Extended Metal Delivery Systems for Horizontal Single Belt Casting Processes
In collaboration with the Hazelett Strip Casting Corporation, and other member companies of the International Advisory Board, a pilot scale Horizontal Single Belt caster (HSBC) was installed in the MMPC foundry of the M.H. Wong Building, in 1998, and then was re-commissioned at MetSim Inc., in the High Temperature Melting, Casting and Solidification facility, Stinson Laboratory, in 2012. Its picture and its associated schematic is presented below. The purpose of this machine is to test various metal delivery systems for near net shape casting, in particular thin strip casting.
Picture and schematic view of the HSBC pilot-scale system.
This data is needed to confirm the practicability of using extended nozzle systems, to test the effects of various belt substrate coatings on surface quality of strip, to determine strip quality and alloy microstructures, and to test the viability of such a machine for the high-speed production of thin sheet products. The alloy systems targeted include light metal grades based on aluminum and magnesium, as well as various steel and copper grades, plus glassy metals.
It was more than twenty-five years after our invention, and Prof. Schwerdtfeger’s, independent invention of this process, that Salzgitter finally designed a commercial belt caster, to be produced by SMS Siemag. Delivered to Salzgitter, Peine Plant, it has since been producing and testing various grades of steel, including the Advanced High Strength, High Ductility (HSHD) Steels, since 2014. The commercial caster at Peine is shown in the figure above. Steel grades being targeted are aimed to strengthen the light-weight steel, to compete for autobody components. To date, low carbon steel products, TRIP and TWIP steels, and now electrical steels have been successfully cast, rolled, and sold commercially, to Salzgitter’s customers.
Extensive studies have also been carried at the MMPC on the microstructure and mechanical properties of AA6111 strips cast on HSBC following rolling and heat treatments (Dr. Donghui-Li, Usman Niaz, Justin Lee, Jason Hsin, Dr. Luis Calzado, Dr. M. Isac, Dr. Roderick Guthrie). Sheet of aluminum alloys based on the 6000 series, including AA6111 alloy, as a potential lightweight alternative to steel for the automotive industry, have been successfully produced via the HSBC technique.
Ab-initio Predictions of Interfacial Heat Fluxes in Horizontal Single Belt Casting (HSBC), Incorporating Surface Texture and Air Gap Evolution
We have also been engaged in the mathematical modeling of the first moments of heat extraction from the melt, once the liquid metal first contacts the belt. For this we have idealized the actual surface topography of the cooling belt, or substrate, by constructing a three-dimensional diamond shaped interface for our mathematical model. With this, we were able to mimic, rather nicely, from first principles, the exponential drop-off in heat fluxes that we observe in practice. For these simulator experiments, we adapted the FLUENT-ANSYS code to the problem of iso-kinetic delivery of metal onto a cooling substrate. We have become increasingly proficient in detecting heat fluxes during the first moments of solidification (<100 ms).
Horizontal Single Belt Casting (HSBC) of Advanced High Strength Steels (AHSS)
The practical usefulness of AHSS is significant. AHSS grades are lighter than regular steels and have unique combinations of mechanical strength and formability that render them a prime candidate material for automotive applications. As a result, AHSS grades are being developed as a competitive steel material that provides a good balance between strength, performance and ease of production, compared with other materials, such as plastics and composites. The main strengthening mechanisms behind AHSS’s increased tensile strength and total elongation are a) dislocation slip and b) the nucleation of symmetric twins for Twinning Induced Plasticity (TWIP) steels, and c) the transformation of austenite (γ) to martensite (α/ε) during plastic deformation for Transformation Induced Plasticity (TRIP) type steels. These competing strengthening mechanisms are strongly dependent on the Stacking Fault Energy (SFE). According to the literature, a critical value of SFE, between 20-40 mj/mole, is suggested for the twinning mechanism, whilst SFE values ˂ 20mj/mole are determined for the TRIP mechanism. When the SFE exceeds 45mj/mole, AHSS gain strength through dislocation gliding mechanisms only.
Casting experiment of the AHSS steel strips produced on the pilot-scale HSBC machine
Computational Fluid Dynamics (CFD) of the HSBC of AHSS
In this research study (performed by Usman Niaz for his PhD studies), the simulation domain was selected in such a way as to investigate firstly the interaction of the molten metal with the refractory inclined plane/moving belt and secondly to analyze the behaviour of the meniscus at the triple point. It is important to analyze these phenomena because they can significantly affect the surface, as well as the bulk, qualities of the cast strip.
Heat transfer is also considered in the present work. Since there is no (or very little) solidification in the immediate regions of the two impingements, it is believed that the very thin solidified metal layer formed (~ 20 microns) will not significantly affect much the flow of molten metal over it. The transient interfacial heat flux was also evaluated. The simulation domain selected to carry out this study is presented in the figure below.
Predicted surface fluctuations of molten steel at the metal-air interface for two different time steps, overlaid on each other.