目的 铁路道岔的结构复杂,车轮与道岔之间的动态相互作用较剧烈,容易出现磨损和接触疲劳损伤,因此提高道岔的耐磨性和滚动接触疲劳性能成为亟须解决的关键问题。激光固态相变技术在提升材料力学性能和耐损伤性能方面展现出巨大潜力,但该技术尚未在道岔应用中得到系统研究,这里旨在探索该技术在道岔钢轨中的应用可行性,并为激光固态相变U75V材料在道岔上的应用提供理论支撑。方法 首先分析不同搭接率下激光固态相变U75V材料的硬度和微观组织分布,并利用MJP-30A滚动磨损与接触疲劳试验机模拟道岔滚动接触载荷,研究激光固态相变U75V的滚动接触疲劳损伤的演变规律,并讨论滚动接触疲劳损伤机理。结果 激光固态相变能够改变U75V材料的微观组织,并提高材料的硬度。在激光固态相变后,形成了以针状马氏体为主的硬化区和以回火马氏体为主的软化区,硬化区表面硬度分布在800HV0.2左右,相较于基体的平均硬度（339HV0.2）提升了1.36倍;软化区表面硬度分布在650HV0.2左右,介于硬化区与基体之间。通过激光固态相变能够提高U75V材料的耐磨性能和抗塑性变形性能,与未处理U75V相比,在干态10 000 r后,激光固态相变U75V材料的磨损量降低了26.3%,硬化区塑性变形层深度减小了97.7%,软化区塑性变形层深度减小了95%。未处理U75V的疲劳裂纹扩展现象严重,在水态下、5 000 r时就发生了严重的疲劳剥落现象。在循环转数较小时激光固态相变U75V的硬化区主要为细小疲劳裂纹,软化区主要为表层细小密集的多层裂纹。在循环转数（130 000 r）较大时,硬化区和软化区发生了疲劳剥落,软化区表层细小密集的裂纹会被磨掉,部分裂纹会扩展,出现枝裂纹。结论 通过激光固态相变能够提高U75V材料的滚动接触疲劳性能。
Abstract
In order to improve the wear resistance and rolling contact fatigue (RCF) performance of railway turnouts which often suffer from severe damage due to their complex geometry and intense dynamic interaction with train wheels, a laser solid-state phase transition technique will be applied to U75V material. This method, although proven effective in enhancing surface properties in other materials, has not yet been systematically investigated for railway turnout applications. The work aims to explore the feasibility of applying this technology in turnout rails and provide theoretical support for the application of laser solid-state phase transition of U75V material in turnouts. A comprehensive experimental approach was employed to evaluate the microstructural evolution, hardness distribution, and RCF resistance of U75V material after laser solid-state phase transition under different overlap ratios.
A series of samples were processed through controlled laser treatment to induce phase transition, resulting in the formation of distinct hardened zone and softening zone. Microstructural characterization revealed that the hardened zone primarily consisted of needle-like martensite, whereas the softened region exhibited tempered martensite. The treated surface exhibited a significant increase in microhardness. The hardened zone reached approximately 800HV0.2, representing a 136% increase over the untreated U75V(339HV0.2), while the softening zone averaged around 650HV0.2, which was between the hardened zone and U75V substrate.
To simulate service conditions of turnouts, a MJP-30A rolling wear and contact fatigue tester was employed under both dry and water conditions. The laser solid-state phase transition U75V samples demonstrated substantial improvements in wear and plastic deformation resistance. After 10 000 revolutions in dry state, the wear volume was reduced by 26.3% compared to the untreated samples. Additionally, the depth of plastic deformation layers in hardened zone and softening zone decreased by 97.7% and 95%, respectively. These results confirmed the enhanced structural integrity of the treated surface under repeated rolling-sliding contact.
In fatigue test, untreated U75V samples showed severe crack propagation and early-stage spalling under water-lubricated conditions, with notable damage occurring at just 5 000 cycles. In contrast, the laser-treated samples exhibited delayed fatigue damage initiation and a different damage mechanism. At lower cycle counts, microcracks in the hardened zone remained fine and dispersed, while the softened zone presented dense, shallow multi-layer cracks confined near the surface. With extended cycles (up to 130 000), fatigue spalling was observed in both zones. However, surface microcracks in the softened region were gradually removed by abrasion, and a portion of them continued to expand downward and form branch cracks.
This study demonstrates that laser solid-state phase transition significantly improves the fatigue endurance and wear resistance of U75V material. The formation of tailored martensitic microstructures and the gradient hardness profile between hardened and softened zones effectively suppress plastic deformation and delay fatigue crack propagation. These findings provide new insights into damage control mechanisms in laser-treated turnout components and also offer experimental basis and theoretical foundation for the application of laser solid-state phase transition U75V material in turnouts.
关键词
激光固态相变 /
U75V材料 /
微观组织 /
塑性变形 /
滚动接触疲劳
Key words
laser solid-state phase transition /
U75V material /
microstructure /
plastic deformation /
rolling contact fatigue
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基金
国家重点研发计划（2023YFB4603400）; 国家自然科学基金（52320105007）; 四川省博士后创新人才支持项目（BX202420）; 中央高校基本科研业务费专项资金（2682024CG007）
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