Submicrocrystalline Structure Formation in Microalloying Low-Carbon Steel During Cold Equal Channel Angular Pressing and Heating

An opportunity of the formation of submicrocrystalline structure (with a grain size less than 1 micron) in a microalloyed steel 0.09%C-Mn-Si upon equal-channel angular (ECA) pressing and heating was investigated. The ECA pressing of the samples of 20 mm in diameter and 80 mm in length was performed by cold deformation (at 20 to 300DGC) for two passes at an angle of 90DG between the channels. The ECA pressing both at 20DGC and at 300DGC leads to the formation of a cellular structure. The study of the dependence of microhardness and microstructure of the samples on heating temperature and holding time revealed their similarity for both regimes of preliminary ECA pressing, at 20 C and 300DGC. New recrystallized grains are found metallographically only after heating to 550DGC and holding for at least 3 h. A decrease in microhardness and the absence of metallographically detectable new grains correspond to the formation of submicrocrystalline structure with a grain size of 200 to 400 nm, which is revealed only by electron-microscopic examination.