TY - JOUR A1 - Kromm, Arne A1 - Kannengießer, Thomas A1 - Gibmeier, J. A1 - Genzel, C. A1 - Van der Mee, V. T1 - Determination of residual stresses in low transformation temperature (LTT -) welds metals using X-rayand high energy synchrotron radiation JF - Welding in the world N2 - Crack and fatigue resistance are relevant evaluation criteria for welded joints and are decreased by tensile residual stresses resulting from the welding and cooling process, while compressive residual stresses can have a positive influence on the characteristics mentioned. In order to generate compressive residual stresses, a set of post weld treatment procedures is available, like shot peening, hammering, etc. These procedures have the disadvantage that they are time and cost extensive and have to be applied after welding. As another point, such technologies can only produce compressive stresses at the top surface, i.e. can only contribute to the reduction of the risk of cracks initiated at the surface, like fatigue cracks. A chance to generate compressive stresses over the complete weld joint during the welding procedure is offered by the so-called Low Transformation Temperature (LTT -) filler wires. Compared to conventional wires, these materials show lower phase transformation temperatures, which can work against coolingrelated tensile stresses, resulting from respective shrinkage restraint. In consequence, distinct compressive residual stresses can be observed within the weld and adjacent areas. The strength of these fillers makes them potentially applicable to high-strength steel welding. Welds produced with different LTT – filler wires have shown different levels and distributions of the resulting residual stresses depending on the specific transformation temperature. The transformation temperatures are determined by temperature measurement. Classical X-ray diffraction as well as diffraction methods using high energy synchrotron radiation have been used for residual stress analysis. By means of high energy synchrotron diffraction in reflection mode residual stress depth gradients can be determined nondestructively. The phase selective nature of the diffraction measurements enables the simultaneous determination of the phase specific residual stresses of all contributing crystalline phases within one experiment. The application of white beam diffraction implies recording of a multitude of diffraction lines within the energy range of the provided energy spectrum of the white beam. By this means phase specific residual stress depth distributions up to distances of 150 ìm below the surface can be analysed for steel using the energy dispersive set-up of the HMI-beamline EDDI at the Bessy site, Berlin, providing an energy range between 20-150 keV. As a side effect quantitative phase analysis can be carried out using white energy dispersive diffraction e.g. the determination of the content of retained austenite in the weld. KW - Filler materials KW - Low temperature KW - Reference lists KW - Residual stresses KW - Temperature KW - Transformation KW - Synchrotron radiation KW - Phase specific residual stresses KW - Energy dispersive diffraction PY - 2009 SN - 0043-2288 SN - 1878-6669 VL - 53 IS - 1/2 SP - 3 EP - 16 PB - Springer CY - Oxford AN - OPUS4-19214 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Kannengießer, Thomas A1 - Kromm, Arne A1 - Rethmeier, Michael A1 - Gibmeier, J. A1 - Genzel, C. T1 - Residual stresses and in-situ measurement of phase transformation in low transformation temperature (LTT) welding materials JF - Advances in x-ray analysis PY - 2009 SN - 1097-0002 SN - 0069-8490 SN - 0376-0308 VL - 52 SP - 755 EP - 762 CY - Newtown Square, Pa., USA AN - OPUS4-19817 LA - eng 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 JF - Soldagem & Inspecao 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 - Kromm, Arne A1 - Kannengießer, Thomas T1 - In-situ-phase analysis using synchrotron radiation of low transformation temperature (LTT) welding material JF - Soldagem & Inspecao N2 - Cold cracking resistance is a relevant evaluation criterion for welded joints and affected by residual stresses which result from the welding procedure. Compressive residual stresses can thereby have a positive influence on preventing cracking. A unique possibility of generating compressive residual stresses already during the welding procedure is offered by the so-called Low Transformation Temperature (LTT) filler wires. Compared to conventional wires, these materials show decreased phase transformation temperatures which can work against the cooling-specific contraction. In consequence, distinct compressive residual stresses can be observed within the weld and adjacent areas. The strength of these fillers makes them potentially applicable to high-strength steel welding. Investigations