Progress in twin roll casting of magnesium alloys: A review

Twin roll casting was commercialized for a strip production from ferrous and non-ferrous alloys in the 1950 s;however,its application to magnesium has proven difficult and still creates major challenges.This report describes global efforts in expanding manufacturing capabilities of magnesium sheet through twin roll casting path,offering many benefits,including a reduction in number of processing steps and energy savings.In addition to hardware design,alloy transformation during processing,product microstructure and properties,examples of successful solutions along with present technology and knowledge limitations are discussed.A particular attention is paid to developments at Canmet MATERIALS,having the only in North America pilot scale twin roll casting facility,devoted to magnesium.Efforts are described that aim at design of new magnesium alloys,which could take advantage of unique processing conditions during twin roll casting and contribute to the overall progress in magnesium sheet manufacturing.

Effect of asymmetric rolling process on the microstructure,mechanical properties and texture of AZ31 magnesium alloys sheets produced by twin roll casting technique

Symmetric rolling(SR)and asymmetric rolling(ASR)processes were carried out on 6 mm thick AZ31 magnesium alloy sheets that were produced by twin roll casting(TRC)technique.Before rolling processes,sheets were heat treated in order to obtain a homogenized microstructure.In this study,for the ASR process the rolling speed ratio between upper roller and lower was selected as 1.25.Both SR and ASR processes were utilized with 40%reduction per passes using 2 pass schedule for a total reduction ratio of 0.67.Symmetric and asymmetric rolled sheets were characterized using optical microscopy(OM),scanning electron microscopy(SEM)and transmission electron microscopy(TEM)techniques.Texture measurements were performed by using X-ray diffraction(XRD)technique and mechanical properties were investigated by tensile tests and also hardness measurements.

Mathematical modeling of thermo-mechanical behavior of strip during twin roll casting of an AZ31 magnesium alloy

The effect of set-back distance on the thermo-mechanical behavior of the strip during twin roll casting(TRC)of an AZ31 magnesium alloy was modeled using finite element method(FEM).Model validation was done by comparing the predicted and measured exit strip surface temperature as well as the secondary dendrite arm spacing(SDAS)through the thickness of the sheet to those measured during experiments.Model results showed as the set-back distance increases,the strip exit temperature decreases and the solidification front moves toward the entry of the roll gap.The cast strip also experiences more plastic deformation and consequently,the normal stress on the strip surface and effective strain at the strip center-line increase.Moreover,higher separating forces were predicted for longer set-back distances.Model predictions showed that changing the set-back distance by varying the final thickness has a more significant effect on the temperature and stress-strain fields than altering the nozzle opening height.

3D stress simulation and parameter design during twin-roll casting of 304 stainless steel based on the Anand model

This study first investigated cracks on the surface of an actual steel strip. Formulating the Anand model in ANSYS software, we then simulated the stress field in the molten pool of type 304 stainless steel during the twin-roll casting process. Parameters affecting the stress distribution in the molten pool were analyzed in detail and optimized. After twin-roll casting, a large number of transgranular and intergranular cracks resided on the surface of the thin steel strip, and followed a tortuous path. In the molten pool, stress was enhanced at the exit and at the roller contact positions. The stress at the exit decreased with increasing casting speed and pouring temperature. To ensure high quality of the fabricated strips, the casting speed and pouring temperature should be controlled above 0.7 m/s and 1520℃, respectively.

3-D Numerical Simulation of the Electromagnetic Dam of Twin Roll Casting using Edge Element Method

The 3-dimension numerical simulation study on the electromagnetic dam used in the twin roll caster has been performed by using the edge element method. It was found that the materials and structures of the roll collars have great influence on the distribution of the magnetic flux density, eddy current density and the electromagnetic force in the molten pool. The conductive collars make the magnetic flux density decreased in the molten pool, but it also makes the magnetic force more uniformly, and the force in the low part of the molten pool where needs greater force have increased some what. The conductive collars make the EMD device more effective than the nonconductive collars.

