Konys, J.

Schroer, C.

Skrypnik, A.

Tsisar, V.

Wedemeyer, O.

KITopen

Corrosion behavior of austenitic steels 1.4970, 316L and1.4571 in flowing LBE at 450 and 550°C with 10-7 mass %dissolved oxygenINSTITUTE FOR APPLIED MATERIALS MATERIAL PROCESS TECHNOLOGY (IAM WPT)Valentyn Tsisar, Carsten Schroer, Olaf Wedemeyer, Aleksandr Skrypnik, Jürgen Konys    –    -KIT – University of the State of Baden-Wuerttemberg and National Research Center of the Helmholtz Association www.kit.eduIn-situ technology of Pb and Pb-Bi melt doping withoxygen in order to form the protective oxide layer on thesurface of steelDissolution Oxidation Severe oxidation316L T91 EP-823BASIS of Pb-Bi technology Pb / Pb-Bi dissolvesand transports theoxygen; Components of steels(Si, Cr, Fe…) havehigh affinity to oxygenSchematic representation of corrosion rate and interaction modes of steels in Pb/Pb-Bi meltsthan Pb or Bi.22nd International Conference on Nuclear Engineering Institute for Applied Materials –ICONE22 Material Process Technology (IAM-WPT)Prague, CZ, July 07–11, 2014 Corrosion Department2             depending on the oxygen concentration in the liquid metal and temperature.Austenitic C Ni M M Si C V W Al Ti C N P S B1.1 Materials(Fe – Bal.)steelsr o n u316L 16.73 9.97 2.05 1.81 0.67 0.23 0.07 0.02 0.018 - 0.019 0.029 0.032 0.0035 -1.4970 15.95 15.4 1.2 1.49 0.52 0.026 0.036 < 0.005 0.023 0.44 0.1 0.009 < 0.01 0.0036 < 0.011.4571 17.50 12 2.0 2.0 1.0 - - - - 0.70 0.08 - 0.045 0.015 -1.4970 (15-15Ti) 316L 1.4571Shape and dimensions of sample for corrosion tests General view of initial sample after finishing turning HV30 = 253; Grain size ranged from 20 to 65 µm; Intersecting deformation twins. HV30 = 132; Grain size averaged 50 µm (G 5.5); Annealing twins. HV30 = 245; Grain size averaged 50 µm (G 9.5).70 µm 22nd International Conference on Nuclear Engineering Institute for Applied Materials –ICONE22 Material Process Technology (IAM-WPT)Prague, CZ, July 07–11, 2014 Corrosion Department3Test parameters T = 550(+5)°C  Tmin ≈ 385°CcO = 10–7 mass%, excursion to 10–4–10–5 mass%Ov = 2(+/–0.2) m/s, initially 1.5–1.6 m/st = 288; 715; 1007; 2011 h T = 450(+5)°CTmin ≈ 350°Cc = 10–7 mass% excursion to 10–5 mass% OO  ,    v = 2(+/–0.2) m/st = 500; 1007; 1925; 2015; 3749; 5015; 8766 h22nd International Conference on Nuclear Engineering Institute for Applied Materials –ICONE22 Material Process Technology (IAM-WPT)Prague, CZ, July 07–11, 2014 Corrosion Department4CORRIDA loopQuantification of corrosion Goal of quantification   Material loss, average of general corrosion andmaximum of local corrosion Thickness of adherent (oxide) scale     Overall change in dimensions, including the scale  Amount of metals transferred to the liquid metal Metallographic method (cylindrical specimens) Measurement of initial diameter in a laser micrometer with 0.1 µm resolution Diameter of unaffected materialand thickness of corrosion scalesdetermined in a microscope (LOM)at minimum ×500 magnification,with 1 µm resolution Occurrence of different corrosionmodes on opposing sides of there-measured diameter isconsidered in the evaluation22nd International Conference on Nuclear Engineering Institute for Applied Materials –ICONE22 Material Process Technology (IAM-WPT)Prague, CZ, July 07–11, 2014 Corrosion Department5Quantification of corrosion modes on surface ofaustenitic steels after exposure to flowing LBE at/ °C / 7 % O450 550 , 2 m s with 10– massGeneral surface topography of austenitic steels (1.4970) after test at 550°C After cleaning in glycerin Aft h i l l i   er c em ca  c ean ngSurface appearance:1007 h 2011 h  Green-colored oxide film;  Light areas with exfoliated oxide film;  Zones of severe local corrosion attack:- hemispherical pits;- longitudinal and transversal grooves; The percentage of surface covered by the