TY - JOUR A1 - Kannengießer, Thomas A1 - Kromm, Arne A1 - Gibmeier, J. A1 - Rethmeier, Michael T1 - In-situ-Analyse der Phasenumwandlungskinetik während des Schweißens N2 - Zugeigenspannungen, wie sie beim Schweißprozess durch inhomogene Temperaturverteilungen und Schrumpfungen hervorgerufen werden, können die Lebensdauer geschweißter Verbindungen signifikant herabsetzen. Eine neue und außerordentlich attraktive Methode, um Druckeigenspannungen bereits während des Schweißens gezielt einzustellen, gelingt mit sogenannten LTT (Low Transformation Temperature)-Legierungen. LTT-Legierungen weisen eine martensitische Phasenumwandlung bei relativ niedrigen Temperaturen auf, wobei die damit verbundene Volumenexpansion zu einer Reduktion der Schrumpfeigenspannungen bzw. Erzeugung von Druckeigenspannungen führt. Zum direkten Nachweis der Phasenumwandlungen und der damit verbundenen resultierenden Schweißeigenspannungen wurden erstmals In-situ-Schweißexperimente unter Nutzung hoch energetischer, polychromatischer Synchrotronstrahlung (Weißstrahl) realisiert, um die Umwandlungskinetik während eines realen Schweißprozesses und die daraus resultierenden Schweißeigenspannungen zu analysieren. Es wird gezeigt, dass mit LTT-Legierungen signifikante Druckeigenspannungen in der Schweißnaht erreicht werden. PY - 2010 SN - 0025-5300 VL - 52 IS - 4 SP - 204 EP - 210 PB - Hanser CY - München AN - OPUS4-21219 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Kannengießer, Thomas A1 - Kromm, Arne T1 - Formation of welding residual stresses in low transformation temperature (LTT) materials N2 - For the safety and cost efficiency of welded high-strength steel structures, precise knowledge of the level and distribution of welding- and cooling-specific stresses and residual stresses is essential, since they exert a decisive influence on strength, crack resistance, and finally on the bearable service load. This paper presents innovative filler materials, of which the phase transformation temperature was deliberately adjusted via the chemical composition. The transformation behaviour of these martensitic Low Transformation Temperature (LTT-) filler materials shows direct effects on the local residual stresses in the weld and the HAZ. These effects can purposefully be exploited to counteract the thermally induced shrinkage of the material and to produce significant compressive residual stresses in the weld. Comparative welding experiments were carried out on 690 MPa high-strength base materials using various LTT-filler materials. High energy synchrotron radiation was used for residual stress measurement. Particularly the use of high energy synchrotron radiation makes it possible to detect the residual stress condition fast without destruction of material. Thereby, residual stress depth gradients can be determined simultaneously without removing material. In steel, gradients of up to 150 µm can be resolved in such a way. Furthermore, the application of high energy radiation permits determination of residual stresses of any available residual austenite contents. Results show significant dependence of transformation temperatures on the resulting residual stress level and distribution. KW - Phase specific residual stresses KW - Phase transformation KW - Low transformation temperature filler wire KW - Energy dispersive diffraction KW - High strength steel PY - 2009 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-205909 DO - https://doi.org/10.1590/S0104-92242009000100009 SN - 0104-9224 SN - 1980-6973 VL - 14 IS - 1 SP - 74 EP - 81 PB - Associação Brasileira de Soldagem, ABS CY - Rio de Janeiro AN - OPUS4-20590 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Kannengießer, Thomas A1 - Kromm, Arne T1 - Characterising phase transformations of different LTT alloys and their effect on residual stresses and cold cracking N2 - Novel martensitic filler materials with specially adjusted martensite start temperatures (Ms) can counteract the cooling specific shrinkage due to expansion effects of the weld metal associated with phase transformations. That can be exploited to create compressive residual stresses in the weld and adjacent areas, i.e. beneficial for increasing fatigue strength. The Ms temperature is shifted via the chemical composition, mainly by the alloying elements nickel and chromium, resulting as well in different retained austenite contents. Investigations were made using different Low Transformation Temperature (LTT) alloys with varying nickel content. The resulting phase transformation temperatures were – for the first time – detected using high energy synchrotron diffraction and Single Sensor Differential Thermal Analysis (SS-DTA). Compared to angle dispersive diffraction, energy dispersive diffraction offers the possibility to measure residual stresses of the martensite and austenite phase