49543

Material hardness required prior to passivation? [California] 

August 1, 2008

I am a mfg. engineer for a supplier of aerospace components. The material I will refer to specifically is 440C, but it could apply to all martensitic alloy SST materials: I have read that the material hardness of 440C must be above Rc58 before passivation should be attempted. When I first read this I experienced an "Aha!" moment. I was investigating why a particular machined component was failing it's final magnetic particle inspection. I discovered the parts receive a passivation (old QQ-P-35 PRIOR to heat treat to Rc58 to Rc62 (Mil-I-6868). I have been scrounging for more information on the hardness necessity before passivation with absolutely no luck (yet). This is an older design (1973), and I do not know the reason behind the sequencing of the processes, but I was told by a long-time employee that it had to be done this way otherwise the passivation would destroy the material. In disbelief, I suspect that they experienced some contamination in the process previously.

Can someone please explain the reason for the hardness necessity, and what happens to the structure of the material? It seems like it does explain why we are all of a sudden failing mag particle. Is there an industry reference that will reference the condition requirements? Thanks to anyone that can help.

David Vranson
Mfg Engr - Valencia, CA, USA

Contact Carpenter Technology. They will give you the background on this.

Lee Kremer Stellar Solutions, Inc. Algonquin, IL, USA