Two Dimension Finite Element Simulations on the Electromagnetic Containment in Twin-Roll Strip Casting

Distribution of magnetic field and electromagnetic force in twin-roll casting of steels was studied by the method of numericalsimulation in this paper. Two-dimension finite element model, which includes the regions of melt, stainless collar, coil andmagnetic core, has been constructed. By solving magnetic vector potential formulations of quasi-static electromagnetic field,distribution of magnetic flux density and magnetic force at different molten height is determined. Calculated results showedthat intensity of the distribution of magnetic flux density increased linearly with the increased coil current; and the magneticforce in the melt increased as a quadratic cure with creased coil current. More attention was given to the distribution of eddycurrent and magnetic force in the melt, the confine effect at different molten height was also discussed.

Effect of Oscillation Parameters to Flow Field in the Pool during the Oscillating Twin-Roll Strip Casting Process

During the oscillating twin?roll strip casting process, the quality of final products is directly influenced by the flow field distribution of molten metal in the pool. The variation in the flow field is caused by oscillating roller benefits, for homogeneous distribution of strip impurity, and decreasing the grain size. Thus, the quality of the strip could be improved. A numerical model was developed using the multiphase flow technology, coupled with heat transfer, fluid flow, solidification, and oscillation. Furthermore, a transient algorithm was adopted for simulating the oscillating twin?roll strip casting process of AlSi9Cu3 and 3104 aluminum alloy. This paper focuses on the flow distribution in the pool, in comparison with the traditional vertical twin?roll strip casting process, while the amplitude or frequency is chang?ing with the definite value of casting velocity, roller diameter, nozzle angle, and the strip thickness. Consequently, the conclusions were experimentally validated by oscillating twin?roll 3104 aluminum alloy strip casting. Vibrating casting technology can change the flow field in the pool by vibration, which can improve the quality of the strip core.

Influence of Feeding Mode on Flow and Temperature Field for Twin Roll Strip Casting Process

A three-dimensional finite element method was developed to simulate the fluid flow,heat transfer and solidification for twin roll strip casting.An improved two-equationκ-εmodel was used to incorporate the turbulence in fluid flow.The influence of vertical feeding and submerged entry nozzle feeding on the flow and temperature field was discussed.The optimum submersion depth and entry angle of submerged nozzle were obtained through comparison of the simulation results.

Microstructure and Eutectic Carbide Morphology of the High Speed Steel Strips Produced by Twin Roll Strip Casting Process

The M2 high-speed steel strip was produced by using the laboratory scale twin roll strip caster. The microstructure and eutectic carbide morphology of thus produced products were observed and analyzed, and the comparison of those with conventional products was carried out. The effects of the processing parameters such as the melting temperature, the pouring temperature, rolling speed and separating force on the microstructure and eutectic carbide morphology and their distribution were analyzed. The spheroidizing process of the strips in the annealing process was investigated. The relations between the growth and spheroidizing of the eutectic carbide and the annealing technology were obtained, and the mechanism of the twin roll strip casting process improving the eutectic carbide spheroidizing was discussed. The theoretical instruction for determining the subsequent treatment process was provided.

