17-4 pH Pickling Problem

Can anyone help. We are an investment casting house. I currently send my 17-4 pH stainless out to be pickled. The vendor uses a 20%nitric-8%HF bath for the operation. He called me today and said that the parts were causing a boil in the tank, and giving off a yellow nitric gas. The parts upon removal also look like copper is being leached out. Could this be a chemistry problem? The parts were solution annealed and aged per ASTM specs. I would greatly appreciate any help on the matter.

Thank You.

1 of 2 simultaneous responses 2000

Shawn:

From what you described, the parts are definitely being attacked by the nitric/hydrofluoric bath! This is a very dangerous situation. This would definitely cause the copper in the 17-4 to come to the surface. We normally have excellent results with our proprietary citric acid formulations. We are willing to test some parts for you, or send a sample to you or your processor.

Regards, Lee Kremer

2 of 2 simultaneous responses if copper has been previously pickled in the same solution i.e. in a cooler then the copper will be suspended in the solution and binds to the steel. We use 18% nitric 2%hf and have no problem with annealed components, we don't suffer from NOX fumes either. How old is the solution?