Solution annealing 17-4, how much vacuum? 1

[musashi99]

I want to solution anneal 17-4 in a vacuum. We have a spare tube furnace (6” tubes) that is used for semi conductor production. Our problem is that it is an atmosphere furnace. How much vacuum do I need to pull and maintain to avoid surface oxidation? Thanks!

 

[israelkk]

From my experience every time I quote heat treatment of PH alloys in a vaccum furnace it did not help to avoid oxidation even if the part looked clear. When we wanted to passivate it a chemical/mechanical removal of some oxidation was needed to recieve a sound passivation that will meet QQ-P-35. The removal caused an uncontrolled change of the part dimensions.

I ended up heat treating PH alloy before machining and machine all dimensionS in the heat treated condition.

If someone else has another experience I will be glad to hear about it.

 

[EdStainless]

We have used both bright anneal and oxide anneal. We like the bright anneal better since these alloys are so easy to over-pickle.
We have has parts vacuum hear treated, but there always is a little surface oxidation so a light pickle was required.
The slight oxidation from the aging isn't enough to cause problem.

= = = = = = = = = = = = = = = = = = = =
Corrosion never sleeps, but it can be managed.

http://www.trenttube.com/Trent/tech_form.htm

 

[mcguire]

Maybe Ed's experience is the same but in sheet bright anneal lines, it's almost impossible to escape a slight oxidation during cooling, so a light nitric acid pickle is used to remove this oxide with no ill effects.

 

[dgallup]

Sorry to hi-jack this thread, but here goes.

EdStainless: What do you mean exactly by "both bright and oxide anneal"? What is the difference and how can you be sure of getting a bright anneal? Also, can you give me a precise definition of "a light pickel". I don't think I can get that from Heinz.

We now return you to our regularly scheduled programing.

 

[metman]

Bright annealing can be accomplished in a H2 atmosphere providing the the dewpoint is below -40C.

 

[lgearhart]

First of all, if you want it clean coming out it has to be clean going in. Traces of oil, grease and other soils become quite visible after the high temp bake.

Secondly, vacuum furnaces are different. We have diffusion pumps on ours, and they get to 10^-3 or 10^-4 Torr readily. We don't have any problem with discoloration. Our LA facility has vacuum furnaces with only mechanical pumps, and theirs gets down to 10^-1 Torr. It's not surprising they see more discoloration than we do.

Oh, and to put in a shameless plug, AMS 2769 is a specification on vacuum heat treatment, so it's a useful reference document when dealing with supplier-purchaser issues. But what's best about it is the charts of metal vapor pressures in the back. They make it easy to explain to folks why we have chromium deposits on the cooler regions of our furnace interior.

 

[Maui]

If you want to solution anneal 17-4PH in an atmosphere furnace, the easiest and least expensive way to avoid surface oxidation is to paint the bars with no-carb paint. The paint will burn off during the solution annealing process, while protecting the surface from oxidizing. I've run several experiments to study oxide formation on solution annealed 17-4PH in atmosphere furnaces. When applied correctly, no-carb paint works surprisingly well.

Maui

 

[mcguire]

Maui
Can you give some brands or specs for the paint for the book?

Michael McGuire

http://stainlesssteelforengineers.blogspot.com/

 

[Maui]

Mike, the following web address lists the type of no-carb paint that I mentioned:

http://www.heatbath.com/Products-link-page.htm

You can contact Heatbath directly at (313)-895-7215 for more specific information regarding this type of paint.

I thought that your book was already in print!

Maui

 

[mcguire]

Believe it or not, it is at the beginning of a two year writing.

Michael McGuire

http://stainlesssteelforengineers.blogspot.com/