Intergranular Corrosion in X39CrMo17-1 – A Review
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A. Neidel
Andreas Neidel studied mechanical engineering at IH Berlin. He got his doctorate there in 1991 with a thesis on high-speed heat treatment of low alloy steel. In 1992 he joined Siemens' Energy Sector at the Berlin Gas Turbine Manufacturing Plant. He has worked ever since there in quality management functions. In 1997, he has been appointed manager of the Materials Testing Laboratory. In 2015, he changed position into an expert role on failure analysis. He was appointed honorary professor for metallic materials by TU Berlin in 2015.
Tobias Gädicke was born in 1986 and joined the Siemens Energy Sector in 2005 as apprentice in the Berlin Gas Turbine Works. As materials testing technician, his main field of expertise is metallographic target preparation of laser-drilled holes in turbine blading. Also, he is expert in the field of portable metallography by means of the replica technique with both putty and replica foils which he regularly applies to microstructural analyses of large gas turbine casings made of ductile iron and steel castings. He is a lecturer in the DGM seminar on portable metallography. Metallurgical failure analysis of gas turbine engine hot gas path components are another field of expertise of his.
Abstract
The aim of this contribution is to review cases of repeated snap ring failures in large gas turbine engine service due to intergranular attack, or intergranular corrosion, IGC, and to shed some light on metallurgical aspects of the wet corrosion resistance of the subject high-alloy martensitic stainless chromium steel X39CrMo17-1, DIN 1.4122. It is important to note that only snap rings, a.k.a. retaining rings for bores or Seeger rings, were affected by those failures, namely fractures resulting from intergranular attack (IGA, Kornzerfall). It was determined that the metallurgical root cause of failure was sensitization, resulting from secondary chromium carbide precipitation at grain boundaries (GB), and the ensuing chromium depletion in narrow bands adjacent to the GB, which rendered the matrix there sensitive to selective corrosion (the chromium content in these narrow seams, measuring only a few 10 nm in width, drops below the corrosion resistance threshold of ca. 10.5 %). Snap rings, as the name suggests, require a certain “snappiness” to serve their purpose. It is because of this requirement that all snap rings that experienced failures in the field were heat treated per DIN EN 10088-2, providing for a low tempering temperature of max. 250 °C, leading to a relatively high hardness of ca. 580 HV 10, providing said “snappiness”. It turned out that the microstructure resulting from this heat treatment (H/T) is sensitized, rendering the material sensitive to IGA. To the knowledge of the authors, no other components made of this martensitic stainless chromium steel are given this H/T, but rather a high-temperature tempering of 650 °C–750 °C per DIN EN 10088-3, producing a lower hardness in the order of ca. 300 HV 10 and largely a lack of “snappiness”, the latter being not required by those non-snap ring applications. Metallurgically, it became clear that high-temperature tempering per DIN EN 10088-3 eliminates sensitization by “backfill” diffusion of chromium from the non-depleted matrix into formerly depleted regions next to GB. It was therefore decided in the authors’ organization to eliminate X39CrMo17-1 per DIN EN 10088-2 as a possible material selection. The metallurgical investigations described in this contribution corroborate and support this decision.
Kurzfassung
Dieser Beitrag soll einen Überblick über wiederholte Versagensfälle aufgrund von Kornzerfall bzw. interkristalliner Korrosion (IKK) bei in Großgasturbinen eingebauten Sprengringen geben und etwas Licht auf metallurgische Aspekte der Nasskorrosionsbeständigkeit des rostfreien martensitischen hochlegierten Chromstahls X39CrMo17-1, DIN 1.4122 werfen. Zu berücksichtigen ist, dass nur die auch Sicherungsringe für Bohrungen bzw. Seegerringe genannten Sprengringe von diesen auf Kornzerfall zurückgehenden Brüchen betroffen waren. Als metallurgische Grundursache des Versagens wurde eine auf die Ausscheidung sekundärer Chromcarbide an den Korngrenzen (KG) und die damit verbundene Chromverarmung in an die KG angrenzenden schmalen Bändern zurückzuführende Sensibilisierung ermittelt, durch die sich an dieser Stelle der Matrix eine Empfindlichkeit gegenüber selektiver Korrosion entwickelte (Der Chromgehalt in diesen schmalen Säumen, die lediglich einige wenige 10 nm breit sind, fällt unter den Grenzwert der Korrosionsbeständigkeit von ca. 10,5 %). Wörtlich übersetzt bedeutet das englische Wort „snap ring“ für Sprengring soviel wie „Schnappring“. Demnach müssen diese „schnappen“ können, also eine gewisse „Bissigkeit“ aufweisen. Aufgrund dieser Anforderung erhielten alle Sprengringe, die im Einsatz versagten, eine Wärmebehandlung (WB) entsprechend DIN EN 10088-2 bei einer niedrigen Anlasstemperatur von max. 250 °C, die eine relativ hohe Härte von ca. 580 HV 10 und somit diese „Bissigkeit“ gewährleistet. Es stellte sich heraus, dass diese Wärmebehandlung das daraus hervorgehende Gefüge sensibilisiert und den Werkstoff so anfällig für Kornzerfall macht. Nach Kenntnis der Autoren wurden keine anderen aus diesem rostfreien martensitischen Chromstahl hergestellten Komponenten dieser bestimmten WB unterzogen, sondern vielmehr bei hohen Temperaturen von zwischen 650 °C und 750 °C gemäß DIN EN 10088-3 angelassen. Eine solche Wärmebehandlung bringt eine geringere Härte von ca. 300 HV 10 hervor, so dass die bei Nicht-Sprengringanwendungen nicht erforderliche „Bissigkeit“ weitestgehend fehlt. Es konnte festgestellt werden, dass ein Anlassen bei hohen Temperaturen gemäß DIN EN 10088-3 metallurgisch gesehen eine Sensibilisierung durch eine „auffüllende“ Diffusion von Chrom aus der nicht verarmten Matrix in zuvor verarmte Bereiche in unmittelbarer Nähe der Korngrenzen beseitigt. Das Unternehmen der Autoren entschied daher, den Werkstoff X39CrMo17-1 nach DIN EN 10088-2 von einer möglichen Auswahl auszuschließen. Die im Rahmen dieses Beitrags beschriebenen metallurgischen Untersuchungen untermauern und stützen diese Entscheidung.
