The materials used and the application of all. The role of materials in modern technology. On the history of the development of materials science as a science. State diagram Fe - C
Materials play a decisive role in technological progress. Above, we considered an example from the field of computer technology, when the improvement of the material and the technology for manufacturing equipment elements from it leads to radically new results. You can give more examples from other areas of technology.
For example, the manufacture of cylinders for the storage of gases under pressure. The weight of the cylinder is determined by the wall thickness of the vessel, which, in turn, is determined by the mechanical strength of the material. The less durable the material, the heavier the vessel. So, a vessel for storing nitrogen, at a pressure of about 100 atm, with a volume of 100 l, made of steel has different weights in different countries, where there is a different technology for the manufacture of steel and, accordingly, its different mechanical strength. For example, the aforementioned vessel in the USA has a weight of 40 kg, in our country - 80 kg, and in China - 150 kg.
Since you understand the classification of materials, this is very important because it allows engineers to know their own conditions in the first case and to recognize which ones are best for them based on the structure or building that they want to create, or in relation to the object that they intend to do.
This is the case with the automotive industry, which deserves attention for assembling the same vehicles that know the properties of materials so that they can know their compatibility with what they are intended for. As you understand, this classification of high theoretical aspects has great theoretical predictions, since it consists in constructing elements of reality, where their use is noticeable, therefore we indicate it in a concise, but stable and quite illustrative way recreated with utility examples, so you can find out what suits you best.
You can give an example with the materials of space shuttles.
The development of new electrical materials with improved or new operational properties helps to improve the operational characteristics of electrical products.
Another example, closer to energy. The working electric field strength in a powerful pulsed energy storage device (a large capacitor in which water is used as the dielectric) is selected at 150 kV / cm in the American Jupiter drive, and only 80 kV / cm in the Angara Russian drive. The Americans have better technology for preparing water and electrodes, therefore, better properties of the material (water) in the drive, so breakdown in water is achieved at a higher tension, and you can choose a higher working tension.
However, with regard to its use, it is known that metallic materials are most often used, given the high degree of strength and durability that are coated with particles and components of the same materials mentioned above. The training offered fully meets the needs of the textile industry. He relies on the work of the sector in this sector for: all textile professions and for all applications.
Advanced Material Science and Technology Specialist
He follows product development from project management to production organization. The course has demonstrated high quality.
Master of Biomass and Waste and Energy Materials
All students have housing in the city or on campus, where they can play sports even on weekends.An even closer example is the insulators of high voltage lines. Historically, porcelain insulators were the first to come up with insulators. The technology of their manufacture is rather complicated, capricious. Insulators are rather bulky and heavy. We learned how to work with glass - glass insulators appeared. They are easier, cheaper, their diagnosis is somewhat simpler. And, finally, the latest inventions are silicone rubber insulators. The first rubber insulators were not very successful. Over time, microcracks formed on their surface, in which dirt accumulated, conducting tracks formed, then insulators made their way. A detailed study of the behavior of insulators in the electric field of overhead lines under external atmospheric influences made it possible to select a number of additives that improved weather resistance, resistance to pollution and the effects of electrical discharges. As a result, a whole class of lightweight, durable insulators for various levels of acting voltage has been created.
Master of Modern Metallurgical Technologies
Do you want to develop technical solutions that meet energy needs, as well as reduce the consumption of non-renewable resources and greenhouse gas emissions? Branch Profile In addition to these areas of specialization, all graduates gain knowledge in the fields of technical materials, industrial furnaces, the preparation of non-ferrous metals and alloys, methods of planning and improving quality, and also economics management. Theoretical knowledge is supplemented by a number of laboratories and calculations of additional practical exercises that use modern laboratory technology, and what tasks are associated with metallurgical processes and their modeling.
