Hydrogen uptake in a ferritic steel was investigated through secondary ion mass spectrometry (SIMS) at 83 K, where hydrogen diffusion is sufficiently suppressed. Additionally, the SIMS was operated with cold trap and Si sputtering to reduce the back ground effect. Thanks to the suppression of hydrogen diffusion during the measurements, the cryogenic SIMS could demonstrate reproducible results which showed a significant difference in hydrogen content between hydrogen-charged and uncharged specimens. Namely, hydrogen in the ferritic steel was successfully detected similarly to austenitic steels.KEY WORDS: chemical and physical analysis; secondary ion mass spectrometry; hydrogen detection; ferritic steel.Hydrogen has been drawing attention as a next-generation clean energy carrier that addresses concerns regarding the exhaustion of existing oil resources and environmental conservation. Practical uses of hydrogen as an energy carrier have been explored, and already achieved in a number of energy-related applications.1,2) Since various parts in the hydrogen systems, e.g. the hydrogen gas tank, pipe etc. are exposed to hydrogen gas, the metallic parts have a potential risk in terms of hydrogen embrittlement (HE). [3][4][5] In particular, this negative effect of hydrogen is known to be remarkable in BCC steels compared to FCC materials such as austenitic steels. 3,4,6) An important factor affecting HE is distribution of hydrogen. More specifically, the presence of diffusible hydrogen has a key role on the HE. 7) Diffusible hydrogen detection has been conducted through microprint technique, 8) silver decoration method, 9) and scanning Kelvin probe.
10,11)Although these methods have a great advantage which enables to visualize microstructure-scale hydrogen distribution, these detect hydrogen only on a surface. Namely, the detected hydrogen has already had a complex history of diffusion before the hydrogen appears on the surface. An alternative technique for detecting hydrogen is secondary ion mass spectrometry (SIMS), which visualizes the hydrogen distribution through scanning the specimen surface with Cs ions and the subsequent detection of the secondary ions ejected. SIMS enables direct hydrogen detection in deep regions from the surface. However, due to the low specific weight and solubility of hydrogen compared to typical solute elements such as carbon in steels, the analytical precision is negatively affected by the hydrogen drifting in the device. This is termed as the background (BG) effect. 12,13) Reducing the BG effect was realized by using a cold trap and a stage cooling system. 14,15) The cold trap absorbed the drifting hydrogen atoms, and the stage cooling system prevented the hydrogen diffusion, enabling a highly accurate hydrogen analysis by SIMS.The previous works on the hydrogen distribution by using SIMS were conducted in austenitic steels, 13,16) or martensitic steel which contains a considerable amount of boundary defects and dislocations. 17) In contrast, to our best knowledge, the use of SIMS to dete...