Recrystallization behavior of twin roll cast low carbon steel strip

The dynamic and static recrystallization behaviors of twin roll cast low carbon steel strip were investigated with an attempt to provide guiding deformation parameters for the on line hot rolling.In order to investigate dynamic recrystallization behavior,as cast strip was reheated and soaked with austenite grain size similar to the width level of the as cast columnar structure.Tensile test was used and the deformation temperature is in the range of 900℃to 1 100℃and strain rates are 0.01 s^(-1),0.1 s^(-1),1 s^(-1).The activation energy and stress exponent were determined as 306kJ/mol and 4.69 respectively.The ratio of critical strain to the peak strain is 0.65,and that of critical stress to the peak stress is 0.92.The dependence of the peak strain on the initial grain size and Zener - Hollomon parameters Z isε_p =9.1×10^(-4)×D_0^(0.48)Z^(0.13).The kinetics of the dynamic recrystallization and recrystallized grain size was predicted using models published.The as cast coarse austenite were dramatically refined after complete dynamic recrystallization.For static recrystallization,the tensile test was carried out on Gleeble -3500 thermo - mechanical simulator.The deformation temperature is in the range of 800℃to 1 200℃with strain rate 0.01 s^(-1) to 1s^(-1).The pre strain is fixed at 0.04 to 0.12 and the inter-hit delay time varies from 1 s to 3 000 s.The activation energy and Avrami exponent of static recrystallization were determined as 241 kJ/mol and 0.54 respectively.A kinetics model was proposed to describe the static recrystallization kinetics.The predicted results were in good agreement with the experimental results.

Low-Energy Multi-Impact Fracture Resistance of Cross Rolled Low Chromium Cast Semi-Steel Containing Rare Earth Grinding Ball

The low-energy multi-impact fracture resistance of the cross rolled low chromium cast semi-steel containing RE grinding balls was studied. Moreover, its damage mode was analyzed by means of metallographic examination, scanning electron microscopic examination and drop ball test. The results show that it can obtain extractive impact fracture resistance after proper heat treatment. More advantages were obtained for the ball worked in the condition of low-imp ductility act. The main reasons are the function of RE and the change in morphology of eutectic carbide network.

Delayed Fracture Behavior of CrMo Type High Strength Steel Containing Vanadium

The netlike eutectic carbide in twin roll casting strip of W9Cr4V2 was dissolved and broken up gradually with increasing heating temperature during annealing treatment. Almost all eutectic carbides exist in granular form with heating temperature up to 950 ℃. It is considered that the refining of lamellar spacing made it possible for eutectic carbide to be granulated.

TiAl ALLOYS FOR INDUSTRIAL USE

Gamma titanium aluminide (γ-TiAl)intermetallic compounds are spotlighted as lightweight heat-resistant materials, and have been investigated extensively to aiming commercial use.Fundamental approaches in which phase diagrams of Ti -Al -Cr and TiAl -Nb have been studied based on the experimental data and calculations , have been performed in the national project For industrial approach, ingot process and direct casting process have been developed to provide sheet form of TiAl. By these approaches, γ-TiAl base ,intermetallic compounds show a great possibility to apply in the variety of fields .However, a more detailed understanding of phase equilibrium in Ti-Al -X and the relationship between the mechanical properties and microstructure will be necessary

Deformation Behavior and Microstructure Evolution of Wrought Magnesium Alloys

There are many researches on the deformation behavior of wrought magnesium alloys, such as AZ31, AZ80, AZ91, and ZK60 magnesium alloys at different temperatures and strain rates, but few of them focuses on the deformation behavior of AZ41M and ZK60M alloys, especially under the twin-roll casting (TRC) state. Meanwhile, the existing researches only focus on the grain refinement law of the magnesium alloys under deformation conditions, the deformation mechanism has not been revealed yet. The hot compression behavior of AZ41M and ZK60M magnesium alloys under the temperature and strain rate ranges of 250-400 ℃ and 0.001-1 s-1 are studied by thermal simulation methods using Gleeble 1500 machine and virtual simulation using finite element analysis software. Simulation results show that sine hyperbolic law is the most suitable flow stress model for wider deformation conditions. The most reasonable selected deformation conditions of ZK60M alloy is 350 oC/0.1 s-1 for TRC and 350 oC/1 s-1 for conventional casting (CC), while AZ41M alloy is 300 oC/0.01 s-1 for TRC and 350 oC/0.1 s-1 for CC. Deformation behavior and dynamic recrystallization (DRX) mechanism of them are analyzed at the same deformation conditions. The microstructures of AZ41M and ZK60M alloys are observed at different deformed conditions by optical microscopy (OM) and electron back scatter diffraction (EBSD) and it reveals the flow behavior and deformation mechanism of them. Working harden and work soften contribute to the activation of basal, non-basal slip systems which promote DRX. The proposed research reveals the deformation behavior and mechanism of the AZ41M and ZK 60M magnesium alloys and concludes their optimized deformation parameters and processes and provides a theory basis for their manufacturing and application.

