Selectivly hardening air hardening steels

[Adamantium]

At the Blade Show I got talking to Mr. Dawson
about his knives. And he told me that he
selectivly hardens them. He said something to the effect of "All you have to do is keep the spine a hundred or so degree hotter than the spine while it is cooling, then it will stall several Rc points below the edge. The task is to find the best way to do that"

That got me wondering a bit. So I’d thought I'd dip into the collective pot of knowledge
here, to help me find out the best way to do that.

I figured the best way might be to, before heat treatment, coat the knife with the same kind of clay that is often used to selectively harden carbon steels. Then heat it up to the critical temp. But instead of letting it cool down slowly by leaving at room temp, maybe putting it in the refrigerator for 1/2 an hour. That way, the cold air would cool all the steel that isn't covered with the clay. Then take it out and let it cool the rest of the way down at room temperature.

Would this work? And, I'd love to hear any more ideas.

Sincerely,
Adam

------------------
Self improvement is a hobby of mine .

 

[jeffj]

From what I've read, I would think that the clay on the spine would cause a large temperature differential and increase the potential for warping and cracking, especially if you place it in a very cold environment to cool. The clay will act as a buffer (insulator) to heat loss. I suspect that the 100 degree differential was necessary to reduce the warpage potential.

Perhaps, you should thin the clay as it approaches the edge of the blade so that the differential is not abrupt. But if you could only calculate the thickness of the clay needed on the spine so that the heat loss would be correct. This is a function of the density of the clay and surface area and is effected by the ambient temperature and initial temperature of the blade. I suspect this would be easier to determine through experience.

This is very interesting and I would like to know the answer myself. I've always heard that you can't do this with air-hardened steels.

jj

[This message has been edited by jeffj (edited 16 July 1999).]

 

[Darrel Ralph]

Try Holding the edge in water . SLOWLY heat the back of the knife pointing down on the spine . UM HUM Watch the side of the knife as not to go to far towards the edge.
Try this with a test part first. I have an Idea that you may end up with a springy spine.
Polish the back first and watch for the color to get the right temper on the spine.