TY - CONF A1 - Schaupp, Thomas A1 - Rhode, Michael A1 - Yahyaoui, Hamza A1 - Kannengießer, Thomas ED - Duprez, Lode T1 - Hydrogen distribution in multi-layer welds of steel S960QL T2 - Proceedings of the Third International Conference on Metals & Hydrogen N2 - High-strength low-alloyed (HSLA) steels with yield strength ≥ 690 MPa have increasing importance in steel construction and civil engineering. However, weld processing of those steels is a major challenge. The susceptibility for degradation of mechanical properties of weld joints significantly increases in presence of hydrogen and can result in hydrogen assisted cracking (HAC). Generally, risk for HAC increases with increasing yield strength of HSLA steels. To minimize the incidence of HAC, it is essential to gain knowledge about both the (1) absorbed hydrogen amount and its distribution in the weld seam and (2) options to lower the amount of introduced hydrogen. Existing standards recommend heat treatment procedures (interpass temperature or post weld heat treatment) to reduce the diffusible hydrogen concentration in weldments. In this context, different weld seam geometries should be considered. For HSLA steel fabrication weld processing with seam opening angles of 45° to 60° is typical. Modern weld technologies allow welding with seam opening angles of 30° - reduced welding time and costs. In the present study, the hydrogen distribution in multi-layer welds of a 960 MPa HSLA steel was analysed. Influence of different seam opening angles as well as heat input, interpass temperature and post weld heat treatments were investigated. The welded samples were quenched in ice water immediately after welding and subsequently stored in liquid nitrogen. After defined warming up, small specimens were machined from the weld seam by water jet cutting. The diffusible hydrogen concentration was measured by carrier gas hot extraction with coupled mass spectrometer. The results showed, that low heat input and post weld heat treatment procedures can lower hydrogen concentrations in welds. Furthermore, a gradient of the hydrogen concentration was identified with increasing weld pool depth. By varying the seam opening angles different hydrogen concentrations were measured. T2 - Third International Conference on Metals & Hydrogen CY - Ghent, Belgium DA - 29.05.2018 KW - Hydrogen concentration KW - Welding KW - High-strength steel KW - Heat treatment KW - carrier gas hot extraction PY - 2018 SN - 978-9-08179-422-0 SP - P44 AN - OPUS4-45358 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Griesche, Axel A1 - Pfretzschner, Beate A1 - Schaupp, Thomas A1 - Schulz, M. A1 - Kardjilov, N. ED - Duprez, Lode T1 - Hydrogen in steel visualized by neutron imaging T2 - Proceedings of the Third International Conference on Metals & Hydrogen N2 - Neutron cameras allow visualizing hydrogen distributions with radiographic or tomographic imaging methods in iron and steel. The necessary contrast between hydrogen and iron stems from the high difference in the total neutron cross section of both elements. This allows e.g. the in situ measurement of hydrogen mass flow inside cm thick steel samples with a temporal resolution of 20 s using neutron radiography as well as the quantitative measurement of hydrogen accumulations at the crack’s inner surfaces in hydrogen embrittled iron samples with neutron tomography. We could detect directly gaseous hydrogen in the crack cavities and we measured the gas pressure. This new quality of the information on a micrometer scale allows new insights for the analysis of hydrogen-induced damage mechanisms. Further, this method is non-destructive and provides local information in situ and in three dimensions with a spatial resolution of 20-30 µm. In this contribution, we show examples that demonstrate the spatial and temporal resolution of the neutron radiography and tomography methods in order to visualize and quantify hydrogen accumulations at cracks. The measurements were performed at the research reactor BER II of the HZB in Berlin and at the FRM II reactor of the neutron source Heinz Maier-Leibnitz in Garching. T2 - Third International Conference on Metals & Hydrogen CY - Ghent, Belgium DA - 29.05.2018 KW - Hydrogen