Why is steel alloyed?

Why steel is alloyed answer

High-alloy steels have a number of unique characteristics and properties, which is why the scope of application of these materials is so wide. The finished product is characterized by the following operational parameters: strength, ductility, deformation and corrosion resistance.

Compared to carbon steels, alloy steels have greater ductility. All alloy alloys have weldability and weldability properties. Engineering materials also have non-magnetic properties, thermal hardening, and elasticity. High strength is achieved by heat treatment of the treated composition.

Classification

Alloy steel is an iron-carbon alloy, into which, in addition to ordinary components, special impurities are introduced to change the basic physical or mechanical properties of the finished metallurgical product. The elements introduced into the alloy are called alloying elements. The most commonly used elements are nickel, vanadium, copper, chromium and many others.

Depending on the percentage of alloying additives, the following types of steel are distinguished:

1. Low alloyed (contains up to 2.5% alloying components);
2. Medium alloyed (additives from 2.5 to 10%);
3. Highly alloyed (over 10 to 50%).

There are several types of high-alloy steels and their alloys, each of which is suitable only for certain operating conditions. Based on their properties, there are two main types of steel:

1. Corrosion-resistant;
2. Heat-resistant, heat-resistant.

Depending on which alloying component is greater, the following types of steels are distinguished:

1. Chrome;
2. Chrome-nickel;
3. Chromomanganese.

Main scope of application

High alloy steel and its alloys are important materials. They are widely used in various spheres of human activity.

The greatest demand is in the oil industry, power engineering, the chemical industry, as well as for the manufacture of special structures that operate in aggressive environments (wide operating temperature range and temperature changes).

High-alloy steel is used in some applications as a cold-resistant element. When alloying it is possible to achieve certain mechanical properties.

Austenitic high-alloy steels are in greatest demand. It is an iron-based alloy, alloyed up to 55%. The composition also includes two main components: nickel (no more than 8%) and chromium (18% content). The selection of alloying components for such an alloy determines its service purpose and key properties.

For gas environments and product operating conditions in alkaline acids, corrosion-resistant alloy steels are used. A characteristic difference is the reduced carbon content in the main composition - only 0.12%. With further alloying and special heat treatment, a stable alloy is obtained that can withstand the destructive effects of a liquid metal or gas environment.

Steels containing 7% molybdenum or tungsten (components belong to the group of hardeners), as well as boron (an additive that allows grains to be refined) can be used for a long time in environments with high temperatures up to 1100 degrees. For special conditions, the alloy is alloyed with aluminum or silicon, which increases the scale resistance of the product. The elements can be used in ovens or as heating elements.

Promex LLC will produce a complex of services for processing high-alloy steel:

Alloy steels are used for the manufacture of heavily loaded parts for critical purposes, as they have significantly higher mechanical characteristics. When alloying steel, it is possible to obtain specified properties, including those that are absent in carbon steels (for example, corrosion resistance, heat resistance).

Alloy steels have a deeper hardenability of parts of the same dimensions than carbon steels. Many of their brands are calcined through even with large sections of parts. The more alloying elements in steel (up to a certain concentration), the higher its hardenability. Most alloying elements reduce the martensitic transformation temperature and improve the quality of retained austenite in the structure.

Depending on the total content of alloying elements, steels are divided into low-alloy (content of alloying elements up to 2.5%), medium-alloy (from 2.5 to 10%) and high-alloy (over 10%).

Alloy steels must contain at least 50% Fe; with less Fe, alloys with special properties are obtained. Steels are considered alloyed if they contain more than 0.8% Si and more than 1% Mn.

According to their purpose, alloy steels are divided into structural, tool, steels and alloys with special properties.

service properties, chemical elements such as Cr, Ni, W, Mo, V, B and others, as well as Mn and Si are introduced into structural alloy steels in quantities exceeding their usual content in carbon steels .

GOST provides the following letter designations for alloying elements included in steels: Mn - G, Si - C, Cr- X, Ni - N, Mo - M, W- B, V- F, Al - Yu, Ti - T, B - P, Cu - D, Nb - B. These letters, combined with numbers, indicate the composition of the alloy steel, for example: 45Х, 12ХН3А, ХВ5, 9ХС. The numbers in front of the letters indicate the carbon content in hundredths of a percent if there are two digits and in tenths of a percent if there is one digit.

The absence of numbers in front of the letters means that the steel contains 1% carbon or more. The numbers behind the letters indicate the average percentage of a given alloying element. The absence of a number after a letter means that this element contains up to 1%. The letter A at the end of the marking indicates high-quality steel, with a reduced content of S and P (less than 0.02% each).

For example, grade 12Х2Н4А means that it is high-quality chromium-nickel steel with a carbon content of 0.12%, Cr - 2%, Ni - 4%.

Of the 90 standard grades of structural alloy steels, most are medium carbon (0.25-0.45% carbon). They are used after improving their properties by hardening and tempering, which is why they are called improved.

The most common among them are: chromium (30Х, 38Х, 40Х, 45Х, 50Х), manganese (30Г, 35Г, 40Г, 45Г, 35Г2, 40Г2), silicon (55С2, 60С2), chromium-nickel (30ХН3А, 40ХН, 45ХН) , chromium-silicon (33ХС, 38ХС), chromium-manganese (35ХГ2, 4ХГ), chromium-manganese-silicon (30ХГС, 30ХГСА, 35ХГСА).

These steels are used in the production of loaded and heavily loaded machine parts.

Structural alloy steels, in comparison with carbon steels, have higher toughness and strength properties.

