Heat treating: Warping fears...

[Dangus]

I made this rapier dimension sword blade and I'm very worried about it warping as I treat it.

Just for some background, I forged it from a piece of leafspring in a forge burning charcoal and hard maple primarily. It is 32 inches blade length, 1 3/16 inches wide, and about slightly over 1/8" thick. So you can imagine my fears of warping... It does not file easily but it does stay bent when I bend it so it definitely needs to be treated..

A master bladesmith I got to work with a while back named Jim Miller told me that a good blade like this from 5160 should, if properly treated, bend tip to tang and go back true. If I try that now I'd have a hoop, lol.

I am thinking about maybe strapping a couple pieces of mild steel, one or two per side and then binding the whole thing with wire and then heating the whole bundle a bit higher than normal for treatment and then quenching it. That should forceably hold it in place during the shock. What do you think?

Btw, here are some pictures of it, it is the blade in the middle. In the picture are my dagger blade on the top, Jim helped me make that one. The blade at the bottom is a heavy bladed backsword. The bottom is my second sword blade ever, middle one is my third blade, and last before the city gustapo shut my shop down

 

[Bugs3x]

Dangus -- I'm no knifemaker, so please make allowances for my ignorance. I thought that heat treating temperatures and tempering temps were based on the steel, pure and simple, and not on the size of the blade. So, am having trouble understanding why you'd want to heat it higher. I would think that changes in the heat treat temp would be more likely to cause warping than the appropriate tmperature. Also, does the support that the blade has during the quench have something to do with warp? You must have a hellacious big quenching pan/whatever, to be able to take a 32-inch blade. WOW!

Wish I could help so far as "splinting" the blade. Sorry. Good luck!

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Asi es la vida

Bugs

 

[Bruce Evans]

First of all heat treating a blade this size is always scarry.The way I did my first sword and all my longer blades is like this.
I made a quech tank out of a old piece of 3 inch pipe.I sealed one end so it wouldn't leak.and thenI fixed it so it would stand up on end without tipping over.Make it long enough that you wont hit the bottom by at least 6 inches when the whoole blade is quenched.You can make this with a 4 inch pipe also.
Now when heating the blade KEEP IT MOVING in the fire and don't let any parts of it get a uneven heat,this means to keep passing through the fire while you are rotating the blade this way it doesn't get hotter on one side or the other.Quench it tip first.
Now tou will need to temper the blade,It really only needs to be at spring steel hardness not skinning blade hardness.To do this temper it back to a blue color and you should be good to go.
I think that your idea will work as long as you make sure that you have the whole piece (all three) heated all the way through.And that it is wired up tight enough that it doesn't slip while heating or quenching,if it isn't tight enough when quenched it will defeat your purpose and the blade could still warp.
If you do it like I first suggested you should come out fine.You may have yo work on the tempering temperature to get the flex that you are looking for.
I thought that most rapiers were only about 3/4 to 1 inch wide maximum...
Hope this helps you out some,
Bruce

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Bruce Evans Handcrafted Knives
The soul of the Knife begins in the Fire!!!!!
Member of,AKTI#A000223 and The American Bladesmith Society

 

[Dangus]

<font face="Verdana, Arial" size="2">I thought that heat treating temperatures and tempering temps were based on the steel, pure and simple, and not on the size of the blade. So, am having trouble understanding why you'd want to heat it higher.</font>

I want to heat it a tad hotter because witht he brace that will be built around it, if I do that anyway, it will be more insulated and will not drop from critical to below critical as fast as I would want... So upping the temp some would add a little of what I call thermal inertia(same reason hot water pipes freeze faster), so it gets the shock from the jig, not from the oil. It's a bit hard to explain. Maybe it doesn't even make sense, lol

My other option is to put two or 4 pieces of mild steel angle-iron in the quench tube and affix them in such a way that the blade goes into them like a sheath. They would be cold this way and would function more like a heatsink, creating the thermal shock I need, but controlling the dispersion rate better.

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I twist the facts until they tell the truth. -Some intellectual sadist

The Bill of Rights is a document of brilliance, a document of wisdom, and it is the ultimate law, spoken or not, for the very concept of a society that holds liberty above the desire for ever greater power. -Me

 

[peter nap]

Dangus, Bruce is right about keeping it moving and his design for the quench tank. I'm odd because I started making swords before I made knives. I have a special forge for swords made from stovepipe and lined with Kaowool. I use a mini mongo burner to heat and I heat with the blade down.

Even heat as Bruce said cures a lot of warp. Even quenching is more important IMHO. Katana swords for instance are curved mostly by the quenching.

You will get some warp. Just take it out after tempering and before the final grind.

Also...remember to normalize before hardening. I do it several times.

To temper, I use the same forge at a lower pressure setting for the mongo and use temple sticks to gauge the tempature.

Good luck...My first came out OK...My second cracked because I didn't normalize. You pays your money and you takes your chance.

By the way Dangus. I wouldn't use the bundle method unless it is all the same steel. If you want to see what a bimetal strip does look at your thermostat.

[This message has been edited by peter nap (edited 06-26-2001).]

