TY - JOUR A1 - Rhode, Michael A1 - Steger, Jörg A1 - Böllinghaus, Thomas A1 - Kannengießer, Thomas ED - Lippold, J. ED - Böllinghaus, Thomas ED - Richardson, I. M. T1 - Hydrogen degradation effects on mechanical properties in T24 weld microstructures N2 - Spectacular failure cases of fossil power stations in the recent years exhibited severe cracking in T24 welds. The results show that hydrogen-assisted cracking up to 200 °C cannot be excluded. Hence, it is important to gain a basic understanding on how hydrogen might affect the basic material properties in the respective weld microstructures. The present study focuses on hydrogen degradation of the respective weld microstructures, i.e., the weld metal and the coarse grained heat affected zone, where actually cracking appeared in practice. Tensile tests were carried out for coarse grain heataffected zone (CGHAZ) and the weld metal in uncharged and electrochemically hydrogen-charged condition. It turned out that both microstructures show distinct tendency for gradual degradation of mechanical properties in the presence of increasing hydrogen concentration. Already for a hydrogen concentration about and above 2 ml/100 g Fe, a significant ductility reduction has been observed. SEM investigations revealed that the fracture topography changes from ductile topography in uncharged condition to intergranular topography for the CGHAZ and to ductile-brittle mix for the weld metal (WM) in hydrogen charged condition. Ti-rich inclusions were identified as central regions of quasi-cleavage fracture areas in the WM. An approximation procedure is applied to quantify the degradation intensity. KW - Low alloy steels KW - Hydrogen embrittlement KW - Heat affected zone KW - Microstructure KW - Creep resisting materials PY - 2016 UR - http://link.springer.com/article/10.1007/s40194-015-0285-5 DO - https://doi.org/10.1007/s40194-015-0285-5 SN - 0043-2288 VL - 60 IS - 2 SP - 201 EP - 216 PB - Springer-Verlag GmbH CY - Heidelberg AN - OPUS4-35390 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Rhode, Michael A1 - Mente, Tobias A1 - Böllinghaus, Thomas T1 - Modeling of hydrogen-assisted cracking (HAC) in duplex stainless steels (DSS) N2 - Modeling of Hydrogen-Assisted Cracking (HAC) in Duplex Stainless Steels (DSS): - Hydrogen causes significant degradation in DSS and consequently HAC - Mechanisms of HAC have not been fully understood in two-phase microstructures - Mesoscale numerical modeling for HAC in DSS was created, coupled to the macroscale, enabling simulation of HAC in both phases independent from predefined crack paths T2 - International Hydrogen Conference - Material Performance in Hydrogen Environments CY - Jackson Lake Lodge, Moran, Wyoming, USA DA - 11.09.2016 KW - Hydrogen KW - Numerical modeling KW - Duplex stainless steel KW - Hydrogen assisted cracking PY - 2016 AN - OPUS4-37404 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Sobol, Oded A1 - Holzlechner, Gerald A1 - Holzweber, Markus A1 - Lohninger, H. A1 - Böllinghaus, Thomas A1 - Unger, Wolfgang T1 - First use of data fusion and multivariate analysis of ToF-SIMS and SEM image data for studying deuterium-assisted degradation processes in duplex steels N2 - Time-of-flight secondary ion mass spectrometry (ToF-SIMS) and high-resolution scanning electron microscopy are well-acknowledged tools in materials characterization. The ability to map chemical species on the surface of an investigated sample with often low mass detection limits makes ToF-SIMS an essential tool in fields where many question marks concerning Degradation processes and damage mechanisms exist. The aim of this paper is to describe the power of data fusion of ToF-SIMS and high-resolution scanning electron microscopy results employing computational methods for multivariate data Analysis such as principal component analysis. As a case study the investigation of hydrogen distribution in an artificially charged Duplex stainless steel microstructure is presented aiming on a better understanding of hydrogen embrittlement. T2 - 16th European Conference on Applications of Surface and Interface Analysis CY - Granada, Spain DA - 28.09.2015 KW - ToF-SIMS KW - HR-SEM KW - Data fusion KW - Duplex stainless steel KW - Hydrogen embrittlement PY - 2016 UR - http://onlinelibrary.wiley.com/doi/10.1002/sia.6015/full DO - https://doi.org/10.1002/sia.6015 VL - 48 IS - 7 SP - 474 EP - 478 PB - John Wiley & Sons, Ltd CY - Surface and Interface Analysis AN - OPUS4-36832 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - GEN A1 - Böllinghaus, Thomas A1 - Mente, Tobias A1 - Wongpanya, Pornwasa A1 - Viyanit, Ekkarut A1 - Steppan, Enrico ED - Böllinghaus, Thomas ED - Lippold, J. C. ED - Cross, C. E. T1 - Numerical modelling of hydrogen assisted cracking in steel welds N2 - Hydrogen assisted stress corrosion and cold cracking represent still a major topic regarding the safety of welded steel components against failure in many industrial branches. Hydrogen might be introduced during fabrication welding or might be taken up from an environment during sour service or at cathodic protection. Additionally, understanding and avoidance of hydrogen entry into weld microstructures from gaseous pressurized environments becomes increasingly important for renewable energy components. There are two types of metallurgical mechanisms associated with hydrogen assisted cracking, i.e. the cracking as well as hydrogen transport and trapping mechanisms. For numerical modelling, it has to be considered that both types are not independent of each other, that the mechanisms are not yet completely clarified and that validation of such models strongly depends on implementation of the correct hydrogen related materials properties. However, quite significant achievements have been made in modelling of hydrogen assisted cracking by indirect coupling of thermal, stress-strain as well as hydrogen uptake and diffusion analyses. After a brief introduction into the subject and by revisiting various proposed cracking mechanisms, the present contribution focuses on recent developments of a numerical model based on a comparison of actual hydrogen concentrations and mechanical loads with respective hydrogen dependent material properties as crack initiation and propagation criteria. The basic procedure for numerical simulation of crack initiation and propagation is outlined and it is shown how such numerical simulations can be validated experimentally. Furthermore, it is highlighted how such a procedure has been extended to a comprehensive model for life time prediction of welded steel pipeline components and experimentally verified. Finally, it is outlined how the model can be extended to simulate cracking in heterogeneous steel microstructures on the different scales. KW - hydrogen assisted cracking KW - numerical simulation KW - supermartensitic stainless steel KW - high strength low alloyed structural steel KW - duplex stainless steel PY - 2016 UR - http://link.springer.com/chapter/10.1007%2F978-3-319-28434-7_18 UR - http://www.springer.com/us/book/9783319284323 SN - 978-3-319-28432-3 SN - 978-3-319-28434-7 DO - https://doi.org/10.1007/978-3-319-28434-7_18 SP - Part VI, 383 EP - 439 PB - Springer International Publishing CY - Switzerland ET - 1 AN - OPUS4-35593 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Holzweber, Markus A1 - Sobol, Oded A1 - Wirth, Thomas A1 - Böllinghaus, Thomas A1 - Unger, Wolfgang T1 - Deuterium permeation and cracking in duplex steels as viewed by ToF-SIMS and HR-SEM with data fusion N2 - Better understanding of hydrogen assisted degradation and trapping mecha-nisms requires sufficient imaging techniques for respective hydrogen-microstructure interaction studies, in particular with multi-phase metallic micro-structures [1]. The present work is focusing on the elucidation of deuterium be-havior in two austenitic-ferritic duplex stainless steels (DSS) under the assumption that deuterium behaves in many ways similarly to hydrogen [2]. For case studies standard 2205 and lean 2101 DSSs were chosen due to the extensive use of these steels in industry [3]. The analyses were conducted by using a novel in-situ permeation and Time-of-Flight secondary ion mass spectrometry (ToF-SIMS) imaging technique or by ex-situ ToF-SIMS imaging following electrochemical charging experiments. Another pioneering procedure was data fusion (including chemometry) of results of powerful laterally resolved chemical analysis and high resolution structural characterization techniques . Results for the ex-situ observations showed a different influence of deuterium loading on the two steel grades as well as different damage