Rolling Steps Research Articles

Effect of increased length fraction of Ʃ3n special boundaries on OAIC response of cold rolled Ni-based alloy 718 thin sheets

Among the well-established Ni-based superalloys, alloy 718 is one of the most widely used in the industry. However, its application is limited up to 650°C due to the occurrence of the oxidation assisted intergranular cracking (OAIC) phenomenon. As a general rule, an increased fraction of special boundaries (3 < Ʃ<29) along the grain boundary network, in replacement of the high energy random high angle boundaries (RHABs), is usually associated with enhanced resistance to several intergranular failure mechanisms. In the present investigation, thin sheets of alloy 718 were subjected to three different thermomechanical processing (TMP) routes, in order to manipulate the grain boundary character distribution (GBCD), aiming to achieve an increased fraction of low-Ʃ special boundaries and, consequently, to reduce the alloy's OAIC susceptibility. Scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD) were used to characterize the different microstructures and GBCD resulting from TMP. Thin sheet specimens underwent hot tensile tests at 650 °C under secondary vacuum at a strain rate of 3.2 × 10−4 s−1. Fractography analyses were performed to quantify the fraction of brittle areas on the fracture surface. The results indicate that the sample processed through iterative steps of cold rolling and solution annealing, followed by a double aging heat treatment, resulted in a microstructure resistant to OAIC, with 100% of ductile fracture. Such good resistance to OAIC was attributed to the higher percentage of special Ʃ3n boundaries, as well as to the best configuration of grain boundaries network, presenting increased fraction of special triple junctions 3CSL and 2CSL as well as a favorable triple junction ratio (TJR).

Creep behaviour of ultrafine-grained CP titanium processed by multi-pass rolling

Two commercially pure (CP) Ti heats containing the same total impurity content have been used under investigation. Both materials were subjected to the processing procedure method of severe plastic deformation (SPD). This procedure consists of two steps of hot rolling (at 673 K) and the final rolling step at ambient temperature. The difference in individual chemical contents of impurities resulted in two states, both with ultrafine-grained (UFG) microstructures. For comparison reason, coarse-grained (CG) state was prepared by annealing of UFG state at temperature 823 K/1h. Microstructure investigations were performed using scanning electron microscope equipped with EBSD unit (SEM/EBSD) and transmission electron microscopy (TEM). Constant load tensile creep tests were conducted at temperature 673 K and applied uniaxial stress of 200MPa. Creep tests were run up to the final fracture of the creep specimens. The main objective of this work was to evaluate how the synergistic effect of SPD and the resulting microstructure affects the creep behaviour and properties of the studied materials.

Effect of thermo-mechanical treatment and strontium addition on workability and mechanical properties of Al Si Cu casting alloy

In this study, the potential application of Al-Si-Cu aluminum alloy (ALDC12), which is widely used in the high-pressure die-casting (HPDC) process, for fabricating a wrought product was evaluated. The effects of thermo-mechanical treatment and Sr addition on the microstructure, workability, and mechanical properties of the ALDC12 alloy were investigated in detail. The introduction of thermo-mechanical treatment significantly reduced the interconnectivity of the brittle eutectic Si phase formed during solidification and average grain size. Therefore, the uniformly distributed spherical Si particles and fine grain size considerably improved both the strength and ductility of the ALDC12 alloy. Furthermore, the addition of Sr effectively modified the eutectic Si phase in the casting process, which significantly reduced the occurrence of edge cracks in the subsequent rolling step and further improved the mechanical properties of the final sheets. Consequently, through microstructural control of the ALDC12 aluminum alloy by the thermo-mechanical treatment and Sr addition, it was possible to obtain suitable workability and significantly improved mechanical properties compared with those of cast products.

