The influence of alloying elements on the properties of steel is very high. Properly using a variety of additives, you can get the most different material, with a variety of properties. However, in order to successfully use alloying elements, you need to know what they are, how they work and what they are called.

General description of substances

So, as already mentioned, the influence of alloying elements on the properties of steel is great. What are these elements? These are substances that are introduced into the steel structure and affect its physical and chemical characteristics. The material that is obtained as a result of such an intervention is called doped. The process itself is a technological procedure, the main task of which is to improve or change the initial characteristics of raw materials. It is thanks to this procedure that it is possible to change any properties of steel, making it suitable for use in almost any field of activity.

Alloying elements of the first order

Naturally, there are several groups of substances that can have any effect on the material. Depending on the degree of use and importance, there are basic and auxiliary reagents. The influence of alloying elements on the properties of steel from the main group is very large.

The most common is carbon. Despite the fact that it is used in almost any procedure, its influence is not entirely unambiguous. On the one hand, the content of this substance in the structure of about 1.2% improves such qualities as strength, hardness and cold brittleness. However, with the growth of these properties, others worsen, for example, thermal conductivity and density of raw materials. In addition, even these indicators are not considered the main ones. Like the introduction of any other substance, the addition of carbon to the composition of steel is accompanied by a certain operation. And here comes an important difference. As a result of this procedure, not all reagents are able to keep their components in their original form, some are simply lost. Carbon, in turn, is completely preserved. In other words, during the procedure, operators have the opportunity to fully control and regulate the quantitative content of this substance in the structure.

Other substances of the first group

Carbon is not the only alloying element that affects the properties of steel in the strongest way. The main category also includes silicon and manganese. Although it is worth noting that, for example, the addition of silicon is always very minimal, approximately 0.4%, and this reagent does not introduce any special changes into the structure. It is used as the main oxidizing and binding agent. In other words, these components are a link that allows you to add others to the steel composition. important components in such a way that the result is a coherent and durable structure.

Second order elements

The number of substances included in this group is much larger. The influence of alloying elements on the structure of steel from this group can be very diverse. Molybdenum has become one of the most used substances. Most often this additive is used in chromium steels. The introduction of this additive significantly affects two characteristics of steel - an increase in hardenability, as well as a significant decrease in the cold brittleness threshold. Most often steels containing molybdenum are used by the construction industry. In addition, molybdenum components are created with its help. These substances are considered very effective, since when added to the material they guarantee the dynamic as well as the static strength of the raw material. At the same time, these components significantly reduce the likelihood of internal oxidation.

Titanium has become another representative of the second category of alloying components. The use of this additive is rather narrow, and it is used only in tandem with chromium-manganese alloys. In such cases, titanium contributes to the refinement of structural grains in this material. The content of alloying elements such as calcium and lead, for example, contributes to the fact that the steel cutting procedure will be much easier. Therefore, they are used only in those metal blanks that, after production, will need to be cut into several parts.

Classification of reagents

It is worth saying that in addition to the conditional division into such two categories as the main and additional elements, there is a more precise classification. For example, this may be due to such a feature as the degree of mechanical impact on the structure of the substance. On this basis, all elements can be divided into three groups:

• the influence of the elements, as a result of which carbides are formed;
• elements that have a polymorphic effect on steel;
• elements whose introduction forms intermetallic compounds.

However, it is very important to note here that the influence of reagents from any category of this class will also depend on which third-party additives will be present in the alloy. In addition, if we delve into the classification of alloying elements in alloys, then it is worth saying that the degree of polymorphic influence can also be divided into several groups according to the nature of their effect on the material.

General description of improvements through alloying

Generally speaking, there are several categories into which all alloying elements can be divided. Some will significantly affect the mechanical properties of the material, improving it technical resource. Most often, indicators such as strength, hardness, ductility or hardenability are improved. Another area affected by these elements is protective properties. Alloy steel is different from regular topics that it resists impacts much better, it has significantly higher red hardness, increased heat resistance, and improved corrosion resistance.

Some areas of human activity require the improvement of such qualities of the metal, which can be attributed to electrochemical. If it is necessary to improve this component, then most often they focus on increasing the electrical and thermal conductivity, increasing the resistance to oxidation of substances.

Harmful additives

Naturally, any process is accompanied by a negative side. For alloyed steels, such a side was the appearance of phosphorus and sulfur, which also belong to alloying reagents. However, they are trying to get rid of them, and not add them to the structure. For example, the presence of phosphorus in the composition of iron will remain even after the whole doping process. And the interaction of these two components causes the brittleness of the steel grains. As a result, the product will have lower strength as well as increased brittleness. Although it is worth noting that if the elements of phosphorus and carbon are combined, the chip separation process will be improved, which will help in the future easier to process steel. Therefore, the minimum content of phosphorus is still present in the composition of the alloy.

