cold forging

T

toddhill

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Sep 28, 2004
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I was recently reading in Ed Fowler's Knifetalk II book and in an article he speaks about cold forging a blade that he had inadvertently left in the heat too long resulting in large grain growth. He wrote that by cold forging the blade, it was transformed into a good blade. What exactly is cold forging? Is it commonly practiced? Thanks, Todd
 
Tod:
It has been a lng time since I thought about that blade. It cut better than the one that had been hardened after a full textbook anneal, but not not as well as a blade that had been kept at low temp all the way though. The Taxidermist who owns it still likes it very well.
Joe Szilaski has taken cold forging a long way, he is a master from the Hungary schools of metalsmithing and has a lot of thoughts about it. If you see him at a show just ask him about it and get ready for a real lesson.
 
Since 'forging' usually implies hot working , then 'cold forging ' should be called cold working .There is a limit to what can be done with it .Did he do anything else to it ? In ancient times bronze and iron blades were cold worked on the edges. It won't do anything with the large grain unless you do a subcritical anneal after .
 
Mete: That was my one and only experiment with 52100 and cold forging or working if you preffer. It had three 350 degree f, draws after three hardenings before, its comparison blade did not cut well. No more thermal cycles after the cold forging. It was just a question at the time and did not seem worth following up on.
 
This is from www.marttiini.fi. “In manufacturing process the sketches of blades are put through the rollers, which change the design of molecules from round to ellipse shape. This processing makes the metal composition more density and therefore makes blades more durable and flexible and the edge remains sharpness notable longer.” The writer is describing the treatment of the steel they use for Marttiini Knives. From what I understand steel is rolled cold and this would confirm a benefit to cold forging. todd
 
it looks like im going to drag this back up as im looking for answers. i have read on line that cold forging reduces grain size by quite a bit. but then others say it just stretches the grains. but my question is this. say someone was forging 2 knives, one hot and one cold. then heat treated them both the same. would one preform beter then the other? would grain size be the same and how about over all forged finish.
 
I would like to see Mete's opinion on this. In the first place, there are no molecules in steel. Steel is a crystaline structure. I could easy be wrong, but I don't believe these crystals are round at any time. The process described would seem to me akin to edge packing. The rollers might break down the grain size, but I don't see the grain being "stretched". Could be, I am no expert. As soon as the steel is heated for hardening the grain is going to come back close to where it was before the rolling. I would think thermo cycling would do as well, if not better, and maybe that is also done, and is the real reason for any measured improvement. I don't know, just my thoughts. What about it Mete'?
 
Cold rolling will indeed elongate the grains in the rolling direction. Cold working, as with a hammer, will "stretch" the grains in whichever direction the metal moves. The grains will not be reduced in size until they recrystalize, which for steel takes heat. Of course, the size is largely determined by heat, and they may just grow to the same size again. There are many variables, and without reading up on it, I'll just say it can get pretty complicated. FWIW, the grains elongate during hot rolling too, but they recrystalize very quickly at those temperatures. This is a pretty interesting topic. I read years ago that Darrell Ralph had some improvement in edge holding when cold forging his D2 blades before heat treating. I personally wouldnt try it on a hardened blade, but that's just me.
 
Cold forging will "work harden" the steel...

The African's and others work hardened their blades and left them in that state without further heat treatment (which would undo the work hardening effect). Work hardening iron/steel was the standard before quench hardening came along,... carried over from the bronze and copper ages. As I understand it the crystals are deformed to the point of resistance in the work hardening process. There is a limit to the amount of deformation it can take, and the closer the crystal gets to that point the harder it gets. Work hardening results in a hard springy structure. Maybe Mete or Kevin can explain it more thoroughly.

It might also help to talk about the malleability of metals in general.

I'm not so sure that combining quench hardening and work hardening is practical or even possible. Work hardening is normally done to a pearlitic structure, not martensitic.
 
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... although, I suppose if you had some kind of funky abnormal macrostructure,... say half pearlite and half martensite, (or a low carbon content)... cold forging might do it some good, and have some unforeseen advantage. However, I think you would probably be better off just quench hardening it right the first time. :)
 
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mete said:
Since 'forging' usually implies hot working , then 'cold forging ' should be called cold working .There is a limit to what can be done with it .Did he do anything else to it ? In ancient times bronze and iron blades were cold worked on the edges. It won't do anything with the large grain unless you do a subcritical anneal after .
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Cold forging is a specific type of cold working. The term cold forging is common in non-ferrous metal work and is the correct term for hammering the metal to shape, planishing, and work hardening, (including iron or steel), while it is in a cold state. The word "forging" traditionally does not necessarily imply hot working from a metalsmithing perspective.

The semantics may not seem to make much sense at first,… but they do use a “forge” or fire to periodically anneal (heat treat) the metal with “cold forging“, in operations other than work hardening.
 
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Do not confuse cold forging with low temp forging. Two different methods, cold forging - the steel is worked at room temperature.

What I call low temp forging, the steel temp runs from 1625 f. to below critical when the steel quits moving under my hammer.
 
Ed Fowler said:
Do not confuse cold forging with low temp forging. Two different methods, cold forging - the steel is worked at room temperature.

What I call low temp forging, the steel temp runs from 1625 f. to below critical when the steel quits moving under my hammer.
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Good point Ed, but now I'm really confused. :)

... So what are we talking about here, "low temperature forging" or "cold forging"?

"Cold forging", right?

... or are we all talking about something different? :D
 
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