As the name suggests, the fundamental difference between a hot-rolled coil and a cold-rolled coil is the process followed to manufacture them. Though made of carbon and alloy, the processing which is typically squeezing the steel to flatten it, changes the physical properties of the steel. Along with that, the different temperatures applied to them made them different. Furthermore, there are differences between the usages of the two types of steel which we will describe below.
What is hot rolled and cold rolled steel coil?
Rolling is a vital process in metalworking. Rolling is widely used for fabricating different applications and techniques. Rolling leads to improve strength and orientation within the steel. The primary metal rolling procedure is to pass the steel from large rolls which provide the steel with the required thickness and shape.
There are two types of steel rolling process followed in the steel manufacturing:
- Hot rolling
- Cold rolling
A hot rolled coil is the steel which is roll-pressed using a temperature more than 1,700˚F. This temperature is used to generate the products which are easy to work with.
Cold rolled coil is a more processed form of a hot rolled coil. A hot rolled coil is re-rolled at lower temperature mostly in room temperature once the hot rolled coil has cooled. This helps to achieve more surface qualities with more accurate dimensions.
What is the difference among hot rolled and cold rolled steel coil in processing?
As described above during hot rolled coil generation very high temperature is applied (more than 1700 degree Fahrenheit). Whereas for cold rolled steel room temperature is enough.
- During the processing of hot-rolled coil, the manufacturers use a rectangular billet of large size to start the process. Once the billet gets heated, manufacturers sent it to pre-process.
- During the pre-processing, the steel is undergoing through a flattening process to generate a hot rolled coil of a large size.
- Next, it goes through a number of compression stages to get the desired dimensions.
- Once the steel starts to cool down, it shrinks gradually
- As it is cooled down after processing it is not possible to control the final shape of the product. Hence, it is not suitable for applications that need precision results.
As described earlier cold rolled coil is generated after cooling down the hot rolled coil. It is rolled further to take it to the more accurate dimensions and better surface. However, the term rolling typically does not mean rolling it over. It describes a series of finishing processes like polishing, grinding, turning, etc.
Hot-rolled coil generation is less costly than cold-rolled steel manufacturing. The reason behind it is cold rolled steel making needs additional processing. Hence, hot-rolled coil making comes at a lesser price. Besides that cold-rolled steel processing creates internal stresses which release tensions and turn to unpredictable twisting of the material.
How are hot rolled and cold rolled steel coil characteristically different?
A hot rolled coil has following characteristics:
- Due to the cooling process from the extremely hot temperature, it consists of a surface that is scaled.
- As it shrinks during cooling, it develops rounded corners and edges for plate and bar products.
- It does not hold perfectly squared angles and undergoes slight distortions due to the effect of the cooling process.
On the contrary, cold rolled steel is identified by the following properties:
- It has closer tolerances with finished surfaces
- The smooth surfaces feel like greasy to the touch
- Bars made out of it are square with well-defined corners and edges
- Tubes made out of it have better uniformity, concentric shape, and straightness
What are the differences in the usage of the hot rolled and cold rolled steel?
Hot rolled coil steel is used in the following scenarios –
- When minute dimension measurement is not crucial.
- When dimensional tolerances is equally important as the overall strength of the material
- Where surface finishing is not a big concern.
Examples of usage of hot rolled coil:
- In the welding
- Tracks for Railroad
- Construction trades like railroad tracks
- Agriculture equipment
- Truck frames
- Wheel rims
- Water heaters
On the contrary, as cold rolled steel has better surface finishing than hot rolled coil, it is mostly used for products where aesthetic appeal matters a lot.
Examples of usage of cold rolled coil:
- Home appliances
- Metal furniture
- Exhaust pipes
- Filing cabinets
- Shelving and similar products
- Water heaters
What are the differences in the mechanical properties of hot rolled coil and cold rolled coil?
The key differences between the cold rolled coil and hot rolled coil are as follows:
|Property||Hot rolled Coil||Cold rolled coil|
|Tensile Strength||67,000 psi||85,000 psi|
|Yield Strength||45,000 psi||70,000 psi|
|Reduction of Area||58||55|
|Elongation in 2″||36||28|
What are the differences between the cold rolled coil and hot rolled coil based on their performances?
From the mechanical engineering point of view, there is no difference in mechanical properties between the cold rolled coil and hot rolled coil. However, as the cold rolled steel undergoes certain hardening process, the yield strength of cold rolled steel is higher than the hot rolled coil.
What are the differences between the cold rolled coil and hot rolled coil based on their formidability?
Due to the difference in the surface qualities of the hot-rolled coil and cold-rolled coil, the forming factors measure their forming performances. As the surface quality of the cold-rolled steel is better than the hot-rolled coil the forming effect of cold-rolled steel is better than the hot-rolled coil.
What are the differences between the cold rolled coil and hot rolled coil concerning their advantages and disadvantages?
Advantages of Hot-rolled coil
A hot rolled coil has its benefits for different applications for forming it as per the desired result. For example, you can mold shapes as per desire using hot rolling coil like
- Large sheets
- Shaped beams
- Arched or angled pieces
Besides that it is available in many pieces. Hence, manufacturers can create large pieces out of it without compromising the integrity of the material. This is the prime reason that hot rolled coil is mostly used for structural projects.
Disadvantages of Hot-rolled Steel
As the hot rolled coil is reconfigured by applying heat on it and then cooling it, the end finish is usually more unusual and rough. In addition to that hot rolled coil is also less durable than cold-rolled steel. Moreover, hot-rolled coil tends to have more carbon content which is nearly 0.29 percent, which is a concern for forging.
Advantages of Cold-rolled Steel
Cold-rolled steel is harder than the hot-rolled coil. Also, it does not carry the same benefits as a hot-rolled coil as it does not undergo any chemical alteration by heat. As cold-rolled steel is harder, it can retain its shape very well and endures strain hardening. It is estimated that cold-rolled steel products can boost its strength up to 20 percent. Additionally, cold-rolled steel is ideal for aesthetic purposes as it maintains a smoother finish. Besides that due to a lower carbon content which is around 0.18 percent, cold-rolled steel is easy to forge.
Disadvantages of Cold-rolled Steel
As cold-rolled steel is less malleable, you cannot mold it into the desired shapes easily. As a result, cold rolled steel product shapes are limited to:
- Rounded rods
- Tubular rods
- Cubical-shaped rods
- Flat sheets
- Flat strips
Additionally, finding the large cold-rolled pieces is harder than large hot-rolled coil pieces. The reason behind it is the cold-rolled steel pieces contain certain strength and resiliency, and if we try to machine together with the pieces, these properties got lost.