Konys, J.

Schroer, C.

Skrypnik, A.

Tsisar, V.

Wedemeyer, O.

KITopen

KIT – University of the State of Baden-Wuerttemberg and National Research Center of the Helmholtz AssociationInstitute for Applied Materials – Applied Materials Physics (IAM-AWP), Corrosion Dep.www.kit.eduInfluence of cold work on solution-based corrosionattack on 1.4970 (15-15Ti) austenitic steel in static liquidlead-bismuth eutectic at 550°C and ≤ 10-8 mass %dissolved oxygenValentyn Tsisar, Carsten Schroer, Olaf Wedemeyer, Aleksandr Skrypnik, Jürgen Konys23rd International Conference on Nuclear EngineeringICONE 23May 17-21, 2015, Chiba, JapanInitial steel structure Steel structure after corrosion in LBE223rd International Conference on Nuclear Engineering (ICONE-23)May 17-21, 2015, Chiba, JapanInstitute for Applied Materials – Applied Materials Physics (IAM-AWP)Corrosion departmentScheme of corrosion loss and interaction modes of steels with Pb and Pb-Bi melts depending on the oxygen concentration in the liquid metalIn-situ technology of doping of Pb or Pb-Bi melt byoxygen in order to form the protective oxide layer on thesurface of steelDissolution Oxidation Severe oxidation316L T91 EP-823BASIS of Pb-Bi technology Pb and Pb-Bi dissolve and transportthe oxygen; Components of steels (Si, Cr, Fe…)have high affinity to oxygen than Pbor Bi.C. Schroer (KIT-2014)Main aim of Pb-Bi technology To mitigate dissolution ofsteel constituents in Pb /Pb-Bi; To provide moderateoxidation of steels bycontinuous control andmonitoring of concentrationof oxygen in liquid metal; To avoid severe oxidationof steels and Pb (Bi).323rd International Conference on Nuclear Engineering (ICONE-23)May 17-21, 2015, Chiba, JapanInstitute for Applied Materials – Applied Materials Physics (IAM-AWP)Corrosion department Oxide layers tend to degrade with timeresulting in penetration of liquid metal to theunprotected steel surface; Solution-based corrosion attack usuallyinitiates preferentially instead of re-passivation; Composition and microstructure of steelbecome dominant factors for furtherpropagation of solution-based attack into bulkof material; Effect of steel composition on the corrosionrate is well understood, i.e., the higher steelis alloyed by high-soluble elements (Ni, Cr,Mn, Al etc.) the more severe is the solution-based attack; Effect of the structural state of the materialhas not yet been elucidated in detail.Motivation of workPorous spinel percolated by Pb-BiPb-Bi at scale-matrix interfacePit-type solution-based corrosion attack423rd International Conference on Nuclear Engineering (ICONE-23)May 17-21, 2015, Chiba, JapanInstitute for Applied Materials – Applied Materials Physics (IAM-AWP)Corrosion departmentEffect of structural state of steels on the corrosion response toPb and Pb-Bi melt – literature review Most of the works concerning effect of material structure on the corrosion resistance of steelsin Pb-Bi are focused on the effect of cold working; Results are contradictory describing positive and negative effect of cold worksimultaneously!Aim of the present work is to reinvestigate the effect of cold work on the corrosion resistance of austenitic steels in Pb-Bi eutectic. Johnson et al. [JNM 328 (2004) 88-96]: cold-rolledaustenitic steel 316L forms a protectivechromium oxide layer in non-isothermal oxygen-controlled (30 - 50 ppb) LBE at 550°C for,3000 h while an annealed sample, forms athicker, less protective oxide, consisting of outeriron oxide and inner spinel; Soler et al. [EUROCOR 2005]: better oxidationresistance of AISI 304L steel is a result ofsurface state of samples caused by coldworking; Rivai et al. [JNM 431 (2012) 97-104]: 20% of coldworking limits dissolution attack on JPCA steel(15-15 Ti) in flowing LBE containing ~ 10-8-10-9 mass% O at 450°C. Fe-Cr