Steel comes in various grades, forms, requirements, and finishes. Each steel grade has its own set of characteristics. Hot rolled vs cold rolled steel is another important word we see regularly, similar to the distinctions between 304 and 316 stainless steel.
Stainless steels are extensively popular in automobiles, appliances, aircraft components, electronic components, and other applications. The comparison between the hot rolled vs cold rolled steel is made possible by understanding the different steel forms.
Changing the chemical composition of steel isn’t enough to optimize its properties for each application.
Rolling is a metal forming technique that uses a succession of rollers to change the shape of materials, increase uniformity, and improve mechanical qualities. Hot rolled steel and cold rolled steel are two types of rolled steel.
These steels have unique properties that make them useful for various applications. It’s critical to understand the distinctions between the two forms of rolled steel and how they affect performance when selecting one for a project.
What is Hot rolled steel?
We often refer to steel subjected to a high level of heat treatment as hot rolled steel. That is, the manufacturing takes place at very high temperatures. Large, rectangular metals, commonly known as billets, are the starting point for manufacturers. The current stage heats the billets before the machine sends them for processing.
The process presses the molten steel at 926° Celsius or 1700 degrees Fahrenheit during the hot-rolling process. Steel ideally recrystallizes between 750 and 1,300 degrees Fahrenheit, allowing for simpler forming and reshaping. It might cool down once the machine rolls the steel into the correct form in the mill.
As hot rolled steel cools, it shrinks somewhat. Manufacturers have less control over the final form as a result of this.
Automobile parts, such as wheel rims and frames, Agricultural equipment, Railway equipment, such as rails and train components, and Construction Materials are all examples of hot rolled steel applications that do not need strict tolerances.
Why should you use hot-rolled steel?
Because hot rolled steel has the following advantages for your needs:
- Low Cost: Hot rolled steel requires much less processing than cold rolled steel, making it less expensive.
- Internal Stresses are minimal or non-existent since hot rolled steel cools at room temperature, thus normalizing it. It has little or no internal stresses due to work-hardening or quenching operations.
- Because the machine carries the hot rolling process at very high temperatures, the resultant steel is simpler to shape and form. UB, UC, RHS, SHS, flats, and other hot-rolled steel forms are the most popular.
- It’s perfect for situations where tolerance isn’t a big problem.
What is Cold rolled steel?
Essentially, cold rolled steel refers to hot rolled steel that undergoes extra processing. As indicated previously, rolling encompasses the spectrum of procedures involved in producing the steel, including turning, grinding, and polishing.
The remaining steps transform existing hot-rolled steel into a more refined product. The phrase cold-rolled generally pertains to steels that have undergone compression.
While hot-rolled steel merely entails heating at high temperatures then cooling, cold-rolled steel includes an extra procedure. The production first cools the steel at the cold reduction mills and then re-rolls it at room temperature either by cold roll forming or press-braking. This procedure helps to get the required form and dimensions.
The best applications for cold-rolled steel need better metal surface polishing and tighter tolerances. Some of the common uses include aircraft parts, Mechanical components, Home appliances, Rods, bars, strips, sheets, and metal furniture constructions.
Why Should you use cold-rolled steel?
The advantages you may receive from employing cold rolled steel are:
- Better Surface Properties: Components of cold-rolled steel frequently have smooth and lustrous surfaces empty of scale or corrosion. Thus, making them helpful when aesthetics is the key.
- More strength: they are often more robust and rigid than hot-rolled steel. It makes cold-rolled steel ideal for high-stress applications.
- Higher Precision: cold-rolled steel does not shrink when forming. It enables the creation of more exact pieces with consistent and accurate geometries.
- It offers a large variety of surface treatments.
Key differences: Hot Rolled vs Cold Rolled Stainless Steel
The fundamental difference between these two forms of steel is one procedure. As you may understand, “hot rolling” refers to processing done with heat. “Cold rolling” refers to procedures done at or near room temperature.
Although these approaches impact overall performance and application, they should not be confused with official standards and classes of steel, which have to do with metallurgical compositions and performance ratings.
Steels of different specifications and grades may be either cold rolled or hot rolled—including primary carbon and other alloy steels.
After you reviewed their forming method and various qualities, you indeed have a notion of the difference between hot rolled and cold rolled steel. The following table represents the variations in their mechanical characteristics:
| Properties | Hot Rolled | Cold Rolled |
| Tensile Strength | 67,000 psi | 85,000 psi |
| Yield Strength | 45,000 psi | 70, 000 psi |
| Elongation in 2″ | 36 | 28 |
| Reduction of area | 58 | 55 |
| Brinell Hardness | 137 | 167 |
Asides from the mechanical qualities, the fundamental difference between hot rolled and cold rolled steel is their production temperature. While the rolling of hot rolled steel happens above the recrystallization temperature, cold rolled steel is treated at an average temperature.
Physical Properties
The physical properties of steel also depend on its grade or manufacturing processes. The following are the common physical properties of hot rolled vs cold rolled:
| Properties | Hot Rolled Steel | Cold Rolled Stel |
| Surface | Scaled Surface: Cooling from high temperatures leave remnants on the steel, the surface to make It looks scaly. Non-oily Surface | Smooth Surface: Smooth surfaces usually have an oily-like touch. Oily Surface |
| Corners and Edges | Rounded | Very Sharp |
Appearances and surface quality
The edges and surfaces of hot rolled steel are generally rough. Cooling from intense temperatures leaves the steel surface, making it seem scaly. Thus, such surfaces may need decarburization or other surface treatments to prepare the steel for future operations.
