Pickling and passivation

2021-10-12

Pickling and passivation

1.    Introduction

Austenitic stainless steel has good corrosion resistance and good cold and hot working performance, so it is widely used to manufacture various kinds of parts with anti-corrosion requirements. The passive film on the surface of austenitic stainless steel has a great influence on its corrosion resistance. The passive film of austenitic stainless steel is mainly obtained by pickling and passivation.

2.    Formula

Pickling solution: 20% nitric acid + 5% hydrofluoric acid + 75% water

Passivation solution: 5% nitric acid + 2% potassium dichromate + 93% water

Pickling passivation solution (two in one): 20% nitric acid + 10% hydrofluoric acid + 70% water

3.    Operation

a.     Pretreatment:

Remove the oxide coating by Shot blasting.

Clean welding spots on both sides, remove oil and other stains on the surface with gasoline or cleaning agent.
Heavy oil to be cleaned with 3-5% alkali washing solution. After washing, clean the surface with clean water.  

     b.  Pickling and passivation

Pickling and passivation (two in one) solution can complete pickling and passivation at one time. The temperature and time shall be strictly controlled. If the temperature is low, the time will be long, and if the temperature is high, the time will be short. Prevent matrix corrosion caused by failure to achieve pickling effect or excessive pickling.  After treatment, it must be thoroughly washed with clean water to make the surface free of residual liquid, so as to facilitate subsequent passivation treatment.