Corrosion Behavior Difference in Initial Period for Hot-Rolled and Cold-Rolled 2205 Duplex Stainless Steels

Abstract

Precipitate phases often play an important role on the corrosion resistance of 2205 Duplex stainless steels (DSS). In the present paper, the microstructure and the corrosion resistance of the hot-rolled and cold-rolled 2205 steels aged for different times at 850 • C was investigated through XRD, SEM, and potentiodynamic polarization. It was discovered that the Chi(χ) phase and Sigm(σ) phase were precipitated in turn following the aging treatment of the hot-rolled and cold-rolled steels, but the precipitate amount in the cold-rolled samples was significantly higher when compared to the hot-rolled samples. The corrosion resistance of the solution-annealed cold-rolled samples was similar to the hot-rolled samples, but the corrosion resistance of the cold-rolled sample with precipitate was weaker when compared to the hot-rolled sample following aging treatment. Pitting preferentially initiates in the Cr-depleted region from the σ phase in the aged hot-rolled 2205, becoming increasingly severe during aging for a long lime. Adversely, the initiation of pitting corrosion might occur at the phase boundary, defects, and martensite in the aged cold-rolled 2205. The σ phase was further selectively dissolved through the electrochemical method to investigate the difference in microstructure and corrosion behavior of the hot-rolled and cold-rolled 2205 duplex stainless steels.

Evaluación ultrasónica de las fases formadas de un acero inoxidable dúplex 2205 tratado térmicamente a 750 °C y su comportamiento frente a la corrosión

“…Además de las fases mayoritarias α y γ, se puede presentar una variedad de fases secundarias indeseables que se forman por efecto de los elementos aleantes y de los tratamientos térmicos, entre ellas destacan los nitruros hexagonales (Cr 2 N), fase sigma (σ), fase chi (χ), austenita secundaria (γ 2 ), fase R, fase π, fase G, M 7 C 3 , M 23 C 6 y fase τ (Gunn, 1997;Mateo y Llanes, 1997;Karlsson, 1999). La precipitación de pequeñas cantidades de las fases χ y σ afecta drásticamente a las propiedades mecánicas y de resistencia a la corrosión características de estos aceros (Gironès et al, 2007;Fargas et al, 2009;Gao et al, 2018). La fase σ es una fase intermetálica no magnética, de estructura tetragonal, cuya precipitación es observada en un rango de temperaturas entre los 600 y 1000 ºC y ocurre principalmente a través de la descomposición eutectoide de α en σ y γ 2 .…”

Influence of Homogenization and Annealing Temperatures on the Microstructure, Mechanical Properties, and Passive Properties of Cold Rolled 2205 Duplex Stainless Steel

“…It can be mentioned that the strain-induced martensite (SIM) could be formed, and it has the same crystallographic parameters as the ferrite, so ferrite and α'-martensite peaks are coincident. Recent studies have shown a consistent decrease in austenite with increased deformation as indicative of SIM 18,[33][34][35][36][37][38] . Furthermore, studies indicate that the peak (200)γ disappearance after cold rolling is due to the SIM formation 20,35,39,40 .…”

“…Furthermore, it modifies the composition of the passive film at room temperature and the results show a less protective ability of the passive film with an increase in deformation level of 2205 DSS duplex stainless steel in simulated concrete pore solution. Gao et al 37 studied 2205 DSS in a 3.5% NaCl solution and the results indicate that σ phase, strain-induced martensite, as well as the defects, induced by cold deformation, lower the corrosion resistance.…”

Effect of Isothermal Treatment on Microstructure and Performance of Micro/Nanostructure 2205 Duplex Stainless Steel Prepared by Aluminothermic Reaction

“…[14] While an initial low crystallographically coherent interface between α and γ phases enhances σ phase precipitation. [15] In addition, it is because of the presence of σ-phase in the austenite/ferrite microstructure of DSSs reduces their lifetime and promotes a brittle fracture in service, [16][17][18][19][20] more research is devoted to reducing the precipitation of this phase by proper heat treatment. Elmer et al [21] studied the precipitation of the σ phase in 2205 DSSs using in situ observation method and found that the σ phase was detected only after aging at 850 °C for 81 s; the precipitation amount reached 13.4% after 30 min, while it will completely dissolve after raising the temperature to 985 °C.…”

“…[ 11,12 ] At high temperatures, the σ phase is mainly at the ferrite ( α )/austenite ( γ ) phase boundary and the α grain boundary, and the growth mechanism is the transformation of the α phase to the σ and the γ 2 phases. [ 14–20 ] Furthermore, thermokinetic predictions confirm that the segregation of Cr and especially Mo at grain boundaries of α plays an important role in the nucleation of σ phase. [ 14 ] While an initial low crystallographically coherent interface between α and γ phases enhances σ phase precipitation.…”