Cold Work Sensitization

It has long been recognized worldwide that also a cold work process particularly severe can contribute to corrosion in austenitic stainless steels by sensitizing the material [15-19]. Grinding must be completely rejected, in particular when high speed without lubricant is used. The sensitization process is due to two simultaneous actions. First, any heavy cold-working may leave a system of traction residual stresses (see Sect. 3.4 and Fig. 3.11) that favor stress corrosion. Secondly, plastic deformations induced by cold working may transform part of the metastable austenite into brittle martensite. 

Martensite is inclined to stress corrosion. Micro-fissuring can easily occur in brittle areas of martensite on the surface of the specimen exposed to the potentially aggressive environment. Stress corrosion may start from this surface scratches and 

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Fig. 14.12 Cold work sensitization and martensite formation in surface grains of austenitic stainless steel, type 304, after grinding...

There is no question that past-plant experience is of crucial importance, since this acts as a "calibration point" that must be explained by any life prediction methodology. For instance, the methodology must be able to explain quantitatively the relative contributions of various system parameters (such as cold work, sensitization, weld repairs, etc.) to the incidents of stress corrosion cracking in piping in BWRs that have been observed in a given operating period (Figure 18.6). 

V. Kain, K. Chandra, K.. N. Adhe, P.K. De, Effect of Cold Work on Low-Temperature Sensitization Behavior of Austenitic Stainless Steels , Journal of Nuclear Materials, 334 (2004), 115-132. 

Because of the sensitivity of the platelets to strain energy, their nucleation should be sensitive to the working history of the billets from which the alloy specimen is made, and, not surprisingly, PtCo responds well to cold working before heat treating. Work by Shimizu and Hashi-moto (35), who tempered PtCo under elastic stress far below its elastic limit, has shown that the alloy develops considerably lower coercivity... 

Unless heavily cold worked, the austenitic stainless steels are resistant to hydrogen stress cracking such as that caused by hydrogen sulfide. They are also resistant to hydrogen embrittlement caused by phenomena other than cathodic charging. If sensitized, austenitic stainless steels can also be susceptible to intergranular corrosion. 

Relationship of Composition and Heat Treatment to Environment-Sensitive Cracking of Aluminum Alloys. Those aluminum alloys strengthened by cold working only, particularly the 1000-series alloys, do not develop susceptibility to SCC. The so-called high-strength alloys are strengthened by thermal/mechanical treatments, which result in solid-state precipitation of one or more intermetallic phases that restrict dislocation motion and, hence, increase strength. Their susceptibility to SCC varies extensively with alloy composition and the thermal/mechanical treatment. While susceptibility tends to increase with... 

Except for chemicals produced in the environment by radiation, such as HNO3 and H2O2, which have a secondary effect on corrosion, or formation of localized displacement spikes during radiation, the effect of radiation may be expected to parallel that of cold work. That is, metals for which the corrosion rate is controlled by oxygen diffusion should suffer no marked change in rate after irradiation. In acids, on the other hand, irradiated steel (but not pure iron) would presumably have a greater increase in rate than would irradiated nickel, which is less sensitive to cold working. 

In heavily cold worked materials as well as in sensitized materials, IGSCC has been observed... 

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