[email protected] (Dave Williams)
fords  01 Nov 1994
- -> Could someone explain to me the difference between ordinary cast iron
  -> and "high nodular" iron?
- The "nodular" part refers to the distribution of carbon in the casting.
  There's white cast iron, gray cast iron, black cast iron, nodular cast
  iron, etc.  For cars you normally see gray or nodular, known as "spheroidal 
  graphite" in England. 
- Iron does strange and wonderful things when mixed with carbon in various 
  proportions.  Entire *sets* of books exist, not on the whole subject, but 
  various *types* of ferrous metallurgy. 
- Steel is, of course, iron.  The practical difference between a cast or 
  forged steel crank and a cast iron crank is that the iron is not malleable.  
  That is, it cannot be forged or hammered into a different shape unless near 
  its melting point.  There is often no *chemical* difference between a forged 
  steel and a cast iron; the vast differences in structure are due to how the 
  metal was processed. 
- Every now and then I get the urge to learn more about the subject, but after 
  a few hours of reading about crystalline structures and looking at etched 
  photomicrographs, I fall asleep. 

[email protected] (Dave Williams)
gnttype  03 Apr 1996
- -> either, when you stress cast iron it dosen't budge, and it doesn't
  -> yeild to strain very much either, once you over do it, cast iron goes
  -> SNAP! steel is not the same, steel will FLEX under stress and when it
  -> yields under too much strain, it bends permanantly into another shape
  -> instead of snaping, continue
- Not necessarily.  Plain old gray iron, otherwise known as "Detroit Wonder 
  Metal" is pretty brittle stuff.  Buick cranks are made of nodular iron, 
  which is relatively flexible.  You can visibly bend and straighten a nodular 
  crank and it will still work just fine. 
- Just because a crank is steel doesn't mean it's immune from breakage or 
  cracking, either.  Steel tends not to be as accomodating of torsional 
  vibration as iron, at least when formed into crankshaft-like shapes. 
- By the way, with energy costs and labor, forged cranks can be cheaper to 
  make in Detroit-sized batches.