STP600

    Micro-Mechanistic Interpretation of Cyclic Crack Growth Behavior in 17-4 PH Stainless Steels

    Published: Jan 1976


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    Abstract

    A fracture mechanics and fractographic study has been made of cyclic crack growth in heat-treated samples of 17-4 PH stainless steel. Two 1/2-in. (1.27-cm) thick rolled plates were studied: a vacuum-melted (VM) sample in the H1050 condition and an argon-oxygen melted (AOM) sample in the H1050 and H1150 conditions. Crack-growth rates, da/dN, were obtained in ambient laboratory air as a function of stress-intensity factor range, ΔK, using single-edge-notched (SEN) tension specimens. Stress ratio, R, values of 0.04, 0.40, 0.67, and 0.80 were investigated. Microscopic modes of crack extension were determined by electron fractography and were utilized to explain differences in macroscopic crack-growth behavior. Cleavage and microvoid coalescence can appear as modes of cyclic crack propagation in this family of steels, to the detriment of cyclic crack-growth resistance. In particular, the following notable features were observed: (1) the amount of cleavage present appears to be independent of ΔK over a wide spectrum of ΔK levels; (2) the incidence of cleavage (and accelerated cyclic crack-propagation rates) increases significantly with R; (3) heat treatment can be adjusted to minimize the incidence of cleavage; and (4) slight variation in alloy processing serves to eliminate cleavage and promote striation formation, while enhancing the fracture toughness.

    Keywords:

    crack propagation, fatigue (materials), fracture properties, fractography, mechanical properties, cleavage, stainless steels, precipitation hardening steels


    Author Information:

    Crooker, TW
    Engineering Materials Division, Naval Research Laboratory, Washington, D.C.,

    Hasson, DF
    U.S. Naval Academy, Annapolis, Md.

    Yoder, GR
    Engineering Materials Division, Naval Research Laboratory, Washington, D.C.,


    Paper ID: STP29199S

    Committee/Subcommittee: E08.05

    DOI: 10.1520/STP29199S


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