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

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  #1  
Old 01-23-2012, 11:26 PM
jdale jdale is offline
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Unique HT situation

I originally posted about this in the newbie?s arena.
I made 3 blades out of an old concrete cutting saw blade (saw blade 1.5' by just shy of 1/4" thick). Heated to just past non-magnetic, quenched vertically in transmission fluid heated to 130degrees. Time from forge to quench was around 1-1.5 seconds. Held in fluid for 30 seconds after convection stopped.
Three passes with a chain saw file put a good size notch in the handle. I tried to see if I could still easily drill through it, after making a shallow depression in the steel it quickly ruined my drill bit. After posting on this forum I realized from the feedback and the original HT I should have scrapped the saw steel.

But having nothing to loose on 3 blades that might be destined for the scrap pile anyway I am going to give HT another try with a different medium. I will let everyone on here suggest the method to HT with using my data gathered on the steel tonight using left over pieces
I used 3 pieces of roughly the same size steel and quenched in 3 differing mediums than put in the vice and pulled till ?pop?.

[IMG][/IMG]

#1 (on left) heated to just past non magnetic quenched in vegetable oil within 1 second of being removed from heat. I had to use 5 or 6 passes with a chainsaw file to get any kind on groove in the steel. Placed in the vice I had to pull extremely hard with a pipe wrench to break the steel. It bent around 25 degrees before breaking in a very jagged edge.

#2 (middle) heated to just past non magnetic quenched in brine within 1 second of being removed from heat. I had to use 5 or 6 passes pressing hard with a chainsaw file to get any kind on groove in the steel. Placed in the vice without much pressure it snapped clean off with a very smooth straight edge

#3 (right) heated to just past non magnetic quenched in super quench (water, salt, liquid soap, and a wetting agent ?jet dry?) within 1 second of being removed from heat. I had to use 5 or 6 passes pressing hard with a chainsaw file to get any kind on groove in the steel. Placed in the vice pulling with more pressure than 2 but less than 1 it snapped off relatively clean but with a small jagged area.

The original non HT steel when put in the vice and pulled bent to close to 115 degrees before tearing apart.

So what is the general consensus, do I HT the 3 blades with Brine, Veg oil, or super quench.
Thanks in advance for any feedback I get
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  #2  
Old 01-24-2012, 03:43 AM
Ed Tipton Ed Tipton is offline
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idale....Based upon your results, the brine would be my first choice followed by the super quench. I would definitely not go with the veggie oil since neither the technique or the results indicate that the sample was adequately hardened. If the sample has been adequately hardened, it should snap off with relatively little pressure and the break should be clean and the grain should be small....ldeally, almost like breaking a porcelain dish. If excessive force is required, or if the grain is too coarse, then the technique can be improved upon. Also, without knowing the exact makeup of the steel, it's something of a crapshoot....but your second sample appears to be pretty close so I'd guess you're in the ball park with the brine.
Using brine, Just be sure that prior to quenching, you have eliminated all of your potential stress risers from your piece, and that it is properly prepared, in order to reduce the possibility of the piece cracking during the quench..

Last edited by Ed Tipton; 01-24-2012 at 09:02 AM.
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  #3  
Old 01-24-2012, 02:37 PM
Doug Lester Doug Lester is offline
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I guess that my estimate that you were not dealing with a shallow hardening low carbon steel could well be wrong. The bodies of those blades may well be a higher carbon simple alloy but how high on the carbon or how simple an alloy is still guess work.

Ed gave real good advice on how to prep for quenching in brine, which is very agressive and puts a lot of stress on the steel during the quench. What I would do now to test the steel further is to make a blade from it, using the brine to harden the steel, and put an edge on it. I would temper at around 375-400 degrees for at least two two hour cycles. I would also normalize X3 before quenching. Dont' go crazy putting a fine finish on the blade or a finely finished handle becuause you will want to break this blade.

After you have a good edge on it see if it will cut into a brass rod or soft iron wire without making an indentation. If the indentation looks like the edges ar rolled over the edge is too soft and you can reharden it and temper at about 25 degrees lower. If the indentation looks chipped just retemper at about 25 degrees higher without requenching. Then repeat the above test until there's nothing but the slightest flattening of the edge, if that.

Then do performance testing. If it is a larger blade you can chop wood with it and see how well the blade holds up and how well it retains an edge. A small blade you can whiddle wood with it, or slice up manilla or hemp rope and see how long it stays sharp. With a longer blade, 4 inches or more, you can see if you can slice through a free standing bottle of water. This does not test the hardness but will give you an idea if you have a good blade geometry. I think even a chopper with a convex edge should be able to cut through one bottle even if the halves are knocked across the yard.

After all that, clamp the knife blade in a vice and see how far it bends before it breaks or how many time you have to bend it to get it to break all the way through. What you should see in the broken edge is a grain structure about as fine as 800-1000 grit sandpaper.

