Environmental Engineering Reference
In-Depth Information
Figure 3.42
Effect of carbon content in very low carbon steels quenched from 920°C
on SCC in a calcium nitrate-ammonium nitrate solution.
SCC in any particular alloy system and the susceptibility varies significantly with
potential and pH.
The electrochemical mechanisms of SCC (see next section) visualize the initi-
ation and growth of crack as an intense anodic dissolution along a narrow front
that is possible only if the metal surface and the crack wall remain inactive. To
provide such a condition, the stress-corroding solution should either be able to
form a protective surface film or locally destroy any such existing film. Therefore,
the alloys with high inherent corrosion resistance due to the presence of protective
or passive films such as aluminum and titanium alloys and stainless steels require
aggressive halide species to promote SCC. On the other hand, inherently reactive
metals like carbon steels or magnesium-base alloys require the presence of an
