Cold-rolled Sheet Research Articles

Enhancement of strength in laser-joined Al-TRIP and Si-TRIP steels: Microstructural insights and deformation analysis

This study highlights the strengthening mechanisms observed during the metal joining of high-strength grade steels (Al-TRIP and Si-TRIP) by providing a concise investigation of microstructural features, mechanical strength evaluation, and employing Finite Element Method (FEM) analysis to understand the deformation behaviour in the joint. The base metals (BMs), Al-TRIP and Si-TRIP are cold-rolled sheets with thicknesses of 0.9 mm and 1.3 mm, respectively. Al-TRIP contains 2.4 wt% Al, while Si-TRIP contains 1.5 wt% Si. The Al-/Si-TRIP joint was processed by laser welding at low energy input 24 J/mm. Electron backscattering diffraction and transmission electron microscopy extensively characterized the microstructural features in the fusion zone (FZ) and heat-affected zone (HAZ) to study strengthening mechanisms induced by welding. Uniaxial tensile tests examined joint mechanical strength, while microindentation hardness (HIT) measurements evaluated mechanical response in the weld zones. The FZ showed a fully martensitic structure, while the HAZs displayed refined grains. Ultrafine-grained structures with an average size of 1 μm were observed in the HAZs, resulting in higher HIT hardness values (∼6.7 GPa) compared to the FZ (∼6.3 GPa). Interestingly, the mechanical tensile properties of the joint were unaffected as failure occurred in the thinner Al-TRIP steel. Finite Element Method (FEM) analysis simulated the tensile testing, revealing localized plasticity in the thinner Al-TRIP and explaining the observed fracture.

The Influence of Adventitious Carbon Groups on the Wetting of Copper: A Study on the Effect of Microstructure on the Static Contact Angle.

Tuning of the wetting behavior of metallic surfaces by chemical and topographical modification has become popular in recent years. Still, there is a lack in the understanding of fundamental relations between intrinsic properties of the material and its resulting water contact angle. It is widely accepted in the literature that transitions from a hydrophilic to increasingly hydrophobic behavior upon exposure to ambient conditions happen due to the adsorption of adventitious hydrocarbons. In order to investigate the role of metallic bulk microstructure in the wetting behavior and its transition properties, we created three different grain sizes and deformation states on copper by preparation combined with heat treatment. We found that for freshly prepared surfaces, differences in the wetting behavior show a higher static contact angle for mechanically prepared surfaces with a fine-crystalline deformation layer compared to the electropolished cold-rolled copper sheet and the annealed defect-free coarse-grained surface. Already after five days of storage time, most of this difference vanishes, and all surfaces show a wetting behavior with a contact angle in the range of 97-100° after 30 days. Though long-term wetting behavior seems largely independent of microstructure, correlated XPS measurements showed an increased adsorption of organic contaminants of the mechanically polished surface. Preparation-induced near-surface defects seem to accelerate adsorption, while varying grain size and slight bulk deformation from rolling processes did not show significant effects. Complex relations between the amount of adsorbed carbon and the polarity of the adsorption film were found to depend on the sample age and influence the contact angle.

Structure Evolution and Mechanical Properties of Sheet Al–2Cu–1.5Mn–1Mg–1Zn (wt.%) Alloy Designed for Al20Cu2Mn3 Disperoids

This work was focused on studying the possibility of increasing the strength of non-heat-treatable sheet alloy Al2Cu1.5Mn (wt.%) by the joint addition of 1% Mg and 1% Zn. The effect of these elements on the structure and mechanical properties of the new sheet Al2Cu1.5Mn alloy designed for Al20Cu2Mn3 dispersoids has been studied by calculations and experimental methods. The obtained data on the phase composition, microstructure, and physical and mechanical properties of the new alloy for different processing routes (including hot rolling, cold rolling, and annealing) have been compared with those for the ternary Mg- and Zn-free alloy. It has been shown that the formation of nanosized Al20Cu2Mn3 dispersoids (~7 vol.%) provides for the preservation of the non-recrystallized grain structure after annealing at up to 400 °C (3 h), while Mg and Zn have a positive effect on the strength due to the formation of alloyed aluminum solid solution. As a result, cold-rolled sheets of the Al2Cu1.5Mn1Mg1Zn model alloy showed a substantially higher strength performance after annealing at 400 °C in comparison with the ternary reference alloy. In particular, the UTS is ~360 vs. ~300 MPa, and the YS is 280 vs. 230 MPa. For the example of the Al2Cu1.5Mn1Mg1Zn model alloy, it has been shown that the system is promising for designing new heat-resistant alloys as a sustainable alternative to the 2xxx alloys. The new alloy has an advantage over the commercial alloys (particularly, 2219, 2024, 2014), not only in manufacturability but also in thermal stability. The sheet production cycle for the model alloy is much shorter because the stages of homogenization, solution treatment, and water quenching are excluded.

Anisotropic plasticity and fracture modelling of cold rolled AA5754

The effect of the anisotropy, the loading rate and stress state on the ductile fracture of AA5754 cold-rolled sheets has been investigated. The plasticity has been analysed experimentally testing biaxial and uniaxial tensile specimens machined at several orientations with respect to the rolling direction and calibrating the Yld2000-3D yield criterion. The strain rate dependency of the material has been evaluated testing notched tension specimens at different loading rates. The resulting force–displacement curves, showing negative loading rate sensitivity, have been employed to identify the work hardening constants of a modified isotropic rate-dependent law through inverse modelling. Finite element simulations of the experiments on central hole, notched, shear and biaxial specimens conducted at several loading rates and orientations, monitored with three-dimensional digital image correlation, have been performed to obtain the Cauchy stress and equivalent plastic strain histories from the critical elements located where fracture is observed in such experiments. The anisotropic Hosford-Coulomb fracture initiation criterion has been modified to accommodate the loading rate effects giving reasonable failure predictions.

Mechanical properties of cryo-rolled aluminium alloy AA2219 at 300, 77 and 20 K

In the present work, AA2219-T87 plates (40 mm thickness) in two different pre-deformation conditions: without solution treatment (WST) and solution treatment (ST) are cryo rolled (at 77 K) into sheets (imparting reduction ratio of ∼97.2%) and rods (reduction ratios of 30, 50 and 70%). The mechanical performance and ageing kinetics of the cryo rolled sheets are compared with cold rolled sheets, to assess any beneficial effect. The as-rolled sheets and rods were subjected to duplex ageing at 175 °C/3 min + 125 °C/8 h, which reduces the effective ageing time by several hours compared to industrially practiced ageing time for peak aged tempers. The microstructures of the ST sheets and rods in as-rolled and peak aged conditions consist of very fine structure with high dislocation density in the form of tangles. Peak ageing treatment generated uniform distribution of semi-coherent θ′ precipitates with slight decrease in dislocation density due to partial recovery of the structure. Tensile properties are evaluated for the sheets and rods in as-rolled and peak aged conditions at ambient (300 K) and cryogenic (77 and 20 K) temperatures. Significant improvement in the strength and ductility values were observed in as-rolled and peak aged conditions for ST sheets and rods, whereas tensile properties in WST condition were significantly lower. The combined effect of suppression of dynamic recovery (DRV), grain size refinement, dislocation strengthening and precipitation hardening from the θ′ precipitates are responsible for achieving optimum strength and ductility balance at temperatures up to 20 K. Based on the outcomes of the present work, severe deformation through cold/cryo/caliber rolling of the ST sheets and rods followed by peak ageing is very effective in improving the cryogenic strength and ductility over conventional processed routes for AA2219 alloy.

