17-7 RH950 Heat treat problem

[64coupe]

I have what amounts to essentially a .005" thick spring made from 17-7 Condition A being heat treated at a secondary supplier to Condition RH950. For years, we have had no issues, but "improvements" over time have deteriorated the heat treat. In the same lot of parts, we are seeing both correctly heat treated parts (C42-C47)as well as parts that are obvioulsy too soft/weak (C29 or so).

Obviously, we are trying to get it back to where we were, but what step would you believe to be most critical in the process? We are currently analyzing run data for austenitizing temp, soak time at temp, quench rate, etc...


Thanks,

Keith

 

[EdStainless]

Check parts at each step.
These parts are thin so it is hard to believe that they are not being cooled fast enough to cold enough.
The time between conditioning and reaching -100F is critical, as is the hold time.

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[metengr]

Check the furnace and conduct a survey of temperatures using thermocouples. You might be surprised at the range of temperatures within a furnace or how the charge is loaded into the furance.

 

[64coupe]

Ed - one of the things that I have underway (not complete yet) is making a dogbone from the same .005" strip to do hardness testing as well as tensile testing after each step starting with raw material. Hopefully, I will learn something there.

At what temperature should the clock start ticking to get into the deep freeze? Room temp? 150°F?


Metengr - One thing lacking at this supplier is good mapping. We want to change suppliers, but the validation will take a while.


Thanks guys,

Keith

 

[EdStainless]

I would start the clock when they drop below 1725F.
I would like to see them reach -100 (well at least -90F) within 1 hour.
The hold at -100 should be 8 hour minimum.
Make sure that they are up to room temp before you go into age.

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