| Abstract Scope |
Because liquefied natural gas (LNG) is stored at approximately −165 °C, LNG storage tanks operate under cryogenic conditions, where sufficient impact toughness is essential because structural materials tend to become brittle at low temperatures. 9% Ni steel has been widely used for this application owing to its excellent cryogenic impact toughness. However, because nickel is costly, efforts have been made to enhance toughness while reducing Ni content through heat-treatment optimization. Among these approaches, lamellarizing heat treatment has recently attracted attention. In this study, the impact toughness of lamellarized 9% Ni steel was evaluated by Charpy V-notch tests at −196 °C and −253 °C. The lamellarized steel exhibited more than twice the impact toughness of conventionally treated 9% Ni steel. SEM, EBSD, and nanoindentation were used to analyze the microstructure and hardness, and to identify the factors responsible for the improved toughness after lamellarizing heat treatment. |