Types of Stainless Steel Treatments
After stainless steel products are manufactured, they have to go through two treatment processes. These are called pickling and passivation.
Pickling treatment is used to remove the “scales” on the surface of a stainless steel product. The scales are often formed during welding operations and heat treatments. The cleaning agent involved is called “pickling paste”, which is made from nitric and hydrofluoric acids. Pickling treatment employed for all stainless steels, except those that have free machining grades, has 8-11% sulphuric acid. The item being treated will go through the process for 5-45 minutes at a room temperature of 80 degrees Celsius.
Passivation is used to remove iron on the surface of stainless steel products to avoid corrosion. If an item has about 16 percent chromium, it is treated for 30-60 minutes with 20-50 percent nitric acid at a room temperature of 40 degrees Celsius. If the grade is not more than 16 percent chromium, the treatment is done for 60 minutes with the same percentage of acid and temperature. For free machining grades, the treatment goes on for 25-40 minutes. 20-50 percent nitric acid is used along with 2-6 percent sodium dichromate at a room temperature of 50 degrees Celsius.