What is the Steel Passivation Process?

Steel passivation refers to the process of chemical removal of iron contaminants left on the surface of stainless steel parts after machining. Passivation maximizes resistance to corrosion. A number of passivation methods exists for various specific types of steel.

Cleaning

The passivation process begins with completely removing any foreign substance, such as grease and shop debris from the freshly machined steel surface. Wiping and grinding or using degreasers and cleansers can all be used as cleaning methods.

Passivating Bath

After rinsing with water, the steel component is placed in a passivating bath consisting of any one of several acid solutions, depending on the grade of stainless steel. The solution chosen, its concentration, immersion time, and temperature of bath all depend on the type of alloy. An unsuitable bath can damage the component. A water rinse follows the bath. Sometimes sodium hydroxide is then used to further neutralize the acid before a final water rinse.

Trained Personnel

Since passivation involves the use hazardous chemicals, only trained and experienced workers wearing protective clothing and following correct safety procedures should be involved in the process. In addition, legal permits may be required.

References

• Imagineering: Passivation
• Gardner Publications: Modern Machine Shop