oxide layer wasformed on the surface of 20% cold-workedsample while it does not formed on the surfaceof annealed sample. However, in-situ formediron-chromium oxide layer did not protect steelsurface perfectly resulting in development oflocal corrosion damages. Kurata [JNM 448 (2014) 239-249]: the higher level of coldworking the deeper ferritization zone (corrosion attack)on austenitic JPCA and 316 steels, tested in static LBEwith ≤ 10-8 mass% O; Kurata [JNM 448 (2014) 239-249]: cold working acceleratesoxidation of austenitic steels at 550 °C for 1000 h inliquid LBE with ~10-5 wt.%; Chopra et al. [FUS.TECH. 8 (1985) 1956-1967]: dissolution rates for20% cold-worked 316 steel are a factor of - 2 greaterthan for the annealed state in Pb-Li eutectic; Tsisar et al. [JNM 454 (2014) 332–342]: importance of structuralstate of solid metal on the corrosion response ofaustenitic steels to flowing LBE with 10-7 mass% O isunderlined. However the difference in the compositionamong the austenitic steels tested with respect to highsoluble element as Ni (10-15 mass%) did not allow us tomake a clear conclusion.523rd International Conference on Nuclear Engineering (ICONE-23)May 17-21, 2015, Chiba, JapanInstitute for Applied Materials – Applied Materials Physics (IAM-AWP)Corrosion departmentAustenitic steelCr Ni Mo Mn Si Cu V W Al Ti C N P S B1.4970 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 < 0.01Tested material: austenitic steel 1.4970 (15-15Ti) HV30 = 253; Grain size ranged from 15 to70 µm; Intersecting deformationtwins and slips. Solution annealed at1100ºC for 30 min;HV30 = 130; Grain size averaged 40µm; Annealing twins. HV30 = 245; Grain size ~ 40 µm; Annealing twins anddeformation twins and slips.(Fe – Bal.)As-received(AR) Solution annealed (SA) 20% CW 40%CW HV30 = 300; Grain size ~ 40 µm; Deformation twins andslips.Cold Worked (CW) 623rd International Conference on Nuclear Engineering (ICONE-23)May 17-21, 2015, Chiba, JapanInstitute for Applied Materials – Applied Materials Physics (IAM-AWP)Corrosion departmentTarget concentration of oxygen in LBE at550ºC should be ≤10-8mass%O in order toprovide preferential dissolution of steelconstituents.Gibbs free energy of formation of oxides (solid lines) and oxygen solutions in Pb-Bi (dashed lines)[C. Schroer et al., NED 2012]Thermodynamic considerations on corrosion test723rd International Conference on Nuclear Engineering (ICONE-23)May 17-21, 2015, Chiba, JapanInstitute for Applied Materials – Applied Materials Physics (IAM-AWP)Corrosion departmentApparatus for  static corrosion tests in liquid metalsSchemeTest conditions: Pb-Bi eutectic (~2kg) – fresh for each test;  550ºC; Ar+5%H2 gas mixture bubbling through the liquid LBE with a rate of 30 ml/min.PhotoAr-5vol%H2Oxygen Control SystemAssembly of cylindrical specimens (Ø8×10 mm)4321823rd International Conference on Nuclear Engineering (ICONE-23)May 17-21, 2015, Chiba, JapanInstitute for Applied Materials – Applied Materials Physics (IAM-AWP)Corrosion departmentQuantification of corrosion loss Goal of quantification Material loss, average of general corrosion and maximum 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 alaser micrometer with 0.1 µmresolution Diameter of unaffected material (12thmeasurements with rotation angle15°) and thickness of corrosionzones determined in a microscope(LOM) with 1 µm resolution Occurrence of different corrosionmodes on opposing sides of the re-measured diameter is considered inthe evaluation (% of surfacecircumference)Transverse circular cross-sectionØPost-test examinationInitial parameters - Ø923rd International Conference on Nuclear Engineering (ICONE-23)May 17-21, 2015, Chiba, JapanInstitute for Applied Materials – Applied Materials Physics (IAM-AWP)Corrosion departmentCorrosion