Continuous Annealing Research Articles

Toward High‐Temperature Stability of PTB7‐Based Bulk Heterojunction Solar Cells: Impact of Fullerene Size and Solvent Additive

The use of fullerene as acceptor limits the thermal stability of organic solar cells at high temperatures as their diffusion inside the donor leads to phase separation via Ostwald ripening. Here it is reported that fullerene diffusion is fully suppressed at temperatures up to 140 °C in bulk heterojunctions based on the benzodithiophene‐based polymer (the poly[[4,8‐bis[(2‐ethylhexyl)oxy]‐benzo[1,2‐b:4,5‐b′]dithiophene‐2,6‐diyl][3‐fluoro‐2‐[(2‐ethylhexyl)carbonyl]‐thieno[3,4‐b]thiophenediyl]], (PTB7) in combination with the fullerene derivative [6,6]‐phenyl‐C71‐butyric acid methyl ester (PC70BM). The blend stability is found independently of the presence of diiodooctane (DIO) used to optimize nanostructuration and in contrast to PTB7 blends using the smaller fullerene derivative PC70BM. The unprecedented thermal stability of PTB7:PC70BM layers is addressed to local minima in the mixing enthalpy of the blend forming stable phases that inhibit fullerene diffusion. Importantly, although the nanoscale morphology of DIO processed blends is thermally stable, corresponding devices show strong performance losses under thermal stress. Only by the use of a high temperature annealing step removing residual DIO from the device, remarkably stable high efficiency solar cells with performance losses less than 10% after a continuous annealing at 140 °C over 3 days are obtained. These results pave the way toward high temperature stable polymer solar cells using fullerene acceptors.

Study of Texture in 6016 Aluminum Alloy during Processing

The evolution of texture in AA6016 alloy during processing was systematically investigated. The hot-rolled 6016 plates were cold-rolled to 0.9mm through three different rolling processes. One was directly rolled to 0.9mm, the other two were rolled to 1.8mm and 2.3mm, respectively, followed by intermediate annealing at 360°C for 2h, and then rolled to 0.9mm. Finally, the three kinds of cold rolled plates were performed continuous annealing at 560oC. The textures and microstructures of each stage were characterized by the X-ray diffraction and electron back scattering diffraction (EBSD) techniques. The results show that the texture of hot-rolled sample is mainly composed of Brass, S and Copper; the relative amount and maximum density changed after 1st cold-rolling. After intermediate annealing, the Cube and Cube+ND20 texture replace the deformation texture and rise with the rolling reduction. Then the conducting of final cold rolling results in the decrease of Cube and Cube+ND20 component and increase of deformation texture. After the continuous annealing, R, Brass-R, Goss, Cube and Cube+ND20 components are observed. Particle stimulated nucleation (PSN) and nucleation at shear bands dominate the competition of recrystallization.

Effect of Hot Rolling Parameters on Excess Phase Precipitation in Two-Phase Ferritic-Martensitic Steels

Results are given for studying the effect of hot rolling parameters on morphological features of the structure and precipitation in hot rolled products destined for further cold rolling and heat treatment in a continuous annealing line. Temperatures for the end of rolling and coiling are varied with hot rolling of a laboratory melt. Depending on the combination of temperatures for the end of rolling and coiling temperature, the amount of precipitates and their preferred location vary.

Vanadium microalloying for ultra-high strength steel sheet treated by hot-dip metallising

Ultra-high strength steel sheets have been subjected to heat treatments that simulate the thermal cycles in hot-dip galvanising and galvannealing processes and evaluated with respect to their resulting mechanical properties and microstructures. The steels contained suitable contents of carbon (∼0.2%), manganese (1.2%) and chromium (0.4%) to ensure that they could be fully transformed to martensite after austenitisation followed by rapid cooling in a continuous annealing line, prior to galvanising. Different contents of vanadium (0–0.1%) and nitrogen (0.002–0.012%) were used to investigate the possible role of these microalloying elements on the strength of the tempered martensite. Vanadium, especially when in combination with a raised nitrogen content, helps to resist the effect of tempering so that a larger proportion of the initial strengthening is preserved after the galvanising cycle, giving tensile strength levels exceeding 1000 MPa. Different deoxidation practices using aluminium or silicon have also been included. These showed similar strength levels at corresponding carbon contents but the bendability of the Si-killed steel sheet was considerably superior. Microstructural examinations have been made on the annealed steels but the reason for the beneficial effect of vanadium is still not fully explained. It is concluded that microalloying with vanadium is a very promising approach in the development of corrosion-resistant ultra-high strength steel sheet products.