Development of Strip Lateral Movement Simulator for Temper Rolling

The temper rolling process of hot-rolled strips is the final rolling step to improve the flatness of the strips and shape slippage of the coiled strips. Poor flatness of a hot-rolled strip causes lateral movement of the strip during the temper rolling process. Manual leveling operations to control this movement result in a much lower line speed and productivity. Moreover, the quality of manual leveling is not consistent, as it depends on the operator’s experience. Lack of understanding of the lateral movement phenomenon has sustained manual operation and discouraged the development of an automatic control system. To solve this problem, the authors propose both a new lateral movement model and a theoretical method. A lateral movement model for temper rolling and a large-deflection strip model are important components in the new model. In the method, lateral movement stability is equivalent to an eigenvalue problem with lateral movement static equations. Their usefulness is confirmed by comparing the results of experimental rolling in the laboratory with those of numerical calculations. The simulation results obtained using the proposed models confirm that actual problems can be solved more exactly than with the conventional linear model. Thus, simulation using the proposed models can support the investigation of lateral movement problems and the development of an automatic control system.

Robot-assisted surface treatment strategies of AA6014 sheet metal for accumulative roll bonding

The application of high strength aluminum sheet metal components in automotive and aviation products effectively saves material and thus weight. Material strengthening can be realized by accumulative roll bonding (ARB), which belongs to the severe plastic deformation processes. Through repeated rolling steps a multilayered sheet metal is produced, which possesses increased strength due to its ultra-fine grained microstructure. Prior to each rolling step a surface treatment via wire brushing is mandatory for removing the oxide layer and roughening the sheet surface, which enables the bonding between the unique layers during rolling. The necessary surface treatment of the sheets is not fully understood by the current state of the art. In the past, it was not possible to achieve a defined and stable surface finish, because the brushing operation was done manually. The improvement of the process stability is essential to determine the relationship between the input parameters for brushing and the resulting bond strength of multilayered ARB sheets. For this reason, a robot-controlled surface treatment is introduced. The investigated material is the precipitation-hardened aluminum AA6014 with a sheet thickness of 1 mm. A suitable brushing kinematic under constant load is implemented and its effects on the surface properties are investigated by roughness measurements. The investigation shows, that the parameter combination leads to comparable or even higher roughness values than through manual brushing. Through 16 consecutive brushing paths a homogeneous and sufficient high surface roughness is realized, which enables material bonding in the rolling step. Thus, the research results indicate, that the robot-assisted surface treatment of ARB sheet metal is a promising method for a better automation and reproducibility of the brushing and the overall ARB process.

Microstructure Evolution during Controlled Rolling of an Nb–Ti Microalloyed Steel

The microstructural evolution of an Nb–Ti microalloyed steel with the application of coiled tubing is studied in detail during hot rolling followed by accelerated cooling and simulated coiling by means of optical microscopy complemented with electron backscattered diffraction and transmission electron microscopy. It is found that the main microstructural characteristics, i.e., grain size, grain morphology, and texture, vary during different thermomechanical steps, largely in finish rolling. Finish rolling at 850 °C, in the nonrecrystallization region, activates the deformation‐induced ferrite transformation (DIFT) mechanism and leads to the appearance of γ‐fiber, and {332}&lt;113&gt; and {113}&lt;110&gt; components. Decreasing the finish rolling temperature to 750 °C promotes this mechanism and results in finer final microstructure consisting of low angle grain boundaries. However, it is found that to obtain a homogenous microstructure with γ‐fiber texture, the final rolling temperature should be high enough for the sufficient occurrence of static recrystallization in ferrite just after finish rolling. More deformation in the nonrecrystallization region, especially for the last rolling steps, strongly affects the DIFT mechanism and leads to fine‐grained microstructure. Refining of ferrite to the grain size of 3.5 ± 0.5 μm results in 65% enhancement of yield strength and reduction of strain hardening by 25%.

Degradation of Fipronil and Its Metabolites during Processing of Yunnan Black Tea and Dietary Exposure Assessment

The purpose of this study was to investigate the residual degradation of fipronil and its metabolites during the processing of black tea and its dietary exposure risk. In this study,ultra-high performance liquid chromatography-tandem mass spectrometry and TPT SPE columns were used to establish a high-sensitivity and rapid determination method for fipronil and its metabolites in black tea. In the negative ion MRM monitoring mode,the linear range of fipronil and its metabolites was 0.5~100 μg/mL,the linear relationship was good,and the minimum detection limit was 0.4 μg/kg. The average recovery rate under different additive concentrations was 84.4%~95.5%,which met the requirements of trace detection. By spraying fipronil and its metabolites in the fresh leaves of the black tea,and simulating the processing of the indigo tea,and sampling and measuring the content of fipronil and its metabolites in the main steps of the processing of the indigo tea,the results showed that the content of fipronil and its metabolites was continuously reduced during the processing of Yunnan black tea,and fipronil and its metabolites were largely degraded in the two steps of rolling and drying,and the degradation rates of these two steps ranged from 37.5% to 41.2% and 65.1% to 70.1%,respectively. The results of HQ calculation showed that the dietary exposure risk of fipronil and its metabolites was low,while the total hazard index HI was greater than 1,and the dietary risk was unacceptable. At present,fipronil and its metabolites have been banned in tea. It is less likely to use four pesticides in sapling tea,but should be taken seriously.