were carried out to determine the phase transformation behaviour of different LTT-filler materials. Transformation temperatures were identified using Single Sensor Differential Thermal Analysis (SS-DTA). Additionally Synchrotron radiation was used to measure the transformation kinetics of all involved crystalline phases during heating and cooling of a simulated weld thermal cycle. KW - In-situ phase analysis KW - Energy dispersive diffraction KW - Phase transformation KW - Low Transformation Temperature filler wire PY - 2009 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-205922 DO - https://doi.org/10.1590/S0104-92242009000100010 SN - 0104-9224 SN - 1980-6973 VL - 14 IS - 1 SP - 82 EP - 88 PB - Associação Brasileira de Soldagem, ABS CY - Rio de Janeiro AN - OPUS4-20592 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Kromm, Arne A1 - Kannengießer, Thomas T1 - In situ phase characterization of low transformation temperature (LTT) alloy by means of synchrotron diffraction JF - Materialovedenie : naucno-techniceskij i proizvodstvennyj zurnal = Materials sciences transactions N2 - Cold cracking resistance is a relevant evaluation criterion for welded joints and affected by residual stresses which result from the welding procedure. Compressive residual stresses can thereby have a positive influence on preventing cracking. A unique possibility of generating compressive residual stresses already during the welding procedure is offered by the socalled Low Transformation Temperature (LTT) filler wires. Compared to conventional wires, these materials show decreased phase transformation temperatures which can work against the cooling-specific contraction. In consequence, distinct compressive residual stresses can be observed within the weld and adjacent areas. The strength of these fillers makes them potentially applicable to high-strength steel welding. Investigations were carried out to determine the phase transformation behaviour of different LTT-filler materials. Transformation temperatures were identified using Single Sensor Differential Thermal Analysis (SS-DTA). Additionally Synchrotron radiation was used to measure the transformation kinetics of all involved crystalline phases during heating and cooling of a simulated weld thermal cycle. KW - In-situ phase analysis KW - Energy dispersive diffraction KW - Phase transformation PY - 2010 SN - 1684-579X VL - 5 IS - 158 SP - 17 EP - 23 PB - Izdat. Masinostroenie CY - Moskva, Russia AN - OPUS4-21829 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Kromm, Arne A1 - Kannengießer, Thomas A1 - Gibmeier, J. T1 - In-situ observation of phase transformations during welding of low transformation temperature filler material JF - Materials science forum KW - LTT filler material KW - In-situ observation KW - Energy dispersive diffraction KW - Transformation temperature KW - Residual stress PY - 2010 DO - https://doi.org/10.4028/www.scientific.net/MSF.638-642.3769 SN - 0255-5476 VL - 638-642 SP - 3769 EP - 3774 PB - Trans Tech Publications CY - Aedermannsdorf, Switzerland AN - OPUS4-20725 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Kannengießer, Thomas A1 - Kromm, Arne A1 - Gibmeier, J. A1 - Rethmeier, Michael T1 - In-situ-Analyse der Phasenumwandlungskinetik während des Schweißens JF - MP materials testing 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 - 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 JF - Scripta materialia 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 - Altenkirch, J. A1 - Gibmeier, J. A1 - Kostov, V. A1 - Kromm, Arne A1 - Kannengießer, Thomas A1 - Doyle, S. A1 - Wanner, A. T1 - Time- and temperature-resolved synchrotron X-ray diffraction: observation of phase transformation and strain evolution in novel low temperature transformation weld filler materials JF - The journal of strain analysis for engineering design N2 - Solid-state phase transformations and the evolution of thermal and elastic strains in novel low temperature transformation (LTT) weld filler materials in the near surface region are monitored in real time by means of an innovative experimental set-up at the PDIFF (powder diffraction) beamline at the synchrotron light source ANKA (Angströmquelle Karlsruhe) at the KIT (Karlsruhe Institute for Technology). The key components of the diffraction set-up are two fast microstrip line detectors, which enables the strain evolution to be followed as a function of time and temperature for a 0.5?s counting time. During controlled heating and cooling cycles, as well as during near welding cycles, the martensite–austenite–martensite phase transitions are analysed. The transformation kinetics are monitored during resistance heating of small chips of the pure LTT alloys and during gas tungsten arc welding of simplified LTT welds using a specially designed welding rig for