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Quenching method:
1. Single liquid quenching -- cooling process in a quenching medium, single liquid quenching microstructure stress and thermal stress are relatively large, quenching deformation is large.
2. Double liquid quenching - purpose: fast cooling between 650℃~Ms, so that V>Vc, cooled slowly below Ms to reduce tissue stress.Carbon steel: water before oil.Alloy steel: oil before air.
3. Fractional quenching -- the workpiece is taken out and stays at a certain temperature so that the internal and external temperature of the workpiece is consistent, and then the process of air cooling. Fractional quenching is the M phase transformation in the air cooling, and the internal stress is small.
4. Isothermal quenching -- refers to the bainite transformation occurs in the bainite temperature region isothermal, with reduced internal stress and small deformation.The principle of quenching method selection should not only meet the performance requirements, but also reduce the quenching stress as far as possible to avoid quenching deformation and cracking.
Chemical meteorological deposition is mainly CVD method. The reaction medium containing coating material elements is vaporized at a lower temperature, and then sent into a high-temperature reaction chamber to contact the workpiece surface to produce high-temperature chemical reaction. Alloy or metal and its compounds are precipitated and deposited on the workpiece surface to form coating.
Main characteristics of CVD method:
1. Can deposit a variety of crystalline or amorphous inorganic film materials.
2. High purity and strong collective binding force.
3. Dense sedimentary layer with few pores.
4. Good uniformity, simple equipment and process.
5. High reaction temperature.
Application: to prepare various kinds of films on the surface of materials such as iron and steel, hard alloy, non-ferrous metal and inorganic non-metal, mainly insulator film, semiconductor film, conductor and superconductor film and corrosion resistance film.
Physical and meteorological deposition: a process in which gaseous substances are deposited directly on the workpiece surface into solid films, known as PVD method.There are three basic methods, namely, vacuum evaporation, sputtering and ion plating.Application: wear resistant coating, heat resistant coating, corrosion resistant coating, lubricating coating, functional coating decorative coating.
Microscopic: strip patterns observed under a microscopic electron microscope, known as fatigue bands or fatigue striations.Fatigue strip has ductile and brittle two kinds, fatigue strip has a certain spacing, under certain conditions, each stripe corresponds to a stress cycle.
Macroscopic: in most cases, it has the characteristics of brittle fracture without macroscopic deformation visible to the naked eye. Typical fatigue fracture consists of crack source zone, crack propagation zone and final transient fracture zone.The fatigue source area is less flat, sometimes bright mirror, the crack propagation area is beach or shell pattern, some of the fatigue sources with unequal spacing are parallel arcs of the center of the circle.The microscopic morphology of the transient fracture zone is determined by the characteristic load mode and size of the material, and may be dimple or quasi-dissociation, dissociation intergranular fracture or mixed shape.
1 .cracking: the heating temperature is too high and the temperature is uneven;Improper selection of quenching medium and temperature;Tempering is not timely and insufficient;The material has high hardenability, component segregation, defects and excessive inclusion;The parts are not properly designed.
2. Uneven surface hardness: unreasonable induction structure;Uneven heating;Uneven cooling;Poor material organization (banded structure, partial decarbonization.
3. Surface melting: the inductor structure is unreasonable;Parts exist sharp corners, holes, bad, etc.;Heating time is too long, and the workpiece surface has cracks.
Take W18Cr4V for example, why is it better than ordinary tempered mechanical properties?W18Cr4V steel is heated and quenched at 1275℃ +320℃*1h+540℃ to 560℃*1h*2 times tempering.
Compared with ordinary tempered high speed steel, M2C carbides are more precipitated, and M2C, V4C and Fe3C carbides have larger dispersion and better uniformity, and about 5% to 7% bainite exists, which is an important microstructure factor for high temperature tempered high speed steel performance better than ordinary tempered high speed steel.
There are endothermic atmosphere, drip atmosphere, straight body atmosphere, other controllable atmosphere (nitrogen machine atmosphere, ammonia decomposition atmosphere, exothermic atmosphere).
