How do alloying elements affect the properties of steel?

Alloying of steel: influence of carbon, manganese and silicon

There are more than two dozen alloying elements used in steels. Here we look at the effects on steel of the most common (often unavoidable) alloying elements - carbon, manganese and silicon.

The influence of carbon on the properties of steels

Carbon is the main strengthening element in all steels except austenitic stainless steels and some other high-alloy steels. The strengthening effect of carbon consists of solid solution strengthening and strengthening due to dispersed precipitation of carbides. With increasing carbon content in steel, its strength increases, but ductility and weldability decreases.

Carbon has a moderate tendency to macrosegregate during crystallization. Macrosegregation of carbon is usually more significant than that of all other alloying elements. Carbon has a strong tendency to segregate at defects in steels such as grain boundaries and dislocations. Carbide-forming elements can react with carbon to form “alloyed” carbides.  

The influence of manganese on the properties of steels

Manganese is present in almost all steels in amounts of 0.30% or more. Manganese is used to remove oxygen and sulfur from steel. It has less tendency to segregate than any other alloying element. Manganese has a beneficial effect on surface quality over the entire carbon content range, with the exception of very low carbon steels, and also reduces the risk of red brittleness. Manganese has a beneficial effect on the ductility and weldability of steels.

Manganese does not form its own carbide, but only dissolves in cementite and forms alloyed cementite in steels. Manganese promotes the formation of austenite and therefore expands the austenite region of the phase diagram. High manganese content (more than 2%) leads to an increased tendency to cracking and warping during hardening. The presence of manganese in steels encourages impurities such as phosphorus, tin, antimony and arsenic to segregate to the grain boundaries, causing temper brittleness.

The influence of silicon on the properties of steels 

Silicon is one of the main deoxidizing agents used in steel smelting. Therefore, the silicon content determines the type of steel produced. Mild carbon steels can contain silicon up to a maximum of 0.60%. Semi-quiet steels may contain moderate amounts of silicon, for example 0.10%.

Silicon is completely dissolved in ferrite at a silicon content of up to 0.30%. It increases the strength of ferrite without almost reducing its ductility. When the silicon content is above 0.40% in general purpose carbon steel, a significant decrease in ductility occurs.

In combination with manganese or molybdenum, silicon provides higher hardenability of steel. The addition of silicon to chromium-nickel austenitic steels increases their resistance to stress corrosion.

In thermally hardenable steels, silicon is an important alloying element; it increases the ability of steels to be thermally hardened and their wear resistance, increases the elastic limit and yield strength. Silicon does not form carbides and does not contain cementite or other carbides.

It dissolves in martensite and slows down the decomposition of alloyed martensite up to 300 °C.

Source: https://steel-guide.ru/klassifikaciya/legirovanie-stali/legirovanie-stali-vliyanie-ugleroda-marganca-i-kremniya.html

Alloy steels: classification and marking

Alloy steel is steel containing special alloying additives that can significantly change a number of its mechanical and physical properties. In this article we will understand what the classification of alloy steels is, and also consider their markings.

Alloy steel round bars

Classification of alloy steels

Based on the carbon content of steel, it is divided into:

Depending on the total amount of alloying elements that alloy steel contains, it can belong to one of three categories:

1. low alloy (no more than 2.5%);
2. medium alloyed (no more than 10%);
3. highly alloyed (from 10% to 50%).

The properties of alloy steels are determined by their internal structure. Therefore, the classification of alloy steels implies division into the following classes:

1. hypoeutectoid - the composition contains excess ferrite;
2. eutectoid - steel has a pearlite structure;
3. hypereutectoid - their structure contains secondary carbides;
4. ledeburite - the structure contains primary carbides.

According to their practical application, alloyed structural steels can be: structural (divided into machine-building or construction), tool, and also steels with special properties.

Purpose of structural alloy steels:

• Mechanical engineering - used for the production of parts for various mechanisms, body structures, and the like. They differ in that in the vast majority of cases they undergo heat treatment.
• Construction - most often used in the manufacture of welded metal structures and are subjected to heat treatment in rare cases.

The classification of engineering alloy steels is as follows.

• Heat-resistant steels are actively used for the production of parts intended for work in the energy sector (for example, components for steam turbines), and they are also used to make especially important fasteners. Chromium, molybdenum, and vanadium are used as alloying additives. Heat-resistant steels refer to medium-carbon, medium-alloy, pearlitic steels.
• Improved steels (from the categories of medium-carbon, low- and medium-alloyed) steels, in the production of which hardening is used, are used for the manufacture of heavily loaded parts that experience variable loads. They differ in sensitivity to stress concentration in the workpiece.
• Case-hardened steels (from the categories of low-carbon, low- and medium-alloyed) steels, as the name suggests, are subject to carburization followed by hardening. They are used for the manufacture of all kinds of gears, shafts and other parts similar in purpose.

