Design of low-Ni martensitic steels with novel cryogenic impact toughness exceeding 190 J

This study aimed to develop steels with reasonable material costs to replace Fe–9Ni (wt.%) steel, which is suitable for cryogenic applications. To this end, a newly designed Fe–2Mn–5Ni-0.1C steel was treated by quenching–tempering (QT) and quenching–lamellarizing–tempering (QLT); subsequently, the microstructural evolutions and resultant impact absorbed energy were systematically investigated. At −196 °C, the QLT-processed steel exhibited a higher impact absorbed energy (∼193 J) than the QT-processed steel (∼168 J), and it was similar to that of Fe–9Ni steel. The excellent impact absorbed energy of the QLT-processed sample was attributed to the high damage tolerance afforded by the active transformation-induced plasticity from the retained austenite and the pronounced plastic deformation of the soft martensitic matrix due to double-step tempering.