Nanomaterial： All the Stats, Facts, and Data You'll Ever Need to Know

Contents hide 1What is nanomaterial? 1.11 nanometer material characteristics 1.1.11.1 Surface and interface effects 1.1.21.2 small size effect 1.1.31. 3 quantum size effect 1.1.41.4 Physical characteristics 1.1.51.5 chemical characteristics 1.22. Preparation of nanometer materials 1.33. Application of nanometer materials in textile field 1.3.13.1 anti-ultraviolet, anti-sun and anti-aging fiber 1.3.23.2 antibacterial fiber 1.3.33.3 far infrared fiber 1.3.43.4 High-strength wear-resistant new materials 1.3.53.5 stealth textile materials 1.3.63. 6 antistatic fiber 1.3.73.7 anti-electromagnetic fiber 1.3.83.8 other functional fiber piles 24 ConclusionWhat is nanomaterial?

Introduction: The nano concept is 1959, and the Nobel Prize was presented by Richard Feynman in a speech. In his “There is plenty of room at the bottom” speech, he mentioned that humans can make machines smaller than their size with macroscopic machines, and this smaller machine can make smaller machines, thus achieving molecular scale step by step. That is, the production equipment is reduced step by step, and finally the atoms are arranged directly according to the wishes, and the products are manufactured. He predicted that chemistry would become a technical problem of accurately placing atoms one by one according to the wishes of human beings. This is the earliest idea with modern nano concepts. In the late 1980s and early 1990s, an important tool for characterizing nanometer scales, scanning tunneling microscopy (STM), and atomic force microscopy (AFM), a direct tool for understanding nanoscale and nanoworld materials, has greatly facilitated On the scale of understanding the structure of matter and the relationship between structure and nature, nanotechnology terminology emerged and nanotechnology was formed.In fact, nano is just a unit of length, 1 nanometer (nm)=10 and negative 3 times square micron=10 and negative 6th power millimeter (mm)=10 and minus 9 times square meters (m)=l0A. Nanoscience and Technology (Nano-ST) is a science and technology that studies the laws and interactions of systems consisting of substances between 1-100 nm in size and possible technical problems in practical applications.1 nanometer material characteristicsNano is a unit of measurement, 1 nm is a millionth of a millimeter, that is, 1 nanometer, that is, a billionth of a meter, and an atom is about 0 1 nm. Nanomaterials are a new type of ultra-fine solid material composed of nanoparticles, which are from 1 to 100 nm in size. Nanotechnology is the study and study of substances and materials on tiny structures below 100 nm, that is, the science and technology of making substances with a single atom or molecule.Nanoparticles are atomic groups or groups of molecules consisting of a small number of atoms and molecules. The surface of a large proportion is originally an amorphous layer with neither long procedures nor short procedures: inside the particles, there is a well-crystallized layer. Periodically arranged atoms, but their structure is different from the completely long program structure of the crystal sample. It is this special structure of nanoparticles that leads to the singular surface effects, small size effects, quantum size effects, quantum tunneling effects of nanoparticles, and thus the physical and chemical properties of many nanomaterials different from conventional materials.1.1 Surface and interface effectsThe surface effect of the nanomaterial, that is, the ratio of the atomic to total atomic number of the nanoparticle increases with the decrease of the size of the nanoparticle, and the surface energy and surface tension of the particle also increase, which causes the change of the properties of the nanometer. For example, the specific surface area of SiC with a particle size of 5 nm is as high as 300 /12/g; while the surface area of nano-tin oxide varies more with particle size, and the specific surface area at 10 lltlfl is 90.3 m2/g, compared with 5 nm. The surface area increased to 181 m2/g, and when the particle size was less than 2 nm, the specific surface area jumped to 450 m2/g. Such a large specific surface area greatly increases the number of atoms at the surface. The crystal field environment and binding energy of these attacking atoms are different from those of internal atoms. There are a large number of defects and many dangling bonds, which have high unsaturated properties, which makes these atoms easy to combine with other atoms. It is stable and has a high chemical reactivity.In addition, the surface energy of the highly activated nanoparticles is also high, and the specific surface area and surface area can make the nanoparticles have strong chemical reactivity. For example, metal nanoparticles can burn in the air. Some oxide nanoparticles are exposed to the atmosphere and adsorb gases and react with gases. In addition, nanomaterials have new optical and electrical properties due to the original malformation of the surface of the nanoparticles, which also causes changes in surface electron spin conformation and electron energy potential. For example, some oxide and nitride nanoparticles have a good absorption and emission effect on infrared rays and have a good shielding effect on ultraviolet rays.1.2 small size effectWhen the size of the ultrafine particles is equal to or smaller than the physical feature size such as the wavelength of the light wave, the wavelength of De Broglie, and the coherence length or transmission depth of the superconducting state, the periodic boundary conditions will be destroyed, sound, light, electromagnetic, thermodynamics, etc. Features will present a new size effect. For example, the light absorption significantly increases and produces a plasmon resonance frequency shift of the absorption peak; the magnetic ordered state is in a magnetic disordered state, and the superconducting phase is converted to a normal phase; the phonon spectrum is changed. These small size effects of nanoparticles are practicalExpanded new areas. For example, silver has a melting point of 900’C, and the melting point of nanosilver can be reduced to 100, C, which provides a new process for the powder metallurgy industry. By utilizing the properties of particle size change of plasmon resonance frequency, the displacement of the absorption edge can be controlled by changing the particle size, and a microwave absorption nano material having a certain bandwidth can be manufactured for electromagnetic wave shielding, stealth aircraft and the like.1. 