For comparison, the weight of suspension insulators for 1150 kV overhead lines is comparable to the weight of wires in the span between supports and amounts to several tons. This forces the installation of additional parallel garlands of insulators, which increases the load on the support. It is required to use more durable, and therefore more massive supports. This increases the material consumption, the large weight of the supports significantly increases installation costs. For reference, the cost of installation is up to 70% of the cost of building a power line. The example shows how one structural element affects the structure as a whole. The use of silicone rubber can dramatically reduce the cost and speed up construction. The basis for this progress is the development and use of new electrical materials for insulators. Lightweight insulators make it possible to lighten the supports, thereby reducing the wind load, making the manufacture, delivery and installation of overhead lines cheaper.
Master of Physics and Technology of Advanced Materials
Abstracts mainly focus on selected research areas or partially extend to related research areas, such as heat engineering and ceramic materials or materials. The Faculty of Physics offers a bachelor's degree and three master's programs, closely related to studies conducted by teachers. The two main programs are fully represented in English. These programs are designed to prepare students not only for graduate school in physics, but also for employment with a graduate in physics and other disciplines related to science and technology.
For example, the creation of heat-resistant organosilicon dielectrics allowed to increase the operating temperatures of electric machines and thereby significantly increase the power of the machine without increasing its dimensions and weight.
ANSWERS
Materials Science. Classification of metals. Atomic-crystalline structure of metals. Types of gratings and their characteristics.
Master of Applied Sciences in Materials Science
The materials research department is focused on the development of new processes and technological models mainly for new materials in the transport sector and biomaterials for medical use, replacement or repair of damaged parts of the body. promotes close collaboration with industry through its industry research departments. Industry-oriented research is combined with basic research to better understand the mechanisms of microstructure and the resulting properties.
2.1. Material science is a scientific discipline about the structure, properties and purpose of materials. The properties of technical materials are formed in the process of their manufacture. With the same chemical composition, but different manufacturing techniques, a different structure is formed, and, as a result, properties.
The purpose of materials science is to study the laws of formation of the structure and properties of materials by methods of their hardening for effective use in technology.
Master in Materials Science and Engineering
What makes the program unique? The long-term goal of our institute is to create a training unit that studies world-class science.
Master of Quantum Physics for Advanced Materials Technology
At the same time, the program considers the basic physical principles of systems and devices of quantum electronics, as well as some important technologies for the production and measurement of the physical and chemical characteristics of quantum structures and quantum materials. Students studied in the volume of university courses in general physics and introduction to theoretical physics for a bachelor's degree, which includes courses: theoretical mechanics and elasticity theory, electrodynamics, quantum mechanics and statistical physics.The main task of materials science is to establish the relationship between composition, structure and properties, to study the thermal, chemical-thermal treatment and other methods of hardening, to form knowledge about the properties of the main types of materials.
2.2. All metals are conventionally divided into black and non-ferrous. Ferrous metals usually have a dark gray color, high density (except alkaline), high melting point, relatively high hardness. Some of them (iron, titanium, cobalt, manganese, zirconium, uranium, etc.) possess polymorphism (allotropy). The most typical ferrous metal is iron.
Master in Complex Materials: Thermal Analysis and Rheology
Study module structure. Basic methods Thermomechanical properties of materials. Best practices Statistical data analysis Environmental applications Heat treatment and laser analysis Thermo-mechanical fatigue. Rheophysics of complex liquids Structured materials. Nanomaterials Physical chemistry of polymers Statistics of polymer physics, methods of light scattering.
Career Opportunities Practical skills acquired during this placement will provide graduates with a competitive edge in applying for final exams. English entry requirements. Bachelor's degree with minimal differences of the second level of higher or international equivalent in the diploma program. matching genius.
Non-ferrous metals are red, yellow, white. They have great ductility, low hardness, low melting point. Tin is known to have polymorphism. A typical representative is copper.
Ferrous metals include:
- iron metals - iron, cobalt, nickel, manganese;
- refractory metals; have a melting point higher than that of iron, i.e. more than 15390С
Master Program in Photonics
Master's Program in Photonics is a two-year program taught in English at the Institute of Photonics of the University of Eastern Finland, Joensuu, Finland. If you are interested in a career in materials science and engineering or want to know more about this exciting field of graduate school, you have come to the right place!
