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Home  >  Journal list  >  Journal of the Society of Materials Science, Japan  >  Vol.64  No.2 (2015)  >  pp.74-79

Journal of the Society of Materials Science, Japan
<<Previous article Vol.64  No.2 (2015)   pp.74 - 79 Next article>>

Study on the Magnification and Area of Observation Appropriate to Measure Type IV Creep Damage of Mod.9Cr-1Mo Steel

Fumiko KAWASHIMA1), Atomu SATO1), Yoshitsugu IRIE1), Kohei YAMAKAWA2), Kazuhito FUJIWARA1), Hidehiro HATA1)
1) Kumamoto University, Graduate School of Science and Technology, Department of Advanced Technology 2) Kumamoto University, Faculty of Engineering, Department of Mechanical System Engineering

Type IV creep damage occurs in welded joints of high chromium steel in power plant. The evaluation method of residual life of the damaged component is demanded. One of them is the methods based on the number density of voids that is defined as the number of voids divided by the area of observation. The parameter represents the life fraction of components and is influenced by the stress tri-axiality, but the influence is hidden by the influence of the area and magnification of observed metallographic structure. The error of the parameter is large if the area of observation is not large enough, because the voids do not uniformly distribute. The parameter varies according to the magnification because voids can’t be seen if magnification of observed photograph of metallographic structure is small. The appropriate areas and magnification are required for obtaining the appropriate parameters, for studying the influence of stress tri-axiality and for evaluating the residual life. In this study, the creep tests with the specimens of simulated fine-grain HAZ of Mod.9Cr-1Mo steel were carried out and samples with Type IV creep damage were obtained. The distribution of voids under the uniform stress was measured under the different conditions of magnifications and areas. We obtained the mean and the standard deviation of the distribution and proposed the area of observation appropriate for allowable error of the number density of voids that depends on the magnification.


Keyword:
Type IV creep damage, Mod. 9Cr-1Mo steel, The number density of voids, Observation, Residual life

Received: July 10, 2014
Published online: February 20, 2015

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