Basic classification of steels and their types

The alloy of iron with carbon with a content of not more than 2.14% is called steel. The main qualities of steel: strength, ductility, viscosity, 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 method of production).
• Degree of deoxidation.
• Appointment.

Chemical composition

Depending on the amount of carbon in the alloy, carbon and alloy grades of steel are distinguished . Carbon content in both types of steel also determines their marking and GOST sign. Classification of carbon steels is divided into:

• Low-carbon (content of C (carbon) is less than 0.3%).
• Medium-carbon (the C content is from 0.3 to 0.7%).
• High-carbon (the C content is above 0.7%).

In order to improve the technological characteristics of the alloy, the 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 alloyed steels distinguishes:

• Low alloy (contain less than 2.5% of the components that alloy the steel).
• Medium-alloyed (contain from 2.5 to 10% of the components that alloy the steel).
• Highly alloyed (contain more than 10% of the components that alloy the steel).

Classification of steels by structural composition

Steel, the past alloying process, is divided into classes by structural composition. The structure of the resulting alloy depends on the content of carbon, alloying components and cooling rate after heating to 900 ° C. There are five types of structural composition:

• Pearlitic alloy.
• Martensitic alloy.
• Austenitic alloy.
• Ferritic alloy.
• Carbide alloy.

Classification of steels in quality

Under the terms of production (the method of smelting, the content of impurities) steel and alloys can be divided into several categories:

• Ordinary quality (content of S (sulfur)> 0.06%, P (phosphorus) <0.07%).
• Quality (content of S (sulfur)> 0.04%, P (phosphorus) <0.35%).
• High-quality (content of S (sulfur)> 0.025%, P (phosphorus) <0.025%).
• Especially high-quality (content of S (sulfur)> 0.015%, P (phosphorus) <0.025%).

The steels of ordinary quality are carbonaceous, the cost and technological characteristics of which are significantly inferior to those of other classes.

By chemical composition, qualitative types can include both alloyed and carbon steels. In the production of quality steels comply with more stringent requirements for manufacturing.

Carbon steel types of ordinary quality and quality are determined by the degree of deoxidation and the nature of solidification as calm, semi-calm and boiling.

High-quality and high-quality steels have high technological characteristics, an increased degree of purification from harmful impurities.

Classification of steels by purpose

For the purpose of steel is classified into:

• Instrumental.
• Constructional.
• Steel with special properties.