Steel mills produce two standard types of surface finishes depending on how the steel was rolled. If sheets of steel are rolled when they are still hot, a dark scale forms on the surface. This scale can be removed by cleaning or machining. If steel sheets are rolled after they have been allowed to cool, it is known as cold rolled steel. Cold rolled steel has a much smoother surface than hot rolled steel. In addition to an improved surface, cold rolling also strengthens the materials and allows for accurate sizing and shaping of the metal.
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