Quantitative characterization of ultrafine grained 12GBA steel with scanning tunnel microscopy

Coarse grained 12GBA steel was machined by multiaxial isothermal forging and warm rolling. Quantitative characteristics of steel structure were studied with scanning tunnel microscopy. Deformation processing was found to lead to ultrafine-grained structure formation, lamellar cementite fragmentation and its further spheroidization. Relative energies of individual ferrite/pearlite and intraphase pearlite boundaries were estimated by grain boundary dihedral angle measurement. It was revealed that ferrite/pearlite boundary energy is 1.5–2 times higher than the energy of intraphase pearlite boundary. Cumulative distribution functions for internal interfaces energy showed the decrease in relative energy after deformation processing as compared to coarse grained state. Obtained results were explained by an increase of low-angle boundary fraction and non equilibrium grain boundary segregation.