Dynamic behavior of hydrogen desorption from pure iron and inconel 625 during elastic and plastic deformations

K Takai,H Shoda

doi:10.1590/s1517-70762010000200026

Abstract

Dynamic behavior of hydrogen desorption from pure iron with a body-centered-cubic lattice and Inconel 625 with a face-centered-cubic lattice was examined during tensile deformation using a quadrupole mass spectrometer in a vacuum chamber integrated with a tensile testing machine. Hydrogen desorption from hydrogen-charged specimens was detected under various strain rates and cyclic stresses. Hydrogen desorption rarely increased under elastic deformation. In contrast, it increased rapidly at the proof stress when plastic deformation began, reached its maximum, and then decreased gradually with increasing applied strain for both pure iron and Inconel 625. This desorption behavior is closely related to hydrogen dragging by moving dislocations. The thermal desorption analysis results showed that the amount of desorbed hydrogen differed at each strain rate. This difference in the amount of desorbed hydrogen transported by dislocations depends on the balance between the hydrogen diffusion rate and mobile dislocation velocity.

Highlights

One of the authors has reported that there is a close relationship between the trapping states of hydrogen in metals and hydrogen embrittlement [1]
The hydrogen desorption behavior was similar to that of the pure iron specimen. It was markedly small under elastic deformation. It increased rapidly at the strain beyond the proof stress when plastic deformation began, reached its maximum, decreased gradually as plastic strain increased, and a sharp peak appeared at fracture
Hydrogen desorption did not increase under cyclic elastic stress. It increased rapidly at the strain beyond the proof stress when plastic deformation began, reached its maximum, decreased gradually with increasing plastic strain, and a sharp peak appeared at fracture

Summary

Introduction

One of the authors has reported that there is a close relationship between the trapping states of hydrogen in metals and hydrogen embrittlement [1] It has been demonstrated with cold-drawn pearlite steels that a weakly trapped state of hydrogen diffusive at room temperature causes a considerable reduction of fracture strain in spite of a low hydrogen content. The results revealed that plastic straining markedly increased lattice defects in the presence of hydrogen in hydrogen-charged specimens. It is to be noted that hydrogen was not necessarily requisite for embrittlement in the final fracture stage [7] These findings demonstrated that an increased density of lattice defects such as vacancies and their clusters introduced by both straining and weakly trapped diffusive hydrogen was a direct factor causing hydrogen embrittlement

Results

Discussion

Conclusion