Rolled Steel Information
An alloy is simply a mixture of metals melted together to
form a new metal with characteristics distinct from those of the metals
from which it is made.
What is a
A steel alloy is an alloy that is primarily iron, with
small quantities of other elements mixed in during the melting
process which vary the properties of the iron to maximize a particular
characteristic of the final alloy.
Some make the iron not rust (chromium and nickel), some
make the iron
possible to harden with heat treatment (carbon), Some make the iron
easy to machine (lead), and so on. By varying the type and amount of
the alloying element, even in minute quantities, a huge range of steels
is produced, used for a myriad of industrial purposes.
Why does Hot
Rolled Steel have a
rough, blue-grey finish, while Cold Finished Steel has a smooth grey
Hot Rolled Steels are just that - They are heated up
red-hot and pushed through rollers that squeeze the metal, literally
squishing it into a particular profile, depending on the shape of the
rollers. The process takes a long time, and because the steel is so hot
for so long in the open air of the steel mill, the surface of the metal
has has a long time to oxidize, producing a thick, tough oxide scale
with the characteristic blue grey finish of the final product.
Cold Finished Steels are just that - the final rolling is
done when the steel is cold (room temperature), the whole operation
bathed in oil, so the finished product is unoxidized, the grey of the
actual steel, and as smooth as the rollers that do the processing.
Why are there
so many shapes available in Hot Rolled Steel and so few in Cold
Steel is a very tough material when it is cold. However,
if it is heated past a particular temperature (usually a red-heat) it
immediately turns plastic and can be bent, formed, hammered, and
squeezed very easily. For example, few of us would be able to bend a
bar of 1” thick steel at room temperature no matter how hard we tried,
but if the middle of the bar were heated until it glowed a healthy
cherry red color (about 1650 degress Fahrenheit), most of us would have very little
trouble bending the
bar back upon itself until both ends touched. And when it cooled it
would regain it’s toughness and strength in that bent condition.
This means that the intricate profiles apparent in, say, a
Beam or Channel are formed fairly easily in the hot condition, but
would be impossible to produce in the cold condition, and only flat,
hex or round shapes that are relatively simple profiles are available
in Cold Finished Steels.
Can Hot Rolled
Steels be chemically
colored or patinated?
No. The chemical coloring of metals relies on the action
of the chemicals with the metal itself. The only surface exposed on a
Hot Rolled Steel product is the blue oxide scale, which is virtually
inert. In order to color the metal, either the grey of the base metal
must be exposed by grinding and then can be colored, or pigmented
lacquers or paints must be used on the surface. Because the surface is
rough, it takes paints and lacquers very well.
necessary to specify the alloy as well as the shape and size?
There are lots of steel alloys, and they are very
important to the eventual success of the
project, but are more an issue for the engineers and fabricators than
the architect. They will be far more aware of which physical
characteristics of each of the alloys will dictate the appropriate
alloy for the job, and their choice of alloy will not affect the final
aesthetic or finish since the Hot Rolled Steel alloys all have similar
finish characteristics. What it all means is, that for aesthetic
purposes all the alloys are interchangeable.
If this area is of interest, look up the ASTM
specifications of all the alloys at www.
Things to be aware of:
1) Hot Rolled Steel products are NOT a consistent blueish color.
This is particularly true with hot rolled sheet, over the surface of which the color
varies dramatically, more blue at the edges,
more grey in the center of the sheet.
2) The shapes available in hot rolled steels are availble in
12ft, 20ft, and sometimes 40ft lengths, so check with your supplier.
3) The blue scale finish on hot rolled products is incidental to
the process of producing the product, and so, is not controlled in any
way. This gives rise to fairly strong inconsistencies in the finish,
particularly in sheet and plate.
4) Again, the blue scale on the metal prevents any chemical
coloring on the surface ot the metal unless the scale is removed,
exposing the bare metal beneath.
5) Most hot rolled products are very soft and bendable. This is
really only noticable in the smaller bar sizes, but it can affect the
final product if you are relying on the product to take a lot of strain.
If you are looking for a stiffer product, use Cold
6) Hot rolled plate is a very rough product, and should be
treated as such.
7) All hot rolled products weld, bend, drill, and form very
easily, and as well are the least expensive of the steels, giving rise
to the least expensive finished product of any of the steels.
8) Nearly all metalwork involves welding or soldering the
metal. How those welds are addressed is often the difference between a
hack job and good craftsmanship. If hot rolled steel is welded, either
the un-dressed welds are left as a part of the aesthetic, or they will
have to be ground down by hand. Grinding and dressing the welds, of
course, removes the blue scale at the weld zone while leaving the blue
scale on the rest of the material. This aesthetic difference must be
addressed at every weld. It is possible to return the color, but not
the texture, of the blue scale at the ground weld joint where the metal
has been exposed by heating up the joint red hot and allowing to cool.
9) A reminder - Pipe is specified by the inside diameter, Tubing
is specified by the outside diameter.
10) Hot rolled steel stock products mostly have a rounded
appearance at the corners and edges and relatively inexact dimensions,
whereas cold finished steels are much smoother and more precise.