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溶解氧和溶解氢对冷变形690 MA合金应力腐蚀开裂的影响规律

Effect of Dissolved Oxygen and Hydrogen on Stress Corrosion Cracking of Cold Worked Alloy 690 MA

    摘要
  • 摘要: 采用直流电压降（DCPD）裂纹长度在线测量技术研究了溶解氧（DO）和溶解氢（DH）对冷变形690 MA合金在360 ℃水环境中应力腐蚀（SCC）裂纹扩展速率（CGR）的影响规律，并结合高分辨微观表征技术观察了裂纹尖端形貌和腐蚀产物特征，解释了溶解气体对SCC的影响机理。结果表明，DH环境下的CGR约为DO环境下的2~4倍。TEM分析表明，冷变形690 MA合金在DH和DO环境中的裂纹尖端形貌相似，裂纹尖端前端均未发现显著的晶界氧化。DH环境下CGR与晶界孔洞密度有较好的对应关系，表明介质中的DH可促进裂纹尖端前端晶界碳化物附近孔洞的生成、降低晶界结合力，进而加速裂纹扩展。

     

    Abstract: The stress corrosion cracking (SCC) behavior of cold worked alloy 690 MA in 360 ℃ water was investigated by direct current potential drop (DCPD) on-line monitoring. Analytical electron microscopy was used to characterize the cracking process for better understanding the dissolved oxygen (DO) and dissolved hydrogen (DH) effect. The crack growth rate (CGR) in hydrogenated water is about 2-4 times higher than that in water containing DO. Similar crack tips and no grain boundary oxidation were observed after CGR testing in both DO and DH water. A good correlation between the grain boundary (GB) cavity coverage and high CGRs was observed in cold worked alloy 690 MA when tested in hydrogenated water. DH may promote cavities formation ahead of the crack tip, and thus decrease the GB strength and enhance the CGR.

     

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