Rolled Sheets Research Articles

Microstructure evolution and its effect on corrosion behavior during cold rolling of Ti–Nb–Ni sheet as bipolar plates substrate for PEMFC

In this work, hot rolled Ti–Nb–Ni sheet with thickness of 1.8 mm was subjected to cold rolling with different reductions (20 %, 40 %, 60 %, 75 % and 85 %). Microstructure evolution and corrosion resistance of sheets with and without being cold rolled were investigated. Mechanical twins are generated for 20 % and 40 % cold rolled sheets, while dislocation slip becomes dominant for reductions larger than 40 %. Typical TD-split basal texture was observed in all of specimens. Corrosion resistance of the sheets in solution of pH = 3 H2SO4 with 0.1 ppm F− at 80 °C were evaluated. All the sheets possessed corrosion current densities lower than 1 μA cm−2, meeting the requirement of Department of Energy. Hot rolled sheet possessed the noblest OCP (−0.212 V), lowest corrosion current density (0.15 μA cm−2) and steady state current density (0.012 μA cm−2), as well as the largest polarization resistance of all the sheets (749.1 kΩ cm2). Besides, corrosion resistance for cold rolled sheets becomes inferior with reduction increasing. This can be attributed to increased dislocation density which provides more available active sites and deteriorates corrosion resistance with reduction increasing. Therefore, to obtain desirable corrosion resistance in PEMFC environment, Ti–Nb–Ni sheets with microstructure possessing massive dislocations should be avoided.

Method for Determination of Friction Coefficient During Cold Rolling of Extra Thin Sheets

Method for Determination of Friction Coefficient During Cold Rolling of Extra Thin Sheets

Physical Simulation of Medium and Low Temperature Rolling of Mg-Li Alloy Sheet

In this paper, LZ91 magnesium-lithium alloy was taken as the research object. At the rolling temperature of room temperature and 453 K, the plane strain compression physical simulation experiment was carried out on the sample with one pass reduction of 15 % and three passes total reduction of 45 %. After each pass of rolling, the sample was annealed at 503 K for 30 min. Then the effects of different treatment processes on the microstructure of LZ91 magnesium-lithium alloy were studied by metallographic microscope, X-ray diffractometer and scanning electron microscope. The results show that under the same strain, the stress of room temperature rolling is larger than that of 453 K rolling; with the increase of annealing passes, the effect of work hardening gradually weakened. With the increase of rolling amount, the original mechanically mixed ' α ' phase and ' β ' phase will deform along the deformation direction, showing a streamline shape. Rolling at 453 K, the diffraction peak of the sample with 45 % total reduction of three passes changes the most.

Experimental investigation and numerical optimization of sheet metal forming limits during deep drawing process of DD14 steel

This work aims to experimentally study the deep drawability of DD14 hot-rolled steel sheets and to optimize numerically the material formability. The material anisotropy was confirmed by metallographic analysis of the material and tensile tests on specimens taken in three orientations with respect to the sheet rolling direction. Where the stress-strain curves show a sensitivity of material to the Piobert-Lüders phenomenon. The die pressure and the blank holder were considered as controlling factors on plastic instability and the success of the deep drawing operation. The forming limit curves (FLC) were plotted to highlight the different deformation modes that the sheet metal underwent during the deep drawing process. The collected deep-drawn parts observation shows severe plastic instability, until fracture. The initial plastic anisotropy is determined by the Hill48 quadratic criterion and the work hardening by the Hollomon power law. It results, during the experimental tests, that the front bottom corners of the deep drawn part are the areas at high risk of damage. The various numerical simulation scenarios followed by comparisons with the experimental results, allowed us to confirm the optimum conditions that minimize the material's plastic instability risks, forming operation “Step” and BHP “Amplitude”.

