STP462: The Influence of Salt Water on Fatigue-Crack Growth in High-Strength Structural Steels

    Crooker, TW
    Materials Research Engineer and Head of Structural Metals Criteria Section, Naval Research Laboratory, Washington, D.C.

    Lange, EA
    Materials Research Engineer and Head of Structural Metals Criteria Section, Naval Research Laboratory, Washington, D.C.

    Pages: 14    Published: Jan 1970


    Abstract

    Fatigue-crack growth is a potential failure mechanism that can be strongly influenced by a salt-water environment. This paper discusses fatigue-crack-propagation studies performed on three high-strength structural steels: 9Ni-4Co-0.25C, 12Ni 180-grade maraging, and 18Ni 200-grade maraging. Each steel underwent a program of fatigue cycling in two environments, a “dry” environment consisting of ambient room air and a “wet” environment consisting of 3.5 percent NaCl salt water. Relationships for fatigue-crack-growth rates as a function of the fracture mechanics stress-intensity factor (K) were obtained experimentally for each steel in both environments. The engineering significance of these relationships is presented in terms of stress levels and flaw sizes relevant to the steels under investigation. The results of this work indicate that, in an air environment, the fatigue-crack-growth rate correlates with the stress-intensity-factor range according to the power-law relationship, da/dN = CK)m. Fatigue-crack growth in each of the steels was accelerated by the salt-water environment. However, the environmental response varied significantly, depending upon the material and the ΔK level. The lower-toughness steel was less affected by environment, and environmental effects in all the steels diminished with increasing ΔK levels. No correlation was observed between fatigue-crack-growth behavior in the salt-water environment and the stress-corrosion-cracking parameter (K Iscc) obtained on the same materials.

    Keywords:

    fatigue, crack growth, high-strength steels, fracture mechanics, salt-water environment


    Paper ID: STP32047S

    Committee/Subcommittee: E08.06

    DOI: 10.1520/STP32047S


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