heat treat soak times...

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brian923

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Jul 20, 2015
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My father just bought a nice electric furnace that we are wanting to use for heat treating knives and melting metals with. I have been thinking about ways to heat treat multiple blades at the same time. One plan was to make a nice steel rack that would sit inside the furnace (top load) and heat all then blanks at once. the issue I am for-seeing is trying to quench a rack of blanks at one time. If I were to bring the blanks up to temp, say 5 at a time, and individually take them out and quench them (using 01 steel right now) would there be any adverse effects of some knife blanks staying at temp longer then the others. essentially asking, can you soak a steel blade at heat treat temp for to long? I hope this makes sense. thanks guys, Brian.
 
Well, my answer may not be correct, but I'll try. I might be more cautious about oversoaking a very simple steel like 1095 Or White steel that has no alloying for grain boundary pinning, but even then, with five blades, we are only talking about the very final blade being soaked only...what...a few minutes longer than the first? If your hardening temp is below 1530F, as it should be, even with no alloying present I would not be concerned.

Especially with O1 I would not worry about it. The W (and sometimes V depending on the O1) will do a great job keeping aus grains from growing any during a soak. I don't know exactly how long O1 can be soaked, at say 1475-1500, with no grain growth at all, but my guess it is MUCH longer than would cause problems quenching five blades in order.
 
thanks SAMURAISTUART. thank kinda what i was thinking. my next worry would be getting them all in the oven for tempering and keeping them around the same temps to keep them consistent. but i guess that could be equaled out by doing 2 tempers.
 
Tempering won't be a problem, just have the tempering oven stabilized to desired temperature when you take first blade from quench. Since the first blade won't be in tempering oven more than 10 to 15 minutes longer than last blade, for temper that is no problem at all. One thing to be aware of, when you open HT'ing oven to remove first blade, that nice 1500ºF (depending on steel, but just round number) is going to drop quite a bit as the oven is opened to remove blade. I'd try to have the door open as little time as possible, then by the time the first blade is quenched and put in oven, the HT oven should be back up to temp ready to remove next blade. Be sure you quench oil doesn't get too hot by the time the 5th blade is quenched. All depending on size of blades and how many gallon of quench oil is used.

Ken H>
 
I'll toss out a few issues that you need to deal with:

A top opening kiln is a pottery/glass kiln. It is a very poor choice for doing knife HT. Just opening it up and removing blades at 1500F is problematic and unsafe. You will need a full HT gauntlet and leather welding sleeve. Wear a face shield, as the hot up-rush of heated ait can damage your eyes. Kiln glasses are also needed, as you are staring directly into the bottom of an intense IR source.

Picking up a blade from above is a lot trickier than pulling one out from the end.


Blades are quenched one at a time. When doing multiple blades, have sufficient quenchant volume to allow for heat rise. Take your time and allow the oven to come back to temp ( which is usually quite quick).

A blade rack is make by sticking pieces of stainless round stock in soft fire bricks.

Re-bound and soak time are not big issues in a normal forge, and probably would be OK in a top opener. Normally, the oven re-bounds by the time the last blade is quenched and checked. Soaking for an extra ten minutes or so won't make any difference in O-1 or any other knife steel. Under-soaking is much more of a problem.

Do a search on "multiple blade HT" and you will find many discussions on this topic.
 
Remember that as far as grain growth is concerned temperature is more important than time ! If i needed to quench up to six blades I'd do them together .Make a fixture to hold the blades separated by at least 1''.
Take care to see that there is very good agitation so that bubble s don't collect and slow the quench !
 
thanks everybody. i know that the equipment i have isn't the best for what we are trying to accomplish, but.... its what i have to work with so i will figure out ways to make it work. i have no problems obtaining all the necessary safety equipment as we already have a bunch of welding garments. i really appreciate the help guys, and i will keep you posted as to how it turns out! Brian.
 
How about running a rod across the top, and hanging the blades by a wire. Grab a wire with tongs, quench, allow furnace to rebound, rinse and repeat.
 
For a top loader, I would suggest cutting a 1/2" x 3-4" slot in the lid. Suspend a blade through the slot using a rod and some stainless wire. Cover the slot with a firebrick during the cycle. Remove the brick and pull the blade through the slot when you are ready to quench. You won't have to open the lid at all. Remember, the heat in your kiln will be stratified with the top being the hottest. Not sure how much that will come into play... but it will.
 
Have often been concerned about this- I do an average of eight blades in a load, and quench one at a time so as to check straightness on each one while it's cooling. Good info, thanks all!
 
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