Effect of ferric ions in AISI 316L stainless steel pickling using an environmentally-friendly H2SO4-HF-H2O2 mixture

A mixture of hydrogen peroxide, sulphuric and hydrofluoric acids has been used as pickling solution at pH 2.0 for AISI 316L austenitic stainless steel (SS). The stability of the H2SO4-HF-H2O2 mixture is assessed varying the ferric ions content from 0 to 40 g/L, the temperature from 25 to 60 degreesC, and with and without stirring of the pickling solution. The AISI 316L SS pickling rate at 50 degreesC was 2.6 and 0.2 mg/dm(2) day (mdd) in the absence and presence of 40 g/L ferric ions, respectively. p-toluene sulphonic acid (PTSA) has been used as stabiliser of hydrogen peroxide.