Crack sensitivity of high-manganese cryogenic steels in initial solidification during continuous casting

Cryogenic steels, i.e., steels with maximum toughness at particularly low temperature, are increasingly becoming the focus of research. Cryogenic steels are usually alloyed with 5%-9% nickel. Ni can also be substituted by manganese as an austenite former. These high-manganese cryogenic grades are a cost-effective alternative to nickel-alloyed steels for use in liquefied natural gas storage tanks. The Mn content can then be more than 20 wt.% and lead to problems in production, particularly in the continuous casting process. In continuous casting of high-Mn-grades, quality issues and even breakout may result from the initial solidification behavior of the steel grades at high temperatures. Hot cracks form when a critical load is exceeded during solidification, close to the solidus temperature of the steel. A selected high-Mn-steel grade was characterized with respect to liquidus and solidus temperatures by means of thermal analysis and computational thermodynamics. In addition, so-called submerged split chill tensile tests were carried out to further understand the crack sensitivity of the solidifying shell for high-manganese cryogenic steels. The results reveal the presence of coarse hot tears, and also, a high frequency of hot cracks was observed at the location with the maximum accumulated strain, which is in line with the applied cracking criterion of Pierer and Bernhard for this investigation. In summary, the initial solidification phase of continuous casting poses a high risk of cracking for high-manganese cryogenic steel.