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Work hardening questions


#1

i’m looking for an explanation of work hardening that goes into a
little more detail that mccreight and untracht do in their books.
but, i am not a scientist, so i need the explanation to be accessible
to a layman. i think i read what i’m looking for at one time, but i
have no idea where. i’m looking for both the technical and practical
aspects of work hardening.

for example, i want to make a bracelet using a wire with as small a
diameter as possible so that i can string beads with small holes on
it. i would like to avoid the distraction of a clasp, so, i would
like the bracelet to act like a cuff and be springy. i want the wire
to allow deformation so that the bracelet can be slipped on and off
the wrist, but i want to prevent the fatigue that will cause the wire
to break in the future. as a practical matter, how do i judge from
the feel of the wire when i have work hardened it enough but not too
much that subsequent use of the bracelet (taking it off and on) causes
it to fail? probably the answer to this last question is
"experience," but what are the hints the metal gives me that i have
achieved the right balance? does the solution involve tempering? how
should i go about this?

another question. i have gotten “wire in design” by barbara a.
mcguire from the library. there is a description of work hardening of
wire in the book that i just don’t understand.

the description starts in the 3rd paragraph of page 82: “…She
calls it ‘work hardening’ as a result of an 'electron flux charge.'
When the wire is bent, it creates friction, which carries an electric
charge, electron to electron, and this charge flows through the wire.
This is the reason a piece of wire can be soft in the middle and hard
at the end. The end hardness is a result of the momentum of the
transfer of energy or the flow of the charge to the end. A hammered
piece also gets hot and work hardens the wire…” In the 4th
paragraph it says: “She leaves an extra length [of wire] so that the
end absorbs the hardening and her design is still workable.”

this explanation doesn’t sound like anything i have read. help?

jean adkins


#2

Hello Jean, What is work hardening, We have to go down to molecule and
crystal levels. and I will try to keep it simple. What you do when you
hammer or roll a piece of metal, you flatten, you extend, the metal
crystals and disturb the atom grid. See the crystal in soft annealed
condition as piled sand bags. al the crystal edged are laying firmly
together, and there are no tensions between the crystal together. When
you hammer you flatten the crystals, pushing the pile of sandbags
flat. The flattened bag will push the one next to him aside. and
spaces between the bags on the outside will occur. At the crystal edged
the atoms are pushed together, or pull from each other. These
increased atom forces give the hardening effect. Metal is ductile as
long these atom forces are in limits. and the structure can repair it
self When you over stretch the sandbags will tear. This happens also
with the atoms. They will move and an shift to there neighbour. trying
to fill the caps which occur. This repairing effect has its limit.
Sometime the caps get so big that a atom jump is impossible. Than
permanent grid deformations and cracks occurs. (still talking atom
level) A certain amount of caps (disturbances) give the springy and
hardening effect. The atoms have to bend over the caps and there
distance changes. The distance changes between atoms will disturb the
electrons who are moving between and around the atoms and gives
electrical tensions. These electrical forces are the bindings between
the atoms. The more disturbance the bigger the electrical
disturbance. This gives the hardening effect.

Also alloy elements who are often bigger than the original basic
metal structure gives a disturbance in the atom grid. This will harden
the basic metal. the original atoms have to bend over these bigger
alloy atoms. and there space will change, and so there electrical
tension. ( Force between the electrons).

Barbara a Mcguire is right about the electrical forces. But not right
in the explanation of the soft middle. In the middle of a wire when
bend, there are no forces. The top of the wire, when bend downwards
has stretching forces, tensioning forces. The bottom piece is push
together and there are pushing forces. You can imagine that in the
middle there is a neutral zone. Without any force. If you bend the
wire up and down the middle will stay soft. (there a no disturbances
in the atom grid) The outsides will harden the most, there where the
biggest elongations. If you hammer a wire you can imagine (I hope
now) a pushing force in the middle of the wire and a tension force at
the outside. A metal grid can easier repair it self , if al the atoms
are pushed together and have to find new places. On the outside the
atoms are torn apart and the caps can easier occur there. This is a
bit explanation the way of hardening of the outside. Absorbing the
hardening at the end really bullshit, Still it handy to have
something to hold when you work on an object.

Also the energy by hammering and the heating of the metal, give no
extra hardening effect. A black smith is also trying to hammer so fast
that the metal stays red hot and then he can go on. and does not
reheat so often. The metal structure, atom grid is than self repairing
the atom can easy fill up every cap.

Fore instance Tin (Sb) is recrystallising at room temperature, that
is the reason you hammer it without cracks. If you put a thick piece
of tin in your freezer and let it cool down to -20 degrees. If you
bend it now you will hear it scream. You will hear the grid snapping
apart. If you hammer this it is brittle, and will give cracks

I hope this explains some, but it stays a try and error to find the
correct amount of hardening, because there are so may alloy and so
many crystal differences due to annealing and on and on and on.

Martin Niemeijer