SYMPOSIA PAPER Published: 01 January 1976
STP29193S

Fractography of the High Temperature Hydrogen Attack of a Medium Carbon Steel

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A systematic study was made of the microscopic fracture processes associated with hydrogen attack of a medium carbon steel in a well-controlled, high-temperature, high-purity hydrogen environment. Exposure to a hydrogen pressure and temperature of 3.5 MN/m2 and 575°C was found to progressively degrade room temperature tensile properties with increasing exposure time. After 408 h, the maximum exposure time of this study, yield and ultimate strengths were reduced by more than 40 percent and elongation was reduced to less than 2 percent. Initial fissure formation was found to be associated with managnese rich particles, mostly probably manganese oxide, aligned in the microstructure during the rolling operation. Fissure growth was found to be associated with a reduction in carbide content of the microstructure and was inhibited by the depletion of carbon. The interior surfaces of sectioned fissures or bubbles exhibit both primary and secondary cracking by intergranular separation. The grain surfaces were not smooth and flat but instead were rough and rounded, suggesting a diffusion-associated separation process. Finally, specimens that were failed at room temperature after exposure to hydrogen were found to exhibit mixed mode fracture having varying amounts of intergranular separation, dimple formation, and cleavage, depending on exposure time.

Author Information

Nelson, HG
Ames Research Center, National Aeronautics and Space Administration, Moffett Field, Calif.
Moorhead, RD
Ames Research Center, National Aeronautics and Space Administration, Moffett Field, Calif.
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Details
Developed by Committee: E08
Pages: 88–96
DOI: 10.1520/STP29193S
ISBN-EB: 978-0-8031-4675-4
ISBN-13: 978-0-8031-0360-3