Heat Treating Large Batches, one at a time or all at once?

[hathegkla]

I've got 24 or so throwing spikes I need to heat treat (all W1 steel). I have a small Paragon electric kiln that's designed for glass but works just fine on metal. I'm worried that if I keep opening and closing the door in between quenches I'm going to lose too much heat and not get the spikes fully hardened.

what do you guys do when you have a lot of blades to heat treat? just wait until the oven comes back up to temp in between quenching?

my other option is to try and grab a few at a time but I really only want to quench the first 3 inches or so, I think this is probably a bad idea

 

[VaughnT]

Losing your heat with constantly opening the door is going to make the heat treat take forever.

It seems to me that throwing spikes are a rather perfect shape for bundling together with wire. I would lash them all into one big bundle, but lashing three or four together would work. Leave a bit of the wire sticking up so you can use it for a handle, unless you have a decent set of tongs for the job.

How many spikes to lash together would be dictated by how large your oil reservoir is. With a five-gallon bucket, I don't think I'd bundle more than six into a bundle, but I could be erring on the safe side.

 

[hathegkla]

Losing your heat with constantly opening the door is going to make the heat treat take forever.

It seems to me that throwing spikes are a rather perfect shape for bundling together with wire. I would lash them all into one big bundle, but lashing three or four together would work. Leave a bit of the wire sticking up so you can use it for a handle, unless you have a decent set of tongs for the job.

How many spikes to lash together would be dictated by how large your oil reservoir is. With a five-gallon bucket, I don't think I'd bundle more than six into a bundle, but I could be erring on the safe side.

well my oil bucket is 5 gallons but all the instructions I've read for W1 say to use water or brine (will fast oil work?), up till now I've only worked with 1075/1080 and 01.

but I really like the wire idea, I think some bailing wire would work. the only problem I see is if you get too many of em together they won't cool quickly enough but maybe 6 of the 5/16" ones or 4 of the 3/8" with a little wire spacer in between would probably work great...as long as they don't slip out when the wire heats up.

but I'll give this a shot.

 

[Patrickknives]

I arrange in the oven so I can grap pretty quickly and practice a couple of times. My oven is in the medium size range but really doesnt loose but a couple of degrees when the door is opened. With the point in.. there should be less heat loss in the center of the oven. I also us a piece of angle iron with slots cut to support the knives and that way I can arrange them pretty easily for removal.

 

[hathegkla]

I arrange in the oven so I can grap pretty quickly and practice a couple of times. My oven is in the medium size range but really doesnt loose but a couple of degrees when the door is opened. With the point in.. there should be less heat loss in the center of the oven. I also us a piece of angle iron with slots cut to support the knives and that way I can arrange them pretty easily for removal.

I think your oven might be a little bit better insulated than mine. I lose about 100f every time I open the door. well I'll see what happens. they're just spikes so if I screw it up its not the end of the world. at least I'll know what do to in the future with real knives.

 

[deker]

well my oil bucket is 5 gallons but all the instructions I've read for W1 say to use water or brine (will fast oil work?), up till now I've only worked with 1075/1080 and 01.

I've got no comment on the bundling other than "make sure you agitate".

As for W-1 in water or brine...don't do it unless you like heartache. Yes, I know the W stands for "water", but that's in larger cross sections generally. A fast oil will do you fine.

-d

 

[Robert Mayo]

To add another thing watch your self because you might have the wire real tight when you put them in the oven but it will be loose when you take them out.

Bob

 

[LRB]

Just my thought, but a bundle is going to hold heat, and you will not get even cooling on both sides on any of the blades. The center blades will suffer most.

 

[Stacy E. Apelt - Bladesmith]

Many people worry about the temperature drop in multiple blades. Lets look at what we are doing and see how that really works:

When we HT the steel, we need to get it to a certain temperature to allow the ingredients to go into solution, for the purposes of this article, lets say that is 1500F. Once at that temp, it needs time to allow the carbides and alloy ingredients time to go into solution. For this we will say 10 minutes. If you heat ten blades to 1500F and hold them at that temperature for ten minutes, then all that is needed to happen has happened. Longer time won't make much difference as long as the temperature does not go HIGHER. Now, when you start opening the oven to make the quenches, the temperature drops and then rebounds a bit. For our example we will say it drops to 1400F. If the temperature does not pass the critical point, there is no change to the steel, so any amount of time above 1350F will not affect the steel, once it has had enough time at 1500F. A look at the Isothermal Transformation Diagram of simple hypereutectoid steel will show you that it is the point at about 1000F that is the crucial spot in getting the austentitic steel to convert to martensite. As long as the individual blades do not drop below about 1350F, you have about an hour before they start to transform into pearlite. During that time the austenite is still a solid solution and will sit quietly until its number is called.