KW - Steel KW - Neutron imaging PY - 2018 SN - 978-9-08179-422-0 SP - J01 AN - OPUS4-45359 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Brunner-Schwer, C. A1 - Graf, B. A1 - Rethmeier, Michael A1 - Schreiber, F. T1 - Hybrides Auftragschweißen: Potentiale des laserunterstützten Plasma-Pulver-Auftragschweißens (PTA) T2 - 12. Fachtagung Verschleissschutz von Bauteilen durch Auftragschweissen N2 - In diesem Beitrag wurden Untersuchungen zu einem neuartigen hybriden Laser-Plasma-Beschichtungsverfahren vorgestellt. Mit dem Ziel, die Produktivität und Wirtschaftlichkeit von Korrosions- und Verschleißschutzschichten zu steigern, wurde das kostengünstige PTA-Verfahren durch einen Laser als zweite Energiequelle ergänzt. Die vorlaufende Laserstrahlung stabilisiert den Plasmalichtbogen und ermöglicht erst eine Auftragsschweißung bei hohen Geschwindigkeiten. Die hohen Auftragraten von 4,2-5,7 kg/h bei gleichzeitig Streckenenergien von 630-720 J/cm zeigen das mögliche Potential des vorgestellten hybriden Ansatzes. In weiteren Untersuchungen muss der Prozess z.B. in Bezug auf die Oberflächenwelligkeit der Beschichtungen über eine Parameteroptimierung weiter verbessert werden. Nach den bisherigen gesammelten Erfahrungen mit dem Hybridprozess ist davon auszugehen, dass durch eine Anpassung der Energiedichteverteilung das Lasers, die Prozessgeschwindigkeiten noch einmal gesteigert werden können. T2 - 12. Fachtagung Verschleissschutz von Bauteilen durch Auftragschweissen CY - Halle, Germany DA - 13.06.2018 KW - Laser- und Lichtbogenenergie PY - 2018 SP - 104 EP - 108 AN - OPUS4-45230 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Petrat, T. A1 - Graf, B. A1 - Gumenyuk, Andrey A1 - Rethmeier, Michael T1 - Build-up Strategies for Laser Metal Deposition in Additive Manufacturing T2 - Fraunhofer Direct Digital Manufacturing Conference - Konferenzband N2 - Laser Metal Deposition (LMD) as a technology for additive manufacturing allows the production of large components outside of closed working chambers. Industrial applications require a stable process as well as a constant deposition of the filler material in order to ensure uniform volume growth and reproducible mechanical properties. This paper deals with the influence of travel path strategies on temperature profile and material deposition. Meandering and spiral hatching strategies are used in the center as well as in the edge of a specimen. The temperature is measured with thermocouples attatched to the backside of the specimen. The tests are carried out on the materials S235JR and 316L. The results show a strong dependence of the maximum temperatures on the travel path strategy and the welding position on the component. T2 - Fraunhofer Direct Digital Manufacturing Conference (DDMC) CY - Berlin, Germany DA - 14.03.2018 KW - Additive Manufacturing KW - Temperature behavior KW - Laser Metal Deposition KW - Stainless Steel KW - 316L KW - Edge effects PY - 2018 SN - 978-3-8396-1320-7 VL - 1 SP - 1 EP - 6 PB - Fraunhofer-Gesellschaft CY - München AN - OPUS4-44719 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Pavlov, V.A. A1 - Zavialov, S.V. A1 - Bakir, Nasim A1 - Gumenyuk, Andrey A1 - Rethmeier, Michael T1 - Development of a measuring technology of strain field in welds T2 - 20th International Conference Digital Signal Processing N2 - In the article considered the problem of hot cracks occurrence during laser welding process. The main reason of their appearance is strain. The optical method for measuring full field strain locally near the solidification front during laser welding process is proposed. The proposed method of optical measurement allows to determine the real values of the critical strain for various materials characterizing the occurrence of hot cracks in laser welding process. T2 - 20th international conference "Digital signal processing and applications DSPA-2018" CY - Moskau, Russia DA - 28.03.2018 KW - Solidification cracking KW - Critical strain KW - Strain rate KW - Optical measurement KW - Laser welding KW - In situ strain PY - 2018 SN - 978-5-905278-33-4 SP - 749 EP - 754 AN - OPUS4-44910 LA - rus AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Rhode, Michael A1 - Böllinghaus, Thomas T1 - Hydrogen