test 1: 550°C, ~10-9-5×10-11 mass%O, 1100 hExperimental parameters of test 1Ferrite layer (Ni and Cr depleted and percolated by Pb and Bi) isformed;Corrosion loss increases with increasing cold working level of steel.SA 20%CW 40%CW ARFerriteFerriteFerriteFerritelog Co(mass%)=-3.2837+6949.8/T(K)-10.080×E(V)/T(K)1023rd International Conference on Nuclear Engineering (ICONE-23)May 17-21, 2015, Chiba, JapanInstitute for Applied Materials – Applied Materials Physics (IAM-AWP)Corrosion departmentCorrosion test 2: 550°C, ~10-9-5×10-11 mass%O, 1500 hExperimental parameters of test 2 SA 20%CW 40%CW ARFerriteFerrite Ferrite Ferrite Uniform ferrite layer is formed on solution annealed (SA) sample; Highly non-uniform in thickness ferrite layers are formed on coldworked (CW) samples; Corrosion loss increases in order SA → 20%CW → 40%CW. AR sample showed comparable smaller corrosion loss (?).? ?1123rd International Conference on Nuclear Engineering (ICONE-23)May 17-21, 2015, Chiba, JapanInstitute for Applied Materials – Applied Materials Physics (IAM-AWP)Corrosion departmentCorrosion test 3: 550°C, ~10-8 mass%O, 2200 hExperimental parameters of test 3General view of sample assembly before and after testSA40%20%ARTotal cross-section appearanceReconstruction of initial diameter of sample in order to determine maximum corrosion depth? ?1223rd International Conference on Nuclear Engineering (ICONE-23)May 17-21, 2015, Chiba, JapanInstitute for Applied Materials – Applied Materials Physics (IAM-AWP)Corrosion departmentGeneralization of the obtained results:Phenomena observed  Austenitic steel 1.4970 (15-15-Ti) underwent in generalthe solution-based attack: formation of ferrite zonedepleted in Ni and Cr and percolated by Pb and Bi; Irregularity of corrosion attack increases with increasinglevel of deformation; Cold worked material reveals pit-type attack whilesolution annealed showed more regular layer typeattack; Rare areas showed protective scaling surface of whichdecreases with increase in deformation level andexposure time;Ferrite zonePit-type attack Layer-type attack Protective scaling1323rd International Conference on Nuclear Engineering (ICONE-23)May 17-21, 2015, Chiba, JapanInstitute for Applied Materials – Applied Materials Physics (IAM-AWP)Corrosion department?Generalization of the obtained results:Corrosion kinetics Incubation time for initiation ofsolution-based attack is about 600 h forcold worked steels and 1000 h forsolution annealed; Steepness of kinetic curves andcorresponding linear corrosion rateincreases in the following sequence:Solution Annealed → 20%CW →40%CW; As-received material does not followexpected dependence !?!?y = 0.4021x – 254.3540%CW20%CWSAy = 0.2931x – 182.9y = 0.1848x – 180.41Linear corrosion rate equation: Possible explanation 40%CW20%CWSAAR1423rd International Conference on Nuclear Engineering (ICONE-23)May 17-21, 2015, Chiba, JapanInstitute for Applied Materials – Applied Materials Physics (IAM-AWP)Corrosion departmentThe macro photographs of cross-sections after corrosion test. Corrosion depth/one side of the specimens.Possible explanation of exceptional behavior of as-received materialbased on the results published by Saito et al.[Journal of Nuclear Materials 431 (2012) 91–96]. Solution annealed 316L steel underwent more severe corrosion attack in flowing LBE (5 L/min,450°C, 10-8–10-9 wt.