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Stain problem after passivation by HNO3

My company have process of passivation the steel by HNO3.
The process is as below:
Pre-degease (Resolve 152) => degrease(Resolve 152 & ultrasonic)=>HCL=>passivation(HNO3) => Neutralising(NaOH)=>Air spray =>oven

I found "brown stain problem on surface after passivation. I can't find the cause of problem.
Please suggest for me.

Thank you very much,

First of two simultaneous responses --

Are you using demineralized water? I suggest you run a sample using distilled water for chemical batching AND rinsing. Rinse VERY well. Measure the rinse water effluent conductivity to ensure it approaches (within 1-2 microsiemens) the original rinse water conductivity. Rinsing with pure water is paramount. Good luck.

Second of two simultaneous responses --

The brown stain is probably rust. Is this a stainless steel? Which alloy?
ASTM A380 is a guide to cleaning, descaling, passivation (and avoiding iron contamination) of stainless steels. HCl treatment isn't recommended; it can etch stainless steels. What is the HNO3 concentration, and when is it changed (at what Fe level or color)?
Rather than using a neutralizing rinse (which may leave rust-inducing salt residues), simply rinse in flowing tap water, with final rinsing in de-ionized water. Heating the DI water aids drying.

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