Effect of Mn Contents on Microstructure Evolution and Recrystallization Behavior of 18.5 Pct Cr Low-Nickel Type Duplex Stainless Steel During Multi-pass Hot Compression

Abstract

This study examined the effect of manganese (Mn) contents (3.12 to 8.97 pct) and three-pass deformation distributions on dynamic recrystallization (DRX) and dislocation evolution during hot compression of low-nickel duplex stainless steel (DSS). With a total deformation of 70 pct and a strain rate of 0.1 s⁻¹, the study revealed that elevated Mn content enhances the ferrite phase's DRX, whereas austenite phase's dynamic recovery (DRV) varied with the deformation pass distribution. Changing the pass sequence (30 pct-10 pct-30 pct to 10 pct-30 pct-30 pct, and subsequently to 25 pct-35 pct-10 pct) in the 8.97 pct Mn sample, a reduction in the percentage of deformed grains in the austenite phase was observed. Furthermore, performing two consecutive passes with significant deformations was not favorable for ferrite DRX. Instead, it facilitated the development of subgrains within the austenite phase. The 25 pct-35 pct-10 pct deformation pattern in the 8.97 pct Mn sample led to twin boundaries formation, refining the coarse grains but impeding DRX, resulting in numerous austenite subgrains controlled by DRV. Conversely, a 30 pct-10 pct-30 pct deformation in the 8.97 pct Mn sample encouraged ferrite grains mainly displayed {001} and {111} recrystallization textures, thereby promoting DRX nucleation. The ferrite DRX process was primarily governed by continuous dynamic recrystallization (CDRX) mechanism, leading to the development of sizable, equiaxed grains with fewer dislocations. Kurdjumov-Sachs (K-S) relationship between the two phases enables dislocation slip from austenite to ferrite during compression deformation. With the increased addition of Mn, the ferrite underwent a gradual transition from a deformation texture to a recrystallization texture, whereas the austenite continued to be predominantly characterized by a deformation texture. The dynamic softening effect exhibited a more pronounced behavior in the 30 pct-10 pct-30 pct deformation condition for the sample with 8.97 pct Mn in comparison to the other deformation conditions.