To assess the failure risk of high temperature structures, it is essential to obtain the creep fracture toughness of materials. In the present paper, Creep crack growth (CCG) tests for 2(1/4) Cr1Mo steel have been carried out by utilizing the side grooved compact tension (CT) specimen and direct current (DC) electrical potential technique. The material parameter of creep fracture toughness, K_(mat)~c, were obtained from analysis of 11 CCG tests at temperatures of 500 and 565℃. It has been found that for 2(1/4) Cr1Mo steel K_(mat)~c decreases with increasing time and increases with elevating temperature. For this reason, the value of K_(mat)~c at lower temperature or longer service time can be used to extract a conservative result in the high temperature defect assessment where the accurate value of K_(mat)~c is unavailable. It is also validated from this test that the proposed formula by Ainsworth et al can be adopted in practice.
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