Pass Reduction Research Articles

Steel Alloy Hot Roll Simulations and Through-Thickness Variation Using Dislocation Density-Based Modeling

Different roll pass reduction schedules have different effects on the through-thickness properties of hot-rolled metal slabs. In order to assess or improve a reduction schedule using the finite element method, a material model is required that captures the relevant deformation mechanisms and physics. The model should also report relevant field quantities to assess variations in material state through the thickness of a simulated rolled metal slab. In this paper, a dislocation density-based material model with recrystallization is presented and calibrated on the material response of a high-strength low-alloy steel. The model has the ability to replicate and predict material response to a fair degree thanks to the physically motivated mechanisms it is built on. An example study is also presented to illustrate the possible effect different reduction schedules could have on the through-thickness material state and the ability to assess these effects based on finite element simulations.

Head curvature of pure titanium sheet influenced by process parameters and controlling in hot rolling process

We investigated the influences of process parameters on the head curvature of pure titanium sheet in hot rolling process and proposed the controlling means. First, the thermal simulation experiments for pure titanium TA1 were carried out to investigate the hot deformation behaviors of pure titanium in the temperature range of 700-800 °C with strain rate range of 1-20 S-1, and the processing map was established to determine optimized deformation parameters. Then, the finite element model has been constructed and used to analyze the effect of process parameters on the direction and severity of head curvature of pure titanium sheet. The process parameters considered in the present study include workpiece temperature, work roll diameter, pass reduction, oxide scale thickness of workpiece surface, and interface friction coefficient. The simulation results show that the workpiece temperature and the interface friction coefficient are the two main factors. The proposed controlling means was carried out on a hot rolling production line and solved the head curvature problem effectively. The rolling practices indicate that the rolling yield is improved greatly.

Cyclic-deformation system for the reduction of continuous-cast slabs

Introducing systems capable of profound reduction in a casting and rolling module improves the product quality, on account of the intense working of large continuous-cast slabs over the whole cross section and the production of uniform fine-grain structure of the metal, and also increases the cross section of continuous- cast billet. Analysis of the formation of nonmetallic inclusions and segregation in the axial zone of the thick rolled sheet is followed by analysis of the nonuniform deformation over the slag height in the reduction of large continuous-cast slabs at the 5000 mill at OAO Magnitogorskii Metallurgicheskii Kombinat. The structure of a cyclic-deformation system for preliminary deformation of large continuous-cast slabs is described, and its capabilities are explored. Hammers for preliminary deformation of large continuous-cast slabs are considered. Experimental data are presented for the deformation of continuous-cast steel 45 and 12Kh18N10T steel billet. The structure of the continuous-cast billet is assessed in the course of reduction on the cyclic-deformation system. The basic parameters of the system for preliminary deformation of large continuous- cast slabs are determined. The capabilities of the cyclic-deformation system are outlined in terms of increase in sheet quality. On that basis, the use of the cyclic-deformation system in the continuous-casting line for preliminary reduction of large continuous-cast slabs is recommended: it permits matching of the speed of continuous-casting and cyclic-deformation processes; and ensures 45–90% reduction in a single pass so as to obtain well-worked cast structure over the whole slab cross section. When using the cyclic-deformation system in the continuous-casting line, the continuous-cast slabs are reduced by means of the heat of the cast metal, thereby greatly reducing the energy consumption in billet production. The cyclic-deformation system may be used with thick-sheet and broad-strip mills for preliminary single-pass reduction of the hot slab, with improvement in sheet quality and reduction in the number of passes in the mills.

Effect of rolling deformation on microstructure and texture of spray-deposited magnesium alloy containing Mg-Nd-Zn typed LPSO

Billets of Mg-9Al-3Zn-1Mn-6Ca-2Nd alloy were produced by spray-deposition (the Osprey process). Effect of rolling deformation (T=350°C, ε=5%, 10%, and 15%, respectively) on microstructure and texture evolution of the Mg-9Al-3Zn-1Mn-6Ca-2Nd alloy was investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). Results show that at pass reduction of ε=5%, 10% and 15% at 350°C respectively, Mg-Nd-Zn typed 24R-LPSO structure was formed in (Ca, Nd)Al2 phase (C15 Laves phase). With the increase in pass reduction (i.e. 5%, 10% and 15%), the texture pole density level of basal texture (0002) changed little and pyramidal texture (101¯3) were increased. In contrast, those of prismatic texture {101¯0} <112¯0> were increased initially and followed by a reduction, indicating texture randomization in the grain-refined Mg alloy. The combined contribution of LPSO phase and C15 phase was key to randomize the texture of the grain-refined Mg alloy. It was noted that the microcosmic plastic deformation of LPSO phase and nanometer-sized dispersed C15 phase impeded dislocation movement, led to dislocation tangles, and facilitated recrystallization.

