Current Challenges and Opportunities Toward Understanding Hydrogen Embrittlement Mechanisms in Advanced High-Strength Steels: A Review

Hydrogen embrittlement(HE) is one of the most dangerous yet most elusive embrittlement problems in metallic materials. Advanced high-strength steels(AHSS) are particularly prone to HE, as evidenced by the serious degradation of their load-bearing capacity with the presence of typically only a few parts-per-million H. This strongly impedes their further development and application and could set an abrupt halt for the weight reduction strategies pursued globally in the automotive industry. It is thus important to understand the HE mechanisms in this material class, in order to develop effective H-resistant strategies. Here, we review the related research in this field, with the purpose to highlight the recent progress, and more importantly, the current challenges toward understanding the fundamental HE mechanisms in modern AHSS. The review starts with a brief introduction of current HE models, followed by an overview of the state-of-the-art micromechanical testing techniques dedicated for HE study. Finally, the reported HE phenomena in different types of AHSS are critically reviewed. Focuses are particularly placed on two representative multiphase steels, i.e., ferrite–martensite dual-phase steels and ferrite–austenite medium-Mn steels, with the aim to highlight the multiple dimensions of complexity of HE mechanisms in complex AHSS. Based on this, open scientific questions and the critical challenges in this field are discussed to guide future research efforts.     

Hydrogen-enhanced lattice defect formation and hydrogen embrittlement of cyclically prestressed tempered martensitic steel

The numbers of lattice defects formed by applying cyclic prestress with/without hydrogen for various numbers of cycles and strain rates during cyclic prestress were compared for tempered martensitic steel. A tensile test was also carried out to evaluate hydrogen embrittlement susceptibility following the application of cyclic prestress. The results showed that when cyclic prestress was applied without hydrogen, the number of cycles and strain rate had no apparent effect on mechanical properties and fracture morphology at the time of the subsequent tensile test. In contrast, when cyclic prestress was applied with hydrogen, the fracture strain and fracture stress decreased with an increasing number of prestress cycles and a decreasing strain rate, and the fracture morphology exhibited brittle fracture, signifying an increase in hydrogen embrittlement susceptibility at the time of the tensile test. The number of hydrogen-enhanced lattice defects also increased with increasing number of cycles and a decreasing strain rate was found when cyclic prestress was applied with hydrogen. These results indicate a correlation between hydrogen embrittlement susceptibility and the number of hydrogen-enhanced lattice defects. The kinds of increased hydrogen-enhanced lattice defects were probably vacancies and vacancy clusters formed by the interactions between hydrogen and dislocation movement during the application of cyclic prestress. The vacancies and vacancy clusters formed during the application of cyclic prestress with hydrogen presumably caused intergranular fracture and increased hydrogen embrittlement susceptibility.     

In situ electrochemical nanoindentation: A technique for local examination of hydrogen embrittlement

Nanoindentation combined with AFM (NI-AFM) has been used to study the effect of electrochemically in situ charged hydrogen on the deformation of small volumes of nickel and copper single crystals. Hydrogen reduces the unstable elastic plastic transition load (pop-in) in nickel, but does not have any effect on copper. It has been shown that the activation energy for the onset of plasticity (dislocation nucleation) is reduced by dissolved hydrogen. This is because hydrogen reduces shear modulus and stacking fault energy in nickel, whereby the former results in hydrogen-enhanced decohesion (HEDE) and the latter in the hydrogen-enhanced plasticity (HELP) mechanism.     

预充氢马氏体时效钢的氢脆性能研究

目的研究预先存在于试样中的氢对材料力学性能的影响。方法对固溶态和三种时效态18Ni马氏体时效钢,采用双电解槽装置测量了其氢扩散系数,用热分析法获得了材料的氢扩散激活能。采用慢应变速率拉伸法评估了在预充氢后镀镉密封试样的力学性能,并由此评估它们的氢脆敏感性。结果固溶态试样的氢扩散系数最大,为1.40×10~(-8)_ cm~2/s;对时效态试样,当时效温度分别为465、490、530℃时,氢扩散系数分别为6.23×10~(-9)、5.52×10~(-9)、2.84×10~(-9) cm~2/s,即随时效温度升高,扩散系数降低。而扩散激活能正好相反,固溶态的最小,其他的依次逐渐升高。四种试样均显示出氢脆敏感性,且随着预充氢电流密度升高而增大。T465和T490的氢脆敏感性均大于58%,T530的氢脆敏感性小于40%。四种试样的断口形貌均表现为由中心起裂,向周围呈放射状扩展。中心起裂源处为典型的沿晶开裂,扩展区为准解理开裂。结论过时效态样品的抗氢脆性能最好。预先存在于试样中的氢在拉伸过程中向中心富集,造成中心沿晶开裂,与动态充氢拉伸断口相反。     

