Strain-rate-dependent dynamic deformation behavior of low alloy steel at low temperature

This study reveals the cryogenic (−100 °C) dynamic response of EH36 steel under varying high strain rates. The averaged yield strength and final compressive strength increase from 3000 to 9000 s −1 , but both decrease at 12000 s −1 , indicating a transition from strain-rate strengthening to ultrahigh-strain-rate softening governed by the competition between dislocation storage and thermally assisted softening. At 3000–9000 s −1 , dislocation multiplication induces shear band formation and dynamic recovery, while the overall strengthening effect is still maintained. At 12000 s −1 , adiabatic heating triggers localized dynamic recrystallization (DRX) within shear bands, generating ultrafine grains and partially offsetting the preceding strengthening effect. Furthermore, the cryogenic environment restricts thermally activated DRX, thereby limiting the extent of softening even at the ultrahigh strain rate. These findings indicate that, within the tested strain-rate range, the transition from strain-rate strengthening to localized thermally assisted softening first becomes evident at 12000 s −1 , which is important for evaluating the impact resistance and microstructural stability of Arctic-grade steel.