Ordinary steels are called carbon steels general purpose, which are also called common steels. These steels are unalloyed carbon steels. However, they cannot be considered pure iron-carbon alloys.. Some elements, such as, silicon, manganese, sulfur and phosphorus, inevitably fall into this alloy during the production of iron and steel. If the content of these elements does not exceed certain limits, then they are not considered alloying elements.
Limits of impurity content
The permitted limits for these elements are as follows:
on silicon - from 0,35 to 0,5 %;
for manganese - from 0,5 to 0,8 %;
on Wednesday - from 0,01 to 0,035 %;
on phosphorus - from 0,01 to 0,035 %.
In addition to these elements, steel may contain other elements in small quantities..
Manganese and silicon - from steel deoxidation
The raw material for steel production is cast iron., which usually contains from 3 to 6 % carbon. This “extra” carbon is burned off by oxidation during the steelmaking process.. However, in this process, part of the iron is oxidized to iron oxide FeO, which dissolves in liquid steel. This adversely affects the strength characteristics of steel.. Therefore, iron oxide FeO is oxidized by its interaction with ferroalloys - ferromanganese FeMn and ferrosilicon FeSi. This process is called steel deoxidation.. In this case, excess manganese and silicon remain in the steel as alloying elements.
Chromium and copper get into steel with steel scrap, and sulfur and phosphorus - with cast iron and steel scrap.
Common steels - unalloyed steels
Therefore, in reality, unalloyed steel in practice turns out to be alloyed with some elements.. but, since these items fall into carbon steel unintentionally, then they are not considered alloying, if they do not exceed the limits, which were mentioned above.
This is perfectly reasonable, since the listed elements in quantities below the permissible limits insignificantly affect the basic properties of two-component iron-carbon alloys. Therefore, unalloyed steels can be considered as two-component iron-carbon alloys with a carbon content of 0 to 2,06 %. Solidification of these steels (primary crystallization) always occurs according to the metastable phase diagram of iron-cementite.
Forms of carbon in steel
Carbon can exist in these steels in two different forms: as a solid solution - in alpha ferrite, delta-ferrite and austenite or in a metal compound - iron carbide Fe3C (cementite). Carbon in steels is always present in a bound form. Presence of carbon in steel as free carbon (graphite) always leads to serious defects in steel, so significantly reduces its strength and leads to embrittlement.
Ordinary steels according to GOST 380-2005
The official name of ordinary steels is as follows, as it is written in the standard GUEST 380-2005: carbon steel of ordinary quality. These steels are the famous St0 steels, St1, St2, St3, St4 St5 and St6 according to GOST 380-2005 contain carbon from 0,06 to 0,49 %. They are widely used for the manufacture of hot rolled products. (varietal, shaped, tolstolistovogo and tonkolistovogo), pipes, forgings and stampings, tapes, wire, hardware and other steel products.