Master in Materials Science
The Master of Science in Materials Science seeks to provide a solid foundation for the chemical, physical and technological behavior of a wide range of materials with a focus on current advances in this field. The course offers advanced and comprehensive theoretical and practical training in the following interdisciplinary areas: chemistry and solid state physics, production of materials, manufacturing and testing, with particular attention to characterizing and modeling the structures and properties of materials.
Titanium, vanadium, chromium, zirconium, niobium, molybdenum, tungsten, technetium, hafnium, rhenium;
- uranium metals (actinides) - thorium, sea anemone, uranium, neptunium, plutonium, etc. (from 89 to 103 elements);
- rare earth metals (with 57 -71 elements), lanthanum, cerium, niodimum, etc.
- alkaline earth metals
Lithium, sodium, calcium, potassium, rubidium, strontium, cesium, barium, France, rhodium, scandium.
Nanotechnology and Nanoscience
The control unit of the nanoworld is a nanometer. Nanotechnology is a multidisciplinary field of research and development that relies on the knowledge and skills of the infinitesimal. They regroup, or rather, all the methods that allow the production, manipulation and characterization of material on a nanometer scale. Nanotechnology is the formalization of concepts and processes from nanoscience, i.e. sciences that are aimed at studying and understanding the properties of matter at the scale of an atom and a molecule.
There are many definitions of the term "nanomaterial." Nanomaterial is a natural material, randomly formed or made of free particles, in the form of aggregate or in the form of agglomerate, of which at least 50% of the particles in the numerical size distribution have one or more external dimensions. between 1 nm and 100 nm.
Non-ferrous metals include:
- lungs - beryllium, magnesium, aluminum;
- noble metals
Ruthenium, radium, palladium, osmium, iridium, platinum, gold, silver and semi-precious copper;
- fusible metals - zinc, cadmium, mercury, gallium, indium, waist, germanium, tin, lead, arsenic, antimony, bismuth.
Metals and alloys include substances obtained by powder metallurgy.
There are two main families of nanomaterials. Nano-objects, which are materials, of which one, two or three external dimensions are at the nanoscale, that is, approximately between 1 and 100 nm. Among nanoobjects, three categories can be distinguished. Nanoparticles, which designate nano-objects, the three external dimensions of which are at the nanoscale: nanoparticles of latex, zinc oxide, iron and cerium, aluminum oxide, titanium dioxide, calcium carbonate, etc .; nanofibers, nanotubes, nanofibers or nanocassettes, which are nano-objects in which two external dimensions are on a nanoscale, and the third size is much larger. Nano-objects can be used as such in the form of a powder, liquid suspension or gel.
Classification of non-metallic materials:
- organic and inorganic polymers;
- plastics;
- composite materials;
- rubbers and rubber;
- adhesive materials and sealants;
- paintwork;
- graphite;
- glass;
- ceramics.
The state diagram of the system with the complete insolubility of the components in the solid state (with eutectic).
Nanostructured materials that have an internal or surface structure at the nanoscale. Among nanostructured materials, several families can be distinguished, among which. Nanoobjects can be in individual form or in the form of aggregates or agglomerates, the size of which significantly exceeds 100 nm. nanocomposites. These materials are compiled for all or part of the nano-objects, which give them improved or specific properties of the nanoscale. Nano objects are included in the matrix or on the surface in order to introduce new functionality or modify certain mechanical, magnetic, thermal properties, etc. examples of nanocomposites are polymers loaded with carbon nanotubes used in the sports equipment sector in order to increase their mechanical strength and reduce their weight. nanoporous materials. Silicone aerogels are nanoporous materials with excellent thermal insulation properties.
- Aggregates and agglomerates of nanoobjects.
- These materials have nanoscale pores.
Figure 1 - State diagram of eutectic alloys
In these alloys, the components in the solid state are insoluble in each other and do not chemically interact.
Single phase areas of the diagram:
1) liquid L - above the line of liquidus DCE;
2) phase A - line 0FD;
3) phase B - line 100-G-E.
