17-4 H1100; increase hardness to 45RC 1

[rrene]

I want to increase the hardness of 17-4 H1100 from 36 Rc to 45 Rc;
Do a supplementary heat treatment at 900F (H900) is enough or do I need to do a solution heat treating before?

 

[israelkk]

No. You need to solution treat it and age to H900. However, solution treatment involves quenching from high temperature in a water and therefore probably will cause warping and dimension changes of the finished part.

 

[unclesyd]

If you had the time and equipment you could get an increase by cycling the part between Rt and 600F/900F. We have this problem with our parts. As these parts increase in hardness there is an appreciable loss in ductility.

The only way to go was posted by israelkk

 

[rrene]

Thanks, both of you.
The quality manager just informed me that we have two batches’of 17-4 that do not meet the min hardness value of 45Rc
The first one was aged at 875F for 1 hour; hardness: 35Rc and the second batch was aged at 1100 for 1 hour: Hardness 32Rc.

From your answer it is clear that the batch aged at 1100F should be solution treat before aging at 900F.
For the one aged at 875, If I well understand Uncleyd, I can cycling the part between Rt / 600F and Rt/900F; Is it what you mean? If yes, how many cycles?
Since the pieces are very small (disk: 1 in. diam. X .062 in. thick) Do you think that hardness of 45Rc would be easier to get if we reduce the holding time of aging ?

 

[unclesyd]

H900 is aged only 1 hour. This the hardest you will get with known properties. Aging below H900 is not recommended.

H925 is aged for 4 hours.

H1100 is aged for 4 hours.

I don't have the data on the specific number of cycles that is required to increase the hardness. Our parts are sent through inspection and repair after each 600F and 900F cycle. The 600F is the operation cycle and 900F is the cleaning cycle. As all our parts are interchangeable we only started keeping records with advent of computers.

I don't have access to my old records at the present time, but am trying to get that. The hardening with temperature cycles was discovered very early when 17-4 PH SS became available to industry. I had several discussions with the people at the old ARMCO Research about this. If I recall there is paper by ARMCO about this. You might give AK Steel a call as they should have the old ARMCO Reasearch papers.

 

[mighoser]

If you aged at 875 for one hour and got HRC 35 then something went wrong. 875 is the peak aging temperature but as unclesyd stated it is not recommended since ductility is minimized. The H900 condition allows +/- 10F so 890 would be the min aging temp allowed by specification (AMS 2759/3). Any chance they sent you 17-7 instead of 17-4. Also, you should check your oven records and material cert. for response to heat treatment.

 

[EdStainless]

Either the wrong alloy or they didn't do the anneal and quench properly. If the 875 is low on hardness then there is something more wrong.

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