Fields of use

After a normalising procedure or cold forming, construction steels are used predominantly in structural engineering, bridge construction, hydraulic engineering, tank construction, vehicle construction and mechanical engineering, due to their tensile strength and yield stress.

Description

Non-alloy construction steels account for the largest quantity in overall steel production. They are usually supplied in a hot-rolled state.

Properties

Welding: Structural steels can be welded very well.

Mechanical properties: In a +N state, construction steels have high yield stresses, connected with sufficient three-dimensional thermoformability, especially with impact pressure. You should heed the temperature at which the impact energy is tested. The following table shows at which test temperature the impact energy of 27J is achieved.

Technical properties:

Properties such as machinability, cold workability (die cutting, deep drawing for plates), weldability, corrosion resistance, etc. are described here.
Physical properties:
Requirements on magnetic properties, thermal conductivity and thermal expansion.

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Weldability

Due to the major significance of welding as a joining process for construction steels, here are some statements on the term of weldability:

Weldability:
The term is given if welding to fit the requirements can be produced on the basis of the metallurgic, chemical and physical properties.
Weld reliability:
It is not influenced by the steel manufacturer, but rather by the steel processor. Weld reliability exists if the welded component remains dependable (free from brittleness and breaks) during the intended operating conditions. It is influenced by the constructive design (plate thickness, type and alignment of the joint, notch effect) and the stress condition (type, size and degree of multiaxiality of the strains, strain speed, operating temperature).
Welding option:
This states whether the relevant connection can be produced with the selected production connections. The three parameters influence one another. The weldability exists for steels if the joints produced in the heat-affected zone remain sufficiently ductile through the rapid cooling process. To do this, the formation of martensite must be avoided or the carbon content of the steel must be so limited that the martensite is still sufficiently ductile.
As well as carbon, alloying elements also affect the tendency to crack of the hardened zones in the heat-affected zone. The combined effect of the carbon and alloying elements is frequently stated by the carbon equivalent Ceq. A formula that is used frequently for construction steels is:
Ceq = C + Mn/6 + (Cr + Mo + V)/5 + (Ni+Cu)/15 [%]

The alloying elements are used in this equation as mass percents. Subsequently, they are considerably less prone to cracking than carbon.
In general, the steel, depending on the workpiece thickness, is pre-warmed to between 100°C and 150°C for welding with Ceq>= 0.45%. The resulting decreasing cooling rate in the heat-affected zone very effectively reduces the martensite quantity, i.e. the hardness in the heat-affected zone and as a result the tendency to crack.