Thoughts on Greenpete's Knife Tempering Methodology

[pradeep1]

Hello everyone,

I am a n00bie here.

I was watching greenpete make a simple knife in this video:

http://www.youtube.com/watch?v=5ysKd1cswlo

And basically this is what he does:

1. Takes an old file and anneals it by putting it in a big fire and letting it reach 800 degrees and then letting it cool down naturally. This is supposed to make the steel really soft.

2. He shapes the blade, etc. and then puts it back into a coal fired furnace (open pit with coals + blower) and gets it back up to 800 deg. (tests using a magnet) and then quenches it in old motor oil. This is to make it brittle and hard.

3. He then takes a blowtorch to the spine of the knife and uses the color change methodology (wheat straw) to soften the spine, but leaves the blade edge brittle?

Questions:

1. I thought you had to re-temper the entire blade. What use is having a hard edge if it is brittle?

2. I have an old carbon steel mora that I accidentally burned out the temper because I was a moron and removed the plastic handle by tossing the knife in a campfire. I basically have an annealed blade now. Could I use greenpete's method to bring the blade back to life, or does his method only work for file steel?

Thanks,

Pradeep

[mete]

As this is an international forum , when listing temperature please use an F or C to avoid confusion ! 800 C = 1472 F. When he tempered the spine some of the heat will temper the edge but not at much as the spine.This method is valid with the simple carbon steels but of course you have to know what you're doing. You could reharden your Mora this way.

[pradeep1]

Originally Posted by mete

As this is an international forum , when listing temperature please use an F or C to avoid confusion ! 800 C = 1472 F. When he tempered the spine some of the heat will temper the edge but not at much as the spine.This method is valid with the simple carbon steels but of course you have to know what you're doing. You could reharden your Mora this way.

Yes you are right. I didn't think about the temperature conversion. We Americans and Britishers like greenpete, losers each one of us, should be chided.

Thanks for the info. I'll try to rework my Mora blade today.

Pradeep

[Cougar Allen]

Welcome to Bladeforums!

[pradeep1]

I heated up the blade in my wood fired brick forge and got it all hot, but didn't have any used motor oil, so I used water instead. Bad move. While I was removing the blade from the fire to dip in the water, I accidentally dropped it into the water and it entered at an angle, which caused the front 1/3 to warp.

I am wondering if I can reheat it to 800 deg. F and flatten it out again?

[Peter_E_Ryt]

800F is generally considered to be far too "cold" to be in forging (or heat treating) range. If the blade is a dark, blackish color, it can actually be harder than when it's cold. Because you're using a fire and don't have a pyrometer, try and use the color of the steel to give you an idea of what's going on. When the steel gets to a dull maroon or red, it's hot enough to be pounded for a bit, and that's when you can straighten it out.

Water isn't very forgiving, so it generally best to be avoided if you're essentially experimenting on a prized possesion. If that Mora has value to you, avoid water for now, because with a bit more heat (what's necessary to temper a blade), you could crack it instead of just warping it.

As a quick note, heating up a piece of simple carbon steel to a bit hotter than 800C (AC3 I think) and then letting it air cool is normalizing, not annealing. It relieves stress and will soften a hardened blade, but not to the extent that annealing will. To anneal simple carbon steal, normalizing temperature needs to be maintained for a longer period of time.

[pradeep1]

Originally Posted by Peter_E_Ryt

800F is generally considered to be far too "cold" to be in forging (or heat treating) range. If the blade is a dark, blackish color, it can actually be harder than when it's cold. Because you're using a fire and don't have a pyrometer, try and use the color of the steel to give you an idea of what's going on. When the steel gets to a dull maroon or red, it's hot enough to be pounded for a bit, and that's when you can straighten it out.

Water isn't very forgiving, so it generally best to be avoided if you're essentially experimenting on a prized possesion. If that Mora has value to you, avoid water for now, because with a bit more heat (what's necessary to temper a blade), you could crack it instead of just warping it.

As a quick note, heating up a piece of simple carbon steel to a bit hotter than 800C (AC3 I think) and then letting it air cool is normalizing, not annealing. It relieves stress and will soften a hardened blade, but not to the extent that annealing will. To anneal simple carbon steal, normalizing temperature needs to be maintained for a longer period of time.

Very good. Thank you for the excellent information. I need to educate myself more on tempering steel. The only knowledge I have is watching that greenpete video, so it is pretty weak. I'll read the Steel FAQ.

[Peter_E_Ryt]

Another good source for information is Kevin Cashen, and his posts. He doesn't post very often, but when it does, it's a long, painful read, full of good information. He also has an explanation of heat treating out there using fish, and it's absolutely brilliant. Hopefully someone still has the link.

Mete also knows what he's talking about, so pay close attention to his posts as well. He's assosciated with the metallurgy field in some way or another (a major, a job, a fulltime hobby, etc.?).

[koyote]

The greenpete video isn't *horrible*, though I'd go for more information - none of it is invalid, in my limited experience. Charcoal forges aren't uncommon, and the "soft back draw" with the torch is a classic, is not as often used, knifemaker's technique.

The main thing for pete is that his methods are simple for 'simple' steels and work.

I don't know what type of steel the Mora is, so I don't know what you want to do to temper it, but blade bends are easy enough to fix. I do that with all the thinner knives I've made. (somehow the 1/8 O1 blades haven't warped)

[langchop]

Originally Posted by Peter_E_Ryt

He also has an explanation of heat treating out there using fish, and it's absolutely brilliant. .

..huh? Peter is right though... Kevin Cashens posts are nothing short of legendary!

The general idea about annealing is that once it is brought up to the right temp, the steel must cool down very slowly. This is simplistically achieved by leaving the steel in the kiln/ fire/ oven etc and letting it cool at that slower rate.

My first attempt at annealing, made a charcoal fir, put a file in the glowing coals, then when the file was glowing dull red I put a piece of slate (salasto, not sure what other names there are for it overseas) on top of the fire and covered that with sand.. to insulate and slow the cooling process... worked like a bomb.

Your best bet it so completely anneal it and then try and straighten.

I stand to be corrected but I dont think wood will generally get you the kind of temperatures you want for any metal heat treatments.

[mete]

Peter , I'm a retired metallurgist !

[pradeep1]

I am honored by your responses. I'll read the articles by the users you guys have suggested. I'll also try again this weekend to straighten the blade.