Of the main alloying elements that are considered harmful, sulfur has become the second. It should be noted that the content of this impurity is even worse than that of phosphorus. In particular, this is due to the fact that sulfur levels the resistance of the metal to external loads. This means that the presence of this reagent in the composition of steel will make it less resistant to corrosion, significantly increase abrasion, and also reduce the resistance to metal fatigue.

How does alloying work

Most often, the alloying process takes place in metallurgical production. In the molten mass or mixture is added required amount the substances described above. As a result of subsequent heat treatment, the process of combining individual reagents into an integral structure and some deformation occurs. Thus, the quality of the alloy is improved.

Detailed description of the elements

It is also worth adding that there is a designation of alloying elements, which serves to quickly understand which substances were used to improve the structure.

What happens when the reagents are injected?

Do not think that the addition of such substances does not affect their interaction with each other. The more various alloying substances are introduced, the more difficult this process is. The introduction of new elements creates new phases, changes the process heat treatment, leads to the creation of new structural components. It is also worth noting here that all the elements are in a different position. Some are in a free state (copper, lead), some form intermetallic compounds - metal-metal, etc.

Martensitic steels

There is a type of steel that is referred to as martensitic. The introduction of certain alloying elements into the composition of such a material will have a rather negative effect. For example, manganese, molybdenum or chromium will lower the martensitic hot point and also increase the austenitic residue. These qualities will negatively affect the final quality of the material after hardening.

Release of raw materials

The presence of alloying elements will also leave its mark on steel tempering. A large number of reagents will decrease the conversion rate and increase the temperature required for the conversion. For this reason, all alloyed alloys are released at a temperature 100-150 degrees higher than conventional ones.

Summarizing

The doping process is complex technological process, which is used to improve or change the original characteristics of steel. During this procedure, the main alloying elements or minor ones are used. Reagents from both groups can be used at once. It is also worth remembering that adding some elements will not only improve certain characteristics, but also worsen others. Therefore, before proceeding with this process, it is necessary to carry out careful calculations. To accomplish this task, there are technologists at plants and factories who set the composition for each steel grade, and also accurately determine the amount that needs to be added to the mass in order to achieve the desired effect.

Used in ferrous metallurgy (i.e. Fe metallurgy); in addition to Fe, this includes Mn, Ti, and Cr; sometimes alloying metals (W, Mo, Ni, Co) are also incorrectly attributed to them. Geological dictionary: in 2 volumes. M.: Nedra. Edited by K. N. ... ... Geological Encyclopedia

Iron and its alloys, the most important structural materials in engineering and industrial production. Almost all structures in mechanical engineering and heavy industry are made from iron-carbon alloys, called steels. Cars, trucks… Collier Encyclopedia

alloying elements - chemical elements, mainly metals introduced into the composition of alloys to give them certain properties (See Alloying). The main alloying elements in steel and cast iron are Cr, Ni, Mn, Si, Mo, W, V, Ti, Zr, Nb, Co, Al, Cu…

- (from the Greek metallon originally, mine, mine), in va, possessing normal conditions characteristic, metallic, high electrical properties. conductivity and thermal conductivity, negative. temperature coefficient. electric conductivity, ability ... ... Chemical Encyclopedia

Chemical elements, mainly metals, introduced into the composition of alloys to give them certain properties (see Alloying). Basic L. e. in steel and cast iron Cr, Ni, Mn, Si, Mo, W, V, Ti, Zr, Be, Nb, Co, Al, Cu, B, Mg; in aluminum... Great Soviet Encyclopedia

dopants- elements specially introduced into metals and alloys in certain quantities in order to change their structure and properties (See also Alloying elements, Alloying). See also: Impurities random impurities permanent impurities ... encyclopedic Dictionary in metallurgy

All metals except ferrous iron and its alloys (steel, cast iron, ferroalloys). Ferrous metals are often conditionally also referred to as Cr and Mn metals, which are in the main. are used as additives to iron, but it is more correct to classify them in a separate group of C. m. ... ... Chemical Encyclopedia

GOST 16482-70: Ferrous secondary metals. Terms and Definitions- Terminology GOST 16482 70: Ferrous secondary metals. Terms and definitions of the original document: 45. Briquetting of metal shavings Ndp. Briquetting Processing of metal chips by pressing to obtain briquettes Definitions ... ... Dictionary-reference book of terms of normative and technical documentation

refractory metals- metals with tmelt > fFe = 1539 °С (for example, Cr, V, W, Mo, Nb, etc.); used as alloying additives in steel, as well as the basis of the corresponding special alloys; See also: Alkali metals... Encyclopedic Dictionary of Metallurgy

Tramp alloys Random alloying elements. Residual alloying elements that are contained in uncontrolled alloyed steel waste loaded into a steel furnace. (

