STP1049

    Influence of Strain on Hydrogen Assisted Cracking of Cathodically Polarized High-Strength Steel

    Published: Jan 1990


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    Abstract

    Evidence is presented that confirms the role of mechanical strain in promoting surface absorption of hydrogen in two high strength steels under cathodic polarization in alkaline 3.5% sodium chloride solution. Data are reported for a 5Ni-Cr-Mo-V steel {896 MPa(130 ksi) yield strength} and is compared to data previously developed for AISI 4340 steel {1207 MPa (175 ksi) yield strength}. Strain induced bare surface generation is shown to substantially influence both alloys' hydrogen cracking susceptibility. Strain enhanced absorption is empirically observed for tensile specimens under slowly straining conditions and is also suggested to explain the hydrogen assisted cracking behavior of slowly strained DCB compact and cantilever beam fracture mechanics specimens with pre-existing fatigue cracks. Enhancement of hydrogen absorption per unit area of bare surface, as determined by straining hydrogen permeation measurements, explain the effect. In the presence of a corroded surface, the kinetics of the hydrogen evolution reaction are modified such that a lower cathodic hydrogen overpotential is observed at a given cathodic current density. This lowers hydrogen absorption at a given applied cathodic current density. Hydrogen permeation rates are increased upon straining independent of changes in the apparent bulk diffusion coefficient. These findings indicate that sustained plus cyclic loading and low-cycle fatigue of steels in seawater are more severe environmental cracking conditions than sustained loading typical of laboratory cantilever beam tests.

    Keywords:

    cracking, environmental effects, adsorption, absorption, diffusion, corrosion, cathodic protection, cyclic loading, dislocation transport, fatigue (materials), film rupture, embrittlement, high strength steel, hydrogen, hydrogen embrittlement, hydrogen evolution, hydrogen permeation, seawater, stress corrosion cracking, sustained load, threshold stress intensity, trapping


    Author Information:

    Scully, JR
    Senior member of Technical Staff, Sandia National Laboratories, Albuquerque, NM

    Moran, PJ
    Associate professor, Corrosion and Electrochemistry Research Laboratory, Department of Materials Science and Engineering, The Johns Hopkins University, Baltimore, MD


    Paper ID: STP24058S

    Committee/Subcommittee: G01.11

    DOI: 10.1520/STP24058S


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