Austenite grain size in the continuous casting process: Metallographic methods and evaluation

Austenite grain size is an important parameter for the ductility of steel at elevated temperatures. Therefore, indirect measurements of austenite grain size on slab samples and a specimen from laboratory experiments were carried out. To reveal the prior austenite grain boundaries three etchants (picric acid, ammonium persulfate and nital 3%) were used. One of the main objectives of the present work was to investigate how far the grain size distribution in the specimen from the laboratory experiment corresponds with the grain size distribution on – and beneath – the surface of a continuously cast slab. The measured grain size distribution of a slab and a laboratory experiment – both with an equivalent carbon content of 0.21 wt.% – show a good agreement. A clear maximum grain size can be found for a carbon equivalent of between 0.15 and 0.17 wt.%. The results of the presented metallographic examinations serve as an important basis for the development of an austenite grain growth model.