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748 K (475 °C) Embrittlement of Duplex Stainless Steel: Effect on Microstructure and Fracture Behavior

“…No phase transformation products could be observed in the austenite. These observations are in good agreement with Nilsson and Liu, [19] Redjaimia et al, [12,37] and Karlsson et al [21] who observed R-phase precipitates at 823 K (550°C), 873 K (600°C), and 948 K (675°C), respectively. They also found Mo-and Si-depleted zones at and adjacent to R precipitates.…”

“…[9][10][11] Embrittlement is usually ascribed to spinodal decomposition of the ferrite, namely, the formation of Fe-enriched a¢ phase and Cr-enriched a¢¢ phase, or the formation of Cr-enriched a¢¢ precipitates embedded in a Fe-rich a¢ matrix after aging in the 523 K to 823 K (250°C to 550°C) temperature window. [9,[12][13][14][15][16] Ferrite is not stable within the miscibility gap and, therefore, decomposes into two phases. However, additional phases can also form in the ferrite and coexist with the spinodal decomposition products, such as G and R phase, as well as other secondary phases, [7,[9][10][11][12][17][18][19][20][21][22][23][24][25][26][27] which also can have significant impact on mechanical properties.…”

Correlative EBSD and SKPFM characterisation of microstructure development to assist determination of corrosion propensity in grade 2205 duplex stainless steel

“…Heat treatment, welding, or prolonged exposure to elevated temperatures may lead to undesired phase reactions in these high-alloyed stainless steels [2][3][4][5]. For example, the ferrite can decompose into a series of meta-stable and thermodynamically stable phases, whilst the austenite has often been stated to be unaffected [2,4,6].…”

“…For example, phase reactions in the temperature range between 250 and 550°C have been known as '475°C embrittlement' [2-5, 17, 18] where in addition to the degradation of mechanical properties a significant reduction in corrosion performance has also been observed [17][18][19][20][21]. Phase reactions occurring in the temperature range between 600 and 1000°C have become known as 'r-phase embrittlement' where numerous secondary phases, such as Frank-Kasper phases (r and v) and, to some extent, R-phase can be formed [5,10,16,[22][23][24][25][26][27][28][29][30][31][32][33][34][35]. These are often accompanied by the precipitation of nitrides (Cr 2 N and CrN) and carbides [2,4,5,16,34,36,37].…”

“…Phase reactions occurring in the temperature range between 600 and 1000°C have become known as 'r-phase embrittlement' where numerous secondary phases, such as Frank-Kasper phases (r and v) and, to some extent, R-phase can be formed [5,10,16,[22][23][24][25][26][27][28][29][30][31][32][33][34][35]. These are often accompanied by the precipitation of nitrides (Cr 2 N and CrN) and carbides [2,4,5,16,34,36,37]. Determination of the identity and the volume fraction of secondary phases have typically been carried out using image analysis of optical and/or electron microscopic micrographs, often supported by analytical semi-quantitative assessment of the chemical composition by energydispersive X-ray (EDX) analysis.…”