Need low-cost heat treating method

L

lonepine

Joined
May 7, 2010
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I've been using a charcoal burning, coffee can forge to heat treat the blades I make. It's a coffee can with an air hose going in the bottom blowing up through the burning charcoal. The blower is a hot water heater fan and I make my own charcoal from scrap wood. I am able to get steel to the point where it is no longer magnetic. I'm limited to about a maximum of a four inch blade which is usually not a problem but it would be nice to be able to be able to treat up to a six inch blade now and then. One thing I don't like is that the charcoal causes the surface of the blades to grow bumps and blisters on them. I don't know what it is but it needs to be ground off for a smooth blade. Sometimes I leave it on for an old-time, rugged look, lots of "character".

I would like to improve my heat treating but need to do it in as low-cost way as possible. I'm thinking that there are people smarter than me who have faced this same dilemma and found a solution.

Is there a form or shape of the burning charcoal that works better? Is there a better way of making a charcoal fired forge? Are there tricks to using charcoal that would improve the results? Whats the best way to use charcoal?

LonePine
AKA Paul Meske, Wisconsin
 
Propane torch and a bottle of propane from your local Home Depot/Lowes/etc... will cost your about $15 give or take. You can hold the knife with vice grips and run the torch down the length of the blade back and forth till its the right temperature. Then dunk it. Easy peasy lemon squeezy!

I'd like to know more about these "blisters" though since I plan on making a charcoal forge sometime over the summer. Pictures would be appreciated :D
 
I did not have much luck with the propane torch, its hard to get a even heat with a small torch when you are trying to get to about 1500 f. Search one brick forge, you can make it out of more than one brick to get larger blades inside. I was using this set up with a propane torch connected to a 5 gallon tank and it works fine and you get less decarb.

This link is a google search for the Bladeforums.

http://www.google.com/cse/home?cx=011197018607028182644%3Aqfobr3dlcra
 
BChou-E29
Here is a picture of the bumps/blisters. This is on 1095 steel. It never happened on D2 though.
BumpsRedwingedBlackbird61.jpg


and another,
BumpsPiggy81.jpg


I don't know what it is nor what causes it.

Lone Pine
 
Using firebrick as a backing will reflect quite a bit of heat, allowing a propane torch to work well.
 
I'm having the same trouble with "blisters" on the steel, I'm also using charcoal for fuel in a... "mexican oven"? with a three stage blower to control the heat a bit. The heat treating works great and the blisters don't affect the steel quality (as far as I know/experience), but there is a lot of clean up work to be done after heat treatment!!!

I often go back to the belt grinder at 80 or 120 grit at slow speed to get the blisters off, and then I need to finish up to 600 grit again (which is done by hand after 240 or so...) on a hardened piece :grumpy: and then polishing...

anyway, I hope someone comes up with a cheap and easy solution for this. I'm not a fan of propane forge's, I like the basics of the simple wood/carcoal fire. Building a fire, getting it really going with flames shooting out of the chimenea. And finally using the charcoal to heat treat a blade... love it! It's just those damn blisters!

As for a solution: I was thinking of a clay coated heat treatment to solve this problem but I haven't tried it yet.

Jasper
 
I believe the blisters are caused by overheating, you should be able to get the blade to non magnetic without blistering like that.
 
try coating the blade at the top with a mixture of sand clay. mix is about as thick as 90 weight gear oil and let it dry and that might protect the spine. you will stock removal the edge and wear away the marks you don't want.

we heat treat swords and knives this way. we do not get that pitting you are showing.
 
The blisters are from overheating and scale. A coating of something may help, but better HT methods would be far better.

I suggest you read up on heat treatment. Building a larger forge would be the smartest idea. A good propane forge can be built for less than $100. A charcoal/coal forge can be built for $20-40. A charcoal chimney like you have is pretty much only good to start the coals for the barbie.

As far as the difference between 1095 and D2...you never hardened the D2 in the rig you described. D2 is hardened in an oven over a much longer period. All you did was mess up the D2 if you tried the same thing as you did with the 1095.

Sending out your HT or taking it over to another makers shop, and having him do it ( and show you how), is a practical alternative to messing up all your work on making a knife. D2 will have to be sent out until you have a HT oven/kiln. Blades can be professionally hardened for about $10.
 
look up one brick or two brick forge and spend the money

your surface blisters are either just overheating the surface, or possibly getting surface infusion of carbon (kind of like case hardening) which lowers the melting temperature at the surface where the charcoal then touches the blade and spot overheats it.

