Hot Rolled Steel

Hot-rolled steel is manufactured by a rolling method of metalworking in which the metallic alloy is passed through paired rolls that determine its shape and size. This metal forming procedure is either classified as hot-rolling or cold-rolling. Hot-rolled steel is produced at temperatures that are above steel's temperature of recrystallization. On the other hand, steel produced by the rolling method at temperatures that are below steel's recrystallization is referred to as cold-rolled steel.

The raw material for the rolling process are large pieces of casting products that are semi-finished such as billets, blooms and slabs. In a continuous casting operation the metal alloy products are put directly into the mills at a high temperature that is recommended for rolling. Smaller metalworking operations start at room temperature, and thus the material has to be heated. Heating can be carried out in oil or gas fired soaking pits in cases involving large work pieces. Small work pieces can use induction heating efficiently. During the working of the material temperature has to be maintained above the recrystallization temperature of steel, and thus constant monitoring has to be done. Re-heating has to be done if the temperature of the material drops below the finishing temperature that is set at 50° or 100° degrees Celsius (122° to 212° Fahrenheit) above the recrystallization temperature.

Hot Rolled Steel Properties:

  • Most hot rolled products are very soft and bendable in small bar sizes
  • The good welding properties and guaranteed strength of hot-rolled structural steel make it suitable for many applications.
  • Hot-rolled plate is a very rough product
  • Hot-rolled steel products are covered with mill scale on their surfaces.
  • The hot-rolled steel comes in plus minus 0.01 inches
  • The cold-rolled steel comes in less than 0.01 inches
  • Steel for pipes is hot-rolled structural steel suitable for manufacture into pipes used for transporting liquids and gases
  • More flexible then cold-rolled steel
  • The finished tolerances are loose

Hot-rolled steel products are covered with mill scale on their surfaces. Mill scale is an oxide which forms on the metal's surface during its exposure to high temperatures and oxygen in the mill. Mill scales do not give a very smooth finish and thus they are removed by the smooth clean surface process or alternatively by pickling. Dimensional tolerances for hot-rolled products are commonly set at 2-5% of the total dimension. (Dieter, n.pag)The hot-rolling method of metal-working is often used in the production of simple cross-sections and metal sheets.