Heat treatment refers to a metal hot working process in which materials are heated, insulated and cooled in a solid state to obtain the expected structure and properties. In the process from the Stone Age to the Bronze Age and the Iron Age, the role of heat treatment was gradually recognized by people.
as early as 77 BC to 222 BC, people in China have discovered in their production practice that the properties of steel will change due to the influence of temperature and pressure deformation. The softening treatment of white cast iron is an important process to manufacture farm tools. Basic Introduction Chinese Name: Heat Treatment mbth? Subject of heat treatment: Physical field: history of material engineering, national standards, definitions of terms, process characteristics, thermal process, process classification, process means, vacuum method, sub-process, surface quenching, local quenching, temperature and pressure, operating rules, common problems, development history. In the 6th century BC, steel weapons were gradually adopted, and in order to improve the hardness of steel, the quenching process was developed rapidly. Two swords and a halberd unearthed in Yanxiadu, Yixian County, Hebei Province, China, have martensite in their microstructures, indicating that they have been quenched. With the development of quenching technology, people have gradually discovered the influence of quenching agent on quenching quality. Pu Yuan, a Shu man from the Three Kingdoms, once made 3, knives for Zhuge Liang in this oblique valley in Shaanxi. According to legend, he sent people to Chengdu to fetch water for quenching. This shows that China paid attention to the cooling capacity of different water quality in ancient times, and also paid attention to the cooling capacity of oil and water. The sword in zhongshan jing wang's tomb of the Western Han Dynasty (26 BC-24 AD) unearthed in China contains .15-.4% carbon in the heart, but more than .6% carbon in the surface, indicating that carburizing technology has been applied. But at that time, as a personal "craft" secret, it refused to spread it, so it developed slowly. In 1863, British metallographers and geologists showed six different metallographic structures of steel under microscope, which proved that the internal structure of steel would change when it was heated and cooled, and the phase at high temperature in steel would change into a harder phase when it was rapidly cooled. The theory of iron isomerism established by Frenchman Osmond and the iron-carbon phase diagram first formulated by Englishman Austin laid a theoretical foundation for modern heat treatment technology. At the same time, people have also studied the protection methods of metal during the heating process of metal heat treatment to avoid oxidation and decarbonization of metal during the heating process. From 185 to 188, there were a series of patents for applying various gases (such as hydrogen, gas, carbon monoxide, etc.) for protective heating. From 1889 to 189, Lake, an Englishman, obtained patents for bright heat treatment of various metals. Since the 2th century, with the development of metal physics and the transplantation of other new technologies, the metal heat treatment process has been greatly developed. A remarkable progress was that from 191 to 1925, rotary hearth furnace was used for gas carburization in industrial production; Dew point potentiometer appeared in 193s, which made the carbon potential in the furnace atmosphere controllable. Later, methods to further control the carbon potential in the furnace atmosphere were developed by using carbon dioxide infrared instrument and oxygen probe. In 196s, plasma field was used in heat treatment technology, and ion nitriding and carburizing processes were developed. With the application of laser and electron beam technology, new surface heat treatment and chemical heat treatment methods have been obtained for metals. The current national standard 1 GB/T7232-212 metal heat treatment process terminology 213-3-1 was implemented instead of GB/T 7232-1999 2 GB/T8121-22 heat treatment process material terminology 22-12-1. Instead of GB/T 8121-1987 3 GB/T9452-23, the method for measuring effective heating area of heat treatment furnace was implemented on June 1, 24. Replacing GB/T 9452-1988 4 GB/T1731.1-1997 Dry thermal effect of textiles and fabrics under low pressure Part 1: Dry heat treatment program for fabrics May 1, 1998 Implementation of 5 GB/T7631.14-1998 Classification of lubricants and related products (Class L) Part 14: Group U (heat treatment) 1999 Z18718-22 Technical Guide for Energy Saving in Heat Treatment was implemented on December 1, 22. The safety and health requirements of metal heat treatment production process of 7 GB15735-24 were implemented on November 1, 24, instead of GB 15735-1995 8 GB/T1263-25, and the code was implemented on January 1, 26. Instead of GB/T 1263-199 9 GB/T19944-25, the fuel consumption quota for heat treatment production and its calculation and determination method were implemented on April 1, 26, and the terminology of 1 GB/T13324-26 heat treatment equipment was implemented on April 1, 27. Instead of GB/T 13324-1991, 11 GB/T 21736-28, the technical conditions of combustion heating equipment for energy-saving heat treatment were implemented on November 1, 28, and the 12 GB/T121-28 thermal treatment was implemented on January 1, 29. Instead of GB/T 121-1988 13 GB/T22561-28 vacuum heat treatment 29-6-1 14 GB/T22894-28 accelerated aging of paper and paperboard at 8℃ and 65% relative humidity 15 GB/ T17358-29 Calculation and determination method of power consumption in heat treatment production implemented on November 1, 29 16 GB/T5953.2-29 Cold heading steel wire Part 2: Non-heat treatment cold heading steel wire implemented on April 1, 21, Replacing GB/T 5953-1999 17 GB/T5953.1-29 cold heading steel wire Part 1: Implementation of heat treatment cold heading steel wire on April 1, 21, Instead of GB/T 5953-1999 18 GB/T24562-29 energy-saving monitoring of fuel heat treatment furnace, 19 GB/T24743-29 technical product file heat treatment representation of steel parts was implemented in September 21, and 2 GB/T15318-21 energy-saving monitoring of heat treatment furnace was implemented in January 211. Instead of GB/T 21 GB/T25745-21, the heat treatment of cast aluminum alloy was carried out on June 1, 211. The limit value of harmful substances in the air of workplace for 22 GB/T27946-211 was 23 GB/T27945.1-211. Management of harmful solid waste in salt bath during heat treatment Part 1: General management of 24 GB/ T27945.2-211 Management of harmful solid waste in heat treatment salt bath Part 2: Detection method of leaching solution 25 GB/T27945.3-211 Management of harmful solid waste in heat treatment salt bath Part 3: Harmless treatment method 26 GB/T7232-212 Terminology of metal heat treatment process No.24 of 212 27 GB/ T8121-212 Terminology of heat treatment process materials No.24 of 212 No.28 GB/T9452-212 Determination method of effective heating area of heat treatment furnace No.24 of 212 No.29 GB/T2899-212 No.28 of 212 No.3 GB 15735-212 Safety of metal heat treatment production process, Hygienic requirements Announcement No.28, 212 31 GB/T28838-212 Code of Practice for Heat Treatment of Wood Packaging Announcement No.28, 212 32 GB/T28992-212 Heat Treatment of Solid Wood Flooring Announcement No.41, 212 33 GB1314-1991 Waste heat treatment reinforcement for reinforced concrete was implemented on March 1, 1992. Normalization: the heat treatment process of heating steel or steel parts to an appropriate temperature above the critical point AC3 or ACM for a certain period of time and then cooling them in the air to obtain pearlite-like structures. 2. annealing: a heat treatment process in which the sub-sub-sub-sub-sub-sub-sub-sub-sub-sub-sub-sub-sub-sub-sub-sub-sub-sub-sub-sub-sub-sub-sub-sub-sub-sub-sub-sub-sub-sub-sub-sub-sub-sub-sub-sub-sub-sub-sub-sub-sub 3. Solution heat treatment: the heat treatment process of heating the alloy to a high-temperature single-phase region and keeping it at a constant temperature, so that the excess phase is fully dissolved in the solid solution, and then rapidly cooled to obtain a supersaturated solid solution. 4. Aging: the phenomenon that the properties of the alloy change with time after solution heat treatment or cold plastic deformation, when it is placed at room temperature or kept slightly higher than room temperature. 5. Solution treatment: fully dissolve all phases in the alloy, strengthen solid solution, improve toughness and corrosion resistance, eliminate stress and softening, so as to continue processing and molding. 6. Aging treatment: heat and keep the temperature at which the strengthening phase precipitates, so that the strengthening phase precipitates, hardens and improves the strength. 7. Quenching: a heat treatment process in which the steel is austenitized and then cooled at an appropriate cooling rate, so that the unstable structure of the workpiece such as martensite changes in all or a certain range of the cross section. Heat treatment 8. Tempering: a heat treatment process in which the quenched workpiece is heated to an appropriate temperature below the critical point AC1 for a certain period of time, and then cooled by a satisfactory method to obtain the required structure and properties. 9. Carbonitriding of steel: Carbonitriding is the process of simultaneously infiltrating carbon and nitrogen into the surface of steel. Traditionally, carbonitriding is also called cyanidation, and it is widely used in medium-temperature gas carbonitriding and low-temperature gas carbonitriding (that is, gas soft nitriding). The main purpose of medium temperature gas carbonitriding is to improve the hardness, wear resistance and fatigue strength of steel. Low temperature gas carbonitriding is mainly nitriding, and its main purpose is to improve the wear resistance and bite resistance of steel. 