Chromium content removal

At the smallest chromium contents (< 1%) the chromium ions are present as isolated ions far removed from each other. This is the extreme S phase. As the chromium concentration increases we pass through a region in which chromium pairs, triplets, quadruplets, and other small clusters predominate. Finally, at even higher concentrations large clumps of chromia (the bulk or j3 phase) account for most of the chromium. Eischen and Selwood s (5) point I appears to correspond to the initial buildup of the )3 phase. 

But wear resistance and corrosion resistance are fundamentally contrary material properties, since in the case of corrosion-resistant steels, adequate corrosion protection is to be anticipated only if the chromium content in the matrix is above 12% by mass. Carbon has a high affinity to chromium and removes it from the matrix to form carbide, so an increase in wear resistance is to be anticipated with increased carbon content, but combined with a reduction in corrosion resistance. This situation is exacerbated by the fact that wear processes and corrosion processes normally occur together. Under certain circumstances there may therefore be corrosive attack, since abrasive wear removes passive layers, which cannot be regenerated quickly enough. Conversely, corrosion can also create wear particles. 

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