Abstract
Commercial low carbon steel AISI 1010 was subjected to Equal Angular Channel Pressing (ECAP) at different temperatures. The paper describes the refinement of a quiet coarsegrained ferrite microstructure to submicrocrystalline range by large plastic strain. The steel was deformed in an ECAP tool with a channel angle φ = 90°, at different temperatures in the range of 150–300°C. The number of passes at each temperature was N = 3. Optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to study the formation of substructure and ultrafine grains in the deformed specimens. The TEM study reveals that even at the lowest deformation temperature the extensively elongated ferrite grains with dense dislocation network dominate in the structure. However, at the lowest deformation temperature of the ECAP process, the randomly scattered polygonized subgrains are already present in the deformed structure. The activation of dynamic recovery process, even at the lowest temperature of equal channel pressing, contributed to the formation of individual polygonized grains. As the temperature of ECAP processing is raised, the process of dynamic polygonization and recrystallization proceeds more effectively and the submicrocrystalline structure is formed by sectioning of elongated ferrite grains. The size of newly generated polygonized grains (subgrains and/or submicrocrystalline grains) is in the range of 300–500 µm. The results proved that the warm ECAP of the low-carbon steel under specific testing conditions leads to the formation of a predominantly submicron grain structure. The formation of such predominant submicrocrystalline structure resulted in significant increase in the yield stress and tensile strength of the steel.

Key words
low carbon steel, warm ECAP, structure evolution, dynamic recrystallization, mechanical properties

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