Microstructure study of cold rolled Al0.32CoCrFeMnNi high-entropy alloy: Interactions between recrystallization and precipitation

The equimolar CoCrFeMnNi alloy is widely studied for its excellent mechanical properties at cryogenic temperatures. Interestingly, it presents a unique combination of strength and ductility mainly due to the occurrence of twinning at these low temperatures. Motivated by the desire to improve its room temperature strength, this study focuses on the optimization of the microstructure through alloying and thermomechanical treatments. More specifically, the effect of alloying with aluminium is studied with the aim of triggering precipitation strengthening. The composition Al0.32CoCrFeMnNi is chosen on the basis of thermodynamic data and submitted to various processing routes including cold rolling and annealing steps. The annealing temperature is shown to be the key parameter determining the governing microstructure transformations. At annealing temperatures below 900 °C, precipitation is the main phenomenon taking place. Above 900 °C, recrystallization is governing the evolution of the microstructure. At 900 °C, both mechanisms occur simultaneously. Recrystallization occurs first on grain boundaries and shear bands while precipitation is activated both in recrystallized and unrecrystallized regions with distinctive morphologies. It is shown to impede further recrystallization. Thermodynamic calculations are performed to explain the precipitation sequence observed in both regions. By increasing the rolling level from 60% to 80%, recrystallization kinetics is accelerated and complete recrystallization reached. A wide range of microstructure is achieved through the variety of thermomechanical treatments explored in this study. These various microstructures in turn translate into a wide range of hardness levels and tensile properties.

Influence of Rolling and Annealing Modes on Properties of Sheet Semifinished Products Made of Wrought Aluminum Alloy 1580

This article analyzes the processability and properties of sheet products made of a large grade 1580 alloy ingot with a lower scandium content in the range of its specifications. The processability of the ingot upon hot and cold rolling are estimated and the influence of percent reduction and annealing modes on properties of cold-rolled semifinished products from the alloy under consideration are analyzed. The experiments are performed with a commercial large ingot with a cross section of 500 × 2100 mm made of 1580 alloy with scandium content of 0.067 wt %. The experimental procedure is comprised of several steps of rolling and thermal treatment of sheet semifinished products at various stages of the developed mode of metal deformation and tests of mechanical properties of the respective samples using an LFM 400 kN universal testing machine. In order to perform experiments, a template with the sizes of 60 × 500 × 900 mm is cut out of the ingot and then billets for rolling are produced with sizes of 50 × 180 × 300 mm, which are exposed to homogenized two-stage annealing predeveloped for this alloy. As a consequence of the hot rolling of annealed billets at 450°C and the cumulative percent reduction of e∑ = 84–90%, sheet semifinished products are obtained with a thickness of 5–8 mm. Then, after their annealing at t = 320°C for 6 h, by means of cold rolling, thin semifinished sheets with a thickness from 2 to 6 mm are produced. Their mechanical properties in deformed and annealed states are analyzed, demonstrating that, upon cold rolling to e∑ = 38%, the strength properties of 1580 alloy increase to σ0.2 = 380 MPa; then, the growth intensity decelerates and, at e∑ = 60%, this variable is 400 MPa. The influence of annealing at t = 250–350°C on the mechanical properties of sheet semifinished products is also analyzed. It is detected that it decreases the strength properties and increases plasticity; the maximum offset yield stress corresponds to the annealing temperature of 250–275° at sufficiently high plasticity. It is established that, in terms of the strength properties, the sheet semifinished products made of 1580 alloy with lower scandium content are superior to those made of similar AW-5083 (United States) alloy without the addition of scandium by 10–15%, and the plasticity properties are 40–60% higher.

