TY - JOUR A1 - Kromm, Arne A1 - Thomas, Maximilian A1 - Kannengießer, Thomas A1 - Gibmeier, J. A1 - Vollert, F. T1 - Assessment of the Solidification Cracking Susceptibility of Welding Consumables in the Varestraint Test by Means of an Extended Evaluation Methodology JF - Advanced Engineering Materials N2 - Various test methods are available for assessing the susceptibility of materials to solidification cracking during welding. In the widely used Varestraint test, the crack length is selected as a criterion as a function of the applied bending strain. Unfortunately, the crack length does not characterize the material behavior alone but depends to varying degrees on the individual test parameters used, which makes the interpretation of the results difficult. In addition, the crack length is not comparable under different test conditions. To overcome these disadvantages, we have developed a novel evaluation methodology that decouples the machine influence from the material behavior. The measured crack length is related to the maximum possible value specified by welding speed and deformation time. This relative crack length is calculated numerically, considering the orientation of the cracks. Experiments on two high-alloy martensitic welding consumables show that, in contrast to the conventional evaluation, a comparison of different welding parameters becomes possible. Furthermore, the strain rate proved to be a suitable crack criterion in agreement with Prokhorov's hot cracking model. KW - Welding KW - Solidification cracking KW - Varestraint test PY - 2022 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-545780 DO - https://doi.org/10.1002/adem.202101650 SN - 1438-1656 SP - 2101650 PB - Wiley online library AN - OPUS4-54578 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Vollert, F. A1 - Dixneit, Jonny A1 - Gibmeier, J. ED - Marais, D. ED - Holden, T.M. ED - Venter, A.M. T1 - Effect of Residual Stress Relaxation due to Sample Extraction on the Detectability of Hot Crack Networks in LTT Welds by means of µCT T2 - Mechanical stress evaluation by neutron and synchrotron radiation, , MECA SENS 2017 N2 - 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. 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). 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. T2 - 9th International Conference on Mechanical Stress Evaluation by Neutron and Synchrotron Radiation (MECA SENS 2017) CY - Skukuza Rest Camp, South Africa DA - 19.09.2017 KW - LTT Weld Filler Materials KW - µCT-analysis KW - Hot Cracks KW - Welding PY - 2018 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-456765 SN - 978-1-945291-66-1 DO - https://doi.org/10.21741/9781945291678-13 SN - 2474-395X VL - 4 SP - 85 EP - 90 AN - OPUS4-45676 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Vollert, F. A1 - Thomas, Maximilian A1 - Kromm, Arne A1 - Gibmeier, J. T1 - Hot crack assessment of LTT welds using μCT JF - The e-journal of nondestructive testing & ultrasonics N2 - Investigations on weldability often deal with hot cracking, as one of the most popular failure during weld fabrication. The modified varestraint transvarestraint hot cracking test (MVT) is well known for the assessment of the hot cracking susceptibility of materials. 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 a new approach, illustrated in the example of low transformation temperature (LTT) weld filler materials, to monitor the entire 3D hot crack network after welding by means of microfocus X-ray computer tomography (μCT). T2 - 10th Conference on Industrial Computed Tomography (iCT 2020) CY - Wels, Austria DA - 04.02.2020 KW - Varestraint testing KW - LTT weld filler materials KW - Hot cracking KW - Welding KW - μCT-analysis PY - 2020 UR - http://www.ndt.net/?id=25121 SN - 1435-4934 VL - 25 IS - 2 SP - 1 EP - 7 PB - NDT.net CY - Kirchwald AN - OPUS4-50341 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Vollert, F. A1 - Gibmeier, J. A1 - Rebelo-Kornmeier, J. A1 - Dixneit, Jonny A1 - Pirling, T. ED - Neu, R. W. ED - Totten, G. E. T1 - Two-dimensional residual stress mapping of multilayer LTT weld joints using the contour method JF - Materials Performance and Characterization N2 - Low transformation temperature (LTT) weld filler materials offer an attractive alternative to cost intensive postweld treatments as they can mitigate detrimental welding residual stresses during the welding process. Compared to conventional weld filler materials, LTT alloys are characterized by a delayed martensite transformation at low temperatures, which can result in compressive residual stresses in the weld. The high strength of these filler materials makes them potentially applicable to high-strength steels as well as for a large amount of requested repair works in steel structures. The focus of the study is on the confirmation of the LTT idea with regard to the residual stress state for multipass weld lines processed by metal active gas welding. It is demonstrated that the contour method is a well-suited technique for measuring the residual stress in the weld joint as it gives an entire two-dimensional map of the residual stress state in the weld line, heat affected zone (HAZ), and base material. The technique was applied at different LTT alloys with varying chemical compositions. Additionally, the results are compared to residual stress maps that were determined by Neutron diffraction using the Strain Analyzer for Large Scale Engineering Applications, an instrument referred to as SALSA, at the Institut Laue-Langevin in Grenoble. For all investigated specimens, compressive residual stress distributions were determined in the area of the weld joint and the HAZ. They are balanced by tensile residual stresses in the surrounding base material. However, it is shown that the size of theregion exhibiting compressive residual stresses and the absolute values of the compressive residual stresses depend on the chemical composition of the weld filler material. KW - LTT Weld Filler Materials KW - contour method KW - neutron diffraction KW - Welding KW - residual stress analysis PY - 2018 DO - https://doi.org/10.1520/MPC20170110 SN - 2379-1365 VL - 7 IS - 4 SP - 545 EP - 558 PB - ASTM International CY - West Conshohocken, PA, USA AN - OPUS4-46694 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -