When hot rolling is referred to the rolling process of a rolling material ( slab , stick , wire , etc.) at a temperature above the recrystallization temperature of the processed metal. For steel , this is usually 720–1260 degrees Celsius, for other metals the temperature ranges are in other orders of magnitude (aluminum, for example, 250 to 500 degrees Celsius).
The advantage of hot rolling is that the rolling stock is softer at higher temperatures and can therefore be formed with less force. In steel, the metal is also in the austenitic instead of the ferritic state (i.e. the iron atoms are face-centered cubic instead of body-centered cubic). In the austenitic area, deformation degrees of up to 250 (i.e. geometric ratios of input to output size up to 1: 250) are possible (example: typical slab thickness in a hot strip mill is 240 mm, final thicknesses are a minimum of 0.8 mm - with lower thicknesses the strip cools between the individual rolling processes too much). In the flat steel sector, degrees of deformation of up to 120 are possible in a typical hot strip mill. For final thicknesses below 3 mm, however, steel is often cold rolled (e.g. rolling in the purely ferritic area of the steel). With cold rolling, only degrees of deformation of up to 10 can be achieved without intermediate annealing.
Plants used for hot rolling are hot wide strip mills for sheet metal as well as wire and bar mills for round and edged material and profiles. Block and slab rolling mills are used to manufacture the required starting material (billets and slabs).
With aluminum , depending on the alloy, hot strip thicknesses of two to six millimeters can be achieved, below which the heat is lost too quickly due to the high conductivity. For further thickness reductions, the sheet must be cold-rolled.
- Comprehensive Metal forming and welding glossary with technical terms for metal processing (accessed on May 15, 2010)