Abstract
This study used scanning electron microscopy with an electron backscatter diffraction system to study the refinement mechanism of proeutectoid ferrite (Pro-F) and eutectoid ferrite (Eut-F) in a D2 wheel steel under rolling contact conditions. The results indicate that as the shear strain increased (γ < 0.21), the dislocation density in the proeutectoid ferrite increased continuously, and the formed dislocation cells were distributed uniformly in the grains. Subsequently, the dislocation cell boundaries were changed into low-angle boundaries (LABs); these LABs gradually became high-angle boundaries (HABs), and the average grain size was refined from 8 μm to 710 nm. Under a shear strain of 0.21 ≤ γ ≤ 0.84, dislocation pile-up occurred at the ferrite side of the eutectoid ferrite–cementite interface, and the spatial misorientation between the two adjacent eutectoid ferrites increased gradually. The ferrite lamellar was divided into bamboo-like grains by the LABs, and the proeutectoid ferrite was refined gradually into equiaxed grains. When the shear strain was at 0.84 < γ < 3.314, the number of HABs inside the eutectoid ferrite lamellar increased, and they were refined into bamboo-like grains. The two kinds of ferrite grains are refined repeatly by the equiaxial grains in an “elongation-bamboo like refinement-elongation” process, which gradually reduced the size difference. As the shear strain further increased, the two ferrites were completely mixed into the same morphology, the dislocation density was reduced dramatically, and ultra-fine equiaxed grains of approximately 110 nm were formed.
Highlights
With the rapid development of high-speed railways, friction and wear between wheels and rails and rolling contact fatigue damage are becoming more and more serious[1,2,3]
The results indicate that with the increase of the shear strain (γ
The dislocation cell boundaries were changed into low-angle boundaries (LABs), and the low-angle boundaries were gradually changed into the high-angle boundaries (HABs), and the average grain size was refined from the original 8 μm to 710 nm
Summary
With the rapid development of high-speed railways, friction and wear between wheels and rails and rolling contact fatigue damage are becoming more and more serious[1,2,3] Such as the white layer will accelerate the peeling of the material[4], and the wheel polygonisation wear will increase the vibration of the train[5].Those problems shorten the repair and maintenance cycle of wheels and rails, and increase railway operating costs[6, 7]. Pan et al studied the detailed changes of microstructure in the wear process of CL65 pearlite wheel steel through sliding wear test, and formed 35 nm nanocrystalline on the wearing surface, and the surface nanocrystalline formation was mainly completed through four stages of transformation[9]. Hua and co-authors applied EBSD technique to preliminary analyze the changes of proeutectoid ferrite at different depths of crest and trough after polygonisation wear in the rolling wear conditions, and found that the surface layer ferrite grains were obviously refined[15]
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