Evaluation of the Influence of Dispersion of Pearlite on the Fatigue of Carbon Steel
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EVALUATION OF THE INFLUENCE OF DISPERSION OF PEARLITE ON THE FATIGUE OF CARBON STEEL Kh. А. Askerov1 and І. О. Vakulenko2, 3
UDC 691.87:691.714:539.434
It is shown that the slope of a tangent to the fatigue curve can be used to analyze the effect of dispersion of pearlite on the fatigue strength of carbon steel. For a constant thickness of the ferrite-pearlite layer, we established an inversely proportional relationship between the indicated parameter and the density of accumulated dislocations. We also estimated the mechanism of influence of the dispersion of pearlite on the transition from low- to high-cycle fatigue of carbon steel. Keywords: carbon steel, dispersion of pearlite, dislocations, fatigue strength.
Introduction The changes in the structural state of carbon steel strongly affect its strength under cyclic loading [1, 2]. In particular, as the thickness of ferrite-pearlite layer ( λ ) decreases, the fatigue strength of carbon steel increases [3, 4]. This is accompanied by a decrease in the slope of tangent to the fatigue curve in its different regions. The transition from the regions of low-cycle fatigue to the regions of high-cycle fatigue is most often realized with violations of monotonicity of the analyzed curves [5]. This anomaly strongly depends on the combined influence of numerous factors. As the most important of these factors, we can mention the structural state of the metallic material, the conditions of cyclic loading, etc. [2, 4–6]. The analysis of the nature of appearance of these singularities in the fatigue curves reveals various causes: the inhomogeneity of development of structural transformations [6] and propagation of deformation [4], the changes in the active crystallographic slip systems [7] observed on attainment of a certain relationship between the amplitude and number of cycles to fracture, and the changes in the stressed state of the metal in front of the propagating crack [4, 7]. The aim of the present work is to clarify the mechanism of influence of the dispersion of pearlite on the short-term fatigue strength of carbon steel. Material and Procedure We studied a carbon railroad-wheel steel with a carbon content of 0.61% alloyed within the limits of the certified composition of 60 steel. Various degrees of dispersion of pearlite were obtained as a result of cooling of the metal down to certain temperatures of isothermal holding with a duration sufficient for the termination of the pearlite transformation. 1 2 3
Prydniprovska State Academy of Civil Engineering and Architecture, Dnipro, Ukraine. Acad. Lazaryan Dnipro National University of Railway Transport, Dnipro, Ukraine. Corresponding author; e-mail: [email protected].
Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 56, No. 2, pp. 71–74, March–April, 2020. Original article submitted September 3, 2019. 214
1068-820X/20/5602–0214
© 2020
Springer Science+Business Media, LLC
EVALUATION OF THE INFLUENCE OF DISPERSION OF PEARLITE ON THE FATIGUE OF CARBON STEEL
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Fig. 1. Influence of the dispersion of
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