[TheForge] Re: Test mail

[Bruce Freeman]

Ugh!  I'm really stretching to answer this, and will certainly defer to any metallurgist...

When you talk about atoms and crystals, "compressing" doesn't compute.  "Distorting", especially with metal crystals DOES make sense with respect to crystals (but not atoms).  Also, I believe that you can reduce crystal (i.e., grain) size by hammering, but I'm not certain of that.  

Anyway, smaller or stressed (distorted) grains apparently are responsible for hardness in metals.

The carbon in steel is not free, but dissolved.  Carbon steel is an alloy.  Hence, it is not an issue of the carbon compressing - that's no more possible than the iron compressing.  The atoms don't get closer together, except to a small extent when crystal FORM changes (which is a whole 'nother issue).  Insofar as small crystals are "closer together" than large crystals, reducing the grain size makes the crystals closer together.  I am under the impression, however, that it is the size of the grains, not their closeness, that renders the metal hard.

(By contrast, there may be free graphite carbon in cast iron, but not necessarily.  The amout and form of the carbon in cast iron is partially responsible for the different forms of cast iron.) 

Bruce
NJ

>>> stephen.viola at gmail.com 11/11/2005 9:18:06 AM >>>
Yep clear as compressed mud atoms ;oP
So if I understand correctly, its the 'matter' (ie, carbon)
surrounding these tiny crystals that can compress, but the atoms that
form these crystals can not.

or is it that the atoms that form these crystals get closer together
(reducing the size of the crystals) making the piece harder.

sorry for making an issue of this it's just that i would like to know.

Stephen

On 11/11/05, Steve Smith <sos at alum.mit.edu> wrote:
>  From somewhere I remember that packing might have been important when
> there was lots of slag in the metal, but doesn't do anything with modern
> steels. No reference, sorry.
>
> Steve
>
> Bruce Freeman wrote:
>
> > (I should have read both these postings before responding.)
> >
> > Yes, hammering springs may harden them.  I am not a metalurgist, so I won't try to explain why that works.  I can give a lable for it, "work hardening", but that is not an explanation.
> >
> > However, I AM a chemist and have taken the usual courses in physics.  NO WAY you can compress atoms or even metal grains (tiny crystals within a solid metal) with a hammer.
> >
> >>From the small amount of metallurgical reading I have done, I believe I recall correctly that you CAN break, distort or otherwise stress metal grains with a hammer.  Annealing is the process of removing such stresses by application of heat (and, for steel, by slow cooling - - which is not necessary for pure iron or other metals).  Anyway, it seems that these small, distorted crystals are HARD.  Hence, hammering leads to hardness.  (I defer to correction in this interpretation to any metalurgist lurking.)
> >
> > Steel is different in that the carbon content radically changes its properties relative to the pure iron metal.  Tiny crystals can arise in steel by heating and quenching.  Since these tiny crystals impart hardness to the metal, a "simple" means of hardening the metal is available.  (This judges work hardening as "not simple" - clearly a judgment call.)
> >
> > Hope this helps.
> >
> > Bruce
> > NJ
> >
> >
> >>>>stephen.viola at gmail.com 11/11/2005 2:25:21 AM >>>
> >
> > I'm not sure about the scientific detail, but I do know that way back
> > when, the making of springs for buggies and carriages were hammered
> > hard and not heat treated. So there must be some truth to the
> > compacting of grain or atoms. Blacksmiths have been doing it for
> > centuries. At college we are taught that the compression of atoms
> > occur when hammered. Thats not to say that other material is
> > displaced, just that there seems to be some kind of allowance for the
> > metal to become harder with the compression. Like I said I don't know
> > the scientific blah blah, but thats the understanding I have.
> >
> > Stephen (Finland)
> >
> > On 11/11/05, Erik Gutfeldt <erikg at apple.com> wrote:
> >
> >>On Oct 31, 2005, at 4:59 AM, Bruce Freeman wrote:
> >>
> >>
> >>>I do vaguely remember his discussion about "packing the edge" of a
> >>>knife.  Pure nonsense.
> >>
> >>I thought the metallurgical effect of "packing" was to reduce grain
> >>size.
> >>
> >>Erik
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