Stacking Fault Energy in Relation to Hydrogen Environment Embrittlement of Metastable Austenitic Stainless CrNi-Steels

Metastable austenitic steels react to plastic deformation with a thermally and/or mechanically induced martensitic phase transformation. The martensitic transformation to α’-martensite can take place directly or indirectly via the intermediate stage of ε-martensite from the single-phase austenite. This effect is influenced by the stacking fault energy (SFE) of austenitic steels. An SFE < 20 mJ/m2 is known to promote indirect conversion, while an SFE > 20 mJ/m2 promotes the direct conversion of austenite into α’-martensite. This relationship has thus far not been considered in relation to the hydrogen environment embrittlement (HEE) of metastable austenitic CrNi steels. To gain new insights into HEE under consideration of the SFE and martensite formation of metastable CrNi steels, tensile tests were carried out in this study at room temperature in an air environment and in a hydrogen gas atmosphere with a pressure of p = 10 MPa. These tests were conducted on a conventionally produced alloy AISI 304L and a laboratory-scale modification of this alloy. In terms of metal physics, the steels under consideration differed in the value of the experimentally determined SFE. The SFE of the AISI 304L was 22.7 ± 0.8 mJ/m2 and the SFE of the 304 mod alloy was 18.7 ± 0.4 mJ/m2. The tensile specimens tested in air revealed a direct γàα’ conversion for AISI 304L and an indirect γàεàα’ conversion for 304mod. From the results it could be deduced that the indirect phase transformation is responsible for a significant increase in the content of deformation-induced α’-martensite due to a reduction of the SFE value below 20 mJ/m2 in hydrogen gas atmosphere.

Correction: Michler et al. Review and Assessment of the Effect of Hydrogen Gas Pressure on the Embrittlement of Steels in Gaseous Hydrogen Environment. Metals 2021, 11, 637

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Fatigue Life Calculation Method of 4130X High Pressure Hydrogen Storage Cylinder With Initial Crack Defect

Hydrogen storage cylinders are often used for medium- and short-distance transportation of hydrogen. The presence of hydrogen tends to increase the risk of using the gas cylinders. The alternating stress caused by factors such as hydrogen charging and discharging during the service process of the gas cylinder leads to the expansion of initial cracks inside the cylinder and the final fatigue fracture. At present, the fatigue life calculation of pressure vessels mainly adopts the S-N curve method, however, some steels do not have the S-N curve under the hydrogen environment, it is necessary to use fracture mechanics methods to analyze the fatigue life of gas cylinders in a high-pressure gaseous hydrogen environment. In this work, a method for calculating the fatigue life of fracture mechanics for hydrogen storage cylinders was established according to ASME VIII-3 KD-10. The development of the program was completed by Matlab. An example was given to illustrate the program. Firstly, basic parameters of the material used for the cylinder were obtained. Then, finite element method was used for stress analysis to obtain the fitting curve and the function expression of hoop stress. Finally, fatigue life calculations of high pressure hydrogen storage cylinder were made. The minimum service life of example was predicted to be 40 years. This result is consistent with the good service history of this type of container. This work could contribute to design, safety evaluation of hydrogen storage cylinders.