Twin-roll Strip Casting Process Research Articles

Microstructure, texture and magnetic properties of strip casting Fe–6.2 wt%Si steel sheet

An Fe–6.2wt%Si strip with equiaxed grains and mild {001}〈0vw〉 fiber texture was produced by twin-roll strip casting process. Then the as-cast strip was treated with or without the hot rolling prior to the warm rolling and annealing. When the hot rolling was not introduced, a fine and heterogeneous warm-rolled microstructure was produced and led to a fine recrystallization microstructure and very weak {001}〈0vw〉 fiber texture in the annealed sheets. When the hot rolling was introduced, a coarse and homogeneous warm-rolled microstructure was produced and led to a very coarse recrystallization microstructure and much stronger {001}〈0vw〉 fiber texture in the annealed sheets. The annealed sheets with hot rolling showed a higher magnetic induction and a higher core loss than those without hot rolling.

Formation of {001} recrystallization texture and magnetic property in strip casting non-oriented electrical steel

A 3.2wt.%Si–0.7wt.%Al non-oriented silicon steel as-cast sheet with developed columnar grains and λ-fiber (<001> ∥ND) texture was produced by twin-roll strip casting process, and subsequently treated with cold rolling and annealing. Texture evolution at each condition was investigated using macro-/microtexture analysis. It was shown that the cold rolled sheet was characterized by pronounced {001} <110> ~{115} <110> fiber and quite weak γ-fiber (<111> ∥ND) texture. After annealing, the recrystallization texture was dominated by desirable λ-fiber with a peak at {001} <510> together with extremely weak γ-fiber, and consequently the magnetic induction was significantly improved. It was indicated that the formation of {001} <510> recrystallization texture could be attributed to the preferred nucleation and grain growth by the strain-induced grain boundary migration (SIBM) mechanism.

Effect of casting parameters on the freezing point position of the 304 stainless steel during twin-roll strip casting process by numerical simulation

This study focuses on the numerical simulation of the temperature fields of the 304 stainless steel during twin-roll strip casting process. The cracks and fratographs of the 304 stainless steel strip with the practical casting parameters were observed by Scanning Electron Microscopy. The exit temperature of the 304 stainless steel during twin-roll strip casting process was measured. Meanwhile, it was simulated by means of finite element model. The observed results show that the strip from outside to inside are composed of refined crystal zone, columnar crystal one, and equated axis crystal one. The cracks occur on the strip surface, extended to interior along the columnar crystal boundary, and then, ended at the juncture between the columnar crystal zone and equated axis crystal one. The simulated result was compared to the measured temperature, which showed a good agreement, thus indicating that this model is valid and accurate. Then, by employing this model, the effects of the casting parameters, such as casting speed and casting temperature, on the freezing point position of the 304 stainless steel during twin-roll strip casting process were simulated too. The simulated results show that, the freezing point position is decreased with the increasing casting speed and casting temperature. For producing high-quality strip of 304 stainless steel during twin-roll strip casting, the limits of casting speed and casting temperature are 1.1 m·s−1 and 1,570 °C, respectively.

Effect of Copper Variation and Thermomechanical Treatment on Microstructure and Properties in Aluminum Alloy Fin Stock for Heat Exchanger

Aluminum alloys are commonly used as a material for heat exchangers due to their higher thermal conductivity and specific strength among various metallic materials. Twin roll strip casting process is considered to produce the high quality and low manufacturing cost aluminum alloy fin stock for automobile heat exchangers. Thermomechamical treatment has carried out to obtain optimum processes for initial cold rolling, intermediate annealing and final cold rolling, which can meet the requirements for high strength and high thermal conductivity after brazing heat treatment. Additionally the effect of copper element variation was considered to determine the optimum content of copper element in Al-Zn-Mn-Si-Fe-Cu based alloys produced by twin roll strip casting process. Mechanical properties and thermal condutivity have been evaluated before and after simulated brazing process. The nuclei of recrystallization might be formed along shear deformation bands during initial cold rolling and should be grown during intermediate annealing to enhance the permeation of molten brazings for the following brazing process. Final cold rolling has allowed strain hardening and controlling of sagging amount as fin stock materials of heat exchanger. In the present study the suitable thermomechnical treatment and optimum copper content was suggested to balance the properties of strength, thermal conductivity, brazing behaviour, corrosion resistance and sagging resistance in Al-Zn-Mn-Si-Fe-Cu based alloys produced by twin roll strip casting process.

