what is decarb?

J

Jack Shen

Joined
Jan 2, 2005
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256
I've seen a few posts lately with hogs talking about getting rid of dimples and decarb.

So what exactly is decarb? How does it happen? How does it affect the blade?
Is it possible for a knife to come brand new from the factory with it?

thanks so much
Jack
 
when you heat treat a knife, some of the carbon leaches out at the micro-surface level, you end with a type of steel scale called "decarb". it is different than black rust wich is Fe3O4, where orange rust is Fe2O3. Black rust is actually a type of corrosion inhibitor because it is a non-active/reactive combination (not +/- ionized), where Fe3O4 actively seeks out more particles to try to complete it's valance shell. decarborization can sometimes be kept in check by using a neutral gas during heat treating (similar to welding with argon keeping oxigen away from the molten metal).

or something like that :confused::confused::confused:


it's a nice rough looking finish, but it's so rough and pitted that it's heavily prone to rust. if you own a competition grade busse you can expect there to be rust under the handle scales because of it.
 
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During the high temperatures of the heat treat process, carbon atoms can vaporize out of the metal in the surface layer of the steel. This is called decarburization. The loss of carbon changes the properties of that very thin layer. Normally, after HT, the blade blank gets further grinding, and that layer is removed.

There were three blades that were released by Busse at Blade 08, as part of the Competition Grade series, where the decarb was not removed. Those knives are subject to surface corrosion.
 
ah gotcha! :thumbup:

I searched a bit earlier, and got lots of stuff talking about it but not explaining what it was.

thanks so much you all :)
 
From what I just read does that mean that if there is still decab left on the blade there woould be less carbon and making the surface levels weaker but busse it would seem to not get rid of all the decarb in the case of infi dimples that people find when they strip the coating off it. If I have them than doesn't that mean the knife surface is not as strong as the rest of the blade and then is that the reason that satin knives pull such a high price becouse it is better with the blade being sand all the way if this is true let me know
 
beaverseat said:
From what I just read does that mean that if there is still decab left on the blade there woould be less carbon and making the surface levels weaker but busse it would seem to not get rid of all the decarb in the case of infi dimples that people find when they strip the coating off it. If I have them than doesn't that mean the knife surface is not as strong as the rest of the blade and then is that the reason that satin knives pull such a high price becouse it is better with the blade being sand all the way if this is true let me know
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uuuh... not quite. The dimples are unique from "decarb", they are a surface features caused by the heat treating process, if I recall correctly it's caused by the air blowers hitting the surface while it's at high heat.

Decarburization will affect less then .002" of the surface, thinner then a sheet of paper. In no way would it have any affect on the overall structural strength of a knife.
 
Perhaps I missed something, we talking about Ferric and Ferrous oxide not Fluorine?
 
I thought decarb was a natural by-product of any heat treat process... as described below.

And the dimples were a result of Nitrogen being introduced in the high temerature heat treat process that Busse uses.

Could be wrong though. :p


From what I understand, he whole purpose of the Competition finish is you make a blade
for the sole purpose of the competition and focus on the cutting edge,
not the "cleaned up" look of the blade.
It's about performance, not beauty.

.

.
 
"When steel is heated in an open furnace in the presence of air or products of combustion, two surface phenomena take place: oxidation and decarburisation.

oxidation: O2 + 2Fe = 2FeO O2 + 4FeO = 2Fe2O3 CO2 + Fe = CO + FeO CO2 + 3FeO = Fe3O4 + CO. Oxidation of steel is caused by oxygen, carbon dioxide and/or water-vapour.

Oxidation of steel may range from a tight, adherent, straw-coloured film that forms at a temperature of about 180C to a loose, blue-black oxide scale that forms at temperature above about 450C with resultant loss of metal.

Decarburisation or depletion of surface carbon content takes place when steel is heated to temperatures above 650C. It progresses as a function of time, temperature and furnace atmosphere.

Typical reactions involved are: O2 + C = CO2 O2 + Fe3C = 3Fe + CO2 CO2 + C = 2CO CO2 + Fe3C = 2CO + 3Fe H2O + Fe3C = CO + H2 + 3Fe. These reactions are reversible."


http://en.wikipedia.org/wiki/Patina
=
http://en.wikipedia.org/wiki/Oxide
and/or
http://en.wikipedia.org/wiki/Carbonate


.
 
That's the most succinct discussion of decarb, orange rust and black rust I've ever seen. I actually believe I understand it. Thanks, Josh!
 
Every time i try to answer a chemistry question I think I knew at one time I have to refind the materials and relearn it. I'm taking chemistry 101 this summer (3rd times a charm), so hopefully i'll actually remember some of this stuff :(

Lycosa said:
In order to lose weight, you have to de-carb.
:p
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I have a really good recipe for a low carb high protein ox-hide soup. HEYOOOOH!
 
Lil' Foo said:

And the dimples were a result of Nitrogen being introduced in the high temerature heat treat process that Busse uses.

Could be wrong though. :p
.

.
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Last Visible Canary said:
http://www.bladeforums.com/forums/showthread.php?t=447673&highlight=nitrogen+dimples&page=4

valleytinworks said:
no, dimples are part of the heat treat and rough blast they get.....
Click to expand...

this is after he talked to jerry about it, so I assume it's straight from the source.
Click to expand...

from
http://www.bladeforums.com/forums/showthread.php?t=703084&highlight=dimples

Nitrogen is introduced into the steel mix during the smelting process so it affects the entire matrix/composition. Heat treating doesn't really add or subtract chemicals throughout the metal, it only rearranges how the particles fit together (and has some chemical interaction at a thin surface layer as shown with decarb-scale). degassing bubbles as large as the pitting you see on some infi would cause structural instability if it were throughout the knife, so it's definitely a surface issue. I'm not sure what causes the pitting during the rough blast though :confused:

Perhaps infi produces a thick irregular scale (pockets of surface decarb) that is knocked off during the rough blast, leaving an irregular surface pattern :confused:
 
wow!
this is so much more info than I, originally thought I would get.
thanks to everyone for the great info..... some of it is down right scholarly :)
 
Here's a question: say we strip a CG tankbuster...is there a decarb layer there to worry about? Or was it only the few 08 competition models that dont get this ground off?
 
Nakatomi said:
Here's a question: say we strip a CG tankbuster...is there a decarb layer there to worry about? Or was it only the few 08 competition models that dont get this ground off?
Click to expand...

I beleive that all of the knives get a surface treatment before being coated. There have been a few instances of people getting rust under their coating, but they are rare, few and far between. Those instances may have been a case of the surfacing treatment not quite getting everything off, and allowing a small amount of water/oxide to remain before coating.

I don't know what kind of surface treatment busse does, be it a wire wheel or a mass finishing bin, but most of the busse's that I've stripped and have seen stripped are clean steel underneath.
 
Busse decarb is Good : it can be GunBlued. I strip only the blade, so the steel under the scale is protected against the rust.

s01c.jpg
 
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Coupchoux said:
I strip only the blade, so the steel under the scale is protected against the rust.
Click to expand...

I never trust open steel to be corrosion resistant, patina or scale. The thing about the decarb scale is that it isn't smooth or consistent, there's a textural roughness and porosity to it that's prone to trapping moisture. While the scale itself may be rust proof, the moisture it traps is hazardous for the surrounding steel.
 
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