POTENTIOSTATIC ETCHING OF DUPLEX STAINLESS-STEELS AND HIGH CHROMIUM WHITE CAST IRONS

The reasons for potentiostatic etching and the way in which it is carried out are explained. The technique was applied to some commercially important materials, and the information obtained is described. It was found that the chromium content of duplex stainless steels had a significant effect on the etching potential, but did not greatly influence the etching time. In high chromium white cast irons (HCWCIs), the composition of the various alloys influenced the etching potential very little, and it was possible to deduce a generally suitable etching range of 950-1050 mV (SCE)for the whole group. Manganous sulphate proved to be a superior etching agent, and very fine detail, e.g. different types of carbide, could be detected in HCWCIs after potentiostatic etching in this solution. Quantitative phase determinations were also possible for all materials investigated, provided that suitable etchants were used. Optimum etching times were from 10 to 15 s, regardless of the group of materials investigated.