3 quantum size effectWhen the particle size drops to a certain value, the electron energy level near the Fermi level changes from quasi-continuous to discrete energy level. The relationship is:Where: ￡ is the energy level spacing; E is the Fermi level; N is the total electron number. Macroscopic objects contain an infinite number of atoms (ie, the number of electrons contained, N), so 0, that is, the energy level spacing of large particles or macroscopic objects is almost zero; while the nanoparticles contain a limited number of atoms, and the value of N is small, Carbide Milling inserts resulting in a certain The value of the energy level is split. The electron energy spectrum of a bulk metal is a quasi-continuous energy band. When the energy level spacing is greater than the thermal energy, magnetic energy, magnetostatic energy, electrostatic energy, photon energy or superconducting condensed energy, the quantum effect must be considered, which leads to the nanoparticle. Magnetic, optical, acoustic, thermal, electrical, and superconducting properties are significantly different from macroscopic properties, known as quantum size effects.1.4 Physical characteristicsThe physical effects of nanomaterials include magnetic and optical properties.The diameter of the nanomaterial is small, and the material is mainly composed of ionic bonds and covalent bonds. Compared with crystals, the absorption capacity of light Threading Inserts is enhanced, showing the characteristics of wide frequency band, strong absorption, and low reflectance. For example, although various block metals have different colors, all metals appear black when they are refined to nano-sized particles; some objects also exhibit new luminescence phenomena, such as silicon itself, which is not illuminating, However, nano-silicon has a phenomenon of luminescence.Due to the small diameter of the nanomaterials, the atoms and molecules are more exposed, the magnetic rows are more random and more irregular, and therefore, the nanomaterials are superparamagnetic.1.5 chemical characteristicsThe chemical effects of nanomaterials include adsorption and catalysis.Nanomaterials have a large specific surface area. It makes it have stronger adsorption properties for other substances.Nanomaterials can be used as high education catalysts. Due to the small size of the nanoparticles, the volume percentage of the surface is large, the bond state and the electronic state of the surface are different from the inside of the particles, and the surface atomic coordination is incomplete, which leads to an increase in the active position of the surface, which makes it have the basic conditions as a catalyst. . There are three main aspects of the role of nanomaterials as catalysts:(1) changing the reaction rate and improving the reaction efficiency;(2) Determine the reaction route and have excellent selectivity, such as hydrogenation and dehydrogenation only, without hydrogenation decomposition and dehydration;(3) Lower the reaction temperature. For example, a catalyst prepared by using ultrafine particles of Ni and Cu-mon alloy having a particle diameter of less than 0.3 nm as a main component can make the hydrogenation efficiency of organic matter 10 times that of a conventional nickel catalyst; ultrafine PL powder and WC powder. It is a highly efficient hydrogenation catalyst; ultrafine Fe, Ni and Fe02, mixed light sintered body can replace precious metal as automobile exhaust gas purifying agent; ultrafine Aug powder can be used as catalyst for acetylene oxidation.2. Preparation of nanometer materialsThere are many ways to prepare nanomaterials. According to whether there is obvious chemical reaction during the preparation process, it can be divided into physical preparation methods and chemical preparation methods. The physical preparation methods include a mechanical grinding method, a dry impact method, a blending method, and a high temperature evaporation method; and the chemical preparation method includes a sol-gel method, a precipitation method, and a solvent evaporation method.3. Application of nanometer materials in textile fieldIt is precisely because of these peculiar properties of nanoparticles that it lays the foundation for its wide application. For example, nanoparticles have special UV resistance, absorption of visible light and infrared rays, anti-aging, high strength and toughness, good electrical and electrostatic shielding effects, strong antibacterial deodorizing function and adsorption capacity, and the like. Therefore, by combining nanoparticles having these special functions with textile raw materials, it is possible to manufacture new textile raw materials, nano-pastes, and to improve fabric functions.3.1 anti-ultraviolet, anti-sun and anti-aging fiberThe so-called anti-ultraviolet fiber refers to the fiber which has strong absorption and reflection properties to ultraviolet light. The principle of preparation and processing is usually to add ultraviolet shielding material to the fiber to be mixed and treated to improve the absorption and reflection of ultraviolet rays by the fiber. ability. The substances that can block ultraviolet rays here refer to two types, that is, substances that reflect ultraviolet rays, which are customarily called ultraviolet shielding agents, and have strong selective absorption of ultraviolet rays, and can perform energy conversion to reduce the amount of permeation thereof. Substance, customarily known as UV absorbers. Ultraviolet shielding agents usually use some metal oxide powders, and there are many varieties of UV absorbers at home and abroad. Commonly used are salicylate compounds, metal ion chelate compounds, benzophenones and benzotriazoles. . A small amount of nano-TiO 2 is added to the synthetic fiber by using the excellent light absorption characteristics of the nanoparticles. Because it can shield a large amount of ultraviolet rays, the garments and articles made of the same have the effect of blocking ultraviolet rays, and have an auxiliary effect on preventing skin diseases and skin diseases caused by ultraviolet absorption.3.2 antibacterial fiberSome metal particles (such as nano-silver particles, nano-copper particles) have certain bactericidal properties, and they are combined with chemical fiber to produce anti-bacterial fibers, which have stronger antibacterial effect and more washability than general antibacterial fabrics. frequency. For example, the ultra-fine antibacterial powder developed by the National Ultrafine Powder Engineering Center can impart antibacterial ability to resin products and inhibit various bacteria, fungi and molds. The core of the antibacterial powder may be a nanoparticle of barium sulfate or zinc oxide, coated with silver for antibacterial, and surrounded by copper oxide and zinc silicate to resist fungus. By adding 1% of this powder to the Taiwanese fiber, an antibacterial fiber having good spinnability can be obtained.3.3 far infrared fiberSome nano-scale ceramic powders (such as zirconia single crystals, far-infrared negative oxygen ion ceramic powders) are dispersed into a melt spinning solution and then spun into fibers. This fiber can effectively absorb external energy and radiate far infrared rays that are the same as the human body’s biological spectrum. This far-infrared radiation wave is not only easily absorbed by the human body, but also has a strong penetrating power. It can penetrate deep into the skin and cause deep resonance of the skin to produce a resonance effect. It activates biological cells, promotes blood circulation, strengthens metabolism, and enhances.Health care such as tissue regeneration.3.4 High-strength wear-resistant new materialsThe nanomaterial itself has the characteristics of super strong, high hardness and high toughness. When it is integrated with chemical fiber, the chemical fiber will have high strength, high hardness and high toughness. For example, carbon nanotubes are used as composite additives, and have great development prospects in aerospace textile materials, automotive tire cords and other engineering textile materials.3.5 stealth textile materialsSome nano-materials (such as carbon nanotubes) have good absorbing properties, and they can be used to add light to the textile fiber. The nano-materials have the characteristics of wide band, strong absorption and low reflectivity of light waves, so that the fibers do not reflect light. It is used to make special-purpose anti-reflective fabrics (such as military invisible fabrics).3. 6 antistatic fiberAdding metal nano-materials or carbon nano-materials in the process of chemical fiber spinning can make the spun filaments have antistatic and microwave-proof properties. For example, carbon nanotubes are a very excellent electrical conductor. Their conductivity is better than that of copper. It is used as a functional additive to stably disperse in chemical fiber spinning solution. It can be made at different molar concentrations. Fiber and fabric with good electrical conductivity or antistatic properties.3.7 anti-electromagnetic fiberHigh dielectric insulating fibers can be obtained by adding nano-SiO 2 to the synthetic fiber. In recent years, with the continuous development of communication and household appliances, the use of mobile phones, televisions, computers, microwave ovens, etc. is becoming more and more common. Electromagnetic fields exist around all electrical equipment and wires, and electromagnetic waves are on the human heart, nerves, and pregnant women. The impact of the fetus has a clear conclusion. According to reports, the United States, Japan, South Korea and other anti-electromagnetic wave clothing has been listed, and domestic research on the use of nano-materials to prepare anti-electromagnetic wave fibers is also underway.3.8 other functional fiber pilesThe different properties of nanoscale or ultrafine materials are used in individual functional fibers. Develop ultra-suspension fibers using high-specific gravity materials such as tungsten carbide, such as “XY-E” from Toray Industries, “July” from Asahi Kasei Corporation, and “Pyramidal” from Toyobo Co., Ltd.; and develop opaque fibers using the refractive properties of Ti02. Japan’s Unijica uses a sheath-core composite spinning method. The cortex and core layer contain different amounts of TiO2 to obtain a polyester fiber with good opacity. The fluorescent fiber is developed by using the luminosity of barium aluminate and calcium aluminate. Japan’s fundamental special chemical company has developed a light-storing material with barium aluminate and calcium aluminate as the main components, and the rest time can reach more than 10 h; some metal double salts, transition metal compounds undergo crystal transformation due to temperature changes. Or the color change of the ligand geometry or the crystallization of water “water”, the use of its reversible thermochromic characteristics to develop color-changing fibers; Mitsubishi Rayon Company uses the addition of colloidal calcium carbonate in the polyester to make hollow The fibers are treated with alkali reduction to form micropores on the fibers, and the fibers have good hygroscopic properties.4 ConclusionNanomaterial science is a new discipline growth point that emerges from the intersection of atomic physics, condensed matter physics, colloid chemistry, solid chemistry, coordination chemistry, chemical reaction kinetics, surface and interface science. There are many unknown processes and novel phenomena involved in nanomaterials, which are difficult to explain with traditional physical chemistry theory. In a sense, the advancement of nanomaterials research will push many disciplines in the field of physics and chemistry to a new level. In recent years, by adding certain ultrafine or nano-scale inorganic material powders to the Taiwanese fiber-forming polymer, it has become a popular functional fiber manufacturing method, such as far-infrared fiber and anti-wear, by spinning to obtain fibers having a certain special function. Ultraviolet fibers, magnetic fibers, super-overhanging fibers, fluorescent fibers, color-changing fibers, antistatic fibers, conductive fibers, and highly hygroscopic fibers. With the continuous progress in the synthesis of nanomaterials and the improvement of basic theories, nanomaterials will develop more rapidly, and the application will cover many fields in the world.

