발간논문

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Vol.44, No.11, 752 ~ 759, 2006
Title
Dependence of Grain Size on Mechanical Properties in Directionally Solidified Buckets of IN738LC
안성욱 Seong Uk An , 구성모 Seong Mo Ku , 송태석 Tae Seok Song , 이경환 Kyong Whoan Lee , 조규섭 Gue Serb Cho
Abstract
The dependence of creep properties on directionally solidified(DS) grain size has been studied. The DB buckets have been manufactured in commercial scale by two different DB growing directions from airfoil and root. From the buckets two grain sizes of coarse (9-12 mm) and fine(3-5 mm) were selected for the tensile and creep tests. Creep tests have been fulfilled to study the dependence of the mechanical properties on the DB grain size in one bucket and the dependence of the crystal directions in the other. The results are (1) at room temperature the fine showed about 3% higher yield strength than the coarse. Especially the longitudinal direction of the bucket had about 26% higher yield and tensile strengths than the transverse. On the contrary (2) at the high temperatures between 600-982℃ the coarse showed about 3% higher strength than the fine. But the longitudinal and transverse showed no differences at the strengths. (3) At 982℃ and low stress range the creep rupture life increased strongly with decreasing stress. (4) Increasing temperature, ductility has been drastically enhanced. Concluded that the microstmcture and creep properties are interdependent.
Key Words
blade, macrostructure, tensile strength, creep
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