Producing and manufacturing steel is accomplished in several different ways, and many people get confused by the terms hot rolling and hot forging. However, they are certainly not the same thing. In producing steel, you can use several processes; however, the rolling method is by far the most common of all of these methods. In rolling, the billet/ ingot / bloom goes through the various shapes of a pair of rotating rolls. As a result, the length of the metal is increased and the material cross-section is reduced. It is used frequently for the making of plates, tubes, solid bars, structural steels like angle, channel, beams etc.
More About Hot Rolling of bars
There are also several types of rolling, including skew-rolling, cross-rolling, and longitudinal rolling. Among the many benefits of rolling are that it deforms the internal structure to create a alloy steel with a structure that is more dense and elongated and also improves the mechanical properties. The higher the reduction ratio the higher are the improved internal properties but then greater are the costs. The only disadvantage is that as we hot roll, it happens at high speeds hence for higher alloy grades, which require controlled cooling etc, it is difficult to control the cooling of materials soon after rolling, special arrangements have to be made. Also the temperature for rolling for alloy steel is slightly higher than other low alloy or mild steel. Hot rolling of bars is usually prevalent for upto 160mm although some mills in India also give higher sizes .
What Is Hot Forging?
Hot forging can be either open die or closed die forging. Open die is used for making long bars, step shafts, rings etc and closed die is for making components with different shapes. Hot forging greatly improves their mechanical properties and microstructures. Open die forging is mainly used for larger cross sections from 150mm onwards to upto 2m or any size , as it depends on the capacity of the equipment. The surface finish of the open die hot forging bar is not as uniform as the hot rolled bars . However, the hot forged bars can be cooled under controlled temperature hence more appropriate for higher alloy steels. It is generally observed that for the same size, hot forging requires a lesser reduction ratio than hot rolling.
Today with advancement of steel making and steel processing technologies, it is more important to study the required mechanical and metallurgical properties of the material as either of the processes can help achieve them. If both processes are able to achieve the properties for example, if both processes can achieve the required mechanical properties but an improved microcleanliness requires higher reduction ratio then hot rolling would be a more reasonable option provided the sizes are less than 160mm.