Temperature: Hot Rolling: Hot rolling is performed at elevated temperatures. The metal is heated above its recrystallization temperature, which is typically higher than 1000°C (1800°F) for most metals. In the case of stainless steel, the temperature range for hot rolling is generally between 900°C and 1300°C (1650°F and 2400°F).
Cold Rolling: Cold rolling is carried out at room temperature or slightly below. The metal remains below its recrystallization temperature during the entire cold rolling process.
Material Behavior: Hot Rolling: During hot rolling, the metal is relatively malleable and ductile due to the elevated temperature. This allows for significant plastic deformation and shaping of the material. Hot rolling reduces the thickness and increases the length of the metal sheet.
Cold Rolling: Cold rolling is performed on the metal when it is in a hardened state. The lower temperature causes the metal to be less malleable and less ductile. Cold rolling primarily focuses on reducing the thickness of the metal sheet while maintaining or improving its mechanical properties.
Mechanical Properties: Hot Rolling: Hot rolling can result in a material with a coarse-grained structure due to the high temperature. This can lead to reduced strength and hardness compared to the cold-rolled material. However, hot rolling can enhance the material's toughness and improve its formability.
Cold Rolling: Cold rolling imparts greater strength and hardness to the metal sheet due to work hardening. The cold-rolled material typically has a fine-grained structure, resulting in improved mechanical properties such as increased tensile strength, hardness, and dimensional accuracy.
Surface Finish: Hot Rolling: Hot-rolled sheets often have a scaled surface due to the exposure to high temperatures. The surface may require additional processing, such as pickling or shot blasting, to remove the scale and achieve the desired surface finish.
Cold Rolling: Cold-rolled sheets have a smoother and more refined surface finish compared to hot-rolled sheets. Cold rolling reduces surface imperfections and enhances the sheet's surface quality.
In summary, hot rolling is performed at high temperatures and offers better formability but may result in reduced strength and hardness. Cold rolling is performed at room temperature, improves mechanical properties, and provides a smoother surface finish. The choice between hot rolling and cold rolling depends on the desired material properties, dimensions, and surface requirements of the final product.