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

The classification of construction alloy steels implies their division into the following types:

• Bulk - low-alloy steel in the form of pipes, shaped and sheet products.
• Bridge construction - for road and railway bridges.
• Shipbuilding cold-resistant, normal and high-strength - well resistant to brittle fracture.
• Shipbuilding cold-resistant high strength - for welded structures that will operate in low temperature conditions.
• For hot water and steam - operating temperatures up to 600 degrees are allowed.
• Low-cut, high-strength - used in aviation, sensitive to stress concentration.
• Increased strength using carbonitrite hardening, creating a fine-grained steel structure.
• High strength using carbonitrite hardening.
• Strengthened by rolling at a temperature of 700-850 degrees.

Application of tool alloy steels

Tool alloy steel is widely used in the production of various tools. But in addition to its obvious superiority over carbon steel in terms of hardness and strength, alloy steel also has a weak side - higher fragility.

Therefore, such steels are not always suitable for tools that are actively exposed to shock loads.

Nevertheless, in the production of a huge range of cutting, impact-stamping, measuring and other tools, alloy tool steels remain indispensable.

Separately, we can note high-speed steel, the distinctive features of which are extremely high hardness and red resistance up to a temperature of 600 degrees. Such steel is able to withstand heat at high cutting speeds, which allows you to increase the speed of metalworking equipment and extend its service life.

A separate category includes alloyed structural steels, endowed with special properties: stainless, with improved electrical and magnetic characteristics. Depending on what elements, as well as in what quantities, are predominantly contained in them, they can be chromium, nickel, chromium-nickel-molybdenum. They are also divided into three-, four- and more-component ones according to the number of alloying additives they contain.

Alloying elements and their influence on the properties of steels

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

Chromium

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

Nickel

The addition of nickel increases the ductility, toughness and corrosion resistance of steel.

Titanium

Titanium reduces the graininess of the internal structure, increasing strength and density, improving machinability and corrosion resistance.

Vanadium

The presence of vanadium reduces the graininess of the internal structure, which increases fluidity and tensile strength.

Molybdenum

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

Tungsten

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

Silicon

At contents of up to 1-15%, silicon increases strength while maintaining toughness. As the percentage of silicon increases, magnetic permeability and electrical resistance increase. This element also increases elasticity, corrosion resistance and oxidation resistance, but also increases fragility.

Cobalt

The introduction of cobalt increases impact resistance and heat resistance.

Aluminum

The addition of aluminum improves scale resistance.

Table of purpose of some types of steel

Separately, it is worth mentioning impurities and their effect on the properties of steels. Any steel always contains technological impurities, since it is extremely difficult to completely remove them from the steel composition. These types of impurities include carbon, sulfur, manganese, silicon, phosphorus, nitrogen and oxygen. Carbon

It has a very significant effect on the properties of steel. If it is contained up to 1.2%, then carbon helps to increase the hardness, strength, and yield strength of the metal. Exceeding the specified value contributes to the fact that not only strength, but also ductility begins to deteriorate significantly.

Manganese

If the amount of manganese does not exceed 0.8%, then it is considered a technological impurity. It is designed to increase the degree of deoxidation and also counter the negative effects of sulfur on steel.

Sulfur

When the sulfur content exceeds 0.65%, the mechanical properties of steel are significantly reduced, we are talking about a decrease in the level of ductility, corrosion resistance, and impact strength. Also, high sulfur content negatively affects the weldability of steel.

Phosphorus

Even a slight excess of phosphorus content above the required level is fraught with an increase in brittleness and fluidity, as well as a decrease in the toughness and ductility of steel.

Nitrogen and oxygen

When certain quantitative values ​​in the steel composition are exceeded, inclusions of these gases increase brittleness and also contribute to a decrease in its endurance and toughness.

Hydrogen

Too much hydrogen content in steel leads to increased brittleness.

Marking of alloy steels

The category of alloyed steels includes a wide variety of steels, which necessitated the need to systematize their alphanumeric designations. The requirements for their marking are specified by GOST 4543-71, according to which alloys endowed with special properties are indicated by markings with a letter in the first position. By this letter it is possible to determine that the steel, by its properties, belongs to a certain group.

An example of deciphering alloy steel markings

So, if the marking of alloy steels begins with the letters “F”, “X” or “E” - we have an alloy of the stainless, chromium or magnetic group. Steel, which belongs to the stainless chromium-nickel group, is designated by the letter “I” in its marking. Alloys belonging to the category of ball bearing and high-speed tool alloys are designated by the letters “Ш” and “Р”.

Steels classified as alloyed may belong to the category of high-quality, as well as especially high-quality. In such cases, the letter “A” or “W” is placed at the end of their mark, respectively. Steels of ordinary quality do not have such designations in their markings. Alloys that are produced by the rolling method also have a special designation. In this case, the marking contains the letter “N” (hard-worked rolled steel) or “TO” (heat-treated rolled steel).

