Unique slip mechanisms and flow behavior during high-temperature deformation of additively manufactured high carbon stainless steel

High-temperature deformation experiments were performed on 420 stainless steels (AM420SS) fabricated using laser powder bed fusion (LPBF) technology, both below and above its Ae3 temperature ranging from 700 to 1150 degrees C and across two orders of magnitude of strain rates from 0.01 to 1 s-1. Prior to the hot compressive tests, the reconstruction of parent austenite grains in the as-3D printed state was carried out, revealing that adjacent grains have similar alignment of primary slip systems along the building direction. The melt pool morphology and layered grain distribution of the as-3D printed AM420SS led to non-uniform texture development during hot compression, caused by the mismatch of dominant slip systems in different regions. Using the Kocks-Mecking (KM) model, we found that dynamic recovery predominates at higher strain rates, while dynamic recrystallization becomes significant at lower strain rates and higher temperatures, as shown by reconstructed austenite grain sizes and recrystallization kinetics via the Johnson-Mehl-Avrami-Kolmogorov (JMAK) model. The activation energy of AM420SS was calculated to be 382 kJ/mol, with dislocation glide identified as the rate-determining deformation mechanism, indicated by an n value of 2.9. The prior austenite grain size increased while the shape factor decreased at higher temperatures, with a high density of stored energy constrained between growing austenite grains promoting preferential grain growth at lower strain rates. The findings from this work can guide the development of a combined net-shape fabrication technique with a high-temperature forming route to produce dense structures with controlled local texture.