On the other hand, cold rolled steel has a smooth and glossy surface as the processing does not necessitate employing high temperatures. Thus, cold-rolled steel is appropriate for industrial operations without any surface treatments.
As cold rolling occurs below the primary sources’ recrystallization temperatures, grains are not susceptible to recrystallization, resulting in a superior surface polish than in hot rolling.
Material Hardness
Material strength and hardness also assisted discussed previously. The technique of creating cold-rolled steel produces a homogeneous microstructure. This method helps to manufacture metal with increased strength and toughness. It is not overly firm, though, making it readily bendable.
On the other hand, the hot rolling technique requires tremendous heat and fast cooling, preventing the stress from recovering its granules. Thus, the produced metal has significantly higher strength and hardness than cold-rolled steel.
Internal stress
Steel strength and hardness considerably impose internal pressures on the material. Therefore, cold-rolled steel with better stability and hardness has more substantial internal stresses than hot rolled steel. It is vital to release such strains before processing the material to avoid the warping of the final product.
The cold rolling process’s enhanced strength and hardness are more substantial internal tensions. It would be best to release these tensions before treating the material; otherwise, the finished component or product may undergo warping.
Recrystallization point
One of the essential aspects of hot rolled versus cold rolled steel is the recrystallization point. Cold rolling happens when the metal substance may create “new grains.” The rolling and twisting of the metal can obliterate previous grains. Cold work on steel may impair its strength.
Therefore, producers add a final annealing phase. This technique requires heating the steel to 1,333 – 1,400 degrees Fahrenheit (just above the recrystallization point of steel).
Cooling of the steel proceeds very slowly without bringing it to room temperature too rapidly. In this technique, the metal may establish a homogeneous microstructure to reset its grains.
In specific, the fabrication of hot rolled steel occurs at over 1700 degrees Fahrenheit, that is larger than the recrystallization temperature of steel. This condition is vital for the easy forming and shape of the metal.
Distortions
Hot rolled steel encounters slight distortions (e.g., sheet metal bending) since the cooling process creates trapezoidal shapes and forms. Cold rolled steel features flawlessly squared angles with well-defined corners and edges. The tubes manufactured also have great concentric consistency and superior straightness.
Cost Differences
Hot rolled steel is often less costly than cold rolled steel. The rationale for this is not far-fetched. The manufacture of this steel type does not entail any delay or subsequent processing.
You don’t need to re-heat and reform, as with cold rolling. Cold finishing frequently comprises additional procedures, including cold drawing, turning, grinding, and polishing. The extra manufacturing steps make cold-rolled steel more costly than hot-rolled steel.
Why is cold rolled steel preferred than hot rolled steel?
Statistics reveal that cold-rolled steel is around 20 per cent stronger than its hot-rolled cousin. Steel is compressed during the cold-rolling process to obtain a lower density but better tensile strength. The result is a more robust metal better suited for high-stress applications than hot-rolled steel.
On the other hand, cold-rolled steel is also more malleable than hot-rolled steel. In other words, it may bend under more severe tension without breaking. With cold-rolled steel being more pliable than hot-rolled steel, producers can deal with it more readily, changing the metal’s form to match their demands.
You should anticipate hot-rolled steel to cost cheaper than cold-rolled steel. Since cold-rolled steel needs a different stage in its manufacturing process, firms must employ more resources to create it. Therefore, companies usually charge more for cold-rolled steel than hot-rolled steel.
Hot rolled vs cold rolled Stainless Steel: Which is better for your application?
Cold rolled steel seems more costly than hot rolled steel due to the extra operations required and the increased strength.
Overall, cold rolled steel will be stronger than hot rolled steel. Cold-rolled steel has grains, whereas hot-rolled steel has not. It’s significant because cold-rolled steel is most effective when used with the grain and is much weaker when used against it. Because hot rolled steel has no grain, its strength is unaffected by its orientation.
Another factor to consider when deciding whether to use hot or cold-rolled metal is what construction methods you intend to attach the metal and what function it will play in your project.
Cold-rolled steel should be avoided if you want to mill your project’s resources further. If you don’t take care, cutting it in the wrong direction might cause warping or otherwise compromise the metal’s structural integrity.
It differs from hot-rolled metal, which does not distort when machined due to grain’s lack. Both of the rolled steels (hot rolled vs cold rolled)will weld just fine if you plan on welding them, but you should keep in your mind that after welding, cold-rolled metal will take the appearance of some of the other characteristics of a hot-rolled metal.
Mill scale accumulates when heated steel, cold-rolled steel will have a better overall finish than hot-rolled steel. However, some people like the “look” of hot-rolled metal. For steel design purposes, they’ve put it on the exterior.
Conclusion
Hot-rolled and cold-rolled steel are similar in that they both entail a manufacturing procedure in which steel is subjected to high temperatures and subsequently pressed. However, only cold-rolled steel receives extra pressing at room temperature. It’s a modest step compared to the overall steel manufacturing process, but it boosts the metal’s strength and flexibility.
However, this article directly compares hot rolled vs cold rolled steel, showing the key differences. Each steel type is more suited for particular purposes than others. Therefore, recognizing their qualities, advantages, and drawbacks is crucial.
Besides, this article will also enable designers and project contractors to guarantee projects’ efficient and effective execution. Stay always with metalpie, and we always try to provide the latest information for your query.