Transgranular stress corrosion cracking

The appearance of stress corrosion cracking may be either intergranular or transgranular in nature. 

Microstructural examinations revealed that the cracks originated on the external surface (Fig. 9.15). The cracks were highly branched and transgranular. The branched, transgranular character of these cracks is typical of stress-corrosion cracking of austenitic stainless steels. The thick-walled fracture faces are also typical of cracking by this mode. 

The fracture mode of stress-corrosion cracks in austenitic stainless steels can be transgranular, intergranular or a mixture of both. One of the earliest environments found to cause problems was solutions containing chlorides or other halides and the data due to Copson (Fig. 8.30) is very informative. The test solution for that data was magnesium chloride at 154°C the alloys contained 18-20alloy with a composition of approximately 18Cr-8Ni has the least resistance to cracking in this environment. 

SSRT TGSCC WOL transgranular stress corrosion cracking... 

Fig. 9. Potential-temperature diagram for sensitized TVpe 304SS in 0.01 m NaCl solution showing regions of different failure modes [29], TGSCC, transgranular stress corrosion cracking. Reproduced from Proc. 9th Int. Congr. Met. Corros., Vol. 2, pp. 185-201 (1984) by permission of the National Research Council of Canada.

Observations of the growth of transgranular stress-corrosion cracks at free surfaces, and examinations of fracture surfaces, have established that for several metal/environment systems, cracks propagate... 

M.G. Alvarez, C. Manfredi, M. Giordano, and J. Galvele, Anodic Rate Controlling Steps in Transgranular Stress Corrosion Cracking of Alpha-Brass in NaN02 Solutions, Corros. Sci., Vol 24, 1984, p 769-780... 

J.A. Beavers and E.N. Pugh, The Propagation of Transgranular Stress-Corrosion Cracks in Admiralty Metal,Metall. Trans., Vol 11A, 1980, p 809-820... 

Another specific version of stress corrosion cracking results from a chloride concentration cell. It is sometimes referred to as chloride embrittlement and can affect stainless steels. For the problem to appear a combination of local chloride concentration and transgranular cracking occurs, leading ultimately to metal failure. 

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