第三代先进高强钢因其优良的力学性能备受关注。然而，钢铁材料的高强化通常导致氢脆敏感性显著增加，氢在材料微观组织中的扩散与偏聚是氢致延迟断裂的主要原因。作为第三代先进高强钢的重要组成相，奥氏体对多相微观组织中的氢扩散与氢致开裂将产生重要影响。本文以第三代先进高强钢——中锰钢为研究对象，围绕奥氏体对氢扩散与氢致延迟断裂行为的影响以及奥氏体的稳定性调控三方面展开研究，旨在阐明中锰钢氢致延迟断裂机理并寻求抗氢脆的组织设计方法。建立了考虑两相氢扩散系数与溶解度差异、铁素体内氢陷阱作用以及铁素体/奥氏体相界面氢偏聚作用的二维氢扩散模型，结合氢渗透实验，研究了中锰钢的氢扩散与偏聚行为。结果表明，奥氏体和相界面对氢扩散过程起主导作用，二者对降低有效扩散系数作用的相对大小与边界氢浓度有关，即边界氢浓度较高时，整体氢扩散主要受奥氏体内氢扩散与偏聚过程影响；随着边界氢浓度降低，相界面氢偏聚作用逐渐增强。通过边界氢浓度的确定，估算出相界面氢结合能为~38 KJ/mol。研究了中锰钢的局部变形行为和奥氏体?马氏体转变特征以及它们对氢致延迟断裂行为的影响。结果表明，局部变形程度增大，中锰钢氢脆敏感性增加。这是由于，局部变形程度增大，吕德斯应变增加，导致吕德斯带扫过区域的局部马氏体转变程度和局部应力水平提高。马氏体转变导致氢致裂纹沿马氏体周围界面形成，而应力水平提高将促进裂纹扩展，这将促进局部变形区域的氢致开裂与失效。因此，降低中锰钢的局部变形程度能降低氢致局部断裂的风险，从而降低氢脆敏感性。通过两步退火工艺在中锰钢中设计出具有成分核壳结构的奥氏体，其中奥氏体核Mn浓度低，形成于第一步高温退火过程；奥氏体壳Mn浓度更高，形成于第二步低温退火过程。变形过程中，稳定性较低的奥氏体核在较低的应变下即发生马氏体转变，而稳定性更高的奥氏体壳在更高的应变水平下才发生转变。相比于具有单一稳定性的奥氏体，在不牺牲中锰钢加工硬化能力的基础上，核壳结构奥氏体的这种逐步转变特征大幅度提高了中锰钢的抗氢脆性能。其主要原因为，低应变下未转变的奥氏体壳能抑制氢致界面裂纹的形成，同时能非常有效地阻碍裂纹的扩展。本文重点关注奥氏体对氢扩散与氢致延迟断裂行为的影响，研究结果对含奥氏体先进高强钢的氢脆行为研究和抗氢脆组织设计具有一定的指导意义。

The 3rd-generation advanced high-strength steel (AHSS) has attracted extensive attention due to its excellent mechanical properties. However, the increase in steel’s strength usually leads to a significant increase in hydrogen embrittlement (HE) susceptibility, and H diffusion and trapping in materials’ microstructure are regarded as the primary causes of the hydrogen-induced delayed fracture (HIDF). As an important constituent phase of the 3rd-generation AHSS, austenite will have an important impact on H diffusion and H-induced cracking in the multiphase microstructure. In this paper, we focused on the effect of austenite on H diffusion and HIDF behavior as well as the austenite stability tailoring in medium Mn steel (MMS), one of the 3rd-generation AHSS. The aim of this study is to elucidate the mechanism of HIDF in MMS and explore the effective microstructure design strategy to enhance the HE resistance of MMS. H diffusion and trapping behavior in MMS were investigated by combining H permeation experiment and numerical simulation. The simulation was performed based on establishing the two-dimensional H diffusion model, which considers the contrast in H diffusivity and solubility of different phase, the effect of H trapping within ferrite phase, as well as the trapping effect of ferrite/austenite phase boundary (PB). The results show that austenite and PB play a dominant role in the H diffusion process in the duplex microstructure, and their relative contribution to the reduction of effective H diffusivity are related to the H concentration at the H-charging side. The overall H diffusion kinetics is governed by H diffusion/trapping within austenite when the H concentration is high and the effect of H trapping at PB is gradually enhanced with the decrease of H concentration. Through the determination of H concentration at the H-charging side, the binding energy of H at the PB is estimated to be ~38 KJ/mol. The localized deformation behavior, deformation-induced austenite-to-martensite transformation characteristics and their influence on HIDF behavior of MMS were investigated. It is found that the increase in the degree of localized deformation results in apparent increase in HE susceptibility of MMS. The Lüders strain increase with increasing the degree of localized deformation, which leads to a higher local flow stress and higher fraction of strain-induced martensite in the region swept by Lüders band. In the presence of H, austenite-to-martensite transformation results in the formation of H-induced cracks at the surrounding boundaries of martensite while the increase in stress level facilitates cracks propagation, thus the increase in Lüders strain promotes H-induced cracking and failure in the locally deformed region. It is thus suggested that reducing the degree of localized deformation could reduce the risk of H-induced local failure and the corresponding HE susceptibility of MMS. Austenite with compositional core-shell structure was designed in MMS through a two-step annealing process. The austenite core formed during the first high-temperature annealing step has a lower Mn content, while the austenite shell formed during the second low-temperature annealing step has a higher Mn content. During deformation, the less stable austenite core transforms into martensite at low strain level. The transformation of Mn-enriched austenite shell, however, occurs at higher strain level due to its higher stability. It is found that such step-wise transformation results in significantly enhanced HE resistance without sacrificing the work hardening ability, compared with the MMS containing austenite with single stability. The capacity of austenite shell to maintain its phase stability at low strain could effectively inhibit the nucleation of H-induced interfacial cracks and suppress their propagation, which accounts for the significantly enhanced HE resistance. The present study foucses on the effect of austenite on H diffusion and hydrogen-induced delayed fracture behavior. The results will provide guidance for the study of hydrogen embrittlement behavior and design of HE-resistant microstructure in AHSS containing metastable austenite.