Multi-pass large strain rolling of as-cast AZ31 magnesium alloy

As-cast AZ31 magnesium alloy subjected to multi-pass large strain rolling was investigated. A successive rolling process up to three passes was carried out at 370°C with a pass reduction of 30%. Deformation microstructure characteristics prove that the dynamic recrystallisation (DRX) mode changed with the increase of rolling passes. In the first pass, DRX related to twinning played a dominant role. But in the third pass, DRX grains mainly appeared around the pre-existing grain boundaries. The ultimate strength and elongation of rolled sheets after three passes rolling are enhanced by 37 and 39%, respectively, compared to the as-cast alloy. Meanwhile, the tensile fracture mode was ductile fracture which was different from the ductile–brittle fracture of as-cast.

Numerical Estimation of Rolling Load and Torque for Hot Flat Rolling of HCSS316 at Low Strain Rates Based on Mean Temperature

Numerical estimation of rolling load and torque often showed large discrepancies when compared with experimental values. This was attributed to difficulty in estimating the mean rolling temperature from the available data. This work is thus directed at obtaining a good estimate for the mean rolling temperature which can effectively be used for load and torque estimates. Hot flat rolling stimulation by use of the Bland and Ford’s cold rolling (HRBF) theory confirmed the reverse sandwich effect in selected carbon steels at low strain rates. In this work, the effect of pass reduction on rolling temperature distribution, yield stress and rolling load were studied for AISI Type 316 stainless steel (HSCSS316). For this new simulation, at low and high strain rates, results showed that the ratio of experimental to calculated rolling load and torque were higher at lower reduction than at higher reduction. These results confirmed excess load and torque in the hot rolling of HSCSS316 low reductions. The results obtained from Hot Rolling Bland and Ford’s Theory based on Root Mean Square rolling temperature were in good agreement with values obtained using Reverse Sandwich Model and the Reverse Sandwich- Hot Rolling Bland and Ford’s Program under the same rolling conditions.

Interfacial layers evolution during annealing in Ti-Al multi-laminated composite processed using hot press and roll bonding

Ti-Al multi-laminated composites have great potential in high strength and low weight structures. In the present study, tri-layer Ti-Al composite was synthesized by hot press bonding under 40 MPa at 570 °C for 1 h and subsequent hot roll bonding at about 450 °C. This process was conducted in two accumulative passes to 30% and to 67% thickness reduction in initial and final passes, respectively. Then, the final annealing treatments were done at 550, 600, 650, 700 and 750 °C for 2, 4 and 6 h. Investigations on microstructural evolution and thickening of interfacial layers were performed by scanning electron microscopes, energy dispersive spectrometer, X-ray diffraction and micro-hardness tests. The results showed that the thickening of diffusion layers corresponds to amount of deformation. In addition to thickening of the diffusion layers, the thickness of aluminum layers decreased and after annealing treatment at 750 °С for 6 h the aluminum layers were consumed entirely, which occurred because of the enhanced interdiffusion of Ti and Al elements. Scanning electron microscope equipped with energy dispersive spectrometer showed that the sequence of interfacial layers as Ti3Al-TiAl-TiAl2-TiAl3 which are believed to be the result of thermodynamic and kinetic of phase formation. Micro-hardness results presented the variation profile in accordance with the sequence of intermetallic phases and their different structures.

EFFECTS OF ROLLING DEFORMATION ON TEXTURE AND LPSO PHASE OF SPRAY-DEPOSITED MAGNESIUM ALLOYS CONTAINING Nd

Mg alloys have been applied widely as structural materials over the past decades, with low density, high specific strength, stiffness, specific elastic modulus, and high recycling rate. However, their features of poor ductility and formability at room temperature have limited their application due to hexagonal close-packed crystal structure with less independent slip systems. Grain refinement and texture randomization are two means to activate other slip systems. In this work, the billets of Mg-9Al-3Zn-1Mn-6Ca-2Nd alloy produced by spraying deposition method (the Osprey process) were studied in order to analyze the effect of rolling deformation at 350 °C and pass reduction e =20%, 25% and 30% on texture and microstructure evolution of an extruded size-asymmetry Mg alloy by SEM, TEM and XRD. The results show that under the condition of reduction of e =20% at 350 °C, a long-period stacking ordered phase with 24R structure was formed in (Ca, Nd)Al2 phase (C15 Laves phase ). All of basal texture (0002), prismatic texture {1010} , and pyramidal texture {1012} were activated, with pole density level weakened while pass reduction increased (e =20% , 25% and 30% ), namely, texture randomization achieved in Mg alloy, with main causes of nanometer-sized dispersed C15 phase impeding dislocation movement 第938-944页 pp.938-944

