Hydrogen Diffusion and Trapping Effects in Low and Medium Carbon Steels for Subsurface Reinforcement in the Proposed Yuc
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INTRODUCTION
CARBON steels have been considered as candidates for rock bolts and I-beams for the subsurface construction materials for the proposed Yucca Mountain (YM) repository. The environment prevailing in the repository may promote corrosion. Understanding the diffusivities of hydrogen through a membrane is significant to the long-term stability of the materials, especially if the steels have significant concentration defects, such as dislocations and stacking faults, among others.[1–4] With regard to the effect of sulfur, Chou and SzklarskaSmialowska[5] examined the hydrogen permeation and mechanical behavior of carbon steels with 0.003 and 0.025 wt pct sulfur content and reported that low sulfur steels are more susceptible to hydrogen effects due to lattice hydrogen mobility. Boniszewski and Moreton[6] showed that carbon steels with higher sulfur contents (~0.25 pct) were more resistant to hydrogen. Garet et al.[7] reported that sulfur containing inclusions in Cr-Mo low alloy pipeline steels are affected by diffusion of hydrogen. Kobayashi et al.[8] emphasized that the JOSHUA LAMB, Graduate Research Assistant, and DHANESH CHANDRA, Professor, are with the Metallurgical & Materials Engineering, College of Engineering, University of Nevada, Mail Stop 388, Reno, NV 89557, USA. Contact e-mail: dchandra@unr. edu VENUGOPAL ARJUNAN, Research Scientist, is formerly with University of Nevada, Reno, USA, is now with the Vikram Sarabhi Space Centre, Thiruvananthapuram, Kerela 695022, India. VINAY DEODESHMUKH, Graduate Research Assistant, is formerly with University of Nevada, Reno, USA, is now with the Materials Science and Engineering Department, Iowa State University, Ames, IA 50011, USA. JAAK DAEMEN, Professor, is with the Mining Engineering Department, MS 173, Mackay School of Mines, University of Nevada, Reno, NV 89557, USA. RAU´L B. REBAK, Scientist, is with the Lawrence Livermore Laboratory, Livermore, CA 94550, USA. 348—VOLUME 38A, FEBRUARY 2007
morphology of sulfide inclusions is more important than the sulfur content in steel. Pressouyre et al.[9] suggested that a greater density of sulfide inclusions in low alloy steels suppresses the permeation of hydrogen to the cracking sites, thus improving the hydrogen embrittlement resistance. In recent years, the Devanathan–Stachurski permeation method has been used to study diffusion and transport behavior of hydrogen in steels in view of its sensitivity and also to observe trapping effects.[10–13] The objectives of the present investigation are (a) to compare the diffusion and trapping behaviors of low and medium carbon steels, (b) to calculate their irreversible trapping, and (c) to measure the extent of hydrogen absorption in YM-simulated ground water at different electrolyte concentrations in order to examine the effect of various ions within the electrolyte. II.
EXPERIMENTAL METHODS
A. Materials and Specimen Preparation The low and medium carbon steels with different C, Mn, and S contents used in the present investigation were furnished by the United States Department of E
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