Twin-roll Strip Casting Process Research Articles

Experimental Study on the Distribution of Heat Flux along Contact Arc in Twin-Roll Continuous Strip Casting

Heat flux between molten metal and casting rolls plays a key role in improving the quality of the strip, studying on the interfacial heat flux has very important theoretical significance and practical value. According to the contact form and the heat flux characteristics of molten metal and casting rolls in twin-roll strip casting process, a set of measuring equipments has been developed, which are used to measure the heat flow of the interface between the molten metal and solid, and a relevant software system has been exploited to acquire and analyze the experiment data. Using the method of combining experimental and numerical computation, we analyze the influence of pouring temperature on the contact interface heat flux. The experimental results show that the higher the pouring temperature , the greater the summit of heat flux density and the shorter time to the summit heat flux are, but when the pouring temperature reaches a certain critical value, the summit of heat flux will decrease with the increase of pouring temperature.

Effect of Hot Rolling on Texture, Precipitation, and Magnetic Properties of Strip-Cast Grain-Oriented Silicon Steel

An ultra-low carbon grain-oriented silicon steel as-cast strip is produced by twin-roll strip casting process, and subsequently subjected to one-pass hot rolling, one-stage cold rolling, primary annealing, and secondary annealing. The effect of hot rolling process on microstructure, texture, and inhibitor evolution is studied. It is shown that the precipitation behavior of AlN particles is significantly affected by the hot rolling temperature and the optimal precipitation temperature is ≈1100 °C. On the other hand, the intensity of Goss texture in hot-rolled sheets is determined by hot rolling reduction, which is limited in the strip casting process and the hot-rolled Goss texture is relatively weak compared to the conventional process. The primary annealed Goss texture can originate from the cold rolling process and this texture is homogeneous through the thickness, besides the inherited hot-rolled Goss texture mainly presented in the subsurface layer. Thus, relatively strong Goss texture in primary annealed sheets is obtained. The results indicate that the hot rolling process is an efficient way to optimize the texture and precipitation in strip-cast silicon steel, and relatively good magnetic properties can be obtained by the strip casting process.

Effect of Rapid Thermal Process on the Recrystallization and Precipitation in Non-Oriented Electrical Steels Produced by Twin-Roll Strip Casting

A Fe-1.3% Si non-oriented silicon steel strip was produced by twin-roll strip casting process, and subsequently treated with cold rolling and annealing. The effect of heating rates on the recrystallization and precipitation behavior of second phase particles (AlN and MnS) was investigated by MMS-200 thermal mechanical simulator. It was found that the recrystallization area fraction decreased obviously with the increase of heating rate. At the heating rate of 5 °C/s, the recrystallization rate gradually decreased with the extension of holding time, but it increased at the rapid heating rates. The particle’s sizes mainly concentrated in 50~200 nm at the heating rate of 5 °C/s during annealing. The number of particles under 50nm increased gradually and the number of precipitates between 50~400 nm reduced significantly when the heating rate was increased to 50~300 °C/s. The results indicated that the rapid heating rate could refine the size of precipitates and decrease the number of particles above 50nm.

Modelling of heat flow and interdendritic crack formation in twin-roll strip casting of aluminium alloys

Preliminary mathematical analyses of different interdendritic cracks associated with variation of heat transfer and generation of interdendritic strain in horizontal twin-roll strip casting have been investigated. A 1-D transient finite difference model of heat flow, dendritic solidification and interdendritic thermo-metallurgical strain has been developed. The model contains two cracking criteria to predict qualitatively and quantitatively the tendency of interdendritic crack formation during dendritic solidification of pure aluminium and 6022 aluminium alloy. The model predictions are compared to available analytical methods and previous measurements. This is to verify and calibrate the model where good and reasonable agreements are obtained, respectively. The variations of heat transfer modes during different contact cooling zones and their effects on the generation of interdendritic thermo-metallurgical strain at the surface and central strip locations have been analysed. The model predictions point out that the different contact cooling zones of strip surface and surroundings control the stages of interdendritic crack formation in different mushy regions. The mechanism of interdendritic crack formation in twin-roll strip casting process with previous and present cracking criteria have been explained and discussed. These discussions show the importance of selection of mathematical treatment to predict the stages of interdendritic crack formation.

Fuzzy Controller Optimized by Genetic Algorithm for the Molten Metal Level in the Twin Roll Strip Casting Process

In the twin roll strip casting process, the control for the molten metal level is difficult owing to non-linear and time-varying of the control parameters. In the paper, on the basis of the geometry shape of the molten metal pool and the continuity of metal, the level mathematic model is built. Then a fuzzy control strategy is adopted to control the level. Moreover GA(Genetic algorithm) is used to obtain better fuzzy parameters. Simulations show the fuzzy controller optimized by GA greatly improves the control performance.