The exact chemical composition of any alloy steel can be found in regulatory documents and reference literature, but the ability to understand its markings also allows one to obtain such information. The first figure allows you to understand how much carbon (in hundredths of a percent) alloy steel contains. After this number, the brand lists the letter designations of alloying elements that are additionally contained.

Designation of alloying elements in steel markings

After each such letter the quantitative content of the specified element is indicated. This content is expressed in whole fractions. There may not be any number after the letter indicating the element. This means that its content in steel does not exceed 1.5%.

State standard 4543-71 regulates the designation of alloying additives included in alloy steel: A - Nitrogen, B - Niobium, C - Tungsten, G - Manganese, D - Copper, K - Cobalt, M - Molybdenum, N - Nickel, P - Phosphorus, P - Boron, S - Silicon, T - Titanium, C - Zirconium, F - Vanadium, X - Chrome, Yu - Aluminum.

Use of alloy steels

Today it is difficult to find an area of ​​life and activity in which alloy steel would not be used. Almost any tool is made from tool and structural steels: cutters, milling cutters, dies, measuring devices, gears, springs, pendants, braces and much more. Stainless alloy steels are actively used in everyday life; they are used to make dishes, cases and other elements of many types of household appliances.

Due to their high cost, alloy steels are used only for the production of the most critical structures and parts, where products made from other metals simply cannot perform the tasks assigned to them.

Source: http://met-all.org/stal/legirovannye-stali-markirovka.html

Steel alloying

Alloying of steel is necessary for the manufacture of tools and semiconductors. In the first case, special attention is paid to the mechanical properties, and in the second - to the conductive characteristics.

This requires not only different additives (for example, alloying steel with aluminum), but also different technological processes.

Alloy steel is an iron-carbon alloy with additional elements (nickel, chromium, molybdenum, cobalt and aluminum) to give it special characteristics such as corrosion resistance, flexibility and hardness, making it superior to ordinary carbon steel.

Alloys are generally designated according to their predominant elements, such as nickel steel, chrome steel and chrome vanadium steel. Alloys can be found in almost all industries, from civil engineering to shipbuilding, oil, automotive and aviation.

The variety of possible alloys is almost endless, as is the variety of characteristics.

Alloying process

Alloy steel can be produced in several ways. Alloying can be surface or volumetric. In the first case, alloying additives are introduced only into the top layer. The alloying element penetrates shallowly, approximately 1-2 mm.

This is necessary to create certain properties (for example, anti-friction) on the metal surface. Surface alloying is much better than sputtering, and therefore is often used in the manufacture of ceramics and glass.

The introduction of additives into the entire volume of the metal is provided for by volumetric alloying.

There can be several alloying additives. They can be either metallic or non-metallic (for example, phosphorus). To obtain different characteristics, alloying can be done at different stages of smelting.

The addition of alloying elements is aimed at creating microstructural changes, which, in turn, contribute to changes in the physical and mechanical properties of the material, allowing it to perform certain functions.

Doping of semiconductors is carried out using thermal diffusion, neutron transmutation doping and ion implantation. Ion doping is carried out in two stages. First, the alloying atoms are driven in, and then they are activated.

The distribution of elements depends on temperature and time, the depth of entry depends on energy. During thermal diffusion, alloying elements are deposited, annealed, and alloyed elements are removed.

Neutron transmutation doping occurs due to nuclear reactions - in this case, the alloying and doped elements are combined into a single crystal material.

Properties and purpose

The most commonly used alloying elements are nickel, manganese, chromium, silicon, lead, selenium and boron. Less commonly used are aluminum, copper, niobium, zirconium and tungsten.

The purpose of these elements is very diverse, and when used in the right proportions, steels are obtained with certain characteristics, which, however, cannot be achieved with ordinary carbon steels.

Alloys are usually classified based on the elements that are most abundant, which are called the base constituents. Elements that are found in smaller proportions are considered secondary components.

Iron itself is not particularly strong, but its strength increases significantly when it is alloyed with carbon and then quickly cooled to produce steel. Some characteristics of steel - soft, semi-soft, semi-hard, hard - are largely determined by the carbon content, which can range from 0.10 to 1.15%.

Risks

Some ferroalloys are produced and used in fine particle form; Airborne dust poses potential toxicity, fire and explosion hazards. In addition, occupational exposure to fumes from the manufacture of certain alloys can lead to serious health problems. A number of tin alloys are hazardous to health (especially at high temperatures) due to the harmful properties of the metals with which tin can be alloyed (for example, lead).

Nickel, osmium, ruthenium, copper, gold, silver and iridium are alloyed with platinum to increase hardness. Alloys formed with cobalt have gained importance due to their ferromagnetic properties. Rhodium is used as an anti-corrosion electrolytic coating to protect silver from tarnishing.

