Vacuum heat treatment furnace technology
Heat treatment process
1. Normalizing: Heat treatment process for obtaining PEARLITE-LIKE structure by heating steel or steel to a suitable temperature above the critical point AC3 or ACM and cooling it in air for a certain period of time.
2. Annealing annealing: the hypoeutectoid steel workpiece heated to AC3 above 20-40 degrees, holding for a period of time, with the furnace slow cooling (or buried in sand or lime cooling) to 500 degrees below in the air cooling heat treatment process.
3. Solid solution heat treatment: the alloy is heated to the high temperature single-phase region to maintain constant temperature, so that the excess phase is fully dissolved into the solid solution, and then rapidly cooled to obtain the supersaturated solid solution heat treatment process.
4. Aging: The properties of alloys change with time after solution heat treatment or cold plastic deformation when placed at or slightly higher than room temperature.
5. Solution treatment: make all phases in the alloy fully dissolved, strengthen the solid solution and improve toughness and corrosion resistance, eliminate stress and softening, so as to continue processing and forming.
6. Aging treatment: heating and holding at the temperature of precipitation of strengthening phase, so that precipitation of strengthening phase can harden and strength can be increased.
7. Quenching: A heat treatment process in which the steel is austenitized and cooled at an appropriate cooling rate, resulting in the transformation of unstable microstructure such as martensite in all or within a certain range of cross-section.
8. Tempering: A heat treatment process in which the quenched workpiece is heated to a suitable temperature below the critical point AC1 for a certain period of time and then cooled to obtain the required microstructure and properties by a suitable method.
Carbonitriding of 9. steel: carbonitriding is the process of simultaneous infiltration of carbon and nitrogen into the surface of the steel. Customarily, carbonitriding is also known as cyanidation. Medium temperature gas carbonitriding and low temperature gas carbonitriding (gas soft nitriding) are widely used. The main purpose of mesophilic gas carbonitriding is to improve the hardness, wear resistance and fatigue strength of steel. Low temperature gas nitrocarburizing is mainly nitriding, and its main purpose is to improve the wear resistance and bite resistance of steel.
10. quenching and tempering: It is customary to combine quenching with high temperature tempering for heat treatment called quenching and tempering. Tempering and tempering treatment is widely used in various important structural parts, especially those connecting rods, bolts, gears and shafts working under alternating loads. Tempered sorbite is obtained after quenching and tempering, and its mechanical properties are better than those of normalized sorbite with the same hardness. Its hardness depends on high tempering temperature and tempering stability of steel and workpiece section size, generally between HB200 - 350.
11. brazing: heat treatment of two pieces of work together by soldering.
Process characteristics of hardware mold heat treatment furnace
Metal heat treatment is one of the most important processes in mechanical manufacturing. Compared with other processes, heat treatment generally does not change the shape and the overall chemical composition of the workpiece, but endows or improves the performance of the workpiece by changing the internal microstructure of the workpiece or changing the chemical composition of the workpiece surface. It is characterized by improving the internal quality of the workpiece, which is generally not visible to the naked eye.
In order to make the metal workpiece have the required mechanical, physical and chemical properties, in addition to the rational selection of materials and various forming processes, heat treatment process is often essential. Steel is the most widely used material in machinery industry. The microstructure of steel is complex and can be controlled by heat treatment. So the heat treatment of steel is the main content of metal heat treatment. In addition, Al, Cu, Mg, Ti and their alloys can also be heat treated to change their mechanical, physical and chemical properties to obtain different performance.
Process of hardware mold heat treatment furnace
Heat treatment process generally includes heating, insulation, cooling three processes, sometimes only heating and cooling two processes. These processes are interconnected and uninterrupted.
Heating is one of the most important processes in heat treatment. There are many heating methods for metal heat treatment. Charcoal and coal were first used as heat sources, and liquid and gas fuels were recently used. The application of electricity makes heating easy to control without environmental pollution. These sources can be used for direct heating, or indirect heating through molten salts or metals, or even floating particles.
When the metal is heated, the workpiece is exposed to air, and oxidation and decarbonization often occur (that is, the carbon content on the surface of the steel parts is reduced), which has a very adverse effect on the surface properties of the parts after heat treatment. Therefore, metals should usually be heated in controlled or protective atmosphere, molten salt and vacuum, or by coating or packaging.