in-situ studies on the diffraction instruments. Under the mechanically unconstrained condition allowing free thermal expansion and shrinkage, the LTT alloys are found to exhibit decreasing transformation temperatures Ac and MS and increasing phase fraction of retained austenite for increasing Ni content. The strain evolution during welding reveals increased compressive stresses upon welding, which is attributed to the martensite formation upon cooling, which counteracts the thermal contraction strains. Comparison of the transformation temperatures reveals higher values than in the pure LTT alloys, but no variation between the different alloys. On the one hand, this is attributed to preferred grain orientation affecting the diffraction measurements and the determination of the transformation temperatures. On the other hand, it is possible that with the different chemical compositions of the LTT alloys and the mechanical constraints during welding, the evolution of the residual strain and stress may vary and result in counteracting affects with respect to lowered martensite start temperatures. KW - In-situ synchrotron X-ray diffraction KW - Low temperature transformation KW - Welding PY - 2011 DO - https://doi.org/10.1177/0309324711413190 SN - 0309-3247 SN - 2041-3130 VL - 46 IS - 7 SP - 563 EP - 579 PB - Sage CY - London AN - OPUS4-24683 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 JF - Quarterly journal of the Japan Welding Society 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 - Kromm, Arne A1 - Brauser, Stephan A1 - Kannengießer, Thomas A1 - Rethmeier, Michael T1 - High-energy synchrotron diffraction study of a transformation induced plasticity steel during tensile deformation JF - The journal of strain analysis for engineering design N2 - Energy-dispersive x-ray diffraction offers the possibility for measurement and evaluation of diffraction spectra containing information of various diffraction lines of all contributing crystalline phases of a material. Combined strain imaging and diffraction analysis was conducted during the tensile test of a low alloyed transformation-induced plasticity (TRIP) steel in order to investigate the transformation induced plasticity, strain hardening, and load partitioning effects. Optical strain imaging allowed for determination of localized true strains from three-dimensional deformations measured in situ. High-energy synchrotron radiation has permitted diffraction analysis in transmission mode to gather information from the material interior. Phase-specific stress evolution during loading could be observed applying the sin2ψ technique during certain load steps. The strains of the individual lattice planes were determined in different locations under varying angles between loading and perpendicular direction. Using energy-dispersive methods it was also possible to determine the transformation behaviour during elastic and plastic regime taking into account a large number of diffraction lines. The results show that the approach practised here enables one to pull together macroscopic and phase-specific microscopic material behaviour in order to improve existing models for prediction of complex load situations. KW - EDXRD KW - Transformation-induced plasticity (TRIP) KW - Residual stress KW - Synchrotron KW - Martensite transformation PY - 2011 DO - https://doi.org/10.1177/0309324711403969 SN - 0309-3247 SN - 2041-3130 VL - 46 IS - 7 SP - 581 EP - 591 PB - Sage CY - London AN - OPUS4-24604 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 JF - Materials science and engineering A 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 - TY - JOUR A1 - Kromm, Arne A1 - Kannengießer, Thomas T1 - Characterizing phase transformations of different LTT alloys and their effect on residual stresses and cold cracking JF - Welding in the world 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 the 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 KW - Temperature KW - Transformation PY - 2011 SN - 0043-2288 SN - 1878-6669 VL - 55 IS - 03/04 SP - 48 EP - 56 PB - Springer CY - Oxford AN - OPUS4-23402 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 JF - Materials science forum 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 - Kromm, Arne A1 - Kannengießer, Thomas A1 - Altenkirch, J. A1 - Gibmeier, J. T1 - Residual stresses in multilayer welds with different martensitic transformation temperatures analyzed by high-energy synchrotron diffraction JF - Materials science forum N2 - Low Transformation Temperature (LTT) alloys were developed in order to control the residual stress development by the martensitic phase transformation already during cooling of the weld metal. The positive effect of such LTT alloys on the mitigation of detrimental tensile residual stresses during welding has already been confirmed on the