To clarify the function of hydrogen in hydrogen embrittlement of various metals, identify of hydrogen existing states, dynamic behavior of hydrogen during deformation, enhanced lattice defect formation, and process to fracture are important. In the present review, determination of hydrogen trapping sites in metals, interaction between dislocation and hydrogen, evaluation of lattice defects such as vacancies and its clusters enhanced by hydrogen and strain, and their relevance to hydrogen embrittlement associated with plastic deformation are presented.
Hydrogen embrittlement of steels and retarding hydrogen absorption from the view point of improvement in steels were reviewed. Ni concentrating at the surface after heat treatment retarded the absorption of hydrogen and delayed fracture properties were improved. High alloy steels such as maraging type steel were fractured in the delayed fracture accelerated test for bolts while they showed extremely low hydrogen embrittlement in the raw materials test. It was revealed that hydrogen absorption due to galvanic corrosion was increased in the bolt test and the much addition of Ni prevented hydrogen embrittlement.
Recent research activities on hydrogen embrittlement, especially Hydrogen Environment Embrittlement (HEE) susceptibility of stainless steels in highly pressurized gaseous hydrogen environments were reviewed from the viewpoints of effects of chemical compositions, hydrogen absorption and fatigue properties. HEE susceptibility of austenitic stainless steels evaluated by Slow Strain Rate Test (SSRT) in high pressure hydrogen environments strongly depended on their chemical compositions which affect strain-induced martensitic transformation. Stainless steels with low levels of alloying elements such as SUS304L showed a remarkable ductility loss in hydrogen environments due to martensitic transformation. Stable austenitic stainless steels such as SUS316L or A286 showed sufficient resistance to HEE. Relationship between HEE susceptibility and an amount of hydrogen absorption was investigated. HEE susceptibility and hydrogen embrittlement under cathodic charging in aqueous solution showed the same dependence on the amount of hydrogen absorption, which imply HEE occurs by hydrogen absorption from external gaseous hydrogen environments. Fatigue properties in high pressure gaseous hydrogen environments were evaluated by internal or external pressurization tests. Metastable stainless steels such as SUS304 showed degradation in fatigue life by hydrogen gas than an inert environment, while stable stainless steels such as SUS316L showed little decrease in fatigue life by hydrogen. A286, precipitation hardened stainless steel, showed a decrease in fatigue life by hydrogen because of planar dislocation or η phase precipitation along grain boundaries.
Hydrogen embrittlement and its related phenomena in pure titanium and titanium alloys are introduced. Hydrogen embrittlement in titanium is closely related to the hydride formation. In case that a considerable amount of hydride forms in the materials, embrittlement can be confirmed by high strain rate testing using notched specimens such as impact testing. In more static low strain rate testing such as sustained load cracking testing, it is considered that hydrogen embrittlement appears due to hydrogen diffusion to crack tips and hydride formation there during testing. In beta type titanium alloys containing a high quantity of Mo and/or V, hydrides formation is not easy and they have high resistance against hydrogen embrittlement.
Two case studies of hydrogen related cracking in chemical plant are introduced. Case one is the cracking of tantalum (Ta) parts in sulfuric acid containing environment. In this case, the hydrogen is absorbed in Ta parts during operation condition. The relationship between hydrogen concentration and mechanical properties, the possibility of de-hydrogen heat treatment and the nondestructive evaluation method for measuring the hydrogen concentration are studied. Case two is the cracking of molybdenum containing nickel base alloy. The controlling factors for cracking are studied by the potential controlled slow strain rate test. It becomes clear that the ordering of the alloy by the heat treatment during fabrication and the absorption of hydrogen during operation are promoting factors for cracking. From these studies, it is recognized that the root cause analysis is important to take the appropriate counter measurement.
Hydrogen entry behavior into steels and its relation with hydrogen overpotential were investigated in wet sour environments and ammonium thiocyanate environments using hydrogen permeation method. Logarithm of hydrogen permeability for 0.04% carbon low alloy steels had a linear relation to hydrogen overpotential in sour environments. This relation is independent of H2S partial pressure. The linear relation between hydrogen permeability and hydrogen overpotential was shown by one line for the steels with different carbon concentration and different hydrogen diffusion coefficient in sour environment as well as ammonium thiocyanate environments. Therefore, the hydrogen permeation performance in steel is largely dependent on the hydrogen overpotential and the linear relation between them supports Gonzalez's equation.
The films formed on boiler tube steels for thermal power plant in the simulated AVT (All Volatile Treatment) water at high temperature are analyzed by X-ray diffraction (XRD) and X-ray Photoelectron Spectroscopy (XPS). In addition, the corrosion resistances of the films are evaluated using electrochemical techniques in the simulated AVT water added with chloride ions (Cl−). The magnetite films formed on STB410 and STBA24 steels in the simulated AVT water at 598 K. The films show better corrosion resistances to Cl− at room temperature. It seems to be related with restraint of the magnetite crystal growth and improvement of the density. On the other hand, the complex film, composed of Fe-oxides and Cr-oxides, is observed on SUS304 steel. Their corrosion resistance is lower than that of the film formed at room temperature. The film formed at high temperature should be unstable by the formation of local cell caused due to partial segregation of Cr.