CONSTRUCTION STEELS EXPRESSED ACCORDING TO TENSILE STRENGTH

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, where tensile stress and yield limit values are taken into account.

These steels are generally defined as unalloyed steel, mechanical properties are more dependent on the amount of carbon, but the elements of manganese, silicon, copper and sulfur originating from the production raw materials and production methods, especially nitrogen and phosphorus, are also very effective.

General structural steels are classified according to their quality groups. As a result of the new regulations made in the standards;
Only St 33 steel is given to the 1st quality group. Chemical analysis values are not given for St 33 steel, the production method and casting style are released. It can be said that; Steels in the 1st quality group are not melted carefully.

Steels in the 2nd quality group contain at most 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 cast as *boiling, **calm poured or ***semi-quiet poured. Fe 44, Fe 50, Fe 60 and Fe 70 steels are cast calmly or semi-quietly.

Steels in the 3rd quality group are cast as ****aging-resistant and fine-grained steel, especially by quenching. Phosphorus and sulfur amounts are limited to 0.040%. They are usually deoxidized with 0.020 Al.

In the machining of general structural steels, mostly normal annealed or cold formed materials should be preferred. Other than normal annealing and stress relief annealing at approximately 600…650 °C, general structural steels are not heat treated. The reason for this is the excess of unwanted elements in the structure; resultant strong precipitation 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 slowly cooled or annealed immediately after welding. If the carbon content in the steels is less than 0.2%, other press welding methods can also be used.

* Boiling cast steel is steel with a thin ferrite layer on its surface, which shows the effect of gas bubbles in its texture by forming carbon monoxide, when the iron oxide in the molten steel combines with some of the carbon in the steel during the solidification of the steel in the mold.
** Calm cast steel is steel in which the iron oxide in the molten steel has been completely deoxygenated by using an oxygen binder (deoxidant) in the ladle or mold. (the structure is homogeneous compared to the others)
*** In the semi-quiet cast steel ladle and mold, it is the steel that has been partially deoxygenated from the iron oxide contained in the molten steel using a deoxidant.
**** Non-aging steel is steel whose impact strength after a long period of time changes little compared to the state in which it was manufactured.