basis of individual laboratory tests. Within the current project it was experimentally investigated whether the phase transformation mechanisms are effective under increased restraint due to multi-pass welding of thicker specimens. The local residual stress depth distribution was analyzed non-destructively for V-type welds processed by arc welding using energy dispersive synchrotron X-ray diffraction (EDXRD). The use of high energy (20 keV to 150 keV) EDXRD allowed for the evaluation of diffraction spectra containing information of all contributing phases. As the investigated LTT alloy contains retained austenite after welding, this phase was also considered for stress analysis. The results show in particular how the constraining effect of increased thickness of the welded plates and additional deposited weld metal influences the level of the residual stresses in near weld surface areas. While the longitudinal residual stresses were reduced in general, in the transition zone from the weld to the heat-affected zone (HAZ) compressive residual stresses were found. KW - Low Transformation Temperature KW - Phase Transformation KW - Residual Stress KW - Synchrotron Diffraction PY - 2011 DO - https://doi.org/10.4028/www.scientific.net/MSF.681.37 SN - 0255-5476 VL - 681 SP - 37 EP - 42 PB - Trans Tech Publications CY - Aedermannsdorf, Switzerland AN - OPUS4-23470 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Kannengießer, Thomas A1 - Lausch, Thomas A1 - Kromm, Arne T1 - Effects of heat control on the stress build-up during high-strength steel welding under defined restraint conditions JF - Welding in the world N2 - Realization and safe operation of modern welded structures are progressively requiring for base and filler materials to cope with continually increasing loads, Analyses with a view to crack prevention therefore need to accommodate particularly the structural design (restraint intensity) and the thermomechanical effects in terms of stresses introduced during welding, Against this background, multi-run welding experiments were carried out in an IRC - (Instrumented Restraint Cracking) Test under defined restraint intensity in order to examine the influence of heat control (preheating and interpass temperatures) on the weldinq-specific forces and stresses, The experiments revealed significant rises in the reaction force and stress after welding with increasing preheating and interpass temperature, Furthermore, various concepts for calculating the preheating temperature are discussed, It is demonstrated that the hitherto existing concepts for high-strength finegrained structural steels can lead to divergent results. KW - Cracking KW - Heat KW - High strength steels KW - Restraint KW - Stress KW - Testing PY - 2011 SN - 0043-2288 SN - 1878-6669 VL - 55 IS - 07/08 SP - 58 EP - 65 PB - Springer CY - Oxford AN - OPUS4-24294 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 JF - Welding in the World 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 - Kromm, Arne T1 - Exploring the interaction of phase transformation and residual stress during welding by synchrotron diffraction JF - Welding in the world N2 - Controlling the level of mostly detrimental residual stresses already during the welding process would be highly attractive as time and cost consuming post processing may be prevented. Therefore, in this study, the approach using suitable alloy concepts with reduced phase transformation temperatures has been evaluated concerning the interactions between transformation temperature, transformation kinetics and resulting residual stresses. Ideal tools for observing these phenomena in-situ are diffraction techniques. For that purpose, a special setup was developed allowing for localized observation of phase transformation kinetics during a real welding process by energy dispersive synchrotron diffraction (EDXRD). In the present work, this setup was successfully applied for the first time in order to characterize a selection of alloys especially designed for residual stress control. The results demonstrate that in-process observation is highly suitable for characterizing and discussing phase transformation sensitive phenomena like residual stress formation. Furthermore, it was proven that residual stresses can be effectively controlled by means of an adjusted alloy design. KW - Austenite KW - Diffraction KW - Martensite KW - Residual stresses KW - Transformation KW - X-rays PY - 2012 SN - 0043-2288 SN - 1878-6669 VL - 56 IS - 09/10 SP - 2 EP - 11 PB - Springer CY - Oxford AN - OPUS4-27482 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 JF - Procedia Engineering 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 - 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 JF - Materials science forum 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 -