Steels continued intergranular corrosion

In boiling water reactors chromium steels behave similarly to those in pressurised water reactors. 13% chromium steels withstand the effects of steam (700 °C) in continuous operation [75]. Chromium steels with 13-17% C are especially sensitive to intergranular corrosion after being welded. Also, riveted joints were seen to have pitting corrosion up to 1.7 mm in depth as well as crevice corrosion after one year [76]. 

The research on corrosion, started in this institute in the 1950s, continued successfully further. The intergranular corrosion of steels was measured by an electrochemical potentiodynamic reactivation method [310-312]. Since the 1960s, the passivity of brass was further studied, the rates of corrosion were measured by polarization resistance, the effect of deformation on anodic dissolution of steels was followed, and the surface roughness of metals was measured other subjects of research were, e.g., the behavior of passive films on steel, the effect of compositirai and motion of electrolyte on corrosion of passivated aluminum, the cathodic protection of passive metals against corrosion, the anodes for cathodic protection of steels, etc.[313-316]. Measurements of polarization resistance in the system iron—concentrated sulfuric acid or boiling nitric acid, of corrosion and matter... 

The postulate states that the presence of a continuous second phase leads to intergranular attack, does not seem to be valid because of the observation that steel 316 in which sigma phase precipitated at the grain boundary showed no acceleration of intergranular corrosion until the solution was made highly oxidizing. 

When the precipitation is relatively continuous, the depletion renders the stainless steel susceptible to intergranular corrosion, which is the dissolution of the low-chromium layer or envelope surrounding each grain. Sensitization also lowers resistance to other forms of corrosion, such as pitting, crevice corrosion, and SCC. 

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