[TheForge] A36 vs 1018

Sat Jun 14 07:58:26 2003

To All,
A-36 is the general spec for hot rolled material used in structural 
applications.  It is made to a rather loose chemistry with about .35% carbon max and up 
to 1.5 % manganese (I think, I don't have my spec book handy).  All of the 
usual suspects like sulfur, phosphorous, silicon and manganese are controlled to 
reasonable limits. It is made to meet certain minimum mechanical properties, 
tensile strength, yield strength and elongation. The final mechanical 
properties are determined by the chemistry and how hot is finishes on the mill.  You 
make it stronger by adding manganese and you control the ductility with carbon. 
 The structure can be variable as well as the quality.  You are buying cheap 
and dirty, do not expect aerospace grade material.  Whether you buy a 36" wide 
I-beam or 1/2" square it is the same material, more or less.
All steel is hot rolled, some is cold finished.  1018 or 1020 or whatever is 
hot rolled to maybe 20% oversize for a finished dimension.  It is then pickled 
to remove the hot roll scale and cold rolled to final size.  Chemically there 
is no difference between hot and cold rolled of the same spec.  Mechanically 
it is a little stronger, i.e., higher tensile and yield strengths in the cold 
finished condition.  It is dimensionally more accurate as the cold rolling 
process can be more carefully controlled. It is done slower and in smaller 
quantities. Hot rolled has sort of rounded corners or maybe natural radii on the 
edges; cold rolled will almost be sharp.  For most applications it does not make 
any difference except you will get what you pay for.
Since the finish on cold rolled is radically different that hot rolled and if 
you combine the two in a project you have to render the final finish to the 
lowest common denominator, which is what hot rolled would look like.
The late and great Francis Whitaker took great pleasure in bemoaning the fact 
that A-36 was crap.  How often was he wrong?

Hochewa
BS, MeTE, Virginia Tech, 1972
Ph.D., MeTE, University of Hard Knocks

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