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  Crack formation in charpy tests of the heat-affected zone of large-diameter linepipe material

Schemmann, L., Stallybrass, C., Schröder, J., Liessem, A., & Zaefferer, S. (2018). Crack formation in charpy tests of the heat-affected zone of large-diameter linepipe material. Proceedings of the Biennial International Pipeline Conference, IPC, 3: IPC2018-78498, V003T05A037.

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Schemmann, Lars1, Author              
Stallybrass, Charles2, Author              
Schröder, Jens3, Author              
Liessem, Andreas3, Author              
Zaefferer, Stefan4, Author              
1Salzgitter Mannesmann Forschung GmbH, 38239 Salzgitter, Germany, ou_persistent22              
2Salzgitter Mannesmann Forschung GmbH, Duisburg, Germany, ou_persistent22              
3EUROPIPE GmbH, Mülheim an der Ruhr, Germany, ou_persistent22              
4Microscopy and Diffraction, Microstructure Physics and Alloy Design, Max-Planck-Institut für Eisenforschung GmbH, Max Planck Society, ou_1863391              


Free keywords: Austenite; Bainite; Bainitic transformations; Linear transformations; Metal analysis; Microcracks; Microstructure; Pipe; Pipelines; Scanning electron microscopy; Submerged arc welding, Austenite grain size; Crystallographic orientations; Electron back scatter diffraction; Geometrically necessary dislocation densities; Large diameter pipes; Materials development; Processing condition; Propagation direction, Heat affected zone
 Abstract: Double submerged arc welding is an efficient process used during the production of longitudinally-welded large-diameter pipes. It is well known that the associated high heat input has a negative influence on the toughness of the heat-affected zone (HAZ). The toughness drop is related to changes in the HAZ microstructure compared to the base metal. The austenite grain size increases significantly and larger carbon-rich martensite/austenite particles (M/A-particles) are formed within a coarse bainitic matrix during the phase transformation compared to the as-rolled base material. The exact relationship between the microstructure, the processing conditions, base metal composition and the weld metal are at the focus of attention of materials development efforts at EUROPIPE and Salzgitter Mannesmann Forschung GmbH (SZMF). In the present study, scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD) were used to investigate the HAZ of X70 large-diameter pipe material as well as tested Charpy specimens from the same material. Secondary cracks in the direct vicinity of the primary fracture surface of tested Charpy specimens from the HAZ were analyzed by EBSD and SEM to investigate the damage mechanism in detail. It was found that these cracks originate at M/A-particles and that the dominant crack path depends on the crystallographic orientation of the surrounding matrix. The analysis of several EBSD measurements and a 3D-analysis of the propagation direction of the crack showed that secondary cracks frequently propagate parallel to 100} and rarely along {110-planes. It is known from literature that these are preferred cleavage planes in ferritic steels. The SEM analysis performed in the HAZ of the investigated steel showed that the volume fraction of elongated M/A-particles is elevated close to the fusion line and decreases within the first few hundred micrometers distance from the fusion line. The EBSD measurements illustrate that the geometrically necessary dislocation density is significantly increased in the neighborhood of M/A-particles. This indicates that the bainitic matrix is work-hardened around the M/A-particles during testing and is therefore more prone to the formation of microcracks than other surrounding regions. Copyright © 2018 ASME


Language(s): eng - English
 Dates: 2018
 Publication Status: Published in print
 Pages: -
 Publishing info: -
 Table of Contents: -
 Rev. Type: -
 Identifiers: DOI: 10.1115/IPC2018-78498
 Degree: -


Title: 12th International Pipeline Conference, IPC 2018
Place of Event: Calgary, Canada
Start-/End Date: 2018-09-24 - 2018-09-28

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Title: Proceedings of the Biennial International Pipeline Conference, IPC
Source Genre: Journal
Publ. Info: -
Pages: 7 Volume / Issue: 3 Sequence Number: IPC2018-78498 Start / End Page: V003T05A037 Identifier: ISBN: 978-0-7918-5188-3