Differences Between Hot Rolled Coil and Cold Rolled Coil

Steel is available in a wide range of shapes, specifications, finishes, and grades. In fact, there are more than 3500 grades of steel as listed by the World Steel Association. A variety of processes are used for manufacturing various grades of steel. The two most popular steel products are hot rolled steel coil and cold rolled steel coil. This article is focused on HR coil vs CR coil.

Hot Rolled Steel (HR Steel)

The hot rolled coil is made of continuous casting slab as raw material. After heating and high-pressure water descaling, it enters the rough rolling mill and the finishing mill. After cooling down, it will be coiled for sale. The hot rolled coil is a kind of steel where the processing is done at a temperature of more than 1700 F. It is higher than the recrystallization temperature of steel which makes it easier to work with. Hot-rolled products have excellent properties such as high strength, good toughness, easy processing and good weldability, so they are widely used in manufacturing industries such as steel, construction, machinery, boilers, and pressure vessels.

The HR steel plate and bar products have slightly rounded edges and corners due to shrinkage during the coding process and the finishing isn’t as precise. One of the biggest advantages of HR steel is that the processing requirements are less than that needed for cold rolled steel. It also results in a cheaper cost of production.

HR steel is mainly recommended for applications where finish and tolerance aren’t as important as the overall structural strength. Hot-rolled coils have excellent properties such as high strength, good resistance, easy processing and excellent weldability, and are widely used as cold-rolled substrates, manufacturing ships, cars, bridges, buildings, machinery, oil pipelines, pressure vessels, etc.

Common Applications:

(1) After annealing, it is processed into cold rolled products;
(2) Can be galvanized for other uses;
(3) A panel that basically does not need to be processed.

Cold Rolled Steel (CR Steel)

Using hot-rolled steel coil as raw material, after pickling to remove oxide scale, cold continuous rolling is carried out, and the finished product is cold rolled coil. The cold hardening caused by continuous cold deformation increases the strength and hardness, but reduces the toughness and plasticity. Cold-rolled coils can be used as raw materials for hot-dip galvanized coil with annealing lines. The weight of the rolled hard coil is generally 6~13.5 tons, and the inner diameter of the steel coil is 610mm.

It is manufactured by processing the hot rolled steel at room temperature. It results in a better finish and precise dimensions as compared to the HR steel. Simply put, cold rolled steel is nothing but hot rolled steel that undergoes a lot of additional processing at close to room temperature leading to better steel products in certain respects. Some of the processes include turning, polishing, and grinding.

Cold rolled steel has a better surface finish as compared to HR steel and it has a smooth surface. It also has better-defined corners and edges.

One of the biggest advantages of cold rolled steel is that it is stronger as compared to HR steel and this is why it is preferred in applications where precision is much more important. Also, it has a better surface finish which makes it the preferred choice in applications where aesthetics are more important.

As far as the technical specifications are concerned, the HR coil has a tensile strength of 67,000 psi whereas cold rolled coil has a tensile strength of 85,000 psi. Similarly, there is a huge difference in the yield strength between these two types of steel.

HR Coil vs CR Coil

By Definition

Steel billets are difficult to deform and process at room temperature. Generally, they are heated to 1100-1250 °C for rolling. This rolling process is called hot rolling. Most steels are rolled by the hot rolling process. However, because iron oxide scale is easily formed on the surface of the steel at high temperature, the surface of the hot-rolled steel is rough and the size fluctuation is large.

In order to meet the needs for smooth surface, accurate size, and good mechanical properties, hot-rolled products are used as raw materials and cold produced by rolling method, that is, rolling at room temperature. From a metallographic point of view, the boundary between cold rolling and hot rolling should be distinguished by the recrystallization temperature. That is, rolling below the recrystallization temperature is cold rolling, and rolling above the recrystallization temperature is hot rolling. The recrystallization temperature of steel is 450 to 600°C. Therefore, cold rolled coil is obtained by pickling and cold rolling of hot rolled coil.

Features

(1) The precision is higher, and the thickness difference of the cold-rolled products does not exceed 0.01~0.03mm.
(2) The size is thinner, and the thinnest cold-rolled steel can be rolled at 0.001mm; the hot-rolled steel strip can now reach the thinnest 0.78mm.
(3) The surface quality is more superior, and the cold-rolled steel sheet can even produce a mirror surface; while the surface of the hot-rolled sheet has defects such as iron oxide scale and pitting.
(4) The cold-rolled sheet can adjust its performance such as tensile strength and process performance such as stamping performance according to user requirements.

Cold rolled coil is rolled at room temperature, and its hardness is high. Hot-rolled steel is rolled at high temperatures. So hot-rolled sheet has low hardness, easy processing, and good ductility. Cold-rolled sheets have high hardness and are relatively difficult to process, but are not easily deformed and have high strength.
Hot-rolled sheet has relatively low strength and poor surface quality, but good plasticity. While cold-rolled sheet features high strength, high hardness and high surface finish. Generally, the HR sheet (0.35~4mm) is thicker than CR sheet (0.2～4mm).

Common Code

China: (hard, high carbon content) Q235, Q215, Q195 (soft, low carbon content)

Japan: SS400-SS330-SPHC

CIS: 08KP–08YU(strong deep drawing, deep drawing)

Germany: ST12-ST13-ST14 (strong deep drawing, deep drawing)

One of the main uses of hot-rolled coil is as the cold-rolled coil substrate. The use of hot-rolled coils after cold-rolling processing mainly includes galvanized sheets, color-coated sheets, and electrical steel.

The demand for hot-rolled pickled coils is mainly concentrated in the automotive industry, compressor industry, machinery manufacturing industry, spare parts processing industry, fan industry, motorcycle industry, steel furniture, hardware accessories, electrical cabinet shelves and stamping parts of various shapes, etc. .

The base metal of the hot-rolled galvanized sheet is a hot-rolled coil. Compared with the hot-dip galvanized sheet, it has obvious cost advantages because the cold rolling process is omitted, which can partially replace the thick-gauge hot-dip galvanized sheet.

Final Thoughts on HR coil vs CR coil

Overall, these are some of the major differences between these two types of steel. The additional processing done for manufacturing CR steel gives it a better finish and more strength. However, cold rolled steel is expensive as compared to HR steel due to additional processing. HR steel is popular in applications where aesthetics and precision aren’t as important as the overall strength. While cold rolled steel is suitable for applications where aesthetics are much more important or in places where steel is going to be seen. In automotive steel, the amount of cold-rolled and hot-rolled steel accounts for more than 50%, of which hot-rolled coils are widely used in trucks and passenger cars, frames, beams, carriage beams, wheels, etc. Here we have reviewed HR coil vs CR coil. If you want more details, please contact Wanzhi Steel.