Low temperature polycrystalline silicon with single orientation on glass by blue laser annealing

We report the achievement of low-temperature polycrystalline silicon (LTPS) thin-films with a single orientation on glass by using continuous wave blue laser annealing (BLA) of amorphous silicon (a-Si). The BLA is administered in multiple shots and with increasing number of shots, grain size increases and all grains follow a single orientation. Because the absorption coefficient of a blue laser (BL) in poly-Si is less than that in a-Si, the amount of the un-melted Si at the bottom is gradually reduced with increasing number of shots, resulting in near complete melting of the whole Si layer. In this study, irradiation of a 150-nm-thick a-Si film with 200 BL (445nm) shots achieves a poly-Si film having an average grain size of about 4μm and single orientation in the (100) direction.

Modelling of strip buckling in the continuous annealing process

This paper considers the equipment and technological characteristics of continuous annealing process (CAP) to solve the issue of strip buckling. It analyses the mechanism of hot buckling and transverse compressive stresses from internal and external forces. A basic description of strip buckling is given together with a new concept of a buckling index. The critical buckling condition is presented, and the model of strip buckling index in the CAP is proposed. The distribution of strip buckling index in different sections of the process is analysed quantitatively along with the influence of incoming strip shape, transverse temperature difference, roller profile, friction coefficient, set tension and strip processing speed on the strip hot buckling index in CAP. Results show that with the influence of thermal stress, the transverse compressive stress that affects the middle part of the strip is largest in the heating section, which is also where hot buckling occurs most easily; centripetal force is dominant in the soaking and slow cooling sections, and in these sections buckling occurs at the roller shoulder. In different sections, the strip buckling index distribution differs, whereas the influence of other parameters on buckling index remains similar.

Effects of annealing cooling rates on mechanical properties, microstructure and texture in continuous annealed IF steel

The mechanical properties, microstructure and texture of interstitial-free (IF) steel processed through continuous annealing routes under five cooling rates (5 °C/s, 50 °C/s, 200 °C/s, 500 °C/s and 1000 °C/s) have been studied. The cooling rates of 200 °C/s, 500 °C/s and 1000 °C/s are defined as ultra-fast cooling rates. This paper focuses on the differences of mechanical properties, microstructure and texture evolution between ultra-fast and common cooling rates (5 °C/s, 50 °C/s) for the first time. The overall structural features of specimens were observed by optical microscopy and nano-sized precipitates were observed by transmission electron microscope (TEM) on carbon extraction replicas. Texture measurement was carried out using D8 advance X-Ray Diffraction (XRD) and the (110), (200) and (112) pole figures were determined. The yield strength increases with increasing cooling rates, from 96 MPa under the cooling rate of 5 °C/s to 136 MPa under the cooling rate of 1000 °C/s, while the ultimate tensile strength changes very little (around 280 MPa). The samples annealed under the cooling rates of 5 °C/s and 500 °C/s have low rave values (2.13 and 2.21 respectively). By contrast, the samples in cases of 50 °C/s, 200 °C/s and 1000 °C/s possess higher rave values (2.32, 2.40 and 2.51 respectively). Three morphologies of TiN particles can be observed in all samples. TiN, with CaO and SiO2 acting as heterogeneous nuclei, is prone to have big size. The size of pure TiN precipitates deceases as increasing of cooling rates. FeTiP is found near TiC precipitates under the cooling rate of 5 °C/s. The sample annealed under the cooling rate of 5 °C/s has the weakest {111} <112> and {111} <110> orientations. The intensity of {111} <110> component increases as the cooling rate increases from common cooling rates of 5 °C/s and 50 °C/s to ultra-fast cooling rates of 200 °C/s, 500 °C/s and 1000 °C/s. The intensity of {011} <100> orientation decreases as the cooling rate increases from 5 °C/s to 500 °C/s. The relationship between r value, microstructure and texture components has been studied in this paper.

