关键词: 非线性超声检测, 汽轮机转子, 蠕变损伤

Abstract: Creep damage is generally produced in the high temperature components of ultra-supercritical steam turbine which will detriment the structural integrity during the long term operation. Therefore, quick and effective identification of the creep damage is very critical for the service safety of steam turbine unit. In the present work, interrupted creep tests of FB2 steel which is commonly used in the ultra-supercritical steam turbine rotor have been conducted. Creep damaged specimens with various damage levels are thus generated. Using the damaged specimens, nonlinear longitudinal ultrasonic evaluation test has been performed and the nonlinear ultrasonic parameters of damaged specimens are obtained. Results indicate that nonlinear ultrasonic parameters increase with the increase of creep damage levels of steam turbine rotor steel. The microstructure of damaged specimens has been analyzed by using the transmission electron microscopy(TEM). Result reveals that the increase of nonlinear ultrasonic parameter can be ascribed to the increase of dislocation density. Furthermore, the increment of nonlinear ultrasonic parameter is related to the dislocation climbing at higher stress and to the dislocation slipping at lower stress. In terms of the dislocation theory, a correlation between the nonlinear ultrasonic parameters   and the steady state creep strain rate has been developed accordingly.

Key words: creep damage, steam turbine rotor steel, ultrasonic nonlinearity