[TheForge] Packing and compression

[schade at acegroup.cc]

so where did all the "packers" go?

Bob

ps. but hey what's wrong with sitting on your anvil?
______




On Nov 11, 2005, at 8:41 PM, Hochewa at aol.com wrote:

>
> To All,
> A gauntlet has been thrown down.  Thank you Jonathan.
> In ferrous materials you have to contend with both recrystallization 
> and
> phase transformation.
> Recrystallization is the materials response to prior work when thermal
> energy is applied.  The work can be cold, warm or hot.  The  
> recrystallization
> response occurs with time and temperature and it depends on  the 
> amount of prior
> work and the temperature at which it was applied. Phase  
> transformations occur
> in response to temperature because of the thermodynamic  stability of 
> the
> phases involved.
> I do not believe in "packing".  Any one who says that it makes the  
> edge of
> the blade more dense probably sits on his anvil, too.  It is as  dense 
> as it is
> going to get and a little bit of tippy-tapping does not make any  
> difference.
>  Working the edge a little may promote some dynamic  recrystallization 
> which
> in turn may relieve some of the forging stresses and  promote a 
> straighter
> edge.  Additional stress relieving is still necessary  before heat 
> treatment.
> Transformation from a ferrite/carbide/pearlite matrix to austenite 
> tends to
> remember where the prior austenite grain boundaries were anyway.  
> Austenite
> formation involves some short range diffusion and a lot of 
> crystallographic
> changes.  Quench induced martensite initiates its lenticular shape 
> across  the
> largest dimension of the austenite grain. So it does not really matter 
> what
> the grain size is below 1333*F.  The hardening occurs from the grain 
> size
> achieved during austenitization.  Grain size is mostly effected by the 
>  temperature
> at which the work is held.  There is a minimum time needed to  achieve 
> full
> transformation and holding it at that temperature for a longer time  
> does not
> radically change the grain size.  Temperature has a more  pronounced 
> effect
> than does time.  It all has to do with the balance  between the energy 
> of the
> volume of the grain and the energy of the grain  boundary volume.
> The specific amount of reduction at the last forging pass sets the  
> austenite
> grain size as the material is then heat treated. Tippy-tapping tends  
> to make
> big grains, smacking it good reduces the grain size because of the  
> increase
> in potential grain nucleation sites.
>
> Hochewa
>
>
> In a message dated 11/11/2005 10:59:25 A.M. Eastern Standard Time,
> jonned at hvc.rr.com writes:
>
> I  remember on a visit to a large forge shop where they made bearings, 
> among
> other things, that they were careful to move the metal a certain 
> amount in
> the last forging heat. This was we were told, to assure a small grain 
> size
> in the material as it relates to the strength of the finished  bearing.
>
> I assume that these were not going to be heat treated because,  in my 
> limited
> knowledge of this subject, when you heat above the critical  temp, 
> also known
> as the heat of recrystallization, you get just that - new  crystal 
> growth,
> and this is the temp that carbon steel has to reach for  heat 
> treatment (ok
> Bill H. you can correct me later). So all the "packing"  in the world 
> is not
> going to get a harder edge if the grain you have  compressed in the 
> last
> forging heat is regrown in the heat treat. Or  something to that 
> effect.
>
> Jon Nedbor
>
>
>
>
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