A New Type of Submerged-Arc Flux-Cored Wire Used for Hardfacing Continuous Casting Rolls

It is expected that the welding hardfacing of continuous casting rolls has better welding performance and higher wear resistance. A new type of submerged-arc hardfacing flux-cored wire has been developed through nitrogen replacing part of carbon and addition of the nitrogen-fixing elements of niobium and titanium. And microstructure, degree of hardness and high-temperature wear resistance of its deposited metal samples were also investigated. It is found that the microstructure is martensite, residual austenite and carbonitride precipitates. As a result, the hardfacing metal with homogeneous distribution of very fine carbonitride particles had high hardness and excellent wear-re- sisting property during high-temperature wear, which could significantly extend the service life of continuous casting rolls.

Microstructure,texture and precipitates of grain-oriented silicon steel produced by thin slab casting and rolling process

A grain-oriented silicon steel strip with AlN as main inhibitor was produced by thin slab casting and rolling（TSCR）process.The microstructure,texture and precipitates of the hot-rolled strip were investigated by use of optical microscope（OM）,X-ray diffractometer,transmission electron microscope（TEM）and energy dispersive spectroscope（EDS）.The result shows that the microstructure and texture exhibit a through-thickness gradient similar to that of the hot-rolled strip produced by conventional high-temperature slab-reheating process;the preferred orientation varies from {110}〈001〉in the surface layer to{001}〈110〉in the center layer,and the Goss texture with a maximum intensity mainly concentrates on the surface layer.In addition,some other texture components,for example rotated Goss texture,form in the 1/4thickness layer,which are not observed in the hotrolled strip produced by conventional high-temperature slab-reheating process.The precipitates in the hot-rolled strip are mainly（Mn,Cu）S and AlN compound particles with dimension of 100-200 nm,and the fine precipitates are significantly less than that in the hot-rolled strip produced by conventional high-temperature slab-reheating process.Moreover,the areal density of the fine precipitates in the center layer is more than that in the surface layer.

The Status quo and future development of Baosteel CC Technology

The status quo and future development trend of Baosteel continuous casting （CC） technology is introduced. Since its commissioning over ten years ago, Baosteel＇ s CC process has made great progress. The construction of Baosteel CC research and development base is also introduced. Two aspects of the future CC technology development in Baosteel are stressed. One is to follow the advanced CC technology and solve problems in real production, making full use of pilot plants, while the other is to integrate the present CC technology and make technical breakthroughs in engineering proiects.

Electrochemical Method to Accelerate Metal-Slag Reaction

According to the principle of similarity theory, a water model of twin roll strip caster was built. The level fluctuation was measured with an ultrasonic level detector. The effect of nozzle design, casting rate, pool depth and nozzles immersion depths on the level fluctuation was studied. And a level fluctuation mathematical model was developed. The experimental results provided a basis to further optimize the nozzle design and technological parameters of twin roll strip caster.

Development of Continuous Casting Technology of Electrical Steel and New Products

The development of continuous casting technology of electrical steel was analyzed. The technologies and products characteristics of conventional continuous casting, thin slab continuous casting and rolling, middle thin slab continuous casting and rolling and twin-roll thin strip were compared. Conventional continuous casting technology was widely adopted in producing electrical steel, thin slab continuous casting and rolling and middle thin slab contin- uous casting and roiling technology industrialized electrical steel~ and study of twin-roll thin strip casting technology was focused on fundamental experiments.