Effect of annealing after strip casting on texture development in grain oriented silicon steel produced by twin roll casting

An ultra-low carbon Fe–3%Si grain oriented electrical steel strip was produced by a twin roll strip casting process. Next, the strip with or without annealing was cold rolled and subsequently annealed. The effect of annealing after strip casting on the texture development was studied using macro-/micro texture analysis. Due to the rapid solidification, the precipitation behavior of second phase particles was suppressed and very few particles were observed in the as-cast strip. The direct cold rolled texture was characterized by strong α (<110>//RD) and weak γ ({111}//ND) fibers. While, in the annealed strip, a large number of particles were precipitated during the annealing of the cast strip and these particles hindered the crystal rotation during cold rolling such that part of the initial solidification texture remained in the cold rolled sheet. In the case of the direct cold rolling process, the precipitation occurred before recrystallization during primary annealing. These fine particles had a significant pinning effect on dislocations and further retarded the recrystallization behavior, leading to relatively strong α-fiber in the primary annealed sheet. On the other hand, compared with the fine and dispersed particles precipitated during the strip annealing process, the distribution of particles precipitated during primary annealing were inhomogeneous. Therefore, there was no secondary recrystallization during secondary annealing, which was distinct from the strip annealing process where abnormal growth of Goss grains were observed and the magnetic properties were significantly improved.

Microstructure evolution of eutectic Al–Cu strips by high-speed twin-roll strip casting process

In the present investigation, microstructural evolutions of functionally graded eutectic Al–Cu strips prepared by high-speed twin-roll strip caster at different casting speeds and liquid melt superheats were studied. The as-cast sample was subjected to scanning electron microscope to study the evolution of microstructure of the strip at different casting speeds and liquid melt superheats. At different casting speeds, non-equilibrium eutectic structure observed on the Al–Cu eutectic strip consists of lamellar as well as wavy structure with a distinct boundary. The lamellar microstructure consists of alternating layers of well-bonded α-Al phase and θ-Al2Cu phase. The globular flowery structure within the eutectic matrix was observed on the strip at different liquid melt superheats. The microhardness of the as-cast strip was studied by Vickers hardness tester, and it was found that hardness value increases with increasing casting speed and decreases with increasing liquid melt superheat.

Numerical study on the heat preservation of the ladle used for twin-roll strip casting

To adapt to the requirements of temperature variations in the process of twin-roll strip casting, a three-dimensional mathematical model was developed to analyze the heat transfer and temperature drop in the ladle using the finite volume method in the present study. The results showed that the temperature drop rate of the melt was 1·1 K·min−1 in the ladle of traditional casting, which could not satisfy with the demands in the process of twin-roll strip casting, and the temperature drop rate of the melt was 0·31 K·min−1 when more than 40 mm of a shielding agent was added on the slag surface and nanoporous materials were used as an insulation layer with thickness of more than 16 mm, which is considered to be favourable to provide the suitable temperature drop of the melt in the ladle to maintain the twin-roll strip casting process and improve the strip quality.

Effect of process parameters on solidification of Al-33Cu strip in high speed twin roll strip casting- A numerical study

In twin roll strip casting process, the solidification behavior in the molten pool affects the process efficiency and the product quality which is influenced by the process parameters. Numerical simulations have been carried out to analyze the fluid flow, heat transfer and solidification in high speed twin roll strip caster at different pouring temperatures and roll gaps and the knowledge of heat flux distribution at the liquid metal-roll interface. In the present study a numerical simulation has been carried out for the solidification of Al-33wt% Cu in the twin-roll strip casting system at different pouring temperatures and roll gaps. FLUENT 6.3.16 was used to model fluid flow, heat transfer and solidification behavior during the casting of Al-33wt. % Cu alloy. From the simulation results, the initial pouring temperature of the liquid metal and the roll gap has been optimized for producing quality strips.

Evolution of recrystallization microstructure and texture during rapid annealing in strip-cast non-oriented electrical steels

Non-oriented electrical steel as-cast strip was produced by twin roll strip casting process, and subsequently cold rolled and annealed at heating rates in the range of 3–450 °C/s with the aim to elucidate the effect of heating rate on the evolution of recrystallized microstructure and texture. The average grain size was rapidly increased when the heating rate was increased from 3 to 25 °C/s, and decreased when the heating rate was greater than 25 °C/s. The average grain size did not increase linearly with heating rate, which was related to different degree of nucleation and growth rate. The recrystallization texture exhibited pronounced improvement during rapid annealing. At high heating rate, the Goss and Cube had a higher probability of nucleation of shear bands with high stored energy, while the intensity of the γ-fiber texture was significantly reduced. The highest B50 value attained was 1.803 T at a heating rate of 300 °C/s. The study indicates that rapid heating has strong effect on the recrystallization behavior in non-oriented electrical steels, which facilitates optimization of microstructure and texture, especially in the coarse-grained structure.