Effect of ferrite-martensite interface morphology on bake hardening response of DP590 steel

The effect of martensite spatial distribution and its interface morphology on the bake hardening characteristics of a dual phase steel was investigated. In one case, typical industrial continuous annealing line parameters were employed to anneal a 67% cold rolled steel to obtain a dual phase microstructure. In the other case, a modified annealing process with changed initial heating rates and peak annealing temperature was employed. The processed specimens were further tensile pre-strained within 1–5% strain range followed by a bake hardening treatment at 170°C for 20min. It was observed that industrial continuous annealing line processed specimen showed a peak of about 70MPa in bake-hardening index at 2% pre-strain level. At higher pre-strain values a gradual drop in bake-hardening index was observed. On the contrary, modified annealing process showed near uniform bake-hardening response at all pre-strain levels and a decrease could be noted only above 4% pre-strain. The evolving microstructure at each stage of annealing process and after bake-hardening treatment was studied using field emission scanning electron microscope. The microstructure analysis distinctly revealed differences in martensite spatial distribution and interface morphologies between each annealing processes employed. The modified process showed predominant formation of martensite within the ferrite grains with serrated lath martensite interfaces. This nature of the martensite was considered responsible for the observed improvement in the bake-hardening response. Furthermore, along with improved bake-hardening response negligible loss in tensile ductility was also noted. This behaviour was correlated with delayed micro-crack initiation at martensite interface due to serrated nature.

Effect of Treatment Temperature Regimes in a Continuous Annealing Unit on Two-Phase Ferritic-Martensitic Steel Mechanical Properties

Features of structure and property formation are studied for cold-rolled product in two-phase ferriticmartensitic steels by modeling heat treatment in a continuous annealing unit (CAU) of six laboratory melts of different chemical composition intended for preparing steels of different strength classes according to EN10338:2013. Steel of some melts, apart from alloying with elements currently used extensively, are additionally alloyed with aluminum. Hot- and cold-rolling processing regimes simulate those used under production conditions. Results of modeling heat treatment in a CAU by different regimes show an increase in strength and a reduction in ductility properties with a reduction in overageing temperature. Rolled product of steel alloyed with aluminum has lower strength properties, ratio of yield to ultimate strengths, but better relative elongation values.

Research of the Continuous Annealing Process to Eliminate the "Band" Feature of Dual Phase Steels

A new continuous annealing process which can eliminate the "band" feature of dual phase steels has been designed. The sheets were annealed in MULTIPAS annealing simulator under variation of annealing temperature. The microstructure evolution of dual-phase steel sheets annealed at intercritical temperatures, were analyzed by optical microscopy and scanning electron microscopy. And the properties were compared with the sheets which annealed by the existing annealing process. The results show that: the "band" feature of dual-phase steel can be effectively eliminated by the optimizing continuous annealing process,and the mechanical properties are improved.

Preparation of Two-Phase Ferritic-Martensitic Steels of Different Alloy Systems in Continuous Annealing Units

Features of structure and property formation, processing aspects for preparation of cold-rolled, including hot-dip galvanized, product of two-phase ferritic-martensitic steels with the most typical alloying system (silicon, manganese, and chromium), and also additional alloying with molybdenum, are studied with heat treatment in continuous annealing units (CAU). Cold-rolled product of different thickness is heat treated (HT) in the intercritical temperature range established from results of dilatometric measurements. It is established that there is formation in the test steels of a ferritic-martensitic structure with some proportion of bainite and residual austenite in the form of an MA-component (region with a size of several microns consisting of martensite and residual austenite). With modeling of the HT regime typical for CAU steel alloyed with molybdenum has strength 100–150 MPa higher than steel of the typical alloy system, and this is connected with a higher proportion of strengthening phase within the structure.