The characteristic point of the diagram is the triple point C, it corresponds to a eutectic alloy containing C "% B. The eutectic in these alloys consists of crystals A and B, its region in the diagram is the SS line." FCG line - eutectic transformation line: L eut -\u003e eut (A + B). The same line is solidus. The crystallization of the alloys of this system begins on the DCE line with the release of solid crystals of the component that is redundant with respect to the eutectic composition, and ends on the FCG line by the eutectic transformation.
Among these manufactured nanomaterials, some of them have been produced for many years in important tonnages such as titanium dioxide, carbon black, aluminum oxide, calcium carbonate or amorphous silica. The later ones are made in smaller quantities, such as carbon nanotubes, quantum dots, or dendrimers.
There are also nanomaterials that are inadvertently produced by people, sometimes called ultrafine particles, as a result of certain thermal and mechanical processes, such as welding or thermal sprays, emissions from internal combustion engines, etc.
Structural components of alloys (and their areas in the diagram):
1) crystals A - line 0FD;
2) crystals B - line 100-G-E;
3) eutectic crystals (eut (A + B)) - SS line. "
The process of graphitization during annealing of white cast iron.
Rockwell Method (GOST 9013)
It is based on pressing into the surface of the tip under a certain load (Fig. 7.1 b)
Finally, natural ultrafine particles are present in our environment, such as volcanic vapors or viruses. The passage of matter into nanoscale dimensions reveals unexpected properties that often completely differ from the properties of the same materials on a micro- or macroscopic scale, especially with regard to mechanical stability, chemical reactivity, electrical conductivity and fluorescence. Nanotechnology leads to the development of materials whose fundamental properties can be changed.
For example, gold is completely inactive on a micrometric scale, while it becomes an excellent catalyst for chemical reactions when nanoscale measurement is required. All major material families relate to: metals, ceramics, dielectrics, magnetic oxides, polymers, carbons, etc.
Indenter for soft materials (up to HB 230) - a steel ball with a diameter of 1/16 ”(Ø1.6 mm), for harder materials - a diamond cone.
Loading is carried out in two stages. First, a preload (10 kf) is applied to tightly touch the tip with the sample. Then the main load P 1 is applied, for some time the general work load P is applied. After removing the main load, the hardness value is determined by the depth of the residual indentation of the tip h under load.
Three hardness scales A, B, C are used depending on the nature of the material.
Hardness is determined by the size of the imprint (Fig. 7.1 c).
A diamond tetrahedral pyramid is used as an indenter. With an angle at the apex of 136º.
Hardness is calculated as the ratio of the applied load P to the surface area of \u200b\u200bthe print F:
The load P is 5 ... 100 kgf. Fingerprint diagonal dmeasured using a microscope mounted on the device.
The advantage of this method is that it is possible to measure the hardness of any materials, thin products, surface layers. High accuracy and sensitivity of the method.
Microhardness Method used to determine the hardness of the individual structural components and phases of the alloy, very thin surface layers (hundredths of a millimeter).
Similar to Vickers method. The indenter is a pyramid of smaller sizes, the indentation loads P are 5 ... 500 gs
Scratch method.
With a diamond cone, pyramid or ball, a scratch is applied, which is a measure. When scratching other materials and comparing them with a measure, they judge the hardness of the material.
A 10 mm wide scratch can be applied under a certain load. Observe the magnitude of the load that gives this width.
Dynamic method (Shore)
The ball is thrown to the surface from a given height, it bounces a certain amount. The larger the rebound, the harder the material.
As a result of dynamic tests for impact bending of special notched specimens (GOST 9454), the viscosity of the materials is evaluated and their tendency to transition from a viscous to a brittle state is established.
Technological properties
Technological properties characterize the ability of the material to undergo various methods of cold and hot processing.
1. Foundry properties.
Characterize the ability of the material to obtain high-quality castings from it.
Fluid flow - the ability of molten metal to fill the mold.
Shrinkage (linear and volumetric) - characterizes the ability of the material to change its linear dimensions and volume during solidification and cooling. To prevent linear shrinkage when creating models using non-standard meters taking into account the shrinkage of a certain metal ...
