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Recoalescense (I think)


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I was normalizing a knife at night and decided to see I could catch the recalesence, which I did. It starts at the tip and is the thin black line that moves through the steel. I thought it was super cool, so I figured I would share it.

 

-wes

 

Edited by Wes Detrick
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Glad you all liked it and you are most welcome. I couldn't help but smile watching it happen. It's one thing to be told what happens, and it's another to actually see it happen.

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Yep, that's the magic. B)

 

Wait until you show it to someone new and explain that what they're seeing is a quantum effect caused by the phase change in the iron crystalline lattice from face-centered cubic, normally only possible at temperatures above 1425 degrees F, to body-centered cubic, the normal form of iron crystals at room temperature, and that the reason there is a dark line is because the transformation absorbs energy, which means there are fewer photons emitted by the atoms involved in the transitional area...

 

Magic, as I said. ;)

 

Now see if you can capture the decalescence on the way up, it's even cooler to watch!

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Its good to see....

recalesence re lit my fire when Howard and Don showed here in 2004.......

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Yep, that's the magic. B)

 

Wait until you show it to someone new and explain that what they're seeing is a quantum effect caused by the phase change in the iron crystalline lattice from face-centered cubic, normally only possible at temperatures above 1425 degrees F, to body-centered cubic, the normal form of iron crystals at room temperature, and that the reason there is a dark line is because the transformation absorbs energy, which means there are fewer photons emitted by the atoms involved in the transitional area...

 

Magic, as I said. ;)

 

Now see if you can capture the decalescence on the way up, it's even cooler to watch!

 

As much as I would love to think that people love the science behind things as much as me, I actually started to explain the face-centered cubic vs body-centered cubic and it was as DK said; eyes just glazed over :rolleyes: Oh well, it makes me happy knowing about it. That was an awesome explanation Alan, so many thanks for that. It makes me happy to know that other folks out there get off on the science as much as I do. (Now it would help to spell it right for the topic title)

I have been trying to catch the decalescence, but it's hard to see in my forge. Maybe I will get lucky one day :ph34r:

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I'm about as big a science geek as you'll find. Two years an honors physics major before i was defeated by 2nd year calculus. Differential equations are just beyond my abilities... :rolleyes:

 

If you do find someone who cares, the reason high-carbon steel is hardenable is because the face-centered cubic lattice is preserved by quenching if there is enough carbon present. This is now called Martensite. Since the face-centered lattice is slightly larger than the body-centered, that is why Japanese swords are curved. ;)

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Ha, I was always a physics major when I first started school, but it turns out that being a pothead isn't conducive to good learning(at least for me).

 

Oh, there are a few people that are interested, and I get to info dump on them, and that makes me happy. Again, thanks Alan for the education.

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  • 3 weeks later...

Wes - Great job getting such a nice video of it. I can never record such light-changing events very well. Any way I can get a copy of the video to show people? Just for fun as well as add it to my "Intro to Metallurgy" presentation that I give at work and sometimes to the machinist class at the local community college.

 

Alan- Couple of small points:

1) Martensite is Body Center Tetragonal (BCT), closer to BCC than FCC. I'm sure you know this and mis-typed, but for the benefit of those that see this later and don't know.

2) Pure iron (Ric's "iron without carbon") should undergo the same effect since it still goes from BCC at room temp to FCC at elevated temps (about 1670 F). Actually, pure iron has another phase (delta phase) so it should do it again if you get it REALLY hot (about 2550 F). Should be able to get the double re/decalescence. I have not tried it with pure iron before. If it truly does not show this effect then it isn't the phase change between FFC austenite and BCC ferrite, but the breaking up and forming of iron carbides (cementite). Same general principle of energy absorption though.

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Very cool video, thanks!

 

I can accept the statement that the phase change requires energy. But I have a problem with it seemingly becoming more luminescent again after the phase change is complete.

-Does it somehow release energy again due to another occurence, say the carbon settling into place for instance, but not enough to bring it to decalescence again?

-Is it rather to do with the way it emits during phase change, something like going from "shiny" orderly chrystals, through "matte" jumbled mess, to another kind of "shiny" orderly chrystals?

-Is it the camera that makes it look like it gets brighter again?

-Is it the scale hugging it's pal tighter because it feels cold?

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Temperature is a measurement of energy. As it cools it is giving off energy, some of that is visible as the pretty glowing. When the phase change happens it takes some energy to change how the atoms are stacked. The energy it takes to rearrange the stack means there is less energy to give off so it emits less light. Once the rearrangement is done it can go back to giving off light. The fact that it seems brighter is because of the slow change throughout the shape/thickness of the part. Each atom in the steel doesn't actually give off a noticeably higher amount of light after the phase change. It is probably less bright (per atom) after the change due to the overall lower energy state, but austenite and pearlite likely do have different black-body radiation coefficients so it could be slightly brighter. I would bet the coeffiecients are close enough to the same that the human eye doesn't detect the difference. Note that that coefficient is the same driving force behind how infra-red thermometers work. If wood and rock are close enough for most purposes, how different can pearlite and austenite be?

 

Bonus food for thought: It is a slow fading change because not all of the metal changes temperature and phase at the same time. If all the metal did change at the same time it would not appear to get brighter at all. It would be a continuous gradual fade to black with only a split second of black at the time of phase change. The phase change would be at the speed of sound for the metal (much faster than in air) so I don't think our eyes/brain would even process the blackness for that brief time.

 

Make sense?

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I am glad that you enjoyed the video Steffen and Jerrod.

@Jerrod - Thank you so much for the additional explanations. You and Alan definitely increased my enjoyment of the phenomenon. Sate my curiously and you will have a friend for life :) I am just glad the iPhone camera was decent enough to capture it. I was hoping it would.
Also, you can absolutely have a copy of the video. The link above goes straight to Youtube, but if you would like a copy of the file itself, I will put it into my shared Dropbox folder, and PM you a URL for the download. The file is a little over 31MB so it shouldn't take long to download.

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  • 3 weeks later...

Correction Brandon: You need to MAKE one. B)

You have the set-up now, I saw your comments in the 1084 HT thread. You can do it (so I don't have to).

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