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M. Lückl, S. Ilie, J. Six, E. Kozeschnik:
"The Influence of Surface Microstructure Control Cooling on the Hot Ductility of Microalloyed Steel";
Talk: MSE 2014, Darmstadt; 2014-09-23 - 2014-09-25.

The problem of transverse cracks during continuous casting of steel has been an issue for over 40 years. Particularly, at temperatures in the region of the second ductility trough, deformation can become critical, because the slab is exposed to severe thermal and mechanical stresses. Low ductility values are often observed in a temperature range of 600°C to 1200°C, where the bending of the slab is commonly performed. The cracks could be related to the presence of an extremely coarse-grained zone with film-like ferrite along the austenite grain boundaries or to precipitation of second-phase particles. In the present investigation, the mechanism of surface microstructure control cooling is investigated to prevent transverse cracks. Tensile samples are taken from regions close to the upper surface of the slab. The microstructure changes are controlled by a double phase transformation as a result of intensive cooling and reheating. This heat treatment was performed using a Gleeble 1500 thermo-mechanical simulator and brings about a film-like ferrite free structure. The effects of the cooling temperature and the reheating temperature on the reduction of area at different test temperatures are examined.

hot ductility, surface structure control cooling, double phase transformation, grain refinement