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How do deep hole drilling inserts handle drilling in thin walled components

Deep hole drilling inserts are a key component of the deep hole drilling process, allowing for precise, efficient drilling of thin-walled components. Deep hole drilling inserts use a combination of cutting edge technology and specialized manufacturing techniques to ensure the highest levels of performance.

Unlike other drilling methods, deep hole drilling inserts are specifically designed to drill in thin-walled components. The unique Indexable Carbide Inserts design of the inserts allows them to drill in very thin sections without compromising the integrity of the component. The inserts are typically made from high-performance carbide materials that are designed to be extremely tough and resistant to wear. This allows them to maintain their cutting edge sharpness even when drilling in thin-walled components.

The inserts also feature precision geometry that helps to provide accuracy and repeatability. The inserts are designed with a variety of angles and cutting surfaces to help ensure that each hole drilled is consistently precise. This helps to reduce scrap and other waste associated with the deep hole drilling process.

In addition, deep hole drilling inserts can be customized to meet specific requirements of the job. This allows for a greater degree of control over the drilling process and ensures that each hole is drilled to exact specifications. This helps to minimize the amount of time and effort that is needed to complete the TNMG Insert drilling job.

Deep hole drilling inserts are an essential tool for anyone working with thin-walled components. They offer accuracy, repeatability, and durability, making them ideal for drilling in thin-walled components. With the right inserts, the deep hole drilling process can be completed quickly and efficiently, helping to ensure that the finished product meets all quality standards.

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Manual Processing Vs CNC Machining

Now with the development of economy, the development of CNC machining customization technology is becoming stronger and stronger. Many CNC machining customization industry is in a hot state at present, but in the factories that need processing, they know little about NC machining customization and do not know how to choose. Next, I’ll introduce it to you.

CNC is the abbreviation of NC machining, which is the process of material removal through precision machining. Precision machining, that is, precision machining, is processed by high-precision machine tools. The main method to realize precision machining of parts is to use high precision machine tools to process high precision parts. Using error compensation technology to improve the machining accuracy of high parts.

There are two main types of machining: manual machining customization and CNC machining customization. Manual processing customization refers to the method that machine operators process various materials by manually operating machine equipment (such as milling machine, lathe, drilling machine and saw).