Segregation - heterogeneity of the chemical composition by volume.
2. The ability of the material to pressure treatment.
This is the ability of a material to change its size and shape under the influence of external loads without collapsing.
It is controlled as a result of technological tests conducted under conditions as close as possible to production.
The sheet material is tested for bending and drawing a spherical hole. The wire is tested for bending, twisting, winding. Pipes are tested for distribution, flattening to a certain height and bending.
The criterion for the suitability of the material is the absence of defects after the test.
3. Weldability.
This is the ability of the material to form permanent compounds of the required quality. Evaluated by the quality of the weld.
4. The ability to process by cutting.
It characterizes the ability of the material to be machined by various cutting tools. Evaluated by the durability of the tool and the quality of the surface layer.
Operational properties
Operational properties characterize the ability of the material to work in specific conditions.
Wear resistance - the ability of the material to resist surface destruction under the action of external friction.
Corrosion resistance - the ability of the material to resist the action of aggressive acidic, alkaline environments.
Heat resistance - this is the ability of a material to resist oxidation in a gaseous environment at high temperature.
Heat resistance - this is the ability of a material to maintain its properties at high temperatures.
Cold resistance - the ability of the material to maintain plastic properties at low temperatures.
Anti-friction - the ability of the material to break in to another material.
These properties are determined by special tests depending on the working conditions of the products.
When choosing a material to create a structure, it is necessary to fully take into account the mechanical, technological and operational properties.
The formation of austenite and its grain growth upon heating. Overheating and burnout.
The formation of austenite when heated
State diagram Fe - C
The transition of perlite to austenite, its kinetics obey the basic laws of phase transformations that occur during heating.
It was experimentally established that austenite nuclei arise at the boundaries of ferrite with cementite. The initial stages of formation of austenite nuclei have not been experimentally studied, and there are only assumptions about them. The conversion of α o.c.c. → γ g.c.c. in pure iron is only possible at temperatures not lower than 911 ° C. If ferrite is in contact with cementite, then, in accordance with the state diagram, the α - γ transformation should occur at temperatures starting from 727 ° С. Austenite at a temperature slightly above point A 1 contains about 0.8% C, while ferrite in steel contains hundredths of a percent carbon.
How, then, does the phase phase arise with the city center. K. lattice and relatively high carbon content?
Most hypotheses of the origin of austenite come from fluctuation representations, and two extreme cases are formally considered. First, one can imagine that the basis for the nucleation of austenite are concentration fluctuations. Inside ferrite, the probability of the formation of a significant number of fluctuation regions of critical size is negligible, since there are very few carbon atoms. At the boundary of ferrite with cementite between the phases, there is a continuous exchange of atoms (dynamic equilibrium) and in the boundary layer (ferrite is much more likely to fluctuate in the occurrence of sections of a critical size with a concentration of about 0.8% C.
Such sites, at any smallest overheating above point A 1, undergo polymorphic α - γ transformation of the solid solution and become stable centers of growth of austenitic grains. Below point A 1, similar sites in ferrite can also arise, but they do not turn into stable centers of austenite growth, since the γ-lattice is thermodynamically unstable here.
Another assumption is that when austenite nucleates, it is not concentration fluctuations that are primary, but the fluctuation rearrangement of the lattice. Inside ferrite, regions with a γ-lattice of fluctuational origin appear and disappear, and carbon from carbide enters these regions at temperatures above A 1 at temperatures above A 1 and, if they are of critical size, they become stable centers of growth of austenite.
22.2.
If you heat the metal to the upper critical point and continue to raise the temperature, then, examining the metal under a microscope, you can detect the growth of its grains.
The higher the temperature, the more vigorously the grain grows and the larger they are, the longer the process of heating to a given temperature. A metal having highly coarse grains is called superheated metal.
In the forging process, strongly overheated metal gives flaws and cracks, especially in the corners of an ingot or billet, and in a fracture has a greatly enlarged structure, which can be relatively easily observed with a simple eye. Overheating depends on two factors: temperature and heating time.