This is explained by the fact that: 1) all of them (except manganese steels) have a fine-grained structure; 2) they are calcined deeper; 3) they are quenched not in water, but in oil (and some in air), due to which they develop very low quenching stresses, and therefore they have higher ductility and viscosity; 4) during their tempering, a higher temperature and holding time are required than for carbon steels, as a result of which the quenching stresses in them are more completely relieved and the toughness is higher.

Source: https://MyTooling.ru/instrumenty/dlja-chego-legirujut-stali-otvet

Welding methods for alloy steels

Alloying of steels is carried out to obtain special properties that allow the material to be used in various extreme conditions for conventional steels.

Welding alloy steels has its own specifics, because it is necessary not only to obtain the necessary physical and mechanical reliability of the weld joint, but also to preserve the characteristics of the base alloy in it.

Material properties

Based on the amount of specially introduced impurities, alloyed (ennobled) steels are divided into:

• low alloy;
• medium alloyed;
• heavily alloyed.

In low-alloy structural steels, the amount of specially introduced impurities does not exceed 2.5%. In medium-alloyed alloys it reaches 10%, in highly alloyed alloys there are more than 10% of impurities.

Alloying additives most often are chromium, nickel, molybdenum, manganese, tungsten, aluminum, cobalt, vanadium, nitrogen, boron, titanium, silicon, niobium. Alloys are alloyed to obtain high mechanical and other properties.

Low alloy

In low-alloy and low-carbon alloys, the presence of carbon is less than 0.18%. They have ductility, good weldability, and are not brittle.

Steels 14G2, 15GS are low-alloy steels. High consumer qualities are achieved through the use of manganese, chromium, nickel, silicon and hardening of the alloy. Additives provide increased resistance to corrosion.

Characteristics

The main characteristics of welding quality is the resistance of the welded seams to cold cracks due to their fragility. Such alloys have a small percentage of carbon, nickel, and silicon. With the correct welding conditions and the use of the required additives, there will be no hot cracks.

For each type of low-alloy steel there is a maximum and minimum allowable cooling rate of the alloy around the weld. Depending on these limits, the range of welding work is selected. The amount of preheating of the workpieces also depends on this.

If the cooling rate limits are observed, cold cracks will not form around the seam.

Technology

For manual electric welding of alloy steels with 2.5% impurities, electrodes E70 and similar electrodes with calcium fluoride flux are used. The current strength is determined by the thickness of the metal, electrode, and its brand.

Welding must take place without stopping. Before the next pass, the temperature of the weld and the entire product must be above the preheating temperature (more than 200 °C).

When using flux, steel is welded using direct current. The current should be in the range of 800 A and the voltage 40 V. The welding speed should be in the range of 13-30 m/hour.

When butt welding, in order to avoid excessive strength of the weld, Sv-08KhN2M is used to fill it. When welding, the workpiece must lie on a flux pad if one-pass welding is used.

When welding low-alloy alloys in an inert gas environment, various materials are used. When working in carbon dioxide, use wire Sv-08G2S, Sv-10KhG2SMA.

When working with argon, the Sv-08HN2GMYU brand is used. It increases the mechanical strength of seams and their resistance to frost. It is recommended to use it for welding corner joints.

When using gas welding for alloy steel, due to strong long-term heating of the heat-affected zone of the welded part, alloying metals burn out, which reduces the corrosion resistance of the weld and its reliability.

To reduce the negative effect of prolonged overheating, filler wire SV-10G2, Sv-18KhGS and the like are used to restore the concentration of alloying metals in the weld.

After completing the welding process, to increase the mechanical strength of the seam, it is forged at a temperature of 800-850 ⁰C, then normalized.

Medium alloyed

Medium alloy steels are mainly alloyed with nickel, chromium, molybdenum, vanadium, the carbon content exceeds 0.4%. After hardening, the steel becomes strong, tough and ductile. Medium alloy steels of the KhVG, KhVSG, 9HS grades are widely used in the manufacture of drills.

These alloys are made from pure charge. It is cleaned of sulfur, phosphorus and other harmful inclusions. If necessary, electroslag remelting is used and refined with artificial slags.

The result is steel with excellent physical and mechanical characteristics. To further improve the characteristics of the alloys, medium-alloy steel is subjected to hardening and forging.

Ensuring seam quality

To ensure the required quality of welds, it is necessary to select welding materials in such a way that after welding the result is a seam that is close in physical and mechanical properties to the material being welded.

Since the base metal of the product is involved in the welding process, the welding materials used should have the amount of alloying impurities slightly less than in the base metal. This allows you to achieve the required level of strength and ductility of the seam.

When high-strength, medium-alloy steels with deep calcination are welded, it is necessary to select welding materials that minimize the presence of hydrogen in the welding zone.

This can be achieved by low-alloy electrodes, which have no organic materials in the coating, and which are subjected to high-temperature calcination before use.

In addition, when welding, you need to get rid of moisture, rust and other substances that can saturate the weld pool with hydrogen.

Electrodes

When welding medium-alloy steels, electrodes E-13Х25Н18, E-08Х21Н10Г6 and wire Sv-08Х20Н9Г7Т and Sv-08Х21Н10Г6 are used.

When using argon arc welding with a non-consumable electrode, you can obtain good quality welds on medium-alloy steels.

The use of activating fluxes increases the depth of the weld pool . Automated welding produces a uniform depth of metal penetration. For activating fluxes, the most resistant tungsten is used.

Gas welding for medium-alloyed metals is used using oxygen acetylene. It produces a high-quality seam, but it is still preferable to use electric welding.

High alloy

Highly alloyed alloys usually contain at least 16% chromium and at least 7% nickel, in addition to other impurities. Thanks to these and other additives, high-alloy alloys are highly resistant to low temperatures, corrosion and high temperatures.

But each brand has its own specialization, in which it has extreme characteristics. According to their purpose, high-alloy steels can be divided into heat-resistant, heat-resistant and corrosion-resistant.

After heat treatment they increase their strength and ductility. When hardened, their ductile properties improve.

Specificity

High-alloy alloys have such outstanding characteristics that they are used wherever the feasibility and price of the product allows.

But each specific product has different requirements. Accordingly, when carrying out welding work, different requirements for strength and ductility are imposed on welded seams, which leads to different approaches to welding work. That is, everything here is individual.

The presence of a large number of approaches in welding high-alloy steels is due to the fact that they have very specific thermophysical properties.

They have a low coefficient of thermal conductivity and a high coefficient of thermal expansion. In combination, they place conflicting demands on the welding process.

Low thermal conductivity leads to an increase in the depth of steel penetration. A high coefficient of thermal expansion causes deformation, including warping of parts. To reduce warping, it is necessary to concentrate thermal energy as much as possible. Laser welding does this well.

When manual electric welding of high-alloy alloys, the same measures are carried out as when welding medium-alloy alloys. The task is to minimize the entry of hydrogen into the welding zone, otherwise it causes the appearance of pores and cracks.

Choice of technology

For high-alloy alloys, gas welding is not recommended for acid-resistant steels, as it causes intergranular corrosion. Even when heat-resistant steels are used in welding, warping of products occurs.

Submerged arc welding has great advantages over manual electric arc welding due to the fact that the welding process takes place under protection in a constant environment with the same components. There is no need to change electrodes, which causes crater formation.

Submerged arc welding ensures a uniform weld with specified characteristics due to the protection of the weld pool from the external environment in the form of hydrogen.

In addition, preliminary work is reduced, since cutting edges is only necessary for thicknesses of more than 12 mm, and manual arc welding requires cutting edges for metal thicknesses of more than 5 mm.

Laser welding is the most effective for alloy steels due to the high concentration of energy in a small area. This allows you to virtually eliminate warping and deformation. Many alloyed alloys can be welded together, regardless of type, only when using laser welding.

Source: https://svaring.com/welding/soedinenie/svarka-legirovannyh-stalej

Steel alloying: classification and description of the process | mk-soyuz.rf

They learned to alloy steel back in the 19th century - the scientist Muschette invented a steel composition containing 1.85% carbon, 9% tungsten and 2.5% manganese; it was used to produce cutters used in metal-cutting machines.

Steel for mass production appeared thanks to the developments of the English metallurgist Robert Hadfield. Alloying the steel made it possible to obtain a composition of 1.0–1.5% carbon and 12–14% manganese; it was distinguished by increased wear resistance and good casting quality. This brand has survived virtually unchanged to this day.

Alloy steel has greater strength, corrosion resistance and ductility.

Types of alloy steels

Steels have a certain classification depending on their structure and application.

According to their structure they are divided into classes:

• martensitic (basic metal structure),
• martensitic-ferritic (structure contains martensite + 10% ferrite),
• ferritic,
• austenitic-martensitic (steels with a combined structure of austenite and martensite, the amount of which can be varied within wide limits),
• austenitic-ferritic (structure: austenite with ferrite content more than 10%),
• austenitic (stable austenite structure).

Based on the percentage of alloying additives, steel is divided into:

• low alloy – 5–10%,
• medium alloyed – 10%,
• highly alloyed – more than 10%.

Additional classification

Alloyed structural alloys are suitable for the manufacture of machine parts and mechanisms in the engineering industry - they produce large-sized parts that are hardened and subjected to high tempering. Most alloying additives in steel increase hardenability. The introduction of additives should be sufficient, but not excessive. A high degree of doping can cause:

• decrease in plastic properties,
• development of temper brittleness,
• lowering the threshold of cold brittleness.

The exception is nickel; it shifts the threshold of cold brittleness to the region of low temperatures, so for machines operating in the North, mechanisms are made from nickel-containing steels. Spring alloy steel contains 0.5–0.7% carbon, and chromium, molybdenum and tungsten are added as additives. Such a composition should provide high resistance to small plastic deformations and high fatigue resistance.

Ball bearings - classified as hypereutectoid - carbon is about 1% with additional alloying of the metal with chromium (1.3–1.65%). In heat-resistant bearings, chromium is increased to 5%. Bearings are subject to special requirements for metallurgical cleanliness. The use of refining remelts, vacuum remelting methods, and treatment with synthetic slags make it possible to reduce the proportion and size of non-metallic inclusions, thereby increasing resistance to contact fatigue.

Instrumental types

Alloy tool steel is intended for the production of metal-cutting tools operated at high cutting speeds and for the production of stamping tools.

High-speed steels are capable of maintaining high hardness and wear resistance of the cutting edge of the tool. Molybdenum, vanadium, tungsten, chromium and cobalt are added to this steel.

Cold work die steels containing 1.0–2.0% carbon have wear resistance and toughness. They are alloyed with chromium up to 12%, vanadium, tungsten, and molybdenum.

Die steels for hot deformation contain carbon in the range of 0.3–0.5%, have high heat resistance, impact toughness, and thermal fatigue resistance. Tungsten, molybdenum, and vanadium are introduced as additives.

Main purposes of alloying

The word "alloying" comes from the German "legieren" (to bind, to connect). The positive effect of alloying components on the properties of steel is associated with ensuring the occurrence of two physical and chemical processes.

Process No. 1

The formation of thermodynamic stable substitution solutions, accompanied by the replacement of part of the iron atoms (ions) in its crystal lattice (ions) of the alloying element. This leads to a distortion of the iron crystal lattice, since the radii of the ions (cations) of alloying elements differ from the radius of the iron cations, which increases the hardness and strength of iron while maintaining its ductility.

Process No. 2

The appearance of strong and practically insoluble chemical compounds in liquid iron between alloying additives introduced into the molten metal and non-metals dissolved in it (oxygen, nitrogen, sulfur, carbon, etc.).

The results of the formation of such compounds are:

• reduction of the residual content of dissolved non-metals in the molten metal, deteriorating its quality,
• reducing the total volume of harmful impurities (dissolved and in the form of non-metallic inclusions) in steel.

And also there is a release (precipitation) from the liquid metal of such small non-metallic inclusions, which serve as crystallization centers and lead to the formation of a fine-grained primary and secondary structure of steel.

Due to this, it has better ductility, low anisotropy of properties after rolling, etc.

Small non-metallic inclusions released during crystallization tend to accumulate on the surface of growing crystals, reducing the growth rate of the faces, and this, in turn, reduces the grain size of the steel.

Alloying process

The main way to alloy steel is the method of volumetric metallurgical alloying. It consists of fusing the main element with alloying elements in various types of furnaces (induction, vacuum-arc, crucible, converters, arc, plasma, etc.). With this method, a significant loss of active substances (manganese, chromium, molybdenum, etc.) is possible.

There are also:

• mechanical alloying,
• recovery,
• electrolysis,
• plasmachemical reaction.

Mechanical alloying is performed in attritors - drums, in the center of which there is a shaft with cams. Powdered components are placed in them to obtain the desired alloy. During rotation, the cams “hit” the mixture, and the alloying additives are “driven” into the base.

In co-reduction, the oxides of the alloy elements are mixed with a reducing agent, for example, calcium hydride (CaH2) and heated. The reaction of reduction of oxides to metals occurs, and the diffusion process occurs simultaneously, leveling the composition of the alloy. The resulting calcium oxide (CaO) is washed with water, and the alloy (in powder form) goes into the next processing. Metallothermic reduction involves the use of metals (magnesium, calcium, aluminum, etc.) as reducing agents.

With the help of surface alloying, the surface of the product is given special properties. A certain element or alloy is applied to the top layer in the form of a small layer, then it is exposed to energy (laser radiation, plasma, high-frequency current, etc.) - the surface is melted, and a new alloy is formed on it.

Difference Between Doping and Impurities

Conventional alloying additives are components that are introduced into the metal in significant quantities - more than 0.10%. They cause a change in the crystal lattice of iron, forming interstitial solutions, and increase the strength and other properties of iron (matrix).

The following metals are used for alloying:

• chromium Cr,
• manganese Mn,
• nickel Ni,
• aluminum Al,
• molybdenum Mo,
• cobalt Co,
• titanium Ti,
• zirconium Zr,
• copper Cu and others.

They are introduced into steel in different quantities and combinations.

Impurities

There is a division of harmful impurities into ordinary and residual. Common harmful impurities include those whose content in the metal can be reduced during smelting - phosphorus, sulfur, oxygen, nitrogen, carbon, i.e., non-metals.

Residual harmful impurities are usually understood as those whose content cannot be reduced during smelting either by oxidative refining or by conventional alloying. This is typical for chemical elements that have solubility in liquid iron. In industrial practice, the most commonly encountered harmful residual impurities are:

• copper,
• nickel,
• tin,
• antimony,
• arsenic.

Marking of alloy steels

In Russia and the CIS there is a brand designation system consisting of letters and numbers.

Designations of structural alloys

The marking of such steel consists of numbers and letters. The letters are the main alloying additives, the numbers after each letter show the content of the designated element, rounded to the nearest whole number (if the content of the alloying component is up to 1.5%, then the number behind the letter is not written). percentage of carbon, multiplied by 100, is written at the beginning of the name of the steel.

Marking of the main alloying components:

Element	Designation
Nickel	N
Cobalt	TO
Molybdenum	M
Chromium	X
Manganese	G
Bor	R
Copper	D
Zirconium	C
Phosphorus	P
Silicon	WITH
Niobium	B
Tungsten	IN
Titanium	T
Nitrogen	A (in the middle of the name)
Vanadium	F
Aluminum	YU
Rare earth metals	H

If steel with a limited sulfur content S and phosphorus P <.0.03% and is high quality, “A” is indicated at the end of the marking. High-quality steels produced by electroslag remelting are marked at the end of the name with the letter “Ш” separated by a dash, for example, 18ХГ-Ш.

Machine designations

The letter “A” is indicated at the beginning of the name. If lead is used as an alloying additive, then the marking will begin with “AC”. To display other elements, the same procedure applies as for structural alloy steels.

Marking of bearings

They are marked like alloyed ones, only with “Ш” at the beginning. For steel produced by electroslag remelting, an “Ш” is added at the end of the name through a dash. For example, ШХ8-Ш.

Designations of tool alloyed

They are marked similarly to structural alloy steels. The percentage of carbon content is indicated at the beginning of the marking, but differs in that it is multiplied not by 100, but by 10. If the carbon content is less than 1%, then the number at the beginning of the name of the steel grade is not indicated.

Marking of high-speed

They are marked at the beginning of the name with the letter “P” and a number indicating the tungsten content in the steel, followed by letters and numbers of other alloying elements.

Corrosion resistant markings

Corrosion-resistant (stainless), heat-resistant and heat-resistant have numbers in the designation and are written in the same way as the markings of structural alloy steels. For foundries, “L” is added.

Source: https://xn----ntbhhmr6g.xn--p1ai/metallyi/osobennosti-legirovaniya-stali

Why are alloying elements introduced into steel?

• Characteristic
• Properties
• Stamps

In the modern world there are a large number of varieties of steel. This is one of the most popular materials, which is used in almost all industries.

Characteristics of alloy steels

Alloy steel is steel that, in addition to the usual impurities, is also equipped with additional additives that are necessary for it to meet certain chemical and physical requirements.

Ordinary steel consists of iron, carbon and impurities, without which it is impossible to imagine this material. Additional substances are added to alloy steel, which are called alloying substances. They are used to ensure that steel has the properties that are necessary in certain situations.

In most cases, the following are added to iron, impurities and carbon as alloying elements: nickel, niobium, chromium, manganese, silicon, vanadium, tungsten, nitrogen, copper, cobalt. It is also not uncommon for such materials to contain substances such as molybdenum and aluminum. In most cases, titanium is added to add strength to the material.

This type of steel has three main categories. The relationship of alloy steel to a particular group is determined by how much steel and impurities it contains, as well as alloy additives.

Types of Alloy Steel

There are three main types of steel with alloying elements:

It is characterized by the fact that it contains about two and a half percent of alloying additional elements.

• Medium alloy steel.

This material contains from 2.5 to 10 percent of additional alloying substances.

• High alloy steel.

This type includes steel materials, the amount of alloying additives in which exceeds ten percent. The amount of these components in such steel can reach fifty percent.

Purpose of alloy steel

Alloy steel is widely used in modern industry. It has a high level of strength, which allows it to be used to manufacture equipment for cutting and chopping rolled metal of various types.

According to their purpose, alloy steels can be represented by a large number of groups.

The main ones are:

• structural alloy steel,
• tool alloy steel,
• alloy steel with special chemical and physical properties.

The characteristics of alloy steels can be varied. They acquire them due to the ratio of the basic elements. Steels of this type are in any case more durable and resistant to corrosion.

Properties of alloy steel

The properties of alloy steels are varied. They are mainly determined by those additives that are used as alloying agents in the production of certain types of steel materials.

Depending on the added alloying components, steel acquires the following qualities:

• Strength. This property is acquired after adding chromium, manganese, titanium, and tungsten to its composition.
• Resistant to corrosion. This quality appears under the influence of chromium and molybdenum.
• Hardness. Steel becomes harder thanks to chromium, manganese and other elements.

Attention: It is worth noting that in order for alloy steel to be more durable and resistant to external environmental influences, the required chromium content should not be less than twelve percent.

Alloy steel, with the correct percentage of all elements included in it, should not change its quality when heated to temperatures up to six hundred degrees Celsius.

Alloy steel grades

Alloy steel grades vary. They are presented in a wide variety. Depending on the purpose of the steel, its marking is determined.

Today there are a large number of requirements for marking alloy steel. Numerical and alphabetic notations are used for this process. First, numbers are used for marking. They are indicators of how many hundredths of carbon are contained in a particular type of alloy steel. After the numbers there are letters, which indicate which alloying additives were used in the production of a particular type of alloy steel.

The letters may be followed by numbers indicating the amount of alloying substance in the steel material. If there is no digital designation after the designation of any alloying element, then it contains a minimum amount of it, not reaching even one percent.

Table 1. Comparison of steel grades of type Cm and Fe according to international standards ISO 630-80 and ISO 1052-82

Steel gradesStFeStFe

One hundred	Fe310-0	St4kp	Fe430-A
St1kp	St4ps	Fe430-B
St1ps	St4sp	Fe430-C
St1sp	—	—	Fe430-D
St2kp	St5ps	Fe510-B, Fe490
St2ps	St5Gps	Fe510-B, Fe490
St2sp	Sg5sp	Fe510-C, Fe490
StZkp	Fe360-A
StZps	Fe360-B	St6ps	Fe590
StZGps	Fe360-B	Stbsp	Fe590
StZsp	Fe360-C	Fe690
StZGsp	Fe360-C	—
Fe360-D

Table 2. Symbols of alloying elements in metals and alloys

ElementSymbolDesignation of elements in grades of metals and alloysElementSymbolDesignation of elements in grades of metals and alloysblackcoloredblackcolored

Nitrogen	N	A	—	Neodymium	Nd	—	Nm
Aluminum	A1	YU	A	Nickel	Ni	—	N
Barium	Va	—	Br	Niobium	Nb	B	Np
Beryllium	Be	L	Tin	Sn	—	ABOUT
Bor	IN	R	—	Osmium	Os	—	OS
Vanadia	V	f	To you	Palladium	Pd	—	front
bismuth	Bi	In and	In and	Platinum	Pt	—	Pl
Tungsten	W	IN	—	Praseodymium	Pr	—	Etc
Gadolinium	Gd	—	Gn	Rhenium	Re	—	Re
Gallium	Ga	Gi	Gi	Rhodium	Rh	—	Rg
Hafnia	Hf	—	Gf	Mercury	Hg	—	R
Germanium	Ge	—	G	Ruthenium	Ru	—	Pv
Holmium	But	—	GOM	Samarium	Sm	—	Myself
Dysprosium	Dv	—	DIM	Lead	Pb	—	WITH
Europium	Eu	—	Ev	Selenium	Se	TO	ST
Iron	Fe	—	AND	Silver	Ag	—	Wed
Gold	Au	—	Evil	Scandium	Sc	—	From km
Indium	In	—	In	Antimony	Sb	—	Cv
Iridium	Ir	—	AND	Thallium	Tl	—	Tl
Ytterbium	Yb	—	ITN	Tantalum	Ta	—	TT
Yttrium	Y	—	THEM	Tellurium	Those	—	T
Cadmium	Cd	CD	CD	Terbium	Tb	—	Volume
Cobalt	Co	TO	TO	Titanium	Ti	T	TPD
Silicon	Si	WITH	Kr(K)

Source: https://masakarton.com/dlya-chego-v-stal-vvodyatsya-legiruyuschie-elementy/

Alloying of steel: influence of chromium, nickel and molybdenum

Chromium , nickel and molybdenum are the most important alloying elements in steels . They are used in various combinations and different categories of alloy steels are obtained: chromium, chromium-nickel, chromium-nickel-molybdenum and similar alloy steels.

The influence of chromium on the properties of steels

The tendency of chromium to form carbides is average among other carbide-forming alloying elements. At a low Cr/C ratio of chromium content relative to iron, only cementite of the type (Fe,Cr)3C is formed.

With an increase in the ratio of chromium to carbon content in Cr/C steel, chromium carbides of the form (Cr,Fe)7C3 or (Cr,Fe)23C6 or both appear.

Chromium increases the ability of steels to be thermally hardened, their resistance to corrosion and oxidation, provides increased strength at elevated temperatures, and also increases the abrasive wear resistance of high-carbon steels.

Chromium carbides are also wear-resistant. They are the ones who provide durability to steel blades - it’s not for nothing that knife blades are made from chrome steels.

Complex chromium-iron carbides enter the solid solution of austenite very slowly - therefore, when heating such steels for hardening, a longer exposure at the heating temperature is required. Chromium is rightfully considered the most important alloying element in steels.

The addition of chromium to steels causes impurities such as phosphorus, tin, antimony and arsenic to segregate to the grain boundaries, which can cause temper brittleness in steels.

The influence of nickel on the properties of steels

Nickel does not form carbides in steels. In steels, it is an element that promotes the formation and preservation of austenite. Nickel increases the hardening of steels.

In combination with chromium and molybdenum, nickel further increases the thermal hardening ability of steels and helps to increase the toughness and fatigue strength of steels. By dissolving in ferrite, nickel increases its viscosity.

Nickel increases the corrosion resistance of chromium-nickel austenitic steels in non-oxidizing acid solutions.

The influence of molybdenum on the properties of steels

Molybdenum readily forms carbides in steels. It dissolves only slightly in cementite. Molybdenum forms molybdenum carbides once the carbon content of the steel becomes high enough. Molybdenum is capable of providing additional thermal hardening during tempering of hardened steels. It increases the creep resistance of low-alloy steels at high temperatures.

Molybdenum additives help refine the grain of steels, increase the hardening of steels by heat treatment, and increase the fatigue strength of steels. Alloy steels containing 0.20-0.40% molybdenum or the same amount of vanadium slow down the occurrence of temper brittleness, but do not completely eliminate it.

Molybdenum improves the corrosion resistance of steels and is therefore widely used in high-alloy ferritic stainless steels and in chromium-nickel austenitic stainless steels. High molybdenum content reduces the susceptibility of stainless steel to pitting corrosion.

Molybdenum has a very strong solid solution strengthening effect on austenitic steels that are used at elevated temperatures.    

Source: https://steel-guide.ru/klassifikaciya/legirovanie-stali/legirovanie-stali-vliyanie-xroma-nikelya-i-molibdena.html

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.

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.

  Classification of steels by weldability

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.

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://steelfactoryrus.com/dlya-chego-v-stal-vvodyatsya-legiruyuschie-elementy/

Classification and scope of alloy steels

The scope of application of alloy steels extends to the field of mechanical engineering. Due to their high strength and temporary resistance from 800 to 2000 MPa, they are used for the production of external structures operating at low negative and high positive temperatures, under the influence of alternating shock loads and aggressive working environments. Some types of such alloy steels are used in the reinforcement of reinforced concrete frames.

Composition of alloy steels

Alloy steels, in addition to traditional impurities, contain specific substances that are deliberately added in a regulated amount in order to ensure specific physical and mechanical characteristics. These elements are called alloying elements.

Alloying elements of steel significantly increase the strength properties of the metal, its corrosion resistance, and reduce brittleness. Among such additives, the most popular are chromium, nickel, copper, nitrogen (in a chemically bound state), vanadium, etc.

Mixing with iron, they change and destroy the symmetrical arrangement of the crystal lattice, since they have different atomic quantities and the shape of the outer electron shells.

Significant structural strength is acquired through rationalized selection of the chemical composition of alloy steel, its structure, thermal processing conditions, surface hardening methods, and increased metallurgical characteristics. The level of alloying elements content increases the cost of steel, this determines the strict validity of the range of additives.

The key role in the composition of alloy steel belongs to carbon, which increases its strength, but reduces its plastic and ductile qualities, which is why the cold brittleness threshold increases. In this regard, its content is limited within certain limits and only in exceptional cases is it higher than 60%. Based on the level of alloying, metals are classified into low-, medium- and high-alloy.

According to this classification, alloy steels in the first case contain less than 2.5% additives, in the second - 2.510%, in the third - 1050%.

In addition, a distinction is made between steel that is corrosion-resistant with respect to electrochemical and intergranular corrosion; scale- and heat-resistant surface relative to chemical decomposition at 550 °C and above; heat-resistant, which is characterized by significant heat resistance and the ability to work under load for a long time at 1000 ° C and above.

Heat-resistant high-alloy steel is a category of metal that can be used at the most critical temperatures (1/3 of the melting point) under the influence of a light load without obvious residual deformation and decay.

The main features of this type of metal are long-term plastic deformation and strength over time, which is expressed in resistance to decay under long-term influence of temperature.

Heat-resistant qualities are mainly determined by the melting point of the base element of the alloy, its alloy additive and the parameters of the previous heat treatment, which determine the structural phase of the alloy.

A significant increase in structural strength in alloyed iron is caused by high hardenability, a decrease in the critical hardening rate, and grain fragmentation. The use of strengthening heat treatment improves a number of mechanical properties. As a result of this, alloyed structural steels have improved mechanical characteristics (heat, heat and corrosion resistance) and significantly changed physicochemical and technical operational properties.

Main characteristics of alloy steels

The advantageous properties of alloy steels are the following:

• combination of significant strength and toughness parameters at positive and negative temperatures; • excellent technological qualities; • efficiency; • large production volumes; • serious parameters of resistance to plastic deformation; • alloying additives help stabilize austenite, which increases the hardenability of such steels; • the possibility of using lightweight coolers reduces the risk of defects due to cracks and warping during hardening, since the destruction of austenite is reduced; • the margin of plasticity and viscosity increases, which ensures high reliability of finished products;

• beneficial properties are revealed only after heat treatment of alloy steel, therefore manufactured products undergo a mandatory stage of thermal exposure.

An alphanumeric algorithm is used to describe alloy steel grades. Alloying additives correspond to a specific letter of the alphabet. The numbers indicated before the letters indicate the carbon level in tenths or hundredths of a percent, depending on the class of steel.

The numbers following the letters indicate the level of alloying additives as a percentage. When their level is more than 1.5%, the digital designation is not used.

Indicating the letter A at the end of the marking of alloy steels indicates that the metal is of high quality.

Low alloy steel is characterized by excellent ductility, sufficient weldability and strong resistance to brittleness. It obtains excellent mechanical qualities during hardening, normalization and further high tempering. It has a low carbon content.

High strength characteristics are obtained by introducing manganese, chromium, nickel or silicon additives. The influence of alloying elements on steel is manifested in excellent weldability and the ability to absorb mechanical stress during deformation and disintegration under impact load with a low cold brittleness limit. This steel has a fine-grained texture.

But high sensitivity to stress concentration causes reduced vibration stability.

Alloy steel welding process

The main welding parameters of low-alloy steels are their resistance to local intercrystalline cracks and brittle fracture. Indicators when choosing modes of welding operations are the maximum permissible maximum and minimum cooling rates of the heat-affected area of ​​the steel.

The maximum cooling rate is selected taking into account the prevention of cold cracks in this area. The current value of the welding process is taken in accordance with the type and thickness of the electrode, the location of the seam, the category of connection and the layer of iron being welded are also assessed.

Welding of technological zones should be carried out continuously, without cooling the seam below the initial heating temperature and preheating it above 200 °C before further passage.

Gas welding of such steels is characterized by a high degree of heating of the welded edges, low corrosion resistance and strong burnout of alloying elements, which significantly worsens the properties of the welded joints. To prevent negative moments during such welding, filler wire is used, forging at 800 °C with further normalization.

Structural low-alloy steels are used for the production of welded devices for various purposes. This category includes heat-resistant steel alloyed with molybdenum, tungsten or vanadium elements to increase the temperature at which the metal softens when heated and with chromium to increase heat resistance.

High-alloy steel is easily subject to intercrystalline corrosion, which precludes the use of gas welding. This connection option is allowed only if heat-resistant specimens are treated with a layer of up to 2 mm, but there is still a risk of warping.

Submerged arc welding of high-alloy steel is the optimal way to join metal up to 5 cm thick, since the processing ensures stable characteristics of the sheet composition throughout the entire seam.

Most alloyed tool steels belong to the pearlitic class. They contain a small number of alloying substances and are excellent for compression processing and cutting.

Tool type steel is in demand in the production of cutting tools and hot deformation forms with increased wear resistance. The metallurgical industry produces a wide range of products from such materials that comply with specific GOST standards.

The main purpose of alloy steels is to produce hot-rolled products.

Source: https://promplace.ru/vidy-metallov-i-klassifikaciya-staty/legiruyushie-stali-1487.htm

Why alloying elements are introduced into steel - Metalworker's Handbook

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.

High-alloy steel: description, welding technology, markings and features

Nowadays, it is quite difficult to overestimate the importance of metallurgical products, which are widely used in industry, construction, and the manufacture of household utensils and household items.

But alloy steels deserve special attention, without which a large number of industries (mechanical engineering, petrochemical, energy, food, manufacturing of special structures, the main purpose of which is to work in aggressive conditions) would not be able to perform their main functions.

A natural question arises: what is alloy steel and its alloys? What is the classification of alloying elements? What are the main characteristics and properties of high alloy steel? We will try to answer these and some other questions as fully as possible in our article.

Types: high-alloy steels, alloys

Let's consider another interesting point. High-alloy steel and its alloys also have a classification. Each of the following types is used in certain conditions:

• Heat-resistant or heat-resistant steels.
• Corrosion resistant.

