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 Ni₃Mo precipitates, which balance strength and ductility.