Construction steel – properties, types and applications

How do you select steel for the right structural elements?

In order to select the right material for structural elements, it is necessary to follow established procedures. The selection of steel should be done according to the following steps:

• analysis of the element's operating conditions and property requirements
• determination of the distribution of required properties on the surface of the element and in its core
• evaluation of how the element is made
• determination of the steel group and grade.

If necessary, the method of heat treatment should also be considered, e.g. the method of quenching, the choice of cooling medium, the temperature range, the determination of the carbon concentration in the steel, and the selection of tempering parameters.

When selecting steel for designed structures, always use standards and tables. These materials contain all the most important information and ensure the correctness of the completed design.

Alloy structural steel?

Alloy structural steels are most often used in the construction industry and for machine and equipment components, operating at room temperature or higher reaching up to 300°C in a low-corrosive environment. Alloy steels, thanks to the appropriate content of alloying elements, are intended for structural elements exposed to high static as well as dynamic loads. The basic criterion for the selection of steel is the mechanical properties, especially the yield strength and strength limit. If plastic deformation is unacceptable in the structure, then the elastic limit becomes the selection criterion. If the structure is exposed to fatigue loads, the designer takes the fatigue limit as a criterion. Another criterion for steel selection is properties determined by fracture mechanics methods, as well as wear resistance.

Chemical composition

To a large extent, the chemical composition determines the properties of steel. The content of individual elements largely influences the hardenability of the steel, the basic criterion used when selecting steel for structural components. Of particular importance here are Mn, Cr, Si, Ni or Mo. An important role is played by carbide-forming elements, i.e. Cr, V, Mo or W, which contribute to the formation of carbides and thus increase hardness, wear resistance, affect the formation of fine-grained structure and thus improve mechanical and technological properties. The most favorable properties of structural steel are achieved after heat treatment operations, usually after quenching and tempering.

Non-alloy structural steel

Non-alloy structural steels are very often used in the construction industry and in general applications for elements that are not highly stressed. Often these components are joined together by welding, bolting or riveting. Typically, these steels are supplied in hot-formed condition, in the form of long and flat products after hot-rolling in the form of thick or thin sheets, bars, sections or strips, among others. The mechanical properties of these steels depend on the chemical composition, as well as the thickness of the metallurgical product. These steels contain basic chemical elements such as carbon, manganese, sometimes silicon, and P, S and N. The most important value for determining mechanical properties is the minimum yield strength given in MPa, the value of which is given after the letter "S" defining the structural steel, e.g. S235, S355.

In the construction industry, elements made of unalloyed structural steels occurring in the form of round, square, rectangular hollow sections with a wall thickness of up to 65 mm, produced seamless and with seam, are often used.