parallel fast in one experiment up to depths of 100 µm. The residual stresses show significant distributions dependent on Ms temperature. The effect on the cold cracking behaviour of these alloys was investigated using the Tekken test. Results show that cold cracking can be avoided when appropriate contents of retained austenite are existent. KW - Austenite KW - Cold cracking KW - Martensite KW - Low themperature KW - Transformation PY - 2011 DO - https://doi.org/10.1007/BF03321286 SN - 0043-2288 VL - 55 IS - 3 SP - 48 EP - 56 PB - International Institute of Welding CY - France AN - OPUS4-38978 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Hensel, J. A1 - Kromm, Arne A1 - Nitschke-Pagel, T. A1 - Dixneit, Jonny A1 - Dilger, K. T1 - Capability of martensitic low transformation temperature welding consumables for increasing the fatigue strength of high strength steel joints N2 - The use of low transformation temperature (LTT) filler materials represents a smart approach for increasing the fatigue strength of welded high strength steel structures apart from the usual procedures of post weld treatment. The main mechanism is based on the effect of the low start temperature of martensite formation on the stress already present during welding. Thus, compressive residual stress formed due to constrained volume expansion in connection with phase transformation become highly effective. Furthermore, the weld metal has a high hardness that can delay the formation of fatigue cracks but also leads to low toughness. Fundamental investigations on the weldability of an LTT filler material are presented in this work, including the characterization of the weld microstructure, its hardness, phase transformation temperature and mechanical properties. Special attention was applied to avoid imperfections in order to ensure a high weld quality for subsequent fatigue testing. Fatigue tests were conducted on the welded joints of the base materials S355J2 and S960QL using conventional filler materials as a comparison to the LTT filler. Butt joints were used with a variation in the weld type (DY-weld and V-weld). In addition, a component-like specimen (longitudinal stiffener) was investigated where the LTT filler material was applied as an additional layer. The joints were characterized with respect to residual stress, its stability during cyclic loading and microstructure. The results show that the application of LTT consumables leads to a significant increase in fatigue strength when basic design guidelines are followed. This enables a benefit from the lightweight design potential of high-strength steel grades. KW - Low transformation temperature KW - Welding KW - Fatigue strength KW - Residual stress PY - 2020 DO - https://doi.org/10.3139/120.111562 VL - 62 IS - 9 SP - 891 EP - 899 PB - Carl Hanser Verlag AN - OPUS4-51180 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Heinze, Christoph A1 - Kromm, Arne A1 - Schwenk, Christopher A1 - Kannengießer, Thomas A1 - Rethmeier, Michael T1 - Welding residual stresses depending on solid-state transformation behaviour studied by numerical and experimental methods N2 - The development of high-strength structural steels with yield strengths up to 1000 MPa results in the requirement of suitable filler materials for welding. Recently designed low transformation temperature (LTT) alloys offer appropriate strength. The martensitic phase transformation during welding induces compressive residual stress in the weld zone. Therefore, the mechanical properties of welded joints can be improved. The present paper illustrates numerical simulation of the residual stresses in LTT-welds taking into account the effect of varying Ms/Mf-temperatures, and therefore different retained austenite contents, on the residual stresses. Residual stress distributions measured by synchrotron diffraction are taken as evaluation basis. A numerical model for the simulation of transformation affected welds is established and can be used for identification of appropriate Ms-temperatures considering the content of retained austenite. KW - Welding simulation KW - Residual stress KW - Low transformation temperature filler material KW - Martensitic transformation KW - Retained austenite PY - 2011 DO - https://doi.org/10.4028/www.scientific.net/MSF.681.85 SN - 0255-5476 VL - 681 SP - 85 EP - 90 PB - Trans Tech Publications CY - Aedermannsdorf, Switzerland AN - OPUS4-23357 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Gibmeier, J. A1 - Obelode, E. A1 - Altenkirch, J. A1 - Kromm, Arne A1 - Kannengießer, Thomas T1 - Residual stress in steel fusion welds joined using low transformation temperature (LTT) filler material N2 - Welding residual stress is of major concern for structural integrity assessment in industrial components. Shear and volume strains resulting from the austenite-martensite-transformation