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I did a post similar to this one earlier, but am still having the same issue. I heat treated my knife backed with clay, none on the edge, and when I pulled it out, finished and etched it it possessed a strange mottled look to it. The blade was just becoming a bright red when I quenched it, is that too hot? 

(P.S. I will attempt to attach a picture to this post so you can see what I mean.)

 

Thanks!

IMG_20200728_145717461_2.jpg

Sorry about the bad picture quality, my phone is quite old...and don't mind the giant crack in the blade, I know what I did wrong in that respect!

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I would say by the looks of it that you did overheat it.  It also looks like your blade cracked.

 

Doug

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Posted (edited)

What colour should the steel be for the quench?

 

Edited by Kael

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Color is not your best gauge of temperature.  The color changes depending on ambient light conditions.  In bright daylight a near molten piece of steel looks grey.  If you have to go by color, do your heat treating in a dark shop, cherry red is what the books say, but again, depending on the light, you could be 400 degrees too hot.  Testing with a magnet is better, you'll still be a little high, but not so much.  Better yet would be a pyrometer.  You can get a cheap digital online for around $50.

 

Geoff

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Ok good to know. I have a small magnet so I'll try that next time!

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Even better still, learn to look for recalescence and decalescence.  

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Would you mind elaborating on that a little? 

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Sorry if that sounded rude, unintentional, I just don't know exactly what that means in regards to blacksmithing.

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Posted (edited)

Google recalescence decalescence vid...and better yet throw the name Wes in that search.

I ended up stumbling on one Wes on here put up.

For lack of a better way to describe it you chase dark out of the blade....and can kind of see it phasing(that also my not be the right term)

Practice ...if you get it right the red steel will cool to dark...then the dark will be chased by more red.

I dont notice it much when working with real thin steel....I suspect the cooling and reheating happens too fast to really see.

Probably arent going to see it real well if its well lit.

Maybe someone with a better blade vocab can elaborate on this.

Again try to find that vid....last time I googled what I told ya here it popped right up.

EDIT; Here is a different vid

  

Edited by Kreg Whitehead

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It's all over the site, in all the heat-treating threads.  Basically it's looking at the steel in the forge to see the moment the crystal structure changes to become hardenable.  The steel will be a low red, then as the temperature rises to the point where the transformation occurs you'll see what looks like a swirling line of shadows inside the steel, starting at the thinner parts and working into the blade.  Once the shadows have disappeared it's time to quench.  That's decalescense, where the shadows represent the energy loss it takes to make the change from body-centered cubic iron crystals to face-centered cubic iron crystals.  You see the opposite as it cools slowly, a bright line will appear and work its way off the edge.  That's recalescence, the release of energy as the crystal slip back into the lower energy state.  

It's easy to use in the dark, it works for all low-alloy steels, and it's a pretty darned cool quantum phenomenon involving electrons, photons, and energy states.   And you can do it at home! B)

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I was just starting my response, then saw Kreg replied.   While I was reading that, Alan replied.  They covered it well.  Thanks guys.  

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That is very cool! I never would have known about that (I am 99% self-taught and don't know a lot of the finer points of forging) thanks for the info!I I'lltake a look for that in my next quench.

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