Microstructure and Texture Evolution of Strip Casting Fe-6.2wt%Si Steel

An Fe-6.2wt%Si as-cast strip with equiaxed grains and obvious {001} fiber texture was produced by twin-roll strip casting process. The as-cast strip was successively performed by hot rolling, warm rolling and annealing. The microstructure and texture evolution at each process stage were investigated by using electron backscatter diffraction and x-ray diffraction. It was found that the finally annealed sheet was characterized by large grain size, mild γ-fiber texture and obvious {001} fiber texture. Therefore, a high magnetic induction and a low core loss were obtained in the sheet.

Improvement of Surface Roughness of Al-Si Alloy Cast Strip by Vertical Melt Drag Process

Strip casting process is possible to shorten for producing strip. Strip is produced from molten metal continuously and directly by strip casting process. Melt drag process is one of the single roll strip casting process. Melt drag process is simpler than general twin roll strip casting process. One of defect of cast strip is surface conditions, for example surface roughness. Cast strip surface roughness is larger than hot rolled strip. Large strip surface roughness is negative effect for cold rolling after strip casting or hot rolling. The aim of this study is improvement of cast strip surface roughness by melt drag process. We suggested vertical melt drag process. And investigations were operated such us producing conditions of Al-Si alloy strip, surface roughness of cast strip and microstructures.

Solidification structure and crystallographic texture of strip casting 3wt.% Si non-oriented silicon steel

► Three as-cast strips with different initial solidification structures were produced by twin-roll strip casting process. ► The equiaxed grained strip displays weak and nearly random texture, but the columnar grained strip reveals pronounced {001} fiber texture. ► The deviation degree of the columnar grain from the normal direction decreases with the increase of melt superheat.

Numerical simulation on the stress field of austenite stainless steel during twin-roll strip casting process

The specimens were taken from the 304 austenite stainless steel. Based on the measured results of the phase transformation temperature and phase structure curves of the 304 stainless steel, the finite element model was established. According to the simulated temperature field of 304 stainless steel during twin-roll strip casting process and the mechanical properties of 304 stainless steel determined, the stress field of the 304 stainless steel during twin-roll strip casting process was simulated. Meanwhile, the effect of different technologic parameters, such as casting speed, casting temperature, roller radius and strip thickness at the exit, on the stress field of the 304 stainless steel during twin-roll strip casting process was simulated too in this work. The results show that the largest tensile stress appears on the contact interface between strip and roller located 5–10° away from exit. The tensile stress appears on the surface and the compressive one in the center of the strip. The larger roller radius and strip thickness at the exit are, the larger the tensile stress on the surface of 304 stainless steel during twin-roll strip casting process is. However, the larger the casting speed and the casting temperature are, the smaller the tensile stress on the surface of 304 stainless steel is.

Three-Dimensional Numerical Simulation of Metal Flow in the Initial Stage of a Twin-Roll Strip Casting Process

A three-dimensional mathematical model has been developed to study turbulent fluid flow, heat transfer and free surface profile in the initial stage of the twin-roll casting strip pool by a commercial software ProCAST. The coupled set of governing equations for mass, momentum and energy balance was solved with the finite element method. The free surface profile of the pool was treated with the Volume of Fluids (VOF) approach. A straight nozzle of metal delivery system has been chosen in the Twin-roll strip casting process. The filling sequences, flow patterns and corresponding temperature profiles in the metal pool of a vertical twin-roll strip casting process were simulated in this study. The calculated results provided a valuable basis for the optimization of process parameters and metal delivery system during the initial pouring stage of twin-roll strip casting.

Effect of phosphorus on the microstructure and mechanical properties of strip cast carbon steel

Carbon steel strips with different phosphorus and carbon contents were produced by using the twin roll strip casting process. Fine grains and dendrite structure were observed in high-P steels. Negative phosphorus segregation was found in strip cast high-P and high-C steels. For the steels with different carbon contents, phosphorus distribution in the thickness direction of the strip is obviously different. This is because solutes are redistributed in the melting pool and the phosphorus segregation rate is associated with the length of the mushy zone and the phosphorus solubility in different phases. Phosphorus as a solute in ferrite can lead to the higher hardness and strength with lower plastic propertyies.