The main alloying elements and their influence on the properties of steels

End of table 5.1

The introduction of alloying elements significantly complicates the interaction of components in steel with each other, leads to the formation of new phases and structural components, changes the kinetics of transformations and heat treatment technology. Moreover, the distribution of alloying elements in steels is very diverse - they can be found in steels:

in the free state (copper, lead, silver);

in the form of intermetallic compounds (metal to metal) with iron or between themselves;

in the form of oxides, sulfides and other non-metallic compounds (aluminum, titanium and vanadium, being deoxidizers, form oxides Αl 2 O 3,TiO2, V 2 O 5);

· in the carbide phase - in the form of a solid solution in cementite or in the form of independent compounds with carbon - special carbides;

dissolved in iron.

Interaction of alloying elements with carbon.

Carbon, interacting with iron, forms the internal structure in steels and mechanical properties. The introduction of alloying elements disrupts this interaction. According to the nature of interaction with carbon, alloying elements are divided into non-carbide-forming and carbide-forming.

To non-carbide forming elements include nickel, silicon, cobalt, aluminum, copper. They dissolve in all crystalline states of iron and change its properties. Carbide-forming elements are chromium, manganese, molybdenum, tungsten, vanadium, titanium, niobium, zirconium. They can dissolve in iron or form carbides ( Mn 3 C,Cr 23 C 6,Cr 7 C 6,Fe 3 Mo 3 C,Fe 3 W 3 C etc.), relatively easily soluble in austenite when heated, and carbides ( MoC,W 2 C,WC,VC, TiC etc.), which practically do not dissolve in austenite when heated.

In addition, all carbide-forming elements can be dissolved in cementite, forming alloyed cementite. All carbides and alloyed cementite have a higher decomposition temperature and hardness, and in a dispersed form significantly strengthen the steel.

Influence of alloying elements on iron polymorphs.

The polymorphic states of iron during the formation of solid solutions by the introduction of alloying elements are shifted in temperature. All alloying elements can be divided into two groups according to their effect on the polymorphic states of iron:

Expanding area Feγ(or alloyed austenite);

Narrowing area Feγ.

The first group includes nickel, manganese, cobalt, copper. Dot A 3 iron with an increase in the content of these elements decreases, expanding the area of ​​\u200b\u200bexistence Feγ on the diagram "Iron - alloying element". Such a state of the alloy can exist from the melting temperature to very low negative temperatures. Such steels are called austenitic. Wear-resistant steel 110G13L containing 13% manganese can serve as an example.

The second group includes silicon, chromium, tungsten, molybdenum, aluminum, vanadium, titanium. Dot A 3 iron with an increase in the content of these elements increases, expanding the area Feα and narrowing area Feγ. Region Feα doped ferrite can also exist from the melting point to very low negative temperatures. Such steels are called ferritic. An example is heat-resistant steel X25.

The properties of ferrite change significantly with the introduction of alloying elements. The reason for the change in properties is the dimensional mismatch between the atoms of alloying elements and iron, leading to distortion crystal lattice iron, the occurrence of internal stresses and deceleration of the movement of dislocations. The strength and hardness of ferrite increases, and the impact strength decreases. The exceptions are chromium (up to 3%) and nickel, with the introduction of which the impact strength increases.

In addition, nickel additions up to 6% reduce the temperature threshold of iron cold brittleness to –200 °C. Therefore, parts of mechanisms and machines operating at low temperatures are made of steels with nickel additives. The remaining elements significantly increase the temperature threshold of cold brittleness, which worsens the reliability of parts at low temperatures due to an increase in the probability of their destruction.

Influence of alloying elements on the equilibrium structure of iron-carbon alloys.

The most important points of the diagram " Fe - Fe 3 C”, allowing to classify iron-carbon steels, are points S and E. Most alloying elements shift these points towards a lower carbon content, which means a shift in the boundaries for steels and cast irons. For example, with the introduction of 5% chromium, hypoeutectoid steels contain up to 0.6% carbon, eutectoid - 0.6%, hypereutectoid - from 0.6 to 1.5%. Over 1.5% carbon - ledeburite appears in the steel structure, therefore such steels are named ledeburite. These steels, having high wear resistance, are used for the manufacture of cold stamps. Similar patterns are observed in steels with tungsten and molybdenum additives, which are used for the manufacture of high-speed tools.

In addition, in alloyed steels, the combined effect of carbon and alloying elements on points A 1,A 3,A m is very complex, so the temperature of these points for each steel is determined experimentally. Knowledge of these points is necessary to assign heat treatment modes, for example, for comparison (from a steel grader):

– steel 45 has A C1= 730 °С, and A C3= 755 °С;

– steel 45X has A C1= 735 °С, and A C3= 770 °С;

– steel 45ХН has A C1= 750 °С, and A C3= 790 °С;

– steel 45KhN2MFA has A C1= 735 °С, and A C3= 825 °С.

