17-4PH Heat treatment specs 4

[foundrydude]

As an investment casting house we provide 17-4 investment castings for aerospace applications. A customer source inspector ran into a contradiction that is causing a huge uproar. Statements made have included grounding of aircraft!!! Wonder if anyone else has run across this?
Main question is, does anyone know how to look up the revision history of an AMS spec? AMS-5344 in this case.
Trying to find out when the "cool to below 70°F" requirement was added. The other specs we work to, AMS-2759 and SAE-AMS-H-6875 both call out a cool below 90°F.
Because the blueprint for the casting stated "material per AMS-5344" double solutionize then "heat treat equipment per AMS-H-6875" we interpreted that to the cool below 90°.
Source guy says he sees it otherwise, and we should have cooled below 70.
By the way, for everyone's info, the 6875 spec has been revised not too long ago to further clarify that it is for "raw materials only" and not parts. Parts are defined as something that has both a drawing and a part number. If heat treating "parts" then it refers you to the AMS-2759 family of specs. Which also calls out a cool below 90 for 17-4. A lot of prints call out the 6875, and this is the wrong spec if heat treating "parts."
Also, what does the extra 20 degrees of cooling impart, if anything? We have not seen any difference in hardness or tensile properties, at least nothing significant.
Comments?

 

[unclesyd]

I'm looking through my literature on 17/4 for any information on the subject. We have heat treated thousands of 17/4 parts using the original specs from ARMCO that state to cool to room temperature.
Personally I can't fathom that a 20F difference could affect any physical properties of the material as there is built in variability in 17/4 heat treating just by the nature of the beast.

 

[EdStainless]

My hunch is that both specs mean 'cool to room temp', but they needed something that could be measured.
The guys that wrote in 90F actually worked in manufacturing, and the guys that wrote in 70F only worked in a office.



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[Gubo]

Hi,
I ran into the same problem with these spec, but on the other side of the fence.

It seems to me that in order to facilitate the HT supplier they are requiring the EQUIPMENT to conform to AMS-H-6875, as the other ones have much stricter requirements.

In other specs I found 80F.

All in all I agree 20F shouldn't change anything

 

[remetaper]

Avoiding to discuss about AMS and talking from a metallurgical point of view, I seem that the reason why the Customer pretends to cool 17.4PH at 20 F under Mf ( 90F)could be due to have a "super assurance "that all Austenite transformed in Martensite. In this case , this steel will give the better results when aged ( expecially at low aging temperature ).
Grade 17.4PH has NOT any rest of austenite when fully hardened ( Cond. A). Therefore, undercooling is not necessary and a simply cooling under 90F is enough.
Nevertheless,when a very constant mechanical properties were required in condition H900- H950, the most important Load cells Makers impose (and prefere) in their process to cooling under zero (Celsius)in order to be sure that all Austenite is completely transformed in Martensite. It's expensive but guarantee best results avoiding adventures.
Just to have an idea , some years ago during the summer, a large quantity of finished load cells were rejected or vacuum re-treated because after the condition A were left "to sunbathe" and ,then, H900 aged.
Results ?? Rp0,2/Rm ratio and mecchanical hysteresis "went crazy". And the Load cell Maker as well!
About manufacturing and office, I fully agree with EdStainless.