So my question is, if I were to heat a piece of steel to a glowing yellow and then stick it in kaowool so that the whole piece is covered, would that slow down the cooling enough for the steel to be properly annealed?

while it slowly kills you? not a good idea to mess with unsealed ceramic wool.  Use ashes or vermiculite, its much safer and has been used for years safely

What alloy? D2, A2?  Nope never for those alloys! 

How large a piece of steel? Knife blade thicknesses usually need a thicker "helper" to slow the cooling down.

What's the ambient temperature in your shop? -20, +20  C, F or K?

How thick of kaowool?

So far this question is much like: "I have a container of water, if I pour it into this glass will it overflow?"  Can you see how difficult answering such a question can be without all the details?

And yellow is too hot for heat treating.

White Nomad,

A bucket of 'Garden Lime' or powdered lime, works well for annealing. No toxic anything. Works good for Fire Welding Flux, too. Lime is the flux in making Steel.

Neil

At the moment I use a bucket of clay, but I also have powdered lime so I might use that. 

The problem would be with the fibers you knock loose from the kaowool becoming airborne. There's so many other things to use it's not worth it. I use wood ash now that I have collected enough but I've also used unscented kitty litter to good effect and plain old dried and pulverized clay I dug out of the ground. Find a metal ammo can or old toolbox and start saving wood ash in it or buy a bag of vermiculite at the garden center. It's that time of year when the box stores are preparing for spring in my neck of the woods so it's already stacked up outside of Walmart. 

Pnut

The short answer is Yes, it will work for any steel that you would otherwise anneal by burying it in ash, lime, vermiculite, and so on (although as noted above, yellow is hotter than necessary). One of my smithing mentors does this all the time, often adding an appropriately sized bar of mild steel heated to the same temperature as workpiece to slow down the cooling rate even more.

The safety issue is non-trivial, but we do have to keep in mind that there is a BIG difference between (a) loose fibers becoming airborne after being subjected to the heat of the forge and blasted out into the air by a gas burner and (b) loose fibers that happen to detach from a kaowool blanket at room temperature. The former behave a lot more like asbestos and pose a much higher risk than the latter.

I know that others here may disagree with me on this, but I think that we sometimes overstate the risks of kaowool and ascribe the worst-case effects to ALL possible situations. While plain kaowool fibers can cause silicosis or even cancer with repeated long-term exposure, they are not toxic and not nearly as dangerous as asbestos. Outside the extreme environment of a gas forge and with appropriate precautions (dust mask, etc), I personally don't consider this usage to be significantly unsafe.

you are forgetting its not just operating temps, in his annealing scenario he is also stirring up the fibers, that does not happen in a forge, so I fear you have a very different idea of what is unsafe than most of us

Steve, how do you mean "stirring up the fibers"? I don't think he's talking about sticking a piece into a bin full of shredded kaowool, but putting it between two layers of blanket. The first would certainly be dangerous, as both the shredding and the sticking would release fibers into the air, but the second wouldn't -- or at least, not nearly as much. 

every time he lifts that blanket it puts more fibers into the air

While I agree with John that this isn't the use case for ceramic blanket that poses the most risk, it's kind of a moot point given the numerous other (much safer) options that are available for annealing that have already been given above. Like many risks, it's a roll of the dice whether or not one has adverse reactions to some degree or another. And the probability goes up with the amount of exposure you get. I guess the question is why roll those particular dice at all if you don't have to. Even if the odds everything will be fine are arguably in your favor.

Using ceramic blanket would work, but it seems like more of a hassle to me to put on my respirator and be all careful when I could just as easily bury the steel in a bucket of vermiculite and call it a day. Just my 2 cents.

So the thought came from hearing about how glassworkers would sit their work in fiberglass insulation or something like that to slow down the cooling process to prevent the work from cracking from uneven cooling. I don't know how true this is but that's how I had the idea to use kaowool. I think I'll just make a wood ash and lime powder bend to anneal my work pieces in. 

IFI member Latticino could probably speak to that, as he has been a professional glassblower (and currently works as an HVAC engineer).

Good Morning W.Nomad,

Thomas Powers asked you a question yesterday, I haven't seen a reply. "What material are you working with? D2, A2, W1, H13, S7, LMNOP? They all have very different Heat Treating characteristics. It is not a case of guessing and hoping you have it right. To Care for what you are building, YOU have to care enough to KNOW what you are working with. Junk Yard Dog material doesn't set a consistent base-line. You are concerned about Annealling, Why?? Different material Anneals at different procedures. Does it need to be annealed or are you just rowing the boat? Row, Row, Row the boat, gently down.........LOL

Neil

Sorry for the late reply, I've been busy. 
The most accurate I can get with the classification is that it's mild steel, and quenches pretty well in water. If there is another way I can find out specifically what I'm working with using some method at home, do let me know.

I'm asking into annealing for these materials because I hand file everything given that I'm only just learning how to effectively use my bench sander/grinder, and it would be easier and quicker if the material were softer, and for the bench sander, I figured a softer material would make the belts last longer. 
I also would just like to learn about the process and whether using kaowool would have been viable (I know it's not now, instead I use lime powder), so that in the future if I had to anneal, I knew what I was doing. 

What do you mean by it quenches well in water? there isnt much to anneal with mild steel, as by definition, it doesnt harden

Yes a definition of very mild steel is that quenching it in water doesn't do anything.

