Beams of steel channel are used for infrastructure in all types of construction, and steel is the most-used structural material in the world. Many grades and shapes of steel are available.
Steel is an alloy of iron and some other element. The most commonly added is carbon, but small amounts of metals such as manganese, silicon, nickel, chromium, molybdenum, boron, and others may be added to yield specific characteristics. The addition of carbon to iron increases its strength. Unalloyed iron is brittle, but various types of carbon steel are harder, ductile (easily bent), and have greater tensile strength (how far a material can bend before breaking). Various organizations around the world set standards which define the grades of steel for steel channel beams.
What is Mild Steel?
Mild steel is also known as plain-carbon steel. According to the American Iron and Steel Institute, mild steel contains 0.16-0.29% carbon. Mild steel is malleable and ductile, but has a lower tensile strength than high-carbon steel. It is also relatively inexpensive to produce, and is the most common type of steel used for structural components.
This contrasts with high-carbon steel, which is expensive but strong. It is most often used in applications such as springs, cutting tools, and metal-working tools such as dies or drills.
What are Cold and Hot Rolling?
Once the grade of steel is produced in a mill, it still needs to be formed into a useful shape. The two basic processes for creating these shapes are cold and hot rolling.
Cold rolled steel is cut from bars while the bar is in a solid state. The resulting product has precise measurements and great strength. The process is more expensive than hot-rolling and is best suited for products with smaller dimensions.
Hot rolling is most often used to produce beams and elements for construction purposes. This means the bars of steel are forced through shaping rollers while the metal is higher than the recrystallization temperature. For steel this is in the range of 1650 degrees Fahrenheit. The actual temperature depends on impurities in the metal, but anyone who has watched a blacksmith work understands that when steel is cherry-red it is plastic and malleable.
Several passes through various rollers are required to change a solid thick bar of steel into a particular shape such as I,H or U-beam (channel). The shape can only be changed a limited amount with each pass. The resulting product will have more size variance than cold-rolled steel, but is precise enough for structural and general manufacturing purposes.
Surface Characteristics of Hot-Rolled Steel
Hot-rolled steel has a distinguishing blue-gray finish from natural oxidation of the surface while the steel passes through the rolling mills. It remains hot for so long that exposure to air produces a tough oxide scale. Although hot-rolled steel is less susceptible to rusting than cold-rolled, paint or other protective coatings are still required.
The surface may also be galvanized through a hot-dip process to further prevent rusting.
Hot rolled, mild steel channel beam may require six or seven millings to create the channel which will have rounded, inside-radius corners. Such beams are useful for all types of construction and manufacture.
Standard sizes range from approximately 2 to 4 inches in width with 3 to 18 inch depth of the channel, and beam lengths of 20 to 40 feet. Thickness of the walls ranges from about 1/3 to 3/4 of an inch.