So does this explain why it took 7 hours and 7 drill bits to drill 2 holes in
the welded on bumper mount on a new shell??
Larry
On Aug 16, 2011, at 14:42 PM, Mark Haynes wrote:
> Only Case Hardening is surface hardening. True hardening of the steel involves
> raising of the temperature of the steel to a point where the grain size is
> modified to be smaller and is more orderly thus increasing the
> intercrystalline bonds reducing the potential for dislocations. The trick with
> hardening is to get the crytalline structure consistent inside to outside and
> then 'freeze' it by quenching at that state.
> Subsequent to quenching, most steels are then annealed to increase the
> toughness (resistance to deformation).
> Harder does not equal tougher. Toughness is an independent variable based on
> the amount of abuse (non-engineering term here) that it will take before it
> starts to show signs of yielding.
> In gross generalities, a stronger steel is more brittle, however this is a
> relative term. My point being that as a steel becomes stronger, the percentage
> difference between the yield point (where it starts to deform plastically) and
> the failure point (where it catastrophically fails) is reduced. Thus as
> stronger steel in the same application will yield later (at a higher load),
> but it won't put up with the same percentage increase in load beyond that as
> long as a weaker steel will before it fails.
> Hardening of steel is more of an art than a science unless you have a
> limitless database of minor variations in each specific steel you are working
> with.
> So to answer the question, at a given load assuming no annealing has taken
> place, a harder steel will fracture more suddenly than a weaker steel, not
> necessarily at a different load though. Some tougher steels are harder, some
> harder steels are more brittle, some softer steels are tougher, it all depends
> on what the alloy and the heat treatment is.
> Sorry for the dissertation, I'm just off of my load frame testing Aluminum at
> 4 K (-269*C or-453*F).
>
> Mark Haynes
> It only goes one way-Pay it Forward
> HAN6L12977
> HAN5L8016
>
>
> Date: Tue, 16 Aug 2011 12:14:00 -0400
> From: Allen Hefner <lbc77mg@gmail.com>
>
>
> Here's a question for you metallurgists out there. If one axle is harder
> than the others, wouldn't it be more brittle and prone to breakage? Is a
> softer metal better able to handle being banged by the engine power and
> brake force?
>
> Just askin'.
>
>
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--
Larry B. Macy, Ph.D.
macy@upenn.edu
System Manager/Administrator
Neuropsychiatry Section
Department of Psychiatry
Perelman School of Medicine
University of Pennsylvania
3400 Spruce St. - 10 Gates
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Ask a question and you're a fool for three minutes; do not ask a question and
you're a fool for the rest of your life.
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