Effects of Mn and Cu on descaling of hot-rolled 304L stainless steel in HCl and H2O2 mixtures

Descaling of stainless-steel black coil is an important step to produce white coil with smooth glossy surface. The AISI 304L black and white coils from a company containing 1.08–1.71Mn and 0.22–0.40Cu (wt%) were used to study the effects of Mn and Cu on descaling rate by potentiodynamic polarization technique at 25 °C. The pickling solutions were 0.5 M HCl and 0.5 M HCl mixed with H₂O₂ of 0.5, 0.88 and 1.76 M. The polarization curves of black and white coil samples measured in HCl–H₂O₂ mixture showed no passive range. The descaling rate of black coil oxide scales, and the corrosion potential (Ecorr) increased with H2O2 concentration. Low-Mn sample, that is 1.08%Mn0.23%Cu sample, showed higher descaling rate than high-Mn samples. No effects of Cu content on the descaling rate were observed. For white coil samples, the descaling rates were almost constant, but pitting on surface was observed. Passive films were eliminated. The corrosion potentials of black and white coil samples increased when adding H2O2 in HCl solution indicating an increase in cathodic reaction due to increase in dissolved oxygen. The corrosion potentials of 1.08%Mn0.23%Cu black