Rolled steel is steel that forms between two large rollers. There are two types: hot rolled and cold rolled. Hot rolled steel goes through the rollers at a temperature of over 1,700 degrees. Cold rolled steel is worked at room temperature. As a result, there is less shrinkage and more accuracy in the measurements of cold rolled steel, so builders prefer it to the hot rolled variety. If you want to be able to tell the two apart, learn a few of the tell-tale signs.
Measure the steel. If it seems to be a bit short on one side and is not completely squared up, then you are more than likely dealing with hot rolled steel. This is because hot rolled steel is much harder to calculate to accurate measurements once it begins to recrystallize. The steel will shrink considerably and in most cases unevenly.
Look at the color and the finish. Hot rolled steel always has a rough blue-gray finish, while cold rolled steel has a smooth gray finish. This is because hot rolled steel takes a considerably longer amount of time to process. As it has to be continually heated, its surface is exposed to the air more, causing it to oxidize faster than cold rolled steel. This accounts for its rougher surface and bluish color.
Assess the number of shapes available. If several different sizes of steel are available in the store's selection, chances are they are hot rolled instead of cold rolled. This is because it is much easier to forge hot steel than cold steel -- so stores carry fewer shapes and sizes of cold rolled steel.
Check how the product bends. Hot rolled steel is much more flexible than cold rolled steel. If the steel you're looking at has very little give, chances are it is cold rolled.
Examine the edges. Hot rolled steel has rounded edges more often than not, while cold rolled steel has exact right angles.
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