TY - JOUR A1 - Steppan, Enrico A1 - Mantzke, Philipp A1 - Steffens, Benjamin A1 - Rhode, Michael A1 - Kannengießer, Thomas T1 - Thermal desorption analysis for hydrogen trapping in microalloyed high-strength steels JF - Welding in the World N2 - Hydrogen can have an extreme degradation effects in steels, particularly concerning the mechanical properties. These effects can lead to hydrogen-assisted cracking in microalloyed high-strength steels during fabrication and/or operation in industrial applications. In order to study these effects, electrochemically charged tensile specimens were tested to elucidate the degradation of their properties. The carrier gas hot extraction (CGHE) method, which functionally combines a mass spectrometer with a thermal desorption analysis (TDA) process, was used for the detection of ultra-low diffusible hydrogen concentrations in the material specimens. The mass spectrometer provided rapid and automatic determination of hydrogen concentration, whereas the TDA presented the activation energy within the respective test specimen at the specific temperature. Additionally, specimen temperature was carefully monitored to reduce the evaluation error for local effusion peaks. A quenching and deformation dilatometer was used for the analysis of typical heat-affected zones during the welding process for a high reproducibility of the homogenous microstructures that were studied. The present work shows the interaction between hydrogen and lattice defects in different microalloyed materials and heat-affected zones of weldable fine-grained steels. These steels were prepared in a quenched and tempered condition and in a thermo-mechanically rolled condition. These preparations were made according to German standard DIN EN 10025-6 and to DIN EN 10149-2, respectively. The trapping characteristics of two steel grades, S690QL and S700MC, were studied with respect to the activation energy dependent on carbon content and microalloying elements such as Ti, Nb, Mo, Cr, and V. The two steel grades exhibited several types of traps: carbide formations, dislocations, and/or grain boundaries were common, which can influence activation energy and hydrogen solubility. The type and dimension of inclusions or particles also affected the hydrogen trapping behavior. A decrease of carbon and specific alloying elements in thermo-mechanically hot rolled steels led to a change in the activation energy binding the trapped hydrogen. This thermo-mechanically hot rolled steel revealed an increased interaction between hydrogen and precipitations. The higher carbon content in the quenched and tempered steel led to a higher interaction between hydrogen and iron carbide, specifically in the martensitic phase. Furthermore, the trapping behavior in heat-affected zones showed a significant increase in activation energy, especially in the coarse-grained microstructure. These previously mentioned various effects were studied to better understand the degradation of mechanical properties in these two steels. KW - Microalloyed steels KW - Hydrogen embrittlement KW - Heating KW - Chemical analysis KW - Microstructure KW - Heat-affected zone PY - 2017 DO - https://doi.org/10.1007/s40194-017-0451-z SN - 0043-2288 SN - 1878-6669 VL - 61 IS - 4 SP - 637 EP - 648 PB - Springer CY - Berlin Heidelberg AN - OPUS4-40190 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Agudo Jácome, Leonardo A1 - Göbenli, G. A1 - Eggeler, G. ED - Göken, M. T1 - Transmission electron microscopy study of the microstructural evolution during high-temperature and low-stress (011) [01-1] shear creep deformation of the superalloy single crystal LEK 94 JF - Journal of Materials Research N2 - The present work describes the shear creep behavior of the superalloy LEK 94 at temperatures between 980 and 1050 °C and shear stresses between 50 and 140 MPa for loading on the macroscopic crystallographic shear system (MCSS) (011)[01-1]. The strain rate versus strain curves show short primary and extended secondary creep regimes. We find an apparent activation energy for creep of Qapp = 466 kJ/mol and a Norton-law stress exponent of n = 6. With scanning transmission electron microscopy, we characterize three material states that differ in temperature, applied stress, and accumulated strain/time. Rafting develops perpendicular to the maximum principal stress direction, gamma channels fill with dislocations, superdislocations cut gamma' particles, and dislocation networks form at gamma/gamma' interfaces. Our findings are in agreement with previous results for high-temperature and low-stress [001] and [110] tensile creep testing, and for shear creep testing of the superalloys CMSX-4 and CMSX-6 on the MCSSs (111)[01-1] and (001)[100]. The parameters that characterize the evolving gamma/gamma' microstructure and the evolving dislocation substructures depend on creep temperature, stress, strain, and time. KW - Dislocations KW - Microstructure KW - Scanning transmission electron microscopy (STEM) KW - Creep KW - Shear test PY - 2017 DO - https://doi.org/10.1557/jmr.2017.336 SN - 0884-2914 SN - 2044-5326 VL - 32 IS - 24 SP - 4491 EP - 4502 PB - Cambridge University Press CY - Cambrigde AN - OPUS4-43756 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Stegemann, Robert A1 - Cabeza, Sandra A1 - Pelkner, Matthias A1 - Lyamkin, Viktor A1 - Sonntag, Nadja A1 - Bruno, Giovanni A1 - Skrotzki, Birgit A1 - Kreutzbruck, Marc T1 - Evaluation of high spatial resolution imaging of magnetic stray fields for early damage detection T2 - AIP Conference Proceeding N2 - The paper discusses the evaluation of elastic and plastic strain states in two low-carbon steels of the same steel group with high spatial resolution GMR (giant magneto resistance) sensors. The residual stress distributions of tungsten inert gas welded plates were determined by means of neutron diffraction as a reference. The normal component of local residual magnetic stray fields arise in the vicinity of the positions of maximum stress. The experiments performed on flat tensile specimen indicate that the boundaries of plastic deformations are a source of stray fields. The spatial variations of magnetic stray fields for both the weld and the tensile samples are in the order of the earths magnetic field. T2 - 43rd Annual Review of Progress in Quantitative Nondestructive Evaluation, Volume 36 CY - Atlanta, Georgia, USA DA - 17.07.2016 KW - Plastic deformation KW - GMR KW - Neutron diffraction KW - Residual stress KW - Microstructure KW - Low carbon steel KW - TIG weld PY - 2017 SN - 978-0-7354-1474-7 DO - https://doi.org/10.1063/1.4974688 SN - 0094-243X VL - 1806 IS - 1 SP - Article UNSP 110010-1 EP - 10 PB - AIP Publishing CY - Melville, NY 11747 AN - OPUS4-39279 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -