Softening Mechanisms in Additively Manufactured 420 Stainless Steel at Elevated Temperatures

The high-temperatureHigh temperature behavior of additively manufactured 420 stainless steel420 stainless steel fabricated via the laser powder bed fusionLaser powder bed fusion (L-PBF) (LPBF) processProcess was investigated through a hot compressive deformation test performed at the temperatureTemperature range of 973–1423 K and strain rates of 0.01–1.0 s−1. Flow stressFlow stress curves were analyzed using materialMaterials constitutive modeling and double differentiation techniques to assess various softening mechanisms and the onset of the dynamic recrystallizationDynamic recrystallization (DRX) phenomenon, respectively. The Johnson–Cook constitutive equation demonstrated higher accuracy in predicting the flow stressFlow stress curves at relatively higher temperaturesTemperature. The flow stressFlow stress peak diminished at higher strain, indicating an increasing presence of dynamic recoveryDynamic recovery (DRV). Based on the calculated critical strains, DRX occurred before peak stress at strains between 0.05–0.14. These observations were confirmed by the electron backscatter diffraction (EBSDElectron back scattered diffraction (EBSD)) analysis, revealing increased grain refinement at low-temperatureTemperature settings due to the high-volume of DRX nuclei. Conversely, at high-temperatureHigh temperature settings, a possible dynamic transformation (DT) occurred alongside DRX, leading to the formation of lath-like grains with low local misorientations. These results were subsequently compared with the hot deformation behaviorHot deformation behavior of conventionally manufactured 420 stainless steelsStainless steel.