Fatigue crack propagation in some PM steels

R.A. Phillips, J.E. King, J.R. Moon

    Research output: Contribution to journalArticlepeer-review

    Abstract

    Mechanisms of fatigue crack growth have been studied for a range of PM steels at relative densities of 0.90 and 1.0, for which strength, fracture toughness, and microstructural information was also available. It is shown that the Paris exponents for steady state crack growth are between 8 and 18 when ρr is approximately 0.9 but when ρr is approximately 1.0 the exponents are between 2.6 and 4.0, i.e in the range typical of wrought steels (2-4). At both densities, threshold stress intensities are between 5.5 and 10.8 MPa m1/2 when R = 0.1. Combinations of these thresholds and yield strengths are comparable with those for wrought steels. When R = 0.8, reductions in threshold to between 2.7 and 5 MPa m1/2 are attributed to crack closure effects. At ρr = 0.90, Fe-0.5C fails by progressive rupture of sinter necks. Astaloy A, with 0.2%C and 0.6%C, and Distaloy AB-0.6C have smaller plastic zone sizes and the cracks follow more difficult paths through particles as well as necks. When ρr is approximately 1.0, fracture is partially by true fatigue modes and partly by cleavage, the bursts of cleavage being more noticeable when Kmax is high.

    Original languageEnglish
    Pages (from-to)149-156
    Number of pages8
    JournalPowder Metallurgy
    Volume43
    Issue number2
    DOIs
    Publication statusPublished - Feb 2000

    Keywords

    • crack propagation
    • fatigue of materials
    • fracture toughness
    • stress intensity factors
    • yield stress
    • Paris exponent
    • steel powder metallurgy

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