The corrosion process of flanges formed by cataphoretically coated micro-alloyed cold-rolled steel and a polymer crevice former is investigated and simulated numerically using the finite element method (FEM). Boundary conditions are determined experimentally, including the effect of corrosion products on the diffusion of diluted species through the porous medium and the reaction kinetics on the surface of magnetite (Fe3O4) as a main corrosion product. Therefore, polarization curves are measured on sintered magnetite pellets. The experimental results as well as the temperature cycle in the test climate are used as boundary conditions in the numerical simulation. Finally, good agreement between the simulation and the experiment is achieved.

End plates are important multi-functional components of the fuel cells. They provide structural support and are responsible for channeling the reactant gases, by-product water, and fuel cell coolant in and out of the fuel cell stack. Among various materials used for end plates, aluminum alloy is used due to its high strength and low density. But its corrosion resistance depends on the environment. The operating fuel cell conditions may cause the fuel cell coolant to become more acidic or basic in nature and thus can lead to corrosion of end plates. In this work, a common die-cast aluminum alloy, AlSi10Mg(Fe), is used for end plates, and its corrosion behavior in direct contact with the fuel cell coolant is analyzed. The electrochemical characterization of uncoated and anodized aluminum alloy was achieved using electrochemical impedance spectroscopy, potentiodynamic and potentiostatic polarization tests at room temperature and at the operating temperature of the fuel cell at 80 °C. It was found that for the uncoated aluminum alloy, the corrosion sensitivity is slightly increased when the temperature increases. In comparison, the anodized aluminum alloy reveals a decrease in corrosion sensitivity after 100 h of potentiostatic control, indicating an ongoing passivation of the surface due to the formation of aluminum oxides/hydroxides and aluminum alcohol corrosion products.

For the spheroidal graphite cast iron materials, also known as ductile cast iron (DCI), EN-GJS-400-18-LT and EN-GJS-450-18, different welding procedures were examined for potential repair welding. A repair weld was performed on thick cast iron plates using the optimum procedure in each case. The weld was evaluated for all areas of the welded joint (weld metal, fusion line/heat-affected zone and base metal). In addition to the metallographic microstructural analysis, the characterization of the repair weld was carried out by means of hardness distribution measurements, static tensile testing and notched bar impact testing as well as fracture mechanics investigations under static and under cyclic loading in a wide load ratio range. On this basis, a generalized description of cyclic crack growth could be made according to the NASGRO® MODEL. NASGRO® is a fracture mechanics and fatigue crack growth software. In accordance with the possible operating conditions of repair-welded, thick-walled components, the static and impact tests were performed in the temperature range down to $$-$$ - 40 $${}^{\circ }\text {C}$$ ∘ C .

In this study, an austenitic CrMnNi–N steel is examined with regard to its solidification behavior of the weld metal. For this purpose, the cooling rate of the weld metal at different welding speeds is determined for tungsten inert gas welding without filler metal. The relationship between secondary dendrite arm spacing () and cooling rate () can be described using . Moreover, the microstructure is characterized by a scanning electron microscope using energy‐dispersive X‐ray spectroscopy (EDS). Based on the EDS measurement, it is possible to describe the microsegregation of Cr, Ni, Mn, Mo, and N. The detected microsegregation behavior is compared with the results obtained from Thermo‐Calc calculations. The microsegregation varies depending on the present phase during solidification and correlate well with microstructure observations. By using the software Thermo‐Calc, the theoretical description of solidification is based on the classical Scheil model with fast diffusion of N. A primary ferritic solidification is calculated, which correlates with the experimental findings.

This study focuses on the effect of pre-deformation on hydrogen diffusion and hydrogen embrittlement of the high alloy austenitic TRIP steel X3CrMnNiMo17-8-4. Different cold-rolled steel sheets with thicknesses of ≤400 µm were electrochemically charged on both sides in 0.1 M sodium hydroxide with hydrogen for two weeks. Comparative measurements on uncharged and immersed samples prove that hydrogen causes embrittlement in this steel for all investigated states. The embrittlement increases with increasing pre-deformation and is accompanied by deformation-induced martensite formation. The corresponding fractured surfaces were examined using electron microscopy and compared to modelled hydrogen distributions with previously determined diffusion coefficients. For this purpose, various diffusion coefficients are determined using the Devanathan–Stachurski permeation test and hot extraction in order to describe the diffusion process. The hydrogen concentration profiles and the fractographic analyses show a good agreement, so this study provides a basis for estimating the embrittlement behaviour for later application.

From modern alloys, increasingly demanding combinations of properties are expected, enabling their use as structural materials in new areas of application such as the energy industry (Liquid Natural Gas and hydrogen tanks), military, or space. One of the fundamental expectations for constructional materials used in these sectors is high energy absorption capacity while maintaining high strength (often at low temperatures where e.g. conventional steels exhibit brittleness). Simultaneously, they require appropriate plastic deformation susceptibility (formability) and other additional parameters (e.g., corrosion resistance, weldability, fatigue resistance). Designing manufacturing technologies for the metal forming of structural elements from modern engineering materials for the aforementioned applications requires a holistic approach and understanding of the relationships between process parameters (time, temperature, deformation, strain rate), microstructural phenomena (recovery/strengthening mechanisms, phase transformations, precipitation processes), and resulting properties (strength, ductility, toughness). In this work I will provide a practical example of designing specific properties of (CoNiFeMn)1-xMox high entropy alloys by controlling microstructure development at each stage of the metal forming process. The role of recrystallisation, grain growth, and the precipitation of the phase in controlling grain size - a key parameter defining the susceptibility to twinning/nanotwinning in this alloy at cryogenic temperatures - will be discussed.

High entropy alloys based on FeMnNiCoMo offer a potential for high energy absorption and high strength, even at low temperatures. In this work, the effects of chemical composition and grain size on the mechanical properties were investigated. Compression tests at a wide range of strain rates and temperatures have been performed. For a strain rate of about 102 s(-1) an instrumented drop weight tower was applied. Furthermore, cryogenic temperature tests at -196 degrees C were carried out. The microstructure was analyzed by means of scanning electron microscopy and transmission Kikuchi diffraction. Hence, the role of grain size, precipitations, and twinning-induced plasticity (TWIP) on the yield strength and the further strain hardening were investigated.

The new QTec Scanning Vibrometer is employed to analyze wave propagation resulting from corrosion. At a distance of d = 1.66 m, Lamb wave characteristics were recorded using an AE sensor and compared to a simulated corrosion event signal. The vibrometer's signal correlation enabled wave path reconstruction, ultimately facilitating the localization of the corrosion source by considering reflections and constructive interference effects in the AE sensor time signal.

Corrosion on a plate of magnesium alloy WZ73 in contact with 0.001 mol/L NaCl solution was analysed by long-range testing using the acoustic emission (AE) technique. At a distance d = 1.66 m to the source, the Lamb wave propagation of resulting AE events was examined and used for corrosion source location. As a first step, pencil lead break test was carried out and corresponding Lamb wave analysis served as reference to the varying corrosion signals of lower intensity. Additionally, the plate was excited by a piezo transducer for imitating a selected corrosion event. For analysis of the propagating wave field, the plate surface was measured by a scanning laser Doppler vibrometer (SLDV), allowing a high-resolution corrosion signal reconstruction and path tracking of direct and reflected Lamb wave packets. Based on the SLDV results, a deeper understanding of the complex wave field propagation during the sensor-based corrosion analysis was achieved. (c) 2024 The Author(s). Published by Elsevier B.V. on behalf of Institute of Metal Research, Chinese Academy of Sciences. This is an open access article under the CC BY-NC-ND license ( http://creativecommons.org/licenses/by-nc-nd/4.0/ )

AbstractThis chapter presents results of investigations on the strength, deformation and toughness behavior of quenched and tempered 42CrMo4 steel. Intentional impurification and, afterwards, filtration by functionalized ceramic foam filters were applied in order to process cast steels with different amounts and distributions of non-metallic inclusions. As references, a hot-rolled steel batch and spark-plasma sintered materials were studied. The investigations focused on the loading rate and temperature effects. Both, tensile and fracture mechanics tests, were performed in order to investigate the damaging behavior due to non-metallic inclusions remaining after the melt processing of the steel. A further goal was to predict the fracture toughness of the material based on the combination of microstructural information on the inclusion distribution and the strain rate and temperature-dependent strength and deformation behavior. It was shown that the damaging effect of non-metallic inclusions, in particular agglomerated inclusions properties, is localized which leads to relatively low strain to fracture and fracture toughness, but also to crack path deflection. Furthermore, it could be observed that the small interparticle distances within agglomerated non-metallic inclusions determine the fracture toughness behavior of the materials. By analyzing the acoustic emissions, the onset of crack growth as well as the size of the plastic zone at the crack tip could be estimated.

The solidification behavior of a novel X1CrCuNiN 18-9-6 (concentrations in wt%) stainless steel is studied by thermodynamic calculations and corresponding microstructure investigations. The thermodynamic calculations of the X1CrCuNiN 18-9-6 steel predict a metastable austenitic structure, which is verified by microstructural analyses. In the as-cast state before heat treatment, a few copper precipitates, mostly over 50 mu m in size, are visible, which are located exclusively in the interdendritic regions. The electrode inert gas atomization process is applied to produce a steel powder using a pre-material in as-cast state with significantly increased Cu content of 9 wt%. After atomization, despite the rapid cooling, micrometer-sized copper precipitates form again, which are homogeneously distributed in the microstructure, but are mostly less than 10 mu m in size and thus much finer than in the initial cast state. The short processing times during field-assisted sintering technique/spark plasma sintering makes it possible to produce a bulk material with a porosity of less than 1%. Miniature samples produced from the as-sintered material exhibit uniform elongation values of 30%-40% with a tensile strength of about 640 MPa under tensile loading conditions.

Conventionally used brass alloy CuZn30 shows problems with corrosion resistance in the form of dezincification when used in brass instruments. Therefore, within the scope of this investigation, a new brass alloy CuZn30 is developed in the microalloy range with corrosion-free or corrosion-inhibiting properties. First, the influence of microalloying elements on the phase composition is investigated by simulation using Thermo-Calc. On the basis of this, suitable alloying elements and contents are selected and a modified CuZn30X alloy with 0.1% phosphorus, tin, and nickel in mass fractions, respectively, is produced. The modified alloy is then investigated with regard to its mechanical and microstructural composition and its corrosion properties. The corrosion properties were examined using stress corrosion cracking tests, dezincification tests, and the recording of polarization curves. The modified alloy exhibited good cold and hot rolling properties as well as good corrosion resistance. The dezincification test confirmed the improved corrosion resistance of the modified CuZn30X alloy, which is attributed to the formation of a protective top layer due to the alloying elements.

The plastic deformation and martensite evolution of austenitic CrMnNi–N stainless steel with 8.6 wt% Mn and 4 wt% Ni is investigated in a temperature range of −40 to 100 °C. Martensite evolution is determined by in situ magnetic measurements during tensile test. The triggering stress and strain for martensite formation decrease with decreasing temperature. Ex situ volumetric magnetic measurements are used to determine the strain‐induced α′‐martensite volume fractions. The characterization of the microstructure is carried out with scanning electron microscope. Using electron backscatter diffraction, strain‐induced α′‐martensite is detected within deformation bands in the austenite. The strain hardening curve at −40 °C shows a typical progression for metastable austenitic stainless steels with pronounced strain‐induced α′‐martensite formation and can be divided into four hardening stages. At this temperature, the studied steel achieves the highest strain hardening rate. The amount of martensite increases with decreasing test temperature and reaches a maximum volume fraction of 76 vol% at −40 °C. The highest ductility of 83% is achieved at 40 °C, accompanied by a tensile strength of 732 MPa. The in situ magnetic measurement confirms that the inflection point in the strain hardening curve coincides with the maximum martensite formation rate.

The study evaluates the effect of electrochemical hydrogen charging on the tensile properties and fracture behavior of the plasma tungsten inert gas weld of the high‐alloy austenitic steel X3CrMnNiMoN17‐8‐4 in comparison to the pure base metal (BM). The weld metal exhibits a higher susceptibility to hydrogen embrittlement than the BM, which is mainly expressed by a loss in ductility. Based on the performed electron backscatter diffraction and X‐ray diffraction examinations, this is attributed to the higher amount of δ‐ferrite and the higher dislocation density in the weld zone. Furthermore, fractographic analyses reveal a change in the manner of fracture mode from ductile to brittle fracture starting from the edge in the hydrogen charged samples. The wider area of brittle fracture in the weld seam in relation to the BM indicates that hydrogen penetrates deeper into the material. Consequently, the diffusivity of hydrogen in the weld seam is determined to be significantly higher than in the BM.

The present study deals with the pitting and repassivation behavior of a nickel‐reduced austenitic stainless steel with different nitrogen contents. While nitrogen promoted the resistance to pitting, no significant effect on repassivation was found. The study also aims to address the experimental difficulties in determining repassivation potentials owing to the occurrence of crevice corrosion. Furthermore, the mechanism of the ongoing reactions was investigated, indicating that pitting was initiated in regions where manganese sulfide inclusions were present next to the remaining δ‐ferrite.

In this study, a Ni-reduced austenitic stainless TRIP/TWIP steel with < 5 vol.% δ-ferrite was investigated before and after plasma arc welding and gas tungsten arc welding. The 4-mm-thick hot-rolled sheet was produced as hot-rolled heavy plate on an industrial scale and manufactured as longitudinally welded pipes without filler metal. Microstructural characterization was done using light optical microscope and scanning electron microscope with electron backscatter diffraction (EBSD). The microstructure consisted of non-recrystallized austenite with a small amount of δ-ferrite. The welds exhibited skeletal and lacy δ-ferrite morphologies. ε-martensite and α´-martensite were found in the weld seam after pipe expansion. Further, the mechanical properties were evaluated using tensile test. The results showed a tensile strength of 823 MPa with a uniform elongation of 69% at room temperature. The change of hardness in the weld seam was studied for welded pipe, welded expanded pipe and welded, post-weld heat-treated (PWHT) pipe with Vickers hardness testing. The lowest hardness was achieved after PWHT. The corrosion resistance tests were conducted in chloride containing environment. The results showed that the susceptibility to pitting corrosion increased with the degree of deformation. Furthermore, the weld metal and heat-affected zone exhibited local attack whereas the base metal seemed unaffected.

