| Abstract |
| Low cycle fatigue(LCF) properties of Nb-stabilized type 347 and unstabilized type 316N austenitic stainless steels(SS) having nitrogen content of about 0.1wt% were evaluated at ambient and nuclear power plant operating temperature of 330℃. The resistance to LCF in two steels was compared in view of the underlying microstructure. Type 316N showed longer fatigue life than type 347 at both ambient temperature and 330℃. Higher test temperature resulted in shorter fatigue life in type 316N but similar fatigue life in type 347. The similar life in type 347 was attributed to the different cyclic peak stress response with temperature-cyclic hardening at ambient temperature and cyclic softening at 330℃. Dislocation microstructure showed more homogeneous behavior in type 347 than 316N, which came from fine Nb carbide dispersion and higher planar slip property. From the fractography of the tested samples, we found different crack initiation mechanisms in the two types of steels. For type 316Nm initial fatigue cracks mostly formed intergranularly at high input strain range while transgranularly at low input strain range. But type 347 showed intergranular initiation regardless of input strain range. This seemed to be attributed to the fine carbide distribution and higher planar slip property which prevent persistent slip band development especially at low input strain range. Coarse Nb(CN) particles in type 347 accelerated fatigue crack growth through forming voids under the repeated small deformations. (Received February 2, 2004) |
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| Key Words |
| Low-cycle fatigue, LCF, Stainless steels, Deformation, Dislocation cell, Fracture, Crack initiation |
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