Effect of Heat Treatment on Mechanical Properties of Welded High-Mn Steels at Very Low Temperature

Abstract

High-Mn steel is a promising material for use in cryogenic applications because of excellent mechanical properties such as high strength and high toughness at low temperatures. In order to use high manganese steel in cryogenic application such as LNG tanks, pipes and valves, it is crucial to comprehend the way it deforms. The deformation behavior of high-Mn steels at extremely low temperatures is dependent on SFE, and it can shift from twin deformation to ε-martensite or α'-martensite transformation as the temperature decreases. Welding is important for making materials like pipes, tanks, and vessels for various industries, and submerged arc welding (SAW) is a popular method for thick pipes or plates in the cryogenic industry. However, SAW welding of high-Mn steels can cause problems like uneven distribution of manganese and a large area affected by heat. To overcome these problems, post weld heat treatment (PWHT) is used to obtain a homogeneous microstructure, improve mechanical properties, and reduce residual stress. In a study, the deformation mechanisms of welded high-Mn steels were analyzed using XRD, EBSD, and TEM at room temperature and cryogenic temperatures. It was found that ε and α'-martensite transformation occurred in tensile deformed as-weld specimen at cryogenic temperature, while heat treated specimen did not undergo α'-martensite transformation.  In addition, ε and α'-martensite transformations did not occur after Charpy impact deformation regardless of whether before or after heat treatment.

Keywords: High-Mn steels, Submerged Arc Welding (SAW), deformation behavior, cryogenic temperatures, martensite