quenching medium

[Noah Wagener]

If i do not know what the steel is, is it better to quench in oil or water? What are most modern files?

When using MAPP torches, do you just heat in the open or do you try and house the item somehow?

[george wilson]

For quenching old files,water should be o.k.. It should not be ice cold. Just room temperature,but NOT warm either,or it will not give full hardness. The quench needs to be large enough that it does not get appreciably warmer when a tool is quenched in it.

I get a lot more heat out of a torch by laying a layer of bricks down,then,putting a few up on edge to form a corner to lay your steel in. You can get something like a plane iron much hotter,and a larger area of it heated by doing this. Two MAPP gas torches are a lot better than one also. For larger jobs,a weed burner with a trailer gas bottle will give a great deal of heat. Use it out doors,for sure.

[Dimitrije Stamenkovic]

Generally it is better to use oil. Water will work, but it will cool the steel much quicker and will make it hard and brittle and large items might crack during the operation, while oil is more gentle.
Old-time blacksmiths used to have their own secret recipe. In my country there is a famous, very traditional scythe shop and the blacksmith there uses a liquid mixture of wax, vegetable oil, beaver and bear fat and something else to quench, and his scythes are top-notch tools, used by scything champions.
Blacksmiths that I know generally use kitchen-grade vegetable oil and it will work fine. If you want something modern and precise purchase special quenching oils or solutions, but I don't think you'll need that, they are designed for industrial use.

Modern files are generally made of high carbon, tool grade steel, the same used for drill bits (the ones for wood, not the HSS ones) and everything else, but they have a harder temper. I have heard that sometimes they are carburized, which is a heat treatment that adds more carbon to the surface, making it even harder but without making the body of the file brittle, but I'm not sure about that and it is not important if you are going to work on them. Files and rasps are the most convenient source of tool steel, when they are worn out.

If you are making something small it's okay to use a torch, but if you need to temper a larger item you'd better make a small furnace, which gives you a uniform heating and also helps with heat dispersion giving you a higher temperature. You can just lay some bricks and it will work.
This is a furnace made by a local hobbyist knife maker and it looks like a very nice design to me:

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He put a tube inside a can, and between them he poured heat-resisting mortar with a hole for the flame. Using more than one can you can stack them and make the furnace as long as you wish. As you see he uses two cans with two simple blow lamps, with better torches you'd get even better results.

Using the furnace outdoors might be safer, but it is better to do it in a darker environment to see better the color of the bright steel, which is essential for a good temper.

[Winton Applegate]

Brick

I would be a CAREFUL of regular old bricks from out in the scrap yard etc.

They take on moisture.
Could explode ! ? ! ?

Fire brick for furnaces is a good idea. Reflects heat, doesn't blow up, are very light weight to move around, easy to cut or shape for special purposes.
Get at a brick yard or Jewelry supply store .

http://en.wikipedia.org/wiki/Fire_brick

As far as oil or water try both.
See which works the best.
Then make your project.

[Winton Applegate]

secret recipe

Dimitrije,

Nice post and photos !
When ever I hear "Old time crafts person recipe"
ha, ha, ha,
I immediately figure it is going to contain some kind of urine.
In this case beaver and bear.
Thanks for making me wrong.

ha, ha, ha,

[Daniel Sutton]

You should visit iforgeiron.com. They have a section on heat treating and many knowledgable smiths. http:// http://www.iforgeiron.com/topic/9030-intro-to-heat-treating/#entry88485.

[Noah Wagener]

Thank you.

Are concrete pavers dangerous too? How about stone?

[Daniel Sutton]

Concrete can be very dangerous. I highly suggest looking into a single brick forge setup. You really need fire brick or an equivalent to be safe. There are many things that can go wrong once you get a fire hot enough to heat treat steel. Also, try choosing an oil that won't ruin your oven when you temper the blade. After you quench the steel it will be very fragile and needs tempering. I've seen water quenched spring steel shatter like glass without tempering.

[george wilson]

LOOK: You MUST use the quenching medium the steel was designed for. There are water,oil,and air quenching steels. I wish people who do not understand this would not post incorrect information. Sorry,that is that way it is. FILES are WATER HARDENING,NOT OIL. I will warn you,files have a lot of carbon in them,and no matter how much you draw(temper) them,they will STILL be pretty brittle,and can snap off in your face if you try to make a wood turning chisel out of them. I had that happen way back in the 60's,before I had enough experience. I drew the chisel blue,and it still shattered,just missing my ear(and,razor sharp,too). A normal steel,like W1 or 01,would have been a spring at a blue temper(clock spring blue). And not at all brittle.

I have been using tool steels for almost 50 years by now,and was the master toolmaker in Williamsburg. I got seriously involved with tool steels in 1970,when I had to make tools for the musical instrument maker's shop I was putting together in the museum. In 1986,I became the master tool maker,and used it all the time. But,I was making tools at night since the early 70's,which led to getting begged into becoming the tool maker.( I'd had enough of dealing with the public by then,anyway).

If you quench water hardening steel in oil,it will not cool fast enough to properly harden. If you quench oil hardening steel in water,it will cool too fast,and can crack,or at least form a poor molecular structure.

Air hardening steel should be allowed to cool just in air. Still air is just fine. A fan is not needed. Again,if it cools too rapidly,as in water or oil,it can crack,maybe violently,and you could get searing hot shards in your face. I recommend that you stay away from air hardening steel. It has to be protected from the air while white hot,or it will decarb. You will not be able to get it hot enough anyway. Use 01. It is a very commonly used tool steel,and not as treacherous about cracking as water hardening steels.

Yes,concrete is dangerous. If it gets hot enough,it will violently release the water,which IS STILL IN THERE. That's why you see piles of collapsed concrete powder after a fire in a concrete building.The best thing to use are fire bricks,which are designed for the heat. They don't cost that much.

For an oil quench,you can use vegetable oil. We used automatic transmission fluid,which worked fine. We had 5 gallon quenches. A 1 gallon quench will be large enough for most home shop use. Our oil quench would catch fire A LITTLE(Not the actual quench,just the oil clinging to the hot part as it goes into the quench). We had 2 large exhaust fans above our quenches in the tool maker's shop to get rid of soot and smoke. If you don't have exhaust fans,do your hardening out side. Your wife might not like the soot on the walls!!

[Noah Wagener]

Also, try choosing an oil that won't ruin your oven when you temper the blade. After you quench the steel it will be very fragile and needs tempering.

I was thinking i would reheat with the torch for tempering to straw color. Should i be using the oven instead? I have read to temper immediately after hardening. Is there anything crucial to the timing? I'm thinking an oven would take a while to get the steel to 500 or whatever but maybe that is inconsequential.

George, should files be tempered at a pretty high temp to make them less brittle? Should they maybe hardened at a higher temp too? I am reading a tool book that has a miniscule section on heat treating. The author states to harden at cherry red and any hotter will cause loss of carbon. Maybe that is a good thing with files? I am just starting small with some marking knives and cutters for mortice gauges. The files were made within the last five years. Well, bought within that time anyways. They are still most surely water quenched? Also, i have seen you write that you should not make a bevel until after hardening and tempering as the thinner metal will warp. Do you mean make no bevel at all or just not take it down to an edge?

[Doug Hobkirk]

I'm clueless. (But I find the thread is fascinating.) I need help in why you are tempering.

1. Are you talking about taking a regular file and tempering it to harden the steel?
   
   1. Is this already done by the manufacturer "never" or "sometimes" or "almost always"?
   
   
2. Or is this a special situation where a particular file lost its temper? (From overheating?)
3. Do these answers apply to chisels? Are you tempering them routinely? Also with a water quench?

[Jim Koepke]

If you quench water hardening steel in oil,it will not cool fast enough to properly harden. If you quench oil hardening steel in water,it will cool too fast,and can crack,or at least form a poor molecular structure.

First let me say my knowledge on this subject is nil.

My question is about the above and how it may relate to something I read someplace. It suggested that it was best to first try hardening in oil and if that didn't work try water.

