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Zur Phänomenologie der Heißrissbildung beim Schweißen und Entwicklung aussagekräftiger Prüfverfahren

  • Zur Ermittlung der Heißrissresistenz beim Schweißen metallischer Werkstoffe können Heißrisstests eingesetzt werden. Obwohl bislang zahlreiche Heißrisstestverfahren entwickelt wurden, kann eine unerwartete Heißrissbildung während der Durchführung von Bauteilschweißungen oftmals nicht verhindert werden. Dies ist einerseits darauf zurückzuführen, dass sich die Bedingungen im Heißrisstest von den thermomechanischen Beanspruchungen einer Bauteilschweißung zu sehr unterscheiden. Andererseits erfolgt die Auswertung der meisten Heißrissversuche mit Hilfe empirischer Parameter, mit denen die eigentlichen Mechanismen der Heißrissentstehung jedoch nur unzureichend quantifiziert werden können. Ein wesentliches Ziel war es daher, aussagekräftige Methoden zur Quantifizierung des Heißrissverhaltens beim Schweißen zu entwickeln und damit einen Beitrag zur Erhöhung der Heißrisssicherheit geschweißter Bauteile zu leisten.
  • For determining the hot cracking resistance of materials during welding of metallic materials it is possible to employ hot cracking tests. Despite numerous hot cracking tests have been developed till now, unexpected hot cracking during welding cannot always be avoided. This is on the one hand ascribed to the fact that the conditions prevalent in hot cracking testing differ too strongly from the thermomechanical loads imposed during component welding. On the other hand, evaluation of most hot cracking tests is carried out using empiric parameters which, however, fall short of adequate quantification of the actual hot cracking mechanism. A key aim of this study was therefore to develop convincing methods for quantifying the hot cracking behaviour during welding, and thus to make a contribution towards improving the hot cracking resistance of welded components. As a prerequisite, the Modified Varestraint Transvarestraint-Test (MVT-Test) was first upgraded with a view to varying theFor determining the hot cracking resistance of materials during welding of metallic materials it is possible to employ hot cracking tests. Despite numerous hot cracking tests have been developed till now, unexpected hot cracking during welding cannot always be avoided. This is on the one hand ascribed to the fact that the conditions prevalent in hot cracking testing differ too strongly from the thermomechanical loads imposed during component welding. On the other hand, evaluation of most hot cracking tests is carried out using empiric parameters which, however, fall short of adequate quantification of the actual hot cracking mechanism. A key aim of this study was therefore to develop convincing methods for quantifying the hot cracking behaviour during welding, and thus to make a contribution towards improving the hot cracking resistance of welded components. As a prerequisite, the Modified Varestraint Transvarestraint-Test (MVT-Test) was first upgraded with a view to varying the specimen loading rate over a very wide range up to quasi-instantaneous loading. As test material, Alloy 602 CA was chosen which exhibits a pronounced dependence of hot cracking resistance on the respective shielding gas. With the use of Ar 4.8 and Ar + 1% N2 as shielding gases, hot crack-critical as well as hot crack-uncritical material behaviour could be investigated. For further elucidation of the solidification cracking mechanism, a combined model was first developed which can be used to demonstrate that the solidification crack-critical limiting temperature TER and the solidification crack-critical strain rate (dε/dt)krit are largely independent of each other and must be determined using various test concepts. Numerical temperature calculations with first implementation of the reproduced real weld pool geometries helped to determine the solidification crack-critical limiting temperature for Alloy 602 CA as a function of different welding parameters and of the investigated shielding gases. It is demonstrated that the solidification crack-critical limiting temperature rises significantly with the use of Ar + 1% N2. In addition to this, the solidification crack-critical limiting temperature is significantly dependent on the applied welding parameters. The MVTTest was also used to conduct experiments with variable specimen loading rate in both the Varestraint and the Transvarestraint mode. Various hot cracking parameters determined in these experiments were evaluated quantitatively. With regard to exclusively qualitative determination of the hot cracking resistance of materials it was found that the measurable differences are more distinct in the Varestraint mode than in the Transvarestraint mode. For hot cracking test transferability investigations, the very critical specimen loading rates at which solidification cracking does not occur yet, were experimentally determined in MVTTests. Using the obtained results in conjunction with thermomechanical simulations, the local critical strain rates in the immediate vicinity of the weld pool were calculated. It is shown that the local critical strains and strain rates constitute a crack criterion for the transferability to the newly developed Controlled Tensile Weldability Test (CTW-Test). Keywords: Solidification cracking, liquation cracking, global strain, local strain, transferability, Modified Varestraint Transvarestraint Test, weld pool geometry, hot cracking parameter, Controlled Tensile Weldability Test, Alloy 602 CA.zeige mehrzeige weniger

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Metadaten
Autor*innen:Martin Wolf
Dokumenttyp:Dissertation
Veröffentlichungsform:Eigenverlag BAM
Schriftenreihe (Bandnummer):BAM Dissertationsreihe (19)
Sprache:Deutsch
Jahr der Erstveröffentlichung:2006
Veröffentlichende Institution:Bundesanstalt für Materialforschung und -prüfung (BAM)
Herausgeber (Institution):Bundesanstalt für Materialforschung und -prüfung (BAM)
Titel verleihende Institution:Helmut-Schmidt-Universität - Universität der Bundeswehr Hamburg, Fachbereich Maschinenbau
Gutachter*innen:Hans Hoffmeister, Thomas Böllinghaus, Gerd Huismann
Datum der Abschlussprüfung:22.09.2006
Verlag:Wirtschaftsverlag NW
Verlagsort:Bremerhaven
Jahrgang/Band:19
Erste Seite:1
Letzte Seite:218
DDC-Klassifikation:Technik, Medizin, angewandte Wissenschaften / Industrielle Fertigung / Industrielle Fertigung
Freie Schlagwörter:Phänomenologie Heißrissbildung; Schweißen und Entwicklung aussagekräftiger Prüfverfahren
URN:urn:nbn:de:kobv:b43-1395
ISSN:1613-4249
ISBN:978-3-86509-599-2
Verfügbarkeit des Dokuments:Datei für die Öffentlichkeit verfügbar ("Open Access")
Lizenz (Deutsch):License LogoAllgemeines Deutsches Urheberrecht
Datum der Freischaltung:23.01.2015
Referierte Publikation:Nein
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