The modern classification is set out in GOST R 54384-2011, which is a national adaptation of the European EN standard 10020:2000 «Definition and classification of grades of steel».
- by chemical composition;
- by main properties or field of application.
1 The term "steel"
Steel is called an alloy of iron with carbon., in which the mass fraction of iron is greater, than the mass fraction of any other element, and the mass fraction of carbon is less than 2 %.
A small number of chromium steels have a mass fraction (content) carbon may exceed 2 %. These 2 % are the conditional border between steel and foundry iron.
2 Steel grades by chemical composition
By chemical composition, steel is subdivided into:
Alloy steels are further subdivided into:
- other alloy steels.
2.1 The boundary between unalloyed and alloyed steels
Unalloyed steels include steels, in which the content of any chemical element does not reach the limit, indicated in the table 1. Cm. more details.
2.2 Stainless steels
Stainless steels are steels with a minimum chromium content 10,5 % and carbon – 1,2 %. Some alloyed stainless steels have a minimum chromium content of 7,5 %.
2.3 Other alloy steels
Other alloy steels are steels, which do not belong to stainless, but have a chemical composition, in which at least one element reaches the limits, indicated in the table 1. This category of alloy steels also includes steels, into which sulfur is introduced to obtain special properties, phosphorus and nitrogen.
3 Steel classification by main quality classes
According to quality classes, steel is divided into:
- unalloyed special;
- unalloyed quality;
- alloyed special;
- alloyed quality.
3.1 Unalloyed special steels
Unalloyed special steels are steels, satisfying at least one of the following requirements:
- normalized impact strength;
- guaranteed hardenability or standardized depth of the surface hardened layer;
- normalized content of non-metallic inclusions;
- normalized upper limit of phosphorus and sulfur content;
- normalized value of impact strength KCV at test temperature minus 50 ° C;
- for steels, used in nuclear reactors – content limitation in steels for nuclear reactors: copper - no more 0,10 %; cobalt - no more 0,05 %; vanadium - no more 0,05 %;
- guaranteed specific conductivity over 9 Cm ∙ m / mm2;
- for dispersion-hardening steel – normalized lower carbon limit 0,25 %; normalized ferrite-pearlite microstructure; normalized content of some alloying elements;
- reinforcing steel.
3.2 Unalloyed quality steels
Unalloyed quality steels are steels, which are not special unalloyed steels.
3.3 Stainless steels
Stainless steels are classified into the following categories:
and) by mass fraction of nickel:
- less 2,5 %;
- 2,5 % and more;
b) by basic properties:
- heat resistant;
3.4 Alloy quality steels
3.4.1 Weldable Alloy Fine Grained Structural Steels for Pressure Vessels and Pipes, satisfying the following conditions:
- yield point not less 380 N / mm2 with product thickness no more 16 mm;
- the content of alloying elements is less than the limit values, indicated in the table 2;
- impact strength KCV at minus temperature 50 ° С - not less 34 J / cm2 for longitudinal specimens and 20 J / cm2 - for transverse samples.
3.4.2 Steel for the manufacture of rails, sheet piles and mine fasteners
3.4.3. Steel for the manufacture of hot-rolled and cold-rolled sheet products for cold forging (except for fine-grained steel 3.4.1).
3.4.4. Become, alloyed with copper only.
3.4.5. Electrical steel - steel, which are doped mainly with silicon and aluminum.
3.5 Alloy special steels
Alloyed special steels include all steels, which are not included in the category of quality steels (3.4), including:
- structural steels for mechanical engineering;
- pressure vessel structural steels;
- bearing steels;
- tool steels;
- high speed steels;
- ferritic nickel steels;
- steels with special indicators of electrical resistance.