Effect of Annealing Temperature on the Pitting Corrosion Behavior of UNS S82441 Duplex Stainless Steel

Abstract

The pitting corrosion behavior of UNS S82441 duplex stainless steel annealed at six different temperatures ranging from 1,000°C to 1,130°C for 1 h has been investigated by means of the potentiostatic critical pitting temperature. The microstructure evolution and pit morphologies of the specimens were studied using optical/scanning electron microscopy. The results demonstrated that the volume fraction of the austenite phase decreased with the increasing annealing temperature. Lower critical pitting temperature values were obtained after annealing at higher temperatures. Pitting was initiated preferentially inside the ferrite domains, indicating that the ferrite phase had inferior pitting corrosion resistance as compared to the austenite phase. The pitting resistance equivalent number of the ferrite phase fell with the annealing temperature, while the values for the austenite phase rose. No equal pitting resistance equivalent number of the ferrite and austenite phases was found for this steel in the range of annealing temperatures.

Investigation of the effect of solution annealing temperature on critical pitting temperature of 2205 duplex stainless steel by measuring pit solution chemistry

“…Since subjecting to thermal cycles like welding could change ferrite/austenite phase fraction and also may lead to microstructural alterations, many investigations have been conducted on the influence of annealing temperature on CPT of duplex stainless steels [25,30]. Investigating the chemical composition of phases in different annealing conditions, several researchers have related the CPT to the PREN (pitting resistance equivalent number) of weakest phase [23,[30][31][32], which itself is related to the content of three most essential elements, i.e. Cr, Mo and N [33,34].…”

Understanding the relation between phase fraction and pitting corrosion resistance of UNS S32750 stainless steel

“…In addition, Figure 5(e) shows the pronounced partitioning of N. Only less than 0.1 wt% N was detected in the  phase, and most of them was partitioned into the  phase. The N solubility in the body-centered cubic structure is reported to be less than 0.1 wt%, preferentially 0.05 wt%, which is considerably lower than that in the face-centered cubic structure [7,10,12,17,[21][22][23]. Furthermore, the N has high diffusivity [23] at the elevated temperature in austenitic stainless steels (approximately 7.5x10 -8 cm 2 s -1 at…”

“…Among the aforementioned alloying elements, Cr, Mo, N, and Mn affect the resistance to the pitting corrosion. Thus, the alteration in the phase fraction causes the change in the individual pitting corrosion resistance levels of the  and the  phases, and, accordingly, it influences the overall pitting corrosion resistance of DSSs [7,[10][11][12][13][14][15].…”

“…As an empirical measure of the resistance to the pitting corrosion of stainless steels, the PREN is expressed in a DSSs such as UNS S32550 alloy (26Cr-5.9Ni-3.2Mo-1.0Mn-0.2N-1.6Cu-Fe balance , [7]), UNS S32750 (25.2Cr-6.7Ni-3.4Mo-0.7Mn-0.27N-Fe balance , [10]), UNS S31803 (22.4Cr-5.7Ni-3.0Mo-1.5Mn-0.17N-Fe balance , [11]), UNS S82441 (24.0Cr-3.4Ni0-1.5Mo-3.0Mn-0.23N-Fe balance , [12]), and 26.2Cr-6.99Ni-2.37Mo-2.88W-0.35N-Fe balance DSS [13] were investigated, and the previous researchers came to the similar conclusion that the highest overall pitting corrosion resistance level of the DSS was achieved in the phase fraction-controlled sample whose two phases exhibited the lowest difference in the PREN values between the  and , , and the overall pitting corrosion resistance level was generally lowered as the value increased.…”

“…Many efforts have been made to find the optimum phase balance for the highest resistance to the pitting corrosion and to explain the relation between the phase fraction and the pitting corrosion resistance [7,[10][11][12][13]. Previous researchers generally agreed with the theory that the overall pitting corrosion resistance of the DSSs was governed by the phase with lower resistance level to the pitting corrosion between the two constituent phases, and they reported that the highest pitting corrosion resistance of the DSSs could be achieved when the two constituent phases exhibited equivalent levels of pitting corrosion resistance.…”