Ultrafine Grained Steels by Advanced Thermomechanical Processes and Severe Plastic Deformations

摘要

On the wake of the advances in Australia and Japan in achieving even finer grain sizes, the European steel companies became particularly interested in the prospects for 1 mm-UFF. For this reason, under the auspices of the European Community for Steel and Coal (ECSC), a preliminary one-year feasibility study was commissioned in 1999 to assess the properties and prospects for bulk manufacture of fine (sub-micron/micron) structures and starting from the results of this project, another project was commissioned. During this new research, different refining mechanisms and innovative deformation cycles applied to a wide range of chemical compositions were studied. The primary objective of the project was to optimise processing routes for 2-3 μm grained mixed microstructures in the bulk or surface layers of strip, plate or rods. The metallurgical aspects were focused on processing routes that do not require extreme strains and significant plant changes, through the study of microalloying additions when necessary. This paper summarizes the results from this new project regarding both ultrafine surface grained steels, obtained exploiting the Deformation Induced Ferrite Transformation mechanism (DIFT), and the Accumulative Roll Bonding technique.