中文摘要：

研究了紧凑拉伸（CT）试样厚度对25Cr2NiMolV钢在566℃时，蠕变裂纹扩展（CCG）速率的影响规律及其机理。结果表明：试样厚度对CCG速率的影响与载荷水平（C＊）相关；在低载荷水平区，随试样厚度的增加，面外拘束水平增大，试样趋向于以沿晶蠕变脆性方式断裂，CCG速率增大；在高载荷水平区，不同厚度的试样均以沿晶和穿晶的混合方式发生蠕变延性断裂，CCG速率基本不受试样厚度的影响；CCG速率与载荷水平在双对数坐标中并非呈单一的线性关系，而是由不同斜率的两段直线构成，低载荷水平区的直线斜率低于高载荷水平区的，如果用高载荷水平区的CCG速率数据外推得到低载荷水平区的CCG速率，将得到非保守的结果。

英文摘要：

The effect of thickness of compact tension （CT） specimens on creep crack growth （CCG） rate and its mechanism for Cr-Mo-V steel at 566 ℃was investigated. The results show that the effect of specimen thickness on CCG rate is related to load level （C ＊ ）. At the lower load level region, with increasing the specimen thickness, the out-of-plane constraint increased and the specimens tended to fracture in intergranular creep brittle fracture mode, and the CCG rate increased. At the higher load level region, all specimens fractured in mixed intergranular and transgranular creep ductile fracture mode, and the CCG rates basically were not affected by the specimen thickness. The CCG rate versus load level curves on log-log scale were composed of two straight lines with different slopes instead of a single linear relation. Because the straight line slope at lower load level region was smaller than that at higher load level region, it would be non-conservative if the CCG rate at lower load level was extrapolated from that at higher load level.