Effect of Intermediate Heat Treatment on the Mechanical Properties of 3003/4343 Aluminum Clad Sheet Manufactured by Strip Casting/Clad Rolling

Effect of intermediate heat treatment on the microstructure evolution and mechanical properties of A3003/A4343 clad sheet manufactured through new processes were investigated. Raw materials® both A3003 and A4343 alloys®were fabricated by twin roll strip casting process, and then cold rolling and roll bonding were performed with final thickness of 215μm. In the manufactured clad sheets, the thickness of 3003 alloy was found to be 191μm, and that of 4343 alloy, 24 μm. Rolled and recovered microstructures appeared at low heat treatment temperatures (260°C, 280°C), and recrystallization/grain growth were noted from the A3003/A4343 interfaces at 573K or higher temperatures, with the area (recrystallization/grain growth) gradually increasing as heat treatment temperatures increased further. According to the results of tensile tests, yield strength was 223.7MPa, and tensile strength was 270MPa in as-rolled state. As the intermediate heat treatment temperature increased, strengths continuously decreased, whereas elongation exhibited an increasing tendency. Until the final tensile fracture, 3003 alloy and 4343 alloy were not separated but maintained well in bonded state. Based on the results of microstructure evolution by which microstructures were divided into three areas and changed following intermediate heat treatment, the tensile properties of A3003/A4343 clad sheets were analyzed and discussed. [doi:10.2320/matertrans.M2014298]

Casting speed optimal design of 304 stainless steel during twin roll strip casting process by 3D modelling

The exit temperature distribution of 304 stainless steel during twin roll strip casting process was measured. The crack morphology of the actual steel strip was observed by scanning electron microscope. Then, by establishing a three-dimensional model including casting rollers, the flow and temperature fields of 304 stainless steel during the twin roll strip casting process were modelled. The modelled temperature result is in accordance with the measured one, so the flow and temperature fields of 304 stainless steel during the twin roll casting process with different casting speeds can be modelled. The results of the flow field show that a large area of vortex forms in the pool. Those of the temperature field show that the temperature in the vortex zone is lower 30–50°C than that in the refluxing zone, and a thin shell forms on the interface between the molten pool and the casting roller. The whole temperature of the molten pool is increased with the increase in the casting speed, and an optimal casting speed is ∼0·7 m s−1.

Research on the Abnormal Grain Growth of Goss Grains in Strip-Cast 4.5%Si Grain-Oriented Electrical Steels

In conventional production of grain-oriented electrical steel, the content of silicon is limited to 3.0%~3.4%, which could control the ‘γ→α’ transformation process to obtain fine grain sizes in hot-rolling and disperse AlN particles in normalizing. In this study, the precipitation behaviors of S ans N in 4.5% Si-Fe alloy are inhibited during twin-roll strip casting process. And then the ideal microstructure and texture was obtained after the two-stage cold rolling and primary annealing. The evolution of microstructure and texture during the subsequent high temperature annealing were investigated. The results revealed that a sharp and developed Goss texture has been achieved by secondary recrystallization in the final annealing step and the magnetic induction B8 /Bsis above 1.76/1.90T.

Numerical Simulation of Filling Process During Twin-Roll Strip Casting

The modeling and controlling of flow and solidification of melt metal in the filling process is important for obtaining the optimal pool level and the formation of the solidified metal layer on the surface of twin-rolls during the twin-roll strip casting. The proper delivery system and processing parameters plays a key role to control flow characteristics in the initial filling stage of the twin-roll strip casting process. In this paper, a commercial CFD software was employed to simulate the transient fluid flow, heat transfer, and solidifications behaviors during the pouring stage of twin-roll strip casting process using different delivery systems. A 3D model was set up to solve the coupled set of governing differential equations for mass, momentum, and energy balance. The transient free-surface problem was treated with the volume of fluid approach, a k–ɛ turbulence model was employed to handle the turbulence effect and an enthalpy method was used to predict phase change during solidification. The predicted results showed that a wedge-shaped delivery system might have a beneficial impact on the distribution of molten steel and solidification. The predicted surface profile agreed well with the measured values in water model.

Characterization of Initial Structures, Texture and Precipitates in Strip-cast 3wt%Si Steel Sheet

A Fe-3wt%Si strip was produced using a vertical type twin-roll strip casting process, and two typical initial structures were observed. One was the solidification structure consisting of coarse columnar grains and the other was the deformed structure which was composed of outer inclined columnar grains and inner fine equxied grains. The solidification structure was characterized by {111}//ND fiber while the deformed structure shows a strong Goss texture. In addition, the size distributions of MnS precipitates, which were used as grain growth inhibiters, were investigated in the as-cast strip. The size of these particles in the deformed grains was smaller than that in the solidified grains, which could be attributed to the strain-induced precipitation mechanism. The differences of the initial structures, texture and precipitation behaviors resulted from the different superheating along the transverse direction of the as-cast strip, which originated from the inhomogeneous flowing of liquid steel.