absorption and diffusion in T24 steel weld joints and effect on mechanical properties T2 - Proceedings of NACE 2nd Conference N2 - The present contribution summarizes results obtained from experiments with low-alloyed boiler steel grades T24 (CrMoV alloy), T22 (CrMo) and thermally simulated T24 HAZ microstructure and pure weld metal. The hydrogen absorption and diffusion behavior was investigated by permeation experiments and thermal desorption analysis (TDA). The results showed significant weld microstructure influence on diffusion by hydrogen trapping. Trapped hydrogen was determined in the T24 BM at temperatures up to 120 °C compared to 75 °C in the T22. In addition, the T24 HAZ showed decreased diffusion coefficients (at room temperature) of approximately one magnitude compared to the BM. For the mechanical properties, tensile tests were conducted with electrochemically hydrogen charged specimens and compared to results obtained from slow strain rate tests (SSRT) in high-temperature water up to 200 °C. The as-welded HAZ had remarkably increased susceptibility compared to the BM already at low hydrogen concentration of 1-2 ppm. The SSRT were conducted for free corrosion and acidic environment and confirmed this behavior at elevated temperatures for both HAZ microstructures of T24 and T22. Summarized, each weld microstructure has specific diffusion coefficients and shows different susceptibility to degradation of the mechanical properties, i.e. delayed hydrogen assisted cracking or stress corrosion cracking. T2 - NACE Italia - 2nd Conference & Expo 2018 CY - Genoa, Italy DA - 28.05.2018 KW - Hydrogen KW - Stress corrosion cracking KW - Welding KW - Creep-resistant steel PY - 2018 SP - Paper 10, 1 EP - 7 AN - OPUS4-45081 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 - CONF A1 - Schröpfer, Dirk A1 - Kromm, Arne A1 - Hannemann, Andreas A1 - Kannengießer, Thomas ED - Seefeldt, Marc T1 - In-situ determination of critical welding stresses during assembly of thick-walled components made of high-strength steel T2 - Residual stresses 2018, ECRS-10 N2 - The performance and safety of welded high-strength low-alloyed steel (HSLA) components are substantially affected by the stresses occurring during and after welding fabrication, especially if welding shrinkage and distortion are severely restrained. The surrounding structure of the whole component affects loads in the far-field superimposing with welding stresses in the near-field of the weld. In this study a unique testing facility was used to restrain shrinkage and bending while analyse multiaxial far-field loads (max. 2 MN) during assembly of thick-walled component. A novel approach for the assessment of the in-situ-measured far-field data in combination with the actual weld geometry was elaborated. For the first time, analyses of the global bending moments of restrained welds based on the neutral axis of the actual weld load bearing section were achieved. Hence, far-field measurements offered the possibility to determine critical near-field stresses of the weld crosssections for the entire joining process. This work presents the approach for far-to-near field in-situ determination of stresses in detail for the 2-MN-testing system based on an extensive experimental work on HSLA steel welds, which demonstrates sources and consequences of these high local welding stresses. Thus, it was clarified, why the first weld beads are crucial regarding welding stresses and cold cracking, which is well known, but has never been measured so far. Accompanying analyses using X-ray diffraction (XRD) after welding show effects on local residual stress distributions. These analyses indicated viable prospects for stress reduction during assembly of thick-walled HSLA steel components. T2 - European Conference on Residual Stresses 2018 - ECRS-10 CY - Leuven, Belgium DA - 11.09.2018 KW - Residual stress KW - Welding KW - Large-scale test KW - X-ray diffraction KW - HSLA steel PY - 2018 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-466053 SN - 978-1-9452-9188-3 SN - 978-1-9452-9189-0 DO - https://doi.org/10.21741/9781945291890-30 SN - 2474-395X SN - 2474-3941 VL - 6 SP - 191 EP - 196 PB - Materials Research Forum LLC CY - Millersville, PA, USA AN - OPUS4-46605 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF ED - Marko, Angelina ED - Petrat, Torsten ED - Graf, Benjamin ED - Rethmeier, Michael T1 - Prognose der Oberflächenbeschaffenheit für die additive Fertigung mittels Laser-Pulver-Auftragschweißen T2 - Prognose der Oberflächenbeschaffenheit für die additive Fertigung mittels Laser-Pulver-Auftragschweißen N2 - In den letzten Jahren hat vor allem die Nachfrage nach additiven Fertigungstechnologien und Reparaturverfahren für Hochfeste Werkstoffe einen starken Aufschwung erlebt. Ein Verfahren, welches sich neben der Herstellung von Beschichtungen besonders für diese Anwendungen eignet, ist das Laser-Pulver-Auftragschweißen. Es wird besonders für Reparaturen bzw. zur Herstellung von teuren Bauteilen, wie Werkzeuge oder Turbinenteilen, eingesetzt. Da diese Teile oft großen mechanischen sowie thermischen Belastungen ausgesetzt sind, ist es besonders wichtig, dass die erzeugte Struktur eine hohe Qualität aufweist. In dieser Arbeit wird die statistische Versuchsplanung genutzt, um Modelle für die Oberflächenbeschaffenheiten von Inconel 718 zu generieren. Als Grundlage dient hierbei ein zentral zusammengesetzter Versuchsplan mit großem Parameterfenster. So wird die Leistung zwischen 550 Watt und 1950 Watt, der Vorschub von 530 mm/min bis 920 mm/min, der Pulvermassenstrom von 3 g/min bis 12 g/min sowie der Spotdurchmesser von 1 mm bis 2 mm variiert. Auf diese Weise wird die Spurgeometrie beeinflusst. Darüber hinaus wird das Überlappungsverhältnis zwischen 20% bis 50% verändert. Die Auswertung der Oberflächenbeschaffenheit erfolgt mit dem auf der Fokusvariation basierendem Oberflächenmessgerät Alicona Infinite-Focus. Dieses Verfahren der 3D Mikrokoordinatenmesstechnik gewährleistet eine zuverlässige Auswertung der Spurgeometrie, der Welligkeit sowie die Messung der mittleren arithmetischen Höhe Sa zur Bestimmung der Oberflächenrauheit. Anschließend werden die generierten Modelle verifiziert. Ziel dabei ist, kostenintensive Vorversuche in Zukunft einzusparen. Darüber hinaus wird das Prozessverständnis erweitert und signifikante Einflussfaktoren identifiziert. T2 - DVS Kongreß 2018 CY - Friedrichshafen, Germany DA - 17.09.2018 KW - Laser-Pulver-Auftragschweißen KW - Statistische Versuchsplanung KW - Oberflächenmessung KW - Additive Manufacturing PY - 2018 SN - 978-3-96144-036-8 VL - 2018 SP - 265 EP - 270 PB - DVS Media CY - Düsseldorf AN - OPUS4-47092 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Brunner-Schwer, C. A1 - Kersting, R. A1 - Graf, B. A1 - Rethmeier, Michael T1 - Laser-plasma-cladding as a hybrid metal deposition-technology applying a SLM-produced copper plasma nozzle T2 - 10th CIRP Conference on Photonic Technologies N2 - Laser-Metal-Deposition (LMD) and Plasma-Transferred-Arc (PTA) are well known Technologies which can be used for cladding purposes. The prime objective in combining LMD and PTA as a Hybrid Metal Deposition-Technology (HMD) is to achieve high Deposition rates at low thermal Impact. Possible applications are coatings for wear protection or repair welding for components made of steel. The two energy sources (laser and Plasma arc) build a Joint process Zone and are configurated to constitute a stable process at laser powers between 0.4-1 kW (defocused) and Plasma currents between 75-200 A. Stainless steel 316L serves as filler material. For this HMD process, a Plasma Cu-nozzle is designed and produced by powder bed based Selective Laser Melting. The potential of the HMD Technology is investigated and discussed considering existing process. This paper demonstrates how the interaction of the two energy sources effects the following application-relevant properties: Deposition rate, powder Efficiency and energy Input. T2 - LANE 2018 CY - Fürth, Germany DA - 3.09.2018 KW - Laser-metal-deposition KW - Plasma-transferred-arc KW - SLM printed plasma torch KW - Laser-plasma hybrid PY - 2018 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-470999 UR - 10.1016/j.procir.2018.08.020 DO - https://doi.org/10.1016/j.procir.2018.08.020 SN - 2212-8271 VL - CIRP 74 SP - 738 EP - 742 PB - Sciencedirect CY - Berlin AN - OPUS4-47099 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -