H.T. Question regarding O1

smitty0331

smitty0331

Joined
Dec 5, 2006
Messages
892
I just heat treated my first blade (3/32'' O1) and I think I screwed it up. After heating it for 45 min. with a mapp gas torch, I couldn't get the whole thing hot enough at the same time. To make a long story short, I thought I got the whole thing hot enough, but after quenching, the spine was still soft, but the egge was hard (confirmed with a file). I'm heat treating it now anyway to see how it comes out. My question is should I, or more importantly, can I re-harden it later if it doesn't turn out? If it don't turn out, I'm planning on hardening it again with a charcoal fire, but I just wanted to know if you guys think I should bother re-doing it, or not.
 
Even though the edge skates a file, I doubt you were able to obtain a fully hardened condition by just heating with a MAPP torch. I've seen makers treat simple carbon steels using Oxy/Acetyline, but MAPP isn't going to have the heat necessary to get a blade hot enough without a concentrating chamber like in a forge. O-1 needs a soak at temperature for several minutes (more like 12) to get fully into solution. Hard (impossible maybe) to do this with a torch. What I would do normalize the blade several times, anneal it, and start over maybe trying the charcoal if you don't have access to a kiln. Or, get some soft refractory bricks and build a crude forge to concentrate the flame and reflect the heat back into a small chamber. Though it's not ideal, it's leaps ahead of a torch alone. Just try not to overheat the steel with either method.

--nathan
 
Normalize - Bring steel to 1600 degrees and let cool to black (still hot!). I think you do this 3 times.
Anneal - Bring steel to 1400 to 1450 degrees then bury in vermiculite or some other really good insulator overnight until cool.

Kind of like "rebooting" your steel :D
 
Thanks for the quick replies everyone. Looks like I'll have to scrap this one and start over, since I have no means to control temperature that precisely.
 
Yea, that's my problem. You CAN eyeball it...I'd rather send my stuff out for HTing.
 
You can just normalize and re-heat treat your blade, no reason to scrap it. Finish the knife as best you can and learn as much as possible. Might as well make your mistakes on the one you've already had trouble with.
 
You need to get a few soft fire bricks and make a very simple forge. Simply make a small tunnel from the bricks make a small window in obe side to stick in the tip of your mapp torch. Try to make the flame kinda swirl in your tunnel. Now get a piece of scrap steel and a magnet. Do this in semi dim light, when the steel gets a little red check with magnet. Keep trying till it don't stick. Remember the color. Now you need about another 150 degrees for O1, so, watch the steel as it changes. Your going to need it a bit brighter than non magnetic. Once you have a clue as to the collor of red, you could go down to a Fastenal store and buy some of the smallest O1 drill rod they have. Should be under $10 for a couple ft of 1/2" Then start heating the end and when it is red above magnetic try too keep it that red for about 10 minutes, then quench in the end in oil (say 2") and then break the end with a hammer. Is the grain fine or course? Break a file and look at it for an example, it should be fine. If the grain is coarse you are too hot. Don't get it that bright of red anymore. If it doesn't break very clean too cold, get it brighter. You could learn this. You want to be able to make the fine grain. You could buy a thermo couple and a pid and set it up to read the temp for under a $100. Check here
http://auberins.com/index.php?main_page=product_info&cPath=1&products_id=14
and
http://auberins.com/index.php?main_page=product_info&cPath=3&products_id=39
 
smitty0331 said:
Thanks for the quick replies everyone. Looks like I'll have to scrap this one and start over, since I have no means to control temperature that precisely.
Click to expand...

No offense Smitty, but if you can't control the heat that precisely on THIS one, what makes you think you could control the heat that precisely on the next?
There is absolutely no reason to "scrap" this one. Simply Re-HT it using a more reliably controlled method. Or send it out to be HT'd until a better means of heat control can be obtained. You will have WAY too much time invested in finishing the knife to make one that won't cut well or hold an edge well.

Matt Doyle
 
While setting up a more controlled method of heat treating is, I feel a must, I think there is a lot to be learned from doing your first knives to the best of your ability in whatever manner you have available. Your torch will get plenty hot enough for small blades, even regular hand held propane torches will as well but as previously pointed out you must make some kind of enclosure to help concentrate the heat. This can be as simple as several firebricks forming a cave or even a tin can of some kind lined with a small amount of ceramic wool insulation. I do suggest reading as much as you can on the procedure, you'll find all you need on this forum alone. Testing with some practice pieces helps, looking at the grain of a broken file so you know what fine grain structure looks like (proper thermal cycling or "normalizing" three times will take overheated large grained steel right back to the silky fine grain you found in the file).

