Forging and Heat Treating
- This topic has 10 replies, 5 voices, and was last updated 10/19/2016 at 4:59 am by
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I’m not a knife maker. What I am, by trade, is a journeyman forger and heat treater. I can answer many, but not all, questions about either one. If someone asks me a question I can’t answer, I will admit it, look it up and post the results.
I don’t hold a degree in metallurgy but understand enough metallurgical principals to perform both jobs.
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Great to have this resource, thanks!!
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This is very cool.
I have a question: Is it really possible to damage the heat treatment on a blade during sharpening? I’ve heard this given as one of the reasons that belt-driven sharpening solutions are not as good as using a slow and controlled method (like sharpening on the Wicked Edge). Obviously, these systems have other problems (removing too much material in a short period of time), but is it true that they can actually change the heat treatment on a knife?
Welcome to the forum!
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Hardenable steels are hardened by heating the material to 1550 degrees F and holding it at temperature for one hour per inch of cross section but never less than one hour and then quenching it in oil.
At this point the material is too hard and brittle for most applications and needs to be “tempered” to the correct hardness suitable to it’s end use. This is called “drawing the temper” or simply “drawing”.
This is accomplished by heating the steel as quenched to somewhere between 300 degrees F and 1100 degrees F depending on the desired hardness of the finished product. The higher the drawing temperature, the softer the steel will become.
When using any powered grinding device of any type, much heat is generated. If you exceed the original drawing temperature of your knife blade, chisel, ball peen hammer or any other heat treated tool or component, the answer is YES, you will soften it. If you absolutely must use a belt sander or bench grinder, take light and fast passes and dip your knife in water after each one. If you get it so hot that it turns blue, it better be one of your own and not someone else’s.
Thanks for asking.
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If edge was damaged by belt overheating, is it ruined forever? Is it possible to shave off some soft metal to reach hard metal and restore the knife?
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If edge was damaged by belt overheating, is it ruined forever? Is it possible to shave off some soft metal to reach hard metal and restore the knife?
Good question. A long time ago I had a nice knife sharpened by a “professional”sharpener.
It’s hard to see, because I cleaned the knife since and the picture is not too good. But far too much metal is removed (the knife was almost new before sharpening) and parts of the edge are black.
I’ve got two questions:
- Has the edge been overheated (since parts of it are/used to be black)?
- If so, what is the impact on the edge?
Thanks!
Molecule Polishing: my blog about sharpening with the Wicked Edge
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Do you know quick test method to determine if edge is hard or soft?
A Rockwell hardness test is fast and easy but who among us has a Rockwell tester in their playroom with all the other fun stuff like knives, guns and ham radio equipment? Besides, Rockwell testing leaves little pinprick dimples behind.
If you have been sharpening high quality knives on your WE or any other contraption for very long, you’ll know a soft blade when you find it.
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If edge was damaged by belt overheating, is it ruined forever? Is it possible to shave off some soft metal to reach hard metal and restore the knife?
Good question. A long time ago I had a nice knife sharpened by a “professional”sharpener. It’s hard to see, because I cleaned the knife since and the picture is not too good. But far too much metal is removed (the knife was almost new before sharpening) and parts of the edge are black.
I’ve got two questions:- Has the edge been overheated (since parts of it are/used to be black)?
- If so, what is the impact on the edge?
Thanks!
If someone belt sanded the edge and let it get so dark blue that it looks black, it’s probably now on the soft side.
People who do stuff like that should apologize on YouTube while drinking hemlock.Thanks! That’s good to know. And actually it was a good incident because it made me decide to sharpen my own knives.
People who do stuff like that should apologize on YouTube while drinking hemlock.
I fully agree. The are too many unprofessional “professional” sharpeners.Molecule Polishing: my blog about sharpening with the Wicked Edge
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