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Fatigue Strength and Fracture Surface Morphology in Ultra-fine Grained Ferritic Stainless Steels
Last modified: 2013-05-03
Abstract
Ferritc stainless steels such as Fe-2.25Cr-1Mo-1Zr,Fe-25Cr-1Zr and
Fe-13Cr-8Ni-2Mo-1Zr with ultra-fine grain size of 0.2μm were prepared by hot
extrusion after mechanical alloying. Fatigue strength expressed as maximum
stress at 3x106 cycles for Fe-2.25Cr-1Mo-1Zr,Fe-13Cr-8Ni-2Mo-1Zr and Fe-
25Cr-1Zr were 1150,1150 and 1350 MPa, respectively. Transgranular fracture
surfaces were predominantly observed at crack initiation and crack propagation
area. Striation like pattern was observed at a restricted crack propagation area.
The mechanism on higher fatigue strength in ultra-fine grained materials is
discussed in terms of fracture surface morphology on the basis of the recent
investigations. It can be concluded that the higher fatigue strength of ultra-fine
grained ferritic stainless steels is strongly governed by delay of crack initiation.
Fe-13Cr-8Ni-2Mo-1Zr with ultra-fine grain size of 0.2μm were prepared by hot
extrusion after mechanical alloying. Fatigue strength expressed as maximum
stress at 3x106 cycles for Fe-2.25Cr-1Mo-1Zr,Fe-13Cr-8Ni-2Mo-1Zr and Fe-
25Cr-1Zr were 1150,1150 and 1350 MPa, respectively. Transgranular fracture
surfaces were predominantly observed at crack initiation and crack propagation
area. Striation like pattern was observed at a restricted crack propagation area.
The mechanism on higher fatigue strength in ultra-fine grained materials is
discussed in terms of fracture surface morphology on the basis of the recent
investigations. It can be concluded that the higher fatigue strength of ultra-fine
grained ferritic stainless steels is strongly governed by delay of crack initiation.
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