Based on the percentage of alloying element, the following types are distinguished:

• Chrome-manganese steel.
• Chrome-nickel.
• Chrome.

Use of high alloy steels

Where is this metal used? High-alloy steels and their alloys are integral components in the production of various products. The following industries cannot do without their use:

• Chemical.
• Oil industry.
• Mechanical engineering.
• Construction.
• Manufacturing of structures whose main purpose is to work in aggressive conditions (high temperature, extremes).

The addition of alloying elements allows one to achieve certain mechanical properties. Therefore, high-alloy steel is used as a cold-resistant component. This metal is especially common in mechanical engineering.

The most popular are high-alloy austenitic steels, in which the alloy component occupies about 55%, and the rest is iron, chromium (about 18%), nickel (8%).

Alloying components of this composition determine the further purpose of the manufactured product.

Corrosion-resistant high-alloy steels are used in a gas environment or alkaline acid. Their characteristic difference is the reduced carbon content - approximately 0.12%. Further alloying and heat treatment make it possible to obtain a special alloy that can withstand the aggressive conditions of a gas or liquid metal environment.

The use of steels containing tungsten or molybdenum at 7% and boron allows operation at temperatures up to 1100 degrees. Tungsten and molybdenum are elements that are classified as hardeners. To increase the scale resistance of manufactured products, silicon or aluminum are added as alloying elements. Such structures can be used as heating elements or furnaces.

Main characteristics of the metal

High-alloy steel has properties and characteristics that allow the products to be used more widely. Such steels have the following characteristics:

• Strength (achieved through heat treatment).
• Corrosion resistance.
• Resistance to deformation processes.
• Plasticity (compared to carbon steel, ductility is many times greater).
• Nonmagneticity (steels used in mechanical engineering).
• Elasticity.
• Hardening.
• Weldability.

Due to the fact that the alloy formula is different, the properties are varied. The structure is easily changed due to heat treatment and alloying components. In this way, it is possible to obtain the properties required by the project conditions. For example, high-alloy 18% chromium steel may contain nickel, which makes it possible to obtain corrosion resistance and cold brittleness.

Welding high-alloy steels allows us to obtain products that can be used in any climatic conditions. Thus, the stamp-welding method allows the final product to be used at critically low temperatures - down to minus 253 degrees Celsius. Special treatment with silicon makes it possible to obtain ferrosilides that can work in strong acids (nitric, phosphoric and others).

High-alloy steel is hard and highly abrasive. Thus, acid-resistant materials are C15 and C17, and chromium, vanadium and manganese increase the wear resistance of the alloy.

Types of high-alloy steels by thermal properties

Based on thermal characteristics, there is the following classification:

• Platinite (EN42) - used for the production of electrodes that are used in incandescent lamps. This is because the expansion coefficient is the same as glass.
• Elinvar (Х8Н36) – ideal for clock springs and measuring instruments. This is explained by the fact that the elastic modulus is constant and does not collapse at temperatures from -50 to +100 degrees Celsius.
• Invar (I36) - used for the production of standards and calibration elements, since the expansion coefficient is zero.

An interesting property of corrosion steel (high alloy stainless steel only) is magnetism. Therefore, non-magnetic and magnetic types of such metals are distinguished. The former are divided into soft magnetic and hard magnetic subspecies, and the latter contain cobalt and chromium.

GOST: high alloy steels

The requirements for such durable metals and heat-resistant alloys are regulated by special standards, namely GOST 5632-72.

High alloy steel grades

The most popular and well-known steel grades are:

• Ferritic: 15Х28, 12Х17, 08Х18Т1, 15Х25Т, 08Х18Тч, 10Х13СУ.
• Martensitic: 15Х11МФ, 40Х9С2, 18Х11МНФБ, 40Х10С2М, 95Х18, 25Х13Н2, 20Х17Н2, 13Х11Н2В2МФ, 40Х13, 20Х13, 20Х17Н2, 13Х14Н3В2ФР.
• Austenitic-martensitic: 07Х16Н6, 08Х17Н5М3, 08Х17Н6Т, 09Х17Н7У1.
• Austenitic-ferritic: 08Х21Н6М2Т, 08Х22Н6Т, 08Х20Н14С2, 20Х23Н13, 12Х21Н5Т, 03Х22Н6М2.
• Martensitic-ferritic: 12Х13, 18Х12ВМБФР, 14Х17Н2, 15Х12ВНМФ.
• Austenitic: 05Х18Н10Т, 45Х22Н4М3, 45Х14НМВ2М, 10Х14Г14Н4Т, 03Х18Н10Т, 08Х16Н13М2Б, 12Х18Н12Т, 03Х18Н12, 03Х16Н15М3Б, 10Х11Н23Т3МР , 20Х23Н18, 10Х11Н20Т2Р, 12Х18Н9Т, 12Х18Н9, 20Х25Н20С2.

Application of alloying steel grades:

• 40Х13, 30Х13 – used for carburetor needles, springs for transport, surgical instruments.
• 12X17 is a grade of high-alloy steel used for the manufacture of kitchen utensils and household items.
• 20Х13, 12Х13, 08Х13 – used for the manufacture of elements of hydraulic installations and structures that operate in slightly aggressive conditions.
• 95Х18 – used for the production of high-hard ball bearings.

Source: https://FB.ru/article/253463/vyisokolegirovannaya-stal-opisanie-tehnologiya-svarki-markirovka-i-osobennosti