Современные тенденции экономического развития прокатных производств черной металлургии

The aim of the work is to determine the directions for further economic development of the Russian metallurgical industry, and rolling production in particular. In the article, based on the current existing state of rolling production, a classification of rolling mills is proposed into the following categories: by rolling temperatures, by the direction of metal movement, by cross-sectional size of rolled profile, by number and location of mills. Based on deductive methods of analysis, the main trends in the development of rolling production are considered: rolling precision, automation, robotization of auxiliary operations, digitalization. The obvious advantages of each trend, possible disadvantages and difficulties during implementation are shown. Based on statistical data, a forecast is made for the development of rolling production in the coming years. The production volumes of special products using rolling method are extremely small, as is the production of large-sized I-beams and shaped profiles, which are mostly produced in welded form, taking into account the small volume of consumption. The leading role, according to production volumes, is played by sheet and small-section products, which are the most universal. Significant changes are taking place in the Russian economy, which may affect both the construction and energy industries. In 2022 the production of seamless pipes increased in contrast to the previous eight years. A number of large-scale projects are expected to be launched for the fullscale development of Siberia and the Far East, the restoration of the economies of regions where construction and transportation will be required, including railways and pipelines. This means that this will fully affect the development of the metallurgical industry to obtain mass production profiles and to create further infrastructure in these regions. It has been determined that, with further large-scale development of the economy and volumes of consumption of mass profiles for their production, it is possible to build specialized mills, as is happening in the PRC with the maximum level of automation and productivity, which is currently inherent in single sheet rolling mills in Russia. Otherwise, on the contrary, it is necessary to carry out technical re-equipment and reconstruction of existing production facilities in order to expand the range, for their maneuverability in an economically unstable situation and to avoid long-term downtime of mills.

Study of penetrating deformation along strip thickness during rolling of composite materials

Numerical modeling of the propagation of plastic deformation across the cross-section of the rolled strip is carried out, which is especially important during secondary compaction rolling of composite products, due to the existing discontinuity of such a material, consisting of individual particles of metal powders. The developed algorithm for determining оf penetrating deformation will avoid mutual overlap of compressive stresses from each roll and prevent the appearance of tensile stresses at half-height of the strip, leading to destruction of the material. The results obtained will find application in the development of sheet rolling technologies (monomaterials and composite products), as well as in modeling the stress-strain state of the material and analyzing the causes of the appearance of layer cracks in rolled products.

The influence of rolling at subcritical temperatures on the low-carbon steel structure and properties formation

Problem. In practice, the rolling of a low-carbon steel sheet due to significant heat losses ends in the austenite – ferrite two-phase structure region, which leads to the metal heterogeneous structure formation, that decreases the sheet steel properties of the and its ability to be drawn.
 Adverse temperature conditions characteristic of traditional hot rolling technology can be prevented by metal processing in the single-phase ferrite structure region below the critical point Ar1. Rolling of a thin sheet in the subcritical temperature range will ensure obtaining a uniform metal structure, which determines the level of its mechanical properties, as well as the quality of stamped parts
 Goal. The purpose of the work is study the rolling modes influence at subcritical temperatures on the low-carbon steel structure and properties formation.Methodology. The microstructure of 08ps steel samples was studied using a metallographic and electron microscope JSM-840 with a "Link-860/|500" microanalysis system, the 08ps steel samples cross-section fine structure was studied using an electron microscope JEM - 200Сx. The metal mechanical properties complex was determined by standard tensile test methods.Results. The 08ps steel structure and properties after rolling at subcritical temperatures were studied. The comparative analysis of the fine structure of the initial blank and deformed samples of low-carbon steel was carried out. It was established that changes are observed in the structure of the deformed samples and the initial blank, which indicate the polygonization and recrystallization processes implementation and do not provide the of metal mechanical properties level provided for by DSTU 2834-94.Originality. Тhe thin structure of a 08ps steel sheet deformed in the subcritical temperature range with air cooling was studied. The development differs in the temperatures of the beginning and end of rolling, as well as the cooling rate in the post-deformation period. It allows to expand theoretical ideas about the patterns of 08ps deformed steel structure formation and to use them in practice. Practical value. The results of the work can be applied in determining rational processing modes, which involve rolling at subcritical temperatures, to increase the complex metal properties and obtain high-quality parts by cold stamping.