1. Endothermic atmosphere is the raw gas mixed with air in a certain proportion, through the catalyst at high temperature, reaction generated mainly containing CO, H2, N2 and trace CO2, O2 and H2O atmosphere, because the reaction to absorb heat, so called endothermic atmosphere or RX gas.Used for carburizing and carbonitriding.
2. In the drip atmosphere, methanol is directly pointed into the furnace to crack, and the carrier containing CO and H2 is generated, and then rich agent is added for carburizing;Low temperature carbonitriding, protection heating bright quenching, etc.
3. The infiltration agent such as natural gas and air mixed in a certain proportion directly into the furnace, at high temperature 900℃ reaction directly generated carburizing atmosphere.Ammonia decomposition gas is used for nitriding carrier gas, steel or non-ferrous metal low temperature heating protection atmosphere.Nitrogen - based atmosphere for high carbon steel or bearing steel protection effect is good.Exothermic atmosphere is used for bright heat treatment of low carbon steel, copper or decarburization annealing of malleable cast iron.
Objective: Good mechanical properties and small distortion of ductile iron can be obtained by isothermal quenching in bainite transition zone after austenitizing.Isothermal temperature: 260~300℃ bainite structure;The upper bainite structure is obtained at 350~400℃.
Carburizing: mainly to the surface of the workpiece into the process of carbon atoms, surface tempering martensite, residual A and carbide, the purpose of the center is to improve the surface carbon content, with high hardness and high wear resistance, the center has A certain strength and high toughness, so that it bears large impact and friction, low carbon steel such as 20CrMnTi, gear and piston pin commonly used.
Nitriding: to the surface of the infiltration of nitrogen atoms, is the surface hardness, wear resistance fatigue strength and corrosion resistance and thermal hardness improvement, the surface is nitride, the heart of the tempering sorbsite, gas nitriding, liquid nitriding, commonly used 38CrMoAlA, 18CrNiW.
Carbonitriding: carbonitriding is low temperature, fast speed, small deformation of parts.The surface microstructure is fine needle tempered martensite + granular carbon and nitrogen compound Fe3 (C, N) + a little residual austenite.It has high wear resistance, fatigue strength and compressive strength, and has certain corrosion resistance.Often used in heavy and medium load gears made of low and medium carbon alloy steel.
Nitrocarburizing: nitrocarburizing process is faster, the surface hardness is slightly lower than nitriding, but the fatigue resistance is good.It is mainly used for machining moulds with small impact load, high wear resistance, fatigue limit and small deformation.General steel parts, such as carbon structural steel, alloy structural steel, alloy tool steel, gray cast iron, nodular cast iron and powder metallurgy, can be nitrocarburized
1. Advanced technology.
2. The process is reliable, reasonable and feasible.
3. Economy of the process.
4. Safety of the process.
5. Try to use the process equipment with high mechanization and automation procedures.
1. The connection between cold and hot processing technology should be fully considered, and the arrangement of heat treatment procedure should be reasonable.
2. Adopt new technology as far as possible, briefly describe the heat treatment process, shorten the production cycle.Under the condition of ensuring the required structure and performance of parts, try to make different processes or technological processes combined with each other.
3. Sometimes in order to improve product quality and prolong the service life of the workpiece, it is necessary to increase the heat treatment process.
1. The coupling distance between the inductor and the workpiece should be as close as possible.
2. The workpiece heated by the outer wall of the coil must be driven by a flux magnet.
3. Design of the workpiece sensor with sharp corners to avoid sharp effect.
4. Offset phenomenon of magnetic field lines should be avoided.
5. Sensor design should try to meet the workpiece can turn when heated.
1. Select materials according to the working conditions of parts, including load type and size, environmental conditions and main failure modes;
2. Considering the structure, shape, size and other factors of parts, the material with good hardenability can be processed by oil quenching or water-soluble quenching medium for easy quenching distortion and cracking;
3. Understand the structure and properties of materials after heat treatment. Some steel grades developed for various heat treatment methods will have better structure and properties after treatment;
4. On the premise of ensuring the service performance and life of parts, heat treatment procedures should be simplified as far as possible, especially materials that can be saved.