oxide film decreases with exposure time in LBE while the number of sites affected by local corrosion attack respectively increases22nd International Conference on Nuclear Engineering Institute for Applied Materials –ICONE22 Material Process Technology (IAM-WPT)Prague, CZ, July 07–11, 2014 Corrosion Department6,            .General surface topography of austenitic steels (1.4970)after test at 450°C for 5015 hSegment of sample is chemically cleanedMacro-defects Micro-defectsMacro-defects: Intersecting corrosion grooves; Grooves form regular network-like structure characterized by similar andrepetitive dimensional parameters which could be associated with finalfinishing turning (a, b); Pre-existing active paths, i.e. grains and/or sub-grain boundaries and twinsare the main paths for selective leaching of Ni and Cr and subsequentpenetration of Pb and Bi into steel matrix22nd International Conference on Nuclear Engineering Institute for Applied Materials –ICONE22 Material Process Technology (IAM-WPT)Prague, CZ, July 07–11, 2014 Corrosion Department7.Surface examination of tested steels (1.4970)450°C 2000 h550°C, 2000 hof Ni and Cr,   Surface of austenitic steels are cowered by thin (≤0 5 µm) Cr-based.oxide film; Porous corroded surface markedly depleted in Cr and Ni andpenetrated with Pb and Bi is also observed.22nd International Conference on Nuclear Engineering Institute for Applied Materials –ICONE22 Material Process Technology (IAM-WPT)Prague, CZ, July 07–11, 2014 Corrosion Department8 Layer-type attack - formation of ferrite layer depleted in Ni and Cr andpenetrated by Pb and BiCross-section examination of tested steels1.4970550°C2011 h22nd International Conference on Nuclear Engineering Institute for Applied Materials –ICONE22 Material Process Technology (IAM-WPT)Prague, CZ, July 07–11, 2014 Corrosion Department9Local pit-type corrosion attackExpected sequence of evolution of corrosion pits wit time22nd International Conference on Nuclear Engineering Institute for Applied Materials –ICONE22 Material Process Technology (IAM-WPT)Prague, CZ, July 07–11, 2014 Corrosion Department10Effect of temporal increase in oxygen concentration Growth of rare magnetite protrusions on the surface of 316L t l (550°C 1007 h) (Fi ) s ee  ,  g. a ; Formation of islands of  Fe-Cr spinel (1.4970 exposed at 550°C (Fig. b). 22nd International Conference on Nuclear Engineering Institute for Applied Materials –ICONE22 Material Process Technology (IAM-WPT)Prague, CZ, July 07–11, 2014 Corrosion Department11Quantification of corrosion loss of austenitic steelsafter exposure to flowing LBE at 450/550°C, 2 m/s with710– mass% O450°C: Corrosion loss measured as decrease in diameter does not exceed 4, 27, and 26 µm after 8766 h for 1 4571 1 4970 and 316L steels respectively;. , .    ,   Thickness of layer-type attack (ferrite) averaged 5, 7 and 4 µm after 8766 h for 1.4571, 1.4970 and 316L steels, respectively;  Depth of pit-type attack average 50, 114 and 136 µm correspondingly. The percentage of circumference affected by selective leaching increases with time and after 8766 h reached 100 %           . 550°C: Decrease in diameter averaged ~ 60, 46 and 51 µm  after 2011 h for 1.4571, 1.4970 and 316L steels, respectively; Layer-type attack averaged 23 30 and 46 µm;22nd International Conference on Nuclear Engineering Institute for Applied Materials –ICONE22 Material Process Technology (IAM-WPT)Prague, CZ, July 07–11, 2014 Corrosion Department12   ,    Depth of pit-type attack averaged 182, 124 and 127 µm. Percentage of circumferenceff t d b l ti l hia ec e y se ec ve eac ngattack that resulted in eitherformation of layer-type (L) or pit-type (P) damage22nd International Conference on Nuclear Engineering Institute for Applied Materials –ICONE22 Material Process Technology (IAM-WPT)Prague, CZ, July 