[TheForge] Shrinking Stainless Sheet metal

[Andrew Vida]

Peter Fels And Phoebe Palmer wrote:
> Dan:
> Good clear explanation, thanks.
> By "shrink", in this context, I was thinking in terms of thinner stock 
> where both faces would heated pretty equally by conduction, but only a 
> small area would be heated. This ought to cause thickening as the heated 
> area tries to expand against the surrounding material. I understand that 
> the only volume change would be from scaling.
> I was speculating that it ought to work well with stainless steel.
> I once had a go at straightening 1" plate with a rosebud and water 
> spray...it was wildly frustrating...felt really dumb at the end.
> A last Q, if i may....If SS alloys conduct heat slower, wouldn't such 
> stuff be good for hydraulic forging press dies, where heat loss to the 
> dies is  a big problem?...Pete f
> 
> Dan Hayes wrote:
>> Peter,
>>
>> You cannot permanently "shrink" a metal object by general heating or
>> cooling. Of course the object will expand if it is heated and contract 
>> if it
>> is cooled but it will return to its original size and shape when 
>> returned to
>> the original temperature.

	There is at least one case where you actually can shrink metal 
"permanently" with heat.  It is in the case where you have a martensitic 
structure.  Locally applied heat will cause the structure to revert and 
shrink.  This is how, for example, bladesmiths can correct curvature of 
a sword.  Japanese smiths use a heated block to pull a blade's curvature 
"in" more wherever it may be a bit too flat, so to speak.

	I know that isn't the context, but I thought I'd bring it up just as a 
point in the broader discussion.
	
	-Andy