Influence of Intermediate Heating in Cross Accumulative Roll-Bonding Process on Planar Isotropy of the Mechanical Properties of Commercial Purity Aluminium Sheet

In this study, the cross accumulative roll-bonding (CARB) process, as an improved technique of the conventional accumulative roll-bonding (ARB), was conducted on the AA1050 sheet up to 10 passes in two processing modes. The specimens were either preheated before the rolling step of CARB passes and promptly roll bonded (warm CARB) or were processed at room temperature (cold CARB). The microstructure of samples was characterized using a scanning electron microscope. The effect of intermediate heat treatment on the planar homogeneity of the mechanical properties in the CARB (and even ARB) deformed sheets has not been examined yet. Hence, the present research focuses on the comparison of the planar isotropy of tensile properties between warm and cold CARB products. Also, the uniformity of microhardness distribution throughout the thickness of samples was evaluated. The warm CARB presented higher elongation, lower tensile strength and microhardness with more uniformity of the microhardness distribution, and also premier planar isotropy of the mechanical properties than the cold CARB.

Simulation assisted process chain design for the manufacturing of bulk hybrid shafts with tailored properties

To manufacture semi-finished hybrid workpieces with tailored properties, a finite element simulation assisted process chain design was investigated. This includes the process steps of cross wedge rolling, hot geometry inspection, induction hardening, and fatigue testing. The process chain allows the utilisation of material combinations such as high-strength steels with low-cost and easy to process steels. Here, plasma transferred arc welding is applied to supply the process chain with hybrid specimen featuring different steel grades. An overview of the numerical approaches to consider the various physical phenomena in each of the process steps is presented. The properties of the component behaviour were investigated via the finite element method (FEM) and theoretical approaches. At first, the manufacturing of a hybrid workpiece featuring a near net shape geometry with improved mechanical properties due to recrystallising the weld was computed, using the example of a cross wedge rolling process. The rolling process was designed by means of FEM to determine suitable process parameters and to reduce experimental testing. An optical multi-scale geometry inspection of the hot workpiece is meant to be carried out after each manufacturing step to detect potential undesired forming or cooling-induced deformations. Due to the heat transfer from the hot component to the ambient medium, an optical measurement is affected by the developing inhomogeneous refractive index field in air. To gain a basic understanding of the refractive index field and induced light deflection effects, computations were conducted using heat transfer and ray tracing simulations. According to the proposed process route, a subsequent local heat treatment of the hybrid component is required to adapt the mechanical properties by a spray cooling assisted induction hardening. The heat treatment step was computed via a 2D FEM calculation. After finishing by machining, the hybrid material shafts are examined in fatigue tests under load conditions. To predict the component’s lifetime under rolling contact fatigue, a damage accumulation model was combined with an FE simulation. The resulting residual stress state after quenching and the geometry after the finishing process were used as input data for the fatigue life calculations.

Effects of Different Wire Drawing Routes on Grain Boundary Character Distribution, Microtexture, δ-Phase Precipitation, Grain Size and Room Temperature Mechanical Behavior of Alloy 718

Over the last decades, alloy 718 usage has expanded and requirements imposed by its industrial applications became more critical. The knowledge about grain boundary character distribution (GBCD) in alloy 718 and its effect on properties improvement is mostly built based on iterative processing through cold rolling steps interspersed with solution annealing. Alloy 718 is found in the industry in many different forms and geometries, and fabricated by multiple thermomechanical processes such as wire drawing, rolling, forging or extrusion. The present study focused on understanding how wires respond to deformation mode related to drawing in regard to GBCD evolution, crystallographic orientation, precipitation of δ-phase and grain size. Lastly, assessing the resulting mechanical properties. The findings show that microstructural evolution is a consequence of competing mechanisms such as strain induced boundary migration, recrystallization, grain growth and phase precipitation. The deformation gradient along wire cross section plays an important role in affecting microstructural features, such as δ precipitation, GBCD and microtexture.

