Papers by Keyword: Twin-Roll Strip Casting

Abstract: High silicon steel was fabricated by twin-roll strip casting. The cracks on the surfaces of the processed strips were obtained and analyzed by digital camera after series of surface treatment. Optical microscopy (OM) and scanning electron microscopy (SEM) were used to observe and characterize the microstructure nearby crack and fracture surface along the normal direction, respectively, and the crack formation mechanism was further analyzed in conjunction with processing parameters utilized during twin-roll strip casting process. The results indicated that morelongitudinal cracks along the rolling direction were observed in comparison with transverse cracks along the transverse direction on the strip surfaces. Trans granular and intergranular fracture modes both worked during the formations of longitudinal and transverse cracks on the processed strips. The dominant factor causing the formation of crack on the surface of the processed strips was the inhomogeneous transfer of heat during casting and rolling. The inhomogeneous transfer of heat induced by gas gap during casting resulted in variations of dendrite length and secondary dendrite spacing (SDAS). Meanwhile, the casting velocity influenced the formation of gas gap, which further influenced the thermal contraction. So the control of velocity of casting above a certain level proved beneficial to enhancing the performance of strip casting and to improving the quality of strip products.

Abstract: 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.

Abstract: Twin-roll strip casting represents a promising alternative production route for clad steel strips. The main idea behind the presented research is the introduction of a prefabricated strip into the melt pool of a twin-roll casting process to exploit the heat of the melt to create bonding between the cast strip and the prefabricated strip. Prior investigations proved the general feasibility of this concept for steel-steel combinations and described the bonding of the two layers. This concept is now further investigated with the aim to understand the influence of the process parameters on the bonding. For the experiments an austenitic high manganese steel is cladded with an austenitic stainless steel. Beginning from a starting point determined in numerical simulations, a process window for the introduction of a 0.3 mm thick strip of 1.4301 was identified by process parameter variation during casting experiments. Up to 25 m long clad strips with a thickness ratio between introduced strip and cast strip ranging from 1:6 to 1:10 were produced this way. Micrographic examinations of the clad strips’ cross sections were carried out to describe the influence of the casting parameters on the joining interface. Higher element diffusion was found in strips with bigger thickness ratios, indicating a stronger bonding of the two layers. Afterwards the observations from the micrographic examination were compared to the results of bonding strength which were obtained by a customised shear test. Supporting the findings of the micrographic examinations the average bonding strength rose from around 100 MPa for a ratio of 1:7 to over 300 MPa for the ratio of 1:10. Although the process parameters with the main influence on the bonding strength, the contact time and the thickness ratio, have been identified more research is needed to quantify their influence.

Abstract: A process for the production of clad steel strips by means of vertical twin-roll strip casting is under investigation at the Institute of Metal Forming (IBF). This production concept is based on the introduction of a solid strip in the casting pool in order to join it with the solidifying melt. The advantages of this concept are a shorter process chain and a higher energy efficiency compared to the existing cladding methods. The contact time and the thickness ratio between solid strip and solidifying melt, their relative position and the alloy combination are fundamental parameters to be considered in the design of this cladding process. A numerical model is used to predict the temperature increase in the solid strip and the solidification of the melt for the material combinations 1.4301/C75 and C75/Cu, and for two process configurations. Carbon steel and copper strips were introduced in the melting pool during casting experiments. Both carbon steel and copper strips could be clad without melting when positioned on the casting roll surface. This indicates that the surface temperature of the copper strip did not rise over 1084°C. Both the copper and the carbon steel strips show partial melting when introduced in a central position.

Abstract: The influence of different secondary cooling conditions (air cooling and water cooling) on microstructure, texture and properties of Fe-1.2wt%Si non-oriented silicon strips prepared by twin-roll strip casting were studied. Specimens were examined by OIM, EBSD and X-RD. The microstructures obtained by water cooling are more homogeneous and coarse in grain size than that obtained by air cooling. The dominant {100} texture can be observed in the case of water cooled, while the air cooled strip show a diffuse texture characteristic. The annealed sheets subjected to water cooling than air cooling show higher permeability and lower core loss due to the presence of relatively larger grain size and more ideal fibre components such as Goss and Cube., It seems that rapid secondary cooling of as cast strips can furtherer optimize the microstructure and texture prior to cold rolling and then substantially the final magnetic properties of 1.2wt% Si non-oriented silicon steels.

Abstract: 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.

Abstract: A process to produce thin steel strips with an optimized cross-section has been recently developed at the Institute of Metal Forming (IBF) as possible alternative to tailor welding and cold profile rolling for the production of tailored flat products. This process was named profile strip casting and combines the advantages of twin-roll strip casting, such as energy efficiency and compact production route, with the attractiveness of tailored products for lightweight applications. A finite difference model for the thermal description of the complete process chain including solidification, air cooling, and rolling is presented in this work. The developed simulation tool is calibrated on the temperature measurements obtained with profile casting experiments and targets the investigation of thicknesses not achievable with the available equipment. The measured surface temperature difference between the thick and thin zone of the profile for a strip with a thickness of 1.5 mm in the thin and 2.2 mm in the thick section cast using selectively coated rolls was ΔT = T_thick - T_thin = 82 K after the casting gap and 109 K at the mill exit. The simulation indicates that increasing the thickness to 3.5 mm in the thin and to 5.1 mm in the thick profile zone the surface temperature difference results 26 K after the casting gap and 126 K at the mill exit.

Abstract: Twin-roll strip casting is a concerned technology for economically producing magnesium alloys sheets. In this paper, numerical simulation of the twin-roll strip casting of an AZ61 magnesium alloy was carried out and the optimal process parameters were obtained. Then, under the conditions obtained through simulation, AZ61 strips of good surface quality were successfully manufactured. The microstructure of the alloy by twin-rolled strip casting is obvious refined compared with that by conventional casting.

Abstract: 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.

Abstract: In this paper, the established control system and its control algorism of a new twin roll strip caster developed by authors is presented. It is illustrated the roll-gap control strategy of the twin roll strip caster based on a feed forward-feedback system. From the experimental results, the susceptibility of control convergence time, stable and accurate are shown on a higher level than traditional control strategy.