温度对Z3CN20-09M不锈钢在含氯高温水中应力腐蚀行为的影响

Efect of test temperature on SCC behavior of Z3CN20-09M stainless steel in high temperature water containing chloride ions

研究了温度对核电用Z3CN20-09M不锈钢在含Cl的高温高压水中的应力腐蚀开裂行为的影响.材料的应力腐蚀开裂敏感性变化趋势与试验温度变化趋势并不一致.320℃时材料的应力腐蚀开裂敏感性最高,290℃时为最低,250℃时开裂敏感性介于两者之间.250℃和320℃条件下腐蚀后试样表面形成了内部致密、外部疏松的双层氧化膜,而在290℃条件下腐蚀后试样形成的是致密的单层氧化膜.大多数点蚀坑产生于铁素体相.应力腐蚀裂纹优先在点蚀坑底部或相界面形核,并倾向于沿相界面或向铁素体内部扩展.铁素体/奥氏体界面对应力腐蚀裂纹的作用取决于裂纹面与相界面的取向关系.当裂纹扩展方向平行于相界面时,裂纹易沿着相界扩展;当裂纹扩展方向垂直于相界面时,相界面对裂纹扩展起阻碍作用.

The effect of test temperature on the stress corrosion cracking （SCC） behavior of Z3CN20-09M stainless steel was studied in high temperature water containing Cl-. It is shown that the changing tendency of sensitivity to SCC is not consistent with test temperature. The sensitivity to SCC achieves maximum at 320 ℃ and minimum at 290 ℃, and it is in the middle at 250 ℃. Bi-layer oxidation films with a compact inner layer and a loose outer layer form on the sample surface when the temperature is 250 ℃ and 320 ℃; but when the temperature is 290 ℃, there is only a single compact layer oxidation film. Most of corrosion pits form in ferrite. SCC cracks usually initiate preferentially at the bottom of corrosion pits or along austenite/ferrite phase boundaries, and they are inclined to propagate along the phase boundaries or within ferrite. The effect of austenite/ferrite phase boundaries on SCC cracks strongly depends on the relative orientation of SCC cracks to the phase boundaries. When the SCC crack propagates parallel to the phase boundary, it is inclined to propagate along the phase boundary; but when the SCC crack propagates perpendicularly to the phase boundary, the phase boundary hinders its propagation.