Rhodium is alloyed with platinum and palladium to make very hard alloys. The purpose of alloying with copper is to increase corrosion resistance. Silver is also alloyed with copper.

In its pure form, silver is too soft for coins, cutlery and jewelry; for all applications, it is hardened by alloying with copper.

Ferrous alloys

Ferrous alloys are iron and its alloys. The significant carbon content makes cast iron very brittle. Despite their brittleness and lower mechanical properties than steel, their low cost, ease of casting and specific characteristics make them one of the world's most valuable products with the largest production tonnage.

Non-ferrous alloys

Non-ferrous alloys are alloys that do not contain iron or contain relatively small amounts of iron. Their characteristics are significant corrosion resistance, high electrical and thermal conductivity, low density and ease of production.

Stainless steel

The general characteristics of stainless steel make it a universal material that adapts well to the requirements of today. Any type of alloy has its own advantages depending on the chemical composition.

Aesthetics. There are a number of surface finishes available, from matte to glossy, satin to engraved. Finishes can also be patterned or painted, making stainless steel a unique and aesthetically pleasing material. Architects often choose this material for construction work, interior design and urban furniture.

Mechanical properties: Stainless steel has better mechanical properties at room temperature compared to other materials, which is an advantage in the construction sector as it allows for weight savings per m² or smaller dimensions of structural elements.

Good elasticity and hardness combined with good wear resistance (friction, abrasion, impact, elasticity) allow stainless steel to be used in a wide range of projects.

In addition, stainless steel can be installed on a construction site, despite winter temperatures, without the risk of brittleness or breakage, which does not prevent construction time from being extended.

Fire resistance. Compared to other metals, stainless steel has better fire resistance in construction due to its high melting point (above 800 °C). Stainless steel does not emit toxic fumes.

Corrosion Resistance: With a chromium content of 10.5%, stainless steel is permanently protected by a passive layer of chromium oxide that forms naturally on its surface when exposed to air humidity.

If the surface is damaged, the passive layer is restored. This provides corrosion resistance.

The influence of alloying elements on the hardenability of steel

It is known that active alloying elements in steel, such as chromium and molybdenum, form carbides in it. This means that these elements will tend to enter the carbide part of pearlite and bainite when they are formed from austenite.

Carbon diffusion during austenite decomposition: from 0.8% to 0.02% and 6.7%

When a certain volume of austenite is converted to pearlite or bainite in ordinary carbon steels, the carbon atoms must rearrange themselves from the uniform distribution they have in the austenite. In a volume already converted from austenite, there may be no carbon at all (0.02%) in the ferrite region and 6.7% carbon in the cementite region. This redistribution of atoms occurs due to diffusion.

More difficult diffusion - slower decomposition of austenite

Similarly, during the transformation of austenite in alloy steel, alloying atoms such as chromium and manganese must also be redistributed from a uniform distribution in the austenite to a high content in the carbides and a low content in the ferrite. However, diffusion redistribution for alloying elements is much more difficult for carbon.

The fact is that their diffusion coefficient is much lower than that of carbon. Therefore, the presence of alloying elements in steel makes the formation of pearlite and bainite difficult.

Accordingly, the curves for the beginning of pearlite and bainite transformations on the austenite transformation diagrams - isothermal and continuous - will shift to the right, at more, so to speak, later times.

All alloying additives in steel, except cobalt, shift the curves for the onset of ferrite, pearlite and bainite formation on the isothermal transformation diagrams to the right.

The effect of nickel on the hardenability of steel

However, it is known that, for example, nickel is a rather inactive element, and they also slow down the rate of formation of pearlite and bainite. In this case, the reason lies in the influence of nickel on the phase diagram. It's just impossible to explain. However, the end result is easy to remember: almost all alloying elements in steel slow down the decomposition of austenite to form ferrite, pearlite or bainite.

How chromium slows down the transformation of austenite

The figure below shows a comparison of the isothermal transformation diagrams of austenite for two American steels - carbon steel 1060 and alloy steel 5160 (analogues of our steels 60G and 50KhGA) - with different chromium contents. We can say that 5160 steel is the same as 1060 steel, but with the addition of 0.8% chromium.

Figure - Isothermal transformation diagrams for steels 1060 and 5160. Alloying 5160 steel with chromium shifts the nose of the transformation curves to the right.

(A - austenite, F - ferrite, C - cementite)

The figure shows that such a low chromium content has a significant effect on the position of the austenite transformation onset curves on the isothermal transformation diagram. Even though the grain size in 5160 steel was smaller than that of 1060 steel, the nose of the isothermal transformation diagram for 5160 steel is shifted to the right by about 5 seconds, and for 1060 steel it is only 0.5 seconds.

  Smoke pipes for boiler rooms made of stainless steel

Effect of steel grain size on hardenability

The influence of grain on the hardenability of steel is due to the fact that the decomposition of austenite always begins at the boundaries of its grains. The area of ​​the grain boundaries naturally depends on the grain size. A large grain size will reduce the overall grain boundary area per unit volume.

