Letter 35063

DISCOLORATION DURING DURING H950 HEAT TREAT  

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We have been experiancing Parts turning Brown during H950 heat treat.We have batches of 25 pieces where 22 parts will come out bright and shiny and 3 pieces will be brown. The material was from 2 different lot numbers. Our parts have been cleaned in Acetone [link is to product info at Rockler] by hand and in a vapor degreaser using a solvent called,
RHO-TRON 225AES-l 3-3 Dichloro 1,1,1,2,2-Pentafluoropropane, we are getting speratic discoloration no matter how we clean the parts. Our Abar Furnaces are calibrated every six months and burn-outs are performed regularly at least monthly. I thought I read some where that 15-5PH material can discolor, am I wrong or is there a process related problem. Is it caused by an increased amount of one or more chemicals in the composition? We also use SST Foil to cover our parts and aluminum oxide on the bottom of our SST Heat Treat Trays. I would appreciate any input.

Bob Blanchard
Aerospace - Costa Mesa, CA, USA

Bob, the brown discoloration is either coming from a leak in the furnace, somehow getting through your gettering foil, or it is from a residue that isn't fully cleaned off your parts before you put them into the furnace. My GUESS is the latter, since a leak would tend to either discolor everything or leave a gradient, brown to yellowish, should the leak be directional and localized. Residue from the cleaning could mean the parts are insufficiently dry when you load them in the furnace, or that something dissolved in say, the acetone, isn't being cut by the polysyllable cleaner you're using.

Good luck!

Lee Gearhart metallurgist East Aurora, NY

Bob,

We have been experiencing the same problem in attempting to heat treat 17-4PH to H900 and still meeting a no-discoloration spec.


I agree with Mr. Gearhart, in that the two main areas of interest would be leak detection and part preparation.

We have been attempting this with an Electra atmospheric furnace. Our best results have come after ultra-sonic vapor degreasing with trichloroethylene,after load we have been drawing down to a vacuum of at least 50 microns, followed by a lengthy purge with Nitrogen. We have had the best results running Hydrogen as our process gas, but not knowing the details of your furnace I would not suggest the Hydrogen unless you have the proper controls in place first.

We have not seen any improvement with foil shielding our parts, but have invested in an Oxygen Sensor as part of the Hydrogen control. Yo may want to check dew point and/or oxygen content of gases you might be using.

Our test runs have been much the same as yours, with sporadic discoloration within a single batch, and we are still trying to identify and isolate factors that might effect discoloration.

Bob Prichard
Williams Tool Inc. - Chadwicks, New York

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