Embrittlement of T-200 maraging steel in a hydrogen sulfide solution

Slow displacement rate tensile tests were carried out to investigate the effect of hydrogen embrittlement (HE) on notched tensile strength (NTS) and fracture characteristics of aged T-200 maraging steel. Hydrogen diffusivity, permeation flux and apparent hydrogen solubility were determined by an electrochemical permeation method, and correlated with the HE susceptibility and microstructures of the specimens. The results indicated that all aged specimens were susceptible to HE in the saturated H₂S solution, to different degrees. The susceptibility in the decreasing order of severity was observed to be under-aged, peak-aged, and over-aged conditions. The main trend was that the specimen with the highest diffusivity and permeation flux of hydrogen had the greatest NTS loss. Reverted austenite, if present in the microstructure, acted as irreversible traps for hydrogen and hence, improved the HE resistance. At similar strength and hydrogen solubility level, the more reverted austenite the less susceptibility to HE of specimens was resulted. The detailed microstructures of distinct specimens and their performances in hydrogen-containing environments are discussed.     

阴极极化对907钢氢脆敏感性的影响

采用慢应变速率拉伸试验方法结合断口扫描电镜观察,研究了阴极极化对907钢在海水中氢脆敏感性的影响。结果表明随极化电位负移,907钢在海水中氢脆敏感性增加,极化电位为-1.06V(vs.SCE)时,拉伸试样出现脆性解理断裂特征,极化电位为-1.16V时,907钢主要为脆性断裂。     

X80管线钢在含氢煤制气环境中的氢脆敏感性

采用慢应变速率试验和缺口试样拉伸试验,并结合断口分析,研究了X80钢在含氢煤制气环境中的氢脆敏感性。结果表明:高压含氢环境中X80钢的强度和塑性指标均有所下降,断口出现脆断形貌,表现出一定的氢脆敏感性,且横向取样方向对氢脆更为敏感;通过对比分析X80钢在高压氢气环境中慢拉伸和缺口拉伸两种状态下的韧性损失,发现缺口试样的三向应力集中区域受氢脆影响更为严重。     

The effects of hydrogen on the deformation and fracture of β-titanium

The hydrogen-induced ductile–brittle transition in the BCC β-titanium alloy, Timetal® 21S, occurs abruptly at a critical hydrogen concentration that decreased with decreasing tensile test temperature. Mechanical property tests showed that solute hydrogen reduced the yield strength of ductile specimens and decreased the fracture stress of brittle specimens. To identify the operative mechanism a series of experiments were performed to test the applicability of the stress-induced hydride mechanism, the hydrogen-enhanced plasticity mechanism, and the decohesion mechanism of hydrogen embrittlement. The experiments showed that no hydrides were associated with the fracture process, indicating that the stress-induced hydride mechanism was not responsible for the observed sharp ductile–brittle transition. In situ straining experiments in a controlled environment transmission electron microscope showed that hydrogen enhanced the mobility of dislocations in both uncharged and hydrogen charged alloys, showing that the hydrogen-enhanced localized plasticity mechanism cannot account for the observed behavior. The experimental results are, however, fully consistent with the decohesion mechanism of hydrogen embrittlement.     

Rapid Hydrogen Transportation Along Grain Boundary in Nickel

The permeability and diffusivity of hydrogen in directionally solidified polycrystalline and single crystal nickel foils were measured by gas permeation method.The results showed that both hydrogen diffusivity and permeability were higher in directionally solidified nickel specimen than those in single crystal one at the temperature ranging from 300 to480 °C,and confirmed the existence of short-circuit diffusion along the grain boundaries(GBs) in the directionally solidified nickel.The results suggested that the rapid diffusion along GBs was more obviously characterized in terms of higher permeability rather than higher diffusivity.The contribution of grain boundary to hydrogen transportation was represented by the differences of diffusivity(and permeability) in single crystal nickel and directionally solidified nickel.By modifying the Fick's first diffusion law and counting the grain boundary density,the hydrogen diffusivity and permeability of rapid diffusion along GBs were calculated.The results suggested both the diffusivity and permeability fit the Arrhenius relationship well at different temperature.     

