Effects of Interstitial Impurities on Dislocation Trapping of Hydrogen in Iron

Abstract

The diffusion coefficient of hydrogen in iron with various interstitial impurity (C, N) contents has been measured at 298 K by an electrochemical permeation method. The diffusivity of hydrogen is significantly reduced by cold-working. In commercially pure iron specimens (high C, N specimens), the diffusivity of hydrogen is slightly restored by aging at room temperature after cold-working. In decarburized-denitrided specimens (low C, N specimens), however, this change by aging is not observed. Annihilation of dislocations by heat treatments causes recovery of the diffusion coefficient. That is, dislocations serve as trapping sites for hydrogen, and the formation of atmosphere of interstitial impurities (C, N) around dislocations weakens the trapping effect of dislocations. The diffusion coefficient of hydrogen has been analyzed on the basis of the trapping theory, and the trap density (i.e., the ratio of the number of the trapping sites to that of total lattice sites) has been calculated. The trap density before the formation of the C, N atmosphere around dislocations is, within experimental error, proportional to the dislocation density.

Micro-Portion Image Analysis of Light Elements in Fe–Cr Based Alloys by Time-of-Flight Secondary Ion Mass Spectrometry

“…One of the limitations in the study on hydrogen embrittlement is the difficulty of microscopic analysis of hydrogen in steels compared to other light elements, since the solubility of hydrogen in the steels at about room temperature is low. [3][4][5][6][7] Thus, it is necessary to establish analysis methods of the microscopic distribution of hydrogen experimentally, although the mechanism of hydrogen embrittlement has been mainly investigated based on atomistic models [8][9][10][11] and the mechanical properties and the relevant phenomena have been investigated in detail. [12][13][14][15] On the other hand, analytical methods for investigating the distribution of hydrogen in steels are limited, as the use of vacuum is generally required in such analytical apparatuses.…”

“…We conclude that the deuterium diffused out of the sample at room temperature, as the diffusivity of hydrogen is quite high in body-centered-cubic (bcc) Fe-based alloys. [4][5][6][7] However, it is noted that deuterium was detected in the depth profiles of the duplex stainless steel charged with 2 H 2 O, while it was not detected after annealing. This indicates that deuterium diffuses out of the sample during annealing, and the diffusion of deuterium is slow in the duplex stainless steel at room temperature.…”

Thermal Desorption Analysis of Hydrogen in High Strength Martensitic Steels

“…Au and Birnbaum [2] first reported the interaction between carbon and hydrogen in iron. Indeed, Hagi and Hayashi [3] reported that the potency of dislocation for hydrogen trapping was lessened considerably presumably by segregation of carbon to dislocations. Moreover, retained austenite, transition carbides, and alloy carbides, which form during tempering, may serve as potential and often effective trapping sites of hydrogen.…”

Effects of Static and Dynamic Strain Aging on Hydrogen Embrittlement in TWIP Steels Containing Al

“…8,12,13) Carbon segregation to the dislocations by static strain aging is known to decrease the number of hydrogen trapping sites due to site competition, resulting in a decrease in the diffusible hydrogen content. [24][25][26] Toji et al 25) investigated the effects of low temperature heat treatment on the hydrogen uptake in ferritic steels. They showed that the hydrogen uptake was suppressed by increasing the solute carbon content when the steels were heat treated at low temperature.…”