Hydrogen embrittlement (HE) in 2 GPa-grade press-hardened steel (PHS) has posed a great risk to its lightweighting application in automotive crash-resistant components. While conventional slow strain rate tensile tests show that the precharged hydrogen concentration of 3.5 wppm induces a severe loss in strength and ductility, the high strain rate tests conducted at 1–10³ s⁻¹ that simulate the crash condition demonstrate no loss in strength and a minimal loss in ductility. Such strain rate dependency cannot be exclusively explained via hydrogen diffusion and redistribution to susceptible prior austenite grain boundaries, as the tensile testing of precharged samples with jumping strain rates offers a sufficient redistribution period at slow-strain-rate loading, but does not necessarily lead to a high level of HE afterwards. Detailed fractography analysis acknowledges that hydrogen-induced microcracks nucleated within early deformation stages are directly responsible for the high HE susceptibility of all test conditions. A phase-field simulation comprising 2 GPa-grade PHS's microstructure features and the hydrogen diffusion under tested loading conditions is applied. The calculation reveals that the hydrogen redistribution behavior is spatially confined to the crack tip areas but to a much greater extent. It thus facilitates continuous crack growth following the main crack with minimal plastic deformation and avoids branching to form secondary cracks. The combined experiments and modeling highlight the vital role of microcracks in the HE performance of 2 GPa-grade PHS, upon which the safety factor of HE in high-strength martensitic steels shall be established.

中文翻译：

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2 GPa级热成形钢在不同应变速率下的氢脆机理研究：实验与建模


2 GPa 级热成形钢 （PHS） 中的氢脆 （HE） 对其在汽车防撞部件中的轻量化应用构成了巨大风险。虽然传统的慢应变速率拉伸试验表明，3.5 wppm 的预充氢浓度会导致强度和延展性的严重损失，但在 1-10^{3 s-1} 下进行的模拟碰撞条件的高应变速率试验表明，强度没有损失，延展性损失最小。这种应变速率依赖性不能完全通过氢扩散和重新分布到敏感的先前奥氏体晶界来解释，因为以跳跃应变速率对预充样品进行拉伸测试在低应变速率加载下提供了足够的再分布期，但不一定会导致之后高水平的 HE。详细的断口分析承认，在早期变形阶段成核的氢诱导微裂纹是所有测试条件的高 HE 敏感性的直接原因。应用了包括 2 个 GPa 级 PHS 的微观结构特征和测试负载条件下氢扩散的相场模拟。计算表明，氢再分布行为在空间上仅限于裂纹尖端区域，但程度要大得多。因此，它有助于在主裂纹之后以最小的塑性变形连续扩展裂纹，并避免分支形成二次裂纹。结合实验和建模强调了微裂纹在 2 GPa 级 PHS 的 HE 性能中的重要作用，在此基础上应建立高强度马氏体钢中 HE 的安全系数。