The Difference between Hot Rolled and Cold Rolled Steel
Steel is a super alloy that has found fundamental resonance with the construction and engineering activities of entire diversity. The invention as steel (as opposed to the iron) re-defined the building tasks because of its noted attributes like sturdiness, high tensile strength and corrosion resistance among others. Dedicated metallurgical interventions were done to develop differentiated matrix of steels. Hot rolled and cold rolled steel types relate to the rolling processes that are employed when forming base products like stainless steel bars, sheets, steel round bars and slabs which are then used for other products of direct utility. While hot and cold rolled steels are not distinguished through different grades (which are more function of alloy composition), the techniques involved in both processes do generate specific distinctions in the two types.
Hot rolled and cold rolled steels
The difference is exemplified in the name – hot and cold rolled. The steel that is rolled at a temperature of 1700 degree Fahrenheit which is the re-crystallization temperature of steel is called as the hot rolled type. The one which is rolled below this re-crystallization temperature is called as cold rolled steel. The significance emanates from this temperature itself. As said, this is the re-crystallization temperature, the steel gets reformed and the atoms are realigned during the hot rolling process. The steel is pressed very hot between the rollers that generate the desired dimensional characteristics through rolling process. However, there is a twist in this process and the hot steel when cools off to room temperature slowly loose the shape and size attributes slightly of course! This means that the finished hot rolled steel displays minor imperfections like scales and other texture imperfections which are superficial only. This makes hot rolled stainless steel bars or other products less suitable for making the components in which very high dimensional precision and surface perfection are required. However, the rolling at a temperature above re-crystallization (hot rolling) also has an inherent advantage because the steel is reformed and the internal stresses that are generally accumulated during mechanical cold rolling are not present.
The cold rolled steels exhibit better finish!
Cold rolling is not a separate process but which is done post hot rolling. The hot rolled steel when cools down is again pressed in the rollers but this time the temperature is near to room temperature as opposed to the re-crystallization temperature of 1700 degrees Fahrenheit in the hot rolling process. The steel is thus not re-formed in cold rolling and stresses may develop to a varying extent due to the same factor. However, the advantage is that cold rolled steel exhibits much smoother finish and texture characteristics. This also means that lesser processing and finishing is required when making components with cold rolled steel. This makes cold rolled steel round bars and sheets suitable for use in high precision applications. Cold rolled steel however also has higher tensile strength and the shape and dimensional features are not lost post rolling. The additional time and process involved in cold rolling make the process expensive as compared to the hot rolled steel manufacture.