TY - JOUR A1 - Griesche, Axel A1 - Pfretzschner, B. A1 - Taparli, Ugur Alp A1 - Kardjilov, N. T1 - Time-Resolved Neutron Bragg-Edge Imaging: A Case Study by Observing Martensitic Phase Formation in Low Temperature Transformation (LTT) Steel during GTAW N2 - Polychromatic and wavelength-selective neutron transmission radiography were applied during bead-on-plate welding on 5 mm thick sheets on the face side of martensitic low transformation temperature (LTT) steel plates using gas tungsten arc welding (GTAW). The in situ visualization of austenitization upon welding and subsequent α’-martensite formation during cooling could be achieved with a temporal resolution of 2 s for monochromatic imaging using a single neutron wavelength and of 0.5 s for polychromatic imaging using the full spectrum of the beam (white beam). The spatial resolution achieved in the experiments was approximately 200 µm. The transmitted monochromatic neutron beam intensity at a wavelength of λ = 0.395 nm was significantly reduced during cooling below the martensitic start temperature Ms since the emerging martensitic phase has a ~10% higher attenuation coefficient than the austenitic phase. Neutron imaging was significantly influenced by coherent neutron scattering caused by the thermal motion of the crystal lattice (Debye–Waller factor), resulting in a reduction in the neutron transmission by approx. 15% for monochromatic and by approx. 4% for polychromatic imaging. KW - Austenite-to-martensite transformation KW - Neutron radiography KW - Bragg-edge imaging KW - Gas tungsten arc welding (GTAW) KW - Debye–Waller factor KW - Low transformation temperature (LTT) steel PY - 2021 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-538016 DO - https://doi.org/10.3390/app112210886 VL - 11 IS - 22 SP - 10886 PB - MDPI CY - Basel AN - OPUS4-53801 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Griesche, Axel A1 - Pfretzschner, Beate A1 - Taparli, Ugur Alp A1 - Kardjilov, N. T1 - Time-Resolved Neutron Bragg-Edge Imaging: A Case Study by Observing Martensitic Phase Formation in Low Temperature Transformation (LTT) Steel during GTAW N2 - Polychromatic and wavelength-selective neutron transmission radiography were applied during bead-on-plate welding on 5 mm thick sheets on the face side of martensitic low transformation temperature (LTT) steel plates using gas tungsten arc welding (GTAW). The in situ visualization of austenitization upon welding and subsequent α’-martensite formation during cooling could be achieved with a temporal resolution of 2 s for monochromatic imaging using a single neutron wavelength and of 0.5 s for polychromatic imaging using the full spectrum of the beam (white beam). The spatial resolution achieved in the experiments was approximately 200 µm. The transmitted monochromatic neutron beam intensity at a wavelength of λ = 0.395 nm was significantly reduced during cooling below the martensitic start temperature M s since the emerging martensitic phase has a ~10% higher attenuation coefficient than the austenitic phase. Neutron imaging was significantly influenced by coherent neutron scattering caused by the thermal motion of the crystal lattice (Debye–Waller factor), resulting in a reduction in the neutron transmission by approx. 15% for monochromatic and by approx. 4% for polychromatic imaging. KW - Neutron radiography KW - Debye–Waller factor KW - Austenite-to-martensite transformation KW - Low transformation temperature (LTT) steel KW - Bragg-edge imaging KW - Gas tungsten arc welding (GTAW) PY - 2021 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-559077 DO - https://doi.org/10.3390/app112210886 VL - 11 IS - 22 PB - MDPI AN - OPUS4-55907 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Pfretzschner, Beate A1 - Schaupp, Thomas A1 - Hannemann, Andreas A1 - Schultz, Michael A1 - Griesche, Axel T1 - On the Genesis of Artifacts in Neutron Transmission Imaging of Hydrogenous Steel Specimens N2 - Hydrogen-charged supermartensitic steel samples were used to systematically investigate imaging artifacts in neutron radiography. Cadmium stencils were placed around the samples to shield the scintillator from excessive neutron radiation and to investigate the influence of the backlight effect. The contribution of scattered neutrons to the total detected intensity was investigated by additionally varying the sample-detector distance and applying a functional correlation between distance and intensity. Furthermore, the influence of the surface roughness on the edge effect due to refraction was investigated. KW - Refraction KW - Neutron imaging KW - Hydrogen KW - Supermartensitic steel KW - Backlight KW - Scattering PY - 2020 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-506587 DO - https://doi.org/10.3390/jimaging6040022 VL - 6 IS - 22 SP - 1 EP - 10 PB - MDPI CY - Basel, Switzerland AN - OPUS4-50658 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Taparli, Ugur Alp A1 - Kannengießer, Thomas A1 - Griesche, Axel T1 - Tungsten inert gas bead-on-plate weld chemical composition analysis by laser-induced breakdown