Creep Performance Modeling of Modified 9Cr-1Mo Steels with Oxidation
- PDF / 2,566,740 Bytes
- 14 Pages / 593.972 x 792 pts Page_size
- 38 Downloads / 172 Views
TION
CREEP phenomena have been studied for more than 100 years, ever since Andrade first observed time-dependent flow of metals under constant load in 1910.[1] Most of the steady-state creep mechanisms were classified into deformation-mechanism maps by Frost and Ashby.[2] Langdon,[3] Lu¨thy et al.,[4] and Wu and Koul[5] also recognized grain boundary sliding as an important deformation mechanism inducing transient creep behavior. However, with regard to creep lifetime prediction, the existing models are mostly data-extrapolation methods such as the Larson–Miller parameter method,[6] the Monkman–Grant relation,[7] and the Wilshire equation,[8] which were established via short-term creep tests. Prediction of long-term creep life remains to be a challenging task faced by the power-generation industry.[9]
X.J. WU is with the Structures and Materials Performance Laboratory, Aerospace Research Center, National Research Council Canada, Ottawa, ON, K1A 0R6 Canada. Contact e-mail: [email protected] X.Z. ZHANG and R. LIU are with the Department of Mechanical and Aerospace Engineering, Carleton University, Ottawa, ON, K1S 5B6 Canada. M.X. YAO is with the Kennametal Stellite Inc., Belleville, ON, K8N 1G2 Canada. Manuscript submitted March 4, 2019.
METALLURGICAL AND MATERIALS TRANSACTIONS A
Among the factors influencing materials’ creep performance, oxidation is an important degradation mechanism. Inevitably, metal oxidation will occur under high-temperature creep test conditions in air, which will definitely have an impact on materials’ creep behavior. However, studies to quantify the oxidation effects on creep rate and creep life have been rarely reported, since vacuum creep tests are almost cost-prohibitive for long-term experiments such that oxidation-free creep data are unavailable for most materials. Most creep data are generated in air with coupon-borne influence of oxidation, and thus empirical creep life prediction methods based on such short-term creep data are questionable, because the extrapolation for prediction of long-term creep performance using these methods does not consider the influence of oxidation as a time-dependent factor. This problem has long been encountered in engineering. For example, long-term creep rupture data generated by the National Institute for Materials Science (NIMS) show that there is a life breakdown phenomenon for Grade 91 steels, especially at high temperatures.[10–12] The in-service experience reviewed by the Electric Power Research Institute (EPRI) of USA demonstrates that ‘‘cracking in creep-strength enhanced ferritic (CSEF) steel components has occurred relatively early in life. In many cases, the occurrence of damage has been linked to less than optimal control of steel making, processing, and component fabrication.’’[13] Apparently, the current creep
life prediction methodology has missed some life-limiting factors for long-term creep—oxidation is one of them. The continuum damage mechanics approach considered the oxidation effect in a single power-law formulation of creep rate.
Data Loading...
