TY - JOUR A1 - Vollert, F. A1 - Thomas, Maximilian A1 - Kromm, Arne A1 - Gibmeier, J. T1 - Solidification Cracking Assessment of LTT Filler Materials by Means of Varestraint Testing and μCT N2 - Investigations of the weldability of metals often deal with hot cracking, as one of the most dreaded imperfections during weld fabrication. The hot cracking investigations presented in this paper were carried out as part of a study on the development of low transformation temperature (LTT) weld filler materials. These alloys allow to mitigate tensile residual stresses that usually arise during welding using conventional weld filler materials. By this means, higher fatigue strength and higher lifetimes of the weld can be achieved. However, LTT weld filler materials are for example, high-alloyed Cr/Ni steels that are susceptible to the formation of hot cracks. To assess hot cracking, we applied the standardized modified varestraint transvarestraint hot cracking test (MVT), which is well appropriate to evaluate different base or filler materials with regard to their hot cracking susceptibility. In order to consider the complete material volume for the assessment of hot cracking, we additionally applied microfocus X-ray computer tomography (μCT). It is shown that by a suitable selection of welding and MVT parameter the analysis of the complete 3D hot crack network can provide additional information with regard to the hot cracking model following Prokhorov. It is now possible to determine easy accessible substitute values (e.g., maximum crack depth) for the extent of the Brittleness Temperature Range (BTR) and the minimum critical strain Pmin. KW - LTT weld filler materials KW - μCT-analysis KW - Hot cracking KW - Varestraint test PY - 2020 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-509126 DO - https://doi.org/10.3390/ma13122726 VL - 13 IS - 12 SP - 2726 PB - MDPI AN - OPUS4-50912 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 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 DO - https://doi.org/https://doi.org/10.58286/25121 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 - Artinov, Antoni A1 - Bachmann, Marcel A1 - Meng, Xiangmeng A1 - Karkhin, V. A1 - Rethmeier, Michael T1 - On the relationship between the bulge effect and the hot cracking formation during deep penetration laser beam welding N2 - Recent studies have confirmed the widening of the weld pool interface, known as a bulge effect, during deep penetration high power laser beam welding. The link between such geometric particularities of the weld pool shape and the hot cracking phenomena is significant. The present work seeks to extend the level of understanding by investigating their relationship. A coupled multiphysics, multiscale numerical framework is developed, comprising a series of subsequent analyses. The study examines the influences of the bulge on the three most dominant effects causing hot cracking, namely the thermal cycles, the mechanical loading, and the local microstructure. The bulge in the weld pool shape forms approximately in the middle of the plate, thus correlating with the location of hot cracking. It increases the hot cracking susceptibility by enhancing the three dominant effects. The numerical results are backed up by experimental data. T2 - 11th CIRP Conference on Photonic Technologies [LANE 2020] KW - Hot cracking KW - Bulge effect KW - Numerical modelling KW - Laser beam welding KW - Deep penetration PY - 2020 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-512783 DO - https://doi.org/10.1016/j.procir.2020.09.002 SN - 2212-8271 VL - 94 SP - 5 EP - 10 PB - Elsevier B.V. CY - Amsterdam [u.a.] AN - OPUS4-51278 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Taparli, Ugur Alp T1 - Development of a LIBS analysis system for time- and space-resolved in situ measurement of chemical compositions during TIG-welding N2 - A laser induced breakdown spectroscopy (LIBS) system was combined with the Gas Tungsten Arc (TIG) Welding process for the in situ monitoring of chemical compositions in austenitic stainless steels during welding. The purpose of this project is to develop a prototype of an online chemical composition control system for welding applications. One of the use cases of this new LIBS-based measurement system can be the controlling of potentially dangerous emissions during the welding process in order to improve the working safety conditions. T2 - Master Diplomanden Doktoranden Kolloquium Otto von Guericke Universität Magdeburg CY - Magdeburg, Germany DA - 19.01.2017 KW - LIBS KW - TIG welding KW - Hot