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blacklionknives

quenching/differential heat treating a sword blade

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i am actually color testing on a chunk of leaf spring

i am not tempering the blade until i get the leaf spring straight.

it will give me a general idea although the blade dimentions are much different.

 

i spoke today with a chemist who worked at the oregon steel mill in portland oregon and he said(keeping in mind he had state of the art stuff...)roughly an hr per inch at a given temperature will allow the molecules to "change" how they attach to each other. and he had no idea about color. he said a propane torch would not keep it hot long enough for the molocules to transform.

 

i said , "so it is AS IF you change the steel into a different material...???"

he said, "no, you are actually changing it in to a totally different material entirely"

 

???

 

so, since i dont have his degree and experience, i will proceed with my wee torch til we straighten the stubborn spring. :mellow:

 

...i know i'm getting color :D i just dont know about the time factor/theory???

 

i will clean both sides of the spring and check color on both sides to see if i am geeting heat all the way through.(so far i have colored one side twice and left the other rusty, i will heat other side this time)

 

i want to finish this thing but have such an awesome quench i dont want to quench again...til my next blade that is.

 

thanks again

edwin

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I think that your friend was making more of a mystery out of it than it is. By heating the steel to what some people call critical you are changing the physical shape of the iron crystal that is the basis of steel. Picture a cube with a iron atom at each corner and one more right in the middle. That is form that iron crystals form in steel at under some where around 1375 degrees, more or less, depending on the exact alloy. In that form the iron crystals can only disolve less than two points of carbon. When you heat the steel to above critical for that alloy the shape of the iron crystal changes. It still has an iron atom at all corners of a cube but there are also an iron atom in the middle of each of the six faces but none in the center of the cube. In that form the iron crystal can hold 77 points of carbon in it's matrix. Now the fun starts. If you cool the steel rapidly enough carbon gets trapped in the body centered cube when it is reformed when it cools. This puts the atomic bonds in the crystal under stress and hardens the steel. Exposing that steel to hot temperatures, mostly from around 375-450 degrees in knife making, releases some of that trapped carbon and softens the steel some. Then there are the crystals that form in the steel if it is allowed to cool slowly enough to allow the disolved carbon to escape as the steel cools. I would suggest that you move "Steel Metallurgy for the Non-Metallurgist up on your want list if you can. You sound like you are really ready to recieve the mysteries of steel.

 

Doug Lester

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:huh::unsure:

 

Wow, Doug. It's definitely on my Christmas list. In fact, I'll check with my typist/wife to see if it might even be here by New Year's. :D Does the book come in French? Then my wife can translate it for me.

 

I agree completely that tempering is more simple ;) than needing to hold for an hour because...

 

I also understand what blue I'm shooting for. Two birds with one stone. Let me explain.

 

I heated my leafspring (well, a piece of a leafspring one inch by 5/16 by 28.5 inches) a third time beyond the sky blue into my second rainbow color pattern and it straightened. Showing me two things:

 

One, that heating with a torch that only gets the steel to 400 degrees or so and allows it to cool as soon as it gets there, so that you don't overheat and thus not holding it for an hour is plenty to accomplish this thing called tempering.

 

And two, that I see what you were saying, Alan, when you said I was going too far by going past the sky blue because not only did it straighten, but now that it is straight, if I push down two inches, it will get a kink in it, indicating that it is too soft.

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Isn't it great when the light comes on? B)

 

That "aha!" moment is harder to get to when you work alone, I'm glad you figured it out. And Doug is again correct: Get a copy of that book and study it until it makes sense. That may take a while, but it makes a huge difference knowing the why you do something as opposed to just the how.

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