Ultra-fine grained high carbon steel by innovative deformation

It is well known that the refinement of grain size in metals leads to a significant improvement in specific mechanical properties. Processing schedules have been investigated aimed at producing an homogeneous ultra-fine ferrite and spheroidised carbide aggregate microstructure in high carbon (CMn) steels (0.6-1.2wt%C), via conventional 'warm' rolling and innovative Equal Channel Angular Extrusion (ECAE). Suitable deformation schedules were determined from dilatometry and thermo-mechanical Gleeble simulations. Evidence of an ultra-fine ferrite and carbide aggregate microstructure following 'warm' rolling was observed. A significant improvement in tensile strength, particularly proof stress was also noted in comparison to material deformed at higher temperatures. Concurrent ECAE experiments investigated microstructural evolution with incremental strain. Extensive analysis was carried out using various techniques, including high resolution Electron Back Scattered Diffraction (EBSD). Evidence of ferrite grain refinement was noted in a eutectoid composition steel. A sub-micron ferrite structure was observed following high strains (ε∼3.33) and the mechanical properties exhibited a marked increase in tensile strength.