Steel is available in a variety of grades, forms, requirements, and finishes. These steel grades each have special characteristics. This is the reason why this metal is frequently used in automobiles, appliances, aircraft components, electronic components, and other things. The hot rolled vs. cold rolled steel comparison results from the necessity to comprehend the many forms of steel that are available.
More than just altering the chemical makeup of your steel is required to optimize its properties for each application. The shape, uniformity, and mechanical qualities of steel materials are enhanced through rolling. Cold rolled steel and hot rolled steel are the two primary subcategories of rolled steel. These varieties of rolled steel are ideal for various applications because of their unique qualities.
When selecting the different kinds of rolled steel for your project, it is crucial to comprehend the variations between them. Such knowledge will enable you to avoid additional procedures while saving money and time. The distinctions between hot- and cold-rolled steel, as well as their advantages, drawbacks, and uses, are discussed in this article.
In order to change the shape, increase uniformity, and/or improve the mechanical characteristics of materials, rolling is a metal forming process that makes use of a number of rollers. The two categories of rolled steel—hot rolled steel and cold rolled steel—show diverse qualities that make them appropriate for various purposes. It’s critical to be aware of the distinctions between the two forms of rolled steel and how they impact performance when selecting one for a project.
Hot rolled steel
Hot rolled steel is commonly used when precise shapes and tolerances are not essential. Steel that has undergone the rolling process at a temperature higher than its recrystallization temperature (about 1700° F or above) is known as hot rolled steel. The material is more formable and workable than untreated steel, making it simpler to handle during future processing steps.
Initially, a huge, rectangular piece of metal known as a billet is used in the hot rolling process. The billet is first heated and rolled into a big roll. It goes through a sequence of rotating rollers while it’s still hot to get the proper proportions. The rolled steel is subsequently wound into coiled rolls and allowed to cool in the manufacturing of sheet metal. The processed material is chopped into the required units and packaged in production processes involving different forms.
Advantages Hot rolled steel
– Easier to make: heat it up, push through, cool down and that’s it!
– Cheaper than cold roll steel
– Hot rolled steel is allowed to cool at room temperature and it’s free from internal stresses that can arise from quenching or work-hardening processes
– Most popular shapes are hot-rolled (UC, UB, SHS, RHS, PFC, flats etc.)
Disadvantages Hot rolled steel
– dimensional imperfections caused by heating (expanding) and cooling down (shrink, warpage)
– rough texture on a surface, need to be removed and buffed before painting
– Slight distortions
The uses of hot-rolled steel
There is less control over the final shape of hot-rolled steel since it contracts significantly when cooling. Because of this, it is frequently employed in applications that do not necessitate exceedingly tight tolerances, such as:
auto components (e.g., frames and wheel rims)
materials for construction (e.g., I-beams)
railroad machinery (e.g., tracks and railcar components)
Cold rolled steel
While hot rolled steel is heated then cooled, cold formed steel is heated and cooled at the room temperature and then rolled after again. The steel is processed further in cold reduction mills, where the material is cooled (at the room temperature) followed by forming the material by either press-braking or cold roll forming to achieve the desired shape.
The term “rolled” is often used just to describe a range of finishing processes such as turning, grinding, and polishing, each of which modifies existing hot rolled stock into a more refined product. Technically, “cold rolled” applies only to rolled sheet metal that undergo compression between rollers. But forms like bars or tubes are “drawn” not rolled. Hot rolled bars and tubes once cooled, are processed into what we call “cold finished” tubes and bars.
Advantages Cold Rolled steel
– accurate shape (consistent and straight)
– a wider range of surface finishes
– a smooth and shinier surface
– bars are true and square and have well-defined edges and corners
– Tubes have better concentric uniformity and straightness.
Disadvantages Cold Rolled steel
– more expensive
– fewer shapes available cold-rolled (sheets, box section shapes: CHS, SHS, RHS)
– additional treatments can create internal stress within the material; this can cause unpredictable warping if the steel is not stress relieved prior to cutting, grinding, or welding.
The uses of cold-rolled steel
Applications that call for tighter tolerances and superior surface finishes frequently use cold rolled steel. Common components and goods include.
- structures for aerospace
- devices for the home
- Metal furnishings
- sheets, rods, sheets, and rods
- Mechanical Substances
Hot rolled vs cold rolled steel
Hot rolled steel comes with a scaly surface, slightly rounded edges and corners and the surface is non-oily. Cold rolled steel has an oily or greasy finish, very smooth surface, and very sharp edges.
As previously mentioned, the temperature at which they are processed is the primary distinction between hot rolled steel and cold rolled steel. In contrast to cold rolled steel, which is rolled below the material’s recrystallization temperature, hot rolled steel is rolled above the temperature at which the material recrystallizes. Beyond this characteristic, there are a few further differences between the two materials, such as the following:
- Surface level. Hot rolled steel typically has rough edges and surfaces that need to be treated, such as decarburization, in order to use it in following production processes. Cold rolled steel, on the other hand, typically has a bright and smooth surface that enables it to be used exactly as is in manufacturing processes.
- Hardness of a material. Compared to steel produced by the hot rolling method, steel produced by the cold rolling process has a substantially higher strength and hardness.
- Internal tension The increased internal stresses caused by the cold rolling process are a result of the increased material hardness and strength. Before the material can be processed, these pressures must be released because otherwise, the finished part or product may warp.
The technical criteria or grades used to categorize steel by composition or physical qualities should not be confused with these two forms of steel. No matter what the metallurgical requirements or grade, steel can be hot or cold rolled.
It’s crucial to keep in mind that certain types of steel will perform better than others for various projects while considering your options. Knowing which kind of steel has the best qualities for a certain application will help you avoid overspending on raw materials and ultimately save time.