Structural steels, which are expressed according to their tensile strength, are preferred for use in steel construction, bridge construction, pressure vessels and equipment, vehicle manufacturing and machine constructions, primarily with their tensile stress and yield limit values.
These steels are generally defined as unalloyed steel, mechanical properties are mostly dependent on the amount of carbon, but manganese, silicon, copper and sulfur elements, mainly nitrogen and phosphorus, are also very effective.
General structural steels are classified according to quality groups. As a result of the new regulations in the standards; Only St 33 steel is given to the 1st quality group. Chemical analysis values are not given in St 33 steel, production method and casting style are released. It can be said that; Steels in the first quality group are not melted carefully.
Steels in the 2nd quality group contain no more than 0.050% P and 0.050% S and are mostly preferred in welding constructions. The amount of silicon and manganese was also determined. Fe 37 steel can be poured * boiling, ** calmly poured or *** semi-calmly poured. Fe 44, Fe 50, Fe 60 and Fe 70 steels must be poured either calmly or semi-calmly.
Steels in the 3rd quality group **** are poured as aging and fine grained steel, especially by calming down. Phosphorus and sulfur amounts are limited to 0.040%. They are usually deoxidized with 0.020 A1.
When machining general structural steels, mainly normal annealed or cold-formed material should be preferred. Except for normal annealing and stress relieving annealing applied at a temperature of about 600 ... 650 ° C, no heat treatment is applied to general structural steels. The reason for this is that there are too many unwanted elements in the structure; as a result of this are strong deposits and hardening cracks.
General structural steels are suitable for resistance welding as well as spot and reel seam welding. Fe 60 and Fe 70 steels should be cooled slowly after welding or annealed immediately. If the amount of carbon in steels is less than 0.2%, other press welding methods can also be used.
* Boiling cast steel is a steel that has a thin ferrite layer on its surface that combines with some of the carbon in the molten steel to form a carbon monoxide during the solidification of the steel and form carbon monoxide.
** Calm cast steel is steel that is completely oxygenated from iron oxide in molten steel using oxygen-binding (deoxidant) material in the bucket or mold. (the structure is homogeneous compared to others)
*** In the semi-calm cast steel bucket and mold, it is steel that is partially de-oxygenated from iron oxide in molten steel using deoxidant material.
**** Ageless steel is a steel that has a very little change in impact when compared to the one in which it was manufactured.