STP743

    Effect of Cyclic Frequency on the Corrosion-Fatigue Crack-Initiation Behavior of ASTM A517 Grade F Steel

    Published: Jan 1981


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    Abstract

    This study was conducted to investigate the effect of cyclic frequency on the corrosion-fatigue crack-initiation behavior in regions of stress concentration in ASTM A517 Grade F steel. The tests were conducted on notched compact tension specimens at a stress ratio of 0.1 in a room-temperature 3.5 percent solution of sodium chloride. The test results showed that the corrosion-fatigue crack-initiation life under full immersion conditions was significantly less than the fatigue-crack-initiation life in air. Moreover, the test results showed no effect of cyclic frequency in the range of 12 to 300 cpm on the corrosion-fatigue life. The data indicate the possible existence of a corrosion-fatigue crack-initiation limit, below which cracks did not initiate, at a ΔK/√ρ of about 172 MPa (25 ksi). This value of ΔK/√ρ corresponds to a maximum stress range, Δσmax, of about 207 MPa (30 ksi) and is one-fourth the value for the fatigue-crack-initiation limit in air.

    Fatigue-crack-initiation tests results on precorroded notched specimens showed a 25 percent reduction in the fatigue-crack-initiation limit. This decrease was attributed to an increase in the stress concentration caused by corrosion pits on the surface of the notch radius.

    Metallographic investigations showed that corrosion-fatigue cracks initiate at corrosion pits on the surface of the notch tip. These cracks initiate as microcracks that form by a sharpening of the corrosion-pit tip under the combined influence of the environment and cyclic loads. No relationship was found between microstructure and corrosion-pit sites.

    Keywords:

    corrosion, corrosion fatigue, crack initiation, cyclic loads, cyclic frequency, crack propagation


    Author Information:

    Taylor, ME
    Cooperative student and division chief, Materials Technology, Research Laboratory, U. S. Steel Corp., Monroeville, Pa.

    Barsom, JM
    Cooperative student and division chief, Materials Technology, Research Laboratory, U. S. Steel Corp., Monroeville, Pa.


    Paper ID: STP28820S

    Committee/Subcommittee: E08.05

    DOI: 10.1520/STP28820S


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