Development of the method for determining the deformation parameters and remidal stresses of metal in the manufacture of straight-seached pipes of large diameter using expansion

Since 2020, in Ukraine, LLC NVP «UKRTRUBOIZOL» began to operate a technological line for the production of large-diameter pipes (TVD) for main oil and gas pipelines with a hydromechanical expander. From 2023, interstate GOST 20295-85 and GOST 10706-76 ceased to be valid in Ukraine. Formulation of the problem. Ukrainian standards are needed. It is necessary to determine the rational values of the deformations and the effectiveness of the expansion to reduce the residual stresses in the metal of the pipes. Goal. Development of Ukrainian standards for TVD production and determination of the effect of expansion on residual stresses. Method. The method of cutting rings was used. The results. Developed and implemented with the participation of author: DSTU 9219:2023; DSTU 9218:2023 and TU 24.2–05757883–095:2022. Pipes with a diameter of 630 mm, with a wall of 8 mm, made of S335 steel and hot-rolled rolled sheet were studied. The opening between the longitudinal edges of the pipe blank after bending was 70-80 mm. For the ring after welding, the opening was 180 mm and for the rings expanded by 0.8%, 1.2% and 0.4% -58-53 mm. This indicates that the residual expansion stresses were much smaller than in the pipe after welding the seam, and the amount of expansion change from 0.4% to 1.2% does not affect the residual stresses. Scientific novelty. For the first time, for the JCOE technology of production of TVD from rolled hot-rolled sheet, the influence of expansion on residual stresses was determined experimentally. It was shown that the opening of the rings during expansion is significantly reduced. For the first time, the influence of the amount of expansion on the reduction of residual stresses was determined for the JCOE technology of TVD production. It is shown that deformations of 0.4-1.2% give the same opening of the rings after expansion. Practical significance. The obtained results can be useful for the personnel of steel welded TVD production enterprises and project organizations sn the design of oil and gas pipelines

Possibility of obtaining rolled sheet from white iron with increased plasticity

Рroblem In the work, a study of the technology of manufacturing sheet metal up to 2 mm thick from white ledeburite cast iron alloyed with vanadium was carried out. Сast-iron purveyances forged preliminary. After forging purveyances were rolled with the different wringing out. At rolling a total degree of deformation was 70%. The additional annealing helped to bring down hardness of sheet and moulding of pipes became possible. White cast-iron has high plasticity because there are phase transformations in a vanadium eutecticum cementite. Goal. The goal of work is a study of sheet rolling of white cast-iron’s bars to use for the armour and weld-fabricated pipes. Methodology. Experimental cast iron contains 2.7 - 2.85% C and up to 2% V. 30 kg of castings were melted. The total degree of deformation was 70%. After forging, rolling was carried out on a two-roll laboratory mill on rolls with a smooth barrel. Results. The technological scheme for the production of white cast iron forgings is applied, which includes preliminary annealing, forging with a degree of deformation from 10 to 15%, intermediate annealing and final forging with a total ε=70%. Оriginality The use of carbide transformation in vanadium-doped cementite made it possible to carry out combined pressure treatment and obtain sheets up to 2 mm thick from iron castings Preliminary hot forging greatly stimulates and accelerates the process of cementite disintegration into austenite and vanadium carbides during high-temperature exposure. Rolling of forging blanks was carried out and the influence of thermal and deformation parameters on the structure of cast iron was investigated. Рractical value. Application of final heat treatment after deformation of cast iron provides a level of mechanical properties that corresponds to the properties of high-strength armor steels, and the hardness indicators even exceed them. Thinner sheets of such cast iron can be used to create compositions of multilayer armor with increased ballistic resistance from several materials with different properties.

Investigation into the anisotropic damage behavior of LA103Z Mg‐Li alloy rolling sheet using X‐ray computed tomography and numerical modeling

AbstractThe anisotropic damage behavior has a great influence on the formability of rolling sheets. This work aimed to investigate the anisotropic damage mechanism of the LA103Z Mg‐Li alloy rolling sheet by combining mesoscale detection and modeling. The X‐ray computed tomography (XCT) and scanning electron microscope (SEM) were applied to characterize the evolution of damage morphology and volume fraction in RD, DD, and TD directions of the rolling sheet. The GTN damage model was calibrated by the experimental results with the representative volume element (RVE) method. The anisotropic damage mechanism was revealed via experimental and modeling results. The micro void nucleation strain εN was critical to determine the initiation moment of the anisotropic damage. The continuous nucleation in RD direction, the severe growth in DD direction, and the massive coalescence in TD direction were the micro void evolution competition results that caused the anisotropy for damage mechanism and fracture strain.

