Decalesense questions

Decalecence questions

I'm like most makers I guess constantly learning and thirsting for more knowledge all the time.

Since I have been doing more heatreating I have been looking to understand whats going on with the steel more.
The last few knives I have heat treated I have really been paying more attention and looking at the decalescence that is happening. The first time I seen it, it was like I had just discovered fire it was so cool to see.
I dont know what exactly is going on in the steel, I think I do but would like for more knowledgeable makers than me to explain and also help new makers in easy to understand language what is going on during this process.

Also a few questions.

Is this what Im wanting to see everytime while I am thermal cyclying a blade or just the first time then progressivly cool temp after that.
Lastly can you quench a blade after the shadow has chased past the edge and it has heated back up to produce a hamon or quench line...or does it not heat back to critical?

Kind of a long post but hope it sparks some interesting conversation.

Justin

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It's what I look for when I'm doing a differential heat treat, using the torch as the heat source.

Concerning thermal cycling, I do it differently. I NEVER allow the blade to get past 1350F when I thermal cycle.... I run blades through three cycles. When I first started thermal cycling years ago, I tried using the "published" method where the first heat was at/above critical, then the two remaining heats were reduced, but I found that it did more bad then good to a blade. The more I experimented, the more I zeroed in the the temp that gives/gave me the most benefit...for me that's no higher the 1350F, and allow to cool to 900F or less before the next cycle.

I'm not following the question about quenching for a hamon after the "shadow" has past.

Thanks for the info Ed.

The hamon thing Im talking about is when it cools then starts to heat back up can you quench it then....I might have to find a pic.

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Like in this pic here Ed, does the part along the edge go back to critical temp or just hotter than it was.


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I'm not sure that I'm really following what you're doing here. If you have heated the blade until the shadow of decallesance has passed over the blade and then have taken it out of the fire and the shadow passes over again what you are seeing is recallesance. The steel is not heating back up when it momentarily gets brighter before going to a black heat. It's still getting cooler. What is happening when the shadow forms is that the energy that had been used to produce light is used to cause the iron matrix in the steel to change from austenite to pearlite. If you wait until the steel starts changing to pearlite to quench the blade you will not get the maximum martensite formation.

To harden the blade you need to hold the steel in the fire until the shadow of the decallesance passes entirely over the blade changing to pearlite to austenite and then quench to convert the austenite into martensite before you allow recallesance to start. You might even want to let the steel get just a little brighter for an minute of so to make sure adequate carbon has dissolved into the austenite to give a good amount of martensite formation. I also would not recommend this heat treating by eye on steels with above a 0.85% carbon content as higher carbon levels can cause a problem with retained austenite if too much carbon is put into solution. As far as Ed's torch heat treating, if you can make it work for you, fine, but there's really no such thing as too much temperature control when it comes to heat treating.

Doug

Call me when you get a chance. I hate to type but love to talk. LOL

Yeah Justin, I agree with Ed and Doug. The brightening again after the blade starts to cool is recalescence and I would not attempt to quench at that point. The carbon is coming out of solution at that point and that transfer gives off energy in the form of heat,which is what you're seeing. It would not be a good time to quench.

However, if you have good heat control, you can do a clay-less/no clay hamon by watching for decalescence and quench when only a portion of the edge has come up to temp before the rest of the upper blade and spine do. But the trick is to catch the steel on the rising temp, not after it has started it's cooling falling temp.

Its starting to make sense now guys.

J.Doyle...so what your saying is when I pull it out of the forge all the carbon it can get is in the steel and then as it cools it transforms and the carbon is coming out?
This is some real Bill Nye the science guy stuff going on here.

So do I have the terms mixed up....when its out of the forge and cooling and you see recalescence then when its in the forge heating up and the temp falls its decalescence?

Darrin I will give ya a call maybe later today, we havnt talked in awhile anyways.



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When the steel cools from red to black the 1st time that is decalescence. Then the phase change in the steel makes it re-heat just enough to brighten slightly which is called recalescence.

Darrin Sanders said:

When the steel cools from red to black the 1st time that is decalescence. Then the phase change in the steel makes it re-heat just enough to brighten slightly which is called recalescence.

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Thank you for the clarification Darrin.

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