Effect of strain-induced martensite reverse transformation on microstructure evolution and electrochemical behaviour of 2304 lean duplex stainless steel

Abstract

The effect of strain-induced martensitic transformation (SIMT) and its reversion (SIMRT) on the microstructure evolution and localised corrosion of 2304 lean duplex stainless steel (LDSS) was investigated. The cold-rolled LDSS was subjected to reverse annealing at 600°C to 900°C for 1800 s. To evaluate the microstructure, scanning (SEM) and transmission electron microscopy (TEM) and electron backscatter diffraction (EBSD) were used as the main techniques. Subsequent electrochemical characterisation included cyclic polarisation and double loop-electrochemical potentiokinetic reactivation test. SIM formation was noticed after cold rolling, and a partial reverse transformation was seen after annealing at 600°C. At 600°C, SIMRT led to decrease in pitting resistance and increase in the degree of sensitisation (DOS). Increasing the annealing temperature favoured localised and intergranular corrosion resistance. The obtained results indicate that reversed austenitic and recrystallised grains have a beneficial effect on desensitisation and corrosion resistance of 2304 LDSS.

Effects of the Volume Fraction of the Secondary Phase After So-Lution Annealing on Electrochemical Properties of Super Duplex Stainless Steel UNS S32750

“…Solution annealing is a heat treatment to optimize the corrosion rsistance [4][5][6]. However, SDSS, in which the secondary phase is precipitated, does not have an optimized corrosion resistance [10][11][12]. The secondary phase is transformed into ferrite, and austenite should be transfromed into ferrite [16].…”

“…Although SDSS is composed of austenite and ferrite, the secondary phase is known to precipitate owing to the segregation of Cr at 975℃ [10][11][12]. To confirm the secondary phase, heat treatment was performed from 900 to 1050℃.…”

“…When the secondary phase is precipitated inside, hot temperature cracking occurs, decreasing the corrosion resistance. Although significant research efforts have been devoted to suppress the precipitation of secondary phases, no studies have been conducted on the effects of the secondary phase on solution annealing [10][11][12].…”

Effects of the Volume Fraction of the Secondary Phase after Solution Annealing on Electrochemical Properties of Super Duplex Stainless Steel UNS S32750

“…In order to obtain excellent corrosion resistance of SDSS, the ratio of the austenite phase and the ferrite phase should be close to 1:1, and appropriate heat treatment temperature conditions are required to control the ratio of the two phases. Although significant research efforts have been devoted to suppressing the precipitation of secondary phases, no studies have been conducted on the effects of the secondary phase on solution annealing at 1100 • C [10][11][12].…”

DL-EPR vs. LSV-KOH: from simple detection of deleterious phases to analysis of morphology and high accuracy on determination of sigma phase in UNS S32750 stainless steel

“…DL-EPR test was developed and optimised to analyse austenitic stainless steel [50,51]. Subsequently, it was adapted and applied in other stainless steels like martensitic [52][53][54], ferritic [55,56] and duplex [57][58][59][60][61][62][63][64][65][66][67].…”