Effect of Strain on Deformation Microstructure and Subsequent Annealing Behavior of IF Steel Heavily Deformed by ARB Process

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Abstract
Ultra low-carbon interstitial free (IF) steel having ferrite (b.c.c.) single phase was deformed to various equivalent strains ranging from 0.8 to 5.6 by the accumulative roll bonding (ARB) process at 500°C. The microstructure and crystallographic feature of the deformed specimens were characterized mainly by FE-SEM/EBSD analysis. Grain subdivision during the plastic deformation up to very high strain was clarified quantitatively. After heavy deformation above 4.0 of strain, the specimens showed the lamellar boundary structure uniformly, in which the mean spacing of the lamellar boundaries was about 200nm and more than 80% of the boundaries were high-angle ones. Annealing behavior of the ARB processed IF steel strongly depended on the strain. The specimens deformed to medium strains exhibited discontinuous recrystallization characterized by nucleation and growth, while the specimens deformed above strain of 4.0 showed continuous recrystallization. The recrystallization behaviors are discussed on the basis of the microstructural and crystallographic parameters quantitatively measured in the as-deformed samples.