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02-15-2018, 10:33 PM
(This post was last modified: 02-15-2018, 10:33 PM by grepper.)
I know very little about different steel types, but I do know that some hard steel is very brittle with others are far less brittle. I’m sure performance wise some hard steel way outperforms others for knives.
Mr. Mark, I don’t know what the hardness is of the 52100 steel that you use is, but I’ve seen videos of you bending them. Scary to watch but amazing! Those seem virtually unbreakable with any kind of “normal” or even very hard use and the ability of the blades returning to straight after bending was stunning!
I have the feeling that a knife could vary several RHC points over the length of the blade. Is that correct?
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What do you consider "hard steel"? Steel that's been hardened, or steel above a certain hardness?
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Thank you for the kind words and interest, Mr. Grepper.
Yes, differentially heat treated blades are hard on the edge, but softer on the spine. There are basically two ways to do this, but I usually do both.
First I harden the edge by heating it to austenization temp with an O/A torch, and quench in oil. This leaves a hardened edge of martensite, but the steel that wasn't *quite* at austenization temp is left as soft pearlite. There is a surprisingly clear distinction, which is brought out as a "hardening line" by etching the blade in mild acid. This just leaves a unique, organic line, which mostly just looks very groovy.
Next, I heat the blades in my kiln to an even temperature of 1465°F, and hold for 20 minutes, after which, I full quench the entire blade, which results in complete martensite, the strongest phase of steel. After cryo in liquid nitrogen, I temper the blades in the kiln.
The last step is what makes the blades flexible, but still strong. I draw the spine back to about HRC 46-48, with two atmospheric propane burners, while protecting the edge from the heat with very fine clay and grape seed oil. This turns the hard but brittle martensite to very resilient spring steel, while leaving the edge about HRC 62, with very fine grain throughout the entire blade.
The result is just what you've seen in the video. Basically indestructible blades with extraordinary cutting capacity, and every blade is uniquely beautiful.
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So you harden the edge first, then harden the whole blade again?
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Unless I leave the blade with the original hand hammered finish.
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Very interesting. I've not heard of that before.
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![[Image: 108ilgp.jpg]](http://i68.tinypic.com/108ilgp.jpg)
This is my chopper. It is made from hard steel blacksmiths use when they change horseshoes. It was so had that i broke of - you can se where this blade are repaired. This was made around 1970 if I remember correct.
I ask a old blacksmith to repaire it - and he did. He also water hardened the edge - and olik hardened he neck - and after that it have been in use during many deccades.
Close to the handle can you se small marks on the neck. That marks was made by the blacksmith during the oil hardening process to find out the best functional hardness (softness).
The combination of hard edge and "soft" neck have work very well for me.
Other thing...
I have, during 2017 untill 31 of January been treted against cancer. thevtreatment is now done and I mist wait until the beginning of 2020 to find out if the treatment was sucsessfull. I have decided at is is Sveaskolan allready.
The treatment and the medication was hard, I lost all energy and power - but now I feel that both energy and power slowly are comming back. This was the reason that I have not percipitate here so much.
Thomas
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It's just good to have you back Thomas! Reading your post here is like receiving a letter from an old friend. We have missed your insight, stories and experiences here on the Exchange.
Välkommen tillbaka Thomas!
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(02-16-2018, 02:29 PM)EOU Wrote: It's just good to have you back Thomas! Reading your post here is like receiving a letter from an old friend. We have missed your insight, stories and experiences here on the Exchange.
Välkommen tillbaka Thomas!
Thanks EOU!
Thomas
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Pardon my complete ignorance, but where can I see Mark Reich's videos?
http://knifeGrinders.com.au
