, leads to an increase in their average size in the rolled stock after annealing, which increases the corrosion resistance of the steels under consideration.

<i>In-Situ</i> Observation of Initial Stage Cosmetic Corrosion Behavior under Wet and Dry Conditions

It is well known that the types of automotive corrosion can be divided into perforation corrosion and cosmetic corrosion. Although the mechanism of perforation corrosion has been studied extensively, the mechanism of cosmetic corrosion has not yet been clarified. The authors investigated the cosmetic corrosion behavior of cold-rolled steel sheets without galvanizing with an in-situ observation device. After coating the samples by cathodic electrodeposition (ED), the sample surface was scribed with a cutter. Corrosion resistance was evaluated under cyclic corrosion test. It was found that the progress of under-film corrosion consisted of 3 steps. The 1st step occurs in the initial stage of the dry process in the 1st cycle. In this step, red rust gradually changed to black rust. The 2nd step occurs in the latter stage of the dry process, and under-film corrosion progressed from the scribed part. The 3rd step occurs in the wet process, and in this step, the tip of the under-film corrosion displayed swelling behavior. In the 2nd cycle, the 2nd step and 3rd step of the 1st cycle were repeated. Under-film corrosion progressed at almost the same rate as in the 1st cycle.

Effect of Copper Concentration and Annealing Temperature on the Structure and Mechanical Properties of Ingots and Cold-Rolled Sheets of Al–2% Mn Alloy

Effect of Copper Concentration and Annealing Temperature on the Structure and Mechanical Properties of Ingots and Cold-Rolled Sheets of Al–2% Mn Alloy

Microstructure, Texture, and Hardness Evolution of Cold-Rolled High-Purity Ti Sheet During Annealing at 350 °C to 550 °C

Microstructure, Texture, and Hardness Evolution of Cold-Rolled High-Purity Ti Sheet During Annealing at 350 °C to 550 °C

MICROSTRUCTURE, MECHANICAL PROPERTIES AND GEOMETRY OF A MODEL BATCH OF SEMI-SPHERICAL STEEL LINERS INTENDED FOR USE IN THE EXTRACTIVE INDUSTRY

The article presents the results of investigation of the microstructure and mechanical properties of Fe-based materials intended for the production of semi-spherical liners for experimental shaped charges. The tests were carried out on samples taken in three directions in relation to the rolling direction: 0°, 45° and 90°, of the following materials: cold-rolled sheets made of DC04 steel, hot-rolled sheets made of 04J steel, and cold-rolled strips made of 004G steel developed at Łukasiewicz – IMŻ and annealed at 650°C. Semi-spherical drawpieces with a diameter of 106.4 mm, intended for liners, were made of the sheets with the use of cold stamping. Tests of the microstructure and HV hardness of samples taken from the test batch were carried out on cross-sections along the pressing direction and the model batch – on sections transverse to the stamping direction The geometry of the model batch drawpieces was also measured. The ferrite grain size evaluation was performed according to the ASTM E112 standard using μgrain software with a grain size evaluation module using counting the number of intersections of grain boundaries with a circle.

Effects of the Al Content on the Evolution of Quadruple Basal Textures in Mg-xAl-1Zn-0.1Mn-0.1Ca-0.2Y Alloy Sheets Processed via Cold Rolling and Annealing

The effects of the Al content on the texture evolution of Mg-xAl-1Zn-0.1Ca-0.2Y alloy sheets fabricated via hot rolling, cold rolling, and subsequent annealing were systematically investigated. A lower Al content led to a higher number of free Ca solute atoms that contributed to co-segregation with Zn, delaying the recrystallization of the cold-rolled sheets during annealing and changing the basal pole figure shape of the annealed sheets. A quadruple basal texture, in which the positions of the four basal poles were developed at tilt angles of ±25° to the rolling direction (RD) and ±40° to the transverse direction (TD) from the normal direction, was obtained in the annealed Mg sheets. A smaller amount of Al caused an increase in the intensity of the main peaks along the TD but a decrease in the intensity along the RD. As a result, the texture of the annealed sheets gradually changed from RD-split to diamond and TD-split in the (0002) pole figure, as shown by the relative comparison of pole intensities in both directions. This texture change strongly affects the Schmid factor for the basal slip. For the alloys with an off-basal texture investigated in this study, as the maximum intensity of the basal poles increased, the average Schmid factor of the basal planes also increased, making the basal slip easier.

