Confirmation of tensile residual stress reduction in electron beam welding using low transformation temperature materials (LTT) as localized metallurgical injections – Part 2: Residual stress measurement

Stefan Gach; Simon Olschok; John Anthony Francis; Uwe Reisgen

doi:10.3139/120.111046

Article

Confirmation of tensile residual stress reduction in electron beam welding using low transformation temperature materials (LTT) as localized metallurgical injections – Part 2: Residual stress measurement

Stefan Gach , Simon Olschok , John Anthony Francis and Uwe Reisgen

Published/Copyright: July 10, 2017

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From the journal Materials Testing Volume 59 Issue 7-8

Abstract

In welding, the change of the aggregate state solid-liquid-solid is, via a localized heat action at the welding point used for the material binding joining of parts. Due to the thermal expansion and also due to structural changes, heat residual stresses and transformation residual stresses develop which often exert a negative influence on the precision of the part. When the shrinkage-induced residual stresses exceed the temperature-dependent yield stress, weldment distortion is the consequence. For reduction of the distortion and the residual tensile stresses in welded seams on carbon manganese steels, low transformation temperature materials (LTT) were developed. These materials use the volume expansion effect during martensitic transformation. The volume expansion counteracts volume shrinkage during cooling. The metallographic analysis of an electron beam welded seam in unalloyed steel with LTT filler material has been demonstrated in Part 1. This second part shows the effect on near-surface residual stresses examined by hole drilling method in combination with an optical evaluation by electronic speckle pattern interferometry.

Kurzfassung

In Schmelzschweißprozessen wird durch lokale Wärmeeinwirkung die Aggregatszustandsänderung fest-flüssig-fest zum Verbinden der Fügepartner eingesetzt. Aufgrund thermischer Ausdehnung und strukturellen Veränderungen entstehen Wärme- sowie Umwandlungsspannungen, die im Allgemeinen einen negativen Einfluss auf die Präzision des Bauteils haben. Überschreiten die schrumpfungsbedingten Eigenspannungen die temperaturabhängige Streckgrenze, ist Verzug die Folge. Zur Verminderung des Bauteilverzuges und der Eigenspannungsbelastung in Schweißnähten an Kohlenstoff-Manganstählen wurden Low-Transformation-Temperature-Werkstoffe (LTT) entwickelt. Diese Materialien verwenden den Volumenausdehnungseffekt während der martensitischen Phasenumwandlung zur Einleitung von Druckspannungen. Die Volumenausdehnung wirkt der Volumenschrumpfung während der Abkühlung aus der Schmelzwärme entgegen. Die metallographische Analyse einer Elektronenstrahlschweißnaht in unlegiertem Stahl mit LTT-Zusatzwerkstoff wurde in Teil 1 dieser Publikation gezeigt. Die in diesem zweiten Teil vorgestellten Arbeiten untersuchen den Effekt auf oberflächennahe Eigenspannungen. Diese werden mittels Bohrlochmethode in Kombination mit einer optischen Auswertung durch Elektronische Spackle-Interferometrie (ESPI) durchgeführt.

*Correspondence Address, Stefan Gach, M.Eng. IWE, RWTH Aachen, Pontstraße 49, D 52062 Aachen, Germany, E-mail: gach@isf.rwth-aachen.de

Stefan Gach, M.Eng., born 1983, studied Mechanical Engineering and Product Development in Mechanical Engineering at FH Aachen University of Applied Science, Germany. Currently, he is actually working as a research engineer at the Beam Welding Department of ISF Welding and Joining Institute of RWTH Aachen University, Germany.

Dr.-Ing. Simon Olschok, born 1972, studied Mechanical Engineering at RWTH Aachen University, Germany. From 2002 to 2007, he worked as research engineer at the ISF Welding and Joining Institute of the RWTH Aachen University and received a doctorate with the thesis „Hybrid Welding of Thick Plates” in 2008. Since 2007, he is Head of Beam Welding Department at the ISF Welding and Joining Institute of the RWTH Aachen University.

Dr. John Anthony Francis, born 1973, studied Mechanical Engineering at The University of Adelaide, Australia and received a doctorate from the same university in 2000. He worked at CSIRO in Australia for 7 years from 1998, as a postdoctoral fellow and a research scientist in welding process technology. Then he moved to the UK and has been involved in various research programs focusing on residual stress development in power plant welds for the past 12 years. He is currently Reader in Welding Technology at The University of Manchester, UK.

Univ.-Prof. Dr.-Ing. Uwe Reisgen, born 1962, studied Mechanical Engineering at RWTH Aachen University, Germany and received a doctorate at the ISF Welding and Joining Institute of the RWTH Aachen University in 1995. His thesis was on the research of wire feeding systems and their components for GMA welding. Since 2007, he is Head of the ISF Welding and Joining Institute at RWTH Aachen University.

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Published Online: 2017-07-10

Published in Print: 2017-07-14

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https://doi.org/10.3139/120.111046