Cold Rolled vs Hot Rolled Steel

At Speciality Metals, we have a lot of products to choose from. There are so many questions about applications, lifespans, etc that need to be asked and answered that we have set up a twice weekly series of guides. Hopefully this will give you an idea of what’s possible and what’s needed for every requirement.

One of the questions that we field regularly is: what is the difference between cold rolled and hot rolled steel? This product is cold rolled steel, but it is important to understand what this means when choosing the ideal metal for your requirements.

As well as these help guides, please do contact us if you need any assistance at all. We’re always happy to help.

Let’s try to clear the issue up…

Hot Rolled Steel

Hot rolled steel is easier to produce. It is simpler to shape and form. It’s production is a basic mill process wherein the steel is rolled at high temperature. It begins as a piece of still billet which is then heat treated up to 1700 degrees Fahrenheit (926° Celsius) in a blast furnace. The piece of steel is then rolled through the mill into the desired shape. The entire heat treatment process is carried out at very high temperatures.

Hot rolled steel is produced and recommended for applications where precision is not essential and tolerances are flexible.

What Are The Advantages Of Hot Rolled Steel?

Advantages of hot rolled steel include:

  1. Lower Cost: Hot rolled steel is less expensive to produce than cold rolled steel.
  2. Speed of Production: The manufacturing process of hot rolled steel is faster than that of cold rolled steel.
  3. Dimensional Tolerance: Hot rolled steel has a higher dimensional tolerance, which allows for easier shaping and bending.
  4. Improved Weldability: The surface finish of hot rolled steel makes it easier to weld compared to cold rolled steel.
  5. Construction Industry: Hot rolled steel is often used in the construction industry due to its suitability for large-scale projects and structural steel applications.
  6. Versatility: Hot rolled steel can be used for a wide range of applications, from simple to complex, due to its ability to be easily shaped and formed.

The main advantages of hot rolled us that it is easier to produce and as a consequence it is cheaper in cost than cold rolled steel plate.

And The Disadvantages?

Disadvantages of hot rolled steel include:

  1. Surface Quality: Hot rolled steel often has a rough and irregular surface finish, which may not meet the aesthetic requirements of certain applications.
  2. Dimensional Accuracy: The dimensional accuracy of hot rolled steel is lower compared to cold rolled steel, which may not be suitable for applications that require precise dimensions.
  3. Scale: Hot rolled steel often has a visible scale that must be removed before it can be used, which can be time-consuming and increase the cost of production.
  4. Rust: Hot rolled steel is more susceptible to rust and corrosion compared to cold rolled steel.
  5. Magnetic Properties: Hot rolled steel is often magnetic, which may not be suitable for certain applications that require non-magnetic properties.
  6. Strength: Hot rolled steel may have lower strength compared to cold rolled steel, which may not be suitable for applications that require high strength.

The main disadvantages of steel produced using the hot rolled method is that dimensional imperfections can occur. These are caused by the heating (expanding) and the subsequent cooling down (shrink, warpage). Hot rolled steel can have a rougher surface texture, which can be easily buffed out.

Cold Rolled Steel

Unlike hot rolled steel, cold rolled steel is heated and cooled at the room temperature and then rolled again. The steel then goes through the cold reduction mills, at which point the material is cooled (at the room temperature) and then the forming occurs followed by either press-braking or cold roll forming to produce the desired shape.

When the term rolled is used it often refers to reference myriad finishing processes including turning, grinding, and polishing. In truth these finishing processes modify existing hot rolled stock into an end product. When the term cold rolled is used it refers exclusively to sheets that undergo the afore described compression between rollers. Other shapes like bars or tubes are drawn and not rolled. Bars and tubes are hot rolls and then, once cooled, are formed into cold finished tubes and bars. These are available through our store.

The advantages given by using steel produced in the cold rolled method is that it allows for a wider range of surface finishes. It has a smoother and shinier surface than hot rolled steel. The edges are truer, better defined and better concentric uniformity and straightness to tubes and bars.

The downside is that it is higher in cost to produce and therefore more costly to the end user. Fewer shapes can be produced using the cold rolled method and it is also worth stressing that internal stress can occur when additional treatments are applied. The steel would have to be stress relieved before cutting, grinding and welding if this occurs.

How To Spot The Difference

There are several ways to distinguish hot rolled and cold rolled steel:

  1. Surface Finish: Cold rolled steel has a smooth, precise finish, while hot rolled steel has a rough, blue-grey finish.
  2. Dimensional Accuracy: Cold rolled steel is typically more precise in dimension, while hot rolled steel may have more variability.
  3. Scale: Hot rolled steel often has a visible scale that must be removed before it can be used, while cold rolled steel does not have a scale.
  4. Price: Cold rolled steel is generally more expensive than hot rolled steel.
  5. Magnetic Properties: Cold rolled steel is often non-magnetic, while hot rolled steel is magnetic.
  6. Microstructure: Microstructure examination using a microscope can reveal the differences between hot and cold rolled steel. Hot rolled steel has a grainy and coarse structure, while cold rolled steel has a fine and uniform structure.

Hot rolled plain steel has scaly, non-oily finish with slightly rounded edges and corners. Cold rolled steel has a very smooth surface, oily or greasy finish and very sharp edges.

Which Is Considered Better? 

It depends on the application.

Hot rolled steel has a rough, blue-grey finish and is often less precise in dimension due to the manufacturing process. It is ideal for use in construction, where dimensional precision is not critical.

Cold rolled steel has a smooth, precise finish and is often used in applications where a high level of precision is required, such as in the automotive and electronics industries. It is also often used to produce steel sheets and bars.

In general, hot rolled steel is less expensive than cold rolled steel.

As always, thank you for checking out our blog. We hope that this helps you with your project. 

Please also check out the other articles in our helpful guide series. We have written about aluminium sheeting and checker plate recently to name but two of our articles.

We are also proud to sell this product on our highly popular eBay store, check us out there too.

If you have any further questions, feel free to contact us.

 

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