Experimental Simulation of the Solidification of Steel at Higher Cooling Rates

Abstract

Today, continuous casting is the common technology for casting commercial steel grades. Conventional casting processes, like slab casting, are characterised by a moderate heat withdrawal and a rather low solidification velocity and cooling rate. Linking the casting and the rolling process demands a higher casting velocity, an increased heat withdrawal and thus, a higher local cooling rate. The absence of phase transformations during cooling and reheating before the rolling process makes the solidification microstructure more important for the behaviour of the steel during rolling and for the final product properties. Over several years the Christian Doppler Laboratory for "Metallurgical Fundamentals of Continuous Casting Processes" has developed an experimental setup for the simulation of solidification at higher cooling rates. The experiment is based on the principle of a dipping test under inert gas atmosphere inside a vacuum induction furnace. Recently, this apparatus has been equipped with a pyrometer in order to measure the temperature of the solidified sample during the subsequent cooling phase and also with a furnace in order to simulate different cooling and heat treatment strategies. Thus, it is possible to reproduce solidification and subsequent cooling of the cast material in casting-rolling processes and to characterise the microstructure and the mechanical properties of the solidified samples. The present work will give an overview on heat transfer in conventional casting processes, present a laboratory scale simulation of solidification a higher cooling rate, touch some aspects like the numerical simulation of the experiment and conclude with some results and an outlook on further planned work. Experimentelle Simulation der Erstarrung von Stahl bei hohenKühlraten. Der konventionelle Stranggießprozess ist der dominierende Prozess für das Vergießen herkömmlicher Kohlenstoffstähle. Die Erstarrung im Stranggießprozess, vor allem beim Brammenstranggießen, ist durch eine moderate Wärmeabfuhr und entsprechend geringe Erstarrungsgeschwindigkeiten und Kühlraten gekennzeichnet. Die Kopplung des Gieß-und Walzprozesses oder das direkte Gießen eines Produktes verlangt die Erhöhung der Gießgeschwindigkeit und deshalb auch die Erhöhung der Wärmeab-fuhr. Da die Phasenumwandlungen, die beim konventionellen Prozess während des Abkühlens und Wiedererwärmens auftreten, beim gekoppelten Gießwalzen fehlen, kommt der Erstarrungsstruktur auch eine größere Bedeutung für den nachfolgenden Walzprozess zu. Am Christian-Doppler-Labor für Metallurgische Grundlagen von Stranggießen wurde in Zusammenarbeit mit Siemens-VAI Metals Technologies ein Versuchsstand zur Nachbildung der beschleunigten Erstarrung entwickelt und umgesetzt. Das Experiment beruht auf einem Tauchversuch in einem Vakuuminduktionsofen unter kontrollierter Gasatmosphäre. Die Apparatur wurde vor kurzem mit einem Pyrometer ausgestattet, um die Temperatur der erstarrten Proben während der Abkühlung bestimmen zu können. Auch das Nachstellen bestimmter Temperaturzykle...

Systematic investigation of acicular ferrite formation on laboratory scale

“…Further details of the dipping procedure are provided in Ref. 28–31. After reacceleration into the simulator chamber, the measurement of the surface temperature by a pyrometer is initiated. Simultaneously with every dipping sample, a tube sample is taken, which is used for chemical analysis. By varying the dip time, samples with different thicknesses can be produced.…”

“…In route B, a dipping test, originally applied to reproduce the solidification during strip casting, 28,29 is used to study the formation of AF in the defined steel grade. For this purpose, a dipping test simulator, which is attached to a vacuum induction-melting furnace (VIM), is applied.…”

Study on Austenite Grain Growth Law of Ultra‐High Strength Hot‐Stamped 22MnB5 Steel During Thin Slab Casting and Rolling Process

“…Due to the difficulties in its simulation process, many studies have separated the continuous casting process and soaking process of TSCR process. [7,27,28] As a result, the experimental results are difficult to fully represent the DOI: 10.1002/srin.202300103…”

“…Due to the difficulties in its simulation process, many studies have separated the continuous casting process and soaking process of TSCR process. [ 7,27,28 ] As a result, the experimental results are difficult to fully represent the austenite growth law of TSCR process. Therefore, it is urgent to clarify the growth law of austenite during the continuous casting and soaking process of TSCR process to provide the necessary theoretical support for achieving the production of high‐quality hot‐forming steel.…”

Stiff, light, strong and ductile: nano-structured High Modulus Steel

“…While larger particle fractions can be easily achieved through higher Ti and B concentrations, the chosen eutectic composition exhibits with ~1400 °C the lowest melting temperature in the Fe – TiB 2 pseudo-binary system 26 , and thus more cost effective production. A charge of 4 kg based on pure metals were molten in a vacuum induction furnace under argon (Ar) atmosphere and cast into a cylindrical copper moulds of 30 mm internal diameter, with a cooling rate of about 10 K s −1 , which is comparable to conventional steel production conditions (solidification rate of about 5 to 10 K s −1 ) such as in continuous casting 27 .…”