Understanding the Differences: Hot Rolled Steel vs. Cold ...

When it comes to processing wear-resistant steel, there are many ways to go about it, including forging, casting, extrusion, machining, as well as hot and cold rolling. Each method has its unique advantages and can be selected based on the required properties and the intended use of the final steel product.

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The main difference between hot rolled steel and cold rolled steel lies in the manufacturing process and the resulting properties of the finished products. Both processes involve the rolling of steel between two or more rollers, which compress the metal to a desired thickness. Somewhat like rolling dough with a rolling pin to make a pie crust, the processes of hot and cold rolling steel produce a product that can be trimmed to a desired width and length.

The Main Distinctions between Hold Rolled Steel and Cold Rolled Steel

Manufacturing Process

• Hot Rolled Steel: This process involves rolling the steel at a high temperature (typically over 1,700°F or 926°C). The hot rolling process makes the steel more malleable and allows it to be shaped and formed easily.
• Cold Rolled Steel: In this process, the steel is rolled at room temperature or slightly above. Cold rolling produces a smoother finish and tighter tolerances compared to hot rolling.

Surface Finish

• Hot Rolled Steel: The surface finish of hot rolled steel tends to be rougher compared to cold rolled steel. It may have scale, oxide layers, and a characteristic mill scale texture.
• Cold Rolled Steel: The surface finish of cold rolled steel is smoother and more aesthetically pleasing. Cold rolled steel sheets are often used in applications where appearance is important.

Dimensional Tolerances

• Hot Rolled Steel: Due to the high temperatures involved in the hot rolling process, dimensional tolerances are not as tight as those in cold rolled steel. Hot rolled products may have variations in thickness and size.
• Cold Rolled Steel: Cold rolling allows for tighter dimensional tolerances and a more precise shape, making it more suitable for applications where precision is crucial.

Grain Structure

• Hot Rolled Steel: The hot rolling process results in a coarser grain structure and the mechanical properties of the steel are influenced by the temperature at which it is rolled.
• Cold Rolled Steel: Cold rolling produces a finer and more consistent grain structure, leading to improved strength, hardness, and other mechanical properties.

Work Hardening

• Hot Rolled Steel: Due to the high temperatures involved, hot rolled steel is typically not as hard or as brittle as cold rolled steel. However, it may be more ductile.
• Cold Rolled Steel: The cold rolling process induces work hardening, resulting in increased hardness and strength but reduced ductility.

Cost

• Hot Rolled Steel: Generally, hot rolled steel is less expensive to produce than cold-rolled steel. The hot-rolling process is faster and requires less energy.

• Cold Rolled Steel:

  Cold rolled steel is generally more expensive than hot rolled steel due to the additional processing steps involved in its production, resulting in a smoother and more precise finished product. The increased cost is often justified by the improved surface finish, tighter tolerances, and enhanced mechanical properties of cold rolled steel.

The choice between hot rolled and cold rolled steel depends on the specific application and the desired properties of the end product. Hot rolled steel is often preferred for structural and abrasion resistance purposes, while cold rolled steel is commonly used where a smoother surface finish and tighter tolerances are important.

Explore Superior Wear-Resistant Steel Solutions from Titus Steel

Titus Steel offers ENDURA, ENDURA DUAL, and TITUS MANGANESE, which are all hot rolled steels created to limit abrasion and reduce downtime in the production line. These work hardening steel products become harder with more impact, which is how Titus Steel formulates them into a high-quality wear-resistant steel for your desired needs.

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Hot rolled steel or cold rolled steel &#; which to choose? One of the crucial parts of an engineer&#;s job is picking the right materials for their application. There&#;s already a lot of types of metal to choose from. Each with its own advantages and uses. Some types of steel make an excellent fit for home appliances, others for the automotive or marine industry, gas tanks, constructions, etc.

Still, there&#;s one more distinction to make. A material grade with the same chemical composition may have varying qualities depending on the manufacturing method. Our customers have asked for the difference. So here it is.

