How do you soften treated metal?

B

blackgrub0331

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Aug 17, 2006
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I just got my 20 inch saw mill blade made from I was told L6 steel now I know its been heat treated but how would I go about making the steel softer so I can make some blades out of it?


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Fire it up until it's non-magnetic then let it cool in the air.

Someone please correct me if L6 is different.
 
Well, if it's the L6 that Carpenter and Crucible sells, the process you've described isn't going to soften it enough to work. That stuff needs to be slowly annealed; something like 100 degrees an hour to soften.
 
Danbo said:
Well, if it's the L6 that Carpenter and Crucible sells, the process you've described isn't going to soften it enough to work. That stuff needs to be slowly annealed; something like 100 degrees an hour to soften.
Click to expand...

How hot does it need to get up to? Or should I ask how many hours to do it?
 
I made a couple thousand knives from old saw blade years ago and none of it acted like L6, I'm beginning to believe saw blades made of L6 is a myth. I used to cut them up with a cutting torch and throw the pieces in my wood stove, next morning they were soft. A good bimetal band saw blade will cut it pretty good it as is.
 
If it's Crucible L6 do NOT heat it above nonmagnetic. It's basically air hardening, and if you do that it'll be harder than when you started...
I've never used an industrial saw blade to make a knife, so I can't help you much. Don may be right; maybe they never used L6. Why doesn't someone who has an old saw blade send a sample to Mr. Doyle and find out???
 
I recently annealed some old bandsaw blade to use as folder liners. I followed Crucible specs for L6 and it worked fine. Heat to 1400F - hold for 2 hours - cool slowly, 50 degrees F per hour to 1100F - then air cool. I wouldn't want to try that with a torch. :) .

That's a long cycle in the oven.... and it did leave a bit of scale, though no deep pitting. When I do it again, I'll do much more at once, for economy, and I'll do it in a large foil envelope to reduce the scale.

Now, I'm just guessing, but I think that 20" blade might have to be cut up first before it would fit in most ovens.

Rob!
 
For those who wish to avoid another opinionated rant (in blue) please avoid the following and proceed to the bottom of this post:

Once again, this nonsense of any scrap steel necessarily being a particular alloy due to the item it was comes from complete misinterpretation by reading certain charts backwards. Those charts being the ones always listed by some knifemakers as saying things like:

L6= saw blades, blanking dies, metal slitters, shear blades, punches / O1= Bushings, punches, paper knives, taps, reamers / W2= Blanking tools, cold chisels, rivet sets, lathe tools.

These charts are listed in just about every basic metallurgy textbook, are being read backwards by most knifemakers, and are no more a guarantee that any item is a particular alloy than one can guarantee that every custom knife is the same steel.

Those charts explain the kind of uses that were considered when developing alloys to perform specific types of tasks and are simply examples of those tasks, a manufacturer can and will use whatever steel they see fit at the time with a whole range of other reasons aside from the alloy intended uses, heck once again look at knifemakers and why they choose the steels they do.

For what it is worth I have yet to work with a chunk of saw blade that behaved like real L6 myself, not to say that it isn't out there but it is very safe to say that saw blades can be made of almost anything.

In another thread there was a bit of a debate whether to use scrap steel or not, I won't rehash that tired topic again, but I would like to point out that one serious drawback to scrap steel is the frustration for folks like Mr. blackgrub0331 and the guys who really want to help him out, but how can we recommend a heat treating method when we don't know what we are heat treating? The internet forums are filled with threads on treating mystery steel that go on and on with dozens of best guesses, while threads where a known alloy is given only take a couple of posts to list the exact heat treatment.

I would, however, like to say that Mr. blackgrub0331 did it the right way, he started out making it clear that it was a saw blade. In forum conversations and private e-mails I have had an irritating amount of time wasted by guys who I wanted to help with heat treating a given steel, lets say L6. I am told I am helping with L6 and we go back and forth for some time with different methods to which this steel doesn't seem to want to respond. Finally, after every possibility has been explored, I will ask where they bought the steel, and it is only then I am informed, after being told it WAS L6, that it is actually saw blade mystery steel. I really don't think I am out of line in finding this a bit inconsiderate, and is the reason I am so draconian about known chemistry on the forum I moderate.

This may get under the skin of some sensitive recyclers, but tell me what is false about it?

Now so as not to hijack Mr. Mr. blackgrub0331's sincere request for information I am going to break one of my personal rules of not getting involved in recommendations for mystery steels, I at least owe him that for using his thread for my release of pressurized hot air.

Mr. blackgrub0331, I would take a sample of the blade and heat it to well above critical and allow it to air cool. If it is then soft and able to be cut with a file, simply use traditional annealing methods (heat to critical and insulate in wood ashes etc...). If the steel is hard from air cooling, you could very well have L6, or at least an alloy that would require similar annealing techniques. in which case you will want to go spheroidal. If you can get access to an oven that will allow complete spheroidizing (one with ramping features) heat to 1375F and hold for some time before cooling no more than 50F per hour until you get below 900F. If all you have is simple tools an acceptable spheroidal structure may be had by heating it to dull red multiple times without ever allowing it to lose magnetism. If it is L6 the spheroidal annealing is almost a must in order to drill or other machining operations, it will also be easier on your belts.
 
To pick up where Kevin left off:
It is a bit hard for the average blade maker to find an oven that will anneal a 20" round blade. Take a cutting torch (or a plasma torch) and slice it into 4" wide strips. These will be easier to handle for testing and annealing.Use the short cuts for testing.Another way is to cut it into pie slices,making long thin triangles. I have cut up several like yours,with varying steel results. As Kevin said,don't assume (or state) that it is L-6.
Stacy
 
Thanks for the help Kevin R. Cashen and everyone else! I called the guy I bought it from and asked him if he know what type of metal it was. He said he did not know but he read in his guide that saw mill blades where made from L6 but he could not tell me if it was L6 or any other type of steel.

He did give me a little history on it he told me that the blade was well over 60 years of age and was used in a local saw mill that had been passed down 3 generations and the grandson thought it was time to retire the old saw blades in the mill. Mine was one of 3- 20 inch blades that the owner know dated back when his grandfather started the mill.

I told him that this mill blade was not going to be placed on someones wall as a painting but it was going to be used to make knife blades from it so it could keep doing the job that it was made for.


I might have to wait until I can get to my Dads shop to get that saw blade cut down as I have nothing that will do that at my place.
 
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