The principle of steel rolling heating furnaces and rolling processes
Release time:
2026-04-23
Purpose and heating process
The purpose of heating is to raise the billet to a uniform temperature (austenitic structure) suitable for rolling. After the temperature is increased, the first thing that happens is that the plasticity of the steel is enhanced, the deformation resistance is reduced, and the steel becomes easier to deform. For example, the deformation resistance of T12 steel at room temperature is approximately 600 MPa, while when heated to 1200°C, the deformation resistance drops to around 30 MPa, which is only one-twentieth of the deformation resistance at room temperature. For steel with an appropriate heating temperature, during rolling, a larger reduction can be used, reducing equipment accidents caused by wear and impact, improving the productivity and operating rate of the rolling mill, and reducing rolling energy consumption. Secondly, heating can improve the internal structure and properties of the billet. Uneven structure and non-metallic inclusions are homogenized through the diffusion effect of high-temperature heating. The heating temperature and uniformity are indicators of heating quality. Steel with good heating quality can easily obtain finished products with correct cross-sectional shapes and precise geometric dimensions. The final heating temperature of the billet in the furnace is determined after considering the rolling process, the structural characteristics of the rolling mill, and the structure of the furnace. The time required to heat to the specified temperature depends on the size of the billet, the steel type, the adopted temperature system, and some other conditions.
The billets receive heat in the furnace through convection and radiation. The former is the flushing of the furnace gas over the surface of the billets; the latter is the radiation heat from the furnace gas and the hot furnace lining. The heating furnace is controlled in three sections along its length: the pre-heating section, the heating section, and the equalizing section. When the billets enter the pre-heating section of the heating furnace, the heat flow gradually increases. When they reach the heating section, the heat flow remains basically unchanged. When they reach the equalizing section, the heat flow gradually decreases. Within the equalizing section, the surface temperature of the billets remains basically constant, while the temperature difference across the cross-section gradually decreases. The heat absorbed by the billet surface is diffused inward through heat conduction. The smaller the heat flow delivered to the surface of the billet, the larger the heating area, the smaller the cross-sectional size of the billet, and the greater the thermal conductivity of the steel, the smaller the temperature difference across the cross-section. Generally, steel with a larger cross-section requires a longer heating time than steel with a smaller cross-section, and alloy steel requires a longer heating time than carbon steel.
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