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Vol.47, No.11, 707 ~ 716, 2009
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| Title |
| Cyclic Deformation Behaviors under Isothermal and Thermomechanical Fatigue Conditions in Nb and Mo Added 15Cr Ferritic Stainless Steel |
| 정재규 Jae Gyu Jung , 오승택 Seung Taik Oh , 최원두 Won Doo Choi , 이두환 Doo Hwan Lee , 임종대 Jong Dae Lim , 오용준 Yong Jun Oh |
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| Abstract |
| This paper deals with cyclic stress and strain responses during isothermal low cycle fatigue (LCF) and thermo-mechanical fatigue (TMF) loadings on Nb and Mo containing 15Cr stainless steel, which is used for exhaust manifolds in automobiles. The test temperatures (Ti) of the isothermal LCF were 600 and 800℃. The minimum temperature of the TMF test was 100℃ and the maximum temperaures (Tp) were varied between 500 and 800℃. In both loading conditions, weak cyclic softening is observed at Ti=Tp=800℃, but the transition to strong cyclic hardening is completed with the temperature decrease below Ti=600~700℃ for LCF and Tp=500~600℃ for TMF. The stress-strain hysteresis loops in the TMF loading show a significant stress relaxation during compressive (heating) half cycle at Tp>500℃, which develops tensile mean stress during cycling. Due to the stress relaxation, the TMF test sample reveals much lower dislocation density than the isothermally fatigued sample at the same temperature with Tp. A detailed correlation between fatigue microstructure and cycling deformation behavior is discussed. |
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| Key Words |
| heat resistant ferritic stainless steels, thermo-mechanical fatigue, Low cycle fatigue, cyclic deformation, fatigue microstructure, exhaust manifolds |
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