Intergranular corrosion curves

Cihal and Prazak determined the resistance of 18/8 stainless steel to this type of corrosion. They claimed that the technique could be used on steels which are difficult to test by other methods, including steels of low carbon content, and steels in which stabilising elements are present. By means of potentiostatic curves and light etching at constant potential they confirmed that the extent of intergranular corrosion depended upon the amount of precipitated chromium carbide. 

Effect of Thermal History of Austenitic Stainless Steels on Susceptibility to Intergranular Corrosion. The time dependence for the local depletion of chromium sufficient to cause susceptibility to intergranular corrosion as functions of temperature and carbon content is of the form represented in Fig. 7.54 (Ref 83). The curves are typical of type 3xx alloys with nominal chromium concentrations of 17 to 25 wt% and, since they represent times for initiation of intergranular corrosion,... 

Fig. 7.54 Time-temperature-sensitization curves for susceptibility to intergranular corrosion. Parameters are carbon concentrations in type 304-based stainless steels. Redrawn from Ref 83...

Fig. 7.56 Time-temperature-sensitization curves for intergranular corrosion of type 347 stainless steel in boiling 65% nitric acid, mpy, mils per year. Source Ref 85...

Fig. 7.67 Correlation of EPR test values on type 316 stainless steel with ASTM A 262E test for susceptibility to intergranular corrosion. Circles indicate time-temperature treatments prior to test. Numbers at points are EPR values (Pa) of the same steel. C-curve defines times beyond which steel does not pass ASTM A 262E. Redrawn from Ref 105...

The susceptibility to intergranular corrosion of a chemically resistant steel depends on the carbon content, the duration of the sensitizing temperature, and the temperature of prior solution annealing, it is represented in a time-temperature diagram. Curves of this type are shown in Fignre 20.26 for an austenitic steel with approximately 18% chromium, 8% nickel, and various carbon contents. The curve encompasses the respective area of susceptibility. 

Fig. 2-18 J U) curves and critical potential range for intergranular stress corrosion (hatched) for a hardened 10 CrMo 9 10 steel (ASTM P21) in boiling 35% NaOH — potentio-dynamically measured with +0.6 V h - - potential change after every 0.5 h At/ = +0.1 V x-x-x potential change after every 0.5 hAf/ = -0.1 V.

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