A SIMS Study of the Diffusion and Trapping of Deuterium in 302 Stainless Steel
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INTRODUCTION
SINCE Darken and Smith ~first proposed that the diffusion of hydrogen in steel was complicated by trapping by lattice imperfections, experimental evidence supporting that view has been obtained by a variety of research investigators. This has been summarized in a number of recent review articles such as those by Wert 2 and Hirth) Among the lattice defects that may trap hydrogen, dislocations are often cited. The core and the strain field surrounding the dislocation provide sites at which hydrogen is retained for periods longer than those for normal interstitial sites. In 1951 Bastien and A z o u 4 proposed that if hydrogen atoms are attracted to dislocations they might even be dragged along by the dislocations when they move. This view seemed to be supported by the experimental work of one of the authors in 1959 when he reported that the plastic deformation of vacuum melted iron caused an enhanced evolution of hydrogen from the surface .5 The increased evolution of hydrogen occurred while the plastic deformation was taking place and was believed to be associated with the dislocation motion. Other experiments carried out in nickel since that time seem to provide confirmation of the e f f e c t . 6'7'8 While much of the research on the diffusion and trapping of hydrogen in steel in the past has been carded out on low alloy steel, there have been some studies carried out on stainless steel. 9'1~ Louthan, Donovan, and Caskey H also studied tritium diffusion in 304L stainless steel and explained some of their results by hydrogen transport by moving dislocations. Studies in plastically deformed stainless steel can b e complicated by the conversion of some of the fcc austenite to bcc martensite o r hcp martensite. The diffusion of hydrogen is certain to be considerably faster in a ' martensite than in austenite. The present work was carried out to obtain a better understanding of both the trapping and the possible transport R. C. FRANK is Director of Research with Augustana Research Foundation, Rock Island, IL 61201. J.E. BAKER, Senior Research Chemist, Materials Research Laboratory, and C.J. ALTSTETTER, Professor of Metallurgy, are both with the University of Illinois at Urbana-Champaign,
Urbana, IL 61801. Manuscript submittedJune i0, 1981. METALLURGICAL TRANSACTIONS A
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of hydrogen by dislocations in nominally austenitic stainless steel. The diffusion coefficients for hydrogen in stainless steels are relatively small at room temperature so that electrolytic charging of hydrogen into the surface for a few hours would be expected to result in only very shallow penetration. If the stainless steel remained at room temperature for a short period after the introduction of hydrogen was terminated, the surface concentration would be expected to go to zero, and evolution would take place from the surface rather rapidly. Thus, the concentration distribution would peak just below the surface with a gradual decrease inwardly, The questions addressed in this study were: What happens to such a distribution of hyd
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