## 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 ρ_{r} is approximately 0.9 but when ρ_{r} 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 m^{1/2} 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 m^{1/2} are attributed to crack closure effects. At ρ_{r} = 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 ρ_{r} is approximately 1.0, fracture is partially by true fatigue modes and partly by cleavage, the bursts of cleavage being more noticeable when K_{max} is high.

Original language | English |
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Pages (from-to) | 149-156 |

Number of pages | 8 |

Journal | Powder Metallurgy |

Volume | 43 |

Issue number | 2 |

DOIs | |

Publication status | Published - Feb 2000 |

## Keywords

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