mechanisms in each phase. Formation of sub-surface blisters between the ferrite and austenite were obtained in both the standard and the lean DSS. In both steels, an increased deuterium concentration was observed around deformed regions such as cracks, confirming that they originate from the presence of deuterium [4]. The formation of parallel cracks was obtained only in the austenite within the standard duplex whereas in the lean duplex the highest intensity of deuterium was obtained in the austenite along the ferrite-austenite interphase. In comparison, application of the novel in-situ permeation technique enabled to register and record the deuterium permeation through the material and the respective saturation sequence of the two phases as well as the interfaces. Faster diffusion of the deuterium was observed in the ferrite and a direct proof for deuterium enrichment at the austenite-ferrite interface has been given [1]. The integration of the specified techniques gives a better insight into the processes leading to hydrogen induced failure. These two experimental techniques provide very valuable tools for elucidation of respective metallurgical failure mechanisms that can be used for the validation of respective numerical models for hydrogen assisted cracking (HAC). T2 - 19. Arbeitstagung Angewandte Oberflächenanalytik CY - Soest, Germany DA - 05.09.2016 KW - ToF-SIMS KW - Hydrogen assisted cracking KW - Data fusion KW - SEM PY - 2016 AN - OPUS4-37484 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - GEN A1 - Böllinghaus, Thomas A1 - Steppan, Enrico A1 - Mente, Tobias ED - Böllinghaus, Thomas ED - Lippold, J. C. ED - Cross, C. E. T1 - Hydrogen assisted cracking of a subsea-flowline N2 - Since the mid-nineties, supermartensitic stainless steels (SMSS) have increasingly been applied to welded subsea-pipeline systems in the North Sea oil and gas fields, especially to flowlines at mild sour service conditions. However, in 2001 cracking and leaks occurred during installation and service start-up of two SMSS flowlines in the Norwegian Tune gas condensate field, welded with a new developed matching filler wire. Brittle transgranular cracking started especially at inter-run lack of fusion and propagated brittle, predominantly through the weld metal. The present paper provides a brief overview of the original failure case and respective sequence of events leading to complete replacement of the SMSS by carbon steel flowlines in 2002. Then, detailed investigations of a circumferential weld sample of the failed Tune flowline are highlighted, targeted at comparison of the failure appearance to previous investigations of this filler material type and to search for possible explanations for the brittle fracture at the crack initiation area. SEM investigations of the fracture surface revealed brittle areas only in the direction towards the top side of the weld while the major part of the investigated surface exhibited ductile fracture. As an approach to clarify, if the fracture was a consequence of hydrogen assisted cracking, five small sized specimens have been cut out of the original sample. Cracking has been introduced parallel to the original fracture surface in these specimens at respective saw cuts and bending. The results show that brittle transgranular cracking appeared only in the specimen cooled down to very low temperatures by liquid nitrogen and in the sample charged with hydrogen to an average concentration of about 15 ml/100 g. However, a fracture similar to the original surface was observed only in the hydrogenized specimen. As a further result, very similar fracture surfaces of supermartensitic stainless steel weld metals had been observed on specimens subjected to hydrogen assisted cold cracking (HACC) as well as to hydrogen assisted stress corrosion cracking (HASCC). In total, the results indicate that brittle fracture starting at the inter-run lack of fusion were not initiated by high notch tip deformation rates, but rather influenced by hydrogen, probably taken up during welding. KW - supermartensitic stainless steel KW - hydrogen assisted cracking KW - fracture topography PY - 2016 UR - http://link.springer.com/chapter/10.1007/978-3-319-28434-7_17 UR - http://www.springer.com/us/book/9783319284323 SN - 978-3-319-28432-3 SN - 978-3-319-28434-7 DO - https://doi.org/10.1007/978-3-319-28434-7_17 SP - Part V, 361 EP - 379 PB - Springer International Publishing CY - Switzerland ET - 1 AN - OPUS4-35592 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Falkenreck, Thora E. A1 - Böllinghaus, Thomas T1 - Blast resistance of high-strength structural steel welds N2 - As consequence for increasing threats by IEDs (Improvised Explosive Devices) on vehicles, the blast resistance of the welded frames and bodies becomes increasingly important. Considering vehicle welds subjected to blasting, the real configurations of the joints in the structure and the position of the blast loads have to be considered. The present contribution thus focuses on a weld joint at the explosion endangered wheel well of a tactical truck. The high-strength steel welds were subsequently impacted by explosion loads within the upper range from those experienced in practical military operation to cause not only deformation, but also to investigate the ultimate fracture behaviour of the high-strength weld. The interaction between cooling time t8/5 and displacement, crack path as well as fracture surface was analysed. The analyses of the fracture surfaces revealed ductile overload failure and also the size of the dimples was influenced by the cooling time t8/5. As a prominent feature, these investigations showed that the crack path of such high-strength steel welds under blasting is less influenced by the final hardness level in the respective weld microstructures but much more affected by the hardness gradient at the fusion line and inside the Heat Affected Zone (HAZ). KW - Explosions KW - High strength steels KW - MAG welding KW - Cooling rate PY - 2016 DO - https://doi.org/10.1007/s40194-016-0307-y SN - 0043-2288 SN - 1878-6669 VL - 60 IS - 3 SP - 475 EP - 483 PB - Springer CY - Heidelberg, Germany AN - OPUS4-36378 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - GEN A1 - Mente, Tobias A1 - Böllinghaus, Thomas ED - Udomkichdecha, W. ED - Mononukul, A. ED - Böllinghaus, Thomas ED - Lexow, Jürgen T1 - Numerical investigations on hydrogen-assisted cracking (HAC) in duplex stainless steels N2 - Duplex stainless steels have been used for a long time in the offshore industry, since they have higher strength than conventional austenitic stainless steels and they exhibit a better ductility as well as an improved corrosion resistance in harsh environments compared to ferritic stainless steels. However, despite these good properties the literature shows some failure cases of duplex stainless steels in which hydrogen plays a crucial role for the cause of the damage. Numerical simulations can give a significant contribution in clarifying the damage mechanisms. Therefore, a numerical model of a duplex stainless steel microstructure was developed enabling simulation of crack initiation and propagation in both phases. The phase specific stress strain analysis revealed that local plastic deformation occurs in both austenite and δ-ferrite already in the macroscopically elastic range. Altogether, phase specific hydrogen-assisted material damage was simulated for the first time taking into account all main factors influencing hydrogen assisted cracking process. The results agree well with experimental observations and thus allow a better insight in the mechanism of hydrogen-assisted material damage. T2 - 4th WMRIF Young scientists workshop CY - Boulder, CO, USA DA - 2014-09-08 KW - Hydrogen-assisted cracking (HAC) KW - Numerical simulation KW - FEM KW - Duplex stainless steel (DSS) KW - Mesoscale model PY - 2016 SN - 978-981-287-723-9 SN - 978-981-287-724-6 DO - https://doi.org/10.1007/978-981-287-724-6_3 SP - 21 EP - 31 PB - Springer AN - OPUS4-35075 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - GEN A1 - Mente, Tobias A1 - Böllinghaus, Thomas ED - Böllinghaus, Thomas ED - Lippold, J. C. ED - Cross, C. E. T1 - Numerical investigations on hydrogen-assisted cracking in duplex stainless steel microstructures N2 - Duplex stainless steels (DSS) are used in various industrial applications, e.g. in offshore constructions as well as in chemical industry. DSS reach higher strength than commercial austenitic stainless steels at still acceptable ductility. Additionally, they exhibit an improved corrosion resistance against pitting corrosion and corrosion cracking in harsh