Adaptive neural network controller for the molten steel level control of strip casting processes

The twin-roll strip casting process is a steel-strip production method which combines continuous casting and hot rolling processes. The production line from molten liquid steel to the final steel-strip is shortened and the production cost is reduced significantly as compared to conventional continuous casting. The quality of strip casting process depends on many process parameters, such as molten steel level in the pool, solidification position, and roll gap. Their relationships are complex and the strip casting process has the properties of nonlinear uncertainty and time-varying characteristics. It is difficult to establish an accurate process model for designing a model-based controller to monitor the strip quality. In this paper, a model-free adaptive neural network controller is developed to overcome this problem. The proposed control strategy is based on a neural network structure combined with a sliding-mode control scheme. An adaptive rule is employed to on-line adjust the weights of radial basis functions by using the reaching condition of a specified sliding surface. This surface has the on-line learning ability to respond to the system’s nonlinear and time-varying behaviors. Since this model-free controller has a simple control structure and small number of control parameters, it is easy to implement. Simulation results, based on a semiexperimental system dynamic model and parameters, are executed to show the control performance of the proposed intelligent controller. In addition, the control performance is compared with that of a traditional PID controller.

Thermomechanical Treatment of Aluminum Alloy Fin Stock for Heat Exchanger Produced by Twin Roll Strip Casting Process

Aluminum alloys are commonly used as a material for heat exchangers due to their higher thermal conductivity and specific strength among various metallic materials. The lightweightening heat exchangers for automobile application are requisite for reducing the evolution of CO2 and improving the efficiency of fuel. The twin roll strip casting process is considered to produce the high quality and low manufacturing cost aluminum alloy fin stock for automobile heat exchangers. Thermomechamical treatment has carried out to obtain optimum processes for initial cold rolling, intermediate annealing and final cold rolling, which can meet the requirements for high strength and high thermal conductivity after brazing heat treatment. Mechanical properties and thermal condutivity have been evaluated before and after simulated brazing process. The nuclei of recrystallization might be formed along shear deformation bands during initial cold rolling and should be grown during intermediate annealing to enhance the permeation of molten brazings for the following brazing process. Final cold rolling has allowed strain hardening and controlling of sagging amount as fin stock materials of heat exchanger. In the present study the suitable thermomechnical treatment was suggested to balance the properties of strength, thermal conductivity, brazing behavior and sagging in Al-Fe-Mn-Si-Zn based alloys produced by twin roll strip casting process.

Self-organizing fuzzy controller for the molten steel level control of a twin-roll strip casting process

The twin-roll strip casting process is a steel-strip production method that combines continuous casting and hot rolling process in a single operation. The quality of strip casting process depends on many process parameters, such as molten steel level in the tundish, solidification position and roll gap. Their relationships are complex and the strip casting process has the properties of nonlinear uncertainty and time-varying characteristics. Hence, it is difficult to establish an accurate process model for designing a model-based controller to monitor the strip quality. In this paper, a model-free control strategy is employed to overcome this problem. The self-organizing fuzzy control (SOFC) strategy is developed to control the molten steel level of a strip casting process. It has on-line learning ability and the rule tables can be modified automatically and continuously for responding to the system's nonlinear and time-varying behaviors. Since this model-free controller has simple control structure and small number of control parameters, it is easy to implement. Simulation results based on semi-experimental system dynamic model and parameters are executed to show the control performance of the proposed intelligent controller.

Investigation of the solute transportation coupled with heat transfer and fluid flow during twin-roll strip casting process

Mathematical model of solute [C] distribution in twin-roll strip casting process has been setup successfully with Calcosoft for the first time. Simulation result shows that in the center of the molten steel pool between the two rolls there is a vortex flow, which is a solute enriched area. But the highest solute concentration position is at the solidification front of the columnar grain zone near the cooling roll surface. Another solute enriched position is in the back flow above the nip point. Combined with the formation mechanism of microstructure in final as cast strip, analysis shows that solute enriched area is in the transitional area between columnar and equiaxed grain zone.

