Cause and prevention of heavy scaling?

[gables]

I am very green at knife making. I have been using a
coal forge to heat treat. I had my blade nice with 300 grit, normalized 3 times and then heated and quenched in 140 veg oil. The pittng and scaling is imense and I am having to start back at 80 grit. Does a gas heated forge prevent some scaling?

[Steve Nuckels]

I'm green too!  But I beleive using a atmospheric propane forge will reduce scaling to a minimum.

Steve
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ABS Apprentice
Potomac Forge
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IN GOD WE TRUST

[Lin Rhea]

gables,
         How much have you used coal to heat steel? I know you said you were green, but you can expect some scaling with either. It may be that you need to learn some more about how to build/manage your fire. Or it may be the type of coal you use. Yes, a gas forge is less trouble, but if coal is all you got it will work, just read or do some research on how to manage the fire to keep it cleaner. Scale is formed when the hot steel is exposed to oxygen. Try to make a fire that has a chamber with a clean atmosphere.
     
        One other thing, since you are in the heat treat process when this happens, you might just be getting your blade too hot. This is very common with new forgers and especially if you happen to be forging outside and cant see the colors good because of the full daylight. If this(too hot) is so, it will cause scaling, not to mention being bad for the grain structure.

      I recommend you get with some experienced forgers, even blacksmiths, and watch them work and give it some time.  Lin

[AdrenalinAddict]

Hey Gables,
I am to pretty green at this also.
I bought some anti scale compound from Brownell's. It works very well. You just heat up to 450 f then brush on and it will protect up to 1650 f " that is the majority of steels upper critical range " The only draw back I have had is you have to monitor heat with a magnet "or temp gun if you have one that goes that high" as the coating darkens the heat color. Anyway after quench in water most coating falls off but when oil quench it takes a couple warm cycles into water to remove rest of coating. But when its off it's beautiful !!

[Ragnarok Forge]

Lin nailed it down for ya.

[ALW]

I have the same problem.  My forge is very crude and I'm also new at this.  Someone on here mentioned putting a piece of pipe in your forge a little bigger than your blade and put the blade in there for heating.  It keeps if away from the coal and I think helps to maintain a less oxidizing environment.  I haven't had a chance to try it yet but will on the next blade.

Aaron

[DANA HOLMAN]

Gables, you know i'm new at this as well, and i had the same problem when i started, with my forge i don't have that problem anymore. if you need to heat treat your blabes bring them out to the house, and you can to it there until you get you forge right. you can also try the pipe in the coal.
dana

[kuch]

gables, do you have "good coal"? coal can differ greatly which directly affects your ability to have a proper fire.if coal is the fuel you're going to use ...buy the absolute best you can acquire...things will go as smooth as they can if you have good coal.it really makes a difference.then one can focus on proper fire construction and variables to change.