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For the new technology of thin slab casting and integrated rolling, the kinetic of the precipitation of different types of particles and the influence of the process (different dimensions of the slab or strip, different solidification rates) on the microstructure, i.e. mainly austenite grain size and segregation effects, were investigated.

For this study tests with soft or high strength Ti or Ti + Nb microalloyed steels were made under laboratory conditions and on pilot lines with realistic thermal cycles.

The results show that, within the typical thermal cycles during casting and cooling to rolling temperature, there is some precipitation of particles in the optical range that are mostly located in segregated areas and that have fixed most part of the nitrogen. In the temperature range of rolling, i.e. below 1 150 °C, precipitation kinetic without deformation proved to be very slow. The main effect of the faster deformation induced precipitation was seen after rolling passes with temperatures of 970 °C or lower.

The analysis showed the influence of solidification rate and material dimension on austenite grain structure (Smaller grains in thinner material) and on the moderate segregation (less segregation at a higher solidification rate).

The experimental data were used to prepare and fit a multiphase precipitation model to simulate nucleation and growth in austenite of carbonitrides and Ti carbosulphides in Tiand Ti + Nb microalloyed steels with particular reference to the thin slab casting process. The models were successfully verified by comparison with multipass rolling tests similar to industrial integrated casting and rolling conditions.

Additional information

Authors: GROSSTERLINDEN R, Thyssen Krupp Stahl AG, Duisburg (DE);DI NUNZIO P E, Centro Sviluppo Materiali (CSM), Roma (IT);HELLER P ET AL, TU Bergakademie, Institut für Eisen- und Stahltechnologie, Freiberg (DE)
Bibliographic Reference: EUR 20813 EN (2003), 241pp. Euro: 35
Availability: EUR-OP reference: KI-NA 20813-EN-C Available from EUR-OP sales agents URL:
ISBN: ISBN: 92-894-6138-1
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