The heating temperature is one of the important technological parameters in the heat treatment process. Selecting and controlling the heating temperature is the main problem to ensure the quality of heat treatment. The heating temperature varies with the object of heat treatment and the metal material being treated, but it is generally heated above the phase change temperature to obtain high temperature microstructure. In addition, the transformation takes a certain time, so when the surface of the metal workpiece reaches the required heating temperature, it must be kept at this temperature for a certain period of time, so that the internal and external temperatures are consistent, so that the microstructure of the transformation is complete, this period is called holding time. When high energy density heating and surface heat treatment are used, the heating speed is very fast, and there is no heat preservation time in general. The longer heat preservation time of chemical heat treatment is also an indispensable step in the heat treatment process. The cooling method varies with the process, mainly controlling the cooling speed. The cooling rate of general annealing is the slowest, the normalizing cooling rate is faster, and quenching is faster. But there are different requirements for different grades of steel, such as air-hardened steel can be normalized with the same cooling rate for hardening.
Classification of vacuum tempering furnace
Metal heat treatment technology can be broadly divided into three categories: integral heat treatment, surface heat treatment and chemical heat treatment. According to the different heating medium, heating temperature and cooling method, each category can be divided into several different heat treatment processes. Different microstructure and properties can be obtained by different heat treatment processes for the same metal. Steel is the most widely used metal in industry, and the microstructure of steel is also the most complex, so there are many kinds of heat treatment process of steel.
Integral heat treatment is the heat treatment process of heating the workpiece as a whole and then cooling it at an appropriate rate to obtain the required metallographic structure to change its overall mechanical properties. The overall heat treatment of steel consists of four basic processes: annealing, normalizing, quenching and tempering.
Hardware mould quenching furnace technology means
Annealing is to heat the workpiece to a suitable temperature, according to the material and workpiece size with different holding time, and then slow cooling, the purpose is to make the internal structure of the metal to achieve or close to equilibrium, to obtain good technical performance and service performance, or to prepare for further quenching microstructure.
Normalizing is to heat the workpiece to a suitable temperature and then cool it in the air. Normalizing is similar to annealing, but the resulting microstructure is finer. Normalizing is often used to improve the cutting performance of materials, and sometimes used for some parts with low requirements as final heat treatment.
Quenching is the rapid cooling of the workpiece in water, oil or other inorganic salts, organic water solution and other quenching media after heating and holding. After quenching, the steel parts harden, but crisp at the same time. In order to eliminate brittleness in time, it is necessary to temper in time.
In order to reduce the brittleness of steel, the quenched steel is kept for a long time at a suitable temperature above room temperature but below 650 C, and then cooled. This process is called tempering. Annealing, normalizing, quenching and tempering are the "four fires" in the whole heat treatment, in which quenching and tempering are closely related, often used together, indispensable.
With the difference of heating temperature and cooling mode, the "four fires" have evolved different heat treatment processes. In order to obtain a certain strength and toughness, the quenching and high temperature tempering process is called quenching and tempering. The supersaturated solid solution formed by quenching of some alloys can be kept at room temperature or a little higher for a long time to improve the hardness, strength or electrical magnetism of the alloys. Such a heat treatment process is called aging treatment.
The method of combining pressure processing deformation with heat treatment effectively and tightly to make the workpiece have good strength and toughness is called thermomechanical treatment; the heat treatment in negative pressure atmosphere or vacuum is called vacuum heat treatment, which can not only prevent the workpiece from oxidation and decarbonization, but also keep the surface of the workpiece clean after treatment. The performance of the workpiece can be improved, and chemical treatment can also be carried out by infiltration agent.
Surface heat treatment is a metal heat treatment process that only heats the surface of the workpiece to change the mechanical properties of its surface. In order to heat only the surface layer of the workpiece without transferring excessive heat into the inner part of the workpiece, the heat source used must have a high energy density, i.e. a large amount of heat is given to the workpiece per unit area, so that the surface layer or part of the workpiece can reach high temperature in a short time or instantaneously. The main methods of surface heat treatment are flame quenching and induction heating. The commonly used heat sources are oxyacetylene or oxypropane flame, induction current, laser and electron beam.
