Effect of Residual Stress Relaxation due to Sample Extraction on the Detectability of Hot Crack Networks in LTT Welds by means of µCT

Article PDF

Description

Effect of Residual Stress Relaxation due to Sample Extraction on the Detectability of Hot Crack Networks in LTT Welds by means of µCT

F. Vollert, J. Dixneit, J. Gibmeier

download PDF

Investigations on weldability often deal with hot cracking as one of the most prevalent failure mechanisms during weld fabrication. The modified varestraint transvarestraint hot cracking test (MVT) is well known to assess the hot cracking susceptibility of materials [1, 2]. The shortcoming of this approach is that the information is only from the very near surface region which inhibits access to the characteristic of the hot crack network in the bulk. Here, we report about an alternative approach to monitor the entire 3D hot crack network after welding by means of microfocus X-ray computer tomography (µCT). However, to provide sufficient high spatial resolution small samples must be sectioned from the MVT-welded joint. The sampling is accompanied by local relaxation of the residual stress distributions that are induced by welding, which can have an impact on the crack volumes prior to the sampling. The studies were carried out to investigate the hot cracking susceptibility of low transformation temperature filler materials (LTT) [3, 4]. As high compression residual stresses up to -600 MPa in the area of the crack networks were determined by means of the contour method, stress relaxation caused by sectioning for µCT sample extraction can affect the detectability of the cracks later on. X-ray diffraction studies revealed surface residual stress relaxations up to about 400 MPa due to cutting. To investigate this effect, the specimens with hot cracks were subjected to a load test with known stress states. The results clearly show that local stress relaxations will have a strong impact on the volume images reconstructed from tomography analysis. This effect must be considered during hot crack assessment on basis of µCT data.

Keywords
LTT Weld Filler Materials, µCT-analysis, Hot Cracks, Welding

Published online 4/20/2018, 6 pages
Copyright © 2018 by the author(s)
Published under license by Materials Research Forum LLC., Millersville PA, USA

Citation: F. Vollert, J. Dixneit, J. Gibmeier, ‘Effect of Residual Stress Relaxation due to Sample Extraction on the Detectability of Hot Crack Networks in LTT Welds by means of µCT’, Materials Research Proceedings, Vol. 4, pp 85-90, 2018

DOI: http://dx.doi.org/10.21741/9781945291678-13

The article was published as article 13 of the book

Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.

References
[1] DIN EN ISO 17641: Destructive tests on welds in metallic materials—hot cracking tests for weldments, part 1, 3—arc welding processes (2005).
[2] Th. Kannengiesser and Th. Boellinghaus, Hot cracking tests-an overview of present technologies and applications, Weld World 58 (2014) 397-421. https://doi.org/10.1007/s40194-014-0126-y
[3] A. Ohta, O. Watanabe, K. Matsuoka, C. Siga, S. Nishijima, Y. Maeda, N. Suzuki and T. Kubo, Fatigue strength improvement by using newly developed low transformation temperature welding material, Welding in the World 43 (1999) 38–42.
[4] Th. Kannengiesser, M. Rethmeier, P.D. Portella, U. Ewert and B. Redmer, Assessment of hot cracking behaviour in welds, International Journal of Materials Research 102 (2011) 8 1-6. https://doi.org/10.3139/146.110545
[5] E. Harati, L. Karlsson, L.-E. Svensson and K. Dalaei, Applicability of low transformation temperature welding consumables to increase fatigue strength of welded high strength steels, International Journal of Fatigue 97 (2017) 39-47. https://doi.org/10.1016/j.ijfatigue.2016.12.007
[6] J. Gibmeier, E. Obelode, J. Altenkirch, A. Kromm and Th. Kannengießer, Residual stress in steel fusion welds joined using low transformation temperature (LTT) filler material. Materials Science Forum 768-769 (2014) 620 – 627. https://doi.org/10.4028/www.scientific.net/MSF.768-769.620
[7] M.B. Prime and A.T. Dewald, Chapter 5 The contour method, in: G. S. Schajer (Ed.), Practical Residual Stress Measurement Methods, Wiley-Blackwell, 2013, pp. 109-138. https://doi.org/10.1002/9781118402832.ch5
[8] D. Bradley and G. Roth, Adaptive thresholding using the integral image, Journal of Graphics Tools 12 (2007) 13-21. https://doi.org/10.1080/2151237X.2007.10129236
[9] S. Beucher and C. Lantuejoul, Use of watersheds in contour detection, workshop on image processing, real-time edge and motion detection (1979).