After-treatment of pickled steel - in heated acid bath contg. ferrous sulphate or chloride, potassium permanganate and nitrate

摘要

Steel, preliminarily pickled in H2SO4 to remove mill scale and rust, is after-treated, without intermediate rinsing, for 1 min., in a pickling bath heated to =80 degrees C, which consists of 0.4% FeSO4 oxidised to Fe2(SO4)3 with a stoichiometrically determined addn. of K permanganate (about 0.1%) with a small excess of H2SO4 (about 0.4%); and then set to pH 2-3 by addn. of 0.3% nitrate. In a modified process, steel is preliminarily pickled in HCl and after-treatment is effected by using FeCl2 and HCl.