Is that an acceptable/safe way to proceed with an unknown steel?

jtk

[Noah Wagener]

Doug, I want to soften (anneal) a useless file to make tools out of it and then re-harden and temper. Tempering is a softening of steel after it is hardened. I know that sounds odd. Apparantely hardening locks in a certain structure and it has too done in a state that would leave a blade too hard for most uses.

[David Weaver]

First let me say my knowledge on this subject is nil.

My question is about the above and how it may relate to something I read someplace. It suggested that it was best to first try hardening in oil and if that didn't work try water.

Is that an acceptable/safe way to proceed with an unknown steel?

jtk

Yes, though it's still better to know what you're using and use the right thing first to limit the number of times you heat it, but if you don't know what you have, that's a decent way to proceed.

It's better ,in general, for hobbyists to stick with oil hardening steel - specifically O1. It's just easier to work and in my experience, it warps less, and you can harden and temper it to 60 hardness without issue if you want, or somewhere in the 58-60 range to have a very nice iron or chisel.

Of course, if you're making tools out of old files, then you'll need to use water, but you don't have much to lose using beat files, though.

[george wilson]

Do not bevel at all before you harden the steel. It WILL warp across the width of the blade because there are 2 different amounts of surface area on either side of the plane or chisel.

A good,normal tempering temperature is 400º for cutting tools made from water,or oil hardening steels(or even air hardening steels. I make punches and dies that will cut 10,000 cycles before re grinding. I use A2 air hardening for them. You should stay with oil hardening for a few years,at least.) For a fully hardened file,750º is not too much,and the file will STILL be brittle.

It is best to temper IMMEDIATELY after the quench,while the steel is still so hot that you can barely hold it in your hand(130º). This will make a longer lasting cutting edge. Have your tempering method ready to go.

A torch is fine for tempering. Heat the blade on the end away from the cutting edge. The steel must be sanded clean so you can see the colors change. Let the heat creep up towards the edge. Heat very slowly. Move the torch back and forth across the WIDTH of the blade. Let the torch go completely off the edge,hesitate,and bring it back. Repeat. You must have patience above all. This is the secret to getting a good,long length of brown on your tool. For instance,you could have 2 or 3 inches of brown color instead of maybe 1 inch if you were patient enough about heating the blade.

You can use the oven,but kitchen ovens can be off by 75º. If you have an electric stove,you can try laying the blade on the burner,with the cutting end hanging off the burner. Try setting the burner to low settings. Patiently wait to see what color it makes the steel. If it heats the blade too fast,quench at once before the blade gets too hot. Then,try again on a lower setting. Or,just use the torch.

I often use a toaster oven,but with the LONG thermocouple of a high temperature thermometer stuck in it. I buy them from Brownells Gunsmithing Supply. I ruined one by accidentally touching a live wire in a toaster oven once,so be careful where you insert it. Toaster ovens are even used industrially by professional heat treaters. That's where I got the tip.

The toaster oven is really the best option. You can get the whole tool tempered evenly. I recommend you get one plus the DECENT thermometer(not an ordinary cooking thermometer). Get the Brownell's one. It is worth the investment. Not that expensive.

Files will be brittle no matter how hot you temper them. They have about as much carbon as a straight razor (1.25% carbon). I will warn you that this may be totally different on modern files as they try to cheapen everything. Files 100 years ago were much better sources of cheap steel than they might be today.

Files ARE also surface treated with cyanide(don't worry,it can't get out!). These days,the file might just be surface hardened,and mild steel inside. If you break the file,and it is hard clear through,it is o.k.. No telling about Asian stuff.

You need to completely grind off the teeth in any case. If you don't,your cutting edge will get serrated as it dulls,because that cyanide sinks in a little below the tooth depth. So,completely eliminate the teeth + a little extra.

If you are making a chisel to be used by hand,it is o.k.. Just do not go twisting it,levering chips out,and NEVER use a file for a wood lathe. VERY dangerous,as I have mentioned. I could have been badly injured in my face so easily. My chisel was 2" wide,and weighed enough to hit me hard,but missed me.

You can draw the file blue,and should,but,it will still be more brittle than it should be due to the high carbon content.