Nonlinear Process Monitoring Using Regression and Reconstruction Method

In this paper, a new regression and reconstruction method for process monitoring is proposed. The main contributions of the proposed approaches are as follows: 1) a new nonlinear regression algorithm is proposed to extract the output-relevant variation, which, compared with the conventional algorithm, builds a more direct relationship between the input and output variables; 2) the fault direction is determined by possible fault magnitude of every possible principal component; and 3) the fault is effectively diagnosed compared with the conventional kernel partial least-squares (KPLS) method. The proposed method is applied to a continuous annealing process and is compared with the KPLS method. Experiment results show that the proposed method can more effectively detect fault compared with the KPLS method. In addition, the selection of fault direction is more accurate using the proposed reconstruction algorithm compared with the KPLS reconstruction approach.

A simulation study of pearlite-to-austenite transformation kinetics in rapidly heated hot-rolled low carbon steel

The main aim of the present research was to obtain an optimized microstructure with adequate mechanical properties in a low carbon steel. The effect of microstructure on kinetics of austenite transformation was simulated. A 3.2mm hot rolled steel was subjected to continuous annealing to obtain properties of Dual Phase 590 grade. Kinetics of austenite transformation was studied with respect to the condition of just pearlite dissolution to form austenite under rapid heating. Annealing parameters were based on process conditions of dual phase steel production in a continuous annealing line. DICTRA was used to simulate heating rates of the order 10–500°C/s with peak temperatures in the range 750–850°C to predict isothermal annealing time required for complete dissolution of pearlite into austenite under different temperature-heating rate conditions. Simulation results showed dependency of temperature and heating rate on austenite transformation time. Interestingly, no significant effect of heating rate on complete pearlite dissolution into austenite was evident. Results were validated with limited experimentation on Gleeble. Microstructure analysis validated the simulation results to be accurate. The observations have pertinent inputs while designing industrial continuous annealing line parameters where rapid heating rates are generally encountered (10–20°C/s).

허스롤 목 부위 형상 변화에 따른 열응력 분포 변화 유한요소해석

Abstract The hearth roll, which transfers the cold-rolled strip sheet in a Continuous Annealing Line (CAL), is always subjected to changes in the surface temperature and subsequently experiences thermal stress in service. These variations lead to the generation of thermal cracks on the hearth roll surface as well local plastic deformation. We performed finite element analysis to predict the thermal stress changes on the hearth roll surface and designed the collar shape of the hearth roll to minimize these thermal stresses. Results show that the hearth roll with a collar having an obtuse angle is much more effective than a hearth roll with collar having a right angle when the tangential stress, which is one of main causes leading to surface cracks, is compared for the various conditions. It was found that the tangential stress and the temperature on the surface of hearth roll can be reduced by 51.9% and 26℃ if the shape of roll on collar is re-designed. Key Words

Physical and Numerical Simulation of Cold Rolling and Heating during Continuous Annealing of DP Steel Strips

Development of fast and efficient finite element model for rolling industrial grades of two DP steels was the subject of the present paper. Basis of the finite element framework, as well as material model development stages, are presented first. Model validation with experimental measurements is shown next. Finally, selected examples of multi scale modelling including microstructure level are presented to complement presented investigation and show possibilities of future developments.

Energy Saving In Continuous Annealing Line Using Heating Optimization

Energy consumption of Iron and Steel Industry sector in Turkey has the highest share in final energy consumption. In the globalized world, day by day, worsening of the conditions of competition and negative environmental pressures, more efficient energy usage is come to the forefront. Growing industries can survive by providing efficient energy consumption and effective energy follow-up. The failure of businesses is become inevitable with ineffective and inefficient usage of energy resources used in the production. Energy savings in the continuous annealing line which is the subject of this article is an important issue and it is based on many parameters. Measuring strip's temperature is so important to continuous annealing line control in the annealing automation system. Increasing or decreasing the oven temperature provides the process control with the adjustment of the heater which is specific heating capacity in these furnaces. Each strip annealing temperature is different which depends on the strip quality. Also strip thickness, strip width and the line speed are the other factors of the oven temperature conditions. It needs to realize the production of an optimal quality ranking to increase the line speed. This improves the production level and because of the oven temperature changes in the order that causes the reduction of costs due to energy savings, optimized production is achieved. Finding the most suitable production sequence is modeled by fuzzy goal programming functions used the above parameters were investigated

Comprised of the Organization and Performance of Non-Oriented Electrical Steel with Cold and Heat Slab