cracking KW - Austenitic stainless steels KW - In situ chemical composition PY - 2017 AN - OPUS4-39025 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Gollnow, C. A1 - Griesche, Axel A1 - Weidemann, Jens A1 - Kannengießer, Thomas T1 - Influence of external loads on a characteristic angle between grains and solidus line as an indicator for hot cracking susceptibility during GTA welding N2 - A long list of criteria determining the hot cracking susceptibility already exists. A main influence on solidification cracking can result from the design of the welded construction, i.e. from the influence of external loads. Using the Controlled Tensile Weldability (CTW) test, an external load hot cracking test, the influence of constant pre-load and different extension rates on the solidification cracking behavior of GTA (Gas Tungsten Arc) welds in an austenitic (AISI 309) and a ferritic (AISI 441) steel were investigated. Compared to specimens welded allowing free shrinkage and welded with an applied constant tensile pre-load, the specimens welded during the application of increasing tensile load show solidification cracks. In the weld seams, a characteristic angle α between the predominantly columnar grains and the fusion line can be observed. Specimens showing solidification cracks show a significantly larger angle α compared to the crack-free specimens. Based on these observations, the characteristic angle α is proposed as a new hot cracking criterion. KW - Hot cracking KW - External load test KW - Component design KW - Crack criterion KW - Grain growth PY - 2017 DO - https://doi.org/10.1016/j.jmatprotec.2016.08.013 VL - 239 SP - 172 EP - 177 PB - Elsevier AN - OPUS4-37278 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Bakir, Nasim A1 - Gumenyuk, Andrey A1 - Rethmeier, Michael T1 - Investigation of solidification cracking susceptibility of laser welded joints of austenitic stainless steels N2 - Laser welding is a widely established manufacturing process in many industry sectors. Solidification cracking represents one of the most inadequately solved problems in welding and has major economic implications. The avoidance of hot crack forms for most fusion welding processes poses a key challenge for an important range of metallic construction materials and affects not only the manufacturers of welding equipment and material manufacturers, but also a large number of customers using welding technologies, as well as welding technical standardization and research. Solidification cracking susceptibility was examined with the help of the Controlled Tensile Weldability Test (CTW) developed by Federal Institute for Materials Research and Testing (BAM), Berlin. The test is based on the fact that hot crack formation depends on a critical strain that emerges within a critical temperature range, the so called brittle temperature range (BTR). Using this test and defined investigation programme a centreline solidification crack was generated. By controlling the applied strain during the laser beam welding process, it was possible to determine the critical strain and strain rate that led to solidification cracking formation. The hot cracking susceptibility of the tested stainless steels was qualified and quantified. The results demonstrate that the crack length increases with increasing applied strain. Furthermore, the strain rate has a significant influence on the formation of the solidification crack. T2 - 3rd International conference in Africa and Asia CY - Luxor, Egypt DA - 02.11.2015 KW - Laser beam welding KW - Hot cracking KW - Solidification cracking KW - Hot cracking test PY - 2015 SP - A-29, 1 EP - A-29, 9 AN - OPUS4-36522 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Rethmeier, Michael T1 - Experimental study and numerical simulation of hot crack formation for novel laser weldability test N2 - Hot cracking susceptibility in laser beam welding was assessed for several stainless steels by means of the CTW test The strain rate has a significant influence on the formation of the hot crack It was possible to determine the critical strain and strain rate that led to shot crack formation A material ranking of hot cracking resistance could be made.A three-dimensional FEM using the contact element technique to simulate hot cracking during LBW under external load conditions was developed. Good agreement between the strain field measured using the DIC technique and the simulation results Susceptibility to hot cracking can be predicted by using FEM with the correct mechanical and thermo-physical material properties T2 - 8th