Investigation of the Effect of Whisker-Defect Size in Strip Plate from a Two-High Reversing Stand on Round-Billet Surface Quality

We present research results on the transformation of whisker defects produced by less-severe reduction modes in the last rolling step in a two-high reversing stand into surface defects in the final metal product. The number and surface distribution of rolling-skin defects were observed to be higher within two strips at diametrically opposite positions along the perimeter and formed from whisker defects.

Induced ferrite formation above the Ae3 during plate rolling simulation of a X70 steel

ABSTRACTPartial amount of austenite can be dynamically transformed into ferrite above the Ae3 temperature when it is being deformed. This happens by a displacive mechanism. On removal of the load, it retransforms back into the stable austenite by diffusional processes. Plate rolling simulation under continuous cooling conditions was carried out on a high Nb X70 steel. Pass strains of 0.2 together with interpass times of 10, 20 and 30 s were employed. The initial and final temperatures for the finishing simulation were 920 and 830 °C, respectively. The mean flow stresses (MFS`s) behaviour indicates that dynamic transformation (DT) and recrystallization (DRX) were taking place during straining. It is shown that ferrite is formed during the roughing passes and increases its volume fraction throughout the finishing rolling steps. The ferrite formation is favoured by strain accumulation, shorter time between passes and also when the temperature reaches the Ae3 line. The results obtained here can be used to design improved models for transformation on accelerated cooling.

Effect of tea processing methods on biochemical composition and sensory quality of black tea (Camellia sinensis (L.) O. Kuntze): A review

Final quality of black tea depends mainly on the chemical composition of the raw tea leaves. Various plucking methods have direct effect both on yield and quality in different cultivated variety and environments. Different literature reports indicated that polyphenols, caffeine, essential oils and amino acids are responsible for aroma and flavor of black tea. The oxidation process begins at rolling step and ends at initial stages of drying process until the heat denature the enzymes, which convert tea polyphenols (catechins) to theaflavins and thearubigins; both are responsible for brightness, color and taste of black tea. TR increased by increasing fermentation period. TF decreased by increasing fermentation period. The essential oils and the amino acids also contribute to characteristic tea taste and aroma. It was found that the essential oils content increased during the withering, rolling and fermentation steps; however this amount decreased during the drying step. But this reduction is compensated by the Millard reaction which is the reaction of amino acids with the sugars during drying, contributing positively to the tea flavor and color. Theaflavin, thearubigins and total color content of black tea stored in accelerated storage condition decreased slightly when compared with tea stored under normal conditions. It is concluded that plucking (interval, season and standard), processing steps and storage system plays major role in maintaining black tea quality. Key words: Tea processing, black tea, biochemical composition, sensory quality.

Aqueous tape casting of alumina using natural rubber latex binder

Abstract Eco-friendly and sustainable tape casting of alumina powder suspensions using concentrated natural rubber (poly isoprene) latex binder has been studied. The high negative zeta potential values of the aqueous alumina slurry (−53 to −72 mV) and rubber latex (−67 to −84 mV) at pH in the range of 9–11.5 enables their co-dispersion to produce tape casting slurries of solids (alumina + rubber) concentration >60 vol% with adequate flow characteristics. Drying of the slurry tape-cast on Mylar substrate is achieved within 15 min at 70 °C due to its high solid concentration. The green tapes containing 14.2 to 18.1 wt% of rubber shows tensile strength and strain at failure in the ranges of 1.85 to 1.61 and 41–254%, respectively. The flexible green tapes turn rigid by annealing at 200 °C due to the self-cross-linking of rubber chains induced by the Lewis acid sites of alumina. Thickness reduction to the extent of 20% by rolling of the green tape before annealing improves the green microstructure which results in an enhancement in sintered density from 93 to 98% of the theoretical value. However, the additional rolling and annealing steps consume extra time and energy compared to the tape casting processes using other reported binders.