The structure, texture, second phase and magnetic properties of non-oriented electrical steel with cold and heat slab were comprised through the production test. The research result shows that the grain size of hot rolled plate by cold slab is less than that of hot rolled plate by hot slab. But after cold rolling and annealing process, the grain size is consistent. Microstructure of hot rolled coil is recrystallized microstructure and the dispersion degree of texture orientation is high. Deformation makes the texture enhancement in cold rolling which become the strong texture based on {001} {111} and &lt;110&gt; texture. The Ti element has aggregation which can form hard impurities as TiN and TiSN to obstruct the recrystallization. Micro fine TiC formed in the annealing process which would block magnetic domain movement and reduce the magnetic properties of the product. MnS is precipitated impurities and the coarsening of MnS phase can reduce the domain block by improving the continuous annealing temperature and the magnetic field would be optimization.

Low-Cost Grain Oriented Silicon Steels Manufactured by Continuous Annealing

Low-cost grain oriented silicon steel produced by continuous annealing, low slab-heating temperature, and omitting normalization annealing is explored and analyzed. This type of grain oriented steel is designed to replace the non-oriented steels used for the production of transformers of medium and small sizes as specified in all GO steel producers catalogs. Fully secondarily recrystallized structure with magnetic properties of P1.7 = 2.04 W kg−1 and B8 = 1.76 T is obtained at temperature of 1050 °C within 10 min in the condition of two-stage cold rolling, whereas one-stage cold rolling method fails to initiate abnormal grain growth in the same processing parameters. The success of fully secondary recrystallization using two-stage cold rolling method is ascribed to the more important role of sufficient amount of Goss seeds in decarburized samples as in CGO steels than the stronger {111} texture as in HiB silicon steels. It is further determined that by two-stage cold rolling technique, a higher secondary stage rolling reduction leads to a lower secondary recrystallization starting temperature and a shorter secondary recrystallization staring time related with a finer grain size. The reasons for the high iron core loss related by continuous annealing are connected to the higher number of deviated Goss grains scattering toward {210} or Brass orientations, the residual inhibitors and the imperfect grain size and morphologies. The reasons for the failure in abnormal grain growth by one-stage rolling are also discussed.

Fabrication of thermal enduring FBG sensor based on thermal induced reversible effect

In this study, the thermal degradation of a fiber Bragg grating written on hydrogen loaded photosensitive Germanium/Boron co-doped fiber with 193nm ArF excimer laser is investigated. A noteworthy increase in the grating reflectivity during annealing at 425°C is observed indicating a thermal induced reversible effect deviating from the general thermal decay behavior. Both stepwise and continuous annealing procedures indicate a similar trend in the accelerated aging characteristics when analyzed with respect to demarcation energy (Ed). In the characterization of the lifetime of the treated FBG, a thermal sustainability of thousand years with less than 2% decay resulting in a grating reflectivity of 98% is observed at 300°C for a grating as short as 10mm. The ease of characterization and obtaining detailed information through the analysis of transmission spectra is also considered as an advantage in this study. These thermal enduring FBG sensors based on thermal annealing over a temperature range of 200–400°C lay the foundation for a new direction of research in the investigation of durable temperature sensors.

Effect of Different Cooling Rates on Microstructure and Property of Continuous Annealing IF Steel

The influence of different annealing cooling rates on microstructure,precipitation of the second phase and mechanical properties of IF steel was studied. The recrystallizing behavior of IF steels was analyzed by batch annealing process. After confirming the recrystallizing temperature of IF steel, the simulations of different continuous annealing cooling rates (5°C/s, 20°C/s, 50°C/s, 200°C/s 500°C/s and 1000°C/s ) were performed. At the same time, combined with TEM and XRD, the precipitating behavior and microstructure texture were analyzed. The results showed that the recrystallization temperature was speculated between 540°C and 560°C. As the cooling rate increased, the grain sizes became smaller and the yield strength increased significantly. And the tensile strength and elongation were more or less static. The tensile strength remained 240MPa and the elongation kept around 50%. With 1000°C/s cooling rate, the sample performed best with the r-value of 3.03. TiN precipitation was observed. The annealed texture is mostly composed of {111} texture.