Manual processing is suitable for the production of small batch and simple parts. High precision machining (CNC machining customization) uses CNC equipment to perform mechanical operations, including machining center, powder machining center, WEDM equipment, thread cutting machine, etc.

In the process of changing from blank to finished product, the total thickness of the metal layer removed from the machined surface is called the total machining allowance of the surface. The thickness of the metal layer removed in each process is called the inter process allowance.

For rotating surfaces (such as outer circles and holes), the machining WNMG Insert allowance is considered according to the diameter, so it is called symmetrical abundance (i.e. bidirectional abundance). In other words, the thickness of the metal layer actually removed is half of the machining allowance diameter. The machining allowance of a plane is actually a single edge allowance, such as the thickness of the metal layer to be removed.

The purpose of leaving machining allowance on the blank is to eliminate the machining errors and surface defects left by the previous process, such as cold hard layer, air hole, cinnabar layer, oxide on the surface of forging, decarburization layer, surface crack, internal stress layer after cutting and surface roughness. High working precision and surface roughness are mentioned.

The size of machining allowance has great influence on machining quality and production Threading Inserts efficiency. Excessive machining allowance will not only increase the processing workload and reduce productivity, but also increase the consumption of materials, tools and power, thus increasing the processing cost.

The machining allowance is too small to eliminate all kinds of defects and errors in the previous process, and can not compensate the fixture error in the process of the process, thus resulting in waste products. The principle of selection is to ensure the quality and make the allowance as small as possible. Generally speaking, the more you finish, the less you have left.

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VARIOUS TYPES OF END MILLS AND WHICH ONE SHOULD YOU CHOOSE

End mills are cutting tools used in CNC machines. The term “end mill” means cutting is done from the active end point. To make different types of shapes, slotting, 3D contouring, various types of end mills are used. These different slotting have different purposes and material requirement so it is necessary for you to understand each type. This will enable you to select the most suitable end mill for your needs.

In this article we will discuss what are the different types of end mills, their application, pros and cons and finally discuss which end mill should you choose.

Side note:?Whether you buy ?” end mill or ?” end mill,?the types of end mill does not have to do anything with material’s brittleness or softness. The flutes on an end mill decides if it will cut softer or harder material. The more number for flutes, the harder the material is cut, the lesser the flutes, the softer material is cut.

And even if you look for a 4 flutes end mill supplier considering you may get a better quality production, you should know that the only purpose of different types of end mills is for creating variety of shapes, milling profiles, contouring, slotting or plunging.

TYPES OF END MILLS

Depending upon the usage, the end mills are divided in many categories. Following ae the most broadly known categories for end mills.

Centre and Non-centre end mills

Finishing and Roughing end mills

Indexing and Non-indexing (solid carbide) end mills

Flat end and Ball nose end mills

Bull nose end mills

T-slot end mills

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CENTRE AND NON-CENTRE END MILLS

The main difference between center and non-center cutting is that center cutting end mills have cutting edges on sides as well as face of cutter while non-center cutting end mills have cutting edges only on sides. The center cutting end mills are used to create slots, pockets, circular pocketing or surface plunging. Whereas the non-center cutting is used to perform side milling (material removing) on the workpiece.

The center cutting end mills are available mostly in two and three flute end mills. They are expensive and cannot be sharpened. The non-center cutting end mills are comparatively economic and can be sharpened again and also clears chips better.

 

FINISHING AND ROUGHING END MILLS

The solid carbide finishing end mills are carbide milling inserts used to achieve smooth finish over a material. They have one end with square shape and a smooth outside diameter that creates smooth finish. They are available in various helix angles and in number for flutes. The greater the helix angle, the smoother the surface and the more number of flutes, the softer material it can plunge.

On the other hand, the roughing end mills have teeth at the periphery of flutes that creates the rough textured surface. During milling operation, these teeth converts the material into small chips. As a result, the material chips-off quickly and avoids vibration.

 

FLAT END & BALL NOSE END MILLS

The flat-end end mills have flat surface and does not have any gap between teeth. Also known as square end mills, their corners are sharp which generates 90° angle. They come in single-end or double-end and are commonly made from solid carbide. They can be used for profiling, plunging, face milling etc. where they give sharp-edged bottom of a slot or pocket in a workpiece.

The ball-nose end mills or full-radius end mills, have a ball-shape edge with radius equivalent to half diameter of tool. It is used for 3D contouring, making arc grooves, creating curvature like turbine blade, and profile milling such like molds.

