Dynamic deformation response of maraging steel 250 produced through directed energy deposition: Deformation behavior and constitutive model

This study investigates the dynamic deformation response of maraging steel 250 (MS250) produced through directed energy deposition-arc (DED-Arc) across various strain rates and temperatures, aiming to develop constitutive models for reliable finite element simulations . Analytical transmission electron microscopy and scanning electron microscopy are subsequently performed to better understand the effects of microstructure features of DED-Arc built MS250 on their dynamic deformation behaviors . Experimental results reveal the variable thermal softening effects and combined impacts of strain rate and strain on the dynamic mechanical performance of as-deposited specimens. The heat-treated DED-Arc MS250 exhibits the synergistic influences of strain and strain rate, along with joint impacts of temperature and strain rate in its deformation characteristics in high-temperature regimes. Conventional Johnson-Cook models fail to capture these effects, causing discrepancies between predicted and experimental data for as-built and heat-treated DED-Arc MS250 alloys. In contrast, modified Johnson-Cook models tailored for each condition align closely with experimental results. Verification tests conducted under new impact conditions further validate the enhanced predictive capabilities of the modified models. Besides, as-deposited MS250 steel shows inferior flow stress and energy absorption, but post-fabrication heat treatment significantly improves its dynamic mechanical performance. The heat treatment also improves the resistance of heat-treated DED-Arc MS250 steel to forming adiabatic shear bands during room temperature impact tests, in comparison with the as-built condition. This improvement is associated with the formation of nano-sized, coherent, needle-shaped Ni 3 Mo precipitates, which balance strength and ductility.