environments. Nevertheless, at specific conditions, as for instance arc welding, cathodic protection or exposure to sour service environments, such materials can take up hydrogen which may cause significant property degradation particularly in terms of ductility losses which, in turn, may entail hydrogen-assisted cracking (HAC). The cracking mechanism in DSS is different from steels having only a single phase, because hydrogen diffusion, stress-strain distribution and crack propagation are different in the austenite or ferrite phase. Therefore, the mechanism of HAC initiation and propagation as well as hydrogen trapping in DSS have not been fully clarified up to the present, as for most of the two-phase microstructures. At this point the numerical simulation can bridge the gap to a better insight in the cracking mechanism regarding the stress-strain distribution as well as hydrogen distribution between the phases, both austenite and ferrite, of the DSS. For that purpose, a two dimensional numerical mesoscale model was created representing the microstructure of the duplex stainless steel 1.4462, consisting of approximately equal portions of austenite and ferrite. Hydrogen assisted cracking was simulated considering stresses and strains as well as hydrogen concentration in both phases. Regarding the mechanical properties of austenite and ferrite different statements can be found in the literature, dependent on chemical composition and thermal treatment. Thus, various stress-strain curves were applied for austenite and ferrite simulating the HAC process in the DSS microstructure. By using the element elimination technique crack critical areas can be identified in both phases of the DSS regarding the local hydrogen concentration and the local mechanical load. The results clearly show different cracking behavior with varying mechanical properties of austenite and ferrite. Comparison of the results of the numerical simulation to those of experimental investigations on DSS will improve understanding of the HAC process in two phase microstructures. KW - duplex stainless steel 1.4462 (2205) KW - numerical simulation KW - hydrogen assisted cracking KW - diffusion PY - 2016 UR - http://link.springer.com/chapter/10.1007%2F978-3-319-28434-7_16 UR - http://www.springer.com/us/book/9783319284323 SN - 978-3-319-28432-3 SN - 978-3-319-28434-7 DO - https://doi.org/10.1007/978-3-319-28434-7_16 SP - Part V, 329 EP - 359 PB - Springer International Publishing CY - Switzerland ET - 1 AN - OPUS4-35591 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Sobol, Oded A1 - Straub, F. A1 - Wirth, Thomas A1 - Holzlechner, G. A1 - Böllinghaus, Thomas A1 - Unger, Wolfgang T1 - Real Time Imaging of Deuterium in a Duplex Stainless Steel Microstructure by Time-of-Flight SIMS N2 - For more than one century, hydrogen assisted degradation of metallic microstructures has been identified as origin for severe technical component failures but the mechanisms behind have not yet been completely understood so far. Any in-situ observation of hydrogen transport phenomena in microstructures will provide more details for further elucidation of these degradation mechanisms. A novel experiment is presented which is designed to elucidate the permeation behaviour of deuterium in a microstructure of duplex stainless steel (DSS). A hydrogen permeation cell within a TOF-SIMS instrument enables electrochemical charging with deuterium through the inner surface of the cell made from DSS. The outer surface of the DSS permeation cell exposed to the vacuum has been imaged by TOF-SIMS vs. increasing time of charging with subsequent chemometric treatment of image data. This in-situ experiment showed evidently that deuterium is permeating much faster through the ferrite phase than through the austenite phase. Moreover, a direct proof for deuterium enrichment at the austenite-ferrite interface has been found. KW - Characterization and analytical techniques KW - Corrosion KW - Imaging technique KW - Mass spectrometry PY - 2016 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-353872 UR - http://www.nature.com/articles/srep19929 DO - https://doi.org/10.1038/srep19929 SN - 2045-2322 VL - 6 IS - 19929 SP - 1 EP - 7 PB - nature publishing group CY - London, United Kingdom AN - OPUS4-35387 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -