Influence of Thermal Condition of ECAP on Microstructure Evolution in Low Carbon Steel

Abstract

Commercial low carbon steel AISI 1010 was subjected to Equal Angular Channel Pressing (ECAP) at different temperatures. The paper describes the refinement of the coarse grained 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 temperature in the ranging between 150 – 300°C. The number of passes at each temperature was N = 3. Optical microscopy, 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 at the lowest ECAP temperature of 150°C extensively elongated ferrite grains with dense dislocation network dominate in the structure. The randomly scattered polygonized subgrains have been observed. 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 was increased the process of dynamic polygonization and recrystallization occurred more effectively and the submicrocrystalline structure was formed by sectioning of elongated ferrite grains. The formation of such predominant submicrocrystalline structure resulted in strength increase of the low carbon steel.