Chemical heat treatment is a metal heat treatment process by changing the chemical composition, microstructure and properties of the workpiece surface. The difference between chemical heat treatment and surface heat treatment is that the former changes the chemical composition of the surface of the workpiece. Chemical heat treatment is to heat the workpiece in a medium containing carbon, salt or other alloy elements (gas, liquid, solid) for a long time, so that the surface of the workpiece into carbon, nitrogen, boron and chromium and other elements. After infiltration, some other heat treatment processes such as quenching and tempering are sometimes needed. The main methods of chemical heat treatment are carburizing, nitriding and metallizing.
Heat treatment is one of the important processes in the manufacturing process of mechanical parts and dies. Generally speaking, it can guarantee and improve various properties of the workpiece, such as wear resistance and corrosion resistance. It can also improve the microstructure and stress state of the blank to facilitate cold and hot processing.
For example, malleable cast iron can be obtained by long-time annealing treatment of white cast iron to improve plasticity; gears with the correct heat treatment process, service life can be times or tens of times longer than the gear without heat treatment; in addition, inexpensive carbon steel through infiltration of certain alloying elements with some expensive alloy steel properties, can be. In order to replace some heat resistant steel and stainless steel, the die and mould need almost all heat treatment.
Supplementary means of vacuum annealing furnace
Types of annealing
Annealing is a heat treatment process in which the workpiece is heated to a suitable temperature, maintained for a certain period of time, and then slowly cooled.
There are many kinds of annealing processes for steels, which can be divided into two categories according to the heating temperature: one is annealing above the critical temperature (Ac1 or Ac3), also known as phase transformation recrystallization annealing, including complete annealing, incomplete annealing, spheroidizing annealing and diffusion annealing (homogenizing annealing); the other is annealing below the critical temperature, including re-annealing. Crystallization annealing and stress relieving annealing. According to the cooling method, annealing can be divided into isothermal annealing and continuous cooling annealing.
1. complete annealing and isothermal annealing
Complete annealing, also known as weight crystallization annealing, is generally referred to as annealing, it is the steel or steel heated to Ac3 above 20 ~ 30 degrees Celsius, holding enough time to make the structure of complete austenitization after slow cooling, in order to obtain near-equilibrium structure of the heat treatment process. This kind of annealing is mainly used for casting, forging and hot-rolled sections of various hypoeutectoid carbon and alloy steels, and sometimes for welding structures. It is usually used as the final heat treatment of some non heavy parts, or as the pre heat treatment of some workpieces.
2. spheroidizing annealing
Spheroidizing annealing is mainly used for hypereutectoid carbon steel and alloy tool steel (such as the steel used for manufacturing tools, measuring tools and dies). Its main purpose is to reduce hardness, improve machinability, and prepare for later quenching.
3. stress relief annealing
Stress relief annealing, also known as low temperature annealing (or high temperature tempering), is mainly used to eliminate the residual stress of castings, forgings, weldments, hot-rolled parts, cold-drawn parts and so on. If these stresses are not eliminated, deformation or cracks will occur after a certain period of time or during subsequent cutting.
4. incomplete annealing
The steel is heated to between Ac1-Ac3 (hypoeutectoid steel) or Ac1-ACcm (hypereutectoid steel) and cooled slowly after heat preservation to obtain a heat treatment process close to equilibrium structure.
The most commonly used cooling medium is brine, water and oil. Salt water quenched workpiece is easy to get high hardness and smooth surface, not easy to produce hardened soft spots, but easy to make the workpiece deformation and even cracking. The oil quenching medium is only suitable for the quenching of some alloy steel or small size carbon steel workpieces with high stability of undercooled austenite.
Three. The purpose of steel tempering.
1. Reducing the brittleness, eliminating or reducing the internal stress, there are great internal stress and brittleness after quenching, if not tempered in time, the steel will often cause deformation and even cracking.
2. To obtain the required mechanical properties of the workpiece, the hardness and brittleness of the workpiece are high after quenching. In order to meet the different performance requirements of various workpieces, the hardness can be adjusted by appropriate tempering to reduce the brittleness and obtain the required toughness and plasticity.
3. stabilize workpiece size
4. For some alloy steels which are difficult to be softened by annealing, high temperature tempering is often used after quenching (or normalizing) so that the carbides in the steels are properly aggregated and the hardness is reduced to facilitate cutting.
