转向架作为铁路车辆的关键部件，其安全性和可靠性直接影响列车的运行性能和使用寿命。研究了转向架用Q355NHC钢材料在不同试验条件下（取样方向和应力比）的裂纹扩展的行为差异，并对试样的微观组织和断口形貌进行了观察和分析。研究结果发现，在不同取样方向下受到的速率影响较小；但是改变应力比却对疲劳裂纹扩展行为的变化产生了显著的影响，裂纹扩展速率随着应力比的逐渐增加而明显加快。基于Q355NHC钢的试验数据提出了一种在已有模型基础上改进的归一化模型，用本文试验数据进行验证，结果表明，疲劳裂纹扩展归一化（fatigue crack growth normalization, FCGN）模型具有较高的精度，能很好地描述应力比对Q355NHC钢裂纹扩展速率的影响，可以为工程构件实际应用提供技术方法。

As a critical load-bearing component of railway vehicles, the bogie's structural integrity significantly influences the operational safety and service longevity of rolling stock. The fatigue crack growth behavior of Q355NHC bogie steel under varying experimental conditions (sampling direction and stress ratio) was systematically investigated, complemented by comprehensive microstructural characterization and fracture surface analysis. The experimental results reveal that the material exhibits minimal sensitivity to variations in sampling direction regarding crack propagation rates. However, a pronounced stress ratio dependence is observed, where the fatigue crack growth rate demonstrates significant acceleration with increasing stress ratio. Building upon the Paris law framework, we proposed an enhanced fatigue crack growth normalization (FCGN) model incorporating stress ratio effects through parameter normalization. Validation using experimental data demonstrates the FCGN model's superior predictive accuracy in characterizing stress ratio-dependent crack propagation behavior for Q355NHC steel. The developed methodology provides valuable technical insights for fatigue life assessment and damage-tolerant design of bogie components in engineering applications.