affect the development of residual stress during welding. Controlling the phase transformation allows adjustment of the welding residual stress. Low transformation temperature (LTT) weld filler materials exhibiting reduced MS-temperatures allow postponing the phase transformation. The associated strain arising from the delayed transformation compensates for the thermal contraction strains and as such may reduce tensile or even introduce compressive residual stress. In this article we discuss the tri-axial residual stress distribution in 15 mm S690Q steel plates joined with LTT filler materials with 10 wt% Cr and a Ni-content that varies from 8 to 12 wt%. Using complementary synchrotron X-ray and neutron diffraction stress analysis the macroscopic residual stress was derived from the phase specific lattice strain and phase fraction of martensite and retained austenite, respectively. The local phase specific unstrained lattice parameters were determined using stress relieved combs. The investigation revealed increasing phase fraction of retained austenite with increasing Ni-content. Further, independent of the Ni-content in each weld in the fusion zone, significant compressive residual stresses were found in the longitudinal direction, which are balanced by tensile residual stresses in the heat affected zone (HAZ). In the weld transverse and normal direction the stress distribution is qualitatively similar but less in magnitude. The increased amount of retained austenite reduces the compressive stress arising from shear and volume strains during the delayed phase transformation and therefore no significant increase in compression was observed for decreasing MS-temperatures. KW - Welding residual stresses KW - Neutron diffraction KW - LTT filler materials PY - 2014 DO - https://doi.org/10.4028/www.scientific.net/MSF.768-769.620 SN - 0255-5476 VL - 768-769 SP - 620 EP - 627 PB - Trans Tech Publications CY - Aedermannsdorf, Switzerland AN - OPUS4-29706 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Gibmeier, J. A1 - Held, A. A1 - Altenkirch, J. A1 - Kromm, Arne A1 - Kannengießer, Thomas A1 - Buslaps, T. T1 - Real time monitoring of phase transformation and strain evolution in LTT weld filler material using EDXRD N2 - For a newly developed 10% Cr and 10% Ni low transformation temperature (LTT) weld filler material, the local phase transformation kinetics and the strain evolution during gas tungsten arc welding (GTAW) under real welding conditions was studied. An experimental set-up and a measuring and evaluation strategy are presented to gain a real time insight into the welding process. The experiments were carried out at the beam line ID15@ESRF using a two detector EDXRD (energy dispersive X-ray diffraction) set-up and high energy synchrotron X-rays. The time-resolved diffraction analysis during welding was carried out locally throughout the weld in longitudinal as well as in transverse direction to the weld line to examine the interdependence of the strain state and the transformation kinetics. This comprehension is crucial for the optimization of the weld process, and thus for the tailoring of the resulting residual stress states, which is one of the main issues for the application of LTT alloys. Using the herein proposed approach EDXRD diffraction pattern can be monitored during real welding with a counting rate of 5 Hz. By means of the time resolved diffraction data the local transformation temperatures and times were determined and the local phasespecific strain evolutions are discussed with respect to the transformation rates and the time-delayed phase transformations. KW - In situ synchrotron X-ray diffraction KW - Low transformation temperature KW - Welding PY - 2014 DO - https://doi.org/10.1016/j.jmatprotec.2014.06.008 SN - 0924-0136 SN - 1873-4774 VL - 214 IS - 11 SP - 2739 EP - 2747 PB - Elsevier CY - Amsterdam AN - OPUS4-30955 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Farajian, M. A1 - Barsoum, Z. A1 - Kromm, Arne T1 - Residual stress engineering in fatigue resistant welds N2 - The developments in the field of residual stress determination during the last decades have contributed to a better understanding of the origins and sources of residual stresses in different engineering disciplines. The many investigations concerning the behavior of residual stresses under mechanical loading have also provided a solid foundation to clarify the important aspects of residual stresses and fatigue. The question that arises now is if this available body of knowledge is being used effectively in the field of welding technology to design and construct structures with better fatigue performances. In this paper the necessity of the development of the concept residual stress engineering for welds in which wanted residual stress states are tailored for specific cases