About the authors
Andreas Neidel studied mechanical engineering at IH Berlin. He got his doctorate there in 1991 with a thesis on high-speed heat treatment of low alloy steel. In 1992 he joined Siemens' Energy Sector at the Berlin Gas Turbine Manufacturing Plant. He has worked ever since there in quality management functions. In 1997, he has been appointed manager of the Materials Testing Laboratory. In 2015, he changed position into an expert role on failure analysis. He was appointed honorary professor for metallic materials by TU Berlin in 2015.
Tobias Gädicke was born in 1986 and joined the Siemens Energy Sector in 2005 as apprentice in the Berlin Gas Turbine Works. As materials testing technician, his main field of expertise is metallographic target preparation of laser-drilled holes in turbine blading. Also, he is expert in the field of portable metallography by means of the replica technique with both putty and replica foils which he regularly applies to microstructural analyses of large gas turbine casings made of ductile iron and steel castings. He is a lecturer in the DGM seminar on portable metallography. Metallurgical failure analysis of gas turbine engine hot gas path components are another field of expertise of his.
References / Literatur
[1] VDI-Richtlinie 3822, Part 3: March 2007: Failure analysis – Failures caused by corrosion in electrolytes. Beuth-Verlag GmbH, Berlin, Düsseldorf 2007.Suche in Google Scholar
[2] Maier, F.; Opielka, H.: Interkristalline Korrosion vonSicherungsringenaus 1.4122(X39CrMo17-1). Prakt. Met. Sonderband 36 (2004), S. 365–366. DOI: 10.5840/intstudphil200436110910.5840/intstudphil2004361109Suche in Google Scholar
[3] Lange, G. (Hrsg.): Systematische Beurteilung technischer Schadensfälle. 3. Auflage, DGM, 1992.Suche in Google Scholar
[4] ASM Handbook, Volume 11: Failure Analysis and Prevention. 6. Auflage, ASM International, 1998.Suche in Google Scholar
[5] Handbook of Case Histories in Failure Analysis, Volume 1. ASM International, Materials Park, OH, Third Printing 2002.Suche in Google Scholar
[6] Engelberg, D. L.: Intergranular Corrosion. In: Shreir’s Corrosion. Volume 2, 2010, pp. 810–827. Elsevier 2010. DOI: 10.1016/B978-044452787-5.00032-910.1016/B978-044452787-5.00032-9Suche in Google Scholar
[7] Streicher, M. A.: In ASTM STP 656: Intergranular Corrosion of Stainless Alloys; Steigerwald, R. F., Ed.; ASTM, 1978;, pp. 3–84.10.1520/STP34842SSuche in Google Scholar
[8] Harders, H.; Barnikel, J.: X39CrMo17-1 Intergranular Corrosion Issue. Internal presentation, January 17, 2022.Suche in Google Scholar
[9] Pohl, M.: Personal communication, Bochum, Berlin, November 2021.Suche in Google Scholar
[10] Harders, H.: Personal communication, Mülheim, Berlin, February 2022.Suche in Google Scholar
[11] Bäumel, A.: Werkstoffe und Korrosion, 16 (1975).Suche in Google Scholar
[12] Pohl, M.: Versagen von Bauteilen aus 13 % Cr-Stählen am Beispiel des Untertage-Sicherheitsventils in Kavernen zur Energiespeicherung. Vortrag VDI-Jahrestagung Schadensanalyse, Würzburg, Oktober 2020.Suche in Google Scholar
[13] DIN EN 10088-2 Stainless steels – Part 2: Technical delivery conditions for sheet/plate and strip of corrosion resisting steels for general purposes; German version EN 10088-2:2014.Suche in Google Scholar
[14] DIN EN 10088-3 Stainless steels – Part 3: Technical delivery conditions for semi-finished products, bars, rods, wire, sections and bright products of corrosion resisting steels for general purposes; German version EN 10088-3:2014.Suche in Google Scholar
[15] Internal Siemens Energy document PCM 3-21014568.Suche in Google Scholar