Experimental Study on the Twin Roll Strip Casting and Warm Rolling Fe-6.5 wt. %Si Steel Sheet

An Fe-6.5 wt. % Si steel sheet with a final thickness of 0.30 mm was produced by twin roll strip casting and warm rolling process. The effects of casting, warm rolling and annealing process on microstructure, texture and magnetic properties were investigated with optical microscopy, X-ray diffraction and magnetic measurement. The microstructure evolution during preparation was shown as follows: columnar grain and a small amount of fine grain in center (as casted) elongated grains and a small amount of the shear bands along the rolling direction (as rolled) a relatively uniform recrystallized microstructure (as annealed). The texture evolution during preparation was shown as follows: {001} λ fiber texture (as casted) the significant α fiber texture and the weak, inhomogenous γ fiber texture (as warm rolled) the strong {001} λ fiber texture and weak, inhomogenous γ fiber texture (as annealed). The excellent soft magnetic properties were obtained with a very small P1.0/400 of 10.751 W/kg and a very high B50 up to 1.438 T at optimum annealing condition (1150 °C for 1 h). The research work was useful to develop electrical steel by twin roll continuous casting process.

Characterization of microstructure, texture and magnetic properties in twin-roll casting high silicon non-oriented electrical steel

An Fe-6.5wt.% Si-0.3wt.% Al as-cast sheet was produced by twin-roll strip casting process, then treated with hot rolling, warm rolling and annealing. A detailed study of the microstructure and texture evolution at different processing stages was carried out by optical microscopy, X-ray diffraction and electron backscattered diffraction analysis. The initial as-cast strip showed strong columnar grains and pronounced <001>//ND texture. The hot rolled & warm rolled sheets were characterized by large amounts of shear bands distributed through the thickness together with strong <110>//RD texture and weak <111>//ND texture. After annealing, detrimental <111>//ND texture almost disappeared while beneficial {001}<210>, {001}<010>, {115}<5 −10 1> and {410} <001> recrystallization textures were formed, thus the magnetic induction of the annealed sheet was significantly improved. The recrystallization texture in the present study could be explained by preferred nucleation and grain growth mechanism.

Investigation on Microstructure, Texture and Tensile Properties of Hot Rolled Strip Casting Grain-Oriented Silicon Steel

An Fe-3wt% Si as-cast strip was produced by twin-roll strip casting process. The as-cast strip was hot rolled at 1150°C by one pass of 20% reduction and coiled at 550°C. The tensile test was carried out and the elongation was measured. The microstructure and texture of the coiled strip and the fracture surface morphology of the tensile samples were characterized. It is found that the microstructure of the as-cast strip was characterized by columnar ferrite grains with pronounced {001}&lt;0vw&gt; fiber texture and martensite. The microstructure of coiled strip consisted of ferrite grains and pearlite, and the texture was mainly characterized by {001}&lt;0vw&gt; fiber texture. The necking was absent during the tensile test and the elongation of coiled strip was as low as 12%. The fracture surfaces of the tensile samples mainly exhibited cleavage fracture mode with coarse cleavage facets and some ligaments.

Thermal Crown Analysis of the Roll Sleeve in Twin-Roll Strip Casting Process

In the twin-roll strip casting process, analyses of heat transfer and deformation for the casting roll sleeve are carried out by using the finite element program ANSYS to examine the the thermal crown. The effects of several factors such as molten pool temperature, heat flux onto the roll surface and roll edge, heat flux onto the cooling channels, and cooling water temperature on thermal crown are investigated. The results show that the thermal crown does not change sharply during the casting process, after the casting roll reaches thermal equilibrium.

Development of λ-fiber recrystallization texture and magnetic property in Fe–6.5 wt% Si thin sheet produced by strip casting and warm rolling method

An 6.5wt%Si–0.3wt%Al non-oriented electrical steel as-cast sheet with strong columnar grains was produced by twin-roll strip casting process, and subsequently treated with hot rolling, warm rolling and annealing. It was shown that the warm rolled sheet was characterized by strong α-fiber (<110>∥RD), quite weak γ-fiber (<111>∥ND) texture and inhomogeneous deformed microstructure. After annealing, desirable λ-fiber (<001>∥ND) mainly including {001}<140>∼{001}<010> components dominated the recrystallization texture while the γ-fiber had all but disappeared, thus the annealed sheet showed a very high magnetic induction. It was indicated that the development of λ-fiber recrystallization texture could be attributed to the preferred nucleation and grain growth under the applied processes. The present study provides a new efficient way to optimize the recrystallization texture and improve the magnetic induction of high-silicon non-oriented electrical steel sheet.