Study On The Creep Crack Growth Rate Of CLAM Steel

Fusion energy was believed to be the ultimate solution to energy crisis with clean and safe characteristics. The long-term reliability of the structure material of the blanket module is one of the key issues for the safety operation of the fusion reactor. Presently, China Low Activation Martensitic (CLAM) steel has been chosen as the primary candidate structural material of the FDS series PbLi blankets for fusion reactors, CN helium cooled ceramic breeder test blanket module (HCCB-TBM) for ITER. With the elevated service temperature of the blanket components, the micro cracks will probably be generated due to the accumulation of creep strains at the internal defects, and then possibly propagate to final fracture. Thus the creep crack growth (CCG) behavior is anticipated to be one of the key issues for the application of the structure material in blanket. Thus it is very necessary to investigate the creep crack growth behavior of CLAM steel.In this work, the effects of temperature and initial stress on the creep crack growth rate were studied by CCG tests. Additionally, creep crack growth rate model was developed by serial single axial creep tests. This work is useful to evaluate the reliability of blanket components fabricated by CLAM steel.Firstly, the CCG behavior of CLAM steel at 500℃,55O℃ and 600℃ was investigated with the compact tension (CT) specimens. The results showed that the incubate time and steady state CCG rate of CCG curves were significantly affected by testing temperature and initial load, and power law relationships were found between the initial load versus the incubate time and initial load versus steady state CCG rate. The CCG rate versus C* parameter revealed a good linear relationship on log-log scale at all the testing temperatures, and the fitted relationship was da/dt= 3x(C*/1000)09. The microstructure observation showed that the propagation of the creep crack was caused by the nucleation, growth and convalescence of micro-voids in the front of the crack.Secondly, single axial creep tests were carried at 500℃,550℃ and 600℃. Creep crack growth rate model of each temperature were developed based on the single axial creep tests results. The results shown the predicted CCG rate under plane stress condition have been in good agreement with the experiment results.