by appropriate means will be discussed. The possibilities of the quantitative consideration of the benefits in the fatigue design codes will be presented in a practical example. KW - Welding KW - Residual stress KW - Fatigue KW - Fatigue improvement PY - 2014 DO - https://doi.org/10.4028/www.scientific.net/MSF.768-769.613 SN - 0255-5476 VL - 768-769 SP - 613 EP - 619 PB - Trans Tech Publications CY - Aedermannsdorf, Switzerland AN - OPUS4-29707 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Falkenreck, Thora E. A1 - Kromm, Arne A1 - Böllinghaus, Thomas T1 - Investigation of physically simulated weld HAZ and CCT diagram of HSLA armour steel N2 - The phase transformation under various cooling rates and in different HAZ regions for high-strength armour steel was analysed by dilatometry. To develop a continuous cooling transformation (CCT) diagram, the samples were heated up to a peak temperature of 1250 °C to achieve a coarse-grained microstructure and then cooled down with a cooling time t 8/5 varying from 3 to 240 s. Analysis of dilatation curves revealed the austenite decomposition process, during which transformation temperatures were determined. The results showed martensitic transformations for all welding-relevant cooling times. Furthermore, to analyse different heat-affected subzones of the weld, the peak temperature was varied between 550 and 1250 °C at a constant cooling time t 8/5 of 6 s. The simulated coarse-grained heat-affected zone (CGHAZ) and fine-grained-heat affected zone (FGHAZ) showed only martensitic transformations with transformation temperatures below 400 °C. The steel exhibited an inhomogeneous hardness with hardening in the CGHAZ and FGHAZ and softening in the intercritical and subcritical HAZ. The physically simulated microstructure was validated by a real hybrid laser-arc weld microstructure. KW - Dilatometry KW - High-strength steels KW - CCT diagrams KW - Heat-affected zone PY - 2018 DO - https://doi.org/10.1007/s40194-017-0511-4 SN - 0043-2288 SN - 1878-6669 VL - 62 IS - 1 SP - 47 EP - 54 PB - Springer AN - OPUS4-44716 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Dixneit, Jonny A1 - Vollert, F. A1 - Kromm, Arne A1 - Gibmeier, J. A1 - Hannemann, Andreas A1 - Fischer, Tobias A1 - Kannengießer, Thomas T1 - In situ analysis of the strain evolution during welding using low transformation temperature filler materials N2 - Compared to conventional welding consumables using low transformation temperature (LTT) filler materials is an innovative method to mitigate tensile residual stresses due to delayed martensite transformation of the weld. For the effective usage of LTT filler materials, a deeper understanding of the complex processes that lead to the final residual stress state during multipass welding is necessary. Transformation kinetics and the strain evolution of multi-pass welds during welding were investigated in situ at the beamline HEMS@PETRAIII, Germany. Compared to conventional welds, the total strain was reduced and compression strain was achieved when using LTT filler materials. For an optimal use of the LTT effect in the root of multi-pass welds, the alloying concept must be adapted taking care of dilution. KW - Low transformation temperature filler materials KW - Synchrotron diffraction KW - Phase transformation KW - Multi-pass welding KW - ADXRD PY - 2018 DO - https://doi.org/10.1080/13621718.2018.1525150 SN - 1362-1718 SN - 1743-2936 VL - 24 IS - 3 SP - 243 EP - 255 PB - Taylor & Francis AN - OPUS4-46039 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Dixneit, Jonny A1 - Kromm, Arne A1 - Hannemann, Andreas A1 - Friedersdorf, Peter A1 - Kannengießer, Thomas A1 - Gibmeier, J. T1 - In-situ load analysis in multi-run welding using LTT filler materials N2 - Modifying the level of mostly detrimental welding residual stresses already during the welding process would be highly attractive as time- and cost-consuming post processing may be prevented. The nature of stress buildup during welding-associated cooling is highly affected by phase transformations. Up to now, it is not clear in which way this is applicable to real component welding exhibiting high shrinkage restraint and complex heat input. In this study, two different low transformation temperature (LTT) alloys have been investigated concerning the stress development in restrained multi-run butt welding in order to evaluate the potential of stress reduction. Pulsed gas metal arc welding (P-GMAW) welding was executed on a testing facility designed to simulate real lifelike restraint conditions of component weldments. The effect of reducedMS-temperatures and the heat control on the globally acting stresses was monitored by in-situ measurement of the reaction forces during welding fabrication. Additional local residual stress measurements allowed analyzing global as well as