From the practice of forging furnaces it is known that if an ingot or billet is kept in a furnace at a high temperature (for example, in the welding part of a method furnace) more than usual, then when forging such an ingot or billet, flaws result from overheating. On the contrary, an ingot located in the furnace at the same temperature, but for a shorter time, is forged quite normally.
Thus, overheating of the metal is possible at any temperature exceeding the critical point, but the amount of overheating at this temperature depends on the exposure time.
Overheated metal can be corrected by subsequent annealing, i.e., by slow heating to a temperature 10-30 above the point, and subsequent slow cooling.
If the heated metal is left in the furnace for a long time at a high temperature, then it will burn out. The burning occurs because the oxygen in the furnace gases penetrates deep into the metal from the surface, the grain boundaries of the metal are oxidized, and the substance formed between the large grains melts. As a result, liquid films form between the grains of the metal, the bond between the grains is broken, and the metal becomes fragile, large cracks appear on the workpiece, and it breaks up into pieces. Further heating leads to the melting or destruction of individual sections of the workpiece. The burning depends mainly on the heating temperature, the composition of the furnace gases and the heating time of the metal at high temperatures.
The burnt metal cannot be fixed, the billet is usually rejected, and the preserved metal can only be used by smelting in an open-hearth furnace.
To prevent burnout of the metal, it is necessary to observe the following basic conditions when heating:
1. Burn fuel with the lowest coefficient of excess air so that there is no free oxygen in the furnace gases.
2. Do not load blanks under the furnace in bulk, but arrange them so that they are washed with furnace gases, if possible, and torch burners or nozzles would not (lick) the surface of the heated blanks.
3. You can load so much metal into the furnace that the forging unit can forge it in the time it takes to heat the workpiece to the forging temperature. It is better to load the furnace by the piece method, that is, one or two heated billets are discharged from the furnace, and cold billets are fed into their place, etc. In case of piece loading, the length of time the metal stays at high temperatures will be what it takes to heat it. And this will make it possible to avoid overheating and burnout of the metal.
Self tempering.
Heated products are placed in a cooling medium and kept until incomplete cooling. After removing the product, its surface layers are reheated due to internal heat to the required temperature, that is, self-tempering is carried out (see. Steel tempering). It is used for products that must combine high hardness on the surface and high viscosity in the core (impact tools: hammers, chisels).
The process technology is as follows: Loading parts into a steel box with an airtight sand shutter. The parts are laid in such a way that they are covered with a carburetor on all sides, not in contact with each other and the walls of the box. Further, the box is hermetically sealed with a sand shutter or covered with refractory clay and loaded into the furnace.
Standard mode: 900-950 degrees, 1 hour exposure (after warming up the box) per 0.1 mm of the thickness of the cemented layer. to obtain 1 mm layer - exposure for 10 hours.
In the "accelerated" mode, cementation is performed at 980 degrees. Exposure is halved and it takes 5 hours to get a 1 mm layer. But at the same time, a cementite mesh is formed, which will have to be removed by multiple normalization of the metal
This process is carried out in an atmosphere of gases containing carbon. Gas cementation has several advantages compared to cementation in a solid carburetor, therefore it is widely used in factories manufacturing parts in bulk.
In the case of gas cementation, you can get a given concentration of carbon in the layer; the duration of the process is reduced, since there is no need to warm up boxes filled with a low-heat carburetor; the possibility of complete mechanization and automation of processes is ensured and the subsequent thermal treatment of parts is greatly simplified, since hardening can be carried out directly from the cementation furnace.
High speed steels
High-speed steels are widely used for the manufacture of cutting tools operating under conditions of significant force loading and heating (up to 600-640 ° C) of cutting edges. This group of steels includes high-alloyed tungsten together with other carbide-forming elements (molybdenum, chromium, vanadium), which acquire high hardness, strength, heat and wear resistance as a result of double hardening: a) martensitic during hardening; b) dispersion hardening at a relatively high tempering (500-620 ° C), which causes the release of hardening phases.