 

[Dangus]

I suppose the idea was just to use mild steel for the straight edges, so to speak. I think I am gonna put them in my quench tube though. I have a plan that is unconventional but will probably work... I will report back after I get a test piece run....

 

[Arthur Washburn]

It's not a good idea to go above the recommended heat treating temp as this will cause grain growth in the steel and result in a poor heat treat. Surrounding the blade will act as too much of an insulator and not allow your to bring the temp below the nose of the curve to get a good heat treat. You can heat your quench oil a bit to help aid in a good heat treat. The advice to normalize and heat evenly are excellent. As for the warpage you should be able to straighten the blade a bit after the initial quench.

Arthur D. Washburn
ADW Custom Knives
Production Manager for Devin Thomas Damascus

 

[Bugs3x]

Thanks for your response, Dangus. I think I understand most of what you're saying now.

I see that you did use the word shock in your first post, but I missed it before. In your last post you talk of thermal shock. I'd not heard of that before. Since you seem to speak of it positively, then it must be good. I've read that 5160 should have the oil for the quench heated to 160 degrees or so. That, I read actually results in a quicker cooling.

If I'm understanding you right, then when heat treating and quenching, the desire is to maximize the quickness with which the steel cools. This thermal shock apparently enhances the quality of the steel. Could you please tell me why that is, or what the quality(s) added is/are?

I know that a good amount of forging results in smaller grain in the finished steel. Does the thermal shock add to this in some manner? I can see the splints could significantly hamper the cooling speed of the blade in the quench.

You or one of the others who posted talked about "spring." I am assuming that this has to do with the shock absorbtion ability of the steel. You don't want a blade of this length to just break on you. It seems to me that differential hardening might help that more than essentially just leaving the steel softer than one would for a knife blade. Is it not possible to differentially treat such a long blade, just because of the difficulties presented by the size? I thought that most of the Japanese sword blades were differentially hardened in one way or another. Don't believe I ever read why they do the clay tempering/hardening, whatever. Is it that used in the tempering process only? So that the clay keeps the edge hotter longer, allowing the bladesmith to draw the spine back quicker, and presumably to a softer level than the edge?

Sorry to ask so many questions, but am fascinated by heat treating as done by bladesmiths. And, am so ignorant, have a great many more questions than answers at this point, and for the foreseeable future.

Any answers you or another smith have the time to provide, would be really appreciated.

Thank you,

 

[Dangus]

If I'm understanding you right, then when heat treating and quenching, the desire is to maximize the quickness with which the steel cools. This thermal shock apparently enhances the quality of the steel. Could you please tell me why that is, or what the quality(s) added is/are?

The best way I have ever heard it explained is like this: Water is a liquid at normal temperatures, as you make it colder, it crystalizes and forms a solid. Different freezing conditions make different grades of ice. This is how layers form and avalanches occur. Water also has different levels of freezing, each has somewhat different characteristics, some expand, some contract. Anyway, the same is the case with steel, or any solid. Solids are just materials that are frozen at room temp. When you heat treat something, you are trying to go from one level of freezing to another, creating crystalization that is literally frozen in a certain way. When it hits critical temp the carbon and the steel are in a certain place, and when you quench it you are literally freezing it, to a different level of solidity. You lock in the qualities you want, so you need "shock" to take it from one stage of freezing to the other as fast as possible. That said, you only wanna take it from stage to stage fast, but not any further fast. So if critical temp is 1500 degrees, you want to get it to 1499 as fast as possible, but then you wanna take it down to room temp from there more gracefully, otherwise you run the risk of fracturing it. Of course this varies depending on the qualities of the steel, but that is basically how it works from what I have been told.

You or one of the others who posted talked about "spring." I am assuming that this has to do with the shock absorbtion ability of the steel. You don't want a blade of this length to just break on you. It seems to me that differential hardening might help that more than essentially just leaving the steel softer than one would for a knife blade. Is it not possible to differentially treat such a long blade, just because of the difficulties presented by the size?

You want a sword to be hardest at the point, and softest at the area around the tang. This is possible in a very simple way. Quench it tip first, don't submerge the tang completely. You also heat the oil with the first parts as they pass into it, and the next parts that pass there don't recieve quite as much shock. It's really not much more complicated. At least for simple treating. There are more bizarre techniques, but that's my method.

 

[Eric M Ericson]

I don't make swords, I have done a couple of blades over 20 in. I was taught always straight in or it will bend on ya. ( I like the pipe idea it's a lot easier than a 55 gal. drum to get the proper depth.) even heating is also critical. before you try to harden, I would aneal it to remove any stress that was introduced in the forging process. make sure that the critical temperature is met (this is easy, when a magnet no longer sticks to the steel its there) hold it at that temp. for a bit. be sure that the heat is even. then quench (Bruce's instructions are great) the only thing that I would add is that I like the dirty 40W from my dad's truck as an oil quench. I've had problems with cracking in lighter oils that don't seem to hapen in the heavier stuff.(besides it's cheep) If you use a water bath try using a heavy salt brine ( a little salt is a cheep insurance policy against the cracking that can sometimes occure )
I hope this is helpfull
have fun Eric