Abstract
High-manganese austenitic steel was developed to improve the fracture toughness and safety of steel under cryogenic temperatures, and its austenite structure was formed by increasing the Mn content. The developed high-manganese austenitic steel was alloyed with austenite-stabilizing elements (e.g., C, Mn, and Ni) to increase cryogenic toughness. It was demonstrated that 30 mm thickness high-manganese austenitic steel, as well as joints welded with this steel, had a sufficiently higher fracture toughness than the required toughness values evaluated under the postulated stress conditions. High-manganese austenitic steel can be applied to large offshore and onshore LNG storage and fuel tanks located in areas experiencing cryogenic conditions. Generally, fracture toughness decreases at lower temperatures; therefore, cryogenic steel requires high fracture toughness to prevent unstable fractures. Brittle fracture initiation and arrest tests were performed using 30 mm thickness high-manganese austenitic steel and SAW joints. The ductile fracture resistance of the weld joints (weld metal, fusion line, fusion line + 2 mm) was investigated using the R-curve because a crack in the weld joint tends to deviate into the weld metal in the case of undermatched joints. The developed high-manganese austenitic steel showed little possibility of brittle fracture and a remarkably unstable ductile fracture toughness.
Highlights
Liquefied natural gas (LNG) is garnering attention as a clean energy source due to global environmental problems and the dramatic increase in the demand for clean energy.In addition, the size of the LNG storage tanks has increased owing to the development of steel manufacturing, welding, and non-destructive inspection technologies
The welding test specimens were manufactured for the brittle and ductile fracture welding test specimens were manufactured for the brittle and ductile fract characteristics of theThe weld metal and the heat-affected zone (HAZ) using a wide-plate test characteristics of the weld metal and the heat-affected zone (HAZ) using a wide-plate via the submerged arc welding (SAW) processes, the typical welding method used for the via the submerged arc welding (SAW) processes, the typical welding method used for construction of LNG tanks
In addition to basic material properties such as tensile strength and impact values in a cryogenic environment, the verification of fracture safety is of the greatest importance for the application of highmanganese austenitic steel in structures. Because it is utilized in a cryogenic environment, it is necessary to investigate the safety of brittle fractures
Summary
Liquefied natural gas (LNG) is garnering attention as a clean energy source due to global environmental problems and the dramatic increase in the demand for clean energy. Regarding STS 304, there is little risk of brittle fracture owing to its austenitic structure, but the possibility of unstable ductile fracture exists [9,10]. Highmanganese austenitic steel, a newly developed cryogenic steel, has an austenite structure similar to STS304; it carries the possibility of unstable ductile failure rather than brittle failure [13]. To utilize high-manganese austenitic steel as a type of novel cryogenic steel in LNG storage and fuel tanks, it is necessary to investigate the possibility of its unstable destruction in a cryogenic environment. The basic properties of the base metal and weld joints of high-manganese austenitic steel were evaluated for their suitability as cryogenic steels and the applicability of the material for use in containers used for the storage of cryogenic materials was assessed. Experimental results were based on research conducted studying the applicability of using high-manganese austenitic steel, a novel cryogenic steel, in a cryogenic environment
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