Strength and ductility of medium carbon steel after equal channel angular pressing

Upon the ECA pressing at 4000C of the AISI 1045 steel with 0.45% C, the processes of dynamic recovery are developed with the formation of subgrains of ∼320 nm in size and isolated grains of submicron size with high-angle boundaries. The fragmentation and partial spheroidization of the cementite lamellae is observed within the pearlite colonies. Deformation in pearlite grains is not sufficient, either to break down the cementite lamellae structure or to produce the refinement of ferrite grains. Annealing of the deformed steel with 0.45%C after ECA pressing causes the perfection of the recovered structure in ferrite and further processes of fragmentation, spheroidization, and coagulation of carbide phase. Annealing at T = 5500C for 5 h leads to almost complete spheroidization of carbides with an average size of ∼280 nm and increases to some extent the average ferrite grain (subgrain) size to ∼410 nm. The submicron grain-subgrain structure of the steel with 0.45%C causes a significant strengthening (YS = 960 MPa) at a retention of satisfactory elongation (EL = 8%). Subsequent annealing at T 5500C for 5 h increases ductility to EL = 14% and decreases the yield strength to YS = 745 MPa.