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Vol.41, No.2, 77 ~ 83, 2002
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| Title |
| Mechanical Behavior : The Influence of Precipitation Hardening Temperature on the Fatigue Crack Propagation Behavior of 15-5 Precipitation Hardening Stainless Steel |
| 남기우 K. W. Nam , 안석환 S. H. Ahn , 박인덕 I. D. Park , 김현수 H. S. Kim , 박주용 J. Y. Park |
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| Abstract |
| In this study, the behavior of the fatigue fracture and the fatigue crack growth for 15-5 precipitation hardening stainless steels which were heat-treated at various temperatures were investigated. The acoustic emission signals were generated during the fatigue crack growth and they(the results) were evaluated by the time frequency analysis method. Shot peening was carried out on artificially degraded Type-A specimen by various methods, and the compressive residual stress of surface was also evaluated. As the heat treatment temperature was increased, the base structure, martensite, remained unchanged but the sub-structure was changed. The crack growth rate of the artificially degraded Type-A specimen was faster than that of Type-B specimen due to the coarse microsturcture. The crack growth of the Type-C specimen was hindered cause of the fine microstructre and the precipitates. The threshold area was a little bit different among three types of specimens due to the microstructure. The frequency ranges of acoustic emission signals have nothing to do with the types of specimens. That is, the fatigue crack length of 13 mm produced burst signals about 0.1-0.15 MH_Z while 18mm crack generated continuous signals about 0.1-0.3 MH_Z. Because the signals due to the interfacial fracture of martensite were too strong, the affection of extraction was indistinguishable. Introduction of compressive residual stress by stress double shot peening (SDSP) was an useful method to improve the fatigue strength of degraded specimen. |
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| Key Words |
| 15-5 Precipitation Hardening(PH) stainless steel, Fatigue crack propagation rate, Heat treatment condition, Degradation, Acoustic emission, Shot peening |
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