The technique employed to eliminate oxide skin and rust on the surface of steel from the surfaces of steel and iron, utilizing acidic solutions, is denoted as pickling.
Iron oxides such as oxide scale and rust (Fe3O4, Fe2O3, FeO, etc.) undergo chemical reactions with acid solutions, forming salts that dissolve in the acid solution and are removed.
undergo a chemical reaction with acidic solutions, resulting in the formation of soluble salts that are subsequently extracted. Acids to the pickling process encompass sulfuric acid, hydrochloric acid, phosphoric acid, nitric acid, chromic acid, hydrofluoric acid, and composite acids. Predominantly, sulfuric acid and hydrochloric acid are favored choices. Pickling methodologies primarily include immersion pickling, spray pickling, and acid paste rust removal.

Generally, immersion pickling is commonly used, and spray method can be used in mass production

Steel components are conventionally subjected to pickling in a 10% to 20% (by volume) sulfuric acid solution at an operational temperature of 40°C. Replacement of the pickling solution becomes imperative when iron content surpasses 80g/L and ferrous sulfate exceeds 215g/L in the solution.

At room temperature, pickling steel with a 20% to 80% (volume) hydrochloric acid solution is less prone to corrosion and hydrogen embrittlement.
Owing to the pronounced corrosive proclivity of acids towards metals, corrosion inhibitors are introduced. Post-cleansing, the metal surface exhibits a silver-white appearance, concurrently undergoing passivation to augment the corrosion resistance attributes of stainless steel.

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