%.O) in comparison with material after grain-boundary engineering (GBEM: 3%pre-straining by cold rolling and subsequent annealing). The frequency of low-energy coincidence site lattice (CSL) boundaries is 86% in GBEM. Due to Grain-Boundary Engineering the dissolution attack is suppressed by interrupting the continuityof grain boundaries.Further plan - electron backscatter diffraction (EBSD) for as-received material !1523rd International Conference on Nuclear Engineering (ICONE-23)May 17-21, 2015, Chiba, JapanInstitute for Applied Materials – Applied Materials Physics (IAM-AWP)Corrosion departmentEffect of structural state of steels on the corrosion response toPb and Pb-Bi melt – literature review. Most of the works concerning effect of material structure on the corrosion resistance of steelsin Pb-Bi are focused on the effect of cold working; Results are contradictory describing positive and negative effect of cold worksimultaneously! Johnson et al. [JNM 328 (2004) 88-96]: cold-rolledaustenitic steel 316L forms a protectivechromium oxide layer in non-isothermal oxygen-controlled (30 - 50 ppb) LBE at 550°C for,3000 h while an annealed sample, forms athicker, less protective oxide, consisting of outeriron oxide and inner spinel; Soler et al. [EUROCOR 2005]: better oxidationresistance of AISI 304L steel is a result ofsurface state of samples caused by coldworking; Rivai et al. [JNM 431 (2012) 97-104]: 20% of coldworking limits dissolution attack on JPCA steel(15-15 Ti) in flowing LBE containing ~ 10-8-10-9 mass% O at 450°C. Fe-Cr oxide layer wasformed on the surface of 20% cold-workedsample while it does not formed on the surfaceof annealed sample. However, in-situ formediron-chromium oxide layer did not protect steelsurface perfectly resulting in development oflocal corrosion damages. Kurata [JNM 448 (2014) 239-249]: the higher level of coldworking the deeper ferritization zone (corrosion attack)on austenitic JPCA and 316 steels, tested in static LBEwith ≤ 10-8 mass% O; Chopra et al. [FUS.TECH. 8 (1985) 1956-1967]: dissolution rates for20% cold-worked 316 steel are a factor of - 2 greaterthan for the annealed state in Pb-Li eutectic; Kurata [JNM 448 (2014) 239-249]: cold working acceleratesoxidation of austenitic steels at 550 °C for 1000 h inliquid LBE with ~10-5 wt.%; Tsisar et al. [JNM 454 (2014) 332–342]: importance of structuralstate of solid metal on the corrosion response ofaustenitic steels to flowing LBE with 10-7 mass% O isunderlined. However the difference in the compositionamong the austenitic steels tested with respect to highsoluble element as Ni (10-15 mass%) did not allow us tomake a clear conclusion. Present work: The higher deformation level of 1.4970austenitic steel the deeper solution-based corrosionattack !!!1623rd International Conference on Nuclear Engineering (ICONE-23)May 17-21, 2015, Chiba, JapanInstitute for Applied Materials – Applied Materials Physics (IAM-AWP)Corrosion departmentSUMMARYDeformation generates dislocations in the crystal structure and as aresult, the number density of structural defects (easy-diffusion pathways)increases;The higher deformation level the higher density of easy-diffusionpathways → the more intensive diffusion processes at constanttemperature → as a result, leaching of steel constituents by liquid metalintensifies;Cold working impairs corrosion resistance of structural materials in LBEproviding that the dissolution corrosion mode dominates !1723rd International Conference on Nuclear Engineering (ICONE-23)May 17-21, 2015, Chiba, JapanInstitute for Applied Materials – Applied Materials Physics (IAM-AWP)Corrosion departmentThank you for attention !!!Example of severe corrosion attack on austenitic steel in LBE

Influence of cold work on solution-based corrosion attack on 1.4970 (15-15Ti) austenitic steel in static liquid lead-bismuth eutectic at 550⁰C and <= 10⁻⁸ mass % dissolved oxygen

https://publikationen.bibliothek.kit.edu/240100823/3816822

Influence of cold work on solution-based corrosion attack on 1.4970 (15-15Ti) austenitic steel in static liquid lead-bismuth eutectic at 550⁰C and <= 10⁻⁸ mass % dissolved oxygen

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