Plate quench->Sub zero->Temper- workflow?

S

StuNY

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Feb 16, 2014
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Did my first HT test parts with CPM 154 yesterday and my new homemade oven- I don't have a tester but I can't scratch it so feels like everything went well. I went directly from plate quench to two hour tempering cycles at 400 degrees since I didn't have any dry ice yet. So I am wondering how I am going to fit this into my schedule as I do most of my work in the evenings after work.

My oven gets through the 1400 degree preheat and hold for 15min and 30 min soak at 1950 in a little over an hour. Assuming I will do the sub zero temper directly after quench and this could be anywhere from an hour to overnight? Do I loose anything if I leave it in sub zero until the next evening and do the 400 degree tempers then? Assuming the dry ice will be gone by then. Am I better off just doing this on the weekend and going through in one shot (with one hour sub zero) so I can do the all the tempering the same day?

Appreciate any guidance !
Stuart
 
I highly recommend using the weekend, and plan it out/write it down. From my own experience, any issue that you introduce in the heat treat can be disastrous. My buddy and I just ruined $350 worth of CPM M4 by decarb'ing it. Take the time and planning to make sure you do it right. ESPECIALLY if you are doing a large batch of blades.
 
I'd wait until the weekend...

You want to get the blade right into sub zero for best performance. I'd say just sub zero for 10-30 minutes (on your workday) but lately I have been reading that a longer cold soak may be better, especially with steels like AEBL (not sure on CPM54). You also need time to deal with issues that pop up and need to be on top of your game mentally as it is dangerous and somewhat complicated.

A snap temper before sub zero is OK but I no longer do one. Don't drop or put the blade under stress... if you must shim anything to straighten a bend wait until the blade has been tempering just a bit and is at least 400 F.

My best advice is to start early on your day off. I usually heat treat as many blades as I can handle when I crank up the kilns.

You must go straight into sub-zero and temper cycles, try to work quickly between stages... when the knife is cool enough to hold in hand dip it in water to cool, dry off well then go straight into sub zero.

I hope this helps. Your heat treat sounds solid as long as you go into temper quickly. If you wait a day on temper or cryo it will not really work.
 
Daniel is right on. The only thing I will add is that I leave the blade/blades in the ice/alcohol until the furnace drops back to the tempering temp.. I may be wrong but I don't believe you gain anything with long freeze soaks unless you're using LN but while waiting on the furnace to cool down its better to leave them in the ice than on the bench.
Once you start the H/T process its best to work through all the steps as quick as reasonably possible and don't stop until they are complete.
 
Thanks guys, I will go for the weekend do it all in one day approach. Looks like I have a dry ice supplier close by that is open sat and sun and they have a 10lb minimum anyway so I may as well plan on doing a few at a time. Yes I noticed yesterday the oven takes quite a while to come back down to tempering temperatures- even while blowing it with air!
 
The 400F tempers stabilize the RA so further change will not do much ! If you are nervous about going from quench to S-Z or LN then you could do a 'flash temper' at 300 F.That will make it safer though I don't hear much broblem from going direct.
 
My opinion is that the drop from austenitization to sub-zero should be more or less continuous. Once at -100F, let it sit for 30 minutes and then warm to ambient. Place in the temper oven as soon as practical after reaching room temp.

In the whole process, a delay of:
minutes doesn't matter
an hour isn't much
several hours is the max
more than six hours should be avoided
 
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