Heat treatment, tricks, methods, and ideas.

[Imakethings]

Alright, so those of us who do our own heat treatment have a couple different ways to get our blades done.

I had an idea earlier tonight and decided to try mixing up some anti-scaling goo since I didn't want to invest in stainless steel foil. So I did a bit of research on the internet and started looking about the lab/kitchen, I mixed up some stuff, and it worked BEAUTIFULLY.
Here's what I used:
Boric Acid (roach killer!)
Borax (laundry stuff)
Bentonite clay (kitty litter)
Denatured alcohol (paint thinner)
Water

Mixed into a thick slurry, painted on a test piece and allowed to dry. Took it up to heat and quenched, no scale at all.

Considering the cost, this is a much cheaper and easier than what I was doing before.

So anyone else have any good tricks they care to share?

[metal99]

What steels are you heat treating? I haven't really had a scale problem with my heat treats.

[Imakethings]

5160, 1090, 1084, 1080, and 1074.
Blown propane for the heat source. Having to call the blade temp by eye since I don't have the cash to invest in a proper HT oven.

[Doug Lester]

You're there with a lot of us having to use a forge or an acetylene torch to heat treat with. You can decrease the oxygen in the forge by making it a little fuel rich to austinize the steel with. Mainly I just use white vinegar to take the fire scale off after the fact. Saves on the grinding belts. The borax is enough to prevent scaling but you need to take it off right away or it will etch the steel. I found that out the hard way.

Doug

[Imakethings]

I suppose that would work, but my concoction should do for coal too. I'm going to keep fiddling with it and see if I can find a way to make it work w/o the hazard of etching the blade.

[Crex]

If the borax melts and drips into the bottom of your forge it will eat the bottom and lining out. With a blown forge it becomes a little harder to regulate the interior heat in the forge and increases the scaling in most cases. Create an inner chamber with a smaller section of black or iron pipe that will work as a stilling well type oven and give you more even heat with less air flow. You can even toss in a chip of wood while you heat a blade up for quenching and reduce the available O2 in the chamber (pretty much what Doug was refering to). Might take just a little longer to reach quench heat but you can despense with all the extra chemistry. White vinegar will remove what little scale developes much cheaper than your solution mix. No muss - no fuss.
Don't stop experimenting though....good for all of us (as long as you keep it safe).

[metal99]

I like the vinigar trick it works really well. I do my heat treating in a coal forge.

[Imakethings]

Update:
I snagged some raku clay and made a slurry, coated the blade and HT. No scale, and the nice thing is it doesn't have any chance to etch the blade. Once again no scale on the blade.

Raku clay is a specific type of potters clay that has a very high thermal shock resistance, so it doesn't flake or pop off when you apply the heat to it.

[NJStricker]

But are you hardening your blade?

Think about it. . . if wanting to get a softer back and develop a hamon, you clay the spine. If you clay the entire blade, what are you achieving?

[Doug Lester]

Wouldn't that be the same as when Japanese swordsmiths coat their blades with a thing slurry of clay but just not putting the thick coat on the spine? It just breaks up the vapor jacket as it forms and helps keep the rate of cooling even without being thick enough to really retard the cooling. Evidently it will also protect the blade from scale formation, though I think it is an over rated problem. It's too easily dealt with by other means.

Doug

[Ed Tipton]

Imakethings...With a propane forge, by cutting back on the air flow or running with a richer fuel mixture, you can eliminate nearly all scale formation. I do my own HT with those same steels, and have very little scale formation on any of my blades. Basically, when you are doing your thermal cycles, if you will just wire brush the blade as the scale forms, and then on the final heat go quickly from the forge into the quenchant, you should almost totally eliminate any problems with scale formation.

[Crex]

I agree with you Ed, but most of these newer guys haven't learned to watch their heats closely enough and tend to overheat the steel, forming more scale than you or I would. They also rarely take the time to control scale build up as they forge a blade. All that comes with a lot of practiced experience.
I like walking around at my and other hammer-ins just to look at scale accumulation around the anvils.....amazing what you can "read" from that alone.

NJ, what Doug said. Makes a diff. Without the thin coating on the edge area of the blade (in a forge type HT process) there is a tendancy to mis-read the heat based on the edge coloration and either quench too soon or overheat the edge. You have also done what Doug descibed as far as steel contact with quenchant. If you are gunning solely for the hammon effect, it will be cleaner and stronger with full coating and differential thickness.
Try it you will see the difference.

[Imakethings]

The coat with both that I've tried has been at or less than 1 mm thick, I know I can eliminate most of my scaling problems by manipulating the fuel/air ratio, but I like to double up on the protection if I can. Most of the time when I'm doing the actual hot forming I don't really worry about scale and run the forge a bit lean, when I do get to the HT or forge welding I go for a much richer mix. I still get some scaling, but nowhere as much as when I'm doing forming.
Mostly I'm just trying to share some of the tests I'm doing to get the same results with different processes. It might be useful to someone at some point, or not. I do know that the clay won't flake off with coal or charcoal (tried both yesterday evening).

[Doug Lester]

One problem that I ran into early on with not watching the scale while I was forging was causing inclusions in the steel by pounding the scale into the work. Some of that was cured by learning to keep the face of the anvil clean. A lean atmosphere in the forge and not overheating the steel also reduces scale formation. However, with welding temperatures scaling is just going to be a problem unless the work is coated with something, like a flux, to keep the oxygen away from the hot steel.

Doug

[NJStricker]

Originally Posted by Crex

I agree with you Ed, but most of these newer guys haven't learned to watch their heats closely enough and tend to overheat the steel, forming more scale than you or I would. They also rarely take the time to control scale build up as they forge a blade. All that comes with a lot of practiced experience.
I like walking around at my and other hammer-ins just to look at scale accumulation around the anvils.....amazing what you can "read" from that alone.

NJ, what Doug said. Makes a diff. Without the thin coating on the edge area of the blade (in a forge type HT process) there is a tendancy to mis-read the heat based on the edge coloration and either quench too soon or overheat the edge. You have also done what Doug descibed as far as steel contact with quenchant. If you are gunning solely for the hammon effect, it will be cleaner and stronger with full coating and differential thickness.
Try it you will see the difference.

Thanks, Carl and Doug. That helps me understand a little better. I've not had a big problem with scale on my blades, at least not when using the forge to heat treat. I've found that it's pretty easy to remove if I take the blades to a little higher finish (320).