Improperly Heat Treated 17-4 PH

[bekks]

I have a client who had their 17-4 PH component (part of a drive roll) improperly heat treated. It was meant to be H1075, but ended up getting 1150F for 2 hours and then furnace cooled. I suggested they take a bar, heat treat it in the same manner as the improper heat treatment and tensile test it. The result was almost identical to a previous test we had done in the H1075 condition. Their main criteria is hardness for wear resistance and I will be checking the hardness tomorrow, but I was quite surprised that the strength was as high as it was (165ksi yield, 167ksi UTS, 16% el). Anyone know how significant the effect is from furnace cooling compared to air cooling? Anyone else surprised at these results?
P.S. in anticipation of background questions, this all started from a WPS development, but I don't have any concern for the 309 weld metal or the SA 516 material it is joined to.

 

[MagBen]

For PH grades, it is often possible to correct the aging to age higher if previously aged at lower temp, but cannot age lower to correct previously aged higher.
Cooling is critical at solution, but not that much at aging. Tesnion of H1075 and H1150 could be overlapped, but the yield of 165 for H1150 seems to me a bit too high, i doubt it was due to slow cool. Something seemed not right. can you repeat to confirm the situation?

 

[EdStainless]

The cooling from aging does not impact properties at all.
How large of a part is this?
It sounds like they messed up the anneal also if the Y and UTS are so close.
Those properties are way too high for H1150.
For H1075 the mins should be 125/145/13% and about 32HRC, with typical values of 150/175/16%/36HRC.

The only way to 'fix' this is to re-anneal the part and then re-age it.
The bad news is that you may get some surface damage unless this can be done in vacuum or dry hydrogen. The good news is that it will improve the ductility and toughness of the part.

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P.E. Metallurgy, consulting work welcomed

 

[bekks]

Thanks for your thoughts - this was what I was thinking too, but I haven't had any experience with a precipitation hardened material. To reemphasize, the heat treatment was at 1150 for 2 hours rather than 4, but I'm assuming the extra two hours only has a marginal effect on the strength. The part is about 2" thick. Right now, my biggest suspicion is the heat treatment and what was actually done. This is the second issue I've dealt with recently from this heat treater. My faith in the tensile test is high as we did that in house.
Re-annealing and re-precipitation hardening is probably not a viable option due to cost of the part and the need to re-evaluate the weld. When this issue came up I anticipated low tensile values and figured it would be a simple proof that the heat treatment was unsatisfactory, case closed.

 

[EdStainless]

If the part is considered lost, then try a re-heat treatment.
We do this a lot. We HT to H1150M and weld a structure, then anneal and reage at 1075 to achieve desired strength.

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P.E. Metallurgy, consulting work welcomed