Passivating Heat Treated Stainless Steel

[msomerville]

I wasn't sure where to start this thread so I started it here.

I am having a problem with the company who passivates my stainless steel parts. The part is .265" long with a .75" diameter head that is .08" thick and a body diameter of .5". There is a .266" diameter hole through the part with a 100 degree countersink on the one side. Anyways the parts are then heat treated to 150 to 170 KSI. After that they go to get passivated to QQ-P-35 Type 2.
The problem is that the parts need to be blasted to remove any scale before passivation. There are usually 800 pieces at a time. They are half a$$ing the blasting so when they do whatever test it is that they do the parts are failing.
Here's my question; Is there something that I can do to them, possibly a vibratory tumble, to remove the scale before I send it over to get passivated?

Oh yeah the material is 15-5 PH.

[bookwurm99]

what do you mean by "passivating"? hard to get somebody to answer a question if they don't know what the terms are.

[cadman]

Originally Posted by bookwurm99 what do you mean by "passivating"? hard to get somebody to answer a question if they don't know what the terms are.

A common process to increase corrosion resistance of stainless steel. My guess is most people here know what it is or are aware/heard of it even if they don't work with SS.

msomerville: If the company is knowingly not removing the scale good enough then you should look elsewhere. If thats not an option, then tumbling may work if the scale is not too bad. Otherwise you may have to do a rough blast yourself.

[msomerville]

The thing is the blast can't be too aggressive becuase they specify the surface finish on the part.

[Geof]

Have you looked into controlled atmosphere heat treatment. The scale will be due to oxygen, or nitrogen or both so if the treatment was done in an inert gas atmosphere such as argon there should be no scale to remove.

[Kool Parts]

Geof is right on. Had the same problem years ago. Built a SS box with a bolt on end...welded 2 tubes (1/8) on the lid and bent them so they would go out the door edges. Had to grove the brick in the door for clearance.
Now I use the heat treat foil to make a bag for all the parts in the run and keep a flow of argon running though the box....no scale! They look brighter than they did going in

[wandrist]

It seems to me you have the wrong idea of passivation it is a nitric acid solution to remove the iron particles that get imbedded in the stainless from useing that type of tooling. When you heat treat and then blast to remove the scale you no longer need to passivate, because the iron which causes rust to form has been removed. If I can help further please let me know. All the parts we make are heat treated stainless.

[Geof]

I was taught that passivation was to create an even oxide coating on the stainless. It was not guaranteed to remove contamination by particles of ordinary steel. In fact sometimes the contaminating particles could act like a catalyst and cause deep pitting in the passivating bath. Other times the passivating would look okay but when the part was put in service it would display localized corrosion. The best example was a spray of corrosion spots on a part that showed how it had been sprayed by someone carelessly grinding mild steel and letting the sparks hit the stainless.

This was on equipment going into acid pulp digester systems not just for appearance. We had to keep all ordinary steel tools away from the stainless shop. It was even possible to cause problems by filing a piece of stainless and all wire brushes, grinder discs, sander belts etc were only used on stainless. The wire brushes themselves were made from stainless.

[msomerville]

I don't know that much about the passivation process. All I know that my print, calls out a passivation code. I can't give them a part that is not certified to their print. (FAA doesn't like that)
Originally we didn't have to blast the parts. They must not have had any scale. My goal here is to do away with the blasting procedure. I think the way I am going to go is to try to find someone with a vacuum furnace. To eliminate the blasting all together.
I think I tried to approach this all wrong. I should have been trying to keep the scale from being an issue, instead of trying to figure out how to get rid of it.