Analysis of temperature asymmetry of aluminum alloy thick plate during snake hot rolling

In order to study the temperature distribution of aluminum alloy thick plate during snake hot rolling, several coupled thermo-mechanical models using finite element method (FEM) were established. Effects of different factors on temperature distribution of the plate and the bending behavior due to temperature difference were analyzed. Temperature asymmetry coefficient was defined in this study. The results show that the temperature distribution of plate is asymmetrical and the temperature of the lower surface is higher than the upper surface during snake hot rolling, in which the maximum α can gd reach 58 °C/m. The asymmetric coefficient was increased with the increase of rolling velocity and speed ratio. Different ways of heat exchange play different roles in the temperature distribution. Friction heat and deformation heat play dominant role in hot rolling process and pass interval time and their weight influences were 47 and 69 %, respectively. The bending curvature is increased with the increase of temperature difference and pass reduction and decreased dramatically with the increase of initial thickness. The FEM results agree well with experimental results.

Review of research status and development direction of dieless drawing

Dieless drawing is a flexible forming technology without using the conventional die to achieve plastic deformation of a workpiece. It has many advantages such as low drawing force, large area reduction in a single pass, high efficiency, low energy consumption. So it has broad potential application prospects in the metal forming field, especially suitable for difficult-to-form metal materials such as low plasticity, high strength and high frictional resistance materials. This paper gives a comprehensive review on the dieless drawing technology, including its applications, principles, deformation law and forming processes. The problems restricting its industrialization, such as instability and size fluctuation, have also been discussed. Precise control of processing parameter particularly temperature distribution of the dieless drawing can reduce the size fluctuation of the product, but the diameter variation is still large compared with classical die drawing. Intelligent dieless drawing technology and semi-constraint forming technology which combines dieless drawing and die drawing or rolling are effective approaches to solve these problems.

Evolution of microstructure, texture and mechanical properties of SiC/AZ31 nanocomposite during hot rolling process

Magnesium matrix nanocomposite (1vol.% nano-SiCp/AZ31) sheets were successfully fabricated by hot rolling at 350°C with per pass reduction of 15% and total reduction up to 84%. Microstructure and texture evolution of the nanocomposites during hot rolling were investigated. Twinning and associated dynamic recrystallization (TDRX) were the dominant features at the initial stage of hot rolling. With the increase of rolling passes, grains were refined gradually due to dynamic recrystallization (DRX) and distribution of nanoparticles was also well modified. Meanwhile, shear bands became denser and longer with proceeding of hot rolling. Basal texture splitting along transverse direction was observed during hot rolling and intensity of the basal texture first increased and then showed a sharp decrease, while the uniformity kept increasing. Mechanical properties of the nanocomposite sheets were substantially enhanced. Compared with that of the as-cast nanocomposite, yield strength of the 11 passes hot-rolled sheet was more than doubled. Mechanical properties of the nanocomposite sheets showed a distinct anisotropy along rolling direction and transverse direction.

Microstructure, texture and mechanical properties evolution of pre-twinning Mg alloys sheets during large strain hot rolling

The effect of pre-twinning process on dynamic recrystallization, texture and mechanical properties of Mg alloys sheets was investigated by rolling pre-compressed AZ31 Mg sheets at 350°C. Two types of pre-compressed sheets with different initial texture component were rolled by 60% thickness reduction in a single pass for observation. Microstructure, texture and mechanical properties evolution during large strain rolling were carefully investigated. The results show that dynamic recrystallization is greatly promoted by pre-compression process. Twin structures are more effective in enhancing dynamic recrystallization than pre-deformation strain stored during compression. Besides slip, detwinning is regarded as an important deformation mode when pre-twinning samples are rolled along their compression directions. Low temperature annealing of pre-twinning samples prior to rolling hinders detwinning process, resulting in an increase of yield stress. The basal texture and plane-anisotropy are greatly weakened in the sample rolled perpendicular to the pre-compression direction. The mechanical properties of rolled sheets were promoted by pre-twinning process.