Effect of hot rolling on microstructure and mechanical properties of hot isostatically pressed 30CrMnSiNi2A ultrahigh strength steel

The prior particle boundaries (PPBs) are a typical powder metallurgy (PM) defect, which usually leads to the deterioration of mechanical properties in PM materials. In this study, two different hot rolling modes (unidirectional rolling and cross rolling) are designed to improve PPBs in hot isostatic pressed (HIPed) 30CrMnSiNi2A ultrahigh strength steel. The microstructure, mechanical properties and fracture features of the HIPed compact, the hot unidirectional rolled (HURed) and hot cross rolled (HCRed) sheets are systematically compared. The results manifests that hot rolling has a significant influence on size and distribution of PPBs. PPBs in HIPed compact are comprised of Al-rich oxides which is distributed along particle boundaries. After hot rolling, large PPBs inclusions are crushed and the size of PPBs are mostly concentrated in 0–0.20 μm. Unidirectional rolling makes continuous PPBs structure broken into short-chain fragments and dispersed oxides completely, while cross rolling makes most of continuous PPBs structure maintained and only a few oxides are dispersed. Excellent mechanical properties are obtained by hot rolling, reflecting on an ultimate tensile strength (UTS) of about 2.0 GPa, a total elongation (TE) of 17.9 %, a Charpy impact energy of 28.6J along rolling direction and a UTS of over 2.1 GPa, a TE of 16.1 %, a Charpy impact energy of 18.1J along transverse direction, respectively. High performances can be attributed to formation of martensite, grain refinement, improvement of PPBs and work hardening. Furthermore, hot-rolled samples manifests an obvious anisotropy in mechanical properties. The HCRed sample reveals a lower anisotropy compared to the HURed sample, mainly owing to differences of PPBs distribution and rolling textures.

On vortex-sheet evolution beyond singularity formation

We consider the evolution of a spatially periodic, perturbed vortex sheet for small times after the formation of a curvature singularity at time $t=t_c$ as demonstrated by Moore (Proc. R. Soc. Lond. A, vol. 365, issue 1720, 1979, pp. 105–119). The Moore analysis is extended to provide the small-amplitude, full-sheet structure at $t=t_c$ for a general single-mode initial condition in terms of polylogarithmic functions, from which its asymptotic form near the singular point is determined. This defines an intermediate evolution problem for which the leading-order, and most singular, approximation is solved as a Taylor-series expansion in $\tau = t-t_c$ , where coefficients are calculated by repeated differentiation of the defining Birkhoff–Rott (BR) equation. The first few terms are in good agreement with numerical calculation based on the full-sheet solution. The series is summed, providing an analytic continuation which shows sheet rupture at circulation $\varGamma =0^+$ , $\tau >0^+$ , but with non-physical features owing to the absence of end-tip sheet roll up. This is corrected by constructing an inner solution with $\varGamma < \tau$ , as a perturbed similarity form with small parameter $\tau ^{1/2}$ . Numerical solutions of both the inner, nonlinear zeroth-order and first-order linear BR equations are obtained whose outer limits match the intermediate solution. The composite solution shows sheet tearing at $\tau =0^+$ into two separate, rolled up algebraic spirals near the central singular point. Branch separation distance scales as $\tau$ with a non-local, $\tau ^{3/2}$ correction. Properties of the intermediate and inner solutions are discussed.

Experiment and analysis on edge chamfering rolling of sheet with various wedge angles

Edge chamfering rolling (ECR) is a variable wedge angle in both the transversal direction (TD) and normal direction (ND). A new method for rolling sheets with various chamfering amount in the TD (0, 2 mm, 4 mm, 6 mm, 8 mm) and ND (2 mm) is investigated in this paper. The technological process was simulated by FEM to test its feasibility and compared to conduct experiments. Three significant process parameters, temperature, stress, and flow velocity were adopted to evaluate chamfering amount on their effects before the optimal angle was confirmed. The edge crack and spread of rolled chamfered sheet were tested with different experiments and theory, and the spread formula of chamfered plate rolling was obtained to evaluate the shape quality of the plate after ECR.