1. Annealing: A heat treatment process in which a metal material is heated to an appropriate temperature, maintained for a certain period of time, and then slowly cooled. The common annealing processes are recrystallization annealing, stress relieving annealing, spheroidizing annealing, and full annealing. The purpose of annealing is to reduce the hardness and plasticity of metal materials, to facilitate cutting or pressure processing, to reduce residual stress, to improve the homogenization of microstructure and composition, or to prepare microstructure for post-heat treatment.
Normalizing: refers to the process of heating steel or steel pieces to or above the upper critical point temperature of the steel and cooling them in still air at 30-50 C for a suitable time. The purpose of normalizing is to improve the mechanical properties of low carbon steel, improve the machinability of cutting, refine the grain, eliminate the structural defects, and prepare the microstructure for post heat treatment.
3. Quenching: A heat treatment process in which steel is heated to a certain temperature above Ac3 or Ac1 (the lower critical point temperature of steel) for a certain period of time and then cooled at a suitable rate to obtain martensite (or bainite) structure. Common quenching processes include single medium quenching, double medium quenching, martensite step quenching, bainite isothermal quenching, surface quenching and local quenching. The purpose of quenching is to obtain the required martensite structure, improve the hardness, strength and wear resistance of the workpiece, and prepare the microstructure for post-heat treatment.
4. Tempering: refers to the heat treatment process in which steel pieces are hardened and then heated to a certain temperature below Ac1 for a certain time and then cooled to room temperature. Common tempering processes include low temperature tempering, medium tempering, high temperature tempering and multiple tempering.
The purpose of tempering is mainly to eliminate the stress produced by quenching of steel, so that the steel has high hardness and wear resistance, and has the required plasticity and toughness.
5. quenching and tempering: a composite heat treatment process for quenching or tempering steel or steel parts. Steel used for quenching and tempering is called quenched and tempered steel. It generally refers to medium carbon structural steel and medium carbon alloy structural steel.
6. carburizing: carburizing is the process of infiltrating carbon atoms into the surface layer of steel. It also makes the workpiece of low carbon steel have the surface layer of high carbon steel. After quenching and low temperature tempering, the surface layer of the workpiece has high hardness and wear resistance, while the central part of the workpiece still maintains the toughness and plasticity of low carbon steel.
Vacuum method for mesh belt heat treatment furnace
Because metal workpiece heating, cooling and other operations, it takes more than a dozen or even dozens of actions to complete. These actions are carried out inside the vacuum heat treatment furnace, and the operator can not approach them. Therefore, the automation of the vacuum heat treatment furnace is required to be higher. At the same time, some actions, such as heating and holding after the completion of the metal workpiece quenching process to take six or seven actions and to complete within 15 seconds. Such agile conditions to complete many movements, it is easy to cause operator tension and constitute a misoperation. Therefore, only higher automation can coordinate the process accurately and timely.
Vacuum heat treatment of metal parts is carried out in an airtight vacuum furnace, and strict vacuum sealing is well known. Therefore, it is very important to obtain and adhere to the original air leakage rate of the furnace and ensure the working vacuum of the vacuum furnace to ensure the quality of vacuum heat treatment of parts. Therefore, a key problem of vacuum heat treatment furnace is to have a reliable vacuum sealing structure. In order to ensure the vacuum performance of vacuum furnace, a basic principle must be followed in the structural design of vacuum heat treatment furnace, that is, the furnace body should be air-tightly welded, at the same time, the furnace body should be as little or no holes, less or avoid the use of dynamic sealing structure, in order to minimize the chance of vacuum leakage. Sealing structures must also be designed for parts and accessories such as water-cooled electrodes and thermocouple outlets installed on the vacuum furnace body.
Most heating and insulation materials can only be used in vacuum. The heating and insulating linings of vacuum heat treatment furnace work in vacuum and high temperature, so the requirements of high temperature resistance, good radiation results and low thermal conductivity of these materials are put forward. The requirement of oxidation resistance is not high. Therefore, tantalum, tungsten, molybdenum and graphite are widely used as heating and heat insulation materials in vacuum heat treatment furnace. These materials are easily oxidized in atmospheric conditions, so they can not be used in ordinary heat treatment furnaces.
