09:00-09:45
Hydrogen related challenges for the steelmaker
Dr Richard Thiessen, Thyssenkrupp Steel Europe, Germany
Abstract
The modern steelmaker of advanced high-strength steels has always been challenged with the conflicting targets of increased strength while maintaining or improving ductility. These new steels help the transportation sector, including that of automotive, achieve goals of increased passenger safety and reduced emissions. With increasing tensile strengths, certain steels exhibited an increased sensitivity towards hydrogen embrittlement. Characterizing the material’s sensitivity in as-delivered condition has been developed and accepted (SEP1970), but the complexity of the stress-states that can induce an embrittlement together with the wide range of applications for high strength steels make the development of a standardized test for hydrogen embrittlement under in-service conditions extremely challenging. Some proposals for evaluating the material’s sensitivity give an advantage to materials with a low starting ductility. In spite of this, newly developed materials can have a higher original elongation while suffering only a moderate reduction in elongation due to hydrogen. This work presents a characterization of new materials and their sensitivity towards hydrogen embrittlement.
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Dr Richard Thiessen, Thyssenkrupp Steel Europe, Germany
Dr Richard Thiessen, Thyssenkrupp Steel Europe, Germany
Richard Thiessen studied Materials Engineering in Canada (University of Alberta), Computational Mechanics in Germany (University of Stuttgart), and completed his PhD in Materials Science from the TU Delft in 2006. His thesis proposed a multi-scale methodology for using physically-based phase-field simulations to understand the microstructure evolution during welding. After a period as post-doc at the Max-Planck-Institute for Iron Research where he investigated damage mechanisms in multi-phase steels, Richard joined the materials development team within R&D at thyssenkrupp Steel Europe in Duisburg, Germany (2007). Richard’s career at thyssenkrupp started with fundamental research topics such as hydrogen embrittlement and comparisons between lab conditions and industrial production, but soon led to development work on 3rd generation advanced high strength steels. He has managed several EU projects with topics ranging from the influence of microstructure on the susceptibility of steels towards hydrogen embrittlement to optimization of “quench and partitioning” steels for industrial applications. Currently Richard leads a group of engineers working on new steel concepts within the materials development team at Thyssenkrupp Steel Europe.
09:45-10:30
Hydrogen embrittlement in structural steels
Professor Norman Fleck FRS, University of Cambridge, UK
Abstract
Hydrogen embrittlement reduces both the ductility and toughness of steels, and such degradation of performance is important in a range of applications from energy storage in transport (hydrogen tanks in automobiles) to the energy supply industry (such as subsea pipelines that are exposed to hydrogen as a consequence of cathodic protection measures).
In the first part of the presentation, it is argued that the reduction in strength and toughness by hydrogen is associated with the embrittlement of grain boundaries and other trapping sites for hydrogen. Elementary kinetic theory suggests that embrittlement is associated with trap binding energies in the range -20 to -30 kJ/mol at room temperature. In order to predict the reduction in macroscopic tensile strength due to the presence of hydrogen at grain boundaries, it is argued that the cohesive strength of the grain boundaries is reduced by hydrogen. This can be modelled in two ways:
(i) macro-level: no elevation in local tensile stress at the grain boundary and the presence of hydrogen reduces the macroscopic cohesive strength to the order of the yield strength;
(ii) meso-level: a stress raising defect (such as a short crack) exists at the grain boundary such that the local stress level much exceeds the yield strength; the presence of hydrogen reduces the cohesive strength but it remains much above the yield strength.
In the second part of the talk, an analytical and numerical analysis is given of the electro-permeation test. This test is commonly used to measure the diffusion behaviour of hydrogen in engineering steels (and other alloys). There is no consensus in the literature on the values of trap binding energy and trap density for particular classes of trap, and this is in-part due to misinterpretation of permeation data, and by not varying the initial concentration of hydrogen over a sufficiently wide range. Our analysis reveals regimes of behaviour, and the resulting permeation map can be used to obtain a clear and unique interpretation of the data.
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Professor Norman Fleck FRS, University of Cambridge, UK
Professor Norman Fleck FRS, University of Cambridge, UK
Norman Fleck has been Professor of Mechanics of Materials at University of Cambridge Engineering Department since 1997. His research is centred on the mechanics of microstructure, ranging from failure of composites to lattice materials. He has pioneered the use of strain gradient plasticity theory to probe size effects in metals.
