应变速率对316LN应力腐蚀开裂敏感性的影响

The Effect of Strain Rates on the Susceptibility of Stress Corrosion Cracking of the 316LN

不锈钢结构材料在压水堆水化学条件下产生应力腐蚀开裂(SCC)影响核电站安全,掌握应力腐蚀敏感性影响因素边界条件具有十分重要的意义。采用恒应变速率拉伸试验方法,结合断口分析技术,研究了应变速率对第三代压水堆核电站主管道材料316 LN在高温B-Li水化学条件下SCC的影响规律。结果表明:在1000 mg/LB、2 mg/LLi、10 mg/LCl饱和氧高温B-Li水溶液中,随着应变速率的降低,316 LN的延伸率、最大破断应力、断裂能呈减小的趋势,而SCC敏感指数呈增大的趋势;只有当应变速率低于或等于4.17×10-6/s时,试样才萌生SCC裂纹,316 LN产生SCC的临界应变速率介于8.34×10^(-6)~4.17×10^(-6)/s范围;当应变速率降低到4.17×10^(-6)/s时,316 LN主要发生穿晶型SCC,裂纹呈扇形向基体内扩展,而当应变速率降为8.34×10^(-7)/s时,316 LN开裂模式转变为沿晶和穿晶混合型SCC。

Stress corrosion cracking(SCC)of stainless steel structural materials under PWR hydrochemical conditions affects the safety of nuclear power plant.It is significant to master the boundary conditions of stress corrosion sensitivity factors.The influence of the strain rate on SCC of 316 LN,the main pipeline material of the third generation PWR nuclear powe r plant,under high-temperature B-Li water chemistry conditions was studied by the constant strain rate tensile test and the fracture analysis technique.The results showed that with decreasing of the strain rate,the elongation,the ultimate tensile strength and the fracture energy of 316 LN decreased,while the SCC sensitivity index increased in the high-temperature B-Li aqueous solution of 1000 mg/L B,2 mg/L Li and 10 mg/L Cl saturated oxygen.Only when the strain rate was lower than or equal to 4.17×10^(-6)/s,SCC cracks will be initiated in the sample,and the critical strain rate of SCC in 316 LN is in the range of 8.34×10^(-6)~4.17×10^(-6)/s;When the strain rate reduced to 4.17×10^(-6)/s,the transgranular SCC mainly occurred in 316 LN,and the crack spread into the matrix in a fan shape.While the strain rate reduced to 8.34×10^(-7)/s,the cracking mode gradually changed to intergranular and transgranular mixed SCC.