| Summary: | 碩士 === 義守大學 === 機械與自動化工程學系碩士在職專班 === 101 === In order to investigate the creep behavior and understand its deformation mechanism of automotive exhaust pipe materials, this study conducted creep experiments of 409L and 436 ferritic stainless steels at both 600ºC and 750ºC under different stress levels. Results show the creep resistance of 436 stainless steel is better than that of 409L stainless steel, because the 436 stainless steel has more Ni, Cr, and Mo contents. From creep data, two important material coefficients, namely, M of Monkman-Grant relationship and K of Coble creep equation are calculated for predicting the material creep life. After creep tests, crept specimens were analyzed on the microstructure and fracture surfaces by the use of scanning electron microscopy. As the creep mechanism, all tests show grain boundary diffusion or Coble creep is the dominate deformation mechanism, except at higher temperature 750 ºC and higher stress levels, because the homologous temperature is 0.43 on the 750 ºC, it is nearer the temperature occurs Nabarro-Herring creep, the creep mechanism is the Coble creep with Nabarro-Herring creep, SEM fractographs show voids of fracture surfaces and SEM micrographs show grain boundary cavities of crept specimens suggest diffusional creep be the dominate deformation mechanism.
|
|---|
