What is stainless steel pickling and passivation?

Thread Content

The main purpose of pickling is to remove the oxide film on the surface of stainless steel. After pickling, a dense oxide film forms on the surface of the stainless steel; this process is known as pickling and passivation. This layer of film is key to preventing stainless steel from rusting or corroding in normal environments; therefore, stainless steel does not necessarily require pickling, except when there is oxide scale on its surface. Stainless steel pickling is often associated with passivation. Stainless steel that requires pickling must also be passivated; otherwise, no passivation film forms on its surface after pickling, or the resulting film is extremely thin and ineffective. Therefore, a subsequent passivation process is necessary to form and perfect the passivation film on the stainless steel surface. For example, by using a protective gas such as pure hydrogen. Stainless steel refers to steel that is resistant to corrosion by weakly corrosive agents such as air, steam, and water, as well as by chemically aggressive agents such as acids, alkalis, and salts; it is also known as acid-resistant stainless steel. In practical applications, steel that resists corrosion by mildly corrosive media is often referred to as stainless steel, while steel that resists corrosion by chemical media is called acid-resistant steel. Due to differences in their chemical compositions, the former is not necessarily resistant to corrosion by chemical media, while the latter generally exhibits corrosion resistance. The corrosion resistance of stainless steel depends on annealing under a protective atmosphere, during which the alloying elements contained in the steel decompose. No pickling is required in this process. 1: The primary and only purpose of pickling is to remove the oxide scale from the surface of stainless steel. Oxide scale forms when heat treatment is carried out at high temperatures without the use of a protective gas. Therefore, stainless steel does not necessarily need to be pickled; it’s only necessary when there is oxide scale on its surface. 2: Additionally, for instance, annealing under the protection of shielding gases such as pure hydrogen or atmospheres generated by ammonia decomposition does not require pickling. 3: Stainless steel pickling is often associated with passivation. Stainless steel that requires pickling must also undergo passivation; this is because after pickling, no passivation film forms on the surface, or the thickness of any such film formed is too minimal to be effective. Therefore, a subsequent passivation process is necessary to form and perfect the passivation film on the stainless steel surface. The stainless steel pickling and passivation agent LD4008 is colorless; it performs passivation for 5–20 minutes at room temperature. It combines pickling and passivation in one product, and is suitable for the pickling and passivation of austenitic materials in dormitories, enhancing their corrosion resistance. The surface resulting from its use appears silver-white. 25kg/bucket, 20 yuan/kg, 500 yuan/bucket. Stainless steel pickling solution KM0201: colorless; it undergoes passivation for 5–20 minutes at room temperature. It does not have passivation properties, but it effectively removes weld scales, stubborn oxide layers, and rust from various stainless steel surfaces, leaving the surface with a silver-white appearance. 25kg/bucket, 16 yuan/kg, 400 yuan/bucket. Stainless steel brightening pickling solution KM0203: colorless and foamy. Passivation at room temperature for 5–15 minutes. It is suitable for both natural and glossy finishes of Su Shi 00 series materials; it also has a certain passivating effect on vegetarian 00 series materials. 25 kg per barrel; price: 20 yuan/kg; total cost per barrel: 500 yuan. Stainless steel pickling solution KM0204, orange-yellow in color. It becomes unavailable for use for 3–8 minutes at room temperature. This solution effectively removes all types of oxide scales and rust from the surface of stainless steel, improving its brightness by more than two levels. It also possesses certain rust-preventing properties. 25kg/barrel, 16 yuan/kg, 400 yuan/barrel