Gregor Arth

Metall-Matrix-Verbundwerkstoffe auf Eisenbasis

ZusammenfassungMetall-Matrix-Verbundwerkstoffe nutzen eine verstärkende Phase um die Festigkeitswerte der Matrix zu erhöhen oder um eine Gewichtsreduktion zu erzielen. Karbide und Boride werden beispielsweise primär zur Erhöhung der Verschleißbeständigkeit im Eisen- und Stahlsektor verwendet. Die Herstellung eines Stahl-Keramik-Verbundwerkstoffes mit reduzierter Dichte bei gleichbleibender oder erhöhter Steifigkeit ist das Ziel laufender Untersuchungen am Lehrstuhl für Metallurgie an der Montanuniversität Leoben. Diese Publikation gibt einen Überblick über mögliche Herstellwege für Verbunde mit einer Stahl- oder Eisenmatrix und einer Keramik als verstärkende Phase. Es wird eine Einteilung der Herstellwege über die Entstehung der keramischen Phase getroffen und auf die Vor- und Nachteile der einzelnen Verfahren eingegangen. Mittels zweier Tabellen entsprechend der zuvor getroffenen Einteilung soll die Vielzahl der bisherigen Forschungen auf diesem Gebiet mit den zugehörigen Untersuchungsmethoden dargestellt werden.AbstractMetal-Matrix-Composites use a reinforcing phase to improve the mechanical properties of the matrix material or achieve a weight reduction. For example in iron and steel industrial applications typically carbides and borides are used to improve wear resistance. The intention of current investigations at the Chair of Metallurgy at the Montanuniversitaet Leoben is to produce a composite with reduced density and consistent or increased stiffness as steel. This paper reviews possible processing routes on steel composites with ceramic reinforcing phases based on a literature survey. A classification of the processing steps based on the origin of the ceramic phase is made and the advantages and disadvantages of these steps are summarized. Two tables are given to present the high amount of possible producing steps and the used investigation techniques for steel-based metal matrix composites.

Experimental study on the formation of non-metallic inclusions acting as nuclei for acicular ferrite in HSLA steels through specific deoxidation practice and defined cooling conditions

Specific types of non-metallic inclusions are known to act as heterogeneous nuclei for the formation of acicular ferrite, which provides excellent toughness. By increasing the amount of acicular ferrite in the microstructure, the properties of HSLA steels can be optimized significantly.Although the formation of acicular ferrite caused by heat treatments (thermomechanical treatments or welding) is quite well described in literature, there is less information to find about the formation of acicular ferrite immediately out of the liquid melt. Within the present study experiments on laboratory scale are carried out simulating the influence of cooling conditions and Ti-content on size, chemical composition and morphology of non-metallic inclusions and consequently on the amount of acicular ferrite. All experiments were carried out with a dipping test simulator enabling very well controllable cooling conditions. Optical microscopy in combination with special etching methods as well as SEM/EDS-analysis was used for microstructure and inclusion characterization.

Experimental and Numerical Investigations on Hot Tearing during Continuous Casting of Steel

This paper focuses on hot tearing in continuous casting of steel and the experimental as well as numerical prediction of the hot tearing susceptibility. As a preliminary point, the current understanding of the appearance of this kind of defects and the resultant requirements for numerical und experimental hot tearing simulation will be briefly summarized. The next section describes the experimental determination of critical strain values by means of the proven SSCT (Submerged Split Chill Tensile) test and their implementation into a 1D-FV-solidification model (one-dimensional-finite-volume) developed in-house. Exemplarily, the model will be applied to the casting of two medium carbon steel grades on a slab casting machine.ZusammenfassungDie vorliegende Veröffentlichung beleuchtet einleitend das heutige Verständnis des Erscheinungsbildes und des Bildungsmechanismus von Heißrissen im Stranggießprozess. Daraus werden die Forderungen an die numerische und experimentelle Simulation dieser häufig auftretenden Fehlerform abgeleitet. Der experimentelle Teil beschreibt die Ermittlung von kritischen Dehnungen im SSCT–Test (Submerged-Split-Chill-Tensile) und die Umsetzung dieser Kennwerte in ein 1D-FV-Erstarrungsmodell (Eindimensionales-Finite-Volumen). Abschließend wird das Modell auf das Beispiel des Vergießens zweier mittelkohliger Stähle auf einer Brammenstranggießanlage angewendet.

Experimental und numerical investigations on cooling efficiency of Air-Mist nozzles on steel during continuous casting

Cooling strategies in continuous casting of steel can vary from rapid cooling to slow cooling, mainly controlled by adjusting the amount of water sprayed onto the surface of the product. Inadequate adjustment however can lead to local surface undercooling or reheating, leading to surface and inner defects. This paper focuses on cooling efficiency of Air-Mist nozzles on casted steel and the experimental and numerical prediction of surface temperature distributions over the product width. The first part explains the determination of heat transfer coefficients (HTC) on laboratory scale, using a so called nozzle measuring stand (NMS). Based on measured water distributions and determined HTCs for air-mist nozzles using the NMS, surface temperatures are calculated by a transient 2D-model on a simple steel plate, explained in the second part of this paper. Simulations are carried out varying water impact density and spray water distribution, consequently influencing the local HTC distribution over the plate width. Furthermore, these results will be interpreted with regard to their consequence for surface and internal quality of the cast product. The results reveal the difficulty of correct adjustment of the amount of sprayed water, concurrent influencing water distribution and thus changing HTC distribution and surface temperature.