Numerical simulation of molten pool and control strategy of kiss point in a twin-roll strip casting process

Coupled turbulent flow, temperature fields of the twin-roll casting strip process were simulated by three-dimensional finite element method. Based on the heat balance calculation and using inverse methods between the simulations and real experiments, the relational models among casting speed, location, and coefficient of heat transfer between molten metal and rolls in different regions are given. In the simulation, the calculated surface temperatures are in good agreement with the measured values. An on-line model of kiss point is derived by simulations and the geometry of molten pool, corresponding control strategy is also proposed.

Thermal crown analysis of the roll in the strip casting process

In the twin roll strip casting process, coupled analyses of heat transfer and deformation for the casting roll are carried out by using the finite element program MARC to examine the thermal crown. The shrink fit effect and plastic deformation are considered. The result shows that the thermal crown is greatly influenced by the shrink fit and that the thermal crown for POSCO Pilot Caster 2 Copper Roll has an “M” shape. The effects of several factors on thermal crown are also investigated. The amount of thermal crown increases as the heat flux, casting speed, sleeve thickness and casting roll width increase. On the other hand, it decreases as the casting roll diameter increases.

Numerical simulation of the twin-roll casting process of magnesium alloy strip

The magnesium twin-roll strip casting process is investigated with a test caster at the IME. The flow field in the melt cannot be investigated optically, therefore numerical simulations have been undertaken to show the flow field in the Mg melt, the solidification between the two rolls and the cooling of the strip. The three-dimensional, turbulent flow field for different steady state casting points, in the process gap, have been calculated, including the solidification of the magnesium alloy melt. Within the process gap of the casting process the flow field shows similar flow structures. A big vortex in the casting channel and a much smaller vortex between the two rolls occur. With the increase of the casting speed the mushy zone is moved towards the kissing point. This can be interpreted due to a smaller force on the rolls. Nevertheless, the solidification on the rolls is so strong, that rolling between the two rolls happens.

Analysis of Casting Roll Temperature Field during Twin-Roll Thin Strip Casting

In twin-roll strip casting process, the temperature variation of casting roll can result in roll thermal stress and fatigue. It not only affects the thermal deformation of casting roll and the generation of the roll surface cracks significantly, but also influences the surface quality, shape and profile of the produced strip, and the service life of the casting roll. In this paper, a 3D coupling thermal-flow finite element modelling has been conducted. For twin-roll casting of stainless steel, the influences of the casting speed and liquid level in molten pool on the temperature field of casting roll have been simulated and discussed. The developed model is very helpful in optimising the processing parameters and the design of casting roll during twin-roll thin strip casting.

Flow and Temperature Analysis of Molten Pool in Twin-Roll Strip Casting Process

In twin-roll strip casting process, metal flow and temperature distribution in the molten pool directly affect the stability of the process and the quality of products. In this paper, a 3D coupling temperature-flow finite element simulation during twin-roll strip casting has been carried out, and the influences of the outlet angle and the submerged depth on the temperature and flow fields in the molten pool were investigated for the twin-roll casting of stainless steel. An inverse method was used to determine the boundary conditions between the roll and molten pool. Simulation results are consistent with the experimental values. Numerical simulation is helpful to optimise the twin-roll strip casting process and to improve the quality of products in practice.

Overview of CAST and Australian Magnesium Research

The CAST Cooperative Research Centre was established in 1993 as a joint venture between industry, research and government partners to carry out research and development in the area of light metals. Over the thirteen years since its formation CAST has developed a world class research program and, in addition to the significant application of outcomes by our industry partners, much of our research is being commercialised. In addition, CAST has developed a significant education and training program, a best practice technology transfer program for small and medium enterprises, consulting and design activities and established an alliance with Advanced Magnesium Technologies as a provider of their research and development needs. The development of CAST has been achieved by cooperation between all our partners who represent most of the light metals research groups and a significant proportion of light metals industries in Australia. The close involvement of the industry partners in all aspects of the operation of CAST has ensured we have a program of activities focused on delivering benefits to Australia’s light metals industry. This paper presents an overview of the magnesium research undertaken by CAST and other research groups such as the Centre of Excellence in Design of Light Metals and the CSIRO including their Light Metals Flagship program. Some highlights are new magnesium powertrain alloys, an alloy suitable for decorative and domestic applications called AM-lite, and new CSIRO casting technologies T-Mag and a twin roll strip casting process.