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Interesting Phenomenon


Niko Hynninen
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Hi all!

 

I did all ready ask this guestion from of you guys. I did get some onfo but , still im little :wacko: about this.

 

 

Any ways!

 

It went like this. I was using electric owen at +800 ( little above non magnetic)

Steel soked 5min and take it out and let it cool in mid air. First it start to cool in edges about 15 s from this edges and whole steel flashed little bit brighter and after this slowely steel turned black.

 

What is this Phenomenon......or was all in my :wacko: head???

 

Is this something to do whit austenit to turn agane perlite or something.... :huh:

 

 

Thanks.

 

 

Niko Hynninen

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Yeah that's probably what it was. I was picturing a flare up ; as in flames exploding out of the electric furnace, but if you mean the colour of the steel, thats the transition between austenite and whatever it's turning into. called recalescence. You weren't imagining things. mabe Howard or Don or Ric or sombody can explain this fenomenon(sp) beter that me.

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It's the phase change from austenite dropping back through to pearlite and releasing the energy of transformation that the heat put in there to raise everything the other way.

 

That phenomena can tell you a great deal about the steel you're working with, for good or ill. Start taking notes.

There are three kinds of men. The one that learns by reading. The few who learn by observation. The rest of them have to pee on the electric fence for themselves. Will Rogers

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Hi you Guys!

Thaks all for reply!

 

 

Bob

dont be modest....you dit kwon this :lol: so you have info berhaps more than you know ;)

 

Jake

Sorry my PM was little pit chaotic..... But it was on my mind playing around....Huh ^_^

 

Mike

 

Ok! i was not on wrong track on this one! I dit made notes, time, temp, soaktime....But now i have another guestion??? What this tells me about stell....

Steel is about 100 years old. I have analysis of it ( C 0,67%, Si 0,25 Mn 0,9 P 0,05 S 0,03)

Im worried about high Mn 0,9...it can take oil for HT but water??

 

 

Niko Hynninen

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Decalesence rocks its one of those magical steel things that lets you know that steel really isnt just another bit of monkeymetal but something quite special .

 

Howard clark did a decalesence demo at docs forge in and before then I had never heard of it or seen it ,its a little special .

 

for a not thermomiter controled heat treater (like myself up till now) it will let you know when your austenite transformation takes place so you know you are at temperature for ht and dont cook the stuff to high .

 

finding out that the steel "tells" you its ready was one of those things that has dragged me back into the love of steel .

 

I managed to go through ABS clases ,smithing school as well as 10 years of blacksmithing before this one was revealed to me .sometimes you dont know what you dont know .

forging soul in to steel

 

owenbush.co.uk

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Hi Owen

 

 

So i dit find something spesiall ;) JEE !

 

Heat was +800 C and i let it cool....phenomenon occours ( little britenig ).... Is TH temp. when this happens or should steel quenst little bit higher about that +800C ???

 

This was Amaising thing.....for long time ;)

 

Ok.. becouse dit see this " like rewerse " cooling ....HT is that +800C just above critical point.

If i quens at this point steel sould have thight gainstucture....Overheats couses grain growth?? RIGHT?? Basic metallurgy!

 

Niko

Edited by Niko Hynninen
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Niko,

 

It's a very cool thing to see on the way down. Now try seeing it happen on the way up to heat.

There are three kinds of men. The one that learns by reading. The few who learn by observation. The rest of them have to pee on the electric fence for themselves. Will Rogers

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How long it takes for this phenomenon to work across the section of a tapered cross section, (like a wide, flat ground knife, or a sword cross section) can tell you about where the nose of the curve (if you were trying to plot an imaginary IT diagram for your material) is for the transformation of your steel.

 

Post script added later. I should add to this a bit. The nose of the curve at the left, or the start line, is when the transformation becomes visible on the thin edge, and with small grain, this happens very quickly. The transformation following across the section, and the time that takes, is more like the second line to the right of the first, or the transformation finish.

 

Example: The 1086 modified I work with a lot will start this transformation at the thin edge, and in about a four to seven second time window will work all the way across the section of a "typical" shinogi zukuri katana forging. In the ideal world, I'd like to have it happen in less than two seconds, but there's no way to do that without making your own steel using little or no manganese.

 

It is going to take a little longer than that (probably) with the 0.9Mn in the steel you have. I'd guess it takes 10 to 12 seconds if you had a section that tapered from 1mm to 8mm in thickness at about 50mm wide, from the time st starts on the thin edge , until it moves all the way across.

 

You can also tie this into a grain size demonstration that is very eye openeing.