Hot Rolled Steel

Hot working is more widely used compared to cold working because it needs less force and energy. It is used in compressive forming methods like rolling, metal extrusion, forging, etc.

Hot Rolling Method

Hot rolling takes place in temperatures above the material&#;s recrystallisation temperature. In case of steel, the temperatures rise above °C.

The starting material is usually steel billets or slabs. First, they are heated above the aforementioned temperature. The next step is feeding them to the rolling machinery. Continuous rolling gives the desired final shape &#; a metal sheet (3 mm and upwards) or profile.

Hot Rolled Steel Properties

As it is easy to form metal in high temperatures without any extra delays, it is possible to produce it in larger quantities than cold rolled steel. This keeps the market price of hot rolled steel lower. The steel cools at room temperature. This is known as normalising. It changes the material&#;s microstructure in a way that results in increased ductility and toughness. Ductility is especially important when forming the material (e.g sheet metal bending) to give it the required shape for your needs.

Hot rolled steel, though, doesn&#;t have the best quality. It shrinks slightly during the cooling process. This leaves the metal with internal stresses. The results are non-uniform measurements and some distortions. The material&#;s dimensional tolerances can vary between 2&#;5%. Also, the surface has a scaly finish. This is a kind of oxide that forms at high temperatures, known as mill scale.

It is easy to identify hot rolled products by touching the surface because of the uneven finish but it is also lacking an oily film. With steel bars, the corners are rounded.

Hot Rolled Steel Uses

Hot rolled steel is a good choice when tight tolerances are not of utmost importance. There are many fields where that is the case. Its great advantage in price matters more than precision. Some common uses for hot rolled steel are:

• Constructions
• Pipes and tubes
• Truck frames
• Doors and shelving
• Railroad tracks
• Railroad car parts

Cold Rolled Steel

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Cold working is a metal forming method that has many advantages over hot working. Technically, cold working includes cold rolling and cold drawing. The former is a process used with sheet metal. The latter finds use with rectangular and round bars.

Cold Rolling Method

Quaker Animation Film Steel Cold Rolling Process

As opposed to hot rolling, cold rolling occurs with the metal below its temperature of recrystallisation. This is still only half the truth. The whole process starts out like hot rolling to give the initial shape without much resistance. After that, the metal is left to cool at room temperature.

The half-products are then fed to cold reduction mills. The metal is rolled to the thickness of 0.5&#;3 mm in case of mild steel and 0.5&#;5 mm in case of stainless steel. The material is cooled by the use of oil which also acts as a lubricant during the rolling process. As the metal sheet gets thinner between the rolls, its speed increases. That would mean material wear and deformation if an oil film wasn&#;t there to minimise the contact. Therefore, cold rolled steel is identifiable by an oily and smooth surface.

As the working takes place in temperatures below the rescrystallisation temperature, strain hardening occurs. The rolls induce plastic deformation. Thus, the yield strength of cold rolled steel is higher than that of hot rolled steel. As an example, a hot rolled steel product may have a yield strength of 235 MPa. In comparison, a cold rolled steel product with the same chemical composition has a yield strength of 365 MPa.

The main advantages of cold working are:

• Accurate finished dimensions
• Clean surface
• Greater strength properties

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Cold Rolled Steel Uses

Although cold rolled steel is more expensive than hot rolled steel, the aforementioned advantages make it useful for many applications. The finished products need less additional surface finishing to achieve a good result, as the surfaces are already smooth. Examples of cold rolled/cold drawn steel uses include:

• Metal furniture
• Structural parts
• Home appliances
• Water heaters
• Metal containers
• Fan blades
• Frying pans
• Computer cabinets

When choosing the right material for your product, make sure to understand the difference of these two material manufacturing methods. There is no point in spending more money on something you don&#;t actually need. Therefore, hot rolled steel is the better choice when the demands aren&#;t high. Otherwise, go with cold rolled steel. It has the answers that hot rolled steel doesn&#;t.

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