spectroscopy N2 - Chemical compositions of a weld can be varying locally as a result of the welding process. These local variations can be due to the vaporization of individual alloying elements. In this work, tungsten inert gas (TIG) bead-on-plate stainless steel welds of EN grade 1.4404 and 1.4435 were investigated using laser-induced breakdown spectroscopy (LIBS) on the completed welds. This study aims to reveal the welding parameters’ influence on the resulting local chemical compositions of the stainless steel welds. We demonstrated Mn vaporize before Cr due to its lower latent enthalpy of vaporization. Hence, Mn accumulates on the heat-affected zone (HAZ) both sides across the weld bead by being swept away through the circulation flow of the welding plasma. Additionally, increasing the heat input tends to enhance the accumulated Mn content on the HAZ as well as increasing the shielding gas flow rate. The results are in good agreement with the literature and proved that LIBS is an effective method to inspect completed welds. T2 - Symposium on Materials and Joining Technology CY - Magdeburg, Germany DA - 07.09.2020 KW - LIBS TIG welding KW - Austenitic stainless steels KW - Chemical composition KW - In situ measurement PY - 2020 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-511595 DO - https://doi.org/10.1088/1757-899X/882/1/012023 SN - 1757-8981 SN - 1757-899X VL - 882 IS - 012023 SP - 1 EP - 8 PB - IOP Publishing CY - Bristol AN - OPUS4-51159 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Taparli, Ugur Alp A1 - Kannengießer, Thomas A1 - Cieslik, K. A1 - Mory, D. A1 - Griesche, Axel T1 - In situ chemical composition analysis of a tungsten-inert-gas austenitic stainless steel weld measured by laser-induced breakdown spectroscopy N2 - The chemical composition of a weld metal determines the resulting solidification mode of stainless steel and the consequent weld metal quality. In this work tungsten inert gas (TIG) welding of EN grade 1.4435 austenitic stainless steel was monitored using laser-induced breakdown spectroscopy (LIBS) for the in situ measurement of chemical composition changes. This research aims to prototype a real-time chemical composition analysis system for welding applications and prove the feasibility of such quality control loop. LIBS was used to investigate in situ the monitoring of metal vaporization during TIG welding. We found Mn vapor formation above the weld pool and subsequent condensation of Mn on the weld metal surface using LIBS. Post-weld line scans were conducted by LIBS on various welds produced with different welding currents. Local changes of Ni and Mn were observed at higher welding currents. The results are in good agreement with the literature and proved that LIBS can be used in situ to inspect the TIG welding process. T2 - 10th Euro-Mediterranean Symposium on Laser-Induced Breakdown Spectroscopy CY - Brünn, Czechia DA - 08.09.2019 KW - LIBS KW - Welding KW - Austenitic stainless steel KW - Metal vapor KW - In situ measurement PY - 2020 DO - https://doi.org/10.1016/j.sab.2020.105826 SN - 0584-8547 VL - 167 SP - 105826 PB - Elsevier B.V. CY - Amsterdam, Niederlande AN - OPUS4-50582 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Pfretzschner, Beate A1 - Schaupp, Thomas A1 - Griesche, Axel T1 - Hydrogen in Metals Visualized by Neutron Imaging N2 - Neutron cameras allow visualizing hydrogen distributions with radiographic or tomographic imaging methods in iron (and steel) and many other metals. The necessary contrast between hydrogen and these metals 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 metal samples with a temporal resolution of at best 10 s using neutron radiography as well as the quantitative measurement of hydrogen accumulations, e.g., at the crack’s inner surfaces in hydrogen embrittled iron samples with neutron tomography. This new quality of the information on a micrometer scale allows new insights for the analysis of hydrogen-assisted damage mechanisms. Further, this method is non-destructive and provides local information in situ and in three dimensions with a spatial resolution of 20 μm - 30 μm. In this contribution, we give a short historical overview of neutron imaging and show examples that demonstrate the spatial and temporal resolution of the neutron radiography and tomography methods in order to visualize and quantify hydrogen accumulations, absorption processes, and diffusion. The examples are taken from the works of researchers dealing with titanium, palladium, zirconium, and iron or steel. More detailed descriptions of the experimental and analytic procedures are given for hydrogen detection using radiography and tomography on iron and steel samples. KW - Hydrogen assisted cracking KW - Neutron imaging PY - 2019 DO - https://doi.org/10.5006/3104 SN - 0010-9312 VL - 75 IS - 8 SP - 903 EP - 910 PB - NACE International AN - OPUS4-48775 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Konadu, D. S. A1 - Pistorius, P. G. H. A1 - Du Toit, M. A1 - Griesche, Axel T1 - Solidification cracking susceptibility of