Effect of Composition on the Formation of Delta Ferrite in 304L Austenitic Stainless Steels During Hot Deformation

Four different AISI 304L austenitic stainless steels with chromium equivalent-to-nickel equivalent (Cr_eq/Ni_eq) ratios of 1.57, 1.59, 1.62, and 1.81 were chosen for this study. The influence of chemical composition on solid-state formation of delta ferrite phase during hot deformation was investigated. Compression tests were performed at temperature, strain, and strain rate ranges of 1200 to 1300 °C, 10 to 70%, and 0.1 to 10 s⁻¹, respectively. Increasing the temperature, strain, and strain rate led to increased formation of delta ferrite. The results show that the formation of delta ferrite during hot deformation is also strongly dependent on chemical composition. The higher the Cr_eq/Ni_eq ratio, the higher the tendency for the formation of delta ferrite. The observed behavior may be attributed to plastic deformation-induced formation of crystallographic defects such as dislocations affecting the diffusion rate.