核级SA-508 Gr.3 Cl.1材料拉伸与压缩蠕变行为的比较研究

堆芯熔融物堆内滞留(In-vessel retention,IVR)是压水堆的严重事故缓解措施。IVR过程中，反应堆压力容器底封头(Reactor pressure vessels,RPV)沿壁厚方向同时存在拉伸和压缩应力。为保证IVR过程中RPV的结构完整性，有必要研究SA-508 Gr.3 Cl.1材料的拉伸和压缩蠕变行为及其差异。基于此，开展了SA-508 Gr.3 Cl.1材料的拉伸蠕变和压缩蠕变试验测试，分析了材料的拉伸和压缩蠕变行为以及变形机制的不同。结果表明：拉伸和压缩蠕变的第一、二阶段基本吻合，但压缩蠕变没有出现明显的蠕变第三阶段；拉伸蠕变在试验应力范围内的变形机制为单一的位错攀移，而随着应力的降低，压缩蠕变变形机制由位错攀移转变为晶界滑移/空位扩散；拉伸蠕变对亚晶组织演化程度的影响大于压缩蠕变，这可能与蠕变变形机制的转变相关。

Comparison of Tensile and Compressive Creep Behavior of SA-508 Gr.3 Cl.1 Steel for Nuclear Applications

The In-vessel retention (IVR) is an important mitigation strategy in severe nuclear accidents. During IVR conditions, the tensile and compressive stress states both exist along the thickness direction of the reactor pressure vessels (RPV). Therefore, the tensile and compressive creep behavior of the SA-508 Gr.3 Cl.1 steel should be discussed to guarantee the structure integrity of the RPV in IVR conditions. Based on this, tensile and compressive creep tests of the SA-508 Gr.3 Cl.1 steel are conducted, and the differences of creep behavior and creep deformation mechanism between tensile and compressive creep are analyzed. Results indicate that the primary and secondary creep regimes of the compressive creep are consistent with that of the tensile creep, while the tertiary creep stage is not observed for compressive creep test. The dominant creep deformation mechanism for tensile creep is dislocation climb within the stress levels studied, while that for the compressive creep changes from dislocation climb to grain boundary sliding or vacancy diffusion with the decrease of the stress. The tensile creep plays a more important role on the evolution of the sub-grain than the compressive creep, which may be induced by the transformation of creep deformation mechanism.