Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
9796258 | Materials Science and Engineering: A | 2005 | 11 Pages |
Abstract
The low-cycle fatigue (LCF) behavior of SAF 2205 duplex stainless steel at the strain amplitudes of 0.9% and 1.5%, combined with strain ratios R = â1.0 and â0.2, exhibits a mixed mode of cyclic hardening and cyclic softening as the cycle life increases until failure. The microstructure of the as-received metal is composed of ferrite (α) and austenite (γ) phases with 51α/49γ, vol.%. The evolution of the α/γ phase in the samples treated by all LCF tests has been revealed under the high-resolution transmission electron microscope. Dislocation cell structures and persistent slip bands (PSB) can be observed in the α phase in the samples of all LCF tests. The tangled dislocations accumulated at the stacking faults in the γ phase can be seen in the sample of strain amplitude of 0.9% with R = â1. At the same strain amplitude of 0.9% but with R = â0.2, the microstructure of the γ phase transforms to the distinct É-martensite intersected mutually, which is promoted by a higher 0.6% tensile mean strain than the previous strain ratio, R = â1, having 0% mean strain. Further, at a relatively higher strain amplitude of 1.5% with R = â1, γ-austenite has transformed to the strain-induced thin lath-like αâ²-martensite sheaths. At the same strain amplitude with R = â0.2, the thin lath-like αâ²-martensite sheaths grows into thicker and longer strain-induced martensite bundles as the tensile mean strain increases from 0% to 1.0%. The strain-induced martensite present at the failure region correlates on intimate terms with the maximum microhardness distribution at the γ-austenite grains of the failure region at strain amplitude of 1.5% with R = â0.2. It suggests that the localized transformation of retained austenite into martensite at a tip of a fatigue crack improves the fatigue resistance by either hindering the crack propagation or reducing the crack growth rate.
Related Topics
Physical Sciences and Engineering
Materials Science
Materials Science (General)
Authors
P.K. Chiu, K.L. Weng, S.H. Wang, J.R. Yang, Y.S. Huang, Jason Fang,