1. Casting performance.
2. Pressure machining performance.
3. Machining performance.
4. Welding performance.
5. Heat treatment process performance.
Decomposition, adsorption, diffusion three steps.The application of segmental control method, compound infiltration treatment, high temperature diffusion, the use of new materials to accelerate the diffusion process, chemical infiltration, physical infiltration;Prevent the workpiece surface oxidation, conducive to diffusion, so that the three processes fully coordinated, reduce the workpiece surface to form carbon black process, speed up the process of carburizing, to ensure that the transition layer is wider and more gentle quality infiltration layer;From the surface to the center, the order is hypereutectoid, eutectoid, hyperhypoeutectoid, primordial hypoeutectoid.
Wear type:
Adhesion wear, abrasive wear, corrosion wear, contact fatigue.
Prevention methods:
For adhesive wear, reasonable choice of friction pair material;Using surface treatment to reduce friction coefficient or improve surface hardness;Reduce contact compressive stress;Reduce surface roughness.For abrasive wear, in addition to reducing the contact pressure and sliding friction distance in the design of lubricating oil filtration device to remove abrasive, but also reasonable selection of high hardness materials;The surface hardness of friction pair materials was improved by surface heat treatment and surface work hardening.For corrosive wear, choose oxidation resistant materials;Surface coating;Selection of corrosion resistant materials;Electrochemical protection;The stress concentration of tensile stress can be reduced when corrosion inhibitor is added.Stress relief annealing;Select materials that are not sensitive to stress corrosion;Change the medium condition.For contact fatigue, improve material hardness;Improve the purity of the material, reduce the inclusion;Improve the core strength and hardness of parts;Reduce the surface roughness of parts;Improve the viscosity of the lubricating oil to reduce wedge action.
It is composed of massive (equiaxed) ferrite and high carbon region A.
Common ball retreat: increase hardness, improve machinability, reduce quenching distortion cracking.
Isothermal ball regression: used for high carbon tool steels, alloy tool steels.
Cycle ball back: used for carbon tool steel, alloy tool steel.
1. Due to the low content of hypoeutectoid steel, the original structure P+F, if the quenching temperature is lower than Ac3, there will be undissolved F, and there will be a soft point after quenching.For eutectoid steel, if the temperature is too high, too much K 'dissolve, increase the amount of sheet M, easy to cause deformation and cracking, increase the amount of A', too much K 'dissolve, and reduce the wear resistance of steel.
2. The temperature of eutectoid steel is too high, the tendency of oxidation and decarbonization increases, so that the surface composition of steel is not uniform, Ms level is different, resulting in quenching cracking.
3. Selecting the quenching temperature Ac1+ (30-50℃) can retain the undissolved K 'to improve the wear resistance, reduce the carbon content of the matrix, and increase the strength plasticity and toughness of the steel.
The uniform precipitation of ε and M3C makes the precipitation of M2C and MC more uniform in the range of secondary hardening temperature, which promotes the transformation of some residual austenite into bainite and improves the strength and toughness.
ZL104: cast aluminum, MB2: deformed magnesium alloy, ZM3: cast magnesium, TA4: α titanium alloy, H68: brass, QSN4-3: tin brass, QBe2: beryllium brass, TB2: β titanium alloy.
Fracture toughness is a property index indicating the ability of a material to resist fracture.If K1 & gt;K1C, low stress brittle fracture occurs.
Phase transformation characteristics of gray cast iron compared with steel:
1) Cast iron is fe-C-Si ternary alloy, and the eutectoid transformation occurs in a wide temperature range, at which there exists ferrite + austenite + graphite;
2) The graphitization process of cast iron is easy to carry out, and the ferrite matrix, pearlite matrix and ferrite + pearlite matrix of cast iron are obtained by controlling the process;
3) The carbon content of A and transition products can be adjusted and controlled in A considerable range by controlling the austenitizing temperature heating, insulation and cooling conditions;
4) Compared with steel, the diffusion distance of carbon atoms is longer;
5) Heat treatment of cast iron can not change the shape and distribution of graphite, but can only change the collective structure and properties.