Here's another thing that may be happening with those blades if you are testing with the file on the spine. With a fine grain, and that middle one is looking good as far as I can see, the spine may be too thick to harden except at the corners of the spine. If you cut through those hardened corners with you file you will be into pearletic steel which will file easily. The edge will still harden to a thickness of twice the depth of hardening giving a martensetic edge with a pearletic spine. Just a possibility. That could be checked out by finishing the steel out to 800-1000 grit and seeing if the blade will differentially etch with vinegar or ferric chloride which, by the way, Radio Shack is once more carrying to etch circut boards.

Doug


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Old 01-24-2012, 02:45 PM
Bearpaw Customs Bearpaw Customs is offline
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I hope you don't take this wrong,But forget about it and buy some steel.Then you will know what it is and how to heat treat it.Unless you just like messing around with metal and not useing your time making knives.


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  #5  
Old 01-24-2012, 07:58 PM
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Eli Jensen Eli Jensen is offline
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I agree with Bearpaw
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  #6  
Old 01-24-2012, 08:31 PM
jdale jdale is offline
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Well we will see how the brine does tonight, i have the blades on there first normalizing cycle now. Ill do it 2x more times than ready for the brine.
I have plenty of steel, i just wanted to make something that i couldnt do with my 5160 or 1095 without having to forge it out first. I have literally hundreds of lbs of this steel and sooner or later it had to be tested. As for making 3 at a time one just seems too slow for me, once one gets hot from the sander i switch out and start on the next. I didnt time it but im going to say i finished sanding the knives in under 2.5 hours.
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Old 01-24-2012, 11:36 PM
Doug Lester Doug Lester is offline
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Well, if you have hundreds of pounds of those blades then you have plenty to figure out the heat treatment. Hopefully they are all the same. This is one of the places where mystery metal can work. It's different if you have to figure out how to treat each individual scap of steel, especially if they will only give you one or two blades per piece.

Actually, there is no guarantee that with a known steel alloy that you won't run into a situation where you will get a different melt of the same alloy that you've been using that's different enough to throw off the heat treatment. That's why all blades must be tested for proper hardness.

Doug


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Old 01-24-2012, 11:39 PM
jdale jdale is offline
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Normalized 3 times, heated to non magnetic and quenched in brine. Three blades in three blades out. No apparent fatalities, but the latgest knife did take on a slight bend. I tapped each blade and i heard the metal ring, file test did a lot better than yesterday. But being that I have made well under a dozen knives im not totally sure if i know what a passing file test looks like anyway. knives are in the oven for 2, 2 hour cycles of 400 deg. I guess if they live through the tempering and final sanding i will pin em up with some spalted maple or zebra wood handles and beat the hell out of them.
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Old 01-25-2012, 12:33 PM
Doug Lester Doug Lester is offline
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It's your call, but if I were putting a handle on a knife that I was going to abuse the heck out of and possibly break to check the grain structure I would choose something cheap to make the handle from. Maybe some maple, walnut, or cherry wood. I'd save the good stuff for a knife that I at least want to give away.

Doug


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Old 01-25-2012, 02:35 PM
jdale jdale is offline
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The place i buy my wood from sells purple heart, zebra wood, leopard wood, blood wood, brazilian satin wood, paduk, canary, and zirkote in the range of 50 cents to $1.75 per block. Strangely enough the only domestic wood in my handle box is spalted maple and thats the stuff i stabilized a few weeks ago.
Two questions:
when you break a knife to look at the grain structure do you use any magnification instruments?
When the file test is preformed, how much pressure do you use when you push with the file? when i did the file test last night i pushed hard enough to flex the chainsaw file before drawing it across the spine
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  #11  
Old 01-25-2012, 03:29 PM
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Eli Jensen Eli Jensen is offline
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1) No. But its nice. Sometimes I use the dissecting scopes at the lab I work at. You should be able to see grain growth with the naked eye or a magnifying glass.

2) You don't have to do it hard. Even light pressure will tell you if it bites or skids. If a chainsaw file is flexing, that's way too much pressure. With enough experience you'll even be able to tell if its a bite or skid by the sound.
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Old 01-25-2012, 06:40 PM
Ed Tipton Ed Tipton is offline
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Idale...Try taking a piece of un-hardened steel and running a file across it. It only requires a minimum of pressure for the file to cut the steel. The file relies upon it's hardness and the sharpness of it's teeth to do the cutting. If the steel is harder than the file, the file will simply skate rather than cut the metal. If you apply pressure, all that you're going to accomplish is that you're likely going to damage the file...but you're still not going to cut the steel. As Cpt-Jens stated, the sound alone is enough to tell you that the steel has hardened and the file is skateing across it rather than cutting. This test is best done using a standard steel file and not a diamond file since a diamond file may be hard enough to actually cut or "bite" the hardened steel, but the steel file will just skate across it.
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Old 01-25-2012, 07:03 PM
jdale jdale is offline
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Great idea Ed, never thought of doing it on the non hardened steel as a compairison.
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