Here's a step by step on how I prepare steel parts I plan on painting with POR-15..
If there is any old paint on the parts..It must be removed before following these steps..Sandblasting is the preferred method, but a wire brush/wheel works too..
Get a jug of Muriatic Acid at your local store..Make sure you buy enough to completely immerse whatever parts are going to be painted..
Then place the parts in a plastic tub of Muriatic Acid, and let them soak for at least a half hour..Smaller parts take less time to soak..
After you have soaked them for enough time..They should have a grey color to them..Don't soak them for too long, or there will be nothing left of the part..
Once the parts are done soaking in the Muriatic Acid..Get another plastic container big enough to completely immerse the parts..
The second container should be filled with plain water, and Baking Soda..Mix the Baking Soda thoroughly with the water..Once you've done that..
Then take your parts out of the Muriatic Acid container, and let them soak in the container full of water, and Baking Soda..
This should only take a few minutes..Usually once the part stops bubbling you know that the acid has been neutralized..
Then rinse the parts in boiling water..Water only this time so you can rinse any Baking Soda that might still be on the parts off..
Next lay the parts on a clean surface, and use a heat gun on it's highest setting to completely dry any liquid that may be left on the parts..
Once you're done with that..Lay the parts on a clean surface, and apply the POR-15..
I've used this method successfully many times..
If you use a different paint..I can't guarantee good adhesion..
This is the process I use when painting steel parts with POR-15..
I almost forgot..Use chemical gloves, and a face shield to prevent any acid from splashing on your arms or face..
Be careful with the acid..It can seriously fuk you up!