STP600

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

    Published: Jan 1976


      Format Pages Price  
    PDF (268K) 9 $25   ADD TO CART
    Complete Source PDF (8.6M) 9 $82   ADD TO CART


    Abstract

    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.

    Keywords:

    fractography, fatigue (materials), tensile properties, carbon steels, high temperature tests, decarburizing, hydrogen attack


    Author Information:

    Nelson, HG
    Research scientists, Ames Research Center, National Aeronautics and Space Administration, Moffett Field, Calif.

    Moorhead, RD
    Research scientists, Ames Research Center, National Aeronautics and Space Administration, Moffett Field, Calif.


    Paper ID: STP29193S

    Committee/Subcommittee: E08.08

    DOI: 10.1520/STP29193S


    CrossRef ASTM International is a member of CrossRef.