Forging and strength

[markb]

I thought that forging metal aligned the grain to conform to the shape of the object and adding strength to the piece?

Soon as you heat treat this alignment is gone?

If this correct the only advantage to forging is the ability to shape the knife.( it's fun too)

:confused: Mark

[TASMITH]

Mark,
You are correct that forging does add strength to the forged piece in the alignment of the grain and, no, heat treating does not nullify this effect. the forged piece still retains the improved strength as opposed to a cast piece where all the grain is random and uniform throughout the piece.

Terry

[ornametalsmith]

So.......once you've forged the blade to shape. AND then you take it to a normalized temp.(non-magnetic) ..........to harden. What happens to the "grain" size and structure at that elevated temp.? Does it grow, stay the same, become more refined?

[Steve Sells]

If you read the Verhoeven papers, there is a long explanation of this, but basically at the conversion of BCC and FCC they reform grain sizes, moving back and forth across the temperature is the precess of refinement to smaller grain.

At or above the Curie temperature there is grain growth toward larger grain, but its very slow growth, this is accelerated at higher temps.

Edited June 15, 2009 by steve sells

[Quenchcrack]

While the grains do re-form, the effect of the flow of the metal remains in effect. However, compare forged knives with stock-removal knives. When using commercial stock steel, the material has already been "forged' from an ingot or billet down to finished stock size. This may involve a reduction of 10 or 20 to 1. Does forging another 10-20% really do as much good as we like to think? Don't misunderstand, I prefer a forged blade but I know the vast majority of commercial blades are stamped and ground and appear to be functional for the average user.

[MattBower]

Not to hijack the thread but, to be a little picky, it's not quite accurate to say that grain growth begins at the Curie point. Curie point isn't diretly related to the BCC/FCC shift, and the temperature at which austenite formation stops and grain growth begins varies from steel to steel. It's usually something other than 1414 F, though it's (again, usually) in that neighborhood.

[Steve Sells]

Very true, good to see someone is paying attention but as I said they should read the Verhoeven paper. Its not easy to condense 205 pages into a quick post without getting a bit off track

I added "at or above" to my prev. post to help clear this...

[Charlotte]

There is a lot of stuff that shows up in photomicrographs in metallurgy text books that is hard to explain here unless you are metallurgist.

[JPH]

Hello:

Hope no one minds...the simple answer is Yes, there is a difference bewteen as rolled and a PROPERLY forged blade. BUT... If you do it IMPROPERLY you can really FUBAR the steel to the point where you will have grain growth, grain boundary problems and a whole lot of other fatal things that can lead to a catastrophic failure.

Watch the temp,. work within the proper temp ranges and learn how to do it PROPERLY.

Most problems involve working either too hot (most common) or too cold depending upon the steel.

Hope this helps.

JPH