The Use of Atomic Force Microscopy to Detect Nucleation Sites of Stress Corrosion Cracking in Type 304 Stainless Steel Available to Purchase

The nucleation of intergranular stress-corrosion cracking (IGSCC) in Type 304 stainless steel was investigated using atomic force microscopy (AFM). A new test technique with an AFM fluid cell and a miniature specimen bending device was used for the in-situ measurements. It was found that upon plastic deformation of the annealed and sensitized stainless steel slip lines piled up at the grain boundaries. As a result of the increased localized stresses, some of the grain boundaries opened, particularly at grain boundary triple points and grain boundary — twin boundary intersections. These openings were typically 1 to 2 μm wide and about 1 μm deep. After exposure of the specimens to an aqueous 1000 ppm sodium thiosulfate solution small cracks (< 1 grain diameter) formed from the opened sites within a few hours of the exposure. This indicated that the opened triple points act as nucleation sites for the cracks.