Deformation behavior of AZ31 Mg alloys sheet during large strain hot rolling process: A study on microstructure and texture evolutions of an intermediate-rolled sheet

Commercial AZ31 Mg alloys sheet was hot rolled by 50% thickness reduction in a single pass. The rolling process was manually interrupted before the entire sheet was rolled, and an intermediate-rolled sample was obtained. The microstructure, texture and mechanical responses on both surface and mid-layer of the intermediated-rolled sample were investigated. Our results show that the thickness gradients of microstructure and texture of as-rolled sheet were mainly caused by heterogeneously severe deformation when the surfaces of the sheet were bitten by the rollers. Both discontinuous and shear bands related dynamic recrystallization were observed. The recrystallized grains inside shear bands first nucleated in twins. The refined grains exhibited a strong basal texture with random distribution of 〈112¯0〉 direction. Discontinuous release of deformation strain during hot rolling led to strain flow localization, which resulted in formation of shear bands. Shear bands helped to coordinate the strain distribution between two nearby regions to prevent cracking in large strain rolling.

Research of Lubrication Model and Surface Quality in Cold-Rolling Copper Alloy Using O/W Emulsions

Abstract A theoretical model for cold-rolling copper alloy in mixed lubrication regime was developed based on the average volume flow model and asperity flattening model. The developed scheme was able to calculate oil concentration λ d at any point within work zone, lubricant pressure, contact area ratio and film thickness ratio with different oil viscosity, pass reduction and the initial oil concentration λ ds . According to the lubrication model, for getting good lubrication and cooling effect of emulsions in rolling process, the rolling oil viscosity was selected in the range from 40 mm 2 /s to 50 mm 2 /s, the pass reduction about 30% and the initial oil concentration λ ds of emulsion in the range from 0.02 to 0.05. For verifying the lubrication model, the last nonseizure load was tested by the four-ball tests to confirm oil viscosity and initial oil concentration, and the rolled copper alloy surface topographies were analyzed to confirm pass reduction. The results show that the calculation data agree well with the measured data from experiment. They provide technical references for selecting rolling process parameters and emulsions.

Bending analysis and control of rolled plate during snake hot rolling

In order to study the bending behavior of aluminum alloy 7050 thick plate during snake hot rolling, several coupled thermo-mechanical finite element (FE) models were established. Effects of different initial thicknesses, pass reductions, speed ratios and offset distances on the bending value of the plate were analyzed. ‘Quasi smooth plate’ and optimum offset distance were defined and quasi smooth plate could be acquired by adjusting offset distance, and then bending control equation was fitted. The results show that bending value of the plate as well as the extent of the increase grows with the increase of pass reduction and decrease of initial thickness; the bending value firstly increases and then keeps steady with the ascending speed ratio; the bending value can be reduced by enlarging the offset distance. The optimum offset distance varies for different rolling parameters and it is augmented with the increase of pass reduction and speed ratio and the decrease of initial thickness. A proper offset distance for different rolling parameters can be calculated by the bending control equation and this equation can be a guidance to acquire a quasi smooth plate. The FEM results agree well with experimental results.

Improved mechanical properties of AZ31 magnesium alloy sheets by repeated cold rolling and annealing using a small pass reduction

Much less attention has been paid to improve the mechanical properties of magnesium alloy by cold rolling due to its poor room temperature workability. So the present work attempts to improve the mechanical properties of AZ31 magnesium alloy sheets processed by repeated cold rolling and annealing using a small pass reduction in correlation with the concurrent microstructure evolution. The obtained results indicated that after 87% total repeated cold rolling reduction and annealing, the grain microstructure of AZ31 alloy sheet was successfully refined from 22.3μm to 7.4μm. The alternating change induced by repeated cold rolling and annealing between deformed microstructure and recrystallized microstructure resulted in the continued refinement of grains. After repeated cold rolling and annealing, the mechanical properties of AZ31 alloy sheets were improved, especially the Erichsen value (IE) of the 87% total rolled sample in annealed condition was significantly increased by more than 36% compared to that of the as-received sample under the same thickness. Improving mechanical properties of AZ31 alloy sheets processed by repeated cold rolling and annealing are ascribed to the grain refinement and weakened basal texture. Finally, 0.40mm thick thin sheets with good comprehensive mechanical properties were obtained by repeated cold rolling and annealing using a small pass reduction.

