Alloy steel - classification, marking, properties, application

Alloy steel is steel, containing special alloying additives, which can significantly change a number of its mechanical and physical properties. In this article we will understand, which is a classification of alloy steels, as well as consider their labeling.

Round rolled alloy steel

Classification of alloy steels

According to the content in the composition of carbon steel is divided into:

1. low carbon steels (to 0,25% carbon);
2. medium carbon steels (to 0,25% to 0,65% carbon);
3. high carbon steels (more 0,65% carbon).

Depending on the total number of alloying elements in their composition, which contains alloy steel, it can belong to one of three categories:

1. low-alloy (not more 2,5%);
2. medium alloyed (not more 10%);
3. high alloy (from 10% to 50%).

Properties, which have alloy steels, determines their internal structure. Therefore, the classification of alloy steels involves the division into subsequent classes:

1. pre-eutectoid - excessive ferrite is present;
2. eutectoid - steel has a pearlite structure;
3. eutectoid - secondary carbides are present in their structure;
4. ledeburite - primary carbides are present in the structure.

According to their practical application, alloy structural steels can be: structural (are divided into machine-building or construction), instrumental, as well as steels with special properties.

Purpose of structural alloy steels:

• Machine-building - are used for the production of parts of various mechanisms, hull structures and the like. They differ, that in the vast majority of cases undergo heat treatment.
• Construction is most often used in the manufacture of welded metal structures and heat treated in rare cases.

The classification of mechanical alloy steels is as follows.

• Heat-resistant steels are actively used for the production of parts, designed to work in the energy sector (example, components of steam turbines), and also from them do especially responsible fastening. Chromium is used as an alloying additive, molybdenum, vanadium. Heat-resistant are medium-carbon, medium-alloyed, pearlitic steel.
• Improved (from the categories of medium carbon, low - and medium alloys) steel, in the production of which use hardening, used for the manufacture of heavily loaded parts, experiencing variable loads. They are sensitive to the concentration of voltage in the working part.
• Cemented (from low-carbon categories, low - and medium alloys) become, as the name implies, are subject to cementation and subsequent hardening. They are used to make all kinds of gears, shafts and other similar parts.

Dependence of the thickness of the cemented layer on the temperature and processing time

Classification of construction alloy steels involves their division into the following types:

• Mass - low-alloy steels in the form of pipes, shaped and sheet rolled products.
• Bridge construction - for road and railway bridges.
• Shipbuilding cold-resistant, normal and high strength - well withstands brittle fracture.
• Shipbuilding cold-resistant high strength - for welded structures, which should work in low temperatures.
• For hot water and steam - operating temperature is allowed to 600 degrees.
• Low-strength high-strength - used in aviation, sensitive to stress concentration.
• Increased strength with the use of carbonitrite reinforcement, creates a fine-grained steel structure.
• High strength with carbonitrite reinforcement.
• Reinforced by rolling at temperature 700-850 degrees.

Application of tool alloy steels

Tool alloy steel is widely used in the manufacture of various tools. But in addition to the clear advantage over carbon steel in terms of hardness and strength, alloy steel also has a weak side - higher brittleness. Therefore for the tool, which is actively exposed to shock loads, such steels are not always suitable. However, in the production of a huge list of cutters, shock-die, measuring and other tools are tool alloy steels remain indispensable.

Separately, high-speed steel can be noted, distinctive features of which are very high hardness and redness resistance to temperature 600 degrees. This steel is able to withstand heat at high cutting speeds, that allows to increase speed of work of the metalworking equipment and to prolong its service life.

A separate category includes alloy structural steels, endowed with special properties: stainless, with improved electrical and magnetic characteristics. From that, what elements, as well as in what quantities they are mainly contained, they may be chromic, nickel, chromonickelmolybdenum. They are also divided into three, four - and more component in the number of alloying additives contained in them.

Alloying elements and their effect on the properties of steels

Marking of alloy steels indicates that, what additives it contains, as well as their quantitative value. But it is also important to know that, what is the effect on the properties of the metal has each of these elements separately.

Chromium

The addition of chromium increases corrosion resistance, increases strength and hardness, is the main component in the creation of stainless steel.

Nickel

Adding nickel increases ductility, steel viscosity and corrosion resistance.

Titanium

Titanium reduces the grain size of the internal structure, increasing strength and density, improves machinability and corrosion resistance.

Vanadium

The presence of vanadium reduces the granularity of the internal structure, which increases the yield strength and tensile strength.

Molybdenum

The addition of molybdenum makes it possible to improve calcination, increase corrosion resistance and reduce brittleness.

Tungsten

Tungsten increases hardness, prevents grains from growing when heated and reduces brittleness when tempered.

Silicon