Overview

Ernst Gamsj ger and Franz Dieter Fischer
Christian Doppler Laboratory - Functionally Oriented Material Design, Institut f r Mechanik, Montanuniversit t Leoben, Austria

Christian M. Chimani
VOEST-Alpine Industrieanlagenbau GmbH, Linz, Austria

Jiri Svoboda
Institute of Physics of Materials, Academy of Sciences of the Czech Republic, Brno, Czech Republic

1. Introduction

During continuous casting of carbon steel the as-cast material is transported from the mold through the strand support rolls to the end of the casting machine. In consequence of a temperature reduced ductility, surface cracking may occur. From the point or region of solidification to a temperature of about 1500K (depending on the steel quality) hot ductility increases during cooling. For several steel grades a minimum in hot ductility has been observed at temperatures between 1400K and 1000K, which is generally associated with the precipitation of non-metallic inclusions and the ?- ? phase transformation, see e.g. [SUZ 84], [MAE 90], [LEW 98], [NAG 99] and [CHI 99]. The properties of the strand depend not only on its chemical composition. Physical quantities and parameters like the austenite grain size before transformation, the cooling regime and global as well as local strains and strain rates determine the quality of the steel slab. The quantities mentioned above are interrelated with the kinetics of the solidification as well as the ?- ? phase transformation.

The Fe-C diagram shows that between 996K and 1184K a binary low-carbon alloy can exist in two phases, the ?-phase characterized by an fcc-crystal structure and...