17/7 PH TH1050 Heat Treat Procedure

[Kim Taylor]

We have a tubular structure made from 0.050" wall 1.5" diameter 17/7 tubing that is 14 ft long x 2 ft x 2 ft that requires heat treat to TH1050. We have determined vacuum heat treat is not necessary and our customer is now thinking that the full UTS and YS is not a necessity. Part of the expense we are considering the need for is the cooling to 60 deg F in one hour after the austenitizing (1400 deg F) stage. The heat treat companies I contacted don't have a good way to do this for so large a structure. In that the structure is primarily 0.050" wall tubing, if the heat treat company cooled with forced air or compressed air and the time to get to 60 deg F was longer, say 2 hours, what affect would that be to the YS and UTS? Can anyone give me some information on the expected YS and UTS in relation to the cool time?

Any input would be appreciated.

Kim Taylor PE
Mechanical Engineer

 

[EdStainless]

OK, I am sure that the guys that wrote that spec lived in sir conditioned offices.
I have found that fan cooling to something under 80F seems to work just fine.
The time is important, you want to cool quickly so fans are fine for thin wall like you have.
But the lower temp really just needs to be below the martensite finish temp, and with today's chemistries that is not 60F.
What is most critical is cooling below 800F, this needs to be as fast as practical. If you can only cool to 80F I would expect only a slight decease in strength after aging.
Now the welds may end up slightly lower strength (I don't know what the Ms of the welds will be) but if you can give up a little strength then you will be fine.
There is plenty of margin since we usually see properties well above the minimums in thin wall tubing.
(is this Plymouth Tube product?)
I know where there are a number of vacuum furnaces longer than 14', but the cost is rather high.
If you do this in air then pickling is critical, if there is any heat tint the corrosion resistance will be very poor (the will rust stain in open air).

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P.E. Metallurgy, Plymouth Tube