A google search on the same question brought me here, though a couple years later on.  I'm looking to anneal ApexUltra and 52100 and was trying to decide between lining a large old metal toolbox with Kaowool, coating it in Satanite, and filling the middle with vermiculite... or just simply filling the thing with vermiculite.  So I did a test run on the ApexUltra, just using vermiculite (about 8" deep total, with the blade in the middle)... and it did not anneal properly.  Couldn't drill it at all.  toolbox is 20" long, 10" wide, 10" deep.  Garage is not heated, and it was about 5 C (41 F).  Piece was a roughed out kitchen knife, 13" long total, 2" wide at max, and 0.1" thick (no bevel grinding yet).  FWIW I put it into the vermiculite straight from the forge after 20 minutes at 1450 F (single burner pile of bricks forge with a thermocouple). I did succeed in another way, by sitting in my garage for an hour, carefully and slowly ramping down the forge temp by 450 F per hour (per Dr. Larrin Thomas) but that's not what I want to be doing.  So ...

I'm guessing I did not have enough vermiculite depth, and/or needed to add a large chunk of equally hot steel or make other adjustments.  So a few questions for this group.  1) would my idea to line the bottom, sides,(and inside top?) of the toolbox with 1" of Kaowool (coated in refractory) add any tangible benefit, or just displace more valuable volume of vermiculite?  2) would the refractory meaningfully reduce risk of airborne fiber (I assume yes but hell, y'all know way more than me).  3) If I just go straight with more vermiculite, I'm assuming I need 12" deep (and to place the blade right in the middle) - is this enough margin of error?  Could I get away with less (so I don't need to find a new toolbox)?  4) If I'm adding other steel at forge temp, does it need to be flat bars or could random chunks (old axe heads) work?  I have a couple I could put down first before putting the blade in.  5) this one is tricky territory... if I built a box from plywood, coated the inside with refractory, then lined with Kaowool and refractory, filled with vermiculite... would there be a risk of the wood charring / catching fire?  I just like the idea of a custom size and a frame material that is not a conductor.

Thanks folks!

Vermiculite and kaowool have approximately the same R-value (2.0-2.7 and 2.5 respectively per inch of thickness), so it probably won't make much difference if you're only putting in the workpiece itself. On the other hand, if you're including other heated metal to slow down the cooling rate, vermiculite might actually insulate that metal from the workpiece, unless they're right up against each other, with no vermiculite in between. Given that, a box (metal or plywood) with several inches of kaowool (rigidized and coated to keep the fibers in) will probably work best in your scenario.

HOWEVER!!!!

This really only applies to more basic steels. You have already found out how poorly an uncontrolled anneal works for ApexUltra, and unless you're going to be making a LOT of these pieces, the time and material costs of making such a setup would probably be much better spent on buying or building a proper heat treatment oven. Either that, or -- if you're only making a few such pieces -- put up with the occasional inconvenience of sitting with the forge while you ramp it down. If you can find something else to do during that process (sanding and finishing other blades, reorganizing the shop, reading "War and Peace", etc), it's not really wasted time.

What are you trying to accomplish by annealing?   If all you are trying to do is drill holes in it then there is an easier way.  Heat to a little below critical temperature (usually a dull red) and then throw it in the vermiculite.  That's more of a high temperature temper rather than annealing, but it should allow you to drill holes. If it doesn't then the carbides are probably the issue and you may have to go the slow route to get what you want.

If you are annealing for other purposes that may not be the way to go.

Rockwool insulation (at least the stuff I have) is rated up to 1200 F.  So, if you want to build an annealing box you could use that to line it, maybe cover it with sheet metal if you think you need it then fill with vermiculite.  As long as the glowing steel doesn't come in direct contact with the insulation or the box there shouldn't be a problem.

You could do that with kaowool as well.  Personally I think coating in refractory is overkill for something like this.  I just use a steel 5 gallon bucket (with a removable lid) filled with perlite for this purpose.

1 hour ago, JHCC said:

...unless you're going to be making a LOT of these pieces, the time and material costs of making such a setup would probably be much better spent on buying or building a proper heat treatment oven. Either that, or -- if you're only making a few such pieces -- put up with the occasional inconvenience of sitting with the forge while you ramp it down. If you can find something else to do during that process (sanding and finishing other blades, reorganizing the shop, reading "War and Peace", etc), it's not really wasted time.

lol.  well, I have kaowool and refractory on hand (free, really).  I was going to use it for a cylinder forge but after a couple years my pile of bricks is still going strong.  I guess I could build a heat treat oven, or buy one... but I was going for "let's start with what I have" since my budget is rather limited and heat treat ovens are prohibitively expensive as it's just a hobby, I don't sell anything.   I can either be pragmatic and do this manually with the forge (the reasonable way, probably) or build something new (and who doesn't like to do that).  Seems folks aren't concerned about using wood for the box, so maybe this weekend I'll try this and see how it goes.  I'm picturing 14" x 14" x 20" lined with 2" (is that enough?) of refractory-coated Kaowool, filled up with vermiculite.  I guess my idea for the axe heads to hold heat is less than ideal - needs to be right up against (makes sense).  I'll look at picking up a couple blocks of steel to put the blade in between, if this insulation box thing doesn't do the trick.  

Hello,

Has anyone ever annealed steel buried in a few inches in sand under the tiniest charcoal fire that eventually goes out? So that the steel cools slowly over several hours. Sand will stay warm for a while too after the fire dies.

Silica sand will melt at around 1,000f so unless you want to glass enamel your blade you want to use a more conventional method. To anneal low alloy steel you need to heat it to critical and slow cool it. critical temp for most low alloys is well above 1,000f, more in the range of 1,400f.

Frosty The Lucky.

I've made camping fires on sandy beaches many times and never saw any glass formation. For annealing, I was thinking a lot smaller of a fire.