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Warm rolling of eutectoid steels: Scale-up from hot torsion testing to pilot hot rolling trials1

par Caruso, Matteo ;Pohu, Benjamin;Schmitz, Alain;Godet, Stéphane
Référence 4th International Conference on Thermomechanical Processing of Steels, TMP 2012(10 September 2012 through 12 September 2012; Code 102936: Sheffield; United Kingdom), TMP 2012 - 4th International Conference on Thermomechanical Processing of Steels
Publication Publié, 2012

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Résumé :

The goal of this research is the development of a new industrial thermomechanical schedule that leads directly to a fine spheroidized microstructure after hot rolling of a eutectoid steel. Hot torsion testing performed at temperatures close to Ar1 demonstrates that hot deformation accelerates the ?-topearlite transformation and leads to the spheroidisation of the cementite lamellae. Extended dynamic recovery occurs during warm deformation of ferrite and the subgrains are shown to transform progressively into high angle boundaries. This process can be referred to as continuous dynamic recrystallization (cDRX) and is responsible for the refinement of the ferrite grains down to 3 μm. To explore the industrial feasibility of this thermomechanical treatment, a similar schedule was performed on an instrumented pilot scale rolling mill. The resulting microstructures are fully spheroidized because warm deformation induces the fracture of the cementite lamellae. The formation of a well developed subgrain network by dynamic recovery is also observed. However, due to the higher strain rates (5-10 s-1) compared to the torsion testing (0,1 s-1), the evolution of low angle boundaries into high angle boundaries during rolling is not observed.