Process cooling is one of the vital elements of metal processing, but it is often overlooked. In the production of steel, cooling is necessary to increase the material strength, reduce the risk of warping, and also create the desired surface finish. Depending on the requirements, the cooling process may be done by either steel bars or raw steel billet.
Steel bars are commonly cooled by passing them through a cooling bed, which is typically a conveyor system with layers of metal plates, often with water or other coolant running between the plates. This serves to cool the steel plates, during which time it may also be rolled and cut, so as to create the desired shape and size. Cooling beds may also be operated without coolant, in which case the steel bars are cooled by passing only air through the bed. Steel bars cooled this way are usually used as cold rolled steel in construction.
Raw steel billets, on the other hand, have to be cooled via different mechanisms. Usually, the process begins with annealing, which is a similar process to normalizing but at much higher temperatures. This heating simulates the natural cooling pattern of steel and eliminates any potential issues such as warping, hardening, and brittleness. After annealing, the steel is cooled slowly. This process can be done either into an inert atmosphere, such as nitrogen or argon, or quenching the steel in a water bath. After quenching, the steel is tempered to its desired hardness level.
The cooling rate of steel billet is important to ensure that the grain structure of the material does not change. To do this, the cooling rate must be controlled to within a very narrow range. Too fast cooling rate will result in a metallurgical structure that is too brittle, whilst too slow cooling rate will produce a structure that is too soft. Thus, the cooling rate must be adjusted to ensure the desired outcome.
In conclusion, the choice of process cooling for steel bars or raw steel billet depends on the end product being produced. For mild steel, a cooling bed or slow cooling process is usually the most suitable, whilst for alloyed steel, a quenching and tempering process may be more appropriate. Nevertheless, it is important to maintain the correct cooling rate in order to obtain the desired metallurgical structure.