Development of Hot Rolled Strips for Internal Plates of Automobile

The hot rolled strips for internal plates of automobile was developed by taking the technologies of low-carbon softening steel, including strictly control the chemical composition content during the steel melting and optimization of the rolling processes in the thin slab continuous casting and rolling line. The results showed that when carbon content was 0.04%, adding aluminum content or reducing silicon content and manganese content, reducing the reduction in previous rolling passes and increasing the reduction of the finishing pass at high temperature was beneficial for reducing the yield strength and tensile strength of the hot rolled strips. The precipitate of the samples after annealing showed that the precipitate of aluminum-nitride increased significantly at 850°C. And the texture of the samples after annealing showed that the main texture was {110} &lt;001&gt; and its intensity was 1.7-2.0, annealing with hot rolled strips did not benefit the advantageous texture. Tension-tension fatigue properties of hot rolled strips and cold rolled ones were determined, the results showed that the fatigue properties of hot rolling strips were rather higher than that of cold rolled ones. In the stamping experiments of some automobile parts, there was not any drawback, and the forming properties of hot rolling strips were equal to that of cold rolled ones. It was feasible to replace the cold rolled strips with the hot rolled ones for the internal plates of automobile.

Effects of rolling parameters of snake hot rolling on strain distribution of aluminum alloy 7075

The realization way of snake rolling was introduced. Flow velocity, strain and stress distribution of 7075 aluminum alloy plate during snake rolling and symmetrical rolling were analyzed in Deform 3D. Effects of velocity ratio, offset distance between two rolls and pass reduction on the distribution of equivalent strain and shear strain were analyzed. The results show that flow velocity and equivalent strain on the lower layer of the plate are larger than those of the upper layer because of the larger velocity of the lower roll and the gap is increased with the increase of velocity ratio and pass reduction. The shear strain of rolling direction in the center point is almost zero during symmetrical rolling, while it is much larger during snake rolling because of the existence of rub zone. The shear strain is increased with the increase of velocity ratio, offset distance and pass reduction. This additional shear strain is beneficial to improve the inhomogeneous strain distribution.

Experimental and Numerical Investigations of the Plastic Deformation during Multi-Pass Asymmetric and Symmetric Rolling of High-Strength Aluminum Alloys

For understanding the distribution of plastic deformation induced by asymmetric rolling (ASR), multi-pass ASR and symmetric rolling (SR) experiments combined with the finite element simulation were used for high-strength aluminum alloy in the present study. The influence of reduction per-pass on the shear / effective strain distributions were studied via different ASR processes. By measuring the shear angle (θ, the angle between the reference mark before and after rolling) of rolled sheets, redundant shear strain and equivalent strain were calculated. It is shown that with equal total thickness reduction for ASR and SR, ASR can induce much more shear deformation through the thickness. By calculating the evolution of redundant shear strain and total equivalent strain for different ASR routines, it indicates that small pass reduction could be much favorable to the strain accumulation than that of the large pass reduction under a same total reduction in ASR process. Also, the influence of shear stress on the strain distribution and the through-thickness strain distribution were studied and evaluated with FEM analyses.

Method for the Depletion of the Basal Texture in Rolled AZ31 Magnesium Sheets

The deformation and hardening mechanisms of magnesium usually lead to a typical basal orientation of crystals during a production of sheets by forming techniques. The basal texture related anisotropic property behavior and especially the further decrease in formability at room temperature is disadvantageous and undesired for subsequent rolling and final forming processes.The objective of this work is to find methods to improve these texture-related properties and the cold forming ability of magnesium sheets. Firstly, rolling at different temperatures and pass reductions, with the goal of weakening the basal texture component in semi-finished products is investigated, based on the advantageous initial texture and microstructure of twin-roll-cast (TRC) magnesium strips. In this context, texture and microstructure development is examined after a particular multi-pass rolling and heat treatment processes. Twin-roll-cast magnesium strips of alloy AZ31, with an initial thickness of 4.5 mm, rolled to a final thickness of 1.2 mm, are used as feedstock.Secondly, a new thermo-mechanical magnesium strip treatment has been developed in order to completely disintegrate the basal texture and intentionally generate only non-basal orientations with high Schmid-factors for the easy-to-activate basal slip systems. This process, which is designed as a final strip treatment, has been investigated regarding its texture change effect on rolled 1.2 mm AZ31 sheets, which also originate from TRC feedstock.It has clearly been found that the developed rolling technology for TRC feedstock leads to a significantly reduced basal texture due to grain boundary rotation and recrystallization at those rotated regions. The application of the separately developed strip treatment effects a complete elimination of the basal texture in a large volume of the sheet. Applying both technologies on magnesium sheets results in a tremendous increase in formability at room temperature as a consequence of the altered texture.