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The phenomenon which occurs when carbon goes into and out of solution in steel, also known as critical temperature. On a rising heat, often invisible to the eye because of a bright forge, the steel will rise in color, until carbon goes into solution, dimming the color of the steel momentarily, before rising again out of the reds into yellow. On the way back down, it is easy to see in a dark room, and as the steel cools, it goes darker until the carbon comes out of solution and locking into place, releasing energy which re-heats the steel momentarily, making it brighter.

 

It is always, even after 10 years of doing this, amazing to see, and always surprising how cool the steel is. Most people in my experience overheat for heat treating, when just above this critical temperature is all that's needed.

 

I captured this event last night while forging a knife, and thought I'd share it with you. The photos show, in sequence, a blade cooling from above critical to below it, and you can clearly see the ring of decalescance happening as it chases the hot spot on the spine of the blade.

 

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Like magic! I still get a kick out of watching this. I always keep a steel bucket handy when working on knives to check on this if I'm not running the drum forge and thermocouple (though holding a steel bucket upside down while sticking a red hot knife in it and also poking your face close at the same time can be a bit hazardous :lol: ). It remains one of the few ways to fairly accurately guage heat treating temps by eye in whatever ambient light conditions you are working in.

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That is the best set of images I have seen of this phenomenom! Very cool! All the written descriptions cannot convey this as well as this series.

Christopher, do you mind the reproduction of these images? It would be worthwhile to have in the files.

Thank you for sharing!

Alden

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Chris,

 

That is an amazing set of pictures. Don Fogg talked about it this weekend at Big Sky, but the light was way too bright to see it, and there were all of these other steel nerds getting in the way.

 

Thank you very much,

 

Geoff

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Very nifty indeed!

 

The trick, of course, is to watch it going the other way in the forge before you quench... :lol:

 

 

No doubt.

 

 

 

I'm glad everyone enjoyed it... I noticed it on the first normalizing cycle I was doing prior to HT, and since it was so bold and obvious, I grabbed the camera for the second run. I'm pleased it worked out, and I'm happy to share so that people can learn from it. That's what this place is all about, right?

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Pah! Photoshop!!!

 

 

:P

 

 

Just kidding ;)

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