[16] Neidel, A. et al.: Metallurgical Investigation of Fractured Snap Rings. Internal report BLN MT/2021/0659, November 24, 2021.Suche in Google Scholar
[17] Neidel, A. et al.: Metallurgical Investigation of Fractured Snap Rings. Internal report BLN MT/2021/0659a, November 26, 2021.Suche in Google Scholar
[18] Bornemann, B.: Personal communication, November 2021.Suche in Google Scholar
[19] Neidel, A. et al.: Metallurgical Failure Analysis of Fractured Disk Spring Package Retaining Rings From Xiamen Engine. Internal report LGT QM QL/2014/0558, November 14, 2014.Suche in Google Scholar
[20] Neidel, A. et al.: Metallurgical Failure Analysis of Fractured Disk Spring Package Retaining Rings From Riverton Engine. Internal report LGT QM QL/2014/0428, August 27, 2014.Suche in Google Scholar
[21] Neidel, A. et al.: Metallurgical Failure Analysis of Fractured Retaining Rings. Internal report GT BLN QM/2013/0153r, March 20, 2013.Suche in Google Scholar
[22] Neidel, A., Fischer, B.: Intergranular Corrosion in Retaining Rings Made of X39CrMo17-1 and X39Cr13. Pract. Metallogr. 51 (2014) 6, pp. 463–474. DOI: 10.3139/147.11024810.3139/147.110248Suche in Google Scholar
[23] Cihal, V.: Intergranular Corrosion of Steels and Alloys; Elsevier, 19„84.Suche in Google Scholar
[24] Lula, R. A.; Davis, J. A.: ASTM STP 656: Intergranular Corrosion of Stainless Alloys; ASTM, 1987, pp. 233–247.Suche in Google Scholar
[25] Cihal, V.; Stefec, R.: Electrochim. Acta 2001, 46, pp. 3867-3877. DOI: 10.1016/S0013-4686(01)00674-010.1016/S0013-4686(01)00674-0Suche in Google Scholar
[26] Henthone, M.: STP 516: Localized Corrosion – Cause of Metal Failure; ASTM, 1972, pp. 66–119. DOI: 10.1520/STP516-EB10.1520/STP516-EBSuche in Google Scholar
[27] Wendler-Kalsch, E.; Gräfen, H.: Korrosionsschadenskunde, Springer 1998. DOI: 10.1007/978-3-642-30431-610.1007/978-3-642-30431-6Suche in Google Scholar
[28] Corrosion tests in artificial atmospheres – Salt spray tests (ISO 9227:2017); German version EN ISO 9227:2017. Korrosionsprüfungen in künstlichen Atmosphären – Salzsprühnebelprüfungen (ISO 9227:2017); Deutsche Fassung EN ISO 9227:2017.Suche in Google Scholar
[29] Kern, T.-U.: Personal communication, March 21, 2022.Suche in Google Scholar
[30] ISO 6931-2 Stainless steels for springs – Part 2: Narrow strip, Second edition 2005-04-15.Suche in Google Scholar
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Artikel in diesem Heft
- Contents
- Editorial
- Dear readers
- Metallographic preparation of a composite of meteorite iron, steel, pure iron, and nickel manufactured by the Damascus technique
- The WG Fractography Online Database – stage of development and planning
- Failure Analysis
- A brief guide to conducting failure analysis on ceramic components
- Intergranular Corrosion in X39CrMo17-1 – A Review
- Picture of the Month
- Picture of the Month
- People
- Nachruf auf Dr. Jörg Trempler
- News
- Eine neue Ära des metallografischen Ätzens – Von der wissenschaftlichen Idee zum Serienprodukt „ThEtching“
- Meeting Diary
- Meeting Diary
Artikel in diesem Heft
- Contents
- Editorial
- Dear readers
- Metallographic preparation of a composite of meteorite iron, steel, pure iron, and nickel manufactured by the Damascus technique
- The WG Fractography Online Database – stage of development and planning
- Failure Analysis
- A brief guide to conducting failure analysis on ceramic components
- Intergranular Corrosion in X39CrMo17-1 – A Review
- Picture of the Month
- Picture of the Month
- People
- Nachruf auf Dr. Jörg Trempler
- News
- Eine neue Ära des metallografischen Ätzens – Von der wissenschaftlichen Idee zum Serienprodukt „ThEtching“
- Meeting Diary
- Meeting Diary
