Features of how pitting corrosion develops on steels in nitrate-chloride media are analyzed, and the disadvantages of certain well-known electrochemical methods used to determine safe ratios of components under such conditions are found. A principally new approach to determining these parameters is proposed, based on the induction of intense pitting in definitely aggressive media with subsequent suppression of this process by continuously dilution of the solution or by gradual addition of an inhibitor. Equations are obtained for determining safe component concentrations depending on the volume of solution passing through the cell. Using the proposed method, safe ratios of components are determined for 12Kh18N10T chromium-nickel steel at chloride ion concentrations within 0.02-2.0 M.
Repeated quenching of steel 08KhiSGSN2T (see Table 2) from l000~ did not eliminate the tendency to intercrystalline corrosion~ Repeated quenching of the specimen of steel of the same melt from 1200~ and subsequent inductive heating at 550~ did not cause intercrystalline-corrosion tendency. This was apparently because after quenching from 1200~ the structure of this steel contained a predominant ferrite component, For steel 08Kh22N6T, intercrystalline-corrosion tendency was observed only after quenching from I050~ and an increase in the time of inductive heating at 550~ to 8 h~ Intercrystalline-corrosion tendency was not detected on specimens of steel 08Kh21N6M2ToBending of the specimens to 30 ~ on a mandrel with a radius equal to twice the thickhess of the specimen caused strain of the outer fiber of the specimen of not more than 5% and, therefore, could not be the cause of crack formation in the absence of intercl~stalline corrosion. An increase in the boiling time of two-phase steels in tests by the ~U method to 56 h should not be considered as a significant increase in the severity of the test conditions in comparison with the conditions recommended by GOST 6032-75 because even during boiling for 56 h and bending of the specimens to 30 ~ , the depth of corrosion in meta!lographic investigation was 5-10 ~m, something which corresponded to low intensity of intercrystalline corrosion determined by a standard method.
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