In this study, we investigate the relation between microstructure and fatigue crack propagation mechanisms in three commercial hot-rolled thick-plate advanced high-strength steels (AHSSs), namely 800CP, 700MC, and 700MCPlus, and compare them with a conventional high-strength low-alloy (HSLA) steel, 500MC, commonly used in heavy-duty vehicle chassis production. Tensile testing, and fatigue crack growth rate (FCGR) assessments have been conducted, and mechanisms controlling the performance of these steels are comprehensively examined through microstructure characterization before and after fatigue testing. Notably, FCGR results reveal that, despite having the highest yield strength among the investigated steels, 700MCPlus exhibits the slowest FCGR in both near-threshold and stable crack growth regimes. This improved fatigue crack propagation resistance of 700MCPlus in terms of its threshold stress intensity factor range (Δ) is attributed to its unique texture, which restricts slip activity, and the presence of martensite at grain boundaries, contributing to fatigue crack deflection. This martensite-induced crack deflection becomes more significant in the stable crack growth regime, where fatigue crack primarily propagates intergranularly as the stress intensity factor range () increases. These mechanistic findings offer new design possibilities for AHSSs, combining excellent strength and fatigue performance.

中文翻译：

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微观结构对先进高强度钢同时强度和抗疲劳裂纹性的影响

在这项研究中，我们研究了三种商用热轧厚板先进高强度钢（AHSS）（即 800CP、700MC 和 700MCPlus）的显微组织和疲劳裂纹扩展机制之间的关系，并将它们与传统高强度钢进行比较。低合金（HSLA）钢，500MC，常用于重型车辆底盘生产。已经进行了拉伸试验和疲劳裂纹扩展速率（FCGR）评估，并通过疲劳试验前后的微观结构表征来全面检查控制这些钢的性能的机制。值得注意的是，FCGR 结果表明，尽管 700MCPlus 在所研究的钢中具有最高的屈服强度，但在近阈值和稳定裂纹扩展状态下均表现出最慢的 FCGR。 700MCPlus 在阈值应力强度因子范围 (Δ) 方面提高了抗疲劳裂纹扩展能力，这归因于其独特的织构（限制滑移活动）以及晶界处马氏体的存在（有助于疲劳裂纹偏转）。这种马氏体引起的裂纹偏转在稳定的裂纹扩展状态中变得更加重要，其中随着应力强度因子范围 () 的增加，疲劳裂纹主要在晶间传播。这些机械发现为 AHSS 提供了新的设计可能性，结合了优异的强度和疲劳性能。