-Page
 
MSC carries a HT Coating that will prevent allot of this if used corectly.
Have used it for years with great results, but with a Kiln not charcoal.
You can use a Cheapo gas burner from HF but you need to watch your color closely! Night time or in the dark is best.
You are overheating the steel in an oxygen rich atmosphere = blistered steel.
Ask me how I know this :D
 
I was actually thinking it could've been the direct blast of the blower over oxidizing the steel and "burning" it. But then again I've never used charcoal.
 
If you're into cheap, you could make a more efficient charcoal forge, like this:
http://www.frycustomknives.com/?page_id=429

I use mine for some forging, and have heat treated blades up to 13 or 14 inches.

And, I second the rest of the guys who are telling you that the bubbles are from overheating, and that D2 won't work well at all in a charcoal forge.
 
3_hard_boiled_eggs, This is a picture of my Coffee Can "forge",
Forgecoffeecanused03sm.jpg


Yea it's cheap. Living expenses currently exceed income and If I didn't do it this way I wouldn't be able to make knives at all.

I make charcoal in my back yard fire fireplace thingy that has a lid. I get a fire going and stack a bunch of scrap wood on it all at once and let it burn until the top pieces are burning and about half charcoal, then I put the lid on it to suffocate the fire. It smokes like crazy for about 5 min then settles down. I let it sit until the next day when it has cooled off and shovel out the charcoal. I find that 2x2 pine will convert to charcoal in this set up but 2x4 won't be completely converted. I use scrap wood, mostly used lumber, so it's mostly softer woods. I get at least a kitty-litter bucket full of charcoal.

I've stopped using D2 steel for the reasons given by others here.

You're right Hengelo_77 they give a knife an old-time look so of course that's not the type of knife I want to make.
The blisters ARE sort of interesting. A person could look at them and say "YUCK! That blade is all screwed up!", or you can look at them and say "WOW! That's really interesting AND they give the blade 'character'."
(What I lack in skill and knowledge I gotta make up for with B.S.)

Hankins, what company is MSC, and what is the coating called that you mentioned?


Quote, "I was actually thinking it could've been the direct blast of the blower over oxidizing the steel and "burning" it. But then again I've never used charcoal."

BChou-E29, Can you explain what you mean by "burning" the blade please? I'll just bet it's not something I WANT to do, right?


Quote: "your surface blisters are either just overheating the surface, or possibly getting surface infusion of carbon (kind of like case hardening) which lowers the melting temperature at the surface where the charcoal then touches the blade and spot overheats it."

Sunshadow, Thank you for the explanation of the over-heating. What you say about the steel touching the charcoal makes sense. Do you know if it damages the functionality of the blades? Are they still usable with all the "character marks" on them?

When I can turn around my financial situation I throw some discretionary funds at a better heat treating method, but for the next 9 - 12 months this will have to suffice.

Are there any other charcoal burners out there that can share their experiences, good or bad, with using charcoal?

LonePine
AKA Paul Meske, Wisconsin
 
Last edited:
LP, I forge and HT with charcoal. Not sure if I am doing things the "correct" way but have turned out some blades that perform surprisingly well under hard use. I agree that your blade looks like it has been too hot. I used to do the same thing, but more is not always better. My forge is made from scrap metal with rebar legs and tool rest. My air supply is a combustion air blower from a gas furnace. By itself the blower puts out WAY too much air so I slow it with a motor speed control. It sounds like you have a similar blower so you may want to look at ways to decrease your air delivery.

For me HT on the forge starts with how the fire is set up. You don't want a new fire, look for the charcoal to be evenly colored and burning well. I form a layer of coals with a U shaped trough in the center. Once happy with the fire setup I start the blower turning slow and add the knife to the center of the trough, edge up. I heat the ricasso area first, watching it closely and checking it with a magnet often. Keep it moving if needed to heat evenly. You are looking for just enough heat, but not too much. I think you will be happier with the way your blades perform if you can avoid overheating during HT.
 
woodzman,
Thanks for the encouragement and suggestions. It never occurred to me that maybe I had TOO much air going to the fire. I was worried just the opposite. However I think I can see what you mean. Thanks again.

LonePine
AKA Paul Meske, Wisconsin
 
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