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

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  #1  
Old 07-22-2004, 01:14 PM
cactusforge cactusforge is offline
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Air harding 5160

Quench or any one who knows the answer. Would you shead some light on a problem that is causing me a lot of trouble. Most of my Knives are built using 5160, I normalize 3 times I quench the whole blade 3 times then temper 3 times at 350* this is done before grinding, the trouble starts when I draw the spine back no matter what I do the spine will get a little softer but not soft enough to file work. I heat the spine only from the top as if I heat it on the side the knife will warp. In cold weather it in almost impossible to get this done but today I had the same problem and it is 100* out side what gives? I have wondered if 5160 air hardens like L6?
Gib


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Old 07-22-2004, 04:08 PM
nate d. nate d. is offline
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i did some stick welding on some 5160 and that plate air hardened so hi that the only way to drill a hole in it was with carbide, and forget about trying to tap a hole in there. hope this helps.
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  #3  
Old 07-22-2004, 05:47 PM
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Ed Caffrey Ed Caffrey is offline
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5160 will exhibit a degree of air hardening, as will 52100. The probelm that your describing is exactly why I discourage soft back drawing blades............ TIME AND TEMP. In order to accomplish a soft back draw on most commonly forged steels, it should take you 20-30 mins with the heat source, followed by a soak at temp to ensure the conversion is accomplished. Far too often folks do it with a torch, or a heated block of steel, and once they achieve the color they want, quench the blade to stop the action.........From the number of broken blades I've examined from various sources, that's about the worst thing a person could do. It weakens the spine terribly, and in some cases the grain is just huge. Most of the samples I have examined that had been "soft back" drawn only have about .005 to .010 of the exterior converted. The rest of the "core" remains as it came out of the tempering cycles.

You can save yourself much grief by edge quenching rather than quenching the whole blade. Keep in mind that when I use the term "edge quench", that doesn't mean you only have to quench 1/3 to 1/2 of the blade. Many times with 5160 I have qunched to within 1/4" of the spine, and still was able to flex the blade to 90 degrees without breaking. If your objective is to leave the spine soft enough to filework, then quenching all but that last 1/4" or so would accomplish that.

One last observation. If 5160 air hardens to a high degree, that is an indicator that the steel was over heated.........not to the point of "burning", but heated too high for the operation being performed.


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Old 07-22-2004, 06:31 PM
Quenchcrack Quenchcrack is offline
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Air Hardening 5160

What Ed said makes sense. If you austenitize at a high temperature, you are dissolving more of the chromium carbides and the steel will have more hardenability. Obviously enough to air harden. Thanks, Ed, I make a few 5160 blades and I will try it your way next time. Oh, do you use oil or water to edge quench 5160? I am always leery of leaving a section of red-hot steel sticking up out of oil fearing that the vapors could ignite. :confused:


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Last edited by Quenchcrack; 07-22-2004 at 06:33 PM. Reason: more questions
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Old 07-22-2004, 06:54 PM
cactusforge cactusforge is offline
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Thanks Ed, You have explained something that has plagued me for a while so I will pay more attention to my heat treat proceeder, One of the problems is that the shop is just under a awning and I work in near full day light. I bought a potentiometer and that helped till I burnt the end off the prob. I have tried the edge quench and I get a lot of fire when I do that. I am using a 50/50 mix of ATF and hydraulic oil. I tried to get quenching oil when I updated my shop and could not get it at any price. Gib


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Old 07-22-2004, 07:54 PM
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I have edge quenched 5160 in Brownell's Tough-Quench without having any bad flame problems; and, luckely no edge warp (yet). I think I preheated the Tough-Quench to about 105 - 107 F.

RL


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Old 07-22-2004, 10:51 PM
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For years now I've been using straight mineral oil purchased from the local farm/ranch supply outfit. If the blade is too hot when you quench in this stuff, it will tell you by flaming a bit. At first I was concerned with it because everything I had previously used flamed like crazy when the blade was quenched. But, after using it a while (along with the magnet to test temp) I found that my blades where getting a better hardening at a lower quench temp than with the mix of trans fluid I was using. (Looking back I realized I was really overheating the steel when I was using the trans fluid) The Mineral oil works best when pre-heated to 130-160F. Whatever you do, if the mineral oil gets to 180F, stop quenching. Once it reaches that temp it won't conduct enough heat away from the blade to get a full hardening. Let it cool down a bit and your ready to go after it again.

Often times when edge quenching you will get some flames, but with the mineral oil they are very minor. They usually will go out by themselves fairly quickly, or a quick puff of breath will blow them out. The main reason I went with the mineral oil was because the type "A" quenchants were very expensive, and I would have had to buy a 55 gal drum. (nobody would sell it in a lesser quantity) At the time it was over $14 a gallon when purchased in a 55 gal drum! The mineral oil is about $9 a gallon and about 2 1/2 gallons fills my quench tank nicely. As mentioned, Brownell's Tough Quench is an excellent quenchant too. I might just have to surf over to their site and see what it's going for these days.


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Old 07-23-2004, 09:25 AM
Burke Burke is offline
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Hi all,

I just thought that I would jump in here to say that I use Texaco type "A" quenching oil and have no problems with fire when edge quenching, until the oil gets to near two hundred degrees F. Like Ed stated above cooling efficency goes down past one eighty or nintey so stay below these temps and you should have no flame at all. Shane Justice was selling texaco type "A" oil in five gallon buckets. Contact him at; 307-673-4432

Bill


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Old 07-23-2004, 09:26 AM
cactusforge cactusforge is offline
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Thanks ED you have explained things very well. Gib


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