采用慢应变速率拉伸测试技术研究了一种新型超高强度不锈钢Cr12的应力腐蚀开裂(SCC)行为,结合扫描电镜对应力腐蚀断口形貌进行观察和分析.结果表明,Cr12钢的空拉试样有明显的颈缩现象,断口四周平齐,为裂纹的起源与快速扩展区,以准解理断裂形貌为主.在弱酸性溶液中SCC敏感性增大,断口仍为准解理形貌,局部出现滑移台阶.在弱酸性气氛环境中,氧在薄液膜中的扩散能更快地到达金属表面,阴极反应的供氧量充足,阴极极化强化,钝化膜的稳定性和完整性受到破坏,点蚀更容易发生,从而增大了其SCC敏感性.Cl－通过诱发点蚀形成和阻碍钝化膜修复显著提高了Cr12钢的应力腐蚀敏感性,降低了钢的强度和塑性.应力腐蚀裂纹起源于点蚀坑处,SCC机制可用滑移－膜破裂理论进行解释.

The Stress Corrosion Cracking (SCC) behavior of a new ultrahigh strength stainless steel Cr12 was studies by Slow Strain Rate Tensile (SSRT) test and microstructure observation of fracture surface. The results indicate that the neck surrounding area of Cr12 steel tested in air is the crack origin and fast-propagating region, mainly with a quasi-cleavage fracture. In the weak acid solution, the SCC susceptibility of Cr12 steel increases and the fracture surface remains quasi-cleavage fracture, and slippage steps appear in some local areas. In the weak acid spray test, the oxygen is able to fast diffuse through the thin film to the reaction interface, therefore the cathodic reaction is enhanced by the sufficient amount of oxygen and the passive films are destroyed. The Cl－significantly increases the SCC susceptibility of Cr12 steel by reducing the strength and plasticity of the steel. The pitting is the origin of stress corrosion crack and the SCC mechanism of Cr12 steel is able to be explained by using the slip and cracking of passive film theory.