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Ultrafine-Grained Structure and its Thermal Stability in Low-Carbon Steel

Research paper by A. V. Korznikov, I. M. Safarov, R. M. Galeyev, S. N. Sergeev, A. I. Potekaev

Indexed on: 17 Nov '15Published on: 17 Nov '15Published in: Russian Physics Journal



Abstract

The influence of annealing temperature on ultrafine-grained structure (UFG) of low-carbon steel 05G2MFB, produced by multiple isothermal forging (MIF) and warm rolling is investigated. Following 1-hour annealing (from 20 to 550°С), the fibrous UFG-structure formed as a result of rolling remains virtually the same. The equiaxial UFG-structure is found to be stable as the annealing temperature is increased up to 600°С. An examination of the resulting UFG-states by the method of electron backscatter diffraction (EBSD) provided a way to identify the differences in softening processes for a number of structure types. When the temperature of annealing treatment of as-rolled steel specimens is increased to 600°С, the fraction of low-angle boundaries (LAB) is found to remain at about 56%, while the average grain/subgrain size in the rod cross-section increases from 0.4 to 0.9 μm. In the MIF-processed specimens, an increase in the annealing temperature up to 625°С gives rise to a gradual decrease in the fraction of LAGBs from 53 to 30%, with the average grain/subgrain size increasing from 0.4 to 0.6 μm.