Article ID: TETSU-2024-044
The effect of the manganese content of 7 % nickel-added steel on cryogenic toughness was investigated. When Charpy absorbed energy was investigated in the steels with wide range manganese content from 0.05 % to 2.16 %, the absorbed energy at −196 °C increased with a decrease of manganese content. The two steels with manganese contents of 0.2 % and 0.8 % were selected for use in a more detailed investigation regarding the dependence of toughness at −196 ℃ on the intermediate heat treatment temperature, fracture behaviors and the retained austenite. Although the 0.2 % manganese steel stably exhibited a high absorbed energy at −196 ℃ at all intermediate heat treatment temperatures examined in this work, it was necessary to select an appropriate intermediate heat treatment temperature for the 0.8 % manganese steel in order to achieve high absorbed energy at −196 ℃. The total amount of the retained austenite and the size and the nickel content locally segregated into an identical retained austenite were quantified by using XRD and SEM/EDS, and the characteristics of the retained austenite in the steels with low manganese alloy designs were investigated. The cleavage-type brittle fracture that appeared in some specimens was discussed from the viewpoint of the stability of retained austenite.
