研究了不锈钢Ⅱ型单晶试样在４２％沸腾ＭｇＣｌ＿２溶液中的应力腐蚀。结果表明，对任何晶面取向的试样，其应力腐蚀裂纹均在最大正应力处形核，而在最大剪应力位置并不发生应力腐蚀．在最大正应力位置的周围虽有滑移线，但在裂纹形核的区域并无滑移线，而在有滑移线的地方却没有宏观裂纹。观察表明，有些滑移线上存在很多蚀坑，在蚀坑较轻微的滑移线上，有许多微裂纹，这些裂纹与滑移线成一定角度（约２０°）．在应力腐蚀裂纹的形核与扩展中起作用的是位错局部塞积所形成的应力集中．位错塞积应力与电化学过程的联合作用下导致了应力腐蚀开裂，金属表面的滑移台阶虽然也会发生腐蚀，但并不起主要作用。
SCC of 321 stainless steel(SS) single crystal was studied under mode II loading in a 42% boiling MgCl2 solution. The results shown that SCC initiated at the maximum normal stress site, while no SCC occurred at the maximum shear stress site. Although there were slip lines around the maximum normal site, most of SCC did not occur along the slip lines. Some micro-cracks could be observed on the slip lines using scanning electron microscope , but cracking direction was inclined about 20 degrees to the slip line and these microcracks did not propagate. The slip lines could appear owing to heat activation when a polished constant displacement specimen was heated at 150℃ for 2 h. The slip lines appeared during heating were polished before SCC experiment, SCC still initiated at the maximum site while no slip step emergence on the specimens. Those results are conflict with the″slip－dissolution ″ model of SCC. The SCC mechanism of austenitic stainless steel may be relative with the stress concentration due to dislocation pile－up, but not with slip steps. The normal stress plays an important part in the SCC.QIAO Lijie, associate professor,(Department of Materials Physics, University of Science and Technology Beijing, Beijing 100083)
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