International Conference Beam Technologies & Laser Application CY - St. Petersburg, Russia DA - 21.09.2015 KW - CTW-Test KW - Investigated materials KW - FEM study KW - Hot cracking PY - 2015 AN - OPUS4-38347 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Artinov, Antoni T1 - On the relationship between the bulge effect and the hot cracking formation during deep penetration laser beam welding N2 - Recent studies have confirmed the widening of the weld pool interface, known as a bulge effect, during deep penetration high power laser beam welding. The link between such geometric particularities of the weld pool shape and the hot cracking phenomena is significant. The present work seeks to extend the level of understanding by investigating their relationship. A coupled multiphysics, multiscale numerical framework is developed, comprising a series of subsequent analyses. The study examines the influences of the bulge on the three most dominant effects causing hot cracking, namely the thermal cycles, the mechanical loading, and the local microstructure. The bulge in the weld pool shape forms approximately in the middle of the plate, thus correlating with the location of hot cracking. It increases the hot cracking susceptibility by enhancing the three dominant effects. The numerical results are backed up by experimental data. T2 - 11th CIRP Conference on Photonic Technologies [LANE 2020] CY - Online meeting DA - 07.09.2020 KW - Hot cracking KW - Bulge effect KW - Numerical modelling KW - Laser beam welding KW - Deep penetration PY - 2020 AN - OPUS4-51277 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Bakir, Nasim A1 - Gumenyuk, Andrey A1 - Rethmeier, Michael T1 - Investigation of hot crack susceptibility of laser welded joints of four austenitic steels N2 - Laser welding is a widely established manufacturing process in many industry sectors. Solidification cracking represents one of the most inadequately solved problems in welding and has major economic implications. The avoidance of hot crack is for most fusion welding processes a key challenge for an important range of metallic construction materials and affects not only the manufacturers of welding equipment and material manufacturers, but also a large number of customers using welding technologies, as well as welding standardization and research. In this study a new investigation programme has been developed to qualify the hot cracking susceptibility of a variety of austenitic stainless steels. The results show the possibility of using this technique to determinate the critical values that occur with initiation of solidification cracking during laser beam welding T2 - The METEC and 2nd European Steel Technology and Application Days CY - Düsseldorf, Germany DA - 15.06.2015 KW - Laser beam welding KW - Hot cracking KW - Solidification cracking KW - Hot cracking test PY - 2015 SP - 1 EP - 5 AN - OPUS4-36525 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Boateng, Francis Twumasi A1 - Ewert, Uwe A1 - Kannengießer, Thomas A1 - Zscherpel, Uwe A1 - Griesche, Axel A1 - Kromm, Arne A1 - Hohendorf, Stephan A1 - Redmer, Bernard T1 - Real-time radiography for observation of crack growth during GTA (Gas Tungsten Arc) welding N2 - In situ crack detection in the mushy zone and the solid weld of a gas tungsten arc (GTA) weld using X-ray imaging during welding is a new research area for NDT inspection. Usually, NDT flaw detection is done after the complete solidification of the weld seam. In this paper, we present the use of real-time radiography with a minifocus X-ray source (YXLON X-ray tube Y.TU 225-D04) and a 75μm pixel size digital detector array (Dexela 1512) for the acquisition of 2D radiographic images by a sequence of exposures with time intervals of 80 ms for hot crack detection during single pass bead-on-plate GTA welding of 3 mm thick plates of aluminium alloy AlMgSi (6060). An analysis of the crack distribution in the weld sample is conducted from the acquired 2D radiographs and its corresponding 3D volumetric reconstruction achieved by linear coplanar digital laminography. This in situ approach opens new possibilities in the field of hot crack research by having the direct information of both the crack initiation and growth and its correlation to the welding parameters. KW - Hot cracking KW - Radiography KW - GTA welding KW - Aluminium alloys KW - Real-time operation PY - 2016 DO - https://doi.org/10.1007/s40194-016-0351-7 SN - 0043-2288 SN - 1878-6669 VL - 60 IS - 5 SP - 931 EP - 937 AN - OPUS4-37128 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -