Abstract
It is well known that the presence of hydrogen decreases the mechanical properties of ferritic steels, giving rise to the phenomenon known as hydrogen embrittlement (HE). The sensitivity to HE increases with the strength of the steel due to the increase of its microstructural defects (hydrogen traps), which eventually increase hydrogen solubility and decrease hydrogen diffusivity in the steel. The aim of this work is to study hydrogen diffusivity in a 42CrMo4 steel submitted to different heat treatments—annealing, normalizing and quench and tempering—to obtain different microstructures, with a broad range of hardness levels. Electrochemical hydrogen permeation tests were performed in a modified Devanathan and Stachursky double-cell. The build-up transient methodology allowed the determination of the apparent hydrogen diffusion coefficient, Dapp, and assessment of its evolution during the progressive filling of the microstructural hydrogen traps. Consequently, the lattice hydrogen diffusion coefficient, DL, was determined. Optical and scanning electron microscopy (SEM) were employed to examine the steel microstructures in order to understand their interaction with hydrogen atoms. In general, the results show that the permeation parameters are strongly related to the steel hardness, being less affected by the type of microstructure.
Highlights
In a global context of environmental awareness, the utilization of hydrogen as an energy source has been the subject of intensive study in the last few years [1]
The HV30 measuredof onall each steel42CrMo4 grade is provided in Table
The present work studies the influence of the steel microstructure on hydrogen permeation by means of partial build-up permeation transient tests
Summary
In a global context of environmental awareness, the utilization of hydrogen as an energy source has been the subject of intensive study in the last few years [1]. A large number of catastrophic structural failures have been attributed to HE [6,7]. These kinds of failure occur under stress levels lower than the design stress; they are brittle in appearance—with minimum previous plastic deformation—and very difficult to predict. It must be borne in mind that the deterioration of mechanical properties—reduction in strength, fracture toughness and ductility, and crack growth rate enhancement [8,9]—due to the presence of internal hydrogen, increases with the strength of the steel [10]
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