Linking Ab Initio Data on Hydrogen and Carbon in Steel to Statistical and Continuum Descriptions

Abstract

Abstract:We present a selection of scale transfer approaches from the electronic to the continuum regime for topics relevant to hydrogen embrittlement. With a focus on grain boundary related hydrogen embrittlement, we discuss the scale transfer for the dependence of the carbon solution behavior in steel on elastic effects and the hydrogen solution in austenitic bulk regions depending on Al content. We introduce an approximative scheme to estimate grain boundary energies for varying carbon and hydrogen population. We employ this approach for a discussion of the suppressing influence of Al on the substitution of carbon with hydrogen at grain boundaries, which is an assumed mechanism for grain boundary hydrogen embrittlement. Finally, we discuss the dependence of hydride formation on the grain boundary stiffness.

Modeling Bainitic Transformations during Press Hardening

“…For a transfer to larger scale descriptions, which do not require this detailed modeling, an effective approach ascribing reduced elastic constants to a “soft” grain boundary allows to capture this effect without spatially resolving the grain boundary contour, e.g., in simulations of bainitic microstructures [ 85 ]. A quantitative matching between the microscopic and mesoscopic descriptions, including a perspective to generalize the approach to precipitation near interfaces between different phases (e.g., carbides near interfaces between ferrite and austenite in bainitic steels) using phase field approaches is discussed in [ 86 ].…”

Influence of Interface Proximity on Precipitation Thermodynamics

“…To transfer the microscopic shear coupling effect to a larger scale, which is useful, e.g., for describing the carbide formation at or inside bainitic sheaves, we follow the strategy developed in [13]. The idea is to introduce an elastic soft layer in the grain boundary region, which can accommodate the slip component at the shear-coupled grain boundary in an effective manner.…”

“…This effect is expected to play a role whenever precipitates show a lattice mismatch with the matrix, and the effect will play the largest effect for coherent interfaces between them. We will discuss here two limiting cases that we have elaborated during the past years for phase separation near free and confined surfaces [12,13] and shear-coupled grain boundaries [14] and show what may happen near interfaces between different phases as a consequence of coherent-incoherent transitions. The aforementioned two limiting cases also lead to a distinction of what we call here "reactive" and "passive" surfaces and interfaces, which influence the range of interaction between interfaces and precipitates in the spirit of a strong thermo-chemo-mechanical coupling.…”

First-Principles Approaches to Metals, Alloys, and Metallic Compounds

“…By considering various effects, they arrive at a fully quantitative agreement for the chemical potential without adjustable parameters. Likewise, Weikamp et al [5] present a selection of scale-transfer approaches from the electronic to the continuum regime for topics relevant to hydrogen embrittlement. Eventually, they develop an approximative scheme to estimate grain-boundary energies for varying C and H contents, and they consider the dependence of hydride formation on the grain-boundary stiffness.…”