Forging heats

panch0

panch0

Joined
Jun 16, 2008
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I am new at forging, and have been reading on the subject. The question I have is when forging a knife, how many heats can you do until it starts to damage the steel? From what I read the fewer the heats the better. Am I correct? Another question, lets say I start forging a knife, and I get pulled off and dont normalize it until the next day or two, will this have a negative effect on the steel? Thanks!
 
how many heats can you do until it starts to damage the steel? From what I read the fewer the heats the better. Am I correct?
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Yes, that is correct. The more heats you do the more carbon leaves the steel. For general forging on a knife I wouldn't worry about it too much though - just think of how much and how many heats damascus is subjected to. Also it is the steel at the surface that is most affected so grinding back the edge a bit after forging and it will be back into the good steel.
Bruce
 
Thanks Bruce, How about the second part. I was practicing on a 1/8" piece of 1084 and didnt finish it and also did not normalize it per se. I simply put it in the forge at a dull red color and shut off the forge and let them both cool down together. Would doing this damage the steel?
 
Good questions Frank. As a new forger myself I'm watching this one. Don't ya hate it when ya got to do honey do's right in the middle of a project.
 
Horsewright said:
Good questions Frank. As a new forger myself I'm watching this one. Don't ya hate it when ya got to do honey do's right in the middle of a project.
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Yep, thats exactly why I called it quits for the day. hehehe...
 
Of course, the goal is to forge with the least amount fo heats but unless you are REALLY burning out the steel at welding temps+ or it is in thin cross sections. The decarb doesn't go very deep into the piece. Plus the decarb layer itself helps to protect it from further decarb. Normalizing NEEDS to be done but not under the same time constraints as tempering. You can leave it and come back later.

Rick
 
What Bruce said is true...but the degree is small. As he pointed out, just the clean up grinding and sharpening will remove the decarb.

The damage to the steel you need to address isn't in carbon loss,..... the grain growth is where you can have problems. Normalizing the steel at the end of a days forging, and doing a careful grain refinement cycling before HT will adjust this to undo any problems.
 
Its insidious how they start it too. "Honey come in for lunch". And there ya are half way through your sandwich and it starts: "While you're in could you........ and the light bulb is out in the hall...... and could you move the sprinkler..... and could you......and I know you're busy but.....and then ....Honey its time for dinner". Which is of course always followed by: "When are those orders going to ship? You're getting behind again."
 
I think you are supposed to be more worried about color as well. I was working on a project (not a knife) and it came out bright yellow and sparking, like a 4th of July sparkler. After that it wouldn't taper properly and had to be cut off.
 
Rick Marchand said:
. Normalizing NEEDS to be done but not under the same time constraints as tempering. You can leave it and come back later.
Rick
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I would really like to know about correct normalizing. Is it the same for similar types of steel? I use 52100 mostly. What do you mean about the time constraints between normalizing and tempering? How does normalizing affect the grain size?
 
Grizz,
Karl Anderson has some youtube videos that show the process and need for normalizing. That really helped me understand what was hapening
 
Without getting into semantics here,... I'm not sure what the correct technical term is, but a type of "thermal fatigue" or "hot work fatigue" can occur at the surface of the steel from too many heats in conjunction with other stress etc., from forging. I've seen it quite a few times when trying to do intricate forgings and/or monkeying around with it too much on my own work and on other's. It actually becomes visual to the naked eye on the surface of the steel. It first appears as a series of very fine "cracks", "stretch marks", "wrinkles" or "hot fractures" on the surface running perpendicular to the length of the blade, (edge, back). It appears as an odd texture on the surface. A couple times I've seen it so deep and wide you could stick a finger nail in it. Needles to say it can travel deeper into the steel and weakens it, if not ground off.

The more heats or hot working the worse it gets. If it goes too far, it ends up in the scrap pile. If you see it at any stage of the game, it’s a good idea to grind it off before going any further. It's especially important to inspect the surface for it on hammer finished blades.

Every heat can be thought of as a thermal stress cycle... expansion and contraction.

Best not to over work the steel.
 
