321-52M-690异种金属焊接接头的应力腐蚀开裂行为研究

Stress Corrosion Cracking Behavior of 321-52M-690 Dissimilar Weld Joint

采用慢应变速率拉伸(SSRT)和高温电化学相结合的方法,研究了外加电位对321-52M-690异种金属焊接接头在含Cl-高温高压水中应力腐蚀开裂(SCC)倾向的影响规律。结果表明,在300℃、50ppm Cl-环境下,焊接接头的SCC敏感性随电极电位(-700^+100mV)的升高而增大,且存在一个介于0^+50mV(vs.SHE)之间的临界电位Ecrit。当电极电位低于Ecrit时,焊接接头的SCC敏感性较小,SCC敏感性指数ISSRT基本在40%左右,断裂形式为外力主导的塑性开裂;当电极电位高于Ecrit时,ISSRT急剧增加至70%以上,断裂形式为腐蚀主导的脆性开裂。试样断裂位置均位于硬度最低的321母材处,表明在321/690异种金属焊接接头中321母材对SCC最为敏感,故进一步探讨了321不锈钢的应力腐蚀开裂行为和机理。

The effect of electrode potential on stress corrosion cracking（SCC）behavior of 321-52M-690 dissimilar weld joint in pressurized water reactor（PWR）was investigated by slow strain rate tensile（SSRT）tests and high-temperature electrochemical test in300 ℃ water containing 50 ppm chloride.The results show that the SCC susceptibility increases with the electrode potential（-700-＋100 mV）,and a critical potential Ecrit between 0-＋50mV（vs.SHE）exists.The SCC susceptibility is low,and no obvious intergranular or transgranular stress corrosion cracks can be found when the electrode potential is belowEcritcorresponding to deoxygenated water chemistry.While,when theelectrode potential is more positive than Ecrit,dramatically,ISSRTis above 70%,and all the brittle fractures locate at 321 base metal,where exhibits significant SCC behavior with large area intergranular and transgranular stress corrosion cracks.The 321 base metal is the most vulnerable to SCC in this dissimilar weld joint,so the stress corrosion cracking mechanism of 321 stainless steel was further discussed in this paper.