PSI - Issue 17

C.R.F. Azevedo et al. / Procedia Structural Integrity 17 (2019) 331–338 C. R F. Azevedo and A. F. Padilha / Structural Integrity Procedia 00 (2019) 000 – 000

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etching with 50% HNO 3 was intergranular and this sensitization was due to the low or lack of Nb + Ti stabilization, which allowed intergranular chromium carbide precipitation (Dowling et al., 1999).

Fig. 4. Precipitation of Laves phase in DIN 1.4575 SFSS solution annealed at 1050°C for 30 min, water quenching and isothermal aged at 850°C from 30 min to 4 hours then water quenching. (a) Sample aged at 850°C for 4 hours, showing intergranular σ phase (darker grey particles) and intergranular submicron Laves phases (white particles), SEM, BEI. (b) Detail of the sample aged at 850°C for 30 min, showing intergranular Laves phase particles of 200 nm, TEM. (c) Selected area diffraction pattern of the Laves phase. Adapted from Andrade et al. (2008). 3. Final comments Janikowski (2005) praised the good combination of mechanical properties, cost, thermal conductivity, erosion resistance and stress corrosion cracking, pitting and crevice corrosion resistances of SFSSs, which lead to their increasing usage in power plant condenser tubes, but there are well known limitations of SFSSs, such as their higher susceptibility to hydrogen embrittlement; their faster precipitation kinetics of deleterious phases at temperatures above 315°C; and the technical difficulties to cold roll SFSS plates to thickness below 0.5 mm. Additionally, their toughness drops significantly as the wall thickness increases, as brittle precipitates can be easily formed after hot rolling and cooling processes. Cooling rate and final annealing temperature must be strictly controlled to avoid the precipitation of deleterious phases and prevent the deterioration of the toughness of SFSS at room temperature (Lu et al., 2018). Andrews, K. W., 1949. A new intermetallic phase in alloy steels. Nature 164, 1015. Andrade, T.; Kliauga, A.M., Plaut, R. L., Padilha, A.F., 2008. Precipitation of Laves phase in a 28%Cr – 4%Ni – 2%Mo – Nb superferritic stainless steel. Materials Characterization 59, 503-507. Anglada, M., Rodriguez J., Isalgué, A., 1989. Influence of the plastic strain amplitude on the stability of the spinodal microstructure in the cyclic deformation of a Fe-28Cr-2Mo-4Ni-Nb alloy. Scripta Metallurgica 23, 1633-1638. Azevedo, C. R. F., Pereira, H., Wolynec, S., Padilha, A. F., 2019. An overview of the recurrent failures of duplex stainless steels. Engineering Failure Analysis 97, 161-188. Bain, E. C., Griffiths, W. E., 1927. Introduction to the iron-chromium-nickel alloys. Transactions of The Metallurgical Society of AIME 75, 166-211. Bandel, G., Tofaute, W., 1942. Die Versprödung von hochlegierten Chromstählen im Temperaturgebiet um 500º. Archiv für das Eisenhüttenwesen 14, 307-319. Bäumel, A., 1964. Vergleichende Untersuchung nichtrostender Chrom- und Chrom-Nickel-Stähle auf interkristalline Korrosion in siedender Salpetersäure und Kupfersulfat-Schwefelsäure-Lösung. Stahl und Eisen 84, 798-807. Bäumel, A., 1973 Korrosion in der Wärmeeinflubzone geschweibter chemisch beständiger Stähle und Legierungen und ihre Verhütung. Werkstoffe und Korrosion 26, 433-443. Bavay , J. C., 1993. The high chromium and molybdenum ferritic stainless steels, in “Stainless Steels”. In: Lacombe P., Baroux B. a nd Beranger G. (Eds.), Les éditions de physique, pp. 537, France. Bechtoldt, C. J., Vacher, H. C., 1957. Phase-diagram study of alloys in the iron-chromium-molybdenum-nickel system. Journal of Research of the National Bureau of Standards 58, 7-19. Bergman, G., Shoemaker, D. P., 1951. The space group of the σ -FeCr crystal structure. Journal of Chemical Physics 19, 515-515. Blackburn, M. J., Nutting, J., 1964. Metallography of an iron-21% chromium alloy subject to 475ºC embrittlement. Journal of The Iron and Steel Institute 202, 610-613. Bond, A. P., 1969. Mechanisms of intergranular corrosion in ferritic stainless steels. Transactions of The Metallurgical Society of AIME 245, 2127-2134. Brandi, S. D., Padilha, A. F., 1990. Precipitação de fase sigma em aços inoxidáveis ferríticos-austeníticos com microestrutura duplex. In: II References