Comprehensive Analysis of Microstructure and Hot Deformation Behavior of Al-Cu-Y-Mg-Cr-Zr-Ti-Fe-Si Alloy

Low sensitivity to hot cracking is very important not only for casting but also for ingots of wrought alloys. Doping of Al-Cu-(Mg) alloys by eutectic forming elements provides an increasing resistance to hot cracking susceptibility, but it also leads to a decrease in plasticity. The quasi-binary alloys based on an Al-Cu-REM system with an atomic ratio of Cu/REM = 4 have a high solidus temperature, narrow solidification range and fine microstructure. The detailed investigation of microstructure, precipitation and hot deformation behavior, and mechanical properties of novel Al-Cu-Y-Mg-Cr-Zr-Ti-Fe-Si alloy was performed in this study. The fine Al8Cu4Y, needle-shaped Al11Cu2Y2Si2, compact primary (Al,Ti)84Cu6.4Y4.3Cr5.3 and Q (Al8Cu2Mg8Si6) phases were identified in the as-cast microstructure. Near-spherical coarse Al3(Zr,Y) and fine Al45Cr7 precipitates with a size of 60 nm and 10 nm were formed after 3 h of solution treatment at 580 °C. S′(Al2CuMg) precipitates with an average diameter of 140 nm, thickness of 6 nm and calculated volume fraction of 0.033 strengthened 36 HV during aging at 210 °C for 3 h. Three-dimensional hot processing maps demonstrated an excellent and stable deformation behavior at 440–540 °C and strain rates of 0.01–10 s−1. The rolled sheets had a good combination of yield strength (313 MPa) and plasticity (10.8%) in the recrystallized at 580 °C, with water quenched and aged at 210 °C for a 3 h state. The main calculated effect in the yield strength was contributed by Al45Cr7 precipitates.

Research on the Recrystallization Process of the Ti-70 Titanium Alloy Sheet

As Ti-70 is a new type of marine titanium alloy, research on the recrystallization process of its sheet is necessary. This article studies the effects of different temperatures and times of annealing on the recrystallization process of 5.0 mm thick Ti-70 titanium alloy cold-rolled sheets by metallographic analyses and hardness tests. The results show that after 30 min of annealing at 620~700 °C, the recrystallization process was mostly complete, and uniform and equiaxed recrystallized grains could be obtained. The recrystallization process starts after 8 min of annealing at 700 °C, and after holding for 15~30 min, the recrystallization process is almost complete and the grain size is about 8.2 μm. The recrystallization activation energy of a Ti-70 titanium alloy cold-rolled sheet is Qr = 11.0645 × 104 J/mol. The ultimate tensile strength (Rm) can be controlled between 705 and 852 MPa, the yield strength (Rp0.2) can be controlled between approximately 623 and 793 MPa, and the elongation percentage (A) can be controlled between approximately 10.0 and 25.0% after rolling and heat treatment of Ti-70 alloy sheets.

Investigation into the fracture behavior of ZK60 Mg alloy rolling sheet under different stress triaxiality

In order to investigate the fracture behavior of the ZK60 Mg alloy rolling under different stress triaxiality, the different nominal stress triaxiality samples were well-designed, and the in-situ DIC tensile tests were carried out. The finite element method (FEM) model was validated by experimental results and the stress triaxiality evolution of samples was determined by modeling. The fracture strain of the ZK60 Mg alloy was non-monotonic with the nominal stress triaxiality increase and the best deformation performance of the central hole sample was indicated via the experimental and modeling results. The low stress triaxiality gradient of the central hole sample led to better deformation performance in terms of the macroscopic mechanical response. The transformation of the fracture mechanism from shear transgranular fracture to intergranular fracture and then to transgranular fracture during the stress triaxiality increased from 0 to 2/3 and was revealed via scanning electron microscope (SEM) characterization and FEM modeling. To further confirm the above fracture mechanism, X-ray computed tomography (XCT) was carried out to characterize the micro damage volume fraction and morphology. Due to the transgranular fracture induced by the high stress triaxiality at the initial fracture position of the central hole sample, the micro damage was smaller, delaying the fracture failure and achieving higher strain.