11:00-11:45
Hydrogen embrittlement investigated by novel critical experiments
Tarlan Hajilou, Norwegian University of Science and Technology, Norway
Abstract
Among the experimental approaches to the hydrogen induced degradation, small scale testing has the capability to resolve the hydrogen interaction with microstructure and the crystal defects in the same length scale. However, small scale testing inquiries in situ examination to avoid hydrogen gradient or depletion on the testing materials. In this approach, in situ nanoindentation experiment capable of registering the onset of plasticity in a sub micro meter scale showed a reduction in dislocation nucleation energy in the presence of hydrogen. Going one step forward, in this study, we used the in situ electrochemical cantilever bending test method to probe the effect of hydrogen on the crack propagation in the micron sized notched beams. The experimantal setup is the integration of a miniaturized three electrode electrochemical cell inside a nanoindenter. This experimental method has the advantage of providing a complete overview of the plasticity and dislocations on the entire sample by post-mortem analyses. For this study Fe- 3wt% Si single and bi-crystal microcantilevers have been investigated. Mechanical behavior of the beams bent under hydrogen charging condition are compared with the air condition. The load-displacement curves reveal a continuous decrease in the flow stress for the cantilevers bent within the presence of hydrogen. Crack initiation and propagation are examined in the presence of hydrogen while the notch blunting occurs for the beams bent< in the air. Post-mortem cross-sectional EBSD analyses of the beams showed a localized plastic region for the hydrogen condition comparing with the air one.
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Tarlan Hajilou, Norwegian University of Science and Technology, Norway
Tarlan Hajilou, Norwegian University of Science and Technology, Norway
Tarlan Hajilou, is a PhD candidate at Norwegian University of Science and Technology. She received the B.Sc. degree in extractive metallurgy in 2010, and the M.Sc. in degree metallic materials selection and characterization in 2012, from Sahand University of technology in Tabriz, Iran. For her master thesis, she did research on the nanostructured, low temperature bainitic steels.
She is doing her PhD, under supervision of Professor Afrooz Barnoush in the field of Hydrogen Embrittlement.
11:45-12:30
Hydrogen induced stress cracking in steels – examples of failures and numerical modelling
Dr Vigdis Olden, SINTEF Materials and Nanotechnology, Trondheim, Norway
Abstract
The occurrence of cracks in offshore structures and pipelines is an environmental and safety risk that should be eliminated. Hydrogen Induced Stress Cracking (HISC) has been a challenge in the Norwegian oil & gas industry since the late 1990s. The main sources of hydrogen are cathodic protection and to some extent also hydrogen from welding. Hydrogen induced stress cracking from cathodic protection is a result of interconnected mechanisms involving electrochemistry, diffusion, metallurgy and hydrogen degradation at different length scales from the nano- to the macro-scale.
Safe service requires predictive tools for assessing the structural integrity under CP conditions. For several years our group at SINTEF has worked with numerical models applying hydrogen informed cohesive zone elements to model HISC fracture as well as hydrogen-induced fracture in general.
Numerical simulation of hydrogen embrittlement requires a coupled approach; on one side, the models describing hydrogen transport must account for local mechanical fields, while on the other side, the effect of hydrogen on the accelerated material damage must be implemented into the model describing crack initiation and growth.
The talk will include examples of HISC fractures from the oil and gas industry as well as a review of numerical cohesive zone approaches for the prediction of hydrogen embrittlement.
13:45-14:30
Effects of hydrogen on fatigue crack growth in steel
Professor Hisao Matsunaga, Kyushu University, Japan
Abstract
In the context of the fatigue life design of components, particularly those destined for use in hydrogen refueling stations and fuel cell vehicles, it is important to understand the hydrogen-induced, fatigue crack growth (FCG) acceleration in steels. In the presentation, existing studies on the hydrogen-induced, FCG acceleration in various steels are first briefly reviewed, together with the acceleration mechanism and some of its influencing factors. The focus is then placed on the peculiar frequency dependence of the hydrogen-induced, FCG acceleration in steels. In a high-frequency regime (e.g., 10 ~ 0.1 Hz), the ratio of hydrogen-induced, FCG acceleration is seen to gradually increase with a decrease in test frequency, later reaching a peak. To justify the interpretation of the mechanism based on the hydrogen-enhanced successive fatigue crack growth (HESFCG) model, using both “internal” and “external” hydrogen, some critical experiments were performed on two types of material: Type 304 stainless steel and ductile cast iron.
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Professor Hisao Matsunaga, Kyushu University, Japan
Professor Hisao Matsunaga, Kyushu University, Japan
Hisao Matsunaga received the degree of Dr. Eng. at Department of Mechanical Engineering of Kyushu University in 2002. After I worked in the same department as a Lecturer until 2005, when Matsunaga moved to Department of Mechanical Engineering of Fukuoka University as an Associate Professor. In 2012, he moved back to Kyushu University as an Associate professor. During my 15-year career in the Universities, Matsunaga has been studying metal fatigue and hydrogen embrittlement. From 2012, he concurrently belongs to the Research Center for Hydrogen industrial Use and Storage (HYDROGENIUS) in Kyushu University, and he is involved in a NEDO project aimed at the revision of domestic regulations and standards for structural materials used for hydrogen service. Matsunaga is also contributing actively to the international discussion about code and standard for hydrogen components in SAE, CSA and IEA.