氢对有序态Ni_3Fe合金脆性的影响(英文)

研究了有序态Ni3Fe合金在不同氢气压力中和在不同电流密度电解渗氢时合金的拉伸性能。结果表明：随着氢气压力或电流密度的增加,合金的延伸率先快速下降,随后逐渐趋于恒定;合金的氢脆因子与氢气压力或电流密度之间呈相同的依赖关系。有序态Ni3Fe合金在氢气中的脆化机制是催化反应生成的氢原子进入合金所致,合金的脆化程度与进入合金的氢原子数量有关。     

Hydrogen transport and degradation of a commercial duplex stainless steel

Hydrogen embrittlement of 2205 duplex stainless steel has been evaluated using electrochemical permeation measurement, hydrogen microprint technique and tensile test in this study. Due to hydrogen transport in 2205 duplex stainless steel is mainly lattice diffusion in ferritic phase, more hydrogen distribution, higher permeation rate and diffusion in ferritic phase were detected. Brittle fracture was observed in both the ferritic and austenitic phases of hydrogen precharged specimen.     

阴极保护下X65钢在模拟海水中的氢脆敏感性研究

采用阴极极化条件下的氢渗透实验和慢应变速率拉伸实验研究了X65钢在模拟海水中的氢渗透行为及其对断裂机理的影响。氢渗透实验结果表明,阴极极化过程中试样表面的钙镁沉积层能显著地降低氢扩散系数,采用Fourier方程、Laplace方程以及时间滞后法计算得出的有效氢扩散系数平均值为1.49×10-7cm2·s-1。结合变电位极化氢渗透测试结果、拉伸试样断口分析以及极化曲线测试,对阴极极化条件下X65钢的氢脆敏感性进行评估。结果显示,随着极化电位的降低,X65钢中的吸附氢浓度呈指数规律上升。当极化电位较高时,X65钢的裂纹扩展受阳极溶解和阴极析氢的双重作用控制。当极化电位较低,如-1200 mV时,钢中的吸附氢浓度急剧增加,脆性断裂区域的比例上升,X65钢发生氢致脆化失效。     

Ti—Al系金属间化合物的氢脆机理

根据固体与分子经验电子理论发析计算了Ｔｉ－Ａｌ系金属化合物及含氢各相的价电子结构与解理能,结果表明：ＴｉｓＡｌ的氢脆是由于高氢含量下易生成δ脆性相引起的,而ＴｉＡｌ的氢脆是由于固溶氢减弱了含氢ＴｉＡｌ晶胞主干键并降低了解理能引起的,同时解释了一些尚有矛盾的实验结果,并提出了一些解决氢脆的实际方法。     

Hydrogen embrittlement risk of high strength galvanized steel in contact with alkaline media

The critical conditions for hydrogen embrittlement (HE) risk of high strength galvanized steel (HSGS) wires and tendons exposed to alkaline concrete pore solutions have been evaluated by means of electrochemical and mechanical testing.There is a relationship between the hydrogen embrittlement risk in HSGS and the length of hydrogen evolution process in alkaline media. The galvanized steel suffers anodic dissolution simultaneously to the hydrogen evolution which does not stop until the passivation process is completed. HSGS wires exposed to a very high alkaline media have showed HE risk with loss in mechanical properties only if long periods with hydrogen evolution process take place with a simultaneous intensive galvanized coating reduction.     

阴极保护电位对E550钢氢脆敏感性的影响

采用慢应变速率拉伸实验方法 (SSRT) 结合断口扫描电镜 (SEM) 观察,研究了阴极保护电位对E550钢在海水中氢脆敏感性的影响.结果表明:随着阴极保护电位负移,E550钢在海水中的氢脆敏感性增加,阴极保护电位为-0.95 V (vs SCE) 时,拉伸试样出现脆性解理断裂特征,电位为-1.05 V时,E550钢断口呈明显脆性断裂特征.     