So, if you use safe procedures, and take your time ( but don't waste any either), and the oven does not drop below 1350F.....you will be fine....as long as the quenchant can drop the blade below 1000F in less than one second once the blade enters the quench.

Transfer from oven to quench tank should be a smooth and reasonable quick movement, but the blade does not normally cool enough during that short interval to matter either. In multiple quenching, since the blade may already be 100-150F lower than normal, do it as quickly, but safely, as possible.

Practice opening the oven, removing a blade, and closing the oven many times with a cool oven first. Having the procedure down is important in multiple blade batches. Monitor the oven, and let it rebound a bit if it starts getting near 1350F. An assistant to open and close the oven door , while you extract the blade and quench it, would be a good idea.

Final analysis:
Once fully austenitized at the target temperature, it does not matter how much ( within reason) the steel see-saws between 1350F and the target temp. If it does not go higher than the target, it will not grow larger grains; and if it does not drop below 1350F, it will not convert from austenite.

Hope this helps.

 

[David Sharp]

Thank you Mr. Apelt I always learn from your posts, I am facing the same situation. I kept grinding until I could afford an oven. This weekend is the time to start heat treating.

Thank you hathegkla for posting the question.

 

[Justin King]

Temp. swing upon opening the door will be less if you allow the oven to warm up for a good length of time before you start cycling blades. You may be surprised how much heat the insulation can absorb, once it is nice and warm around the chamber you will come back up to temp. much quicker after opening and closing the door.

 

[sunshadow]

bring your kiln up to temp and let it equilibrate at temp for about an hour before you put your metal in, the insulation is a big thermal mass you are less likely to overheat your tips if the coils are not trying to push that whole mass up to temp, and that mass will work for you with thermal recovery from opening the door as Stacy hinted

-Page

-

 

[LRB]

Stacy, please explain this one second temp drop in the quench. I thought that was a 1095 thing. 01 doesn't have to drop that fast. It shouldn't drop that fast. Never mind. I see that it is W1 he is asking about.

 

[tattooedfreak]

are they round spikes? if so, there should be enough space between that they should quench properly, you may have to hold them there for a bit as the greater mass of the bundle will travel. Also be aware that the bundle may act as a tube does when quenched and shoot some steam up the center.

 

[hathegkla]

Thank you bladsmth for the post, I'll keep an eye on my temperatures.

and I'll definitely pre heat my oven for a while before I start. I'll likely run a normalizing cycle or two before I harden anyway.

as for the wire, I think I'm only going to try it on a couple just to see what happens, maybe I can wire them together like a picket fence and do 3 at a time. that way they should cool at the same rate.

 

[Stacy E. Apelt - Bladesmith]

The OP was using W1, which is a hyper-eutectoid similar to 1095. O-1 is an alloy steel, and has a much wider pearlite nose. Depending on the exact composition, it has between six and nine seconds to escape the nose.

Whenever you add alloy ingredients the quench speed needed drops dramatical. Even a tad of manganese can make a big difference.
Stainless steels, often with more than 20% alloy ingredients, have a pearlite nose of as much as 4-5 minutes.

 

[P.Brewster]

I posed a very similar question a while back, and got one very good piece of advise from Stacy: the task of straightening the spikes will probably be the slow-down in the operation. Open the door, grab a spike, close the door (without latching) and immediately quench. Latch the door, straighten while it cools down. The next spike will be plenty hot by the time you get to it.

I tried HTing in a bundle before; I got a lot of warp.

 

[hathegkla]

I posed a very similar question a while back, and got one very good piece of advise from Stacy: the task of straightening the spikes will probably be the slow-down in the operation. Open the door, grab a spike, close the door (without latching) and immediately quench. Latch the door, straighten while it cools down. The next spike will be plenty hot by the time you get to it.

I tried HTing in a bundle before; I got a lot of warp.

so, I know its been a while but I thought I'd post my results. I didn't end up doing bundles, I quenched 2 at a time using tongs. and didn't have any trouble with warping (I normalized them a couple times first).

I heated up 4 at a time (yeah it took me half the day) and only opened the small door on the bottom of my kiln, it was designed for glass so it has a separate little door for beads. after they had soaked long enough I pulled out 2 at a time and quenched. only opening the little door really helped as I got about a 50-75 degree drop instead of a 100-150 degree drop from opening the big door.

all 12 came out great, I tempered them around 500f and they've stood up to abuse pretty well. no big scratches even after hitting the pavement/rocks quite a few times. my mild steel spikes are looking pretty messed up in comparison.