By the name, it is quite understood that cold & hot rolled steel hold some differences. But it is not due to the difference in their grade or specification, it is due to how they are treated inside the mill or factory during the manufacturing process.
Hot rolled steel utilizes the high temperatures to roll the steel, whereas, steel is processed in cold temperature once it is off with the annealing (heating element & allowing it to cool slowly) process.
What is Hot Rolled Steel?
• It is prepared by rolling the steel at a high-temperature point (usually 1700 degree F) which is even beyond the re-crystallization temperature of the steel.
• Once the steel reaches beyond its re-crystallization temperature, it gets easy to shape, mold or form the steel into larger sizes.
• This type of rolled steel is cheaper comparative to old, as it doesn’t require re-heating or any further process.
• However, this type of rolled steel doesn’t give much scope to manage the size & shape of the material – once it cools off & shrink as compared to cold.
Uses of hot rolled steel
This type of steel is utilized in the making of steel bars for making railroad tracks & I-beams by the welding & construction settings. This type of steel fits best in product engineering where there is not much need for précised shape & tolerance.
What is Cold Rolled Steel?
• It is basically the extension of hot rolled steel – the one which has been further processed.
• The steel is later processed inside the cold reduction meals and when the material is cooled enough it is again heated and brought slowly to the cooling point with help of the process annealing.
• This process makes the steel have finished surface & close dimensional tolerances.
• The process is followed by “cold finishing” which involves 4 steps – cold drawing, Turning, Grinding and Polishing.
• These four stages are performed as each has its own advantages. Cold drawings discard the need to have costly thermal treatments and increases the tensile strength & yield of the material. Turning helps to scrape out the imperfections from the surface. Grinding helps to narrow the tolerance range and polishing helps to bring the surface finish to the finished product.
• The cold is in demand over hot rolled one as it brings superior surface finish, tolerance & straightness to the product.
Uses of Cold Rolled sheet
It fits well to the project requirements where there is immense need of surface condition, concentricity, tolerance and straightness.
So, these were the few factors of hot and the Cold Rolled sheet that makes them different from each other.