[TheForge] To ring or not to ring - chilled face

[Hochewa at aol.com]

To All,
When melting iron to make a gray iron casting, you keep the silicon up a  
little to make sure that the carbon comes out as flakes when the casting cools  
slowly.  If you keep the silicon low in the iron and essentially cast it  
against another block of iron, the cooling rate at the iron-iron interface is  very 
fast.  The combination of low silicon and rapid cooling creates a  columnar 
layer of iron carbide crystals perpendicular to the surface of the  casting.  
The resultant material is VERY hard and wear resistant.  It  is not very 
ductile but you have the rest of the casting to support it.  A  lot of big mill 
rolls are "duplex" cast with a chilled shell for the working  surface and a 
relatively ductile core.
 
Hochewa
 
In a message dated 4/27/2006 4:07:29 A.M. Eastern Standard Time,  
michael.a.porter at comcast.net writes:

Cast  iron can be very hard, but I don't understand the term "chilled  face."
Could you please explain it?
Mikey