The possibility of applying new high-strength steels with excellent forming behaviour (TRIP, TWIP and LIP steels) in automotive manufacturing is a significant potential for improvement in the area of reducing weight while simultaneously increasing crash safety. The present work investigates endogenous inclusions in some high-alloy TRIP and TWIP steels because the most stringent product requirements are tightly related to cleanness. The expected formation of inclusions is discussed based on thermodynamic observations made with ThermoCalc. The solidification conditions were varied in experiments with the so-called SSCT (submerged split chill tensile) apparatus. Furthermore, different treatment times were set in order to investigate this influence on the inclusions. A catalogue of endogenous inclusions in these new steel grades is currently being created with the help of the automated SEM/EDX inclusion analysis system at voestalpine Stahl GmbH in Unz. Further studies will follow to systematically determine the interactions between steel, slag and refractory materials.
The possibility of using new, high-strength steels with an attractive forming behaviour (e.g. induced plasticity steels) in automotive manufacturing, offers a significant potential for improvement in the area of reducing the weight while simultaneously increasing crash safety. Induced plasticity steels not only possess high strength but also excellent elongation properties and high energy absorption capacities due to the TRIP and TWIP effects, Table 1. [1±4] This profile of mechanical properties is of great interest for crash-relevant automotive components.Common TWIP steel concepts are based on high Mn and Al contents, which are known to cause various problems during steelmaking. The search for suitable primary and secondary steelmaking processes, and the feasibility of casting these steel grades on conventional continuous casting machines, is the focus of ongoing research. The aim of the work presented here is to provide a basis for decisions on the subsequent development of the industrial production of high-Mn and -Al steels.At the very beginning, the following potential difficulties for the continuous casting of high-Mn, high-Al steels were identified: [5] ± high-temperature strength: is expected to be extremely high for these steels, and thus may be a problem for the strand guiding and soft reduction system in casting machines;± hot tearing: the wide brittle-temperature range during the solidification of high-Mn and -Al steels indicates a high crack susceptibility;± segregation at the micro-and macroscopic levels: possible formation of banded structures, resulting in difficulties during further processing;± non-metallic inclusions: the possible interaction between precipitates and mechanical properties means that steel cleanliness levels (secondary metallurgy) should be defined;± scale formation: partial oxidation plays a role in the formation of surface cracks in the casting and rolling process.This list does not consider necessary process adjustments, such as the development of suitable mold powders for highAl steels.The work presented here is concerned with the high-temperature mechanical properties of an high strength structural steel (HSSS) steel and the high-Mn, high-Al steel X50MnAl 25 1 in comparison to common ultra low carbon (ULC) and electrical sheet (ES) steels, the latter both known not to cause many problems during the continuous casting process. MethodologyThe high-temperature mechanical properties and the crack susceptibility were analyzed using the SSCT (submerged split-chill tensile) method. The principle of this testing method is described in detail elsewhere. [6±8] The SSCT test was developed to simulate the shell straining during the continuous casting process. A steel cylinder, split in two halves, is submerged in a liquid steel melt inside an induction fur- COMMUNICATIONS
In this work were compared two nitrogen and vanadium microalloyed steels in terms of the nitride or carbonitride phases present. The Thermal Evolved Gas Analysis (TEA) clearly showed that the one steel contains a higher volume fraction of nitrogen bound as vanadium carbonitride compared to the other steel in the natural relation to the total nitrogen content in steels. For promotion of this statement, the content of free nitrogen with using of the Hot Hydrogen Extraction (HHE) method was analysed and the thermodynamic prediction of the equilibrium composition of precipitating phases in microalloyed steels by the CALPHAD method with use of the Thermo-Calc software was carried out. Ironmaking & steelmaking. 2008, vol. 35, no. 2, p. 124-128. http://dx.doi. Ironmaking & steelmaking. 2008, vol. 35, no. 2, p. 124-128 AbstractIn this work were compared two nitrogen and vanadium microalloyed steels in terms of the nitride or carbonitride phases present. The Thermal Evolved Gas Analysis (TEA)clearly showed that the one steel contains a higher volume fraction of nitrogen bound as vanadium carbonitride compared to the other steel in the natural relation to the total nitrogen content in steels. For promotion of this statement, the content of free nitrogen with using of the Hot Hydrogen Extraction (HHE) method was analysed and the thermodynamic prediction of the equilibrium composition of precipitating phases in microalloyed steels by the CALPHAD method with use of the Thermo-Calc software was carried out.KEY WORDS: microalloyed steel; carbonitride; thermal evolved gas analysis (TEA); hot hydrogen extraction (HHE); Thermo-Calc.
Neu entwickelte hochmanganhaltige IP-Stähle stellen aufgrund der chemischen Zusammensetzung besondere Anforderungen an die Herstellung. In dieser Arbeit wird versucht, einen Überblick über die metallurgischen Fragestellungen und die Forschungstätigkeiten des Lehrstuhls für Metallurgie, Montanuniversität Leoben, auf dem Gebiet von IP-Stählen in der Zeit unter der Leitung von Prof. Krieger zu geben. Metallurgical Challenges of New Alloy Concepts Illustrated by Induced Plasticity (IP) Steels.Recent progresses in materials development of high manganese steels are due to their extraordinary chemical composition very demanding in the view of production. This work tries to give an overview on metallurgical questions and research activities in the field of IP-steels at the Chair of Metallurgy, Montanuniversität Leoben, under the responsibility of Prof. Krieger.Abb. 1: Entwicklungslinien in der Stahlwerksforschung von Karosseriestählen
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