[TheForge] rigid vs. springy steel

[Peter Fels & Phoebe Palmer]

Hi Bruce:
Till the adults chime in....
Forging steel within the proper heat parameters refines the grain structure and seems to make steel stiffer.
I've read that in theory, steel has the same rigidity across the board, 
but the difference is in how far it will deflect before permanently distorting.
This still is counterintuitive to me. It seems to me that the harder a steel is, the less it will deflect, all things being equal.
Given sufficient carbon, you can change the hardness of steel by heat treating.
The more carbon, the greater the heat treating difference.
 Steel alloys also add different properties.
There is a spectrum of hardness to be obtained by tempering hardened steel, 
ranging from very hard but brittle, to soft and tough.
Tools are tempered to some compromise along the spectrum. 
Corkscrews, springs and prybars tend to be towards the softer/tougher end of the spectrum.
An old time blacksmith might quench a prybar in oil from 1550F to harden,
then temper to a surface oxide color of blue (375 F?), or the flash point of oil.
Same for a pocket knife, spring or corkscrew.
This is a very rough and generalized answer.

On Jul 25, 2013, at 2:06 AM, Bruce . wrote:

Here's a question you metal munchers might be able to field:

I have had a few applications in which I need thin but rigid steel.
What steel is best?

Consider for example a corkscrew -- it's a helix that holds its shape,
it's rigid.  But a spring with a comparable shape is flexible.  What's
the difference?  I suspect that it's simply the relative dimensions --
a spring is relatively thinner wire wrapped on a relatively larger
mandrel, and vise-verse the corkscrew.

But is that all there is too it, or is there a metallurgical difference as well?

Although I've contemplated making corkscrews, the immediate
application is a prybar for roofing and siding nails and similar
stuff.  It would be flat, like these:
http://www.homedepot.com/p/Dasco-Pro-Pry-Bar-Set-3-Piece-91/202585548#.UfDoym1cWgw
but of thinner steel.  (If I can't make it thinner, I'll just use a
commercial one.)

I'd like it as thin as possible for a number of reasons, but I don't
want more than minimal flex to the thing.  So I'm wondering what steel
to use.

I have, BTW, considered using thin steel and putting longitudinal
bends ("ribs" or "nerves" or "corrugations" -- whatever you want to
call them -- as are used in larger HVAC ducts to prevent oilcanning of
the large flats) in it, but this partially defeats the purpose, as the
result would effectively be thicker -- so why not use thicker metal
and be done with it?

This is not any sort of critical problem, but I've had similar
problems before and left them unaddressed.  This time I thought I'd
ask....

-- 
Bruce
NJ
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