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To de-scale or not de-scale... that is the question.


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I have a steel box/pipe in my blown forge to heat the blades without being directly in the blower blast.

 

I go in with clean blades to normalize. Blades are 1084.

 

As soon as they come out into the air, I get that thin layer of scale across the whole blade.

 

I am interested to know if it is common practice to remove the scale before hardening.

 

Do you take your blade back to bright before hardening, or will it sufficiently harden straight from the normalizing cycles?

 

I've always cleaned 'em up first, but I am thinking things thru to eliminate unnecessary steps and speed the process a bit.

 

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I can't say that it is best practice, but I do not take the scale off that forms during normalizing before I quench.  (The quench usually blows it off though :) )

 

Just for further data to compare, most of my work is a made from a mix of either 1095 or 1084 with 15N20.  I don't have an accurate way to measure my as quenched hardness, but I get files to skate.

Edited by Brian Dougherty
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3 hours ago, Don Abbott said:

I am interested to know if it is common practice to remove the scale before hardening.

I don't do this,  But I've gotten into the habit of using anti-scale compound on my blades before hardening.  

3 hours ago, Don Abbott said:

Do you take your blade back to bright before hardening, or will it sufficiently harden straight from the normalizing cycles?

You have to get the blade up to (and hold if necessary) the correct austentizing temp for the specific steel you are using in order to quench/harden.  And many smiths will up the temp on their furnace immediately after the last normalizing step and quench/harden right away.  

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For me, I  normalize after forging, and harden from a clean 400 grit finish. If I'm using the muffle tube, I put a chunk of wood in the back. Prevents scale in the tube, and the blade gets in the quench fast enough that it doesn't scale.  Well, the tang does a little.

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Many thanks.

 

I had 2 hours last night to normalize 5 identical blades. Going to try to harden & temper this evening.

 

Been seeing too much of Garry Keown's work... I need to get things moving!

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  • 1 month later...
On 9/2/2021 at 10:28 AM, Alan Longmire said:

For me, I  normalize after forging, and harden from a clean 400 grit finish. If I'm using the muffle tube, I put a chunk of wood in the back. Prevents scale in the tube, and the blade gets in the quench fast enough that it doesn't scale.  Well, the tang does a little.

Now that's thinking - the smoke from the wood removes oxygen from tube which prevents scale from forming - is that correct?  I've used boric acid (roach powder) as anti-scale on blades.  

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3 minutes ago, KenH said:

the smoke from the wood removes oxygen from tube which prevents scale from forming - is that correct?

More or less.  It isn't the smoke itself, but the fact that smoke was made.  The wood sacrificially/preferentially oxidizes before the steel, using up all the oxygen and the space is filled with (relatively) inert gasses that keep more oxygen out.  

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1 hour ago, Jerrod Miller said:

The wood sacrificially/preferentially oxidizes

Now that's a 50¢ phrase for "the wood burns" thus removing the oxygen. :)

 

This is a GREAT forum for learning, not sure why I've not been present more often.  Getting stuck on knifemaking and reloading forums I guess. 

 

Thanks to all for such a GREAT forum.

 

Ken H>

Edited by KenH
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