[TheForge] Quenching mild steel - Hochewa ?

[theforge@mailman.qth.net]

To All,
Martensite is the hard stuff.  It is supersaturated (with carbon) ferrite.
Pearlite is what you have 100% of at the eutectoid composition, 0.8% C.  It 
is comprised of lamella of ferrite and iron carbide.  It is harder than ferrite 
but softer tham martensite or bainite.
Ferrite is basically low carbon iron.
Bainite is sort of in between pearlite and martensite.  Pearlite is lamellar, 
martensite can appear "lath"-like at low carbon percentages and acicular or 
even lenticular at higher percentages.  Bainite is best described as feathery.
If you make martensite and then temper it back, you begin to precipitate out 
the carbon as spheroids of iron carbide.  This relieves the strain in the 
lattice and makes it softer.

I have been looking for my copy of the A-36 spec from ASTM.  I thought it was 
0.35%.  Oh, well.  A-36 is made to meet certain mechanical properties.  It is 
made to meet a certain yield strength minimum and a tensile ductility of 25% 
or so, minimum.  No where in the spec is there anything about forgeability.  
It may not be the best stuff for what we do but it works if you do not abuse it.

Steelmaking involves a lot more than gathering up a pile of scrap, melting 
it, casting it into an ingot or continuos billet and rolling it to shape without 
having any idea what the composition is.  Even in the late 19th century, 
carbon analysis and control was relatively well know.  


Hochewa


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