An alloy of iron with carbon with a content of the latter of not more than 2.14% is called steel. The main qualities of steel: strength, ductility, toughness, elasticity, wear resistance and others. The main classification of steels is determined by:
- Chemical composition.
- Structural composition.
- The quality of steel or alloy (depends on the amount of harmful impurities and the production method).
- Degree of deoxidation.
- Destination.
Chemical composition
Depending on the amount of carbon content in the alloy, carbon and alloyed steel grades are distinguished . The carbon content in both types of steel also determines their marking and GOST mark. The classification of carbon steels is divided into:
- Low carbon (C (carbon) content less than 0.3%).
- Medium carbon (C content - from 0.3 to 0.7%).
- High carbon (C content is above 0.7%).
In order to improve the technological characteristics of the alloy, steel is alloyed. In addition to the main components and impurities, special chemical elements (nickel, chromium, molybdenum, aluminum, boron, vanadium, thallium, etc.) are introduced into the alloy, which provide complex alloying. In turn, the classification of alloy steels distinguishes:
- Low-alloyed (contain less than 2.5% of the components alloying steel).
- Medium-alloyed (contain from 2.5 to 10% of steel alloying components).
- Highly alloyed (contain above 10% of the alloying components of steel).
Steel classification by structural composition
Steel that has undergone the alloying process is subdivided into classes by structural composition. The structure of the obtained alloy depends on its carbon content, alloying components and the cooling rate after heating to 900 ° C. There are five types of structural composition:
- Pearlite alloy.
- Martensitic alloy.
- Austenitic alloy.
- Ferritic alloy.
- Carbide alloy.
Steel classification by quality
According to the production conditions (smelting method, impurity content), steels and alloys can be divided into several categories:
- Of ordinary quality (content of S (sulfur)> 0.06%, P (phosphorus) <0.07%).
- Qualitative (content of S (sulfur)> 0.04%, P (phosphorus) <0.35%).
- High quality (content of S (sulfur)> 0.025%, P (phosphorus) <0.025%).
- Particularly high quality (content of S (sulfur)> 0.015%, P (phosphorus) <0.025%).
To steels of ordinary quality are carbon steels, the cost and technological characteristics of which are significantly inferior to steels of other classes.
According to the chemical composition, both alloyed and carbon steels can be classified as qualitative types. In the production of high-quality steels, they comply with more stringent manufacturing requirements.
Carbon types of steels of ordinary quality and quality are determined by the degree of deoxidation and the nature of solidification as calm, semi-quiet and boiling.
High-quality and especially high-quality steels have high technological characteristics, an increased degree of purification from harmful impurities.
Destination classification
According to the purpose, steel is classified into:
- Instrumental.
- Structural.
- Steel with special properties.