Tailoring the Mechanical Properties of Copper‐Added Transformation‐Induced Plasticity‐Aided Multiphase Steel by Thermomechanical Processing

Herein, the microstructure and mechanical properties of a low‐alloy Cu‐bearing transformation‐induced plasticity (TRIP) steel and their dependence on the processing history are investigated. The distributions of the retained austenite and bainite are found to be dependent on the initial cold‐rolled microstructure, which can be tailored by the preceding hot‐rolling route (unidirectional/cross rolling) and the subsequent cooling rate (furnace/air cooling). Mechanical properties and TRIP effect strongly depend on the initial microstructure, where the air‐cooled sheet shows remarkable mechanical properties; while the cross‐rolled sheet shows isotropic properties. The addition of copper results in an increase in the amount of the retained austenite, enhancement of strength‐ductility balance, and improvement of the hardening behavior of TRIP‐assisted high‐performance steel.

The Production of Hematite Powder from Spent Pickling Hydrochloric Acid

This research aimed to study the recycling process and the feasibility of recovering iron as hematite or red oxide powder (Fe2O3) from spent pickling acid (hydrochloric acid). The spent hydrochloric acid waste from the pickling bath in the sheet rolling steel industry contains approximately 233 g of iron dissolved in one liter of the spent acid. To recover iron, 2 M NaOH was added to the spent acid until reaching pH 7. The iron was precipitated as iron oxide and/or hydroxide. Next, the oxidation of ferrous oxide was carried out by adding H2O2 35%v/v to control the shade color. The precipitates were subsequently separated from the acid solution by a filter press. The precipitates were dried at 110°C for 24 h and calcined at 700°C for 2 h to synthesize and modify the crystallinity of ferric oxide. Ferric oxide was subject to water washing, where contaminating sodium chloride could be dissolved and filtered out. After drying at 110°C for 24 h, high-purity hematite was achieved. Hematite recovered from the spent pickling acid via this process provided more than 97% purity at 94.4% recovery.

Optimization of CMT welding process parameters of dissimilar hot rolled E250 and polymer sandwich steel lap joints

Lap joints of 1.5 mm thin sheets of dissimilar hot rolled E250 with polymer sandwich steel (MPM) were produced by cold metal transfer (CMT) process, closer to the real application. The polymer layer polystyrene-butadiene-styrene sandwiched between two DC06 sheets of MPM was found to be intact at significantly lower heat inputs (0.16 − 0.24 kJ/mm), which otherwise had been quite challenging during TIG welding leading to huge rejections. After several iterative trials for acceptable weld quality, experiments were conducted as per L9 orthogonal array, Taguchi technique with welding speed (WS), wire feed rate (WFR) and welding torch orientation (TO) as the process parameters. The joints were investigated through optical macrograph, micrographs, hardness, tensile lap shear tests and fractography on the fractured specimen. Optimum parameters were determined for maximizing shear strength. The sample with optimized parameters exhibited 6% improvement in shear strength achieving 152.09 MPa and polymer layer retention. ANOVA analysis suggested WS to be most significant parameter with 69.85% contribution affecting shear strength. Coefficient of determination (R 2) for the shear strength was 87.26% derived from the linear regression model. Significantly, lower error 0.96% computed from the confirmatory test concluded very effective optimization. Highlights Thin sheets of polymer sandwich steel (MPM) sheets were joined successfully with hot rolled E250 sheet without thermal disengagement of the polymer layer in MPM by CMT welding. Under optimal parameters MPM/E250 joints exhibited excellent mechanical properties. Fractography analysis revealed ductile failure mode. The error between experimental and predicted results by Taguchi was significantly lower and very well within the acceptable range.

Statistical investigation of deformation mechanisms in rolled Mg sheet during compression

A statistical investigation of the operating slip/twinning modes and their interactions at grain scale over a large area, containing ~400 grains, was carried out on rolled Mg sheets during room-temperature compression based on EBSD and slip trace analysis. For 10% strain, the slip mode was dominated by basal slip (89%). All the 363 identified twins were tension twins. The concave-up stress−strain curve indicated a twinning-dominated deformation behavior, which was further confirmed by the large twinned area fraction (41%) after the deformation. Most twin variants (79%) followed the Schmid law. The Luster−Morris parameter (m′) did not correlate well to twin transmission. However, most twin transmissions (82%) exhibited larger normalized m (Schmid factor) and m′ values. Additional slip systems were frequently active in the twin domains while not in the parent, which can be explained by Schmid law. Slip transfer across the twin boundaries was also observed. Statistical m analysis revealed that twinning activity was closely related to prismatic slip.