The Structure and Mechanical Properties of Rolled Sheets of the Multicomponent Al–2.5Ca–2.5Mg Alloy Doped with Scandium and Zirconium

Using the Al–2.5% Mg–1% Mn–0.4% Fe base alloy (wt %) as an example, the effects of calcium, scandium, and zirconium additives (at about 2.5, 0.1, and 0.2 wt %, respectively) on the strength of rolled sheets has been studied. Ingots of the alloy of the chosen composition and the hot and cold rolled sheets obtained from them were used as objects for the experimental study. Based on microstructural studies, it isshown that calcium binds iron into compact inclusions (presumably, into the Al10CaFe2 phases), which has a positive effect on the mechanical properties of the alloy, as well as on the technological plasticity during therolling operation. Zirconium and scandium additives make it possible to form thermally stable nanoparticles of the Al3(Zr, Sc)–L12 phase, which is favorable for maintaining a partially unrecrystallized structure in coldrolled sheets during annealing at least up to 400°C. Using the alloy of the selected composition as an example, the fundamental possibility for producing sheet products from cast (unhomogenized) ingots with the properties of thermally hardenable alloys of the AlSiMgMn and AlZn4.5Mg1.5Mn types without using quenching has been demonstrated.

Influence of Si content on selective oxidation and oxide scale phase transition during hot-rolled coiling

The internal oxidation formed during the advanced high-strength steels hot-rolled coiling process can be inherited into the cold-rolled sheet and impact the final product quality. Herein, the influence of Si on the internal oxidation and oxide scale phase transition behavior of Fe–Mn–Si advanced high-strength steel after hot-rolled coiling are investigated. The results indicate that the internal oxidation depth increases with the increase of Si content and is accompanied by severe intragranular oxidation. Moreover, the interface between Mn–Si oxide and substrate provides a direct diffusion path, which accelerates the rate of internal oxidation. In addition, the displacement reaction of Si/Mn is the primary cause for the formation of continuous pure Fe at the interface of oxide scale/substrate.

Superior tensile properties and formability synergy of high-entropy alloys through inverse-gradient structures via laser surface treatment

Heterostructuring is an emerging method for achieving an excellent combination of strength and ductility; however, its usage is often limited in the industry because of poor formability. The high mechanical incompatibility between domains in heterostructured materials facilitates crack initiation and propagation during forming. To broaden the industrial applicability of heterostructured materials, it is necessary to balance their tensile properties and formability. Herein, we propose a new strategy for designing heterostructures that are optimized for non-uniform deformation during forming. Cold-rolled CoCrFeMnNi high-entropy alloy sheets were laser treated on both sides to fabricate an inverse-gradient structure (soft outer and hard inner regions) with superior strength-ductility synergy. Furthermore, the inverse-gradient samples exhibited excellent bendability because the outer coarse-grained region prevented the generation of external cracks, and the decrease in the strength difference between neighboring domains reduced the damage evolution. Consequently, the present heterostructured high-entropy alloys exhibit superior tensile properties and formability.

Improvement of magnetic properties via normalizing annealing for high-strength Fe-4.5wt.%Si electrical steel

Both excellent magnetic and mechanical properties are desired for electrical steels used in high-speed motors and engines of electric vehicles. Existing high-strength electrical steels (HSES) usually sacrifice magnetic properties for a trade-off of strengthening effect. In this work, Fe-4.5wt.%Si alloy was employed to fabricate HSES by dislocation and solution strengthening, and the magnetic properties were further improved by normalizing annealing after hot rolling. The effect of normalizing annealing (NA) on micro structure and magnetic/mechanical properties was investigated. The iron loss of the cold-rolled sheets can be significantly decreased with NA treatment. The iron loss P1.0T/400Hz of 20.7 W/kg with a yield stress of 656 MPa, and P1.0T/400Hz of 30.3 W/kg with a yield stress of 865 MPa can be achieved.

An eco-friendly electric pulse treatment process for improving the microstructure and properties of cold-rolled pure copper sheet

In this study, we performed electric pulse treatment (EPT) on the cold-rolled pure copper sheets. And the effects of the current density of EPT on the microstructure and mechanical properties of the cold-rolled pure copper sheets were investigated. It has been found that the change in the current density of EPT has a remarkable influence on the surface temperature, microstructure, strength, plasticity and microhardness of the samples. Compared with the untreated sample, the elongation after fracture increased by about 3.2 times at a current density of 200 A mm−2, whereas the ultimate tensile strength decreased by only 38.0%. Microstructures indicate that the electric pulse can induce rapid recrystallization in cold-rolled pure copper sheets within a short time, while reducing the dislocation density, weakening the rolling textures and increasing microstructure uniformity, thereby improving the plasticity of the material. Therefore, the present research has the potential to provide an effective alternative way to the traditional heat treatment of copper sheets and strips.