 

INDEXING AND NON-INDEXING END MILLS

The indexing end mills are also known as solid end mills. Unlike end mills with teeth, they have recess to add insert. They have positive cutting edge which removes workpiece by slicing action rather than scrapping that reduces the cutting force and vibrations. You can change the insert here when they get damaged or worn out. They are more load bearing and can take higher feed rates because they produce thicker and manageable sized chips. The biggest con of indexing end mill is they do not come in smaller sizes.

Solid carbide non-indexing end mills have tooth. If it gets damaged, you will have to purchase a new non-indexing end mill. They produce great finishes and are available in small diameters. They apply less pressure on tools and can deliver deeper cuts.

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BULL-NOSE END MILL

These are corner radius end mill cutters. They are single-ended tools that makes corner radii and a milled shoulder’s bottom. Compared to square end mills, their milling edges are stronger. It is why they can take higher feed rates, deliver greater productivity and are long-life tools.

 

T-SLOT END MILLS

The T-slot millers are special category tools. They have 2 insert at upside and 2 inserts in downside. They can be used to make screw slots for beds and tables fixings. Their operation is very advanced because first you need to cut vertical slots to allow shank and neck of T-slot millers enter the cut. They also give good finishing surface and their inserts are also changeable which makes their usage economical.

 

CONCLUSION

Various types of end mills can perform different function. Some give rough texture while some give smooth finished surface and some are used to provide smooth 3D profiling. Their selection depends on what type of milling action you require. Having a deep understanding of their various types and functions will help you make the right choice.

 

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8 Common Microstructures of Metal and Alloy

Modern materials can be divided into four categories: metals, polymers, ceramics and composite materials. Despite the rapid development of macromolecule materials, steel is still the most widely used and most important material in the current engineering technology. What factors determine the dominant position of steel materials? Now let’s introduce it in detail.

Iron and steel are extracted from iron ore, rich in sources and low in price. Iron and steel, also known as iron-carbon alloy, is an alloy composed of iron (Fe) and carbon (C), silicon (Si), manganese (Mn), phosphorus (P), sulfur (S) and other small elements (Cr, V, etc.). Various metallographic structures can be obtained by adjusting the content of various elements in steel and heat treatment process (four firings: quenching, annealing, tempering, normalizing), so that steel has Surface Milling Inserts different physical properties. The structure observed under metallographic microscope is called metallographic structure of steel after sampling, grinding, polishing and etching with a specific corrosive agent. The secrets of steel materials are hidden in these structures.

        In Fe-Fe3C system, iron-carbon alloys with different compositions can be prepared. Their equilibrium structures are different at different temperatures, but they are composed of several basic phases (ferrite F, austenite A and cementite Fe3C). These basic phases are combined in the form of mechanical mixtures, forming a rich and colorful metallographic structure in steel. There are eight common metallographic structures:

Contents hide 1I. Ferrite 2Ⅱ.Austenite 3Ⅲ. Cementite 4IV. Pearlite 5V. Bainite 5.1a. Upper bainite: 5.2b. Lower bainite: 5.3c. Granular TCGT Insert bainite: 6VI. WEISHER’S TISSUE 7Ⅶ.Martensite 7.1a. lath martensite: 7.2b. acicular martensite: 7.3c. The martensite formed after quenching can also form three special metallographic structures after tempering: 7.3.1(i) Tempered martensite: 7.3.2(ii) Tempered troostite: 7.3.3(iii) tempered sorbite: 8Ⅷ.LedeburiteI. Ferrite

 The interstitial solid solution formed by dissolving carbon in the interstitial of a-Fe lattice is called ferrite, which belongs to BCC Structure and is equiaxed polygonal grain distribution, which is expressed by symbol F. Its structure and properties are similar to pure iron. It has good plasticity and toughness, but its strength and hardness are lower (30-100 HB). In alloy steel, it is a solid solution of carbon and alloy elements in alpha-Fe. The solubility of carbon in alpha-Fe is very low. At AC1 temperature, the maximum solubility of carbon is 0.0218%, but with the decrease of temperature, the solubility decreases to 0.0084%. Therefore, the third cementite appears at the ferrite grain boundary under slow cooling condition. With the increase of carbon content in steel, the number of ferrite decreases and the number of pearlite increases. At this time, the ferrite is network and crescent.

