Changes in the substructure of tempered martensitic steel during the application of cyclic elastic stress in the presence of hydrogen

Abstract

Changes in the substructure of tempered martensitic steel during the application of cyclic elastic stress in the presence of hydrogen have been investigated. Three types of specimens were prepared. The first type was subjected to cyclic elastic stress (strain rate: 3.0×10-4 s−1, number of cycles: 70000, and stress level: 0.8±0.1 σB) without hydrogen. The second type was subjected to cyclic elastic stress with hydrogen. The third type was prepared by annealing the second type at 200 °C for 2 h. These specimens are denoted here as [(n)-cycled], [H+(n)-cycled] and [H+(n)-cycled+annealed] specimens, respectively. Tracer hydrogen was used as a probe for clarifying changes in the specimen substructure. After tracer hydrogen charging, hydrogen states present in the specimens were examined using low-temperature thermal desorption spectrometry (L-TDS). Tracer hydrogen desorption in the high-temperature range from the [H+(n)-cycled] specimen increased compared with that from the [(n)-cycled] specimen. In addition, tracer hydrogen desorption in the high-temperature range from the [H+(n)-cycled+annealed] specimen was reduced by annealing at 200 °Cto the level of the [(n)-cycled] specimen. As a result, it is inferred that the formation of vacancy type defects was enhanced under the application of cyclic elastic stress in the presence of hydrogen.