Development of high temperature creep properties evaluation method using miniature specimen

In this study, a Small Punch Creep(SP-Creep) test using miniaturized specimen(10x10x0.5mm) has been described for the development of the newly semi-destructive creep test method for high temperature structural components such as headers and tubes of boiler, turbine casing and rotor, and reactor vessel. The SP-Creep testing technique has been applied to 2.25Cr-1Mo(STBA24) steel used widely as boiler tube material and the creep test temperature are varied at 550 .deg. C∼600 .deg. C. The overall deformations of SP-Creep curves are definitely depended with applied load and creep test temperature and show the creep behaviors of three steps like conventional uniaxial creep curves. The steady state creep rate(δss) of SP-Creep curve for miniaturized specimen increases with increasing creep temperature, but the exponential value with creep loading is decreased. The activation energy(Qspc) during SP-Creep deformation with various test temperatures shows 605.7kJ/mol that is greater than 467.4kJ/mol reported in uniaxial creep test. This may be caused by the difference of stress states during creep deformation in two creep test. But from the experimental results, e.g. SP-Creep curve behaviors, the steady state creep rate(δss) with creep temperature, and the exponential value(n) with creep loading, it can be summarized that the SP-Creep test may be a useful test method to evaluate the creep properties of the heat resisting material