Ⅱ.Austenite

 The interstitial solid solution formed by the dissolution of carbon in the interstitial space of the gamma-Fe lattice is called austenite. It has a face-centered cubic structure and is a high temperature phase, which is represented by symbol A. Austenite has a maximum solubility of 2.11% C at 1148 C and solid solution of 0.77% C at 727 C. Its strength and hardness are higher than that of ferrite, its plasticity and toughness are good, and it is non-magnetic. Its specific mechanical properties are related to carbon content and grain size, generally 170-220 HBS,=40-50%. TRIP steel is a steel developed on the basis of good plasticity and flexibility of austenite. The strain-induced transformation and transformation-induced plasticity of retained austenite are used to improve the plasticity of steel plate and the formability of steel plate. Austenite in carbon or alloy structural steels transforms into other phases during cooling. Only after carburizing and high temperature quenching of high carbon steels and carburized steels can austenite remain in martensite gap, and its metallographic structure is white because it is not easy to be eroded.

Ⅲ. Cementite

 Cementite is a metal compound synthesized by a certain proportion of carbon and iron. The molecule formula Fe3C shows that its carbon content is 6.69%, and (Fe, M) 3C is formed in the alloy. The cementite is hard and brittle, its plasticity and impact toughness are almost zero, its brittleness is very high and its hardness is 800HB. In iron and steel, the distribution is usually network, semi-network, flake, needle-flake and granular.

 IV. Pearlite

 Pearlite is a mechanical mixture of ferrite and cementite, expressed in symbol P. Its mechanical properties are between ferrite and cementite, with high strength, moderate hardness and certain plasticity. Pearlite is a product of eutectoid transformation in steel. Its morphology is that ferrite and cementite are arranged in layers like fingerprints. According to the distribution pattern of carbides, it can be divided into two types: flake pearlite and spherical pearlite.

 a. Flake pearlite: It can be divided into three types: thick flake, medium flake and fine flake.

b. Spherical pearlite: obtained by spheroidizing annealing, the cementite is spheroidized and distributed on the ferrite matrix. the size of cementite spheroids depends on the spheroidizing annealing process, especially the cooling rate. Spherical pearlite can be divided into four types: coarse spherical, spherical, fine spherical and punctate.

V. Bainite

Bainite is the product of transformation of austenite below pearlite transformation zone and above MS point in medium temperature zone. Bainite is a mechanical mixture of ferrite and cementite, a structure between pearlite and martensite, expressed in symbol B. According to the formation temperature, it can be divided into granular bainite, upper bainite (upper B) and lower bainite (lower B). Granular bainite has low strength but good toughness. lower bainite has both high strength and good toughness. granular bainite has the worst toughness. Bainite morphology is changeable. According to its shape characteristics, bainite can be divided into three types: feather, needle and granular.

a. Upper bainite:

Upper bainite is characterized by the parallel arrangement of strip ferrite, with fine strip (or short rod) cementite parallel to the ferrite needle axis, feathery.

b. Lower bainite:

fine needle flake, with certain orientation, more vulnerable to erosion than quenched martensite, very similar to tempered martensite, very difficult to distinguish under light microscope, easy to distinguish under electron microscope. carbide precipitates in acicular ferrite, and its alignment orientation is 55-60 degrees with the long axis of ferrite sheet, lower bainite does not contain twins, there are more dislocations.

c. Granular bainite:

Ferrite with polygonal shape and many irregular island-like structures. When the austenite of steel is cooled to a little higher than the forming temperature of upper bainite, some carbon atoms of precipitated ferrite migrate from ferrite to austenite through ferrite/austenite phase boundary, which makes austenite unevenly rich in carbon, thus restraining the transformation from austenite to ferrite. These austenite regions are generally island-like, granular or strip-like, distributed on ferrite matrix. During continuous cooling, according to the composition of austenite and cooling conditions, the austenite in grain bails can undergo the following changes.

(i) Decomposition into ferrite and carbide in whole or in part. Under the electron microscope, granular, rod or small block carbides with dispersive multidirectional distribution can be seen.

(ii) partial transformation into martensite, which is fully yellow under light microscope.

(iii) still retains carbon-rich austenite.

Granular carbides are distributed on the ferrite matrix of granular bainite (the island structure was originally carbon-rich austenite, which was decomposed into ferrite and carbide when cooled, or transformed into martensite or remained carbon-rich austenite particles). Feather bainite, ferrite matrix, strip carbide precipitated at the margin of ferrite sheet. Lower bainite, acicular ferrite with small flake carbide, flake carbide in the ferrite of the long axis is roughly 55 ~ 60 degrees angle. 

