Analysis of low-temperature performance strengthening technology of 18Ni（250） maraging steel

ObjectiveThis study aims to investigate the influence of multiple cyclic phase transitions on the micro-structure and low-temperature mechanical properties of 18Ni(250) ultra-high-strength steel to meet the stringent requirements of low-temperature wind tunnel tests.MethodsAn ultra-pure melting simulation model for vacuum induction and vacuum consumable smelting was constructed using MeltFlow software. The formation mechanism of the micro-structure inside the molten pool was analyzed and discussed. Based on the derived optimal parameters, the test steel was obtained through ultra-high-purity smelting. Subsequently, the steel was subjected to multiple cyclic phase transitions at 940 ℃, 900 ℃, 860 ℃ and 820 ℃, followed by conventional aging treatment.ResultsThe results demonstrate that using a flow rate lower than 4.6 kg/min leads to an ingot with low segregation and low inclusions, which significantly improves the plastic toughness of 18Ni(250) steel. After undergoing the specific cyclic phase transitions, the original austenite grain size is notably refined to 12 μm. Consequently, the steel exhibits excellent mechanical properties under low-temperature and high-load conditions, characterized by the successful combination of ultra-high strength and high plasticity.