Theoretical evaluation of the role of crystal defects on local equilibrium and effective diffusivity of hydrogen in iron

Hydrogen diffusion and trapping in ferrite is evaluated by quantum mechanically informed kinetic Monte Carlo simulations in defective microstructures. We find that the lattice diffusivity is attenuated by two to four orders of magnitude due to the presence of dislocations. We also find that pipe diffusivity is vanishingly small along screw dislocations and demonstrate that dislocations do not provide fast diffusion pathways for hydrogen as is sometimes supposed. We make contact between our simulations and the predictions of Oriani's theory of ‘effective diffusivity’, and find that local equilibrium is maintained between lattice and trap sites. We also find that the predicted effective diffusivity is in agreement with our simulated results in cases where the distribution of traps is $\textit{spatially homogeneous}$; in the trapping of hydrogen by dislocations where this condition is not met, the Oriani effective diffusivity is in agreement with the simulations to within a factor of two.We are grateful to the European Commission for Funding under the Seventh Framework Programme, Grant No. 263335, MultiHy (multiscale modelling of hydrogen embrittlement in crystalline materials) and Engineering and Physical Sciences Research Council under the HEmS programme grant EP/L014742

On the increase of intrinsic workability and hot working temperature range of M42 ledeburitic super high speed steel in as-cast and wrought states

In order to remain competitive to powder metallurgy and spray forming, further improvements of a classical production route are needed and desired. This paper describes the means by which the intrinsic hot deformability may be improved and the temperature range of the safe hot working extended for AISI M42 super high speed steel, one of the most challenging materials with respect to hot deformability. A special hot compression procedure is described to determine appropriate soaking temperatures of as-cast and semi-wrought states. Moreover, conventional hot compression tests in the extended temperature range (850–1150 °C) and strain rates range 0.001–5 s−1 were carried out. The complex behaviour of carbides is discussed, which depends on the soaking temperature and time, deformation temperature and strain rate. Deformation conditions for improved crushing of initial eutectic carbides networks during the first stages of hot working are identified. Apparent activation energies for hot working in two temperature ranges and constants of the hyperbolic sine function are determined. The microstructure and respective carbides are characterised by field emission scanning electron microscope, optical microscopy, X-ray diffraction and the results compared to equilibrium thermodynamic calculations using ThermoCalc.This work was supported by the Slovenian Research Agency (ARRS) under programme grants P2-0344 and P2-0268

Understanding and mitigating hydrogen embrittlement of steels: a review of experimental, modelling and design progress from atomistic to continuum

Hydrogen embrittlement is a complex phenomenon, involving several length- and timescales, that affects a large class of metals. It can significantly reduce the ductility and load-bearing capacity and cause cracking and catastrophic brittle failures at stresses below the yield stress of susceptible materials. Despite a large research effort in attempting to understand the mechanisms of failure and in developing potential mitigating solutions, hydrogen embrittlement mechanisms are still not completely understood. There are controversial opinions in the literature regarding the underlying mechanisms and related experimental evidence supporting each of these theories. The aim of this paper is to provide a detailed review up to the current state of the art on the effect of hydrogen on the degradation of metals, with a particular focus on steels. Here, we describe the effect of hydrogen in steels from the atomistic to the continuum scale by reporting theoretical evidence supported by quantum calculation and modern experimental characterisation methods, macroscopic effects that influence the mechanical properties of steels and established damaging mechanisms for the embrittlement of steels. Furthermore, we give an insight into current approaches and new mitigation strategies used to design new steels resistant to hydrogen embrittlement

Understanding and mitigating hydrogen embrittlement of steels: a review of experimental, modelling and design progress from atomistic to continuum

Hydrogen embrittlement is a complex phenomenon, involving several length- and timescales, that affects a large class of metals. It can significantly reduce the ductility and load-bearing capacity and cause cracking and catastrophic brittle failures at stresses below the yield stress of susceptible materials. Despite a large research effort in attempting to understand the mechanisms of failure and in developing potential mitigating solutions, hydrogen embrittlement mechanisms are still not completely understood. There are controversial opinions in the literature regarding the underlying mechanisms and related experimental evidence supporting each of these theories. The aim of this paper is to provide a detailed review up to the current state of the art on the effect of hydrogen on the degradation of metals, with a particular focus on steels. Here, we describe the effect of hydrogen in steels from the atomistic to the continuum scale by reporting theoretical evidence supported by quantum calculation and modern experimental characterisation methods, macroscopic effects that influence the mechanical properties of steels and established damaging mechanisms for the embrittlement of steels. Furthermore, we give an insight into current approaches and new mitigation strategies used to design new steels resistant to hydrogen embrittlement

Correction to: Understanding and mitigating hydrogen embrittlement of steels: a review of experimental, modelling and design progress from atomistic to continuum (Journal of Materials Science, (2018), 53, 9, (6251-6290), 10.1007/s10853-017-1978-5)

The original paper contains a mistake in the acronym AIDE. The AIDE acronym mistake occurs in the title of the section heading and in the following text on p. 6276, and in the text in the section “Discussion and outlook on the HE mechanisms” on p. 6277

Understanding and mitigating hydrogen embrittlement of steels: a review of experimental, modelling and design progress from atomistic to continuum

Hydrogen embrittlement is a complex phenomenon, involving several length- and timescales, that affects a large class of metals. It can significantly reduce the ductility and load-bearing capacity and cause cracking and catastrophic brittle failures at stresses below the yield stress of susceptible materials. Despite a large research effort in attempting to understand the mechanisms of failure and in developing potential mitigating solutions, hydrogen embrittlement mechanisms are still not completely understood. There are controversial opinions in the literature regarding the underlying mechanisms and related experimental evidence supporting each of these theories. The aim of this paper is to provide a detailed review up to the current state of the art on the effect of hydrogen on the degradation of metals, with a particular focus on steels. Here, we describe the effect of hydrogen in steels from the atomistic to the continuum scale by reporting theoretical evidence supported by quantum calculation and modern experimental characterisation methods, macroscopic effects that influence the mechanical properties of steels and established damaging mechanisms for the embrittlement of steels. Furthermore, we give an insight into current approaches and new mitigation strategies used to design new steels resistant to hydrogen embrittlement