Abstract
Rotating bending fatigue tests, together with microstructural
characterization, have been performed on the high nitrogen martensite
bearing steel Cronidur30. The results show that the fatigue stress
amplitude gradually decreases with the increasing number of fatigue
cycles, with a fatigue strength limit of 867 MPa after 1.0 × 107fatigue
cycles. Crack sources due to both inclusions and twin-martensite
volumes are found from inspection of fracture surfaces, with nearly 40%
of the fatigue failures identified as originating from twin-martensite
volumes. Based on a detailed microstructural examination, it is
concluded that twin-martensite volumes first fracture locally along the
maximum shear stress direction, and these locations then act as the
sources for crack propagation and finally resulting in fatigue failure.
The stress intensity factors calculation of two types of crack sources
initiated by the subsurface shows that the two types of crack sources
play basically the same role in fatigue crack initiation. Granular
bright facet (GBF) will be formed around the crack source to meet the
threshold value of crack propagation. When the initial size of these two
crack sources is large enough, the crack can directly propagate without
forming GBF. The novel observation of twin-martensite induced crack
nucleation highlights the fact that fatigue failures of the investigated
bearing steel do not only originate from inclusions, and help to
provide an in-depth understanding on the fatigue mechanisms of bearing
steels.
Original language | English |
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Article number | 144402 |
Journal | Materials Science and Engineering A |
Volume | 861 |
Number of pages | 8 |
ISSN | 0921-5093 |
DOIs | |
Publication status | Published - 2022 |
Keywords
- Fatigue crack initiation
- High-cycle fatigue
- High-nitrogen martensitic stainless steel
- Stress intensity factor
- Twin martensite