Practice with the file itself even, grow it's grain by overheating and quenching/breaking it and then thermal cycle it three times and then quench/break it. Look for the decalescense and recalescense points in the ambient light you have to help determine the vicinity of heating you need to be in by color. This can be done during the normalizing sequence by letting the steel air cool in a dark bucket and carefully watching, the steel will fade from bright to dark and at some point the blade will flare and brighten again at the phase transition point, quickly pull out the steel and look at the color in the light levels you are working in. If you heat treat at different times of the day you'll have to do this everytime as the colors will be off depending on how bright/dim your lighting is. Learn as much as you can and then test your knife to see how it works but don't think that whatever you are doing is just good enough, find ways to do it better, more reliably and most importantly repeatably.
 
Good points, Guy. I performed my first heat treats using a propane torch and a one brick forge. They weren't the best as far as heat treatments go, but they were a learning and growing tool. Of course, I would never consider selling one of these learning blades, but it's all part of the process of growing as a maker.

--nathan
 
TekSec said:
...Kind of like "rebooting" your steel :D
Click to expand...

I like that analogy! Like a Windows operating system, the steel will acumulate all kinds of internal and uneccesary crap and eventually get buggy, normalizing is indeed like rebooting the steel for a fresh start.
 
In heating too long and gettng a lousy subsequent heat treatment, a simple redo is a possibility but there are a couple of factors to consider. There are temporary issues to resolve before moving on and there are permenant issues that will keep you from proceeding. The temporary would include things like grain size and residual stress which would increase distortion on each subsequent heat and quench unless dealt with. The permanent would be overheating to the point of burning and decarb (very likely with a torch). Overheating is easily fixed with subsequent treatments as long as those horrible little sparkers didn't appear, which is the end for that piece. Decarb would need to be removed so if your piece is thicker than your final plan you may be all right.
 
I did have a simple encosure built with 6 fire brick, but the blade still didn't seem to get hot enough, I could get it from black to red, but it wouldn't stay red over the whole blade at the same time. After quenching, I HT'ed it in a toaster oven at 400 for 1 1/2 hrs twice, do you guys think it would be okay to try hardening it again?
 
Only after normalizing the steel. If you HT without doing that, you will more than likely crack the blade.
 
I'd recommend setting up a “muffle furnace” and using a propane weed burner as a heat source. For small blades you can build a simple chamber by lining the inside of a coffee can with thermal blanket and glazing or saturating it with clay. For the muffle tube you can use a thick walled mild steel pipe and close it on the back end. Suspend the muffle tube through the center of the chamber. Before you put the blade in get the whole tube hot and place a wood chunk in the back to create a contained reduction atmosphere inside. The muffle will also help even the heat out. You can do the same thing with charcoal/wood for larger blades, etc... With charcoal, suspend the muffle tube over the coals so they aren't touching or too close and drape a piece of thermal blanket over the top. Charcoal/wood also works better for slow cooling than the propane.
 
I wish I had tried charcoal as the first heat source for heat treating, it's probably the most accesible and reliable heat source for a beginner. I have to admit, my first two knives were heat treated using two hand held propane torches so I could heat from both sides simultaneously and a simple hard fire brick enclosure and small blades of course. That's all it took though, I started building a real forge immediately after that.
 
I personally tried the 6 fire bricks with a propane torch once. I didn't have any luck either. Best I could figure was the 6 hard firebricks were absorbing way too much of the heat from the torch and I couldn't heat ALL of that mass.

Switch to soft, insulating firebricks or a can lined with ceramic insulation. That should get you a nice hot chamber.
 
Even just google the one-brick forge. The idea is you carve a chamber about 2-3" tall and 1.5" wide in a soft firebrick with a window for the torch. Like was suggested, make the flame swirl around the chamber. The problem with this type of setup is the inherent hot-spots/cool-spots. This means you have to move the blade in/out/around for more even heating. I like Tai's suggestion of a muffle forge. That way the tube will even out the heat for more consistent temperatures.

--nathan
 
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