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High-Performance Blades Sharing ideas for getting the most out of our steel.

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  #16  
Old 12-09-2002, 08:42 PM
Jason Cutter Jason Cutter is offline
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Dan, I know what you mean, I accidentally oil-quenched 440C once !! One shard 1x1-1/2inch across and doing a good impression of a ninja throwing star, got stuck in the roof hard enough I couldn't knock it out with a broomstick. Another good reason to wear all that protective gear.

Of course, we're talking only about carbon steels.

Over the months, I've grown accustomed to having that certain percentage of warped blades, and its weird, but I almost look forward to that challenge of getting it ground straight again. I need more therapy.

Cheers.


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  #17  
Old 12-10-2002, 10:22 AM
Dan Graves Dan Graves is offline
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warpage

Jason, the knife that I find hard to heat treat is a filet knife. They seem to just want to warp. Unfortunatly, there is not much steel to grind after heat treat. They somehow end up being a small knife. I have a knife that is probably 100 years old and is a 10 inch carver. The blade starts at the ricasso and has a taper all the way to the end of the blade. It starts at 1/8 thick aat the ricasso. The blade can bend like a filet knife. I know I would have warped that blade. What I do is grind after I heat treat to get the thinness I desire. I grind bare hand so I can feel the heat. Warpage does seem to be a way of life. I was talking to a heat treater and he uses a steel called A-2. I am not familar with it but he swears by it as not warping. Know anything about this steel?


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  #18  
Old 12-10-2002, 10:29 AM
Jerry Shorter Jerry Shorter is offline
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I'm kinda new to knife making. but it seems to me that warping may be accentuated when you dunk your blade jif you lay it flat on the bottom of the tray. The first kinvesw that I made were from O1 and 5160. and I never had much of a warpage problem after I started puting a large buuldog clip on the tang just before dunking to hold the blade verticaly while it cooled in the oil bath.

Jerry S.
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  #19  
Old 12-10-2002, 05:14 PM
Jason Cutter Jason Cutter is offline
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Dan, I'm not even going to TRY to make a fillet knife at the moment given my warpage problems. It seems like a lot of the air-hardening steels are a better choice for such thin knives, given the nature of the heat treatment process. I imagine many people do it differently, but I call it a "NO-TOUCH" process. When heating up and air-quenching, nothing touches the blade except for the blast of air. The blade is hung from a rail.

This is the way that the professional heat treaters I use, do it. They very very rarely have any warpages on air hardening steels since there is no physical pressure applied, even accidentally, eg.- when you pull the blade from the forge, dunk, accidentally touch the bottom of the tank etc.

If you think about how a lot of straightening techniques go, it works on the principle that even at tempering ranges of 350-450F, steel is malleable enough that it can actually be bent back into shape from a warped position. So even when fully quenched, a blade can be hot enough to still do al sorts of weird stuff if you just plonk it on the bottom of the tank, resting up against who knows what. Hence, to me, Jerry's comments make perfect sense.

Dan, perhaps thats why the heat treater suggested A-2. A-2 steel is a carbon tool steel with about 1% carbon, 5% chrome and molybdenum. It is one of those cold work carbon steels that is air-hardening due to the chrome and molybdenum content. Because it air-hardens, they can do it possibly with that no-touch technique I was referring to, with minimal chance of warpage.

The other solution is to use any of the other stainless alloy steels - 440C is the most obvious choice for me. After all a fillet knife is exposed to probably the most severely corrosive environment of any working knife. Blood, salt, water etc. I read that Phil Wilson uses CPM S30V to good effect for fillet knives. As much as I like carbon steels, a fillet knife is one where I would use only stainless.

I know that the above are theoretical and I obtained the info about A-2 from articles. I have no experience with A-2 myself but understand that it is a great steel. A lot of the guys who make "whacking" blades like Japanese swords, katanas, and tantos use it. Eg.- Phil Hartsfield, RJ Martin to name a couple. It is a high carbon steel that is still very tough.

Will be making 3 or 4 really thin (3/32inch) kitchen knives this weekend, so I'll put a lot of the info gleaned from this thread to the test / practise.

Cheers.


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  #20  
Old 12-10-2002, 08:15 PM
Dan Graves Dan Graves is offline
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warpage

Jason, thanks for the info. I also use 440c and like the results I get. But My carbon knives seem to just cut better, hold the edge longer and easier to sharpen. Thats just what I think as I know others who feel different. Think I will try some A-2 and see the results in thin blades.


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  #21  
Old 12-12-2002, 12:13 AM
John Frankl John Frankl is offline
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some more thoughts

You wrote:

"As this happens, the unquenched spine starts to cool to black. As soon as it cools completely to black, I dunk the entire blade to fully cool it. I've discovered that on O-1 steel, it takes a certain amount of time for the spine to cool to black, which later gives me the best performance in terms of edge quality as well as a visible temper line without etching. On 3/16inch stock, the spine takes between 15 to 20 seconds to cool sufficiently before I dunk the entire blade."

Two things come to mind. Are you quenching in a fairly dark space? Red lasts a very, very long time in a dimly lit workshop. Also, when you do submerge the entire blade, are you laying it over to one side as it enters the oil? This could also warp it.

As for Ed Fowler, he ONLY edge quenches, never full quenches.

As for Japanese swords, the water quench appears what gives it the curvature. Long blades quenched edge first in oil tend to curve the opposite direction.

John


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  #22  
Old 12-16-2002, 07:45 PM
Jason Cutter Jason Cutter is offline
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Cool

Gotcha.

Yes, I crank up the forge inside m y workshop and turn all the lights down. I ONLY heat treat at a certain time of day to account for the amount of ambient light. Yup, I do wait till the spine is completely black before a complete quench. I do try to make sure that the edge goes in absolutely 90degrees to the oil, but anything can happen when you try ...

The hardening process and grain structure doesn't seem to be a problem - I've tested and broken and inspected numerous blades before settling on this technique.

This past weekend, I cut out some blades from D-2 plate and noticed that after bandsawing, the blade materials were all slightly bent. I'm sure that the steel would have its inherent internal stresses that are more exposed as bits are removed (kind of like wood) and it starts to warp in the direction it previously couldn't. Perhaps the same principle applies when heat treating.

Tried triple normalising method on the weekened. Rough ground and heat treated 8 blades of 1/8inch O-1 stock. Not sure if it worked because I didn't get a single warpage !! The 4 that I didn't triple normalise also didn't warp, so there was nothing to compare. Haven't gotten around to testing them yet though. I will break test one from each batch.

I think educationalists call this experiential learning - I love it !

Cheers. And thanks for all the suggestions and sharing of information.


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