Modification of Microstructure and Texture in Highly Non-Flammable Mg-Al-Zn-Y-Ca Alloy Sheets by Controlled Thermomechanical Processes

The influence of rolling temperature and pass reduction degree on microstructure and texture evolution was investigated using an AZXW3100 alloy, Mg-3Al-1Zn-0.5Ca-0.5Y, in wt.%. The change in the rolling schedule had a significant influence on the resulting texture and microstructure from the rolling and subsequent annealing. A relatively strong basal-type texture with a basal pole split into the rolling direction was formed by rolling at 450 °C with a decreasing scheme of the pass reduction degrees with a rolling step, while the tilted basal poles in the transverse direction were developed by using an increasing scheme of the pass reduction degrees. Rolling at 500 °C results in a further distinct texture type with a far more largely tilted basal pole into the rolling direction. The directional anisotropy of the mechanical properties in the annealed sheets was caused by the texture and microstructural features, which were in turn influenced by the rolling condition. The Erichsen index of the sheets varied in accordance to the texture sharpness, i.e., the weaker the texture the higher the formability. The sheet with a tetrarchy distribution of the basal poles into the transverse and rolling directions shows an excellent formability with an average Erichsen index of 8.1.

Microstructural Analysis of the Recrystallization Behavior of Low Alloyed Steels

The recrystallization behavior of five low alloyed steels is investigated using double hit deformation tests. It is shown, that Niobium has the biggest influence in retarding the recrystallization kinetics. Further, the microstructural evolution dependent on strain and temperature during deformation is studied with a picric acid etchant and light‐optical analysis. It is shown how the microstructure of two differently alloyed ultra‐high strength steels changes along with the peculiarities of the corresponding stress–strain curves including the evolution of grain size and aspect ratio of the prior austenite grain. The findings on the different recrystallization kinetics with the role of recrystallization retarding elements are further reinforced by investigations on the Zener‐Hollomon parameter and the activation energy needed for dynamic recrystallization. A rolling scenario on a deformation dilatometer is simulated on a hardenable and a micro‐alloyed steel to illustrate the microstructural evolution between the rolling steps. It is shown, how the two ultra‐high strength steels perform different in their microstructural evolution, as the waiving of micro‐alloying elements (MAE) provides finer austenite grains.

Non-equiatomic FeNiCoAl-based high entropy alloys with multiscale heterogeneous lamella structure for strength and ductility

A new method based on conventional thermomechanical processing is proposed for design of non-equiatomic FeNiCoAlTaB (NCATB) high entropy alloy (HEA) with multiscale heterogeneous lamella (HL) structures to achieve outstanding mechanical properties. Two kinds of microstructures are produced in this study: 1) specimens annealed at 1050 °C exhibit structure composed of fine grains and ultrafine grains, which exhibits a combination of high strength (UTS ~1050 MPa) and good ductility (elongation ~23%); and 2) specimens annealed at 1200 °C which exhibit structure composed of fine grains and coarse grains, which demonstrates excellent synergy of good strength (UTS ~890 MPa) and exceptional ductility (elongation ~43%). It has been shown that shear bands formed in the cold rolling step are responsible for the fine-grain area in both specimens. Additionally, precipitation of NiAl (B2) particles also affects the formation of HL structures due to Zener pinning effect. The back-stress strengthening mechanism, responsible for high strength and ductility, is verified through combined “loading-unloading-reloading” (LUR) cyclic tensile tests and electron backscatter diffraction (EBSD) based geometrically necessary dislocation (GND) density analysis.

Stiffness-Induced Endothelial DLC-1 Expression Forces Leukocyte Spreading through Stabilization of the ICAM-1 Adhesome

Leukocytes follow the well-defined steps of rolling, spreading, and crawling prior to diapedesis through endothelial cells (ECs). We found increased expression of DLC-1 in stiffness-associated diseases like atherosclerosis and pulmonary arterial hypertension. Depletion of DLC-1 in ECs cultured on stiff substrates drastically reduced cell stiffness and mimicked leukocyte transmigration kinetics observed for ECs cultured on soft substrates. Mechanistic studies revealed that DLC-1-depleted ECs or ECs cultured on soft substrates failed to recruit the actin-adaptor proteins filamin B, α-actinin-4, and cortactin to clustered ICAM-1, thereby preventing the ICAM-1 adhesome formation and impairing leukocyte spreading. This was rescued by overexpressing DLC-1, resulting inICAM-1 adhesome stabilization and leukocyte spreading. Our results reveal an essential role for substrate stiffness-regulated endothelial DLC-1, independent of its GAP domain, in locally stabilizing the ICAM-1 adhesome to promote leukocyte spreading, essential for efficient leukocyte transendothelial migration.