Strain Partitioning and Softening Mechanisms of δ/γ in Lean Duplex Stainless Steels during Hot Deformation

Abstract

A novel lean duplex stainless steel (DSS) with excellent hot workability is successfully developed, referred as 21Cr‐DSS. The strain partitioning and softening mechanisms of the constituent phases in the novel steel are elucidated and compared with the conventional DSS. The strain is preferentially accommodated in the soft ferrite phase, leading to the significant strain localization and a faster restoration of dynamic recovery and dynamic recrystallization (DRV or DRX) in ferrite, whereas conventional DSS is characterized by inhomogeneity in softening and incompatibility in deformation between ferrite and austenite, which promotes the propagation of cracks along the δ/γ interface during hot deformation. However, the novel 21Cr‐DSS exhibits homogeneous strain–stress partitioning in δ/γ, especially at low deformation temperature, resulting in superior deformation compatibility between ferrite and austenite.

Effect of Ferrite Proportion and Precipitates on Dual‐Phase Corrosion of S32750 Super Duplex Stainless Steel with Different Annealing Temperatures

“…[ 9 ] The chemical compositions of δ, γ, σ, and γ 2 phases were analyzed by SEM–EDS, as shown in Figure 3b–d, which is consistent with the result from the studies. [ 9–13 ] Cr and Mo were rich in ferrite, whereas Ni mainly partitioned in austenite. The Mo and Cr contents in σ phase were higher than those in δ phase and γ phase.…”

“…[9][10][11][12][13][14][15] Generally, Cr and Mo are enriched in ferrite, whereas Ni and N are austenite-stabilizing elements. [9][10][11][12][13] According to the pitting resistance equivalent (PRE ¼Cr þ 3.3% Mo þ 16% N), [4,6,9,[16][17][18] the partitioning of the alloying elements results in the difference of corrosion resistance of each phase. In addition, several works [4,9,10] indicated that partitioning of alloying elements in each phase was affected by annealing temperature.…”

Constitutive Modeling of Hot Deformation of Carbon Steels in The Intercritical Zone

“…In this research, this equation is only applied considering the percentages of each of phase present as a function of the temperature, strain rate, and chemical composition of the alloy, therefore it does not consider the strain and stress distribution between phases 39,40 . In the future, it is possible to compare these results considering the effects of this phenomenon for this kind of steel.…”

Modelling of Hot Flow Stress of Duplex Steel in Dependence of Microstructure Using the Rule of Mixture

“…Even at the end of the forming process, the strain distribution shows higher strains in ferrite than in austenite [7]. Due to the high strain accumulation in ferrite, a faster softening behavior of ferrite can be observed [8].…”

“…This rule of mixture was validated for cold forming of a 1.4507 (AISI F255) super duplex steel by Cho et al [9] using measurements of micro-strains in ferrite and austenite and calculated stress-strain curves of ferrite and austenite single phase based on Ashby's one-parameter theory. For hot deformation, the rule of mixture was used by Zhao et al [8] to estimate the stress-strain partitioning coefficient at a total strain of 0.25, which indicates the degree of stress transfer from soft ferrite to hard austenite. The partitioning coefficient increases with the deformation temperature, which means that strain at high temperatures is more homogenously distributed between both phases.…”