Aging behaviour of a duplex stainless steel

Influence of Solution Treatment Temperature on Microstructural Properties of an Industrially Forged UNS S32750/1.4410/F53 Super Duplex Stainless Steel (SDSS) Alloy

“…The microstructure of SDSS alloys usually contain a mixture of primary phases, such as δ-Fe (ferrite) and γ-Fe (austenite), and other secondary phases, such as: σ (Cr-Fe) (sigma), χ (chi), Cr 2 N (chromium nitride), M 23 C 6 (carbides) and γ 2 -Fe (secondary austenite) [27][28][29][30][31][32].…”

“…According to the experimental results obtained in this study, increasing the content of σ (Cr-Fe) and δ-Fe phases led to a higher global microhardness. Furthermore, considering also the solution treatment temperature influence on constituent phases, it was shown that during heating at temperatures below 1000 °C [25][26][27][28][29], secondary phases, such as: σ (sigma), χ (chi) and Cr2N are formed [30][31][32][33], being known that these phases exhibit a higher microhardness in comparison with δ-Fe and γ-Fe phases.…”

“…dimensions of 20 mm × 10 mm × 5 mm, were used for solution treating processing. The solution treatment temperatures were chosen taking into account that at temperatures below 1100 • C secondary phases may precipitate, as σ (Cr-Fe), Cr 2 N and γ 2 -Fe (secondary austenite), with high Metals 2017, 7, 210 3 of 13 negative effects on the corrosion resistance of SDSS alloy [25][26][27][28][29]. Four solution treatment temperatures were selected: 800 • C, 900 • C, 1000 • C and 1100 • C. Considering the sample dimensions and the rapid dissolution kinetics of deleterious secondary phases [14], the solution treatment duration was set to 10 min (0.6 ks) for all treatments, including also the transitory time needed to reach the heat treatment temperature (the samples being fed into the preheated furnace) and the time required for temperature homogenization.…”

“…The solution annealing improves the mechanical and corrosion characteristics of SDSS by dissolving the secondary deleterious phases at high temperatures, but also the annealing temperature can affect the δ-Fe and γ-Fe phases proportion, modifying this way the alloying elements partitioning in the two phases (δ-Fe being enriched in Cr and Mo and γ-Fe in N) and consequently the corrosion resistance of each phase [1,26]. In this regard, studying the correlation between the solution treatment parameters and microstructural characteristics can be very helpful [27][28][29].…”

Effect of short duration solution treatment at temperatures below 1000 °C on σ‐phase precipitation in a super duplex stainless steel alloy

“…Super duplex stainless steels are characterized by high chromium (20 % -30 %), nickel (6 % -8 %), molybdenum (3 % -6 %) and nitrogen (0.2 % -0.3 %) contents. The role of chromium, nickel and molybdenum in these alloys is to improve corrosion resistance, while the role of nitrogen is to promote structural hardening by the interstitial solid solution mechanism and as a consequence to improve the mechanical properties of the steel [6][7][8]12] The microstructure of super duplex stainless steels consists of primary phases, such as ferrite (d-Fe) and austenite (g-Fe), usually in a mixture containing roughly 50 % ferrite and 50 % austenite, but may also contain other secondary phases, such as: sigma (s -CrÀFe), chi (c), chromium nitride (Cr 2 N), carbides (M 23 C 6 ) and secondary austenite (g 2 -Fe) [16][17][18][19][20][21]. The high content of chromium, molybdenum, nickel and nitrogen must be completely dissolved in ferrite and austenite phases in order to promote high corrosion resistance for the steel, otherwise the formation of secondary phases and intermetallic compounds will be promoted [13][14][15][22][23][24][25].…”