a question about carbon loss

samuraistuart

samuraistuart

Joined
Dec 21, 2006
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You may recall some of Aldo's 15n20 was not fully annealed, but at 42hrc. I had already made a knife out of some of it....it was definitely more of a chore than fully annealed stock, and it was severely warped out of the quench (not sure if that warp was the steel or me). I have this kiln now, and decided to do a quick spheroidizing job on it. Decided on 1250 for one hour. Well, the 12" bar I placed in there vertically fell down at an angle while it was at temp, and developed a slight bow in it because of that. CRAP....I HATE straightening warps....with a passion. I put it back in the kiln the next day, this time programmed the thing to reach 1500F, then cool down to 1250F at 50 degrees per hour, and then hold at 1250 for one hour. And this time I just laid it on the floor of the kiln....flat. It came out nice and flat, for sure. Nice and soft, too. I always have to preface my question with info for you!!!! What, if any, carbon loss can I expect? I would assume minor decarb...maybe a few thousandths per side...not too sure, tho. It's .065 thick steel. I had no anti scale coating on it....nothing. Thanks for any thoughts you might have!!! BTW, when I was talking to Aldo on Monday, he said that the .065 15n20 has very little Mn in it....and he was getting reports of great hamons...even with the nickel present. Just passing that along for you hamon-heads!!!
 
The 1/8" is low manganese as well. I got a great accidental hamon in it last winter, then bought a bunch of that steel. I tried to get a hamon in the .078 and 0.90 15N20, and it looked more like you would see in 1084. The low Mn 15n20 will get a hamon similar to 1095. Not quite as active, but darn close.
 
The treatment of about 1200 F for an hour or two is referred to " sub-critical anneal" The 1200 F is below critical temperature therefore below any significant oxidation [scale] or decarburization It also stress relieves the steel. As you found , it works !
You can then inspect the blade and easily straighten if necessary. Then try again.A simple holder vertical with blade edge on top will help keep it straight in the furnace.
Sometimes steel from the mill has stresses or has not been HT'd properly and is hard to drill can be fixed the same way !
 
Carbon loss is negligible in a treatment like you did. Even with many forging sessions over 2000F in making damascus the carbon loss is very small. carbon loss is from the surface, which then becomes a protected layer of oxide....preventing further carbon loss.
 
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