Influence of an alloying element on the isothermal decomposition of austenite, as well as on its decomposition during continuous cooling.

This is expressed in an increase in the stability of supercooled austenite. C-shaped regions (diffusion and partial diffusion transformations) on isothermal and thermokinetic diagrams shift to the right along the time axis (the stability of supercooled austenite increases), which is due to the lower diffusion mobility of alloying element atoms (except for cobalt) compared to carbon atoms (Fig. 5.1) . Moreover, with the introduction of non-carbide-forming elements (nickel, manganese, silicon), the shape of the C-shaped region remains the same as for carbon steel. The introduction of carbide-forming elements (chromium, tungsten, molybdenum) changes the appearance
C-shaped region: regions of diffusion and partial diffusion transformations are distinguished, and between these regions austenite can have an abnormally high stability.

In general, an increase in the stability of supercooled austenite increases the hardenability of alloyed steels. The introduction of individual elements, for example, 0.001–0.005% boron, can increase the hardenability tenfold.

Rice. 5.1. Diagrams of isothermal decomposition of austenite:
a– carbonaceous (1, region A p → F + C) and alloyed with non-carbide-forming
elements (2, region A p → F + K) become; b– carbon (1) and alloyed

carbide-forming elements (2, area A p → F + K) become

During hardening (heating, holding, cooling at a rate V > V CR) in carbon steels, martensite is formed from supercooled austenite. The influence of alloying elements on the growth of austenite grains during heating depends on their ability to form carbides when interacting with carbon. Elements that do not form carbides (nickel, cobalt, silicon, copper) practically do not prevent the growth of austenite grains, and elements that form carbides (chromium, tungsten, molybdenum, vanadium, titanium) prevent the growth of austenite grains. Preservation of the fine-grained state of austenite up to temperatures of 930–950 ºС is due to the high heat resistance of carbides, which are barriers to the movement of austenite grain boundaries. Fine-acicular martensite, obtained from fine-grained austenite, provides the steel with increased toughness.

Influence of alloying elements on martensitic transformation of steels.

With the introduction of alloying additives, the temperature range of martensitic transformation changes, which is reflected in the amount of residual austenite in the hardened steel (Fig. 5.2). As can be seen from the figure, aluminum and cobalt increase the martensite point and reduce the amount of retained austenite, but most of the alloying elements (manganese, molybdenum, chromium) reduce the martensite point and increase the amount of retained austenite, which degrades the quality of steel after quenching. To eliminate residual austenite, such steels are cold treated after quenching.

Rice. 5.2. The influence of alloying elements on the temperature of the martensitic
transformations ( a) and the amount of retained austenite ( b) in steel with 1.0% carbon

Moreover, the influence of alloying elements on the behavior of steels can be so significant that the point M N shifts below room temperature. In this case, there is no martensitic transformation and the austenitic state is fixed by cooling, for example, with the introduction of 5% manganese.

Influence of alloying elements on steel tempering.

After hardening, a mandatory thermal operation is performed to increase the toughness of the steel - tempering. In the process of tempering, non-equilibrium phases - martensite and retained austenite - are transformed into ferrite and cementite. This transformation proceeds by diffusion and depends on the heating temperature.

The effect of alloying elements on steel tempering is expressed quantitatively and qualitatively. Quantitative Influence alloying elements - a decrease in the rate of transformations and an increase in the temperature of transformations (carbon release from Feα and coagulation of carbides). This is most noticeable with the introduction of chromium, vanadium, titanium, tungsten, molybdenum, silicon. Therefore, the temperature intervals of all types of tempering of alloyed steels are 100–150 ºС higher than those for carbon steels.

Qualitative influence alloying elements - carbide transformations (transformation of alloyed cementite into special carbides) and the effect of secondary hardness (transformation of residual austenite into martensite and precipitation of dispersed carbides).

Thus, alloying, by changing the rates and temperature of transformations, as well as the thermal properties of steel, significantly affects the heat treatment regimes. The main features of hardening heat treatment of alloy steels compared to carbon steels are as follows:

· Products are heated at a slower rate due to a decrease in the thermal conductivity of steels. Reduced thermal conductivity increases the temperature difference across the cross section of the products, and consequently, increases the stresses that cause warping and cracking;

The heating temperature for obtaining austenite increases with the introduction of carbide-forming elements. Sparingly soluble carbides inhibit the growth of austenite grains and maintain its fine-grained state;

· cooling of products is possible at a much lower rate, since the process of decomposition of supercooled austenite slows down. Reducing the critical hardening rate allows you to cool products in a softer cooler. This reduces internal stresses, warping of parts, the likelihood of cracking;

· the hardenability of steels increases, which makes it possible to harden large products in the entire cross section by quenching.