local loading of the welded construction. Although phase transformation has a significant influence on unloading the joint during each weld pass, the reaction stress upon cooling to room temperature seems to be determined mainly by the heat input. On the surface, low longitudinal residual stresses were observed in case of LTT whereas transverse residual stresses are less affected. T2 - 69th IIW Annual Assembly and International Conference CY - Melbourne, Australia DA - 10.07.2016 KW - Phase transformation temperature KW - Residual stress KW - Welding KW - Dilution KW - Restraint PY - 2016 DO - https://doi.org/10.1007/s40194-016-0373-1 SN - 0043-2288 VL - 60 IS - 6 SP - 1159 EP - 1168 PB - Springer CY - Heidelberg AN - OPUS4-37892 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Dixneit, Jonny A1 - Kromm, Arne A1 - Boin, M. A1 - Wimpory, Robert A1 - Kannengießer, Thomas A1 - Gibmeier, J. A1 - Schröpfer, Dirk T1 - Residual stresses of LTT welds in large-scale components N2 - Residual stresses of welds become more and more important influencing cold cracking as well as the fatigue life of welded components. Low transformation temperature (LTT) filler materials offer the opportunity to alter the residual stresses already during the welding process by means of ad- justed martensite phase transformation temperature (MS). In the current paper, welding residual stresses are studied putting the focus on MS while joining heavy steel sections with a thickness of 20 and 25 mm, respectively. The residual stress state was determined at the top surface using X-ray diffraction as well as in the bulk by neutron diffraction. The results com- pare the residual stresses present in a conventional weld and LTT welds when multi-pass welding of large-scale compo- nents was applied. Repeated phase transformation in the case of the LTT weld is more vital for the residual stresses present in the real-life-like joints. This accounts for the top surface in longitudinal direction but is most pronounced for the bulk of the welds. Detrimental tensile residual stresses are mainly re- duced in the bulk in comparison to a conventional filler wire even in multi-pass welds of thick steel sections. T2 - IIW AA 2016 CY - Melbourne, Australia DA - 10.07.2016 KW - LTT KW - Welding residual stress KW - Phase transformation KW - Interpass temperature PY - 2017 DO - https://doi.org/10.1007/s40194-017-0502-5 SN - 0043-2288 SN - 1878-6669 VL - 61 IS - 6 SP - 1089 EP - 1097 PB - Springer CY - Heidelberg AN - OPUS4-41169 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Dieck, S. A1 - Rosemann, Paul A1 - Kromm, Arne A1 - Halle, T. T1 - Reversed austenite for enhancing ductility of martensitic stainless steel N2 - The novel heat treatment concept, “quenching and partitioning” (Q&P) has been developed for high strength steels with enhanced formability. This heat treatment involves quenching of austenite to a temperature between martensite start and finish, to receive a several amount of retained austenite. During the subsequent annealing treatment, the so called partitioning, the retained austenite is stabilized due to carbon diffusion, which results in enhanced formability and strength regarding strain induced austenite to martensite transformation. In this study a Q&P heat treatment was applied to a Fe-0.45C-0.65Mn-0.34Si-13.95Cr stainless martensite. Thereby the initial quench end temperature and the partitioning time were varied to characterize their influence on microstructural evolution. The microstructural changes were analysed by dilatometer measurements, X-ray diffraction and scanning electron microscopy, including electron backscatter diffraction. Compression testing was made to examine the mechanical behaviour. It was found that an increasing partitioning time up to 30 min leads to an enhanced formability without loss in strength due to a higher amount of stabilized retained and reversed austenite as well as precipitation hardening. T2 - 19th Chemnitz Seminar on Materials Engineering – 19. Werkstofftechnisches Kolloquium CY - Chemnitz, Germany DA - 16.03.2017 KW - Quenching and partitioning KW - Martensitic stainless steels KW - Heat treatment KW - Transformation induced plasticity KW - High ductility PY - 2017 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-395328 DO - https://doi.org/10.1088/1757-899X/181/1/012034 SN - 1757-899X SN - 1757-8981 VL - 181 IS - Conference 1 SP - Article UNSP 012034, 1 EP - 8 PB - IOP Publishing CY - Bristol, UK AN - OPUS4-39532 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Brauser, Stephan A1 - Kromm, Arne A1 - Kannengießer, Thomas A1 - Rethmeier, Michael T1 - In-situ analysis of solid state phase transformation in TRIP-aided steels by synchrotron diffraction N2 - Energy dispersive synchrotron diffraction (EDXRD) analysis and 3 dimensional digital image correlations were