This leads to a shift in the transformation onset curves - an increase in the delay of the onset of transformation - and, thereby, increases the hardenability of steel. That is why the position of the curves on the isothermal transformation diagram depends on the austenite grain size.

For the same reason, the isothermal transformation diagrams always indicate the austenite grain size.

Source: https://steelfactoryrus.com/vliyanie-legiruyuschih-elementov-na-prokalivaemost-stali/

Steel - alloying elements

Influence of alloying elements. The presence of alloying elements in steel improves its properties.

Alloy steel has high strength and toughness

Some alloying elements, such as nickel, silicon, cobalt, copper, do not form chemical compounds with carbon - carbides - and are mainly distributed in ferrite.

Other elements - tungsten, chromium, vanadium, manganese, molybdenum, titanium, etc. - form carbides with carbon .

The presence of carbides in alloy steel increases its hardness and strength, and in tool steel, its cutting properties.

Alloying elements not only improve the mechanical properties of steel (mainly in the heat-treated state), but also significantly change its physical and chemical properties. The influence of individual alloying elements on the properties of steel comes down mainly to the following:

• Manganese increases the strength and hardness of steel , increases hardenability, reduces warping during hardening, increases the cutting properties of steel, but at the same time, it promotes grain growth when heated, which reduces the resistance of steel to impact loads.
• Chromium inhibits grain growth when heated, increases the mechanical properties of steel under static and impact loads, increases hardenability and heat resistance , cutting properties and abrasion resistance. With significant amounts of chromium, steel becomes stainless and heat-resistant.
• Silicon significantly increases the elastic properties of steel, but slightly reduces impact strength .
• Nickel increases the elastic properties of steel without reducing viscosity, counteracts grain growth, and improves the hardenability and mechanical properties of steel. With significant amounts of nickel, the steel becomes non-magnetic, corrosion-resistant and heat-resistant.

• Molybdenum counteracts grain growth, increases the hardness and cutting properties of steel due to the formation of carbides, reduces the tendency of steel to become brittle during tempering, and increases the heat resistance of steel.
• Cobalt increases the strength of steel under impact loads , improves the heat resistance and magnetic properties of steel.
• Tungsten, like molybdenum, increases the hardness and cutting properties of steel , reduces grain growth when heated, and increases heat resistance.
• Vanadium promotes deoxidation of steel, counteracts grain growth, increases the hardness and cutting properties of steel.
• Titanium is a deoxidizer of steel , also helping to remove nitrogen from it, making the steel more dense, homogeneous and heat-resistant.

The most effective improvement in the properties of steel under the influence of alloying elements is observed in the heat-treated state. Therefore, in the vast majority of cases, parts made of alloy steels are used after hardening and tempering.

The maximum value of mechanical properties is achieved by the simultaneous presence of two or more alloying elements in the steel.

Thus, in mechanical engineering, along with chromium, manganese, silicon and other steels, more complex steels are also widely used - chromium-nickel, chromium-silicon-manganese, chromium-tungsten and other steels.

Almost all alloying elements lower the value of critical points during cooling and reduce the critical hardening rate of steel.

In practice, this means that alloy steels containing these elements should be cooled during quenching not in water, as is necessary for carbon steels, but in oil.

Thus, alloy steel satisfies the most diverse requirements of the engineering industry and in many cases replaces more expensive non-ferrous metals and alloys.

The use of alloy steel is continuously expanding due to improvements in the designs of machines and devices.

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Source: http://www.Conatem.ru/tehnologiya_metallov/stal-legiruyushhie-elementy.html

The influence of alloying elements on the properties of steel. Types, grades and purpose of steels

Steel is one of the most sought after materials in the world today. Without it, it is difficult to imagine any existing construction site, engineering enterprises, and many other places and things that surround us in everyday life. At the same time, this alloy of iron and carbon can be quite different, therefore this article will consider the influence of alloying elements on the properties of steel, as well as its types, grades and purpose.

general information

Today, many steel grades are widely used in almost every area of ​​human activity. This is largely due to the fact that this alloy optimally combines a whole range of mechanical, physico-chemical and technological properties that no other materials have. The steel smelting process is continuously being improved and therefore its properties and quality make it possible to obtain the required performance indicators of the resulting mechanisms, parts and machines.

Classification by purpose

Each steel, depending on what it is created for, can necessarily be classified into one of the following categories:

• Structural.
• Instrumental.
• Special purpose with special properties.

The most numerous class is structural steels, designed to create a variety of building structures, instruments, and machines. Structural grades are divided into upgradeable, cemented, spring-spring, and high-strength.

Tool steels are differentiated depending on the tool for which they are produced: cutting, measuring, etc. It goes without saying that the influence of alloying elements on the properties of steel in this group is also great.