VI. WEISHER’S TISSUE

Widmanstatten structure is a kind of superheated structure, which consists of ferrite needles intersecting each other about 60 degrees and embedded in the matrix of steel. Coarse Widmanstatten structure decreases the plasticity and toughness of steel and increases its brittleness. In hypoeutectoid steel, coarse grains are formed by overheating and precipitate rapidly when cooling. Therefore, in addition to the network precipitation along the austenite grain boundary, some ferrites are formed from grain boundary to grain in accordance with shear mechanism and separately precipitated into needles. The structure of this distribution is called Widmanstatten structure. When superheated supereutectoid steel is cooled, the cementite also extends from grain boundary to grain and forms Widmanstatten structure.

Ⅶ.Martensite

The supersaturated solid solution of carbon in alpha-Fe is called martensite. Martensite has high strength and hardness, but its plasticity is poor, almost zero. It can not bear impact load expressed by symbol M. Martensite is the product of rapid cooling of undercooled austenite and transformation of shear mode between MS and Mf points. At this time, carbon (and alloying elements) can not diffuse in time, only from the lattice (face center) of gamma-Fe to the lattice (body center) of alpha-Fe, that is, the solid solution (austenite) of carbon in gamma-Fe to the solid solution of carbon in alpha-Fe. Therefore, martensite transformation is based on the metallographic characteristics of martensite, which can be divided into lath martensite (low carbon) and acicular martensite.

a. lath martensite:

also known as low carbon martensite. Fine martensite strips of roughly the same size are aligned in parallel to form martensite bundles or martensite domains. the orientation difference between domains and domains is large, and several domains with different orientations can be formed in a primitive austenite grain. Because of the high temperature of lath martensite formation, the phenomenon of self-tempering will inevitably occur in the cooling process, and carbides will precipitate in the formed martensite, so it is vulnerable to erosion and darkening.

 b. acicular martensite:

also known as flake martensite or high carbon martensite, its basic characteristics are: the first martensite sheet formed in an austenite grain is relatively large, often throughout the whole grain, the austenite grain is divided, so that the size of martensite formed later is limited, so the size of flake martensite varies, irregular distribution. The acicular martensite is formed in a certain direction. There is a middle ridge in the martensite needle. The higher the carbon content, the more obvious the martensite is. At the same time, there is white retained austenite between the martensite.

 c. The martensite formed after quenching can also form three special metallographic structures after tempering:(i) Tempered martensite:

the composite of sheet martensite formed during quenching (with a crystal structure of tetragonal body center) which is decomposed in the first stage of tempering, in which carbon is desolved in the form of transition carbides, and extremely fine transition carbide sheets dispersed in the solid solution matrix (whose crystal structure has changed into body-centered cube) (the interface with the matrix is a coherent interface) Phase structure. this kind of structure can not distinguish its internal structure even when magnified to the maximum magnification under metallographic (optical) microscope, only can see that its whole structure is black needle (the shape of black needle is basically the same as that of white needle formed during quenching). This kind of black needle is called “tempered martensite”.

(ii) Tempered troostite:

product of quenched martensite tempered at medium temperature, characterized by gradual disappearance of needle shape of martensite, but still vaguely visible (chromium-containing alloy steel, its alloy ferrite recrystallization temperature is higher, so it still retains needle shape), precipitated carbides are small, difficult to distinguish under light microscope, carbide particles can only be seen under electron microscope, pole Susceptible to erosion and blackening of tissues. If tempering temperature is higher or retained for a longer time, the needles will be white. At this time, the carbides will be concentrated on the edge of the needles, and the hardness of the steel will be slightly lower and the strength will decrease.

(iii) tempered sorbite:

product of quenched martensite tempered at high temperature. Its characteristics are: fine granular carbides are distributed on the sorbite matrix, which can be distinguished clearly under the light microscope. This kind of structure, also known as conditioned structure, has a good combination of strength and toughness. The finer the fine carbides on ferrite, the higher the hardness and strength, and the worse the toughness. on the contrary, the lower the hardness and strength, and the higher the toughness.

Ⅷ.Ledeburite

The eutectic mixtures in FERROCARBON alloys, i.e. liquid FERROCARBON alloys with a mass fraction of carbon (carbon content) of 4.3%, are called ledeburite when the mechanical mixtures of austenite and cementite crystallize simultaneously from the liquid at 1480 degrees Celsius. Since austenite transforms into pearlite at 727 C, ledeburite is composed of pearlite and cementite at room temperature. In order to distinguish the ledeburite above 727 C is called high-temperature ledeburite (L d), and the ledeburite below 727 C is called low-temperature ledeburite (L’d). The properties of ledeburite are similar to those of cementite with high hardness and poor plasticity.

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