conducted to investigate the stress and strain effected transformation behavior during tensile loading of low alloyed TRansformation Induced Plasticity (TRIP) steel. This technique allowed for phase specific stress measurement during certain tensile load steps in the elastic and also plastic regime. Additionally the simultaneous determination of the load dependent phase content was realized. The results show that the martensite transformation starts only after exceeding the overall yield point and is finished before reaching the uniform elongation, whereas a large portion of the austenite remains unchanged in the structure. Furthermore, the martensite transformation related to the stress in the γ-phase and α-phase was analyzed and quantified. KW - Synchrotron KW - EDXRD KW - Phase transformation KW - TRIP steel KW - Digital image correlation KW - Residual stress PY - 2011 UR - https://www.jstage.jst.go.jp/article/qjjws/29/3/29_3_81s/_pdf DO - https://doi.org/10.2207/qjjws.29.81s SN - 0288-4771 VL - 29 IS - 3 SP - 81 EP - 85 CY - Tokyo, Japan AN - OPUS4-24693 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Brauser, Stephan A1 - Kromm, Arne A1 - Kannengießer, Thomas A1 - Rethmeier, Michael T1 - In-situ synchrotron diffraction and digital image correlation technique for characterizations of retained austenite stability in low-alloyed transformation induced plasticity steel N2 - Direct measurement and quantification of phase transformation in a low-alloyed transformation induced plasticity steels depending on the tensile load as well as determination of the real true stress and true strain values were carried out in-situ using high energy synchrotron radiation. Digital image correlation technique was used to quantify more precisely the true strain values. The aim of the work was to obtain a better understanding of the phase transformation of commercial low-alloyed transformation induced plasticity steel depending on the true strain and true stress values. KW - Transformation induced plasticity KW - In-situ synchrotron diffraction KW - Austenite stability KW - Digital image correlation PY - 2010 DO - https://doi.org/10.1016/j.scriptamat.2010.08.007 SN - 1359-6462 SN - 1872-8456 VL - 63 IS - 12 SP - 1149 EP - 1152 PB - Elsevier CY - Oxford AN - OPUS4-22164 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Brauser, Stephan A1 - Kromm, Arne A1 - Dabah, Eitan A1 - Kannengießer, Thomas A1 - Rethmeier, Michael T1 - Thermal stability of retained austenite in low alloyed TRIP-steel determined by high energy synchrotron radiation N2 - TRIP-steels offer a good combination between strength and ductility. Therefore TRIP-steels are widely used in the automobile industries. The aim of this work is to study the stability of involved phases during heating and to identify the kinetics of the occuring phase transformations. For that purpose, in-situ diffraction measurements, using high energy synchrotron radiation were conducted. The analysis revealed the decomposition of the metastable austenitic phase into carbide and ferrite along the heating process and the regeneration of the austenite by further heating of the sample. KW - Austenite stability KW - Phase transformation KW - TRIP steel KW - Energy dispersive synchrotron X-ray diffraction PY - 2014 DO - https://doi.org/10.4028/www.scientific.net/MSF.772.129 SN - 0255-5476 VL - 772 SP - 129 EP - 133 PB - Trans Tech Publications CY - Aedermannsdorf, Switzerland AN - OPUS4-29700 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 - TY - JOUR A1 - Bhatti, A.A. A1 - Barsoum, Z. A1 - Van der Mee, V. A1 - Kromm, Arne A1 - Kannengießer, Thomas T1 - Fatigue strength improvement of welded structures using new low transformation temperature filler materials N2 - The results reported in this research study are part of a larger EU RFCS (Research Fund for Coal and Steel) project where the aim is to study the fatigue behavior of improved welds in high strength steels by utilizing different improvement techniques. In this particular study LTT (Low Transformation Temperature) weld filler material have been investigated and their possibility to improve the fatigue strength. The characteristic of these filler material is that they undergo phase transformation at temperature close to room temperature which will reduce the tensile residual stress in the weld and in some cases result in compressive residual stresses. Two different LTT alloy compositions have been developed, with different Ms (Martensite Start) temperatures in order to study the amount of tensile/compressive residual stresses produced by these wires. Welding residual stress measurements were carried out by X-ray diffraction technique. Plates with welded longitudinal attachments were fabricated in 700 MPa and 960 MPa steel grades using different LTT filler materials. These specimens were fatigue