EBSD Study on Proeutectoid Ferrite and Eutectoid Ferrite Refinement Mechanism of D2 Wheel Steel Under a Rolling Condition

Abstract

In this paper, the SEM (with EBSD system) is used to study the re nement mechanism of proeutectoid ferrite (Pro-f) and eutectoid ferrite (Eut-f) of D2 wheel steel in a rolling contact. The results indicate that with the increase of the shear strain (γ<0.21), the dislocation density in the proeutectoid ferrite increased continuously, and the dislocation cells formed were uniformly distributed in the grains. Subsequently, the dislocation cell boundaries were changed into low-angle boundaries (LABs), and then the low-angle boundaries were gradually changed into the high-angle boundaries (HABs), and the average grain size was re ned from the original 8 μm to 710 nm. When the shear strain is at 0.21≤γ≤0.84, dislocation piled up occurred at the ferrite side of the interface of eutectoid ferrite/cementite, and the spatial misorientation between adjacent two eutectoid ferrites increased gradually, then the ferrite lamellar is divided into bamboo-like by the low-angle boundaries, and proeutectoid ferrite the grains are gradually re ned into equiaxed grain. When the shear strain is at 0.84<γ<3.314, the number of high-angle boundaries inside the eutectoid ferrite lamellar increased, and it is re ned into bamboo-like grains. The two kinds of ferrite grains are repeatedly re ned many times by the equiaxial grains "elongation-bamboo like re nement-elongation", which gradually reduced the size difference. As the shear strain further increases, the two kinds of ferrite are completely mixed into the same morphology, the dislocation density is dramatically reduced, and ultra-ne equiaxed grains about 110 nm is formed.