... ° C, or with HCl 20%, methenamine 3 ~ 5g / L, 20 ~ 40 °C for pickling. Adding corrosion inhibitors prevent ... coating and the substrate binding. NH4Cl 100-150g / L, ZnCl2 150-180g / L, 70 ~ 80 °C, 1 ~ 2min. And ... and different holding time, the amount of dissolved iron, i.e. the amount of the iron loss is not the ... ferrous content, does not allow more than 4g / l, PH value is always maintained at 4.5-5 ...