17-4 SS condition 900 2

[mw1st]

Following austanitizing this steel can be further process by aging at temperatures based on properties required.
Condition 900 calls for holding at this temp. for 1 h. Question is: what if part is "chunky" ie. 5'' or 6'' in dia.
Shouldn't I hold at this temp. for much longer?

 

[WKTaylor]

Your concern is valid to a point.
What does the heat treat spec state about extra time for thickness above X?

Are you HT'ing per a material spec or per a steel HT Spec... AMS 2759-3 or mil-H-6875 or ASTM??, or...? The spec should be definitive.

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

 

[EdStainless]

If the part is that thick and you want uniform properties you should use 15-5PH.
It is a modified version of 17-4PH that works better in thick sections.

That said most thick 17-4PH parts are not real critical of the core properties, so give it claose look.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[mw1st]

WKTaylor Actually, all of the above.Customer clearly spelled out "1 h @ 900F", so that's what we did. I was just concerned
as to properties being uniform for shaft that thick. If there's a problem, I'll recommend H925 for 4 h
(slight decrease in hardness may not matter), or take Ed advise and suggest 15-5 PH alloy.
We heat treated dozen parts so far, - one cracked in service. Customer doesn't seem to care or complain for now.
I just want to be prepared just in case. Thank you both.

 

[tbuelna]

mw1st-

I checked a copy of AMS 2759/3 and section 3.4.2.2.1 Soaking/Aging/Furnace Control Thermocouple states, "It is permissible to increase the soaking time by up to 50% of the time specified in Table 3 to compensate for the lag in part temperature due to specific characteristics of the parts or load, for example part thickness, load weight, etc.....". Table 3 lists a soaking time of 1.0 hour at a set temp of 900 degF for 17-4PH cond H900, with a soaking time tolerance of +15/-0 minutes (note 7). The spec also has additional information regarding how to determine when the soaking time commences and ends. As WKTaylor noted, this particular HT spec is fairly explicit.

Hope that helps.
Terry

 

[EdStainless]

Terry is spot on, a 1hr age on a 5" diameter part will likely take 3 or 4 hours in the furnace.
Parts will heat very slowly at 900F.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[WKTaylor]

MW...
Now that we've come around the abbreviated SStl PHT explanation, the real question begs 'why' the customer was so explicit about soak-time but NOT explicit about the overall HT Process...?

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

 

[EdStainless]

Wil,
I take that you mean some details such as the annealing temp, quench rate, hold temp before aging and such things.
Likely for the same reason that people spec aging temp and not mechanical properties, because they don't understand the metallurgy.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[MagBen]

OP raised a good question! I bet the explicit requirements are driven by an industry spec. not directly from customer. Lots of times, customers just ask to comply with the spec to sell their products regardless not knowing what the spec says.

AMS 5643 explicitly says time tolerance 1 hour +/-0.1 hour (+/- 5 minutes) for H900 and then you have no choice although it is not reasonable for big size bars.

ASTM A564 is more flexible here. it says aging time refers to minimum time and may be extended to obtain required ductility. So if only ASTM a564 requested, you may have the freedom to increase time.

Ed brought up a valid point. 17-4 is normally made smaller than 5''. For larger than that, we often use re-melt version, or recommend 15-5.

 

[WKTaylor]

BTW... for military aerospace...

MIL-STD-1587 MATERIAL AND PROCESS REQUIREMENTS FOR AEROSPACE WEAPONS SYSTEMS
TABLE I. Commonly restricted structural materials.

This table specifically highlights restricted usage of CRES PH-HT <1025F [<H1025], IE... be very careful with [higher strength, reduced toughness, SCC prone] temper conditions H1000, H950, H925 or H900.

For parts machined after PH-HT** I always prescribe a stress relief HT operation.

** Parts should be finish machined... or rough machined-close to finished dimensions... in the final PH-HT condition due to measurable dimensional changes during PH-HT. The stress relief will not affect dimensions but provides 'value-added' improvement by mitigating embedded stresses due to the machining.

Also, some parts will fare better in-service with high-hardness steel shot peening.

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

 

[Carburize22]

Is aging it in a salt bath acceptable?

 

[FilipekEng]

Very good question! I used to treat 5-6" thick parts made of 17-4PH.
Basiclly, to heat treat those parts you have to use a furnace with a work thermocouple inside. Chose between an air furnace or a vacuum furnace (if the part is finished), then apply a thermocouple inside a test piece (heat sink) which has the same thickness as the part. The end of thermocouple should reach the very core of the test piece through a tight hole to imitate the treated part as well as it is possible. Treating a part this way, dwelling at 900F starts when the core of the test piece reach required temperature (usually +/- 7*F).