Effect of Ni on the hot ductility and hot cracking susceptibility of high Mn austenitic cast steel

In the present study, the hot ductility behavior and hot cracking susceptibility of high manganese cast steel were investigated. Based on the 18Mn-0.6C alloy, a nickel was added for cryogenic impact toughness by maintaining the low temperature austenite stability to prevent strain induced martensitic transformation considering the appropriate stacking fault energy for mechanical twinning. A hot ductility test and Varestraint test were carried out to clarify the behavior of heat affected zone (HAZ) liquation and ductility dip cracking that were observed at the multi-pass weld heat affected zone of a nickel added high manganese weld metal for cryogenic uses. The heating and cooling rates were calculated by the three-dimensional Rosenthal׳s equation based on the actual welding heat input. A brittle temperature range, and a critical strain temperature range for each alloy showed no significant difference, but the overall ductility of the nickel added alloy was lower than the 18Mn alloy due to the lower degree of dynamic recrystallization by the higher stacking fault energy and the existence of the M3P/γ eutectic and MnS formed by the severe P segregation and higher S content, respectively. As a result of the longitudinal Varestraint test, the total and maximum HAZ crack length and cracked HAZ length of the nickel added alloy were larger than those of 18Mn alloy. The solid-state fracture, i.e. the ductility dip cracking was observed both in the on-cooling hot ductility tested and Varestraint tested alloys.