Abstract

TEM and X-ray diffraction studies were carried out to examine changes in the structure, phase composition, and defect substructure in the head of a differentially hardened rail after 691.8 and 1411 million gross tons (MGT) of traffic. The rail material was examined along the central axis of the head and along the gauge corner radius at distances of 0, 2, and 10 mm from the tread surface. The redistribution of carbon atoms was quantitatively analyzed. It was shown that long-term operation of rails is accompanied by two simultaneous processes related to the evolution/degradation of the structure and phase composition of lamellar pearlite colonies, namely, cutting and cold dissolution of cementite lamellae. The first process involves the cutting of carbide particles and the subsequent dragging of their fragments, which causes changes only in their linear dimensions and morphology. The second process is the fracture of cementite lamellae in pearlite colonies due to the migration of carbon atoms from the cementite lattice to dislocations, which creates favorable conditions for a structural-phase transformation in the rail metal. The reason of this is the low average binding energy of carbon atoms with dislocations (~0.6 eV) and with iron atoms in the cementite lattice (~0.4 eV). Cementite nanoparticles were revealed in the ferrite matrix; their appearance was accompanied by dislocation glide and deformation-induced decomposition of carbon solid solution in α-iron. The curves of the change in the total yield strength versus the distance to the tread surface along different directions in the rail head were plotted. The carbon content in the structural elements of rail steel was estimated. It was found that carbon in the initial state is mainly contained in cementite particles, while in rails subjected to traffic loading it is located, along with cementite particles, at crystal structure defects (dislocations, grain boundaries, subgrains). In the surface layer of steel, carbon is also present in the crystal lattice of α-iron. The results on the redistribution of carbon atoms are interpreted using the concept of interstitial bifurcation structural states in lattice curvature zones.

中文翻译：

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长期运行过程中轨道金属的精细结构和性能的演变

摘要

进行了 TEM 和 X 射线衍射研究，以检查经过 6.91.8 和 14.11 亿总吨 (MGT) 的交通量后差异硬化钢轨头部的结构、相组成和缺陷子结构的变化。在距胎面表面 0、2 和 10 毫米的距离处，沿轨头的中心轴和轨距角半径检查钢轨材料。对碳原子的重新分布进行了定量分析。结果表明，钢轨的长期运行伴随着两个与层状珠光体群的结构和相组成的演化/降解相关的同时发生的过程，即渗碳体层状体的切割和冷溶解。第一个过程涉及切割碳化物颗粒并随后拖动它们的碎片，这只会导致它们的线性尺寸和形态发生变化。第二个过程是由于碳原子从渗碳体晶格迁移到位错，珠光体群中渗碳体片层的断裂，这为钢轨金属的结构相变创造了有利条件。其原因是具有位错的碳原子 (~0.6 eV) 和渗碳体晶格中的铁原子 (~0.4 eV) 的平均结合能较低。在铁氧体基体中发现了渗碳纳米颗粒；它们的出现伴随着位错滑移和碳在α-铁中固溶体的变形诱导分解。绘制了总屈服强度随轨头不同方向到踏面距离的变化曲线。估算了轨道钢结构元素中的碳含量。发现初始状态的碳主要包含在渗碳体颗粒中，而在受到交通载荷的钢轨中，它与渗碳体颗粒一起位于晶体结构缺陷（位错、晶界、亚晶）处。在钢的表层中，碳也存在于α-铁的晶格中。使用晶格曲率区中间隙分叉结构状态的概念来解释碳原子重新分布的结果。在钢的表层中，α-铁的晶格中也存在碳。使用晶格曲率区中间隙分叉结构状态的概念来解释碳原子重新分布的结果。在钢的表层中，碳也存在于α-铁的晶格中。使用晶格曲率区中间隙分叉结构状态的概念来解释碳原子重新分布的结果。