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Temp affect on steel in diferent stages of production


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Hello, gentlemen. New guy here with a question.

Something I have wondered about for a while. Why is a blade considered ruined when it is over heated during a grinding process, but it gets much hotter during the forging , annealing process?

Much of what I have learned comes from trial and error, or the Foxfire books. I have been making knife like objects for a little over one year now, and have more questions now than when I started.

Thank you.

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If you grind and overheat after you have tempered your blade you ruin the heat treat or hardness.
I think that's right. Others with much more knowledge will chime in and set me straight.

Welcome and let us know where you are located.

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Thank you, profile edited.

It seeams to me that if the blade was heated to , say brown or blue, that I could re-aneal it then continue working.

I have read, and been told, that overheating during the grinding procces " burns out the carbon", and the steal is useless there after.

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It really depends on the steel, letting us know what steel may help. One thing to keep in mind is temperature affect stee when a certain temp is reached for a lentgh of time. A thick piece of a simple carbon steel may be brought to that color you mentioned and not do harm as it would have to soak at the temp to change the hardening. However a thin piece of steel may not tolerate it at all. A simple test is check it with a file and see if the colored part is as hard as the other parts. BP0187 I think is the best I have read on heat treat. enjoy

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Mark pretty much had the right idea. What the problem is, is when you over-heat the blade AFTER it has been forged, ground, hardened and tempered. Consider that the tempering will relieve the forging stresses and SLIGHTLY soften the hardness as low as 350 degrees. Get too high, say 450-500 or so, and you can completely remove any hardness that you have acieved at this point and the blade will be uselss AS A KNIFE! It will lose its hardness. Not necessarily carbon.
If you are grinding a hardened blade and see RED heat, or sparks, it's toast. That is burnt carbon and probably about 1000 degrees in the surrounding steel. You've ruined it. You have destroyed the temper.
However, if you get some color, blue or slightly above, during the grinding process, PRIOR to heat treat, you have done no lasting harm or caused any carbon loss.
The solution that a lot of makers practice, is to grind free-hand and without gloves. (Never work with gloves around any type of rotating or oscilating equipment anyway. Good way to lose a finger).
The rule is, that if it's too hot to hold by your bare hand, it's TOO HOT! Dip it in your bucket of water.
Does all that make sense?
After hardened and tempered, always just make a few passes on your grinder, and then cool the knife. A lot of work has gone into that knife by this time.
Don't ruin it.

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anneal will make it as soft as possible, did you mean harden?

And it doesn't ruin the knife; you could: remove the pommel, grip and guard and re-heat treat (normalize, harden and temper is a general heat treat) the blade and then repolish it to remove heat treat scaling and re-hilt it and be back to where you started from... of course since handles are usually mounted permanently you may have to re-fashion them as well.

Since most people do not have proper heat treat equipment and skills to redo the heat treat, messing up the original heat treat generally is considered to "ruin" the item.

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