异材焊接件A508/52M/316L在高温水环境中的应力腐蚀破裂

STRESS CORROSION CRACKING BEHAVIOR OF DISSIMILAR METAL WELD A508/52M/316L IN HIGH TEMPERATURE WATER ENVIRONMENT

采用慢应变速率实验(SSRT)方法,研究了先进的异材焊接件A508/52M/316L在模拟压水堆一回路290℃高温水环境中的应力腐蚀破裂(SCC)特性.实验在-780 mV至+200 mV范围的电位下进行,模拟一回路水化学从低O含H的理想低电位状态到溶解O_2明显超标的高电位状态的服役环境.该焊接件显微组织和化学成分分布较复杂,显著的变化发生在A508/52M和52M/316L 2个界面附近.在SSRT拉伸试样的典型位置处加工了同样尺寸的尖锐缺口,以模拟应力集中和加速实验,并比较这些典型位置的SCC敏感性.结果表明,当电位位于-780 mV至-300 mV范围时,SSRT试样总是以韧性断裂形式在镍基合金焊缝中部发生断裂.当电位升到-200 mV至+200 mV范围时,试样发生显著的SCC脆断,A508/52M界面区周围是该焊接件最脆弱的部位,在该界面和附近的A508热影响区发生穿晶应力腐蚀破裂(TGSCC),在紧邻界面的镍基合金焊缝薄层发生沿晶应力腐蚀破裂(IGSCC).讨论了破裂机理和实验结果的工程意义.

The stress corrosion cracking （SCC） behavior of advanced dissimilar metal weld A508/52M/316L in simulated primary water environments of pressurized water reactor （PWR） at 290℃was investigated by means of slow strain rate testing （SSRT）. The tests were performed at various applied electrode potentials which correspond to the electrochemical conditions of the weld in various water environments, from low potentials with ideal water chemistry to high potentials with oxygen-contaminated water chemistry. The weld exhibits complicated microstructure and chemical composition distributions, especially, significant changes appear around the A508/52M interface and the 52M/316L interface. For tensile specimens in SSRT, sharp notches were machined at important and typical places, i.e., at the two interfaces and in the bulk parts of the low alloy steel, Ni base weld metal and stainless steel of the weld. Results showed that the specimens always failed in bulk zone of the Ni base weld metal with ductile appearances when tested in the potential range from -780 mV to -300 mV （vs SHE）. When electrode potential was raised into the range from -200 mV to ＋200 mV which corresponds to oxygen-contaminated water chemistry, the weld exhibits significant SCC. The area around the A508/52M interface is the weakest place, transgranular stress corrosion cracking （TGSCC） happened both along the interface and in A508 heat affected zone （HAZ）, intergranular stress corrosion cracking （IGSCC） occurred in the Ni base weld metal close to tile interface. The cracking mechanism and the engineering practical significance were discussed.