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Heat Treating and Metallurgy Discussion of heat treatment and metallurgy in knife making.

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  #1  
Old 04-05-2014, 06:07 PM
darrylbiscuit darrylbiscuit is offline
 
Join Date: Jul 2013
Posts: 5
New heat treater has a questions

image.jpg

Hello everyone-

I am new to doing my own heat treating, and my first run raised more questions than anything.

I tried a couple of knives I shaped out of what I was told is L6, then normalized 3X in my one brick propane forge. After that, I got them to non- magnetic again and edge quenched in vegetable oil.

After tempering at 375 degrees for 3 one hour cycles, I started removing the scale and found this pattern in the steel. While it looks cool, it is not what I was going for, and now I guess I have to sand the pattern out.

I'd appreciate any info on what caused this, how to avoid it, and anything else I did wrong!

Thanks,

DJ
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  #2  
Old 04-05-2014, 07:30 PM
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GHEzell GHEzell is offline
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I hate to say it, but this is a usually a clear sign of over-heating....


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  #3  
Old 04-05-2014, 07:33 PM
Doug Lester Doug Lester is offline
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Off hand I would say that you really overheated the blades and you had some scale build up. Yes, you can grind it out but I would also worry about what you did to grain growth.

What you need to do to prevent this is to try to catch the steel at just the point it goes non-magnetic and then try to get it just a little brighter and hold it there for at least 2-3 minutes then quench.

To repair any grain growth that you might have done I recommend that you repeat the normalization for three more times trying to make sure that the steel doesn't more than just a little above non-magnetic. If that is L6 you do have the advantage that it has vanadium in it that will put a drag on grain growth so you could cross your fingers and omit re-normalization.

One of the problems with the steel is, assuming that it is correct that it's L6, is that it has a wide range on the carbon content. It can go from 0.70-0.90% carbon and that difference is significant. On the lower end you can do a shorter soak at 1550-1600?. If the carbon content is towards the higher end then you have more carbides to dissolve and the possibility of more retained austinite that can be formed.

I'll give you the advice that is usually given to beginners. Go with a known steel and actually I would recommend against tool steels unless you have the assay for that melt you are using or you will still be close to using mystery metal. Keep it simple, as in simple alloys. Something like 1080, 1084, 80CrV2 or 5160 would be a good choice.

Doug


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Old 04-05-2014, 08:23 PM
darrylbiscuit darrylbiscuit is offline
 
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Overheating...I didn't think about that, but I guess my forge is working well!

I will play with it more and see if I can get the process worked out better.

I do realize that some other steels are probably easier to learn on, but I trust the pedigree on this L6, but I didn't read up on it too much before I tried it.

Thank you both for your replies- very helpful information, and it is always great to learn fro others that have been down this road before!

I'll let you know how the next ones turn out, and I will try to normalize these again too.

Thanks again,

DJ
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  #5  
Old 04-06-2014, 08:21 AM
Ed Tipton Ed Tipton is offline
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Darrylbiscuit... Your picture shows de-carbonization...which is another way of saying you overheated your steel. You can probably re-normalize the blade, and save it from the scrap pile, but I think a better plan would be to do some destructive testing on it ...as is...to see the full effect of how the steel responded. If you decide to do this, place the blade into a vise and then bend it until it breaks. Once broken, look closely at the grain structure of the broken area. If done correctly, there should be very little if any individual grains visible, and the result should be about the same as a piece of broken porcelain china. The surface should be light gray and silky smooth. I suspect you will see individual grains which results from overheating...and this grain structure greatly reduces the strength of the blade.
A good way to see exactly what your steel should look like is to sacrifice an old file and break it. Old files were very accurately heat treated, and you will very quickly see the difference.
Another pitfall is un-even heating of the blade. This will result in different parts of the blade being heat treated differently.
Don't give up. It is possible to do your own heat treating, but as with anything, it is difficult to reach your final destination if you don't know how to get there.
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  #6  
Old 04-06-2014, 12:23 PM
jmccustomknives jmccustomknives is offline
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Where did you get the steel, I've never seen L-6 do that. I'm thinking you got some large band saw blade material, it isn't L-6 (some how a myth got started that they used L-6 in band saw blades, I've never found on single blade manufacturer that does). L-6 is very forgiving in the heat treat. I'm giving to think you may be running a bit too lean also.
It always helps to know what you are dealing with for sure. You've already got holes, did you anneal?
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  #7  
Old 04-07-2014, 05:00 PM
darrylbiscuit darrylbiscuit is offline
 
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The steel came from a friend that is a retired ship's engineer, so I assumed he knew what he had. Of course, his memory isn't what it used to be either, so it may not be L6.

I will play wit bit some more, then get some known steel for sure.

Since this is pretty thin stock (just over 1/8"), I am pretty sure I overheated it now. I guess I was worried about not getting it hot enough, so I poured the heat to it without worrying about overheating.

I did anneal to drill the holes.
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