Metallurgical factors such as heat treatment and cold-work are not important when corrosion in aqueous media is controlled by diffusion of reactants, e.g. dissolved O2, from the environment. They become important when corrosion control is focused at the metal surface, e.g. steel in acids. In this instance, galvanic cells depend less on where or how metal atoms are placed in their lattice, and more on compositional differences along the metal surface produced by heat treatment or plastic deformation.
At elevated temperatures, compositional gradients within a metal are less important. The rate depends instead on diffusion through thick corrosion product layers and on the tendency for spalling to occur during temperature fluctuations. Metallurgical factors assume greatest importance during initial oxidation, or for thin film formation.
