Patent ID: 6068001
Filing Date: 2000-05-30
Classification: C23C,C23G

Abstract:
Pickling process for chromium containing stainless steel comprising the steps of:placing the material to be treated in a pickling bath kept at a temperature ranging from 30.degree. C. to 70.degree. C., having the following composition:a) HCl from 20 to 100 g/lb) Fe.sup.3+ at least 15 g/lc) HF from 5 to 50 g/ld) additives selected from the group consisting of emulsifiers, wetting agents, polishing agents, and acid attack inhibitors; wherein the total amount of the additives is about 1 g/l of pickling bath,keeping said bath under agitation by a continuous air flow or equivalent agitation means;feeding said bath continuously or periodically with quantities of ingredients a) and c) securing the above stated concentration levels in the bath and a bath pH lower than 2.5;and feeding an oxidizer quantity suitable for keeping the bath redox potential at values of at least 200 mV, said oxidizing agent being selected among the following compounds:a) H.sub.2 O.sub.2, peroxidized acids, and salts thereof;b) oxidized chlorine acids: chlorous and chloric acids as alkaline salts thereof,said oxidizing agents being fed to the bath as such or as an aqueous solution thereof.