07–11, 2014 Corrosion Department13The percentage of surface affected by selective leaching attack increases with timeComparison of results at 10-7 and 10-6 mass% O  10-6 mass% O – preferential oxidation(spinel); 10-7 mass% O preferential selective–leaching; At constant CO[LBE] ~ 10-7 mass% O, thedepth of pits increases with temperature1 4571increasing from 450°C (solid symbols) to 550°C(open symbols); At constant T = 550°C the maximum depth.550°C10-6 mass%O ,of pits increases when concentration of oxygenin the melt decreases from 10-6 to10-7 mass% O;316L Under the other similar conditions of test(550°C, ~10-7 mass% O), the finer grains ofsteel the deeper corrosion attack: one cancompare curves 1 in Fig (fine grained 1 4571). .and 3 (coarse-grained 316L) and curves 2(1.4571) and 4 (316L) fitted for 550°C andconcentrations of oxygen 10-7 and10-6 mass% O respectivelyMaximum depth of pit-type corrosion attack on austenitic steels tested in flowing LBE (~ 2 m/s) depending on temperature and oxygen concentration in the melt22nd International Conference on Nuclear Engineering Institute for Applied Materials –ICONE22 Material Process Technology (IAM-WPT)Prague, CZ, July 07–11, 2014 Corrosion Department14, .      . Conclusions Austenitic steels (1.4970, 316L and 1.4571) showed complex corrosion behavior in flowing (2 m/s) LBEwith 10-7 mass % O at 450 and 550°C. Interaction was accompanied by formation of a thin (≤ 0.5 µm) Cr-based oxide film characterizing the incubation period followed by the selective leaching of Ni and Cr fromthe sub-oxide layers resulting in development of general layer-type and local pit-type attack. Cr-based oxide film, formed in-situ on the surface of austenitic steels, is not a sufficientt ti b i ith t t th l ti l hi d th i diti f t t !!!pro ec ve arr er w respec o e se ec ve eac ng un er e g ven con ons o es In the LBE with 10-7 mass%O the selective leaching is a main corrosion mechanism of austenitic steelscausing substantial corrosion loss, while in LBE with 10-6 mass%O the oxidation prevails. The local deepcorrosion attack due to selective leaching seems to be a critical factor affecting corrosion resistance ofaustenitic steels in oxygen-controlled LBE while oxidation is only postpones the unavoidable start ofselective leaching. The residual surface pattern and stresses resulting from the mechanical preparation of samples (turning)in combination with local flow conditions facilitates the local breakdown of the oxide film. As the localcorrosion attack initiated, the bulk structure of steel became dominant for its further development. In thiscase, substantial number of preferential diffusion paths, such as deformation twins (1.4970) and fine-grained structure (1.4571) characterized by high grain boundary density, both favor the selective leaching22nd International Conference on Nuclear Engineering Institute for Applied Materials –ICONE22 Material Process Technology (IAM-WPT)Prague, CZ, July 07–11, 2014 Corrosion Department15attack.AcknowledgementsThe construction and operation of the CORRIDA loop wasfinancially supported by the Nuclear Safety Programme of KIT.The presented work is part of the MATTER project that hasreceived funding by the 7th Framework Program of the EU(Grant Agreement No. 269706).22nd International Conference on Nuclear Engineering Institute for Applied Materials –ICONE22 Material Process Technology (IAM-WPT)Prague, CZ, July 07–11, 2014 Corrosion Department16

Corrosion behavior of austenitic steels 1.4970, 316L and 1.4571 in flowing LBE at 450 and 550⁰C with 10⁻⁷ mass % dissolved oxygen

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Corrosion behavior of austenitic steels 1.4970, 316L and 1.4571 in flowing LBE at 450 and 550⁰C with 10⁻⁷ mass % dissolved oxygen

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