Passivation is still one of the essential processes which can maximize the level of corrosion resistance with various components and parts made out of stainless steel. What is important to understand about passivation is that it can be very beneficial by making materials resistant but only if done properly.
However, if not, it can actually go in the opposite direction and cause corrosion. This is why it is important to understand how the process is done and to do it correctly to avoid wasting money and valuable time.
1. Start with cleaning
No matter which material is passivated the cleaning process should always come first. It is essential to remove any remaining coolant or grease from the surface to achieve the best possible resistance to corrosion. Some parts can be wiped off with a cleaning cloth while others will require cleansers or degreasers.
Some additional residue from thermal oxides should be grinded-off as well. If this is not done, the remaining substances and materials on the surface will simply react to the passivating solution and cause negative effects while weakening the material.
2. Put the parts into passivating baths
After you’ve thoroughly cleaned your parts, prepare a passivating bath and immerse them in it. There are three types of passivating baths for passivation cleaning:
- Nitric acid passivation
- Citric acid passivation
- Combination of sodium dichromate and nitric acid passivation
All of these different approaches are meant for different kinds of stainless steel. Before you start the process, you will have to determine two things – which one is best for your type of steel and how long does it last. Adding the right solution for your material is essential or you might end up damaging it.
3. Testing the parts
It is often required to analyze the surface of the parts that have been passivated to see what their capabilities are. However, the most important thing that needs to be determined is whether the process of passivation improved corrosion resistance and did it remove all of the free iron?
The test method needs to be matched with the grade that is analyzed. If it is too severe, it could damage the material while the one that is weak will simply pass materials that aren’t up to the standards. As it is with baths and the process of passivation, the tests also need to be adjusted based on those factors as well as the type of steel.
These are the three essential steps for passivation, and without them, it isn’t possible to end up with quality, high-resistant stainless steel.