How many 10XX blades can I HT in oven at one time?

P.Brewster

P.Brewster

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Jul 25, 2007
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I'm debating on whether to build a 6" x 6" x 18" ID oven, or a 9" x 6" x 18".

I usually make throwing knives and spikes in lots of 20. I use 10XX and W-1. Assuming I'm quenching them (in Parks #50) one-at-a-time (as opposed to using some kind of rack), how many should I heat at a time?

There's no point in making a 9" x 6" if I can only heat 3 or 4 knives.

Other options are: build two ovens, or make a 6" x 6" with doors on both ends (so I can load both ends).

Thanks as always!
 
It depends on the size and mass of the blades. I place my blades no more than two in a a foil pouch at a time, and maybe get between 4 to 6 blade in my paragon furnace, which is roughly 6X6X15. I try to leave spaces between the foil pouches for even heating. Packing the knives and pouches closer together may result in low temperatures in the middle of the batch.

Think of a roast in the oven. The outer sides of the meat cook faster than the center. In other words, the knives on the outside of the batch may be heated properly, but the pouches in the middle may not reach soaking temp.
 
It would depend on the volume of quenchant you have you do not want it to get too hot to cool properly.

Bob
 
Thanks.

My blades are 3/16" thick, 8 to 12" long; spikes are 5/16" to 7/16" square; same length.

I was assuming that the limiting factor would be the time that it takes to remove the blades and quench them. In other words, say I've got 10 knives in the oven, and it takes me 30 seconds per knife to quench. From the time the oven door is opened, knife #2 is pulled out at 0:30, and knife #10 is pulled out at 4:30. Won't this delay be detrimental to the HT process? Do I open the door and leave it open as I quench, or do I pull out knife #1, close the door, quench, and repeat?

Bufford, you are suggesting that the limiting factor is physical space alone.
 
It will depend on the steel and how cool the blades get while they wait. It is okay if a blade cools slightly from austenitizing temperature before the quench. That cool down is part of the quench and as long as it stays under the nose of the steel you're fine. But the acceptable amount of heat loss over an acceptable amount of time varies from steel to steel. 1095 is very critical. 1084, not so much. O1 is not real picky about quench.

I expect that you will run into problems with a 1095 blade that cooled off to 1200 over five minutes before the quench - it will probably be forming pearlite, especially on the tip and edge which will have cooled the most. But O1 might be just fine. I haven't looked at the quench rate charts in a while, you may want to look into that.


I close the door between blades. The clock doesn't start ticking fast until you get to cooler temps.



Metal in an oven does not heat like a roast. Meat has moisture in it that limits the temperature to 212 until that moisture is gone, due to an endothermic reaction that occurs as water evaporates. Also, metal conducts heat pretty fast. So there can be a large and stable heat gradient in a roast that you won't see in metal. Within a reasonable soak time, the metal in the center will be the same as the outside.
 
I have done as many as 5 blades at one heat in my oven. I take one out and close the door. Quench. By the time it is cooled in the quench my oven is back up to temp wait a couple minutes and do another. Works fine for D2 and I have several sets of plates. The only problem I can see with doing this with 10xx steels and the like is that every time you open the oven some oxygen gets in and maybe more decarb would occur.
 
Assuming that the quench tank can handle the rise in temperature, the limiting factor is the ability of the oven to retain the set temperature. If the oven is fully soaked ,say for 30 minutes, at set temp before the blades are put in.....and the oven is allowed to return to set temp before you start clocking the initial soak time , then I would say you are fine for 20 blades. Use of the correct quenchant will be important. An oil cooling radiator on the tank will be very useful in maintaining the quench temperature. Use a transmission cooler and a small pump.

The procedure should go something like this:
Open the door, remove a blade, close the door, quench, check for straightness after 6-10 seconds,straighten as needed, put in a second tank/pan of oil to cool.

As Nathan pointed out, a small amount of cooling is acceptable, and the oven will be rebounding somewhat between blades, so that should not be a problem. 30 seconds a blade is not sufficient planning time to allow a proper 1095 quench and check/correct for warp. Figure about 1 minute per blade. That will also allow the oven a little more rebound time, so more time between blades is probably good. I will assume that you are using somewhere around 1475F as the set point. If the temperature falls below 1300F, allow it to return to 1475 before the next blade .This may happen once or twice during the quenching of 20 blades, but will assure that each blade is fully austenitized at quench.

None of the blades, even in a bundled stack, will be any different temperature than the others. This is to to the thermal conductivity of the steel and the fact that the soak time does not start until all the blades are at the set point.
Stacy
 
When quenching W2 blades, i usually limit to 2 at a time in the over. I quench the smaller one first and then let the larger blade soak for a few more minutes while I mess with the first one.
 
I use foil pouches to keep oxidation down, but the air trapped within the pouches acts like insulation. When several pouches are lined up side by side vertically on the rack, there is less air circulating between the pouches.

As a result the pouches on the outer sides of the batch will heat up faster, thus insulating those within the batch. While the inner pouches will heat up to soaking temp, they may not have the required length of soaking time at the correct temps. I remember having a problem with orange peel effect from overloading the HT oven.

The othe problem that can arise from packing in too many blades is warpage. I find that warpage is reduced by allowing some room between blades.
 
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