During the hot rolling process, steel is heated at above its recrystallization temperature, which is typically higher than 1700°F. Once this is done, the steel can be easily shaped and formed. Hot rolled steel is used across diverse industries and comes in multiple grades, each of which offer their own unique characteristics.
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The hot rolling process has a significant effect on the properties of steel. By heating steel above its recrystallization temperature and then cooling it at room temperature in a process known as normalization, the steel’s microstructure undergoes permanent changes, resulting in enhanced toughness and ductility. This additional ductility makes the metal easy to form and bend.
The hot rolling process also affects the overall shape of the finished metal piece. Hot rolled forms can be much larger than cold rolled forms. However, since hot rolled steel is heated and cooled, it is susceptible to shrinkage, giving less control over the shape and size of the finished product. One of the easiest ways to tell the difference between hot rolled and cold rolled steel is by touching the surface: hot rolled steel has an uneven surface while cold rolled steel is oily to the touch.
One of the primary benefits of hot rolled steel is its cost-effectiveness. Hot rolled steel can be formed and shaped immediately after heating without the need of reheating. Since the hot rolling process can take place without any delays, hot rolled steel can be produced in large quantities, which keeps its market price lower when compared to cold rolled steel.
To begin the hot rolling process, billets of steel are heated in a furnace until they reach temperatures above the recrystallization point. At McDonald Steel Corporation, we typically heat steel to 2300°F. The furnace evenly distributes heat throughout the length of the metal to make it malleable and easy to form.
Next, the steel billets exit the furnace and travel through our eleven stand cross-country bar mill. This system includes a roughing stand and multiple two-high roll stands. As the metal travels through the stands, it is squeezed, shaped, and elongated until it leaves the last roll stand as a 140 foot long section.
After that, the rolled lengths of metal are set in a cooling bed. The entire process, from the heated furnace to setting a newly rolled shape on the cooling bed, takes less than two minutes. At the end of the process, the original square or rectangle profile of the billet has changed to an asymmetrical or irregular section.
Hot rolled steel is cost-effective, ductile, tough, and easy to produce quickly. However, the cooling process can leave the final product slightly uneven and smaller than it was during the initial forming process. This makes hot rolled steel ideal for heavy-duty industrial applications.
Some of the most popular applications in different industries include the following:
Ultimately, hot rolled steel forms are an excellent choice for projects that require tough but cost-efficient material options.
Hot rolled steel processing methods can be used to produce a wide variety of steel grades, each of which have their own unique properties and best use cases. At McDonald Steel Corporation, we produce the following types of hot rolled steel:
This low carbon steel is between 0.25% and 0.29% carbon by weight. The composition of the metal makes it easy to machine and weld, and it has excellent strength and mechanical characteristics during its lifespan. In fact, it’s named “A36” steel because its minimum yield tensile strength is 36,000 psi. This is an ASTM-designated steel.
A36 steel is commonly used to make structural components and is available in rectangular bars, round bars, square bars, round tubes, shafting, channels, angles, plates, and tread plates.
These two grades of hot rolled steel are very low carbon. C1010 steel is composed of 0.08% to 0.13% carbon by weight, and C1018 ranges between 0.14% and 0.20% carbon by weight. These low carbon amounts make the two metals very structurally similar, though the minute differences result in slight differences in tensile strength and ductility. Manufacturers can easily form, machine, and weld these metals. Common applications include fasteners, bolts, and tubing.
This AISI-designated metal is between 0.42% and 0.50% carbon by weight, making it a medium carbon steel. This metal is stronger than most other metals on this list, and the carbon increases its responsiveness to heat treatments like quenching and annealing. C1045 steel is primarily used for structural components due to its high strength.
A572 is a high strength, low alloy steel plate that is produced in Grades 42, 50, 55, 60 & 65, with each grade signifying the material’s yield strength. This metal is used for a range of structural applications, such as buildings, bridges, rail parts and more.
This metal, also known as weathering steel. is a corrosion-resistant, high-strength, low-alloy steel plate. Due to its resistance to atmospheric corrosion, it is often used for welding, riveting or bolting in construction applications, primarily for bridges and buildings.
This through-hardened material contains 0.05 to 0.15% alloying elements used to refine the grain microstructure. Its yield strength is between 40 and 110 ksi with good weldability.
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Hot rolling is a cost-effective process that results in strong and ductile steel that is easy to work with. At McDonald Steel Corporation, our 14” production line is an eleven stand cross-country bar mill, and our system is one of the only systems in the world that can produce both symmetrical and asymmetrical forms. Our equipment and expert technicians enable us to create high-quality hot rolled forms with reliable mechanical properties and excellent shape control. Contact us today to learn more about our capabilities or to start your order.
When considering steel products, mechanisms, or structures, one seldom contemplates the metal-making process behind them.
As with every stage of steel production, multiple methods are employed during the rolling process to create rolled steel.
Like any other stage of steel production, the process of rolling comprises various methods to produce rolled steel.
Rolled steel has globally recognized methods namely hot rolling and cold rolling. Hot-rolled steel is believed to account for up to 80% of global commercial production of rolled steel. Let's discuss it in detail.
Metallurgy begins with raw materials like iron ore and coke. In traditional processes, they are utilised to create iron via blast furnaces (BF).
Subsequently, this iron is employed to manufacture steel and semi-finished steel products, including slabs, blooms, or round and square billets and beam blanks. In some cases, these processes do not require the use of BF. Consequently, electric arc furnaces (EAF) are utilised, where ferrous scrap and direct reduction iron (DRI) serve as the primary materials.
Whilst several global producers offer slabs and square billets for sale, these items are unsuitable for direct use in the production of machinery, cars, goods or steel structures. Such semi-finished products should be subjected to further processing at rolling mills, where steel is rolled to the desired shape and its physical and mechanical properties are achieved.
All semi-finished steel products undergo hot rolling initially. The process occurs at hot-rolling mills where the semi-finished product undergoes plastic deformation by passing between two rolls. This results in a change in its initial shape. It should be noted that the material temperature must exceed the steel recrystallisation temperature.
Essentially, hot-rolled steel needs to be soft and malleable enough to be shaped by rolls, comparable to dough under a rolling pin. Additionally, the metal is typically very hot – starting rolling temperatures are frequently above 1,100°C, with finishing temperatures being at least 900°C. As a result, this type of rolled steel is called hot-rolled.
If we were to attempt to convert a cold steel slab into a flat product by means of specialized rolling equipment, it would be highly challenging given its hardness, strength and thickness. This is where reheating semi-finished products becomes advantageous.
The main advantage of hot-rolled steel is that it costs less than cold-rolled steel. Therefore, it is widely used in applications where less attention is paid to the surface quality and super high-dimensional accuracy, e.g., to make support steel structures for large construction projects or in the engineering industry.
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