Water-cooled device: shell, cover, electric heating element, water-cooled electrode, intermediate vacuum heat insulation and other components of vacuum heat treatment furnace, all work in vacuum and heating state. Under such extremely unfavorable conditions, it is necessary to ensure that the structure of each component is not deformed and damaged, and that the vacuum sealing ring is not overheated or burned. Therefore, each component should be set up water-cooled device according to different conditions to ensure that the vacuum heat treatment furnace can operate normally and have sufficient service life.
Low voltage and high current: glow discharge will occur in the vacuum vessel when the vacuum vacancy is within the range of several torches of lxlo-1 torches. In vacuum heat treatment furnace, serious arc discharge will destroy the electric heating elements, insulation layer and so on, causing serious accidents and losses. Therefore, the working voltage of the electric heating element of the vacuum heat treatment furnace generally does not exceed 80 1 100 volts. At the same time, effective measures should be taken to prevent glow discharge or arc discharge, such as avoiding cutting-edge components as far as possible, and the spacing between electrodes should not be too small.
Tempering of high temperature vacuum furnace
According to the different performance requirements of the workpieces, tempering can be divided into the following types according to their tempering temperature.
(1) tempering at low temperature (150-250 degrees)
The tempered microstructure is tempered martensite. The purpose is to reduce the internal stress and brittleness of quenched steel on the premise of maintaining high hardness and high wear resistance, so as to avoid cracking or premature damage. It is mainly used for various high carbon cutting tools, measuring tools, cold stamping dies, rolling bearings and carburized parts, etc. The hardness after tempering is generally HRC58-64.
(two) tempering at medium temperature (250-500 degrees)
The tempered microstructure was tempered at the intermediate temperature. The purpose is to obtain high yield strength, elastic limit and high toughness. Therefore, it is mainly used for various springs and hot working dies, and the hardness is HRC35-50 after tempering.
(three) high temperature tempering (500-650 degrees)
The microstructure obtained by tempering at high temperature is tempered Soxhlet. It is customary to combine quenching with high temperature tempering heat treatment called quenching and tempering treatment, the purpose is to obtain strength, hardness and plasticity, toughness are better comprehensive mechanical properties. Therefore, it is widely used in automobiles, tractors, machine tools and other important structural parts, such as connecting rods, bolts, gears and shafts. After tempering, the hardness is generally HB200-330.
The deformation causes of precision and complex dies are often complex, but as long as we grasp the deformation law, analyze the causes, and adopt different methods to prevent the deformation of dies can be reduced, but also can be controlled. Generally speaking, the following methods can be used to prevent the heat treatment deformation of complex and complex dies.
(1) reasonable selection. For precision and complex dies, micro-deformed die steels (such as air-quenched steel) with good materials should be selected. Die steels with serious carbide segregation should be reasonably forged and quenched and tempered. For larger and non-forgeable die steels, solid solution double-refining heat treatment can be carried out.
(2) The design of the die structure should be reasonable, the thickness should not be too different, the shape should be symmetrical, the deformation law should be grasped for the large deformation die, the machining allowance should be reserved, and the combination structure can be used for the large and precision complex die.
(3) precision complex dies should be pre heat treated to eliminate residual stresses during machining.
(4) Reasonable selection of heating temperature, control of heating speed, for precision and complex molds can be taken to slow heating, preheating and other balanced heating methods to reduce mold heat treatment deformation.
(5) under the premise of ensuring mold hardness, precooling, grading cooling quenching or temperature quenching are used as far as possible.
(6) Vacuum heating and quenching and cryogenic treatment after quenching should be adopted as far as possible for precise and complicated dies and moulds as conditions permit.
(7) Precision of some precision and complicated dies can be controlled by pre-heat treatment, aging heat treatment, quenching and tempering nitriding heat treatment.
(8) When repairing the defects such as sand holes, air holes, wear and tear, cold welding machines and other repair equipment with little heat effect are selected to avoid deformation during the repair process.
In addition, the correct heat treatment process operation (such as plugging hole, binding hole, mechanical fixation, suitable heating method, correct choice of cooling direction of the mold and the movement direction in the cooling medium) and reasonable tempering heat treatment process are also effective measures to reduce the deformation of precision and complex mold.