Unalloyed structural steel

Steel is a metal that is an alloy of iron and carbon, and also contains small amounts of other elements. The mixture undergoes plastic and sometimes heat treatment. Structural steel, however, is often unalloyed, which means that the content of carbon and other elements does not reach the limit values.

Carbon content in unalloyed steel is approx. 0.2%, compared to the limit value distinguishing steel and cast iron – 2.11%. In the case of other elements, the limit values ​​only indicate that a given steel is considered alloyed or non-alloyed. According to the analysis, the limit values ​​of the steel components are as follows:

• Manganese – 1.65%
• Silicon – 0.5%
• Copper and Lead – 0.4%
• Chromium and nickel – 0.3%
• Aluminum, bismuth, cobalt, selenium, tellurium, vanadium, tungsten – 0.1%
• Molybdenum – 0.08%
• Niobium – 0.06%
• Boron – 0.0008%
• other (excluding carbon, phosphorus, sulfur, nitrogen) – 0.05%

To qualify as unalloyed, the amount of any of the elements must not exceed the limit value. If the customer so wishes, a detailed analysis of the chemical composition is carried out in the smelter, using a sample from the finished product.
Designations of unalloyed steel

Determining the steel grade is possible in two ways, by:

symbols (letters and numbers)

– taking into account the application and mechanical properties

– taking into account the chemical properties

steel numbers

The first method is used by designers (taking into account the application) and welding technologists (checking the chemical composition). However, the numbers are necessary to create legible statements and settlements.
What do the different symbols mean?

The symbolic designation of non-alloy steel consists of two main symbols – a letter and a three-digit number. Below, the meaning of individual letters symbolizing steel grades:

• B – steel for reinforcing bars
• G – cast steel
• L – steel for pipes securing the wires
• P – steel for the construction of pressure equipment
• R – steel for rails
• Y – compression strings steel

  As for the main number symbol, it stands for the so-called the minimum yield strength Re, for the steel product thickness range of ≤ 16 mm (the smallest possible), expressed in MPa. In the case of steel marked with the letter R or Y, the number changes its meaning. In this case, it is the symbol for the minimum tensile strength RM.

Structural steels are marked with the following numerical symbols: 235, 275, 355, 420, 460, 500, 550, 620, 690, 890, 960 MPa, with the most common non-alloy steels in bold