Special steels have their own division, which includes the following groups:

• Stainless (aka corrosion-resistant).
• Heat resistant.
• Heat resistant.
• Electrical.

Steel groups by chemical composition

Steels are classified according to the chemical elements that form them:

• Carbon steel grades.
• Alloyed.

Moreover, both of these groups are further divided according to the amount of carbon they contain into:

• Low carbon (carbon less than 0.3%).
• Medium carbon (carbon concentration is 0.3 - 0.7%).
• High carbon (carbon more than 0.7%).

What is alloy steel?

This definition should be understood as steels that contain, in addition to permanent impurities, also additives introduced into the structure of the alloy in order to increase the mechanical properties of the ultimately obtained material.

A few words about steel quality

This parameter of a given alloy implies a set of properties, which, in turn, are determined directly by the process of its production. Similar characteristics that alloy tool steels are subject to include:

• Chemical composition.
• Uniformity of structure.
• Manufacturability.
• Mechanical properties.

The quality of any steel directly depends on how much oxygen, hydrogen, nitrogen, sulfur and phosphorus it contains. The method of producing steel also plays an important role. The most accurate method from the point of view of falling into the required range of impurities is the method of steel smelting in electric furnaces.

Alloy steel and changes in its properties

Alloy steel, the grades of which contain in their markings the letter designations of forcedly introduced elements, changes its properties not only from these third-party substances, but also from their mutual action with each other.

If we consider carbon specifically, then according to their interaction with it, alloying elements can be divided into two large groups:

• Elements that form a chemical compound (carbide) with carbon are molybdenum, chromium, vanadium, tungsten, manganese.
• Elements that do not create carbides are silicon, aluminum, nickel.

It is worth noting that steels that are alloyed with carbide-forming substances have very high hardness and increased wear resistance.

Low alloy steel (grades: 20KhGS2, 09G2, 12G2SMF, 12KhGN2MFBAYU and others). A special place is occupied by the 13X alloy, which is hard enough to make surgical, engraving, jewelry equipment, and razors from it.

Decoding

Alloying elements in steel can be determined by its marking. Each of these components introduced into the alloy has its own letter designation. For example:

• Chromium – Cr.
• Vanadium –V.
• Manganese –Mn.
• Niobium – Nb.
• Tungsten –W.
• Titanium – Ti.

Sometimes there are letters at the beginning of the steel grade index. Each of them carries a special meaning. In particular, the letter “P” means that the steel is high-speed, “W” indicates that the steel is ball-bearing, “A” is automatic, “E” is electrical, etc. High-quality steels have a number and letter designation at the end the letter “A”, and especially high-quality ones contain the letter “Ш” at the very end of the marking.

Impact of alloying elements

First of all, it should be said that carbon has a fundamental influence on the properties of steel. It is this element that, with increasing concentration, provides an increase in strength and hardness while reducing viscosity and plasticity. In addition, increased carbon concentration guarantees deterioration in machinability.

chromium in steel directly affects its corrosion resistance. This chemical element forms a thin protective oxide film on the surface of the alloy in an aggressive oxidizing environment. However, to achieve this effect, the steel must contain at least 11.7% chromium.

Aluminum deserves special attention. It is used in the process of alloying steel to remove oxygen and nitrogen after purging it in order to help reduce the aging of the alloy. In addition, aluminum significantly increases impact strength and fluidity, and neutralizes the extremely harmful effects of phosphorus.

Vanadium is a special alloying element that gives alloyed tool steels high hardness and strength. At the same time, the grain in the alloy decreases and the density increases.

Alloy steel, the grades of which contain tungsten, is endowed with high hardness and red resistance. Tungsten is also good because it completely eliminates brittleness during the planned tempering of the alloy.

To increase heat resistance, magnetic properties and resistance to significant impact loads, steel is alloyed with cobalt. But one of those elements that does not have any significant effect on steel is silicon. However, in those grades of steel that are intended for welded metal structures, the silicon concentration must necessarily be in the range of 0.12-0.25%.

Magnesium significantly increases the mechanical properties of steel. It is also used as a desulfurizer in the case of off-furnace desulfurization of cast iron.

Low-alloy steel (its grades contain alloying elements less than 2.5%) very often contains manganese, which provides it with an inevitable increase in hardness and wear resistance while maintaining optimal ductility. But the concentration of this element must be more than 1%, otherwise it will not be possible to achieve the specified properties.

Carbon steel grades, smelted for various large-scale building structures, contain copper, which provides maximum anti-corrosion properties.

To increase red-hardness, elasticity, tensile strength and corrosion resistance, molybdenum is necessarily introduced into the steel, which also increases the resistance to oxidation of the metal when heated to high temperatures. In turn, cerium and neodymium are used to reduce the porosity of the alloy.

When considering the influence of alloying elements on the properties of steel, one cannot ignore nickel. This metal allows steel to achieve excellent hardenability and strength, increase ductility and impact resistance, and lower the cold brittleness limit.

Niobium is also widely used as an alloying additive. Its concentration, 6-10 times higher than the amount of carbon necessarily present in the alloy, eliminates intergranular corrosion of stainless steel and protects welds from extremely unwanted destruction.

Titanium allows you to obtain the most optimal strength and ductility indicators, as well as improve corrosion resistance. Those steels that contain this additive are very well processed with various special-purpose tools on modern metal-cutting machines.

The introduction of zirconium into a steel alloy makes it possible to obtain the required grain size and, if necessary, influence grain growth.

Random impurities

Extremely undesirable elements that have a very negative impact on the quality of steel are arsenic, tin, and antimony. Their appearance in the alloy always leads to the steel becoming very brittle along its grain boundaries, which is especially noticeable when winding steel strips and during the annealing process of low-carbon steel grades.

Conclusion

Nowadays, the influence of alloying elements on the properties of steel has been quite well studied. Experts carefully analyzed the impact of each additive in the alloy.

The theoretical knowledge obtained allows metallurgists, already at the stage of placing an order, to formulate a schematic diagram of steel smelting, determine the technology and the amount of required consumables (ore, concentrate, pellets, additives, etc.).

Most often, steelmakers use chromium, vanadium, cobalt and other alloying elements, which are quite expensive.

Source: https://FB.ru/article/288755/vliyanie-legiruyuschih-elementov-na-svoystva-stali-vidyi-marki-i-naznachenie-staley

Composition and application of alloy steel

[Alloy steel] is a material whose physical and chemical properties are improved by the addition of alloying elements to the composition.

It is durable, less susceptible to corrosion, and is used in various fields, including mechanical engineering, as well as to create various structures, pipes for various purposes, and parts that will subsequently be subject to high temperature fluctuations.

Chemical composition

The quality of steel depends on the amount of carbon in it, which is one of the main elements included in the composition. Another essential element is iron.

Chromium, nickel, vanadium, copper and other elements are added to improve the properties of the material.

Let's take a closer look at the influence of alloying elements on the properties of steel:

• Nickel - allows you to make the material not only durable, but also ductile. It is this element included in the composition that is responsible for resistance to corrosion;
• Chromium is also responsible for resistance to corrosion, thanks to it stainless steel is obtained, making it hard and durable;
• Vanadium - thanks to this element, the steel structure becomes fine-grained and dense;
• Copper - in addition to corrosion resistance, resists acids;
• Tungsten - allows the material to remain solid when the temperature increases (heating);
• Manganese, which is part of the composition, is responsible for wear resistance;
• Silicon – makes the metal elastic, responsible for magnetism;
• If the composition includes aluminum, then it allows the material to become heat-resistant.

What happens to the structure when various impurities are added? When they are introduced, the crystal lattice collapses due to differences in the forms of electrons, as well as atomic quantities. The characteristics of steel may vary depending on the composition.

The composition may include two, three or more impurities. It depends on what kind of final product you want to get.

The composition may also include titanium, cobalt, molybdenum, which are responsible for the strength, hardness and ductility of the material, which acquires all of the listed properties mainly after heat treatment has been completed.

Types of metal

There are carbon and alloy steels. Let's consider the difference.

Carbon steel is an alloy containing, in addition to iron and carbon, silicon and manganese. Sulfur and phosphorus, also included in the composition, are considered harmful impurities that reduce mechanical properties.

Based on the amount of carbon, such steel is divided into high-, medium- and low-carbon. The more carbon the composition is equipped with, the harder and less ductile the final product will be.

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Carbon steel, in turn, is divided into structural and instrumental types. Structural steel finds its application in the creation of metal structures, pipes, reinforcement for reinforced concrete and other building materials.

Instrumental types - after hardening they become harder, but brittle, their processing requires caution (GOST 1435-54).

Steel also comes in structural, instrumental types, and another type with special chemical properties is added (according to GOST).

Structural alloy steel is also used in mechanical engineering and construction, but it contains alloying impurities that improve the properties of the material from which structures, pipes and other building materials will be made.

The chemical composition of the alloyed metal may vary, based on this, the classification is presented below:

1. Low alloyed – the composition of alloyed additives does not exceed 2.5%. Structural steel is presented in GOST 5958-57 (depending on composition);
2. Medium alloyed - additives included in the composition are in the range of 2.5-10%;
3. Highly alloyed - the percentage of impurities included in the composition exceeds 10% (up to 50%).

The classification is also divided into heat-resistant (more than 1000 degrees), corrosion-resistant, and according to chemical decomposition into heat-resistant and scale-resistant (at 550 degrees).

It should be noted that the GOST classification applies to properties, as well as to the scope of application.

Metal marking

What does the marking of alloy steels mean? Marking according to GOST says the following: the letter means the name of the chemical element, and the number that is located after it indicates the percentage content of this impurity.

