OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 26 No. 4 2024 fi ne-grained ferrite. The material hardness of the lower compression ring is less than HB85. The lower ring is subjected to lower temperatures, so the structural changes here are signifi cantly lower. However, cyclic loads and deformation eff ects lead to the formation of fatigue cracks and a decrease in mechanical properties. The cementite inclusions in the upper compression ring occupy a larger area than the cementite inclusions in the lower compression ring. This indicates more signifi cant mechanical and thermal stresses on the upper ring. Also, according to the microphotographic images, microcrystallites are observed to be crushed in the most stressed material, which correlates with the X-ray diff raction data (Table 1). Fig. 3. Photo of the microstructure of the lower compression ring Ta b l e 1 Results of X-ray diff raction data processing Phase a, Å V, Å3 hkl 2θ β, grad D, Å Dislocation density ρD, см -2 Lattice micro-distortions Δd/d Fe, lower ring 2.8785 23.9 110 44.20 0.5 180 9.3·1011 0.00758 Fe, upper ring 2.8870 24.1 110 44.07 0.63 142 14.8·1011 0.00998 Fig. 4, a and b show fragments of X-ray diff raction patterns of the surfaces of the lower (a) and upper (b) compression rings. The results of X-ray diff raction data processing are summarized in Table 1. As shown by the X-ray diff raction studies (Table 1), the upper compression ring shows an increase in dislocation density (approximately 60 %) as well as larger values of lattice microstrains (approximately 30 %) compared to the lower ring. In addition, in the upper compression ring there is a greater refi nement of the coherent scattering Fig. 4. X-ray patterns of the surfaces of the lower (a) and upper (b) compression rings a b
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