High-speed steels are marked with the letter "P" (rapid - fast) and a number showing the average content of W, as well as subsequent letters and numbers indicating other alloying elements and their quantity, as in the standard marking of alloyed steels. Carbon and chromium do not indicate high-speed steels (their mass fraction is 1% and 4%, respectively), as well as molybdenum up to 1% inclusive and vanadium in steels P18, P9, P9K5, P6M5, etc.
The chemical composition of high-speed steels is given in table. 6.7.
According to the main properties, high-speed steels are divided into five subgroups: 1) steel of moderate heat resistance (type P9, P6M5); 2) increased wear resistance (type R12F3, R6M5F3); 3) increased heat resistance (type P6M5K5, P9K5); 4) high wear and heat resistance (type R18K5F2); 5) high hardness and heat resistance with improved grindability (type P9M4K8, V11M7K23).
However, these steels have many common characteristics. Therefore, to simplify the consideration of structural features, properties and heat treatment modes, they can be divided into three groups according to processing performance:
· Steel of normal performance (steel of moderate heat resistance);
· Steel of increased productivity (steel of increased heat and wear resistance);
· High-performance steels (steels of high heat and wear resistance).
· The structure of steels with carbide hardening (steel type "P") is approximately the same for all groups. After the final heat treatment (quenching + tempering), their structure consists of martensite with the release of dispersed particles of alloyed carbides mainly of the type M 6 C and MS. Such a structure provides heat resistance of the tool up to 600–640 ° С.
· The highest heat resistance (up to 700–720 ° С) are observed in highly alloyed Fe-Co-W-Mo alloys with intermetallic hardening (grades V4M12K23 and V11M7K23). After the final heat treatment, the structure of these alloys consists of carbon-free (or low-carbon) martensite with a low hardness (30–40 HRC E) and finely divided intermetallic compounds (Fe, Co) 7 (W, Mo) 6, Fe 3 W 2 (Fe 3 Mo 2) , (Fe, Co, Ni) 7 (W, Mo) 6.
· High hardness (HRC E 68–70) and heat resistance (720 ° C) are ensured by: a) higher temperatures (900–950 ° C) of the onset of phase transformations, which is 100 ° C higher than that of steel with carbide hardening; b) large quantities of hardening phases, characterized by high dispersion (up to 2-3 microns) and uniform distribution in the main matrix.
· High-speed steels belong to the ledeburite (carbide) class and their structure is approximately the same. Ingots of these steels contain carbide eutectic in the form of a grid along the boundaries of austenitic grains (Fig. 6.1, a), which sharply reduces the usual mechanical properties, especially ductility. In the process of hot pressure treatment (forging, rolling), the carbide eutectic is crushed and the crushed carbides are more evenly distributed in the main matrix (Fig. 6.1, b).
· After rolling or forging, high speed steels are subjected to isothermal annealing to reduce hardness and facilitate machining. Steel is maintained at 800–850 ° С until austenite is completely converted into a pearlite-sorbitol structure with excess carbides
Heat treatment.High hardness and heat resistance with satisfactory strength and toughness tools from high-speed steels acquire after hardening and repeated tempering.
Quenching . When heating under quenching, it is necessary to ensure maximum dissolution in austenite of insoluble carbides of tungsten, molybdenum and vanadium. Such a structure increases hardenability and makes it possible to obtain highly alloyed martensite with high heat resistance after quenching. Therefore, the quenching temperature is very high and amounts to 1200–1300 ° С
To prevent cracking and deformation of the tool due to the low thermal conductivity of the steels, quenching is carried out with one or two heatings in molten salts: the first at 400–500 ° С, the second at 800–850 ° С. The final heating is also carried out in a salt bath (BaCl 2) with a very low shutter speed at T c: 10–12 s per 1 mm of tool thickness made of “P” steels and 30–60 s for steel of type B11M7K23. This avoids the growth of austenitic grain (no larger than No. 10), oxidation and decarburization.