If there is no number behind the letter, then the percentage of content of this element is small and does not exceed 1%.

How much carbon is contained in steel can be understood by the first two numbers; it is also indicated as a percentage, but in hundredths. If instead of two there is one digit, it means that the percentage is indicated not in hundredths, but in tenths.

Classification and designation of brands by chemical composition:

Back in the USSR, GOST was developed, according to which this marking system was adopted. The remarkable thing is that it still remains relevant.

It should be noted that the classification and designation of chemical elements by letters does not always correspond to the initial letter of their name: manganese (g), chromium (x), nickel (n), copper (d), vanadium (f), tungsten (v), aluminum ( u), nitrogen (a), etc.

If there is a letter “A” in the middle of the marking, indicating nitrogen, then it indicates the nitrogen content.

If the letter “A” is at the end, then, therefore, sulfur and phosphorus are contained in small quantities (less than 0.03%), such steel is considered pure.

The double letter “A” at the end indicates a particularly pure material containing the above elements. The amount of sulfur is also determined in accordance with GOST.

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Also at the beginning of the marking you can find an additional designation: high-speed steel is designated by the letter “P”, ball-bearing steel is designated by “W”, automatic steel is designated by “A”, electrical steel is designated by the letter “E”, the letter “L” indicates that the steel was produced by casting.

For example, steel marking: 18ХГТ – carbon content is 0.18%, contains chromium, manganese and titanium.

Application of metal

As mentioned earlier, alloy steel has a number of properties that ensure its wide application. It allows the product to increase its service life, ensure its reliability and even save money in some way.

The use of alloy steels can be found in various fields, not only in mechanical engineering and construction, but also in surgery (equipment), the production of pipes for various purposes, and even knives are made from it, which remain sharp for a long time.

The scope of application directly depends on the composition of the elements, what kind of heat treatment was applied, etc. Previously, the classification by purpose (according to GOST) was considered: structural, instrumental and with special properties.

Machine parts, as well as various structures, are often made from pearlitic steels.

Low-alloy materials are characterized by good weldability, therefore they are used to create structures, and pipes are also made from them.

Alloyed tool steels are used to create parts designed to work under pressure (for example, Kh12MF). In the manufacture of cutters, drills and milling cutters, tool steels are also used.

According to GOST 5950-2000, the alloyed material has found its application in the creation of scalpels and knives, band saws, stamps, dies, gear rollers, etc. This GOST specifies the designation of steel and its scope of application.

Stainless steel, which contains chromium (in large quantities), is used in the creation of pipes and pipelines.

Such pipes are resistant to rust and resistant to temperature changes.

Welding alloy steels

Welding of alloy steels and their processing must be carried out taking into account certain points, for example, some elements begin to burn out, the metal at the welding sites begins to self-harden, carbides are released, and cracks may also appear due to the low level of thermal conductivity.

By the way, the thermal conductivity of carbon steel is higher than that of alloy steel.

The welding process must proceed correctly, excluding the phenomena described above.

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To do this, the temperature regime must be observed, thus eliminating the possibility of overheating of the structure; fluxes of various compositions should also be used.

The quality of welding primarily depends on the carbon content: the lower this indicator, the better the quality of welding.

Chromium stainless steel has its own characteristics when welding: due to the low carbon content, the welding process proceeds well.

To prevent stainless chrome steel from fading, use protection for the surface of the future product, as well as electrodes that contain chromium.

To restore viscosity, it is advisable to heat the metal before the process itself (up to 300 degrees), and after welding, anneal the seam (up to 800 degrees). In this case, it is better to use an electric arc.

An important point is that heat treatment of alloy steel with chromium must be carried out at high temperatures. The temperature directly depends on the amount of this element: the more there is, the higher the heat treatment temperature should be.

Stainless chromium-nickel steel at high heat treatment temperatures loses chromium carbides, because of this, the steel’s ability to resist corrosion in the seams is reduced, which is not suitable for the operation of many metal structures and various types of pipes.

To ensure the preservation of stainless properties, niobium or titanium is introduced. Annealing, processing and hardening (cooling) of the weld will ensure resistance to rust.

Manganese metal seams may crack during the welding process. To avoid this, welding is carried out with electrodes whose composition does not differ from the composition of the metal being welded.

Welding and processing must be done quickly, and the seams must be cooled upon completion.

In order for the welding quality to be “at the level”, it is necessary to pre-clean the surface. All scale, slag, and grease must be removed.

It is necessary to clean not only the surface of the intended seam, but also the area next to it (about 10 cm).

Welding or otherwise - heat treatment of alloy steel must occur without interruption and very quickly.

If the material is prone to cracking, then welding (heat treatment) should be carried out indoors, the temperature limit is minus 40 degrees.

The current strength must be constant; condensation, frost, or snow should not form on the surface of the material. It is better to entrust this process to specialists.

Source: https://rezhemmetall.ru/legirovannaya-stal.html