Heat treating files.

V

VintageMike

Member
I'm new here. I saw a video on making knives from files. What temp do you "cook 'em" at and for how long to soften them up? Obviously a dedicated heat treat oven would be best but at this point cash is not flowing freely. The kitchen oven might have to do for now. Any help would be appreciated.
 
First off, a kitchen oven isn't going to do, nowhere near hot enough to anneal steel.
Secondly, you'll see alot of the more experinced members here telling folks not to use "mystery steel". That's exactly what files are, especially newer ones. They may not even be any more than "case hardened" and you won't be able to harden them again...
Let me offer you a little advice in this regard, from experience that I'm still living. I'm working on my first knife, I didn't listen to the advice I just mentioned, and descided to use a pry bar. Now I find myself with questions that I can't get good answers for because I don't know what kind of steel I have. I don't know what steps I might be able to take at certain points to increase my chances of a better result. Take that for what it's worth, but you can get 1084 quite cheaply from NJsteelbarron, and other places also. I'd say it's well worth it.
Now, as to how to anneal (unhardening the steel) on a budget, it can be done easily with charcoal if that's what you have access to. I annealed my pry bar by simply building a small firebox on my driveway out of old bricks, getting the coals going good, and setting the bar in. I just left it there untill it burned out and cooled. That worked for me...
Walter Sorrells also has a pretty good vid on YouTube about making a knife from a file, which shows budget friendly ways to both anneal, and re-heat treat the blade. If nothing else, I think it's worth watching for that, and it will give you some basic knife building techniques as well.
 
Welcome to Knifedogs!

First, theres the question of the particular file being made of a type of steel that is usable for a knife blade. To explain, the majority of files these days are made from the cheapest material possible, and then "case hardened" (case hardening means they are chemically and themally treated to develop a hard "skin". What this means for someone trying to produce a knife blade is that IF the file you are using is of the case hardened variety, your just wasting a lot of your time and effort, because no matter what you do to it, it will not harden.

OK, that being said, the best thing to do is to take a small, thin piece of the file, heat it to approx. 150F or so ABOVE non-magnetic, quench it in a light weight oil (vegtable, canola, mineral oil, etc). Once its cooled, you can lock the edge of the piece in a vise, and tap it with a hammer. If it break like glass, then you have a usable piece of steel (the file it came from)

"Hardening" and "tempering" are two very different steps in heat treating. Essentially hardening is accomplished by heating the steel to its austinzing temp (roughly 1450-1550F depending on the steel grade), and quenching (sumerging) in a light weight oil. Ideally this should take the steel to is hardest possible state. There can be problems encountered such as warping, twisting, cracking, etc). At this point the steel is very hard, but also very brittle. Neither are ideal for a cutting tool. Thats where "Tempering" comes in. Tempering is a "controlled softening" of the steel, to the point where its still hard enough to hold an edge, but no so hard that it will chip or break. Tempering is accomplished by placing the blade into a pre-heated oven, of between 350F and 500F. The exact temp depends greatly on the type of steel, its carbon content, how thick or thin the grind is, and its desired end use. For what you're working with, IF its actually usable blade steel, I would recommend pre-heating an oven to 375F, bake it for 2 hours, then sharpen and test it. If the edge chips in rough cutting situations, retemper at 25F higher (400F) and test again. And so on..... this is how you experiement to determine the correct tempering temp for a given steel.

To anneal, is going to require temps in the 1500F range, and simply can't be achieved with a kitchen type oven. Again, ideally, you want to heat the steel as evenly as possible, and then it must be forced to slow cool, by being place in a heat retaining material such as vermiculite. Folks also sometimes use things as simply as dry ashes, dry lime, or even hot sand. The idea being to force as slow a cool as possible on the steel. The forced slow cooling in what "anneals" the steel, making is soft, ductile, and easy to work. Annealing also sets up the steel's grain structure for further "heat treatment", but thats best saved until you gain more experience. :)

Hope that's helpful!
 
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So tempering is what the file needs. Got it. A shopping I will go....for a heat treat oven.
Is there a chart or book that has the formula for different types of steel?
 
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No, first you need to test the steel to make sure that the file is not case hardened by heating up to a bit above non-magnetic, quenching the steel, and then seeing if it will break. If it fails that test you are at a dead end.

If it passes then you will need to soften the file so t hat you can grind or file it. You can do this by normalizing which is taking the file up to above non-magnetic and then letting it air cool which will relieve stresses that may have occurred in file. At this point it will be nearly as soft as steel gets.

After you shape the blade to near finished then you need to harden the steel again. You do that by heating to above non-magnetic and cooling rapidly in a quenchant. As soon as the steel has cooled enough to handle you need to get it into a tempering oven starting at 375° as Ed said. Finish the grinding on the edge, you my have to resort to stones or diamond hones if you don't have a grinder because the blade my be harder than you files at this point, then test the edge as Ed said.

Doug
 
You will need something a little fancier than a fire in the back yard. You will need something that will supply an air blast to get the temperature up to where you need it. That could be a pit fire with a black pipe tube, called a tuyere, with an old hair dryer attached. I've also build a Lively forge, google that one up, that was powered by a large raft foot pump. One thing to keep in mind building any forge is not to use galvanized pipe anywhere that it might get hot. Another thing about solid fuel forges is that they can be a bit of a pain learning to manage the fire. Gas forges are probably the easiest way to go. They run off a propane bottle, 20# or larger, and are pretty easy to make. Most of the material can be had at a local hardware store or from somewhere like High Temperature Tools and Refractory. There are several plans out there and I've even built one in a mailbox.

Doug
 
Take a torch (if you don't have one, hopefully you know someone who does), heat the tang of the file up to bright red, hot enough that a magnet will no longer stick. Immediately quench in water. Lock it in a vise and wack the tang with a hammer.... if it is suitable steel, it will break almost like a piece of glass (wear eye protection), it will not bend If it bends, it is not high carbon steel and is not suitable for making a knife. This is not a proper, controlled hardening, but it should be enough to let you know if the file is made from high carbon steel or if it is just case hardened.

There are two basic methods to making a knife from a file. One is to anneal the file, grind/forge/file it to shape, then re-harden and temper. This will require heating the blade up to austenizing temp, which will be around 1500f, both to remove the hardness from the blade so it can be worked with files and drills, and then to re-harden it once you have it shaped. This method requires a heat-treating oven, forge, or some other method to bring it up to temp... a kitchen oven will not do.

The other method is to temper the file by heating it up to approximately 450-500f, this will remove a little bit of the hardness but by no means all of it... grind it to shape without heating it beyond 450-500f... and then you're done. You will not be able to use a file for shaping as the steel will be too hard, nor will you be able to drill it without carbide bits or cut it with a saw, but grinding belts and sandpaper will cut it. With this method all you need heat-wise is a kitchen oven to temper it. How hot you need to heat the file depends on which method you use.
 
In Peterson's, "First History and Collector's Guide to American Knives," there were a lot of knives made from repurposed files. Today, many people look upon that as a second-tier sort of approach, since so much good steel can be had so cheaply. Known steel. After all, the filemakers won't give you their specs. It is proprietary (I suspect, I have never actually tried).

Still, there is actually a very sound historical basis for making files into knives, especially right here in the good ole USA. It may have happened here more than other places, due to the extended period of, "the frontier."

just fyi. But, you absolutely have to do the things these guys suggest. Or, get an old file from Nicholson back when they used W1 or W2, or a very old file from Disston from 1960's or before (when they used their own crucible steel that would now be called W2).

But, as Ed already told ya', modern files are hit-and-miss.
 
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