ferritic stainless steels using Modified Varestraint Transvarestraint (MVT) method N2 - The Modified Varestraint Transvarestraint (MVT) test was used to investigate the solidification cracking susceptibility of an unstabilised, a Nb-stabilised and two (Ti + Nb) dual-stabilised ferritic stainless steels. Two different welding speeds of 6 and 3 mm/s using autogenous gas tungsten arc welding were employed. At the welding speed of 6 mm/s, the high-content (Ti + Nb) steel was resistant and the Nb-stabilised steel was marginally susceptible to solidification cracking. At the welding speed of 3 mm/s, the Nb and the high (Ti + Nb) steels were found to be marginally susceptible to solidification cracking while the unstabilised and low-content (Ti + Nb) grades were resistant to solidification cracking. The weld metal microstructures transverse to the welding direction revealed columnar grains in all the samples for both welding speeds. The ferritic stainless steels were generally resistant to solidification cracking, except the Nb-stabilised steel, which was marginally susceptible to solidification cracking. KW - Susceptibility KW - Modified Varestraint Transvarestraint KW - Solidification cracking KW - Ferritic stainless steel KW - Microstructure KW - Welding PY - 2019 DO - https://doi.org/10.1007/s12046-019-1175-0 SN - 0973-7677 VL - 44 IS - 9 SP - Article Number: UNSP 194 PB - Springer AN - OPUS4-48938 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Taparli, Ugur Alp A1 - Jacobsen, Lars A1 - Griesche, Axel A1 - Michalik, Katarzyna A1 - Mory, David A1 - Kannengießer, Thomas T1 - In situ laser-induced breakdown spectroscopy measurements of chemical compositions in stainless steels during tungsten inert gas welding N2 - A laser-induced breakdown spectroscopy (LIBS) system was combined with a bead-on-plate Tungsten Inert Gas (TIG) welding process for the in situ measurement of chemical compositions in austenitic stainless steels during welding.Monitoring the weld pool's chemical composition allows governing the weld pool solidification behavior, and thus enables the reduction of susceptibility to weld defects. Conventional inspection methods for weld seams (e.g. ultrasonic inspection) cannot be performed during the welding process. The analysis system also allows in situ study of the correlation between the occurrence ofweld defects and changes in the chemical composition in theweld pool or in the two-phase regionwhere solid and liquid phase coexist. First experiments showed that both the shielding Ar gas and the welding arc plasma have a significant effect on the selected Cr II, Ni II and MnII characteristicemissions, namely an artificial increase of intensity values via unspecific emission in the spectra. In situ investigations showed that this artificial intensity increase reached a maximum in presence of weld plume. Moreover, an explicit decay has been observedwith the termination of thewelding plumedue to infrared radiation during sample cooling. Furthermore, LIBS can be used after welding to map element distribution. For austenitic stainless steels,Mnaccumulations on both sides of theweld could be detected between the heat affected zone (HAZ) and the base material. T2 - th International Conference on Laser-Induced Breakdown Spectroscopy (LIBS) CY - Chamonix-Mont-Blanc, France DA - 12.09.2016 KW - LIBS KW - TIG KW - Welding KW - Austenitic KW - Stainless steels KW - Chemical composition KW - In situ KW - Measurement PY - 2018 UR - http://www.sciencedirect.com/science/article/pii/S0584854717301064 DO - https://doi.org/10.1016/j.sab.2017.11.012 SN - 0584-8547 VL - 139 SP - 50 EP - 56 PB - Elsevier CY - Amsterdam, Niederlande AN - OPUS4-43122 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Dabah, Eitan A1 - Pfretzschner, Beate A1 - Schaupp, Thomas A1 - Kardjilov, N. A1 - Manke, I. A1 - Boin, M. A1 - Woracek, R. A1 - Griesche, Axel T1 - Time-resolved Bragg-edge neutron radiography for observing martensitic phase transformation from austenitized super martensitic steel N2 - Neutron Bragg-edge imaging was applied for the visualization of a γ-Austenite to α'-martensite phase transformation. In the present study, a super martensitic stainless steel sample was heated until complete austenitization and was subsequently cooled down to room temperature. The martensitic phase Transformation started at Ms = 190 °C. Using a monochromatic neutron beam with λ = 0.390 nm, the transmitted intensity was significantly reduced during cooling below Ms, since the emerging martensitic phase has a higher attenuation coefficient than the austenitic phase at this wavelength. The phase Transformation process was visualized by filming the transmission images from a scintillator screen with a CCD camera with a temporal resolution of 30 s and a spatial resolution of 100 µm. KW - Neutron imaging KW - Bragg-edge imaging KW - Phase transformation PY - 2017 DO - https://doi.org/10.1007/s10853-016-0642-9 SN - 0022-2461 SN - 1573-4803 VL - 52 IS - 6 SP - 3490 EP - 3496 AN - OPUS4-38574 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 -