Influence of cold deformation on the structure, texture, elastic and microdurometric properties of biocompatible beta-titanium alloys based on the Ti–Nb–Zr system

The influence of cold rolling with degrees of 85, 90% on the structural and textural state, microdurometric and elastic properties of hardened biocompatible -titanium alloys (at.%) Ti-26%Nb-3%Zr, Ti -26%Nb-5%Zr, Ti-26%Nb-6%Zr, Ti-26%Nb-3%Zr-1%Sn, Ti-26%Nb-3%Zr-1%Sn-0.7Ta . It is shown that an increase in the degree of deformation during cold rolling contributes to the formation of a more pronounced two-component texture {001}, {112} an increase in microhardness and a decrease in the values ​​of the elastic modulus in the rolling plane . A good agreement between the calculated and experimental values ​​of the modulus of elasticity of alloys in the quenched and cold-rolled states has been established.The influence of alloying and anisotropic state of alloys (through the molybdenum equivalent and the Zener anisotropy factor, respectively) on the level of their microhardness, contact modulus of elasticity E, including the difference in E in different sections of a cold-rolled sheet, is considered. It has been established that the minimum average value of Е=51±2 GPa in the rolling plane is given by the Ti-26Nb-3Zr alloy rolled with ε=90%, and the minimum level of average values Е (52±2 GPa in the rolling plane and 62±1 GPa in cross section) is typical for the Ti-26Nb-3Zr-1Sn alloy after rolling with ε= 85%

Advantages of lean duplex stainless steels in the pulp and paper industry

The performance of lean duplex stainless steels has been utilized by the pulp and paper industry since their introduction to the market almost 20 years ago. Experience has shown that this group of stainless steels has exceptional performance in, for example, alkaline environments towards typical deterioration mechanisms, i.e., uniform corrosion and stress corrosion cracking. The chemistry of the “lean” duplex steels is designed so that the content of volatile and expensive elements like nickel and molybdenum can be reduced to an absolute minimum without sacrificing the technical performance. This reduces the raw material cost and most importantly provides predictability of the steel price, which is often challenging with conventional austenitic and duplex stainless steels.Thanks to a dual phase microstructure and high nitrogen content, lean duplex steels have at least two times higher strength compared to standard austenitic stainless steels. This is often a preferred feature in pulp and paper construction, as it enables lighter structures and less material to be utilized. Today, lean duplex steels are widely available in various dimensions, from thin cold rolled sheets up to thick hot rolled plates. Lean duplex steels are also fully recyclable after the decommissioning stage of the equipment, thereby contributing to the circular economy.

Microstructures and Mechanical Properties of Annealed Ti50Ni47Fe3 Shape Memory Alloy

The effect of annealing temperature on the microstructures and mechanical properties of Ti50Ni47Fe3 (at. %) shape memory alloy was investigated by using a cold-rolled alloy sheet. For this purpose, a scanning electron microscope, electron backscatter diffraction, a transmission electron microscope, X-ray diffraction, tensile tests and Vickers hardness tests were used. The evolution of the microstructures, mechanical properties and fracture morphology of Ti50Ni47Fe3 alloy was studied. The results show that the recovery occurs at an annealing temperature of 500 °C, and the recrystallization occurs at 600 °C. Because of the recrystallization at 600 °C, the <110>//RD texture disappears, and the intensity of the <111>//RD texture decreases; the alloy reaches its maximum elongation while maintaining a high strength, and at this annealing temperature, the alloy has excellent comprehensive mechanical properties. After the temperature exceeds 600 °C, the mechanical properties of the alloy decrease sharply. With the increase of the annealing temperature, the quantity and distribution of elliptical Ti2Ni-phase particles show almost no specific changes. Additionally, with the increase of annealing temperatures to 600 °C, the fracture surface of Ti50Ni47Fe3 alloys becomes flatter.

Characterisation of out-of-plane shear behaviour of anisotropic sheet materials based on indentation plastometry

This paper presents a new methodology for characterising the out-of-plane plastic anisotropy behaviour of sheet metal, based on indentation testing. Conventionally, advanced yield criteria are used to describe plastic anisotropy, requiring multiple in-plane mechanical tests (such as uniaxial and biaxial tests) to calibrate a model. However, in certain forming applications (e.g. blanking, ironing and incremental forming), the influence of mechanical behaviour through thickness cannot be ignored, necessitating the characterisation of out-of-plane material behaviour. To do this, a 3D plastic anisotropy model must be used and calibrated for the out-of-plane shear parameters, which can be difficult to determine. Researchers often assume an isotropic case or equal shear parameters for in-plane and out-of-plane behaviour. More advanced calibrations involve the crystal plasticity model. In this work, we propose a two-stage calibration procedure. In the first stage, we calibrate the in-plane parameters of the YLD2004–18p yield function conventionally. In the second stage, after fixing the in-plane parameters, we determine the remaining out-of-plane shear parameters based on the results of the ball indentation test. We show for the first time that out-of-plane shear parameters can be determined from a macro-mechanical test for a 2.42 mm thick cold-rolled AA5754-H22 series aluminium sheet.

Real-Time Detection of Nickel Plated Punched Steel Strip Parameters Based on Improved Circle Fitting Algorithm

Nickel-plated punched steel strip is a product obtained by punching holes on the surface of cold-rolled white sheet steel strip and then electrochemical nickel plating. It is necessary to make accurate and fast detection of punching circle parameters, since it is of crucial importance to ensuring the quality of nickel-plated punched steel strips. Accordingly, in this article, an improved circle fitting algorithm of nickel-plated punched steel strip is proposed. Firstly, the least squares fitting is performed to obtain the circle center and radius dataset by iterative algorithm with different values for the initial point positions and intervals. Then, the mean shift algorithm is used to optimize the results after iteration, and the segmented fitted circle centers are all concentrated around the true circle center to obtain the best radius and center coordinates. Finally, comparison experiments with different numbers of circular holes and verification experiments with nickel-plated punched steel strips are carried out. As the results show, the algorithm proposed in this article is more robust than the least squares algorithm in detecting multiple circles and has better real-time performance than the Hough transform. Therefore, it can meet the industrial production needs with high accuracy and real-time requirements, such as nickel-plated punched steel strips.

Comparison of K-doped and pure cold-rolled tungsten sheets: Microstructure restoration in different temperature regimes

For tungsten in divertor parts of future fusion reactors, a fine-grained microstructure is preferred to reduce its brittle-to-ductile transition temperature and minimize cracking events due to cyclic thermal and mechanical loading. In our ongoing study on tungsten sheets with different degree of deformation by warm- and cold-rolling, the potential of potassium-doping to stabilize the microstructure at high operation temperatures is assessed. Successful production of technically pure and equivalently rolled potassium-doped tungsten sheets up to very high logarithmic strains of 4.6 was already shown in the past with in-depth analysis of the evolution of microstructure and mechanical properties after rolling steps. Our current study investigates the microstructure changes in the same material batch by recovery, recrystallization and grain growth in temperature regimes between 600 °C and 2400 °C. Annealing studies with subsequent microhardness and SEM analysis reveal increased retardation of recrystallization in potassium-doped tungsten with higher rolling strain, but abnormal grain growth at high temperatures is also increased. However, potassium-doped tungsten with low rolling strain shows promising results with much less grain growth than its pure tungsten counterpart.

Refinement mechanism and optimization for compact strip production process

To avoid the fracture of cold-rolled sheets, this study investigated the refinement mechanism for the compact strip production process and proposed an optimised method. The primary austenite grain size was 50–475 µm, and the grain size of the hot-rolled strips was 3.6–4.8 µm. The Gleeble-3500 simulator was applied to simulate the hot rolling process. Grain refinement was realised through dynamic recrystallization and the supply of more nucleation sites for transformation by sub-structures. Increasing the coiling temperature from 620 to 730 °C increased the ferrite fraction from 3.95 to 24.16%. The adjacent cementite distance changed from 0.33 to 0.84 µm, resulting in decreased yield and tensile strengths and increased elongation. Thus, the fracture of cold-rolled sheets was avoided.

Effect of cold-rolling deformation and rare earth yttrium on microstructure and texture of oriented silicon steel

Abstract In order to study the effect of cold-rolling deformation and rare earth Y on the microstructure and texture of 3.0% Si-oriented silicon steel, the microstructure and texture of cold-rolled oriented silicon steel with 60, 72, and 86% deformation are analyzed using electron backscatter diffraction and image analysis software. The experimental results show that the deformation band becomes narrower and the distribution of shear bands becomes denser with increasing cold-rolling deformation. Compared to the Y-free steel, cold-rolled sheet containing rare earth Y has greater shear bands. The pinning effect of rare earth Y hinders the dislocation movement, which leads to the increase of kernel average misorientation value and shear bands. With the increase of cold-rolling deformation, the texture concentrates on α and λ. This is mainly due to the change from {100} 〈001〉 to {001} 〈110〉, intensifying λ texture, and the change from {111} 〈112〉 to {111} 〈110〉, thus strengthening the α texture. The texture strength of cold-rolled sheets can be decreased by rare earth Y. But the γ texture strength in cold-rolled sheets containing Y is significantly higher than in those without Y. The γ texture strength can reach up to 7.3, and the strong points are mainly {111} 〈112〉. This is because the number of inclusions in steel increases with the addition of rare earth Y. In the process of grain nucleation, the {111} oriented grains nucleate heterogeneously on the inclusions. It forms a large number of {111} oriented grains and improves the γ texture strength.

Control of the Microstructure in a Al5Co15Cr30Fe25Ni25 High Entropy Alloy through Thermo-Mechanical and Thermal Treatments

The effect of thermos-mechanical processing and thermal treatments on the microstructure of a single phase fcc-based Al5Co15Cr30Fe25Ni25 high entropy alloy is evaluated in this study. As-cast ingots of the high entropy alloy were thermo-mechanically processed following different routes involving forging, cold rolling, warm rolling or hot rolling. In addition, the microstructural evolution of highly deformed cold rolled sheets with the annealing temperature was analyzed. The data reveal that a high-volume fraction of the microstructure commences to recrystallize from 600 °C. In the absence of recrystallization, i.e., below 600 °C, the hardness of thermo-mechanically processed and annealed samples was very close. When recrystallization takes place, the thermo-mechanically treated alloys exhibit higher hardness than the annealed alloys because the recrystallized grains are strengthened by dislocations generated in further steps of the processing while the alloys in the annealed condition are free of dislocations. Maximum hardening is found for the alloy warm-rolled at 450 °C and the alloy cold-rolled plus annealing at 500 °C for 1 h. Diffusion of solute atoms to the core of dislocations, pinning its movement, accounts for the additional hardening.

Elucidating the effects of cold rolling route on the mechanical properties of AISI 316L austenitic stainless steel

The evolution of mechanical properties of an AISI 316L austenitic stainless steel was studied during cold rolling via unidirectional and cross-rolling routes. It was shown that the low thickness reduction of 25% in cross-rolling leads to the formation of greater amounts of strain-induced martensite (based on the transformation-induced plasticity effect) and higher dislocation density, leading to a remarkable combination of transformation strengthening and work hardening effects. At the high thickness reduction of 75%, while the strengthening effects of both rolling routes became comparable, cross-rolling resulted in a less pronounced directionality of mechanical properties. In this regard, an alternative method for the evaluation of anisotropy in the cold rolled sheets (based on the obtained values of ultimate tensile strength for tensile samples prepared in different directions) was proposed. Accordingly, it was demonstrated that cross-rolling has a high potential for the enhancement of mechanical properties at low thickness reductions, preservation of equiaxed structure even at high thickness reductions, and decreasing of anisotropy and directionality of properties compared to the unidirectional rolling.