tested in constant and variable amplitude loading and the fatigue test results were compared with results from specimen welded with conventional weld filler material. KW - Residual stresses KW - LTT KW - Welded joints KW - Fatigue testing PY - 2013 DO - https://doi.org/10.1016/j.proeng.2013.12.074 SN - 1877-7058 VL - 66 SP - 192 EP - 201 PB - Elsevier Ltd. CY - Amsterdam [u.a.] AN - OPUS4-30609 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Becker, Amadeus A1 - Schröpfer, Dirk A1 - Kromm, Arne A1 - Kannengießer, Thomas T1 - Determination of residual stress evolution during repair welding of high-strength steel components N2 - During the assembly of steel structures, unacceptable weld defects may be found. An economical solution is local thermal gouging of the affected areas and re-welding. Due to high shrinkage restraints of repair weld and sur- rounding structure, high global and local welding stresses superimpose, and may lead to cracking and component failure, especially in connection with the degraded microstructure and mechanical properties of high-strength steels during the repair process. Component-related investigations of high-strength steels (FOSTA P1311/ IGF20162N) focus on welding residual stress evolution during local thermal gouging and rewelding. In this study, repair welding of S500MLO (EN 10225) is carried out using in-situ digital image correlation (DIC) and ex- situ X-ray diffraction (XRD) to analyse strains and stresses. Self-restrained slit specimen geometries were identified representing defined rigidity conditions of repair welds of real components, which were quantified using the restraint intensity concept. The specimens were rewelded with constant welding heat control and parameters. Weld specimens exhibited significantly increased transverse residual stresses with higher transverse restraint intensities, in the weld metal, and in the heat affected zone. Transverse stresses along the weld seam decrease at the weld seam ends leading to different stress state during gouging and welding. XRD analysis of the longitudinal and transverse local residual stresses after cooling to RT showed a good comparability with global DIC analyses. KW - Repair-welding KW - High-strength steels KW - X-ray diffraction KW - Digital image correlation KW - Residual stresses PY - 2022 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-555672 DO - https://doi.org/10.1016/j.finmec.2022.100073 SN - 2666-3597 VL - 6 SP - 1 EP - 6 PB - Elsevier CY - Amsterdam AN - OPUS4-55567 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Altenkirch, J. A1 - Gibmeier, J. A1 - Kromm, Arne A1 - Kannengießer, Thomas A1 - Nitschke-Pagel, T. A1 - Hofmann, M. T1 - In situ study of structural integrity of low transformation temperature (LTT)-welds N2 - We discuss the stability of weld residual strain under static and quasi cyclic transverse tensile loading in the elastic and elastic–plastic region. The test welds were joined with low transformation temperature weld filler materials with 10 wt% Cr and varying Ni-content from 8 to 12 wt%. Using neutron diffraction the residual lattice strain in the martensitic α'- and austenitic γ-phase in the fusion zone as well as the ferritic α-phase in the heat affected zone and base metal as induced by welding, superimposed by stepwise tensile loading and after unloading was measured. The amount of retained austenite in the fusion zone increases with increasing Ni-content, but it decreases with increasing load level due to stress induced martensite formation. In the as-welded condition the transverse macroscopic residual lattice strain was found to be in low compression in the fusion zone in each weld, while the heat affected zone was in tension. Local plastic deformation of the γ-phase as a result of yielding during tensile loading in combination with the change in phase fraction resulted in increased macroscopic compression in the fusion zone. The reduced yield strength in the heat affected zone resulted in plastic deformation and a considerable shift into compression. Comparison with the cross weld distribution of the hardness and FWHM of the neutron diffraction interference lines supported the assumption of plastic deformation of the γ- and α-phase in the fusion and heat affected zone, respectively, while the α'-phase in the fusion zone was stressed within the elastic regime only. Microstructural observations as well as measurement of the local γ-phase fraction by means of laboratory X-ray diffraction in the fusion zone strengthen these observations. KW - Low transformation temperature KW - Residual stress KW - Neutron diffraction PY - 2011 DO - https://doi.org/10.1016/j.msea.2011.03.091 SN - 0921-5093 SN - 1873-4936 VL - 528 IS - 16-17 SP - 5566 EP - 5575 PB - Elsevier CY - Amsterdam AN - OPUS4-24359 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -