Powder metallurgy: production technology, products

The powder metallurgy process is relatively new and has several advantages over the metal casting process. However, this process cannot completely replace the casting function and has its advantages and disadvantages.

The advantages of powder metallurgy are that the quality and efficiency of the resulting material is high. As a result of the process, it is possible to make a resulting material whose density and melting point will be quite high.

The disadvantage of the powder metallurgy process is the limited shape and precision that could be made.

Powder for raw materials (particles ranging in size from 0.01 to 500 microns) is one of the fundamental problems that also needs to be addressed. Although the ore reserves are large, this powder needs to be produced. In addition, to identify the advantages and disadvantages of powder metallurgy, it is necessary to consider:

how the powder material is prepared;
what are the stages of the manufacturing process;
how the pressure must be set in order to obtain a product that is sufficiently strong;
how the sintering temperature and time must be set so that the resulting binding atom is considered strong enough;
how the workpiece design can be processed using powder metallurgy.

The process of producing metal using powder metallurgy has been fairly well known since the 18th century.

Powder metallurgy is the process of forming a workpiece from a commercial metal in which the metal is first broken down to form flour, then pressed in a mold and heated below the melting point of the powder so as to form the workpiece. So the mixing of metal particles is due to the mechanism of mass transfer due to the diffusion of atoms between the surfaces of the particles. The method implies a scrupulous attitude to the composition and use of the mixture. A powder product may consist of a mixture of powders of various metals and other materials to increase the hardness and quality of the objects as a whole.

Cobalt or iron binds tungsten particles, graphite is added to metal bearings to improve the quality of bearings, etc.

Pros of production

This method of producing parts has a number of advantages that allow it to replace more expensive metal processing methods: casting, forging and stamping.

The existing number of advantages:

Cost-effective – the starting material for the production of powders is various types of waste, for example, scale. This waste from metallurgical production is not used anywhere else, and powder metallurgy methods make it possible to compensate for such technological losses.
Accuracy of geometric shapes of parts. Products made by powder metallurgy do not require subsequent cutting processing. Consequently, production is carried out with a low percentage of waste.
High wear resistance of products.
Simplicity of the technological process.

The production technology of powder metallurgy has much in common with the production of ceramic products.

What these processes have in common is that the raw material (in one case sand and clay, in the other metal) is immersed in a hot furnace. The result is a porous structure of the material. This similarity of technological processes has led to the fact that parts made by powder metallurgy are called metal-ceramic.

Production stages in powder metallurgy

Steps to follow to determine the benefits of powder metallurgy include:

Preparation and production of powder.
Mixing.
Molding and compaction.
Heating (sintering).

There are several ways to make the powder, among others:

Decomposition occurring in a material containing a metallic element. The material will decompose/separate elements when heated to a high enough temperature. This process involves two reagents, namely metal compounds and a reducing agent. The second reactant may be a tangible solid, liquid, or gas.
The spraying of liquid metals onto a nozzle through which water is supplied under pressure so that the resulting granules are small.
Electrolytic deposition, the manufacture of powders using an electrolysis process, which typically produces a powder that is highly reactive and brittle. This material needs to be given a specific annealing treatment. The shape of the granules obtained by electrolyte deposits is dendritic (the shape of Christmas tree branches).
Mechanical processing of hard materials, production of powders using ball milling. The material produced by machining should be a material that cracks easily, such as pure metals, bismuth, antimony, a metal alloy that is relatively hard and brittle, and ceramics.

Mixing

Powder mixing can be done by mixing different metals and other materials to provide better physical and mechanical properties. There are two types of mixing, namely:

Wet mixing, which is a process in which the powder matrix and filler are mixed first with a solvent. This method is used if the material used (matrix and filler) is easily subject to oxidation. The purpose of the solvent is to facilitate the process and coat the surface to prevent oxidation from occurring on the material being used.
Dry mixing, that is, the mixing process is carried out without the use of solvents to promote dissolution, and is carried out in the outside air. This method is used when the material used is not easily oxidized.

The determining factors for uniformity of particle distribution are mixing speed, length of mixing time, particle size and type, temperature and process environment. The higher the mixing speed, the more uniform the particle distribution is. The homogeneity of the mixture greatly affects the pressing (compaction) process, since the compression force specified at the moment of compaction will be distributed evenly, so the quality of the connection between particles will be better.

Pressing (compaction)

Compression is the process of compressing powder into the desired shape according to the mold. There are 2 types of compaction methods, namely:

Cold pressing, namely emphasis without strong heating, but with pressure from 100 to 900 MPa. This method is used when the materials used are easily oxidized, such as aluminum. The cold pressing process may consist of pressing a die which is done on a mold containing powder. Cold pressing, focusing on room temperature powder that has equal pressure on all sides. Rolling is also used, namely focusing on powder metal using a rolling mill.
Hot pressing at temperatures above room temperature. This method is used when the material used is not oxidized.

The essence of pressing is so that the powder can stick to each other until its bond is improved by the sintering process. In the process of producing an alloy by powder metallurgy, the binding powder is formed as a result of adhesion between the surfaces, interaction by adhesion and diffusion between the surfaces, which can occur during the sintering process. The shape of the items that are removed from pressing, the so-called compact raw materials, should resemble the final product, but its strength is still low.

To avoid differences in density at the time of pressing, a lubricant is used to reduce friction between the particles and the walls of the mold. When using a lubricant, select one that does not react with the powder mixture and that has a low melting point so that the original level of lubricant evaporates during the sintering process.

During the compaction process, 3 bonding models are possible:

Drawing of glue balls. Occurs when the magnitude of the given compressive force is less than the yield strength of the matrix and filler, so that the powder does not change shape permanently or deform elasticity better on the matrix and filler, so that the powder remains spherical.
Ball type gluing pattern. Occurs when the magnitude of the compressive force is provided between the yield strength of the matrix and the filler. This leads to the fact that one material (matrix) is plastically deformed, while the other (filler) is not, so that the resulting particles seem to form a spherical field.
Drawing of communication zones. Occurs when the magnitude of the compressive force provided is greater at the yield point of the matrix and filler. This leads to the fact that the two materials (matrix and filler) are plastically deformed, so that the resulting particles seem to form fields.

Heating (sintering)

Heating at temperatures below the melting point of composite materials is called sintering.

During the sintering process, solid objects are formed due to the bond formed. Heat causes particle unity and the efficiency of the surface tension reaction increases. In other words, the sintering process causes particles to coalesce in such a way that the density increases. During this process, grain boundaries are formed, which is the stage of recrystallization. The sintering temperature is usually 0.7-0.9 from the melting temperature. Heating time depends on the type of metal. The environment directly inside the die is very important because the raw material is made up of small particles that have a large surface area. Therefore, the environment must consist of reducing gas or nitrogen to prevent the formation of an oxide layer on the surface during the sintering process.

Sintering parameters include temperature, time, cooling rate, heating rate, atmospheric sintering and material type. Based on the nature of the bonding that occurs during the compression process, we can distinguish 2 phenomena that can occur at the time of sintering, namely:

Shrinkage

If at the moment of compaction a bonding pattern of the ball field is formed, then during the sintering process shrinkage occurs, which occurs due to the fact that during the sintering process the gas (lubricant) located on the porosity experiences degassing (gas release at the time of sintering). And if the sintering temperature constantly increases, then diffusion will occur on the surface between the particles of the matrix and the filler, on which the liquid bridge of the neck is finally formed (a phase mixture is formed between the matrix and the filler). The liquid bridge covers the porosity.

Cracks (cracking)

It is possible that during compaction, adhesion between particles is formed in the form of closed volumes, causing gas/lubricant to be trapped inside the material. At the moment of sintering, the trapped gas did not have time to escape, but the liquid bridge had already occurred, so the path was closed. Gas trapped in this trap will be pushed in any direction such that it will swell (expand) so that the pressure will be higher than the pressure outside. If the quality of the bonding surface of the particles in a composite material is poor, then it will not be able to withstand more pressure and cracks (cracking) will occur. Cracks can also occur as a result of a less perfect compaction process, the presence of thermal shock at the time of heating due to thermal expansion of the matrix and filler.

The sintering process includes a 3-stage heating mechanism:

Pre-sintering is a heating process that is aimed at: – reducing the residual stress caused by the compaction process – displacing gas or solid lubricant that is retained in the porosity of the composite material (degassing). Do not change the temperature too quickly during the sintering process to avoid thermal shock. The pre-sintering temperature is usually carried out at 1/3 of the melting temperature.
Diffusion procedure During the heating process, until mass transfer occurs on the surface between powder particles interacting with each other, low-temperature sintering (2/3) is performed. Atoms on the surface of the particles diffuse between the surfaces, thereby increasing the strength of the material.
Eliminating Porosity The ultimate goal of the substrate sintering process is to produce a material that has high strength. It is precisely because of the presence of diffusion between the surface of the powder particles that a neck (liquid bridge) appears between the particles. Heating leads to the elimination of porosity (formation of sintered density).

Finishing

At the time of finishing, the porosity of the fully sintered material is still significant (4-15%). To improve properties, heat treatment can be carried out.

Technological process for the production of powders

The production of a metal-ceramic part begins with the production of powders. Powders come in different fractions and sizes. Hence the difference in the methods of their production.

There are two groups of fundamentally different methods for producing powders:

Physico-mechanical methods - grinding through mechanical action on metal particles in the solid or liquid phase. These methods are based on a combination of static and shock loads.
Chemical-metallurgical methods – changing the phase state of the feedstock. This is the reduction of oxides and salts, electrolysis, thermal dissociation of carbonyl compounds.

There are key points about the methods used for the production of metal powders:

Ball method - small metal scraps with shavings are crushed and ground in a ball mill.
The vortex method is the injection of a strong air flow in special mills (using fans), leading to mutual collision of metal particles. The output is a high-quality crushed powder with saucer-shaped grains.
Use of special crushers. The operating principle of such devices is based on the crushing of metal particles using the impact of a falling load.
Spraying – a low-melting metal in the liquid phase is sprayed with a stream of compressed air. After this, it is sent to a rapidly rotating disk for grinding.
Electrolysis - metal is reduced from the melt under the influence of electric current, which makes it brittle. This property allows it to be easily ground in a mill to a powder state. The shape of the powder grains is dendritic.

Metal cutting

The production of powders by metal cutting is used very rarely in practice. Powders are obtained during machine processing of compact metals, selecting a cutting mode that ensures the formation of particles rather than drain chips.

In this case, it is advisable to use the generated waste in the form of large chips for further grinding in ball, vortex and other devices, and small chips and sawdust with a powder particle size of about 1 mm can be used for the manufacture of products without additional crushing. In some cases, the use of this method for obtaining powder is almost the only one. First of all, this applies to those metals that are very reactive towards oxygen, especially in a state of high dispersion. For example, magnesium powder is obtained using this method.

Physico-mechanical methods

The powder of the required fractions is obtained in centrifugal mills of various types.

Centrifugal mill

Primary grinding is an intermediate stage in the production of powders. It is carried out in cone and roller crushers. These devices will produce small metal particles with a size not exceeding 1 cm.

The grinding procedure can last, depending on the technology used, from one hour to 3–4 days. When it is necessary to shorten this process, vibration mills are used rather than ball mills.

In such mills, the intensity of the process increases due to the presence of cutting forces and the creation of alternating stresses. The final powder particle size ranges from 0.009 mm to 1 mm.

In order to increase the productivity of the grinding process, it is carried out under conditions of liquid exposure - to prevent metal atomization. The volume of liquid involved is 40% of the mass of the crushed particles.

Planetary centrifugal mills are used to grind carbide particles. The negative side of the operation of such a device is the frequency of its operation.

Physical-mechanical methods are not suitable if it is necessary to grind non-ferrous metals with high ductility. Ductile metals are crushed by vortex mills; their operating principle is based on the grinding of particles by their mutual impacts.

Vortex mill

III. Physico-chemical methods for obtaining powders

Physico-chemical methods for obtaining metal powders. Compounds are metal halides that are reduced either by hydrogen or by active metals (sodium and magnesium). The mechanism for the reduction of most solid compounds by gaseous reducing agents is based on the adsorption-autocatalytic theory.

Reducing agents are gases (hydrogen, carbon monoxide, dissociated ammonia, natural convertible, water, coke or blast furnace gases), solid carbon (coke, charcoal, soot) and metals. The choice of reducing agent depends not only on thermodynamic assessments, but also on volatility, which should be minimal, since otherwise the process must be carried out at elevated pressure using argon or other inert gases.

Iron powder —

the basis of a multi-tonnage PM. There are methods for producing powders from FeCl 2. Iron powder reduced with hydrogen has high purity and cost.

Reduction with carbon monoxide is carried out at temperatures above 1000°C based on the adsorption-catalytic mechanism. Reduction with solid carbon occurs at 900-1000°C.

The soda method is used to obtain powder of increased purity. 10-20% soda is added to the charge, with which impurities interact during reduction, forming water-soluble sodium aluminates.

The combined process includes restoration with magnesium, and after washing - with calcium, the consumption of which is halved. Reduction with calcium hydride produces powder of titanium and its hydride. Reduction of titanium chloride with sodium. Titanium chloride is obtained by chlorination of ore concentrate, purification and fractional distillation. Reduction of titanium chloride with magnesium is the most economical method. The reaction occurs at 800 - 900°C. A sealed steel apparatus is filled with magnesium ingots, the air is pumped out, filled with argon, the magnesium is melted, and a limited amount of titanium chloride is fed on top to prevent overheating.

Recovery from solutions, gaseous compounds and in plasma.

From solutions of Ni, Cu, and Co compounds, metals are displaced with hydrogen in autoclaves.
You can shift the hydrogen potential in the negative direction by increasing the pH or increasing the hydrogen pressure. It is more effective to change the pH, an increase of which per unit is equivalent to a 100-fold change in hydrogen pressure. Thermal calculations show that these metals can be deposited already at 25°C and 0.1
MPa
.
The reduction of gaseous compounds with hydrogen is carried out in a fluidized bed of tungsten, rhenium, molybdenum, niobium and titanium halides.
The production of highly dispersed powders in plasma is promising for metals, carbides, nitrides, etc. Reducing agents are
hydrogen or plasma conversion products at high temperatures and without oxidizing agents. Nickel oxide is reduced in a stream of Ar - H2 or Ar - CO, and the hydrogen content is close to stoichiometric, and heat exchange and plasma formation occur due to argon. The reaction is limited by the dissociation of NiO; its complete reduction is achieved at 7000°C.

Physico-chemical basis for producing powders by electrolysis. The process is a kind of reduction: the transfer of electrons to the metal with simultaneous restructuring of the structure occurs not with the help of reducing agents, but due to electrical energy. The method is universal and ensures high purity of powders. Electrolysis is one of the most complex physical and chemical processes for the production of powders. The process involves the decomposition of aqueous solutions of compounds of the released material. The presence of chlorine or fluorine on the anode forces measures to be taken to prevent its interaction with the electrolyte and powder. The electrolyte is separated from the powders by distillation, heating or centrifugation and washing.

Electrolysis of aqueous solutions.

A method for producing powders of copper, silver, iron, nickel, cobalt, tin, etc. Nickel, zinc, cobalt form uniform dense fine-grained sediments, regardless of the nature of the electrolyte. Silver or cadmium grows in the form of separately highly branched crystals during the electrolysis of simple salts; from a solution of cyanide salts they are released in the form of an even, smooth layer.

Obtaining copper, nickel, iron powder. Copper powder is obtained from a solution of copper sulfate; it has high purity and adjustable dispersion. Nickel powder is obtained by electrolysis of ammonia solutions of nickel chloride. The peculiarities of obtaining iron powder are associated with the fact that in the series of voltages iron is located to the left of hydrogen, so the latter is released together with hydrogen, worsening the yield

19) Classification of metal-cutting machines

The USSR adopted a unified system of classification and symbols for domestically produced machine tools, based on assigning a special code (number) to each machine.

Depending on the type of processing, metal-cutting machines are divided into nine groups: 1) turning; 2) drilling and boring; 3) grinding, polishing, finishing and sharpening; 4) special; 5) gear and thread processing; 6) milling; 7) split; planing, slotting, broaching;

9) different. In turn, the machines of each group are divided into nine types. For example, machines of the second group (drilling and boring) are divided into the following types: 1) vertical drilling, 2) single-spindle semi-automatic, 3) multi-spindle semi-automatic, 4) jig boring, 5) radial drilling, 6) horizontal boring, 7 ) diamond boring, horizontal drilling, 9) various drilling. Within each type, metal-cutting machines may differ from each other in design features. These features, as well as some other characteristics, are reflected in the code (number) of the machine. For example, the symbol of the machine model is 1K62. The first number indicates that the machine belongs to the first group - lathes. The second digit indicates the type of machine within the group. In this case, the number 6 indicates that this is a screw-cutting lathe. The third and fourth numbers conventionally indicate the main dimensions of the machine (for lathes, for example, the height of the centers above the bed, for milling machines - table dimensions, etc.). In the model under consideration, the third number - 2 - indicates the height of the centers above the frame, which is 215 mm. In addition to numbers, the symbols of a machine model often include letters. If the letter appears between the first and second digits (as in the above example), this means that the design of the machine has been improved compared to the previous model. If the letter appears at the end of the machine number, then this indicates a change in the main, or, as is commonly called, “basic” model of the machine. The most numerous group of metal-cutting machines are lathes (45). They are used in mechanical, tool and repair shops of machine-building and other factories, as well as in repair shops. Lathes are usually used for processing parts that have the shape of bodies of revolution. These machines produce external and internal cylindrical and conical surfaces, shaped surfaces and end planes, threads on cylindrical and conical surfaces, etc. Thus, rollers, bushings, axles, bolts, screws, studs, boards, washers, etc. are made on lathes. .d. The main dimensions characterizing a lathe include the largest permissible diameter of the workpiece being processed, the height of the centers above the bed and the distance between them. Using these dimensions, you can determine the maximum diameter and length of the workpiece that can be installed and processed on this machine. A significant part of metal-cutting machines are milling machines. The most common are console-milling machines. The table of a console-milling machine with a slide is located on the console and moves in three directions: longitudinal, transverse and vertical. Cantilever milling machines are designed to perform various milling operations using cylindrical, disk, shaped and other cutters in single and batch production. This type of milling machine can be used to mill planes, grooves, shaped surfaces, gear teeth, etc. In addition, universal cantilever milling machines (having a rotary table) allow you to mill various types of helical grooves. The main dimensions of milling machines, by which one can determine the possibility of installing and processing specific workpieces with certain dimensions, are the dimensions of the working surface of the table (length and width) and the working stroke of the table in the longitudinal, transverse and vertical directions. Planing machines are used in mechanical shops of machine-building plants for individual, small-scale and serial production, as well as in repair and tool shops. They are designed for processing by planing the surfaces of parts of various geometric shapes and sizes made of steel, cast iron, non-ferrous metals and plastics. Cross-planing machines (47) are more widely used. The main dimensional characteristics of cross-planing machines, which make it possible to determine the possibility of processing certain workpieces, are as follows: the dimensions of the working surface of the table, the largest and smallest stroke of the slider, the largest and smallest distance between the upper plane of the table and the slider, and the overhang of the cutter. Grinding machines (48) are designed for finishing parts by removing a thin layer of metal from their surface with grinding wheels. These machines can be used to process external and internal cylindrical, conical, shaped and flat surfaces, cut workpieces, grind threads and gear teeth, sharpen tools, etc. Grinding machines are used both in serial and mass production. The main dimensional characteristics of cylindrical grinding machines are the largest diameter. of the workpiece being processed and its greatest length, the greatest transverse movements of the grinding head.

