Thats right. Thats why mostly stainless steel is pickled before passivation.
Other reasons can be that the environmental conditions are not "agressiv" enough to form a passivation layer.
The chemical passviation process is actually a cleaning operation that removes traces of free iron from the surface to assure that the passive film is as robust as possible.
The parts that are machined, are made from bar stock. In our manufacturing process we use carbide tooling, T-15 tooling with a TIN coating. I have machined many parts and placed the parts in a copper sulfate solution (10 min.) with no signs of copper what so ever. So I have to believe the section of ASTM-380 and ASTM-967-05 states that my clean parts are in fact passivated.
So my question is, "Do I need to passivate myparts?"
(I am trying to justify not passivating)(It could save a lot of process time / money)
We have no idea what your requirements are. Maybe you can eliminate passivation, maybe not. Regardless, passivation after your machining operation will improve corrosion resistance.
Do you use the exact same carbide tool or T-15/TiN coated tool to machine plain carbon steels? Does the stainless steel come into contact with any fixtures, tubs, conveyors, etc. that are used to process plain carbon steels? If the answer to these questions is yes, then the parts need to be passivated.
How well do you clean your parts? You can have free iron particles within your coolant that isn't filtered out or mineral deposits from hard water that adhere to your part that can drive corrosion over time. If using a water-based coolant, are you using DI water, RO water, or just normal tap water? Each poses an issue.
Take a sample part and soak it in a 5% NaCl salt bath for 48 hours (if you don't have a dip tester or salt spray capabilities) and see what comes of it. That might be a quick way to see if you have a potential problem.
