316Ti在含氯离子300℃高温水中的应力腐蚀开裂

STRESS CORROSION CRACKING OF 316Ti IN 300℃HIGH TEMPERATURE WATER CONTAINING CHLORIDE IONS

采用慢应变速率拉伸(SSRT)试验方法研究了316Ti在300℃高温水中的应力腐蚀开裂(SCC)行为。结果表明,在空气饱和条件下,试样的断裂时间、延伸率以及断裂能的值随着C1-浓度的增大显著降低,应力腐蚀敏感指数随着Cl-浓度的增大则显著递增,二者具有一定相关性。316Ti不锈钢在300℃空气饱和水中发生SCC的临界Cl-质量浓度为5 mg/L,只有在Cl-质量浓度高于或等于5 mg/L,试样才发生穿晶型和部分沿晶混合型SCC。SCC裂纹多萌生于滑移台阶或蚀坑,也可能萌生于接近表面的铁素体相处;裂纹在向基体扩展过程中,铁素体相的存在阻碍了其扩展过程,从而提高了316Ti的抗SCC能力。氧在SCC裂纹萌生和扩展过程中都起着非常重要的作用。

The stress corrosion cracking （SCC） of 316Ti stainless steel （SS） in 300 ℃ high temperature water containing chloride ions was investigated with slow strain rate tensile （SSRT） techniques. The results showed that the values of fracture time and extension ratio and fracture energy of specimens significantly decreased with the concentration of chloride content increased, while stress corrosion sensitive index would significantly increase with the concentration of chloride ions increased. 316Ti SS was not susceptible to SCC when the chloride content was below 5 mg/L while transgranular and partially intergranular cracked when the chloride content was above 5 mg/L in aerated water. Stress corrosion cracks generally initiated from slipping steps or pits, maybe from the secondary phase ferrite. In propagation into the base metal, the cracks would be arrested by the secondary phase ferrite, so as to improve the resistance of SCC for 316Ti SS. Oxygen played a crucial role in SCC initiation and propagation of 316Ti SS in high temperature water.