Metal-cutting machine , a machine for cutting metal and other materials, semi-finished products or workpieces for the purpose of obtaining products from them by removing chips with a metal-cutting tool.

20) The destruction of surface layers of a material under the influence of external influence of electrical discharges is called electrical erosion. The principle of electrical discharge machining (EDM) is based on this phenomenon.

Electrical discharge machining involves changing the shape, size, roughness and surface properties of a workpiece under the influence of electrical discharges as a result of electrical erosion (GOST 25331-82). Under the influence of high temperatures in the discharge zone, heating, melting, and partial evaporation of the metal occur. To obtain high temperatures in the discharge zone, a large concentration of energy is required. To achieve this goal, a pulse generator is used. The EDM process occurs in the working fluid, which fills the space between the electrodes; in this case, one of the electrodes is a workpiece, and the other is a tool electrode.

Under the influence of forces arising in the discharge channel, liquid and vaporous material is ejected from the discharge zone into the working fluid surrounding it and solidifies in it with the formation of individual particles. At the site of the current pulse, holes appear on the surface of the electrodes. In this way, electrical erosion of the conductive material occurs, shown by the example of the action of one current pulse in Figure 1, and the formation of one erosion hole. Figure 1 — EEE process diagram

The materials from which the electrode tool is made must have high erosion resistance. The best indicators regarding the erosion resistance of EI and ensuring the stability of the electrical erosion process are copper, brass, tungsten, aluminum, graphite and graphite materials.

1. 2 Working environment

Working fluids (WF) must meet the following requirements: — ensuring high technological performance of EEE;

— thermal stability of physicochemical properties when exposed to electrical discharges with parameters corresponding to those used in electrical discharge machining;

— low corrosion activity to EI materials and the workpiece being processed; — high flash point and low volatility;

— good filterability; — no odor and low toxicity.

Low-molecular hydrocarbon liquids of various viscosities are used in electrical discharge machining; water and, to a small extent, organosilicon liquids, as well as aqueous solutions of dihydric alcohols. For each type of EDM, working fluids are used to ensure optimal processing conditions. In roughing modes, it is recommended to use working fluids with a viscosity (a mixture of kerosene-industrial oil), and in finishing modes (kerosene, hydrocarbon feedstock).

1. 3 Tool electrodes

Tool electrodes (EI) must ensure stable operation over the entire range of EEE operating modes and maximum performance with low wear. Electrode-tools must be sufficiently rigid and withstand various conditions of mechanical deformation (forces of pumping the liquid fluid) and temperature deformations.

There should be no dents, cracks, scratches or delamination on the surface of the EI. The surface of the EI must have a roughness

When processing carbon steels, tool steels and heat-resistant nickel-based alloys, graphite and copper EIs are used. For rough EDM of workpieces made from these materials, EDM made from aluminum alloys and cast iron is used, and when processing holes, EDM made from brass is used. When processing hard alloys and refractory materials based on tungsten, molybdenum and a number of other materials, EIs made from composite materials are widely used, since when using graphite EIs, high productivity is not ensured due to the low stability of the electrical discharge process, and EIs made of copper have high wear, reaching ten percent, and high cost.

The wear of the EI depends on the material from which it is made, on the parameters of the working pulse, the properties of the RL, the area of the surface being processed, and also on the presence of vibration.

The choice of material and design of the EI is significantly influenced by the material of the workpiece, the area of the machined surface, the complexity of its shape, the requirements for accuracy and serial production of the product.

INTRODUCTION

In modern mechanical engineering, technological problems arise related to the processing of new materials and alloys (for example, heat and acid-resistant, special nickel steels, refractory alloys, composites, non-metallic materials: diamonds, rubies, germanium, silicon, refractory powder materials, etc.) the shape and condition of the surface layer of which is difficult to obtain by known mechanical methods.

Such problems include the processing of very strong or very viscous materials, brittle and non-metallic materials (ceramics), thin-walled non-rigid parts, as well as grooves and holes measuring several micrometres in size; obtaining surfaces of parts with low roughness and a very small thickness of the defective surface layer.

Under these conditions, when the possibility of cutting is limited by the poor machinability of the product material, the complexity of the shape of the machined surface, or processing is generally impossible, it is advisable to use electrophysical and electrochemical processing methods. Their advantages are as follows:

1) mechanical loads are either absent or so small that they practically do not affect the total processing accuracy error;

2) allow you to change the shape of the processed surface of the workpiece (part);

3) allow you to influence and even change the state of the surface layer of the part;

4) hardening of the treated surface does not form;

5) no defective layer is formed;

6) surface burns caused by grinding are removed;

7) increase: wear resistance, corrosion resistance, strength and other performance characteristics of the surfaces of parts.

The kinematics of shaping the surfaces of parts using electrophysical and electrophysical processing methods is, as a rule, simple, which ensures precise control of processes and their automation.

Purpose of the work: to prove the advantages, and in some cases the indispensability of electrochemical dimensional processing. Understand the mechanism of action of electrochemical processing methods.

HISTORICAL REFERENCE

The development of the fundamentals of the electrochemical method and its technological application belongs to the talented scientist V.N. Gusev (1904...1956). In 1929 he received a patent for electrochemical processing. The first experiments on dimensional electrochemical processing of metals were carried out in the 40s of the last century. In 1954, he received a patent for sharpening drills with carbide tips.

The initial period of development of the method is characterized by the fact that, along with its use in production (to obtain the airfoil profile of turbine and compressor blades, forging dies, molds, ring parts, piercing holes and slots, sharpening tools, removing burrs, etc.), there was an accumulation of experimental and static data; Attempts were made at theoretical generalizations that would make it possible to predict in advance, without testing, the final results of processing.

Chemical methods, in addition to etching methods, include electrochemical processing.

This method can be used to process particularly hard and viscous electrically conductive materials. This achieves:

a) high metal removal rate (more than 1000 mm/min);

b) high accuracy class;

c) there is no tool wear;

d) there are no residual stresses;

e) there is no damage to the material of the part;

e) there are no burrs on the edges of the cut.

The famous Russian chemist E.I. Shpitalny in 1911. developed an electrolytic polishing process. In 1928, V.N. Gusev used this process for dimensional processing of beds of large metal-cutting machines. The electrolyte was not pumped. The cathode plate was temporarily removed and the layer of dissolution products was removed using a hand tool. The process was labor-intensive and slow. V.N. Gusev and L.A. Rozhkov proposed to reduce the gap between the electrodes to tenths of a mm, and force the electrolyte to be pumped through the interelectrode gap.

This was the birth of a new type of processing - dimensional electrochemical processing (ECM) - due to the anodic dissolution of the metal.

In 1948 An electrochemical installation was created for making holes in armor steel. At the same time, the first experiments on processing turbine blades were carried out. Significant advances in the development of theory and improvement of technology were achieved thanks to the work of Yu.N. Petrova, I.I. Moroz, L.B. Dmitrieva and others.

Chemical-metallurgical methods

The iron recovery method is used more often than others. It is made from ore oxides or scale formed during hot rolling. During the metal reduction reaction, it is necessary to constantly monitor the amount of gaseous compounds in the powder.

Exceeding the maximum permissible norm of their content will lead to increased fragility of the powder. And this, in turn, makes the pressing operation impossible. If this excess cannot be avoided, vacuum treatment is used to remove a large amount of gases.

The method based on spraying and granulation is the cheapest and easiest to obtain powders. Crushing occurs under the influence of jets of melt or inert gas. Spraying is carried out using nozzles. Adjustable parameters of the spraying process are temperature and pressure of the gas flow. Cooling – water.

The use of electrolysis as a method for producing powders is most appropriate for the task of producing copper powders that have a high degree of purity.

Production of powder products

Electrolysis

Among the physicochemical methods for producing metal powders, the electrolytic method in industrial distribution ranks second after reduction. The production of powders by electrolysis involves the decomposition of aqueous solutions of compounds of the isolated metal or its molten salts by passing a direct electric current through them and the subsequent discharge of the corresponding metal ions at the cathode.

During electrolysis, the transfer of electricity in an electrolyte, which is a solution of salts, acids and bases, is carried out by the movement of positive and negative ions formed as a result of the dissociation of the molecules of these chemical compounds. Ions in the electrolyte move chaotically in the absence of an external electric field. When an electric field is applied, the movement of ions becomes ordered, and cations move to the cathode, and anions move to the anode.

An electric current source is a kind of motor or pump that moves electrons from one pole to another. As a result of this forced movement of electrons at the cathode, an excess of negatively charged electrons is formed; an excess of negatively charged electrons is formed at the cathode and it acquires a negative charge, and the anode, having lost some electrons, acquires a positive charge.

The source of the released metal ions is an anode consisting of this metal and an electrolyte containing its soluble compound. In the case of using an insoluble anode, the source of released metal ions is only the electrolyte.

The transformation of a metal ion into an atom involves the expenditure of a certain amount of energy. Therefore, the discharge process that requires less energy takes place first. In this regard, electrolysis is also a refining process, since not all cations present in the electrolyte can be released at the cathode under given conditions. In this case, the electrolysis method makes it possible to obtain high-purity powders, allowing the use of even contaminated starting materials.

Depending on the electrolysis conditions at the cathode, it is possible to obtain hard brittle deposits in the form of dense layers, spongy soft deposits and loose deposits. Solid and spongy sediments are crushed to obtain powder, and loose sediments are used as finished powder. The main factors influencing the structure of the cathode deposit are:

concentration of released metal ions;
electrolyte temperature;
current density.

Concentration of metal ions released

The concentration of released metal ions affects the quantity and quality of the cathode deposit. During electrolysis, the release of metal on the cathode does not begin over its entire surface, but in separate places, in the primary centers of crystallization. An increase in the concentration of released metal ions creates accelerated nutrition of these centers, resulting in the formation of a dense precipitate. A decrease in the concentration of metal ions in the electrolyte creates conditions for the formation of a loose precipitate. However, if the concentration is too low, other ions will be involved in the electrotransfer process, which will reduce the amount of cathode deposit.

Electrolyte temperature

As the temperature increases, the mobility of ions increases, their transfer accelerates, and an increased concentration of cations at the cathode remains. At the same time, the intensity of the chemical interaction of the released metal with the electrolyte increases, which leads to a decrease in the amount of metal deposit on the cathode. In addition, the volatility of the electrolyte increases, worsening working conditions. In practice, the electrolysis of aqueous solutions is carried out at an electrolyte temperature of 40–60 ºС, and the electrolysis of melts is carried out at a temperature below the melting point of the released metal, ensuring minimal occurrence of side processes.

Current Density

Current density is the current passing through 1 m2 of electrode. It connects the current strength, which is the main factor characterizing its performance, with the total working area of the cathodes or anodes in the bath:

П=J⁄S, where

P – current density, 2 mA;
J – current strength, A;
S – total working area of cathodes or anodes, m2.

The cathode and anode current densities in the bath do not coincide, since the total surfaces of the cathodes and anodes always differ from each other for a number of reasons. At a high current density, more ions are discharged per unit area of the cathode and thus many primary crystallization centers are created. Due to the low rate of crystal growth, small, dispersed precipitates are formed. However, high current density leads to the release of by-products at the cathode and reduces the amount of deposited metal deposits. In addition, with an increase in the cathode current density, the anodic current density also increases, as a result of which the discharge of side ions begins at the anode, leading to a deterioration in technical and economic indicators. Therefore, the current density should be the maximum permissible and not exceed the optimal value.

The change in current density is carried out by changing the current strength in the bath or by changing the number of cathodes (cathode surface) at a constant current strength.

Other factors also influence electrolysis and the properties of the cathode deposit. In particular, the distance between the electrodes, the duration of powder build-up, the acidity of the electrolyte, the presence of foreign ions in it, the circulation rate of the electrolyte, the shape and condition of the surface of the electrodes and other factors.

Electrolysis can be used to obtain powders of all metals. Currently, powders of copper, iron, silver, zinc, nickel, cadmium, tin, antimony, and their alloys are produced by electrolysis.

The electrolytic method of producing powders is characterized by low productivity and a fairly high cost of the resulting powder. However, the purity and high technological properties of electrolytic powders largely compensate for the disadvantages of the method.

Properties of metal powders

Powders, like any other material, have a number of standard properties that affect its technological suitability. Experts include the following properties:

the density of powders, called pycnometric, is determined by the chemical purity of the powder and the degree of its porosity;
the bulk density of a powder is its mass obtained by freely filling a container of a certain volume;
The fluidity of powders is the speed at which a container of a certain volume is filled. This is a very important technological parameter, because the performance of subsequent pressing depends on it;
plasticity is the property of powders to take a given shape and retain it after the load is removed.

Molding

Forming powders is a preparatory operation preceding the pressing process. Includes heat treatment, mixture preparation and dosage. Thermal annealing helps improve the plasticity properties of powders.

Heat treatment takes place in a protective gas environment at a temperature of 40 to 60 percent of the melting temperature of the metal. To obtain a homogeneous composition of powders, they must undergo a separation operation: sifting metal particles through special sieves. Only after the powder has been sifted should one proceed to preparing a mixture of powders of the desired composition.

Compacting

Powder metallurgy also involves a procedure that is based on the production of semi-finished products in the form of rods and strips. After pressing, you can obtain a product almost ready for use.

The features of the compaction process include the following points:

A bulk substance is used as a raw material when carrying out the process under consideration.
After compaction, the bulk powder becomes a compact material with a porous structure. The strength of the resulting product is acquired during other processing processes.

Principle of Powder Metallurgy

Considering the powder pressing process, we note the use of the following technologies:

rolling;
slip casting;
isostatic pressing by applying pressure with gas or liquid;
pressing on one or both sides when using special metal matrices;
injection method.

In order to speed up the compaction process, the powder product is exposed to high temperature. In most cases, the distance between individual particles is reduced by exposure to high pressure. Powders made from soft metals have great strength.

Pressing

The essence of the pressing process is the tight connection of metal powder particles with each other. The operating pressure of a mechanical press ranges from 1 to 6 thousand kg per square centimeter.

Products obtained by pressing do not have high strength characteristics. Therefore, they require heat treatment, which consists of sintering powders. During the melting process, metal particles form strong interatomic bonds with each other, making the part homogeneous in its structure.

It is worth noting that often the pressing and sintering operations are combined into one - hot pressing.

Moreover, heating in this case is carried out with high-frequency currents. The production of parts from powders by hot pressing significantly reduces the time spent on their production.

This factor allows you to save energy resources and reduce the cost of production.

Manufacturing parts from metal powder

Eurobalt Engineering is a powder metallurgy company. We accept applications for the production of parts using pressing and sintering. Thanks to the modern technological base, our company quickly and efficiently produces large quantities of these products. We will ensure strict control over the production process at all its stages, which guarantees high quality products and compliance of their characteristics with the requirements of project documentation.

Features of pressing and sintering technology

The technology of pressing and sintering metal powders has long been used in industry. Powder metallurgy allows you to create parts with complex shapes or with a large number of holes with minimal material loss. This technology is used in the manufacture of flanges, gears and other elements that fall into the category of sintered products.

The production process consists of several stages:

Preparation of a working mixture, which can consist only of metals or with the addition of other components. To obtain powder, the metal is crushed mechanically, sprayed in molten form, or chemical reaction methods are used.
Molding of the workpiece by cold pressing.
Sintering the mixture to create a monolithic product.

The finished sintered parts are calibrated to achieve ideal geometry and dimensional accuracy. The products are also subjected to additional mechanical processing and impregnated with lubricant.

The advantages of products made using the technology of forming and sintering metal powders include increased strength, resistance to deformation and temperature changes. Using additional components in the manufacture of a powder mixture, you can increase the hardness, coefficient of friction or other parameters of the finished part. These properties allow the parts to be used in various industries.

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Application areas of powder metallurgy parts

The powder industry as a method of manufacturing and processing metals is very diverse in its technological methods. This makes it possible to obtain parts of the required composition and properties.

Using powder metallurgy production methods, specialists can produce the latest composite materials, which cannot be obtained using traditional methods. The production of machine parts and mechanisms from metal powders provides significant savings on material due to a low consumption coefficient.

Metal-ceramic products are used in a wide range of areas of instrument making, radio electronics and mechanical engineering. Powders are also used in the production of cutting tools: cutters, drills.

Drills are made of powder metal

The production of products from metal powders currently has a high degree of automation. The technological simplicity of operations allows the use of workers without high qualifications. These factors have a positive effect on the cost of powder metallurgy products.

At a porosity level of powders that does not exceed the norm, they are not inferior in terms of corrosion resistance. Especially parts manufactured using standard methods.

Powder metallurgy products have the ability to withstand sudden temperature changes. Therefore, they are used in environments operating under such conditions.

Technology for obtaining and using flux-cored wire for the production of quality steels

Among metal products for industrial use, flux-cored wire

(PP) occupies a special place both in terms of high growth rates of production volumes and in terms of the raw materials and equipment used.

In Western Europe and Japan, the technology for processing liquid steel with the so-called flux-cored wire appeared in 1980-81. In our country, the beginning of work on the production of domestic PP for out-of-furnace processing of ferrous alloys can be dated back to 1988, when a corresponding decision was made by the USSR Ministry of Ferrous Metallurgy. In 1989, TsNIIchermet and MSTU named after. Bauman developed the first pilot complex of equipment for the production of metallurgical PP. In 1990, NPO Tulachermet, together with the Tula Cartridge Plant, began work on creating the first samples of domestic tribal devices and equipment for the production of PP. In 1990-91 Work began in this direction at the Chepetsk Mechanical Plant in Glazov.

In 2004, the Vulcan-TM Research and Production Enterprise (Tula) began production of lines for the production of flux-cored wire and tribe devices. Currently, NPP Vulkan-TM carries out a complete supply of flux-cored wire production lines and processing devices as part of a technological complex for the out-of-furnace processing and casting of steel and alloys (Appendix). The manufactured equipment is not inferior in quality to imported analogues and has significant advantages.

Structurally, cored wire

"wire with a core") consists of an extended metal sheath filled with a powdered reagent.

The wire is fed into the ladle using a special "cored wire injector" machine.

allowing the speed and quantity of input materials to be adjusted within a wide range depending on the mass of the metal and the depth of the ladle. In the ladle, the wire sheath is melted and the supplied substance falls directly into the liquid metal.

The method of out-of-furnace processing of steel using powder reagents in an extended metal shell has a number of undeniable advantages, such as:

low capital investments and production costs, simplicity and reliability of machine designs, compatibility with existing technological processes in metallurgical shops;

high and stable absorption of introduced additives, low consumption of materials and precise control of the specified chemical composition of the finished metal;

lack of contact and interaction of introduced additives with oxygen and moisture in the air and with slag;

short duration of the operation, absence of excessive bubbling, cooling and entrapment of gases in the metal;

minimal labor costs for the servicing work crew, compliance with strict safety and industrial sanitation requirements, explosion safety, absence of dust and gas emissions, ease of control, mechanization and automation of the technological operation;

ease of transportation and storage of PP, ease of preparation for introducing filler materials into the metal;

possibility of use, including with preliminary storage and transportation of hydrophilic, flammable and toxic reagents;

increasing the productivity of melting units, simplifying and reducing the subsequent technological process for the production of deformed and cast billets;

increasing and stabilizing at a high level the quality characteristics, composition and properties of the metal, reducing defects, achieving a certain economic effect.

Flux-cored wires are used to bring steel grades such as St3, 10, 20, 40, 45, 30X, 35X, 40X, 45G, 48A, R6M5, 09G2S, 09G2D, 09G2FV, 15KhGMNT, 16D, 17G2AF, 17G1S to the required chemical composition, 18G, 18ХГТ, 20УЧ, 22ГУ,

23Х2Г2Т, K-74, as well as Grade45, Grade50, Grade55

(according to US standard
ASTM A 607-92a)
, etc.

In addition to the out-of-furnace processing of metals and alloys, small-diameter flux-cored wire has become widespread in the welding industry since the 50s. XX century

Details of friction units

The specificity of the use of metal-ceramic products is due to their ability to retain lubricants well. This feature is determined by their porous structure.

This property facilitates the manufacture of parts from powders that experience friction in their work: sliding bearings, guide bushings, liners, electric motor brushes.

The porous structure of powder bearings allows them to be impregnated with oil. Subsequently, the lubricant gets onto the rubbing surfaces. Such bearings are called self-lubricating.

Self-lubricating bearings

They have the following advantages:

profitability - the use of such bearings allows to reduce oil consumption;
wear resistance;
saving on material. Replacing expensive bronze and babbitt with iron.

Experts can enhance the porosity property of metal-ceramic parts by adding graphite to them during manufacturing, which is known to have high lubricating properties. Bearings with a high graphite content do not require the use of oil.

Composite materials

The powder industry has developed greatly with the development of high-tech technology requiring products made of composite materials. The difference between composites and alloys is the ability to obtain strong compounds of dissimilar metallic and non-metallic components.

Traditional smelting in metallurgical furnaces does not create solutions, for example, tungsten and copper. After the advent of composite materials, this problem was solved.

This result is achieved by simply mixing the necessary components, shaping it on a press, followed by sintering.

Nuclear fuel is also a composite material.

Hard alloys

Carbide products are produced using metal-ceramic methods. Increased hardness is achieved by including carbide inclusions in the composition. As is known, with an increase in the proportion of carbon in a metal, its hardness increases.

Carbide compounds provide high viscosity while maintaining the strength properties of the powder. Metal-ceramic parts are needed where their high wear resistance is required. Most often, these are cutting tools, as well as carbide dies and punches for sheet stamping.

Powder metallurgy

Other applications of powders

Another useful property of powders is their heat resistance, which allows them to be used in various brake mechanisms. The heat-resistant properties of metal ceramics increase with the addition of chromium, nickel and tungsten to its composition.

Almost all modern magnetic parts are made from metal powders. Powder metallurgy technology makes it possible to obtain iron compounds with various silicates.

Metal-ceramic products are also used to filter gases and flammable substances.

Disadvantages of powders

Among the disadvantages of powder metallurgy methods, one should highlight the impossibility of manufacturing parts with complex geometric shapes, as well as the relatively small size of products. The strength and uniformity of the structure of the powders is inferior to parts made by die forging, hot forging and drawing.

Parts made from powders have a lower density compared to parts made by metal forming. This factor is of increased importance when it is necessary to lighten any component of the mechanism. This enables design engineers to solve problems of reducing metal consumption without losing the performance properties of parts.

Powder metallurgy requires strict adherence to fire safety measures. The tendency for powders to spontaneously ignite is a dangerous production factor that requires strict adherence to safety regulations.

Powder steel manufacturing technology

Powder steels have been used to make knives for over 30 years. Over the years, the price of such steels has decreased significantly, they have become more accessible and are applicable in a wide variety of knives, including those not only in the premium segment. What is the difference between powder steel and “regular” steel and how is it created?

Powdered steel is steel crushed to a powder state, which is sprayed in an inert gas, then the suspension is fed to a special crystallizer, and then the resulting micro-ingots are pressed at ultra-high temperatures and sintered in a special furnace. As a result of these actions, the so-called powder processing occurs - the steel receives a large amount of carbides, which are responsible for cutting the knife, and at the same time it can be alloyed with additional strength-enhancing elements.

The structure of any hardened steel consists of two important elements: carbides and martensite.

Martensite is the main structural component of hardened steel (matrix). It is an ordered supersaturated solid solution of carbon in α-iron of the same concentration as the original steel material (austenite). The structure of martensite is nonequilibrium, and there are large internal stresses in it, which largely determines the high hardness and strength of steels with a martensitic structure.

Carbides are compounds of metals and non-metals with carbon. A special feature of carbides is the high electronegativity of carbon compared to other elements. Carbides are refractory solids. They are non-volatile and insoluble in any known solvent. Carbides are used in the production of cast iron and steel, ceramics, various alloys, as abrasive and grinding materials, as reducing agents, deoxidizers, catalysts, etc. Grinding wheels and other abrasives are made from silicon carbide SiC (carborundum); Iron carbide Fe3C (cementite) is a component of cast iron and steel; tungsten carbide and chromium carbide are used to produce powders used in thermal spraying.

Most steels used for the production of blades, after heat treatment, have the structure: martensite + carbides (+ retained austenite + non-metallic inclusions, etc.). Carbides, which are harder and more brittle than the martensitic matrix, increase the wear resistance of steel, but degrade its mechanical properties, negatively affecting strength and toughness. The degree of reduction in strength properties depends on the amount of the carbide phase, its type, the size of the carbides and their clusters, and the uniformity of the distribution of carbides in the structure.

In addition, pronounced carbide heterogeneity creates problems during grinding and increases the tendency for leads and cracks. Steels with a large number of large and unevenly distributed carbides are less susceptible to hot deformation. During heat treatment, such steel acquires a non-uniform structure, and the results of heat treatment themselves become less predictable.

Therefore, in order to increase the wear resistance of steel and long-term sharpness retention, it is necessary to increase the amount of the carbide phase, and to maintain acceptable mechanical characteristics, reduce and improve their distribution. This goal can be achieved in several ways. Among them:

1. Optimization of steel composition.

For example, it is possible to saturate steel with other types of carbides, most often large amounts of vanadium.

2. Microalloying.

Saturation of steel with elements that improve the distribution of carbides and slightly reduce their size.

3. High-intensity plastic deformation.

As the degree of deformation increases, the carbides are partially crushed, and their distribution improves (especially when using special deformation techniques).

4. Increasing the rate of crystallization. It is this principle that underlies powder metallurgy technology. In order to increase the cooling rate, it is necessary to reduce the size of the ingot. With an ingot size of about 150 microns, the cooling rate reaches 104,105 k/s; at such speeds and sizes, the eutectic (a liquid solution that crystallizes at the lowest temperature for alloys of a given system) turns out to be very thin, and the size of the carbides does not exceed 23 microns. In order to achieve this, you need to use the powder method or the powder processing method.

Powder method (powder processing).

Processing is one of the stages of obtaining or processing metal in ferrous and non-ferrous metallurgy. Processing processes include: melting and casting of metal, crimping, rolling, pipe and hardware production. The essence of the technology of the powder metallurgy method is to obtain powders of pure metals and multicomponent alloys with their subsequent step-by-step waste-free transformation into ready-to-use materials, products and coatings with the required functional parameters.

Properties of powders

Metal powders differ in their physical, chemical and technological properties. The category of physical properties includes the shape dimensions and granulometric composition of particles, the characteristics of their specific surface area, as well as density and ability to deform, which is called microhardness.

The set of chemical properties is determined by the chemical composition of the raw materials and the manufacturing method/method. The permissible concentration of undesirable impurities in finished powder products should not exceed 1.5-2%. One of the most important chemical properties is the degree of gas saturation of the powder, which is especially important for powders obtained by reduction, from the composition of which it can be difficult to remove a certain part of the gaseous reducing agents and reaction products.

The main methods for producing powders from raw materials are:

1. Physico-mechanical method

Within the framework of this method, the feedstock is converted into powder without disturbing the chemical composition, through mechanical grinding, both in a solid aggregate state and in the form of a liquid melt. Physical and mechanical grinding is carried out using the following methods: crushing and grinding; spraying and granulation. When crushing and grinding solid raw materials, the initial particle size parameters are reduced to specified values.

2. Chemical-metallurgical method

This method of producing metal powders can also be implemented in various ways, among which the most popular are:

Chemical recovery of metal from raw materials (reduction method). It uses various chemical reducing agents that act on salts and metal oxides to separate the non-metallic fraction (salt residue, gases).

Electrolysis - a method of producing powders consists of deposition of particles of pure metal on the cathode under the influence of direct current on the corresponding electrolyte in the form of a solution or melt.

Thermocarbonyl dissociation (carbonyl method). Carbonyl powders are made by decomposing carbonyl metal compounds at a given temperature into their original components: particles of pure metal and gaseous carbon monoxide CO, which is removed.

The process of manufacturing powder steel includes a number of stages: preliminary preparation of the powder mixture (charge); molding; sintering.

Preliminary preparation of the powder mixture

The transformation of already manufactured metal powder into final products begins with the preliminary preparation of the initial mixture (charge), which will subsequently be subjected to molding and sintering. The process of preparing the initial charge is a three-stage process and is sequentially carried out in the form of: annealing, then sorting into fractions (classification) and direct mixing.

Recrystallization annealing of powders is necessary to increase their plasticity and compressibility. By annealing, it is possible to restore residual oxides and remove internal stress - hardening. For annealing, powders are heated in reducing-protective gas or vacuum environments.

The classification of powders is carried out by dividing them into fractions (depending on certain dimensional parameters of the particles) using special vibrating screens with cells of appropriate diameters. Air separators are also used for fractionation, and centrifugal dispersed sedimentation is used to classify liquid mixtures.

The powder material is directed by the air flow forced by the turbine into the separation area, where, under the influence of centrifugal force, heavy large particles are separated and settled, removed in the downward direction through the unloading valve. Small light particles are carried upward by the cyclonic air flow and sent for additional separation.

Mixing is the most important of the preparatory operations; it is carried out by preparing a homogeneous substance - a charge - from metal powders of various chemical and granulometric compositions (alloying additives of powders of non-metallic elements are possible). The homogeneity of the charge depends on how thoroughly the mixing occurs, which is extremely important for the final functional properties of the finished metal-ceramic product. Most often, mixing powder components is carried out mechanically using special mixers. Mixing not accompanied by grinding is carried out in continuous mixers of drum, screw, paddle, centrifugal and other types. Upon completion of the process, the resulting mixture is thoroughly dried and sifted.

Molding

Molding (molding) in powder metallurgy is a technological stage, the purpose of which is to compact a given amount of finished bulk charge entering the mold and compress it to give the shape of the product ready for subsequent sintering. The deformation of particles during molding, in its genesis, can be simultaneously elastic, brittle and plastic. Forming of the charge in most cases is carried out by placing it in durable steel molds and subsequent pressing under pressure from 30 to 1200 MPa on press units of a mechanical, pneumatic or hydraulic operating principle.

Sintering

The last stage of the powder metallurgy technological method is the heat treatment of the molded blanks. It is carried out using the sintering method. Sintering is one of the most critical technological procedures within the PM method, as a result of which low-strength workpieces are converted into exceptionally strong sintered bodies. During sintering, the gases adsorbed in them are removed from the workpiece, undesirable impurities are sublimated, and residual stresses in the particles and points of contact between them are removed, oxide films are eliminated, a diffusion transformation of the surface layer occurs, and the shape of the pores is qualitatively transformed. Sintering is carried out in two ways: solid-phase (as the workpieces are heated, a liquid melt of one of the components does not form), and liquid-phase. As a result of sintering, a metal bar or plate is obtained, which becomes the basis for making a knife.

Advantages of powder steels

Due to the small size and uniform distribution of carbides in powder steels, it is possible to significantly increase the degree of alloying and the volume of the carbide phase, and thereby increase the resistance properties of steel. Better mechanical characteristics are achieved, in particular, powder steels are much better ground and forged. When steel is hardened, a more saturated solid solution, finer and more uniform grain is obtained, which contributes to a slight increase in hardness, heat resistance, mechanical properties and corrosion resistance. Powder technology makes it quite easy to produce high-nitrogen steels using solid-phase nitriding methods. In general, powder processing has virtually no disadvantages, increasing all the qualities of steel.

The future of powder metallurgy

The development of powder metallurgy must pursue the goal of increasing the range of products that craftsmen can produce using this method.

Parts with complex configurations, which are currently produced in factories only by cutting, should in the future be manufactured using powder metallurgy methods. This will reduce the material intensity of production of complex parts.

Further automation of the production process is a distinctive feature of modern industrial enterprises. It also concerns the production of products from metal powders.

Reducing the influence of the human factor on the technological process increases the accuracy of parts manufacturing.

Over time, the quality of powder metallurgy products must compete with advanced technologies for the production of machine parts and mechanisms. Improving the quality and reducing the cost of finished products is a priority task for powder metallurgy enterprises.

Advantages and disadvantages of powder metallurgy

The advantages of the powder metallurgy process, among others:

ability to control the quality and quantity of material;
processing uses low temperature so the energy efficiency of production is high;
the speed of obtaining the product is high;
the process is economical because no material is wasted during processing.

Disadvantages of powder metallurgy, including:

the cost of producing and storing the powder is expensive;
it is impossible to obtain critical tolerances, since the metal powder is not able to flow into the casting space;
It is difficult to obtain uniform density.