In this paper, the effect of microstructure of a thick-walled rotor shaft for wind turbines on fracture toughness properties has been investigated. The relevant nodular cast iron grade EN-GJS-600-3 was processed using chill casting technology. Due to different solidification conditions over the wall thickness, heterogeneous microstructures were formed. To illustrate the influence of the microstructure gradient caused by chill casting technology, specimens were taken from different sample positions in the cross section of the casting component. A detailed metallographic analysis revealed essential differences in microstructure. The crack growth resistance under quasi-static loading conditions and the fatigue crack propagation under cyclic loading conditions were measured. The results of the static fracture mechanics investigations revealed that fracture toughness is strongly influenced by the microstructure of this pearlitic ductile iron grade. On the other hand, cyclic fracture mechanics analysis showed that the complex formation of the microstructure has only a minor effect on the fatigue threshold value, but microstructure has a significant effect on the stable crack growth. For the assumed load cases, it was shown that microstructure can be a dominant factor on the mechanical and fracture toughness properties.

Austenitic steels are known to exhibit a low hydrogen diffusion coefficient and hence a good resistance to hydrogen embrittlement. Therefore, it is an experimental challenge to investigate their hydrogen diffusion properties. In this study, the electrochemical perme-ation technique is used to determine the hydrogen diffusion coefficients in different pre -deformed states (4 = 0, 0.32, 0.39, 0.49) of the high-alloy austenitic TRIP steel X3CrMnNiMoN17-8-4 in a temperature range of 323 K-353 K. In combination with micro -structural analysis, a correlation between phase transformation from g-austenite to a'- martensite and dislocation density is shown. As a result of the lattice transformation from fcc to bcc, the diffusion rate of hydrogen is significantly increased (Dapp, 4 = 0-= 3.6 x 10-12 cm2 s-1, Dapp, 4 = 0.32 = 1.6 x 10-11 cm2 s-1at 323 K). With higher degrees of deformation, the dislocation density also increased in the martensite islands, resulting in a degressive growth of the diffusion coefficient (Dapp, 4 = 0.39 = 5.3 x 10-11 cm2 s-1, Dapp, 4 = 0.49 = 1.1 x 10-10 cm2 s-1at 323 K). Moreover, detailed calculations are performed to describe the way of hydrogen trapping and to give a possible mechanism of diffusion.(c) 2022 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

The main objective of this work was to obtain information about the hydrogen diffusion behaviour in a cold-worked austenitic stainless steel (X3CrMnNiMoN17-8-4) in which deformation-induced martensite formation occurs during mechanical deformation. Three different states of pre-deformation (31 %, 39 % and 49 %) that showed induced phase transformation from austenite to α’martensite as well as the solution-annealed material were part of this study. All samples were charged with hydrogen in a 0.1 M NaOH solution. This charging took place electrolytic with 10 mA cm-2 at three different temperatures (50 °C; 65 °C and 80 °C) in the double cell according to Devanathan and Stachurski. Due to the very slow diffusion of hydrogen through austenite, the samples were not charged until the equilibrium state was reached. To find out the necessary diffusion parameters, the data were fitted with numerical optimisation. Using this method, the effective diffusion coefficients of charging could be determined for all material states. The study also contains microscopic analyses to visualize the effect of cold working on the microstructure of the material. The appearance of α’-martensite significantly contributes to the susceptibility to hydrogen uptake leading to increasing diffusion coefficients in relation to higher pre-deformation.

The effect of the spatial orientation of e‐coated hot dip galvanized test sheets on edge corrosion is investigated. Therefore paint delamination from corrosion sample edges at different steps in time of samples at different angles relative to the horizontal during a corrosion test is analysed. Two general relations are found: Horizontally oriented edges exhibit significantly increased coating delamination compared with vertically oriented edges. This is due to increased exposure to the electrolyte, resulting from the pinning of electrolyte droplets along the upper edge. With increasing angular displacement relative to the ground, electrolyte exposure and edge delamination decrease. The edges of the upward‐facing specimen side showed a higher delamination width compared with the downward‐facing side at the same angle. These results are supported by electrochemical impedance spectroscopy and a wetting test. Ultimately, a semi‐empirical model to numerically predict the edge delamination over time, incorporating electrochemical impedance spectroscopy and polarization curves, is presented.