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Tai Goo said:
Without getting into semantics here,... I'm not sure what the correct technical term is, but a type of "thermal fatigue" or "hot work fatigue" .
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A few years back at a blacksmithing meet I watched an old Italian smith forge an intricate flower all day long. I think he was using Pure Iron, but he was very conscientious about forging at the lowest heat with which he could do the job. No noticeable fatigue.
But then, masters can get away with stuff that normal smiths would fail at.
Andy G.
 
I have experienced exactly what Tai is describing. Excessive, prolonged heating and working seem to rot away at the surface of the steel. Scrolling always seemed to be a breaking point for me. The steel would get surface cracking where it was stretched apart. That really was an eye opener that I needed to get control of my heat. I was also guilty of forging way below the proper temperature. Unless you are testing your blades, you may never realise how many stress cracks you introduce with improper forging.
 
Wait, is Tai talking about science? Thermal dynamics??? What?!?!?!? :p :D

Frank, another thing is that 1/8" steel is pretty hard to forge when you're starting out. Especially if it's fairly wide, and it will want to fold over when you're hammering in the point, rather than draw out.

IMHO- one thing that can make a forged blade excell, is that every heat is part of the blade's thermal cycling. One thing that can really make a forged blade suck, is that every heat is part of the blade's thermal cycling. ;) :)

You can "undo" a lot of the damage that forging can inflict with accurate thermal cycling, but I don't think a guy should go out of his way to screw up the steel because of that.

The very best thing you could do is find a good blacksmith or bladesmith and watch his process in person. :)
 
NickWheeler said:
IMHO- one thing that can make a forged blade excell, is that every heat is part of the blade's thermal cycling. One thing that can really make a forged blade suck, is that every heat is part of the blade's thermal cycling. ;) :)
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I love this... Ha! The beauty is that you can turn it over for stock removal guys, too!

IMHO- one thing that can make a stock removal blade excell, is that it avoids the process of thermal cycling, all together. One thing that can really make a stock removal blade suck, is that it avoids the process of thermal cycling, all together. ;) :)
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It is important though for the novice forgers not to confuse this surface phenomenon with the lateral stress wrinkles caused by working bar stock with an inproportionate ratio of cross sectional thickness to height. When you get minor collapse from trying to forge down the "width" of thin stock it will appear as horizontal wrinkles when you straighten it back out often times. These of course should be forged or ground out also, but I wanted to mention it so somebody doesn't scrap good steel after the first couple of heats when they see them.

Of course, working from round or square stock eliminates this issue. ;)

Tai Goo said:
Without getting into semantics here,... I'm not sure what the correct technical term is, but a type of "thermal fatigue" or "hot work fatigue" can occur at the surface of the steel from too many heats in conjunction with other stress etc., from forging. I've seen it quite a few times when trying to do intricate forgings and/or monkeying around with it too much on my own work and on other's. It actually becomes visual to the naked eye on the surface of the steel. It first appears as a series of very fine "cracks", "stretch marks", "wrinkles" or "hot fractures" on the surface running perpendicular to the length of the blade, (edge, back). It appears as an odd texture on the surface. A couple times I've seen it so deep and wide you could stick a finger nail in it. Needles to say it can travel deeper into the steel and weakens it, if not ground off.

The more heats or hot working the worse it gets. If it goes too far, it ends up in the scrap pile. If you see it at any stage of the game, it’s a good idea to grind it off before going any further. It's especially important to inspect the surface for it on hammer finished blades.

Every heat can be thought of as a thermal stress cycle... expansion and contraction.

Best not to over work the steel.
Click to expand...
 
Rick, so true!!!!!! :thumbup: :D

It's just like "mom" "dad" and "dog." Oh wait, that's not right. :foot: ;)
 
javand said:
It is important though for the novice forgers not to confuse this surface phenomenon with the lateral stress wrinkles caused by working bar stock with an inproportionate ratio of cross sectional thickness to height.
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It is possible, though... Without the wrinkles...;)

From .162" x 3" x 12" to .188" x 1.5" x 18"

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