Hydrogen Embrittlement of Pulse-Plated Nickel

The objective of the European-funded project MultiHy (Multiscale modeling of hydrogen embrittlement in crystalline materials) is the development of multiscale models for hydrogen transport in complex microstructures. The validation and application of the models will be carried out by investigating the role of the microstructure in industrial problems involving hydrogen embrittlement (HE) of advanced materials. Pulse-plated nickel (PP-Ni) material, as used in various industrial applications, has shown a susceptibility to HE that may cause premature failure of a structure. Due to the nature of the pulse-plating process, H is incorporated into the microstructure of the material. This H may lead to crack initiation when combined with localized stress concentrations due to subsequent manufacturing steps, e.g., welding. This article provides an overview of experimental studies aimed at evaluating the influence of the microstructure on the susceptibility of PP-Ni to HE and, ultimately, at improving the plating process.     

湿润环境下球墨铸铁的脆化现象

主要对在水的环境下包括奥贝球铁在内的球墨铸铁的机械性能进行了试验研究,发现了球墨铸铁在湿润环境下的脆化现象;对湿润环境下球墨铸铁环境脆化现象的机理地行了分析研究,认为其起因是在塑性变形时水发生了分解,导致氢脆;提出了氢的发生模型。     

Hydrogen Embrittlement of Zirconium Alloys

The process of hydrogen embrittlement of zirconium alloys caused by the pressure of molecular hydrogen in voids formed near threefold junctions of grain boundaries and by volume changes due to formation of hydride phases is considered. The embrittling mechanisms are physically based on the diffusion processes near structural imperfections, the leading role among which belongs to threefold junctions of grain boundaries. These structural defects possess strong stress fields and directly adjoin grain boundaries.     

Hydrogen uptake in 316L stainless steel: Consequences on the tensile properties

Different charging conditions aimed at introducing significant hydrogen concentrations without microstructural damages in a 316L austenitic stainless steel were investigated. The equivalent hydrogen pressure developed at the surface of the samples during cathodic charging was estimated from hydrogen concentration measurements. A clear hydrogen absorption, controlled by diffusion, was evidenced during the immersion of 316L steel samples in 30% MgCl₂ at the open circuit potential at 117 °C. Deuterium profiling by SIMS was performed to check the validity of the few literature data on hydrogen diffusivity in the near room temperature range in this material. On the other hand, the macroscopic effects of hydrogen on the tensile characteristics of the steel were investigated and compared at 20 °C and at −196 °C with samples cathodically pre-charged, charged during tensile straining or pre-charged at high temperature-high pressure in gas phase. Hydrogen is shown to affect both the short range and the long range forces exerted on the strain-induced mobile dislocations. The hydrogen-induced softening effect observed at 20 °C and the systematic decrease of the ductility support a mechanism involving the enhanced transport of hydrogen atoms by mobile dislocations. This mechanism is confirmed by the absence of softening and of ductility loss at −196 °C and by the strain-enhanced tritium desorption from samples cathodically pre-charged with tritium, measured by β counting during tensile deformation.     

Hydrogen permeable Ta–Ti–Ni duplex phase alloys with high resistance to hydrogen embrittlement

Crystal structures, microstructures and hydrogen permeability Φ of as-cast Ta–TiNi alloys on the line connecting the compositions of the primary (Ta, Ti) and the ternary eutectic phases have been investigated to find out highly hydrogen permeable duplex phases alloys with high resistance to the hydrogen embrittlement. The alloys on this line show microstructures of (1) the eutectic {(Ta, Ti) + TiNi} phase, (2) the primary (Ta, Ti) phase + the eutectic {(Ta, Ti) + TiNi} phase, and (3) the (Ta, Ti) solid solution, although a little amount of unidentified (impurity) phases are included in these samples. The value of Φ increases with increasing Ta content and the volume fraction of the primary (Ta, Ti) phase, which indicates that the primary phase contributes mainly to the hydrogen permeation. The Ta₅₆Ti₂₃Ni₂₁ alloy, containing the 61 vol.% primary phase, shows the highest Φ of 2.18 × 10⁻⁸ mol H₂ m⁻¹ s⁻¹ Pa^−0.5 at 673 K, which is 1.3 times higher than that of the previous most high Φ alloy (Ta₅₃Ti₂₈Ni₁₉). The more Ta-rich alloys on this line, i.e., containing a small amount of the eutectic phase, are broken down by the hydrogen embrittlement, suggesting that the eutectic phase suppresses the hydrogen embrittlement.