 

Take one piece of the stock and throw it in the fire and get it really hot (1100C) and soak it there for a while, then pull it out and see how long it takes. Cycle the same piece (or another treated the same way) to black, back up to 800, to black, back up to 800, to black, then see how long it takes. :) Interesting stuff to learn from simple, direct observation (in low light).

 

It is much more difficult to see on the way up, because it is not quite the same. On the way up, the piece absorbs heat more or less evenly from the fire until you get to the critical temperature, then it absorbs a good bit more energy, and seems to not get any brighter, or to "lag" there for a while, then when it has absorbed enough heat to kick it over, the phase changes to austenite, and the heating rate again resumes at a more even rate of climb. It is endothermic on the way up (absorbing energy) and exothermic on the way down (giving off energy) which is why you can see it at all.

 

52100 also shows it pretty well. The best for visibility is right around .8 C and not much else.

 

This is one of the reasons I love carbon steel so much. :)

Edited by Howard Clark
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Thanks Howard! I didn't know that the timing of the phase change was keyed to grain size as well. I'm going to have to try that soon! That adds a whole 'nuther dimension to decalescense/recalescense. Everytime I learn something new about this it's like opening a door or looking from a new angle.

 

Mike, I still have the hardest time seeing the phase change on the way up when the steel is in the forge.

 

I was staying with my cousins at a cabin back in early December and we had a roaring campfire going with an excellent bed of coals. My 13 year old son decided to get the fire place poker red hot and I decided that being outside at night it was an excellent time to demonstrate recalescense. The campfire easily got the steel of the poker hot enough but the phase change on cooling was barely noticeable. Would low carbon content affect this as well?

Guy Thomas

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Guy, it's sort of a joke, the lag that Howard mentioned is a much better way to put it. If your eye was really good, it might darken oh so slightly as it absorbs energy. I like lag much better, the color is too subtle at that point. It's like watching the green flash when the sun comes up, blink and you can miss it.

There are three kinds of men. The one that learns by reading. The few who learn by observation. The rest of them have to pee on the electric fence for themselves. Will Rogers

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I have been using the heating lag as my indication of corect heat treating temp and as long as I keep the forge down low it can take a long time for a whole blade to cross through the temp lag It seems to coinside with the non magnetic almost exactly .

I am coming to the conclusion that its time to really get into the technical side of heat treating what books would youall recomend ?

forging soul in to steel

 

owenbush.co.uk

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I have been using the heating lag as my indication of corect heat treating temp and as long as I keep the forge down low it can take a long time for a whole blade to cross through the temp lag It seems to coinside with the non magnetic almost exactly .

I am coming to the conclusion that its time to really get into the technical side of heat treating what books would youall recomend ?

forging soul in to steel

 

owenbush.co.uk

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.

I am coming to the conclusion that its time to really get into the technical side of heat treating what books would youall recomend ?

 

"Principles of Heat Treatment" by M.A.Grossmann, ASM 1935---1953, Scranton, Pa. USA

 

"The Alloying Elements in Steel" by Edgar C. Bain, ASM 1939

Edited by daryl meier
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"Principles of Heat Treatment" by M.A.Grossmann, ASM 1935---1953, Scranton, Pa. USA

 

"The Alloying Elements in Steel" by Edgar C. Bain, ASM 1939

 

Thank you daryl I shall look them up

forging soul in to steel

 

owenbush.co.uk

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"Principles of Heat Treatment" by M.A.Grossmann, ASM 1935---1953, Scranton, Pa. USA

 

"The Alloying Elements in Steel" by Edgar C. Bain, ASM 1939

 

These two books should be on every knifemakers shelves. I'm still working my way through them but I feel they contain the foundations of practically everything we need to know.

 

On another forum Howard made the suggestion to find any good introductory text book for Physical Metallurgy for an undergrad college class which will help with concepts and terminology prior to tackling those two books. Not bad advice!

Guy Thomas

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  • 1 year later...

What do you guys think of this one?:

 

Metallurgy of Steel for Bladesmiths & Others

who Heat Treat and Forge Steel, John D. Verhoeven

 

a.k.a Steel Metallurgy for the Non-metallurgist

Edited by Ben Hartley
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Yes, it is the same book. The ASM edition is later, and has a few things that the download does not. At this point in time, that download is a reproduction of copyrighted material (because ASM international bought the book from John), and as such it is an infringement of copyright law and is operating illegally. John had initially offered it as a free download from his own web site on the Iowa Sate University server, but after ASM bought the rights to it, that is no longer possible for him to do. I would have sold it to them in a heart-beat if it had been me, just as He did.

 

I dunno who's web site it is, and I don't really care, but it is a copyright law violation at this point.

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