电站主管道用铸造奥氏体不锈钢断裂韧度尺寸效应试验研究

为了探究电站主管道用铸造奥氏体不锈钢韧性断裂的尺寸效应,对五种不同厚度的标准紧凑拉伸试样在室温下进行了断裂韧度试验,通过SEM观察并分析了断裂面的显微结构.结果表明:试样厚度在12～20 mm时,断裂韧度随着试样尺寸的增大呈上升趋势,在20～50mm厚度范围时断裂韧度随试样尺寸的增大而减小；撕裂模量随试样尺寸的减小而增加.断裂面上接近中截面的位置容易产生以大型韧窝为主的沿晶断裂,在接近外表面位置较易产生以大量微小韧窝为主的穿晶断裂.利用断裂韧度的定义进行理论分析,用约束水平和断裂影响区域体积的变化解释不同尺寸效应,通过有限元分析模拟得到断裂面上三向应力比的分布变化是影响断裂应变和断裂韧度的重要因素.

Experimental Study of Size Effects on the Fracture Toughness of Austenitic Stainless Steel Used in Power Plant Main Pipe

For investigating the effect of the specimen size on the fracture toughness of the casting stainless steel for power plant main pipe,fracture toughness test was carried out at room temperature using five compact tension specimens of varying thicknesses and the detailed fracture surfaces were observed by SEM.The results show that the ductile fracture toughness increases with the increasing of specimen thickness in the range of 12-20 mm,and drops down with the increasing of specimen thickness from 20 to 50 mm;the tearing modulus increases with the decrease of the thickness of the specimens.In the zone near the middle section,the intergranular ductile fracture takes place,of which characteristics are large dimples in the fracture surface.Near the outer surface of the specimens,there are many little dimples resulted from transgranular ductile fracture.Theoretical analysis with the primary definition of the fracture toughness J integral,the constraint level and the fracture affected volume was performed to investigate the different size effects.Finite element analysis simulation shows that the distribution and variety of the stress triaxiality ratio are important factors of fracture strain and fracture toughness.