Piotr R. Scheller

Model Investigations on the Stability of the Steel-Slag Interface in Continuous-Casting Process

In the continuous-casting mold, the mold powder in contact with the liquid steel surface forms a liquid slag layer. The flow along the steel-slag interface generates shear stress at the interface, waves, and leads to fingerlike protrusions of liquid slag into steel. Reaching a critical flow velocity and thereby shear stress, the protrusions can disintegrate into slag droplets following the flow in the liquid steel pool. These entrained droplets can form finally nonmetallic inclusions in steel material, cause defects in the final product, and therefore, should be avoided. In the current work, the stability of a liquid-liquid interface without mass transfer between phases was investigated in cold model study using a single-roller driven flow in oil-water systems with various oil properties. Applying the similarity theory, two dimensionless numbers were identified, viz. capillary number Ca and the ratio of kinematic viscosities ν1/ν2, which are suitable to describe the force balance for the problem treated. The critical values of the dimensionless capillary number Ca* marking the start of lighter phase entrainment into the heavier fluid, are determined over a wide range of fluid properties. The dimensionless number ν1/ν2 was defined as the ratio of kinematic viscosities of the lighter phase ν1 and heavier phase ν2. The ratios of kinematic viscosities of different steel-slag systems were calculated using measured thermophysical properties. With the knowledge of thermophysical properties of steel-slag systems, Ca* for slag entrainment as a function of v1/v2 is derived. Assuming no reaction between the phases and no interfacial flow, slag entrainment should not occur under the usual casting conditions.

Verbesserung der Kaltumformbarkeit austenitischer CrNi-Stähle durch Nutzung des Trip-Effektes

Die Kaltumformbarkeit ist neben der Korrosionsbestandigkeit eine bedeutende Eigenschaft bei der Herstellung und Weiterverarbeitung der austenitischen CrNi-Stahle. Das hohe Kaltumformvermogen dieser Stahle wird masgeblich durch den Trip-Effekt hervorgerufen. Dieser Beitrag der TU Bergakademie Freiberg behandelt Verfahren zur Ausschopfung der Werkstoffreserven bezuglich eines hohen Kaltumformvermogens.

Improvement of the cold workability of austenitic CrNi steels using the trip effect

For the production and further processing of the austenitic CrNi steels the cold workability is a significant property in addition to the corrosion resistance. The high cold deformation behaviour of these steels is caused to a high degree by the trip effect. This article of the TU Bergakademie Freiberg deals with methods concerning material ressources relating to a high cold deformation.

Solidification Behaviour of Slags: The Single Hot Thermocouple Technique

Abstract With the Single Hot Thermocouple Technique the solidification behaviour of metallurgical slags has been studied, building TTT and CCT diagrams, with in situ observation for melting and solidification under various thermal conditions. Slags in the system CSTNA were studied, analysing the kinetics of crystals growth. Following findings are reported: (i) for the slag CS (%CaO/%SiO2 = 0.7) no crystal is observed during continuous cooling even to low cooling rates, but on the other hand intense crystallisation is obtained when increasing the temperature after reaching a particular range of lower temperatures; (ii) it was observed that the longer the duration of the superheating is, the longer the incubation times for a slag CST (41 %CaO, 29 %SiO2, 30 %TiO2) becomes; (iii) the addition of Na2O into the CST slag system shortens intensely the crystals incubation times at TTT diagrams to the range of seconds.

Institute of Iron and Steel Technology at the TU Bergakademie Freiberg

The Institute of Iron and Steel Technology was founded more than 130 years ago. In the 90s and in the last years the institute was equipped with modern devices for vacuum melting, casting and heat treatment, the slag laboratory was enlarged, the analytic laboratory completed and the material development and metallography were strengthened with new instruments. The large range of research fields allows to meet industrial needs from process metallurgy over casting and solidification to control of microstructure and resulting material properties. Besides research with industrial partners the basic research is a strong motor for future practice.ZusammenfassungDas Institut für Eisen- und Stahltechnologie wurde vor mehr als 130 Jahren gegründet. In den 90er und in den letzten Jahren wurde das Institut mit modernen Anlagen zum Vakuumschmelzen und-gießen sowie zur Vakuumwärmebehandlung ausgestattet, das Schlackenlaboratorium erweitert, das analytische Laboratorium mit neuen Geräten ergänzt und die Materialforschung von Stahlwerkstoffen sowie die Metallographie gestärkt mit neuen Forschungsapparaten. Mit der breiten Palette von Forschungsfeldern begegnet das Institut den Anforderungen der Industrie von der Prozessmetallurgie über Gießen und Erstarren bis zur Entwicklung des Gefüges und resultierender Materialeigenschaften. Neben der Forschung mit industriellen Partnern stellt die Grundlagenforschung einen starken Motor für zukünftige Anwendungen in der Praxis dar.