Effect of copper concentration and annealing temperature on the structure and mechanical properties of Al–2wt.%Mn ingots and cold rolled sheets

This study focuses on the development of new Al–Cu–Mn alloys with enhanced strength and heat resistance achieved without hightemperature exposure. Seven alloys were considered including ones containing permanent Mn content of 2 % and variable Cu content of 0– 4 %. It was found that ~ 2 % Mn is completely dissolved in the solid solution of aluminum, while copper in the cast structure is distributed between the solid solution of aluminum and Al 2 Cu eutectic phase inclusions. It was experimentally established that when the copper content is 2 and 3 %, the solid solution of aluminum contains approximately the same amount of copper – up to 1.5 %. The deformation plasticity of experimental alloys in the cold rolling mode with the reduction rate of 80 and 95 % was investigated. It was shown that no preliminary treatment is required for alloys containing up to 3 % Cu as they feature high rolling workability. Then, the effect of heat treatment in the annealing temperature range of 200–600 °C on the structural and phase parameters of the alloys was studied. Alloy hardening in the process of multistage annealing by means of hardness measurement was analyzed. The data obtained allowed us to determine the influence of copper and analyze the thermal stability of model alloys. Tensile tests of cold rolled sheets with a thickness of 0.5 mm with a reduction rate of 95 % of alloys containing 2 and 3 % copper showed high performance. Particularly, the alloy containing 3 % Cu has strength compatible with that of the 1201 alloy in the T6 state.

Microstructure, superelasticity and elastocaloric behavior of Ti-18Zr-11 Nb-3Sn strain glass alloys by thermomechanical treatment

To analyze the effect of thermomechanical treatment on the superelasticity, phase transition behavior and elastocaloric properties of Ti-18Zr-11 Nb-3Sn alloys, several cold-rolled sheets were annealed at temperatures between 923 K and 1173 K. With increasing annealing temperature, the precipitated Zr5Sn3 phase in the samples gradually dissolves until it completely disappears. All samples undergo strain glass behavior, and the ideal freezing temperature T0 gradually decreases from 371.3 K to 195.3 K with increasing annealing temperature. Moreover, the superelasticity and elastocaloric working window can be widened to 110 K by adjusting the annealing temperature. The elastocaloric properties of the sample were obtained with an adiabatic temperature change of 2.5 K.

Investigation of annealing on CR-2 grade steel using Taguchi and Taguchi based gray relational analysis

ABSTRACT Low-carbon steels are widely used in domestic appliances, the automobile industry and sheet metal work due to high drawability. Therefore, the cold-rolled sheet products are annealed to improve their ductility. In this paper, annealing parameters, namely, temperature, heating rate and soaking time, have been considered control factors for studying mechanical and microstructure behaviour of the drawing quality (DQ) grade steel. A Taguchi-based L18 orthogonal array is used to find the effect of parameters (temperature, heating rate and soaking time) on the mechanical properties and microstructure characteristics of the DQ grade steel. The optimal value of mechanical properties such as yield strength, ultimate strength and hardness was obtained at 650 °C (temperature), 120 °C/hr (heating rate) and 30 min. (soaking time), whereas the optimal value of elongation was obtained at 750 °C, 40 °C/hr and 60 min. The ANOVA technique is used to summarise the contribution of each variable. Temperature is the most significant parameter for the responses: yield strength, ultimate tensile strength, elongation and hardness with the contribution factor of 46.51%, 82.50%, 82.41% and 84.09% (respectively). Taguchi Grey Relational Analysis (TGRA) was applied to evaluate analytical data results in the highest value of GRG 0.733.

Microscale thermal characteristics of cold-rolled aluminum alloy using a thermoreflectance method

Abstract In this study, the microscale thermal propagation behavior of cold-rolled aluminum alloy sheets was characterized using a thermoreflectance (TR) method from the micro and macro perspectives, and the relationship between the crystallite sizes of cold-rolled aluminum sheets with different rolling reduction rates and their thermal propagation characteristics was described. The crystallite sizes were analyzed by X-ray diffraction using Scherrer’s equation. The microscale thermal propagation characteristics of these specimens were measured using a TR method with a high spatial resolution of several micrometers through a focused laser beam and by controlling the thermal diffusion length. The macroscale thermal propagation characteristics of these specimens were then measured using two methods: the spot periodic heating method and the electrical resistance measurement method with the Wiedemann–Franz law. Experimental results showed that the microscale thermal propagation correlated with a change in the crystallite size. However, the macroscale thermal conductivity decreased with an increase in the rolling reduction rate regardless of the crystallite size. It is expected that the thermal propagation characteristics at the microscale can be controlled by a change in the crystallite size.