17-4 H1075 to H900 Condition 3

[suthagarqa]

Hi Team,

Recently our customer request for 17-4 H900 part. We use material 17-4 H1075 & did solution annealed and HT to H900 condition.
Once we done annealing & HT to H900 Condition, will be the material yield strength and tensile strength as per H900 or different from H900 mechanical properties?
Please advise.

Thanks.

 

[EdStainless]

When you checked a test piece what did you find?
It should be H900, if you did everything correctly.

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P.E. Metallurgy, Plymouth Tube

 

[MagBen]

Agreed, it should be reversible unless you did something wrong. Solution HT too high or too long could cause coarse grains.

 

[EdStainless]

Though large grains could be fixed by doing the HT over.
In the PH grades you get grain refinement with re-heattreating.
The other main fault is not cooling low enough and fast enough between anneal and age.

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P.E. Metallurgy, Plymouth Tube

 

[suthagarqa]

Hi,

The HT process as below,

Base material 17-4 H1075, Required 17-4 H900...

Annealing @ 850°C for 2 Hours
Quenching @ 1020°C for 2.5 Hrs (Gas Cooling)
Tempering 1 @ 480°C for 3 Hrs & Tempering 2 @ 475°C for 3Hrs to achieve hardness Min 40HRC.

Please advise.

 

[EdStainless]

I believe that the recommended process is:
1900F +/-25F for 30 min (once temp is reached)
cool to below 90F within 1 hour
age 900F +/-10F for 4 hours

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P.E. Metallurgy, Plymouth Tube

 

[BiPolarMoment]

age 900F +/-10F for 4 hours

I thought H900 treatment for 17-4 was only 1 hour? I know it's longer times for some other treatments. Though I don't know if there is any negative to doing it longer. (That said, I've never had to do it myself so I'll trust you if I'm mistaken )

 

[EdStainless]

The aging curve for 900F is very flat out to about 48hrs. Since heating is so slow at the lower temp we always use longer times. for thin parts we might use 2hr, but longer does not hurt at 900F. It also helps with stress relief.
At 950 the limit is a bit over 2hrs, at higher temps you don't really want to go beyond 1hr or you will start reducing properties.



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P.E. Metallurgy, Plymouth Tube

 

[MagBen]

For H900, I would go with >2 hrs aging. It won't have a negative effect as long as time is not over 24 hours, while 1 hour aging could degrade toughness.

what is the need for 850C anneal? Also, why aging twice? I see no benefit from these two additional HT.

 

[EdStainless]

Ben is correct, splitting the aging has no benefit
And I hadn't converted the anneal temp, I hope that the 850C was a typo because it won't work.

You can re-anneal and re-age these alloys over and over. You will loose a small amount of strength (compensate by lowering aging 25F) but the toughness should improve (as the grain size gets finer)

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P.E. Metallurgy, Plymouth Tube

 

[WKTaylor]

Ed...

Your definition of the process, with the exception of certain testing protocols for load coupons, is in-line-with AMS2759/3.

NOTE, for aerospace: MIL-HDBK-1587 MATERIALS AND PROCESS REQUIREMNTS FOR AIR FORCE WEAPON SYSTEM, Table 1 Restricted Materials, indicates that 17-4PH HT to H900 and H925 [and sometimes H950] are generally prohibited... mostly due to poor SCC, low fracture toughness and possibly premature elevated temperature corrosion issues.

Regards, Wil Taylor

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