What is Hot Rolling?
Definition: Hot rolling is a metal rolling operation in which the metal is heated above its recrystallization temperature and its plastic deformation occurs when it is passed through the rollers.
What is Hot Rolled Steel?
Hot rolled steel (also known as HR Steel) is a steel which is heated above its recrystallization temperature (above 930 °C) and then it is rolled pressed to a desired shape.
Because of very high temperatures, it is easy to roll-press any steel with less loading on the equipment.
Hot rolling of metals involves reheating of ingots, slabs, blooms or billets at the temperature range of 1200 °C to 1300 °C and then they are passed between two opposite spinning rollers.
The same heated metal piece is sometimes passed back and forth in the same roller with a roll gap being reduced gradually.
Hot rolling of metals is used to manufacture sheets and well as other cross sections like rail tracks, beams, etc.
Why is metal heated before shaping?
Well, the main purpose of heating the metals at very high temperature (above its recrystallization temperature) is to reduce its yield strength.
Also due to such high temperatures, the deformation of metals takes place easily without damaging the mechanical rolling equipment.
For hot rolling of steels, the number of times for which the steels are passed through the rollers depends upon its input size as well as required size of the final product.
Sometimes the metals are passed for 60 to 70 times through the rollers before the metal becomes too cold to roll down further.
There are different types of rollers used for hot rolling operation depending upon the type of applications.
The plain barrel rolls are used for hot rolling of plates, strips, and sheets. While the grooved rolls are used for hot rolling of sections like rails, beams, sheet piles, square section, round section, etc.
Hot rolled steel examples/uses
The uses/examples of hot rolled steel are;
- Hot rolled rail tracks
- Hot rolled I-beam
- Hot rolled steel rods
- Hot rolled steel sheet
- Hot rolled square sections
#1) Hot rolled rail tracks
In this image, you can see the rail track manufacturing being done using a hot rolling of steel.
#2) Hot rolled I-beam
The I-beams which are generally used in construction industries are also manufactured by hot rolling operations.
#3) Hot rolled steel rods
You have already seen this type of rods at least once in your life. These are hot rolled steel rods which are mainly used for construction work.
#4) Hot rolled steel sheet
Hot rolled steel sheets are manufactured from the hot steel metal by gradually reducing the thickness of the heated metal piece.
If these steels are having less thickness, then it can be rolled into coils. And if the thickness of steel sheets is more, then it is kept in a sheet pile.
#5) Hot rolled square sections
Square sections as well as other sections can be manufactured by using hot rolling operation.
Advantages of hot rolling
Advantages of hot rolling are mentioned below.
- Work hardening of the metal does not take place due to hot rolling operation.
- Deformation of large parts is possible in one single pass.
- As the metal is heated above its recrystallization temperature, it possesses low stress and the power required is less.
- The ductility of metal is high, which results in large deformations.
- Through hot rolling, the complex parts can also be manufactured by roll-pressing.
Disadvantages of hot rolling
Disadvantages of hot rolling are mentioned below.
- Friction between the workpiece and roller is very high.
- The cooling of rollers is necessary.
- Handling the heated workpiece is difficult.
Hot rolled steel sheet: Image credits indiamart