Formation process: the formation of A crystal nucleus, the growth of A grain, the dissolution of residual cementite, the homogenization of A;Factors: heating temperature, holding time, heating speed, steel composition, original structure.
Methods: subsection control method, compound infiltration treatment, high temperature diffusion, using new materials to accelerate the diffusion process, chemical infiltration, physical infiltration.
Heat transfer mode: conduction heat transfer, convection heat transfer, radiation heat transfer (vacuum furnace above 700℃ is radiation heat transfer).
Black organization refers to black spots, black belts and black webs.In order to prevent the appearance of black tissue, the nitrogen content in the permeable layer should not be high enough, generally greater than 0.5% is prone to spotty black tissue;The nitrogen content in the permeable layer should not be too low, otherwise it is easy to form tortenite network.In order to inhibit the torstenite network, the addition amount of ammonia should be moderate. If ammonia content is too high and the dew point of furnace gas decreases, black tissue will appear.
In order to restrain the appearance of torstenite network, the quenching heating temperature can be appropriately raised or the cooling medium with strong cooling ability can be used.When the depth of black tissue is less than 0.02mm, shot peening is used to remedy it.
Heating method: induction heating quenching has two methods of simultaneous heating quenching and moving heating continuous quenching, depending on equipment conditions and parts type.The specific power of simultaneous heating is generally 0.5~4.0 KW/cm2, and the specific power of mobile heating is generally greater than 1.5 kW/cm2.Longer shaft parts, tubular inner hole quenching parts, middle modulus gear with wide teeth, strip parts adopt continuous quenching;Large gear adopts single tooth continuous quenching.
Heating parameters:
1. Heating temperature: Due to the fast induction heating speed, the quenching temperature is 30-50℃ higher than the general heat treatment in order to make the tissue transformation full;
2. Heating time: according to the technical requirements, materials, shape, size, current frequency, specific power and other factors.
Quenching cooling method and quenching medium: The quenching cooling method of quenching heating usually adopts spray cooling and invasion cooling.
Tempering must be timely, after quenching parts within 4h tempering.Common tempering methods are self-tempering, furnace tempering and induction tempering.
The purpose is to make the work of high and medium frequency power supply in resonant state, so that the equipment play a higher efficiency.
1. Adjust electric parameters of high-frequency heating.Under the condition of 7-8kV low voltage load, adjust the coupling and feedback the position of the handwheel to make the ratio of gate current and anode current 1:5-1:10, and then increase the anode voltage to the service voltage, further adjust the electrical parameters, so that the channel voltage is adjusted to the required value, the best match.
2. Adjust the electric parameters of intermediate frequency heating, select the appropriate quenching transformer turns ratio and capacitance according to the size of parts, shape hardening zone length and inductor structure, so that it can work in resonance state.
Water, salt water, alkali water, mechanical oil, saltpeter, polyvinyl alcohol, trinitrate solution, water-soluble quenching agent, special quenching oil, etc.
1. The influence of carbon content: with the increase of carbon content in hypoeutectoid steel, the stability of A increases and the C curve moves right;With the increase of carbon content and unmelted carbides in eutectoid steel, the stability of A decreases and the curve of C shifts right.
2. Influence of alloying elements: Except Co, all metal elements in solid solution state move right in THE C curve.
3.A temperature and holding time: The higher the A temperature is, the longer the holding time is, the more completely the carbide is dissolved, the coarser the A grain is, and the curve of C moves to the right.
4. Influence of original tissue: The thinner the original tissue is, the easier it is to get uniform A, so that the CURVE of C moves right and Ms moves down.
5. The influence of stress and strain causes the C curve to move left.
Post time: Sep-15-2021
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