Tools of a simple form are quenched in oil, and complex ones in solutions of salts (KNO 3) at 250–400 ° С.
After quenching, the structure of high-speed steel (Fig. 6.1, c) consists of highly alloyed martensite containing 0.3–0.4% C, not dissolved during heating of excess carbides, and about 20–30% of residual austenite. The latter reduces the hardness, cutting properties of the tool, degrades sandability, and its presence is undesirable.
Vacation With multiple tempering, dispersed carbides precipitate from residual austenite, austenite doping decreases, and it undergoes a martensitic transformation. Usually, triple tempering is used at 550–570 ° С for 45–60 min. The heat treatment mode of the tool made of high-speed steel P18 is shown in Fig. 6.2. The number of leaves can be reduced by cold treatment after quenching, which reduces the content of residual austenite. Cold processing tools are subjected to a relatively simple form. Hardness after hardening HRC E 62–63, and after tempering it increases to HRC E 63–65.
Surface treatment. To further increase the hardness, wear resistance and corrosion resistance of the surface layer of cutting tools, technological operations such as cyanidation, nitriding, sulfidation, steam treatment and other surface hardening technologies are used. They are performed after the final heat treatment, grinding and sharpening of tools.
ianization is carried out at 550–570 ° С for 5–30 min in liquid media and 1.5–3.0 h in a gas atmosphere. For liquid cyanidation, baths with molten NaCN (90 or 50%), Na 2 CO 3, NaOH (KOH) are used. Gas cyanidation is carried out in a mixture of ammonia and carburizing gas.
Nitriding of the instruments is carried out at 550–660 ° С for a duration of 10–40 min in an ammonia atmosphere. Gas nitriding is also carried out in a mixture of 20% ammonia and 80% nitrogen; the latter is preferable, since in this case less fragility of the layer is ensured.
Sulphidation is carried out at 450–560 ° С, lasting from 45 minutes to 3.0 hours in liquid melts, for example, 17% NaCl, 25% BaCl 2, 38% CaCl 2, 3-4% K 4 Fe (CN) 6, which add sulfur-containing compounds FeS, Na 2 SO 4, KCNS.
When steaming, the tools are placed in a sealed oven and kept at 300–350 ° С under a pressure of 1-3 MPa for 20–30 min to remove air. Then, the temperature rises to 550–570 ° С, holding is carried out for 30–60 min, cooling in the atmosphere of steam to 300–350 ° С, after which the steam supply stops. Cooling ends in an oven or in air, then the instrument is immediately rinsed in hot spindle oil.
Application. A competent choice of the steel grade for a particular tool, depending on the conditions of its operation and the material being processed, makes it possible to maximize the use of the properties of the selected steel and, as a result, rationally consume alloying materials, as well as determine the need for certain coatings, surfacing and other surface hardening methods. In the table. 6.9. recommended areas of application of the most common brands of high-speed steels are presented depending on the types of processed materials and types of processing. This approach to the selection of tool steels for any purpose helps to increase both productivity and production efficiency.
ANSWERS
The role of materials in modern technology. On the history of the development of materials science as a science
Material science can be attributed to those branches of physics and chemistry that study the properties of materials. In addition, this science uses a number of methods to study the structure of materials. In the manufacture of high-tech products in industry, especially when working with micro- and nanoscale objects, it is necessary to know in detail the characteristics, properties and structure of materials. To solve these problems and called science - materials science.
The beginning of the development of materials science can be considered the moment when a person first began to choose what to take in his hand - a stick or a stone, that is, the birth of materials science coincides with the beginning of the Stone Age.
Therefore, material science is one of the oldest forms of applied science, which, together with humanity, has come a long way from primitive stone processing and the manufacture of simple ceramics to modern superpopular nanotechnologies. For a long time, metallurgy and metal science prevailed in materials science, that is, the science of materials was equated in fact with the science of metals.
Modern materials science is also based on metal science, however, in addition to metals and alloys, material science studies many other diverse materials, both by purpose (plastics, semiconductors, biomaterials) and composition (carbon materials, ceramics, polymers, etc.)