Description:
The objectives of this project were: 1. To establish the best processing routes to promote the formation of ultrafine ferrite (preferably 1-3 μm) and mixed (e.g. ferrite-cementite) microstructures for a wide range of C contents (0.05-1.6%C). 2. To assess the benefits that can be achieved in terms of strength, ductility and toughness by the formation of UF microstructures. 3. To produce very fine bulky microstructure using two innovative deformation methods : Accumulative Roll Bonding and Equal Channel Angular Extrusion. 4. The programme of work was a multi-partner collaboration among CSM (Italy), CRM (Belgium), MPI (Germany) and CORUS Sheffield (England) and was coordinated by CSM. Results showed that the grain size of ferrite can be refined to 1-3 μm by different methods using advanced thermomechanical processes that can be applied on already existent pilot mills. Innovative techniques like Accumulative Roll Bonding and Equal Channel Angular Extrusion showed to be very effective in grain refinement, because they can easily impose high deformations giving ultrafine grains but that, at this stage, are still in laboratory scale. Further, the mechanisms of ultrafine grain refinement were clarified. As expected, large enhancements in strength and toughness and a reduced work hardening in the ultrafine grained steels were observed. A second phase such as globular cementite resulted to be beneficial to improve both strength and work hardening rate of steels. In addition to grain refinement strengthening, precipitation hardening can also contribute to an obvious improvement in strength.