TY - THES

T1 - Design of hydrogen resistant high-strength steel fasteners

AU - Pötz, Melanie

N1 - embargoed until 20-09-2026

PY - 2021

Y1 - 2021

N2 - The aim of this thesis is to contribute to the determination of design guidelines for materials and manufacturing of high-strength steel fasteners with reduced susceptibility to hydrogen embrittlement. This is achieved using the so-called "beneficial trapping" concept where energetically favorable "traps" extract hydrogen from the interstitial lattice and consequently hinder its adverse effects. For quantifiability, the frequency and binding energy of the traps must be known. This concept is used as bottom-up microstructural approach, thus enabling the incorporation of production routes and microstructure evolution and the study of their interaction with hydrogen on a theoretical basis. For the use of this concept, detailed knowledge of the types and corresponding numbers of traps is necessary. Therefore, on the one hand, the manufacturing process from wire to fastener is investigated using a forming simulation. These results are taken into account for the calculation of the number of traps. On the other hand, trap densities depending on certain microstructural features of the material are calculated. The resulting trap densities in combination with their respective binding energies give a generalized trapping description. This allows to investigate the distribution of a given total amount of hydrogen between interstitial lattice and traps in a material for different production stages and material compositions using simulation methods. The results show that the detrimental mobile hydrogen concentration in the component can be minimized by a sufficient amount of small carbides. The existence of such precipitates but in an insufficient amount and/or size leads to a much higher mobile hydrogen concentration at a constant total concentration. In addition, the manufacturing process of the fastener influences the local distribution of mobile as well as trap hydrogen concentration in it due to the resulting plastic deformation. The presence of an inhomogeneous microstructure, i.e., grain size, does also contribute to this local dependence. Summarized, this approach is a first step for the examination of the hydrogen trapping capacity along the manufacturing route of high-strength steel fasteners and enables the consideration of further parameters like temperature or deformation. This is of great relevance for the future design of manufacturing processes and materials since this work represents a theoretical basis for investigating the interaction of the manufacturing routes and the microstructure with hydrogen.

AB - The aim of this thesis is to contribute to the determination of design guidelines for materials and manufacturing of high-strength steel fasteners with reduced susceptibility to hydrogen embrittlement. This is achieved using the so-called "beneficial trapping" concept where energetically favorable "traps" extract hydrogen from the interstitial lattice and consequently hinder its adverse effects. For quantifiability, the frequency and binding energy of the traps must be known. This concept is used as bottom-up microstructural approach, thus enabling the incorporation of production routes and microstructure evolution and the study of their interaction with hydrogen on a theoretical basis. For the use of this concept, detailed knowledge of the types and corresponding numbers of traps is necessary. Therefore, on the one hand, the manufacturing process from wire to fastener is investigated using a forming simulation. These results are taken into account for the calculation of the number of traps. On the other hand, trap densities depending on certain microstructural features of the material are calculated. The resulting trap densities in combination with their respective binding energies give a generalized trapping description. This allows to investigate the distribution of a given total amount of hydrogen between interstitial lattice and traps in a material for different production stages and material compositions using simulation methods. The results show that the detrimental mobile hydrogen concentration in the component can be minimized by a sufficient amount of small carbides. The existence of such precipitates but in an insufficient amount and/or size leads to a much higher mobile hydrogen concentration at a constant total concentration. In addition, the manufacturing process of the fastener influences the local distribution of mobile as well as trap hydrogen concentration in it due to the resulting plastic deformation. The presence of an inhomogeneous microstructure, i.e., grain size, does also contribute to this local dependence. Summarized, this approach is a first step for the examination of the hydrogen trapping capacity along the manufacturing route of high-strength steel fasteners and enables the consideration of further parameters like temperature or deformation. This is of great relevance for the future design of manufacturing processes and materials since this work represents a theoretical basis for investigating the interaction of the manufacturing routes and the microstructure with hydrogen.

KW - Wasserstoffversprödung

KW - Wasserstofffallen

KW - Verbindungselemente aus hochfestem Stahl

KW - Finite-Elemente-Modellierung

KW - Stahldesign

KW - Herstellung von Verbindungselementen

KW - Mikrostruktur

KW - hydrogen embrittlement

KW - hydrogen trapping

KW - high-strength steel fasteners

KW - finite element modeling

KW - steel design

KW - fastener manufacturing

KW - microstructure

M3 - Master's Thesis

ER -