An EBSD-based methodology for the characterization of intercritically deformed low carbon steel

Heavy gauge structural plates has been widely rolled in the austenite/ferrite two phase region, in order to meet the demanding market requirements regarding tensile properties. Even though strength levels can be increased by intercritical rolling, toughness properties may be impaired. Therefore, a greater knowledge of how different austenite-ferrite balances affect the microstructural evolution during intercritical deformation is required. With the aim of gaining a deep comprehension of the evolution of the microstructure during intercritical deformation, dilatometry tests were performed simulating intercritical rolling conditions. Different ferrite populations are identified in the resulting microstructures, composed of intercritically deformed ferrite and non-deformed ferrite transformed during final air cooling. In the deformed ferrite grains well defined substructure is clearly noticed, whereas the non-deformed grains formed during air cooling step do not show any evidence of substructure. In the current work, EBSD advanced characterization technique was used to develop a methodology that is able to differentiate the intercritically deformed ferrite from non-deformed ferrite for low carbon steels. Based on the Grain Orientation Spread (GOS) parameter, a threshold value of 2° was defined to distinguish deformed and non-deformed ferrite grains. The proposed procedure allows distinguishing both ferrite populations and quantifying microstructural parameters of each family. The effect of the addition of C and austenite-ferrite balance on the microstructural evolution of each ferrite type was analyzed.