固溶态控氮不锈钢在高温水中的应力腐蚀破裂

Stress Corrosion Cracking of Solution-Annealed Nitrogen- Containing Austenitic Stainless Steels in High Temperature Water Environments

采用高温电化学测控和慢应变拉伸实验方法,研究了304NG超低碳控氮不锈钢(固溶态)在250℃高温水中的应力腐蚀破裂(SCC)与电极电位和水中Cl-浓度的关系,并与316LN控氮不锈钢对比。结果表明,在不同环境下两种不锈钢的SCC敏感性随电极电位的升高而升高,并且存在一个临界电位EC,当电位高于该EC时,才发生SCC。该临界电位EC随水中Cl-浓度升高而下降,即发生SCC的环境范围扩大。304NG钢在含5mg/LCl-的250℃高温水中的EC处于0～+200mV标准氢电极(SHE)之间,更高时发生穿晶型SCC,表明该Cl-浓度下只有在高氧(高电位)环境中才能发生SCC。当Cl-浓度升高到50mg/L时,EC降到-700mV(SHE)以下,表明该浓度下即使完好除氧(低电位)也可能发生SCC。316LN的SCC抗力高于304NG,其在含5mg/LCl-的高温水中的EC位于+300～+400mV(SHE)之间,主要是穿晶型SCC。

Effects of electrode potential and Cl^- content in water on stress corrosion cracking （SCC） of solution-annealed nitrogen-containing stainless steels 304NG and 316LN in high temperature water environments at 250℃ were studied by using slow strain rate test and high temperature electrode potential control technology. Results showed that, for steel in each water environment, the susceptibility to SCC increased with the increasing of potential and there was a minimum potential for SCC （Ec） below which no SCC occurred. The Ec decreased with the rise of Cl^- content in water, that is, the environmental range suitable for SCC increased. In the solution containing 5mg/L Cl^-, the Ec of 304NG was in the range of 0～＋200mV（SHE） above which transgranular SCC occurred, which means that this steel may exhibit SCC at such Cl^- content when the water contained high content of oxygen. When Cl^- content was increased to 50mg/L, Ec decreased to less than -700 mV（SHE）, which means that this steel may exhibit SCC at such Cl^- content even when the oxygen in water has been well eliminated. 316LN exhibited higher resistance to SCC than 304NG, as its Ec was in the range of ＋300～＋400mV（SHE）. The main cracking of 316LN was transgranular.