1. quenching and tempering: It is generally customary to call the heat treatment combining quenching and high temperature tempering as quenching and tempering. Quenching and tempering treatment is widely used in various important structural parts, especially those connecting rods, bolts, gears and shafts that work under alternating load. Tempered sorbite structure is obtained after quenching and tempering treatment, and its mechanical properties are better than normalized sorbite structure with the same hardness. Its hardness depends on the tempering temperature at high temperature and is related to the tempering stability of steel and the cross-section size of workpiece, generally between HB 2 and 35. Process characteristics of metallographic structure of 5CrVA spring steel quenched at 88℃ Metal heat treatment is one of the important processes in mechanical manufacturing. Compared with other processing technologies, heat treatment generally does not change the shape and overall chemical composition of the workpiece, but endows or improves the working performance of the workpiece by changing the microstructure inside the workpiece or changing the chemical composition on the surface of the workpiece. Its characteristic is to improve 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 properties, physical properties and chemical properties, in addition to reasonable selection of materials and various forming processes, heat treatment process is often essential. Steel is the most widely used material in machinery industry, and its microstructure 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, aluminum, copper, magnesium, titanium and their alloys can also change their mechanical, physical and chemical properties through heat treatment to obtain different performance. Heat treatment thermal process heat treatment process generally includes three processes of heating, heat preservation and cooling, and sometimes there are only two processes of heating and cooling. These processes are interconnected and uninterrupted. Heating is one of the important processes of heat treatment. There are many heating methods for metal heat treatment. At the earliest, charcoal and coal were used as heat sources, and recently, liquid and gas fuels were used. The application of electricity makes heating easy to control and has no environmental pollution. These heat sources can be used for direct heating or indirect heating through molten salt or gold or even floating particles. When the metal is heated, the workpiece is exposed to the air, which often leads to oxidation and decarbonization (that is, the carbon content on the surface of steel parts decreases), which has a very adverse effect on the surface properties of parts after heat treatment. Therefore, metals should usually be heated in controlled atmosphere or protective atmosphere, molten salt and vacuum, and can also be protected by coating or packaging. Heating temperature is one of the important process parameters of heat treatment process, and the selection and control of heating temperature is the main problem to ensure the quality of heat treatment. The heating temperature varies with the metal material to be treated and the purpose of heat treatment, but it is generally heated above the phase transition temperature to obtain high-temperature structure. 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 time, so that the internal and external temperatures are consistent and the microstructure is completely transformed. This time is called heat preservation time. When high-energy density heating and surface heat treatment are used, the heating speed is extremely fast, and there is generally no holding time, while the holding time of chemical heat treatment is often longer. Cooling is also an indispensable step in the heat treatment process, and the cooling method varies from process to process, mainly controlling the cooling speed. Generally, the cooling rate of annealing is the slowest, that of normalizing is faster, and that of quenching is faster. However, there are different requirements due to different steel grades. For example, air-hardened steel can be hardened at the same cooling rate as normalizing. Classification of heat treatment processes Metal heat treatment processes can be roughly divided into three categories: overall heat treatment, surface heat treatment and chemical heat treatment. According to the difference of heating medium, heating temperature and cooling method, each category can be divided into several different heat treatment processes. The same metal can obtain different structures by different heat treatment processes, thus having different properties. Steel is the most widely used metal in industry, and its microstructure is also the most complex, so there are many kinds of heat treatment processes for steel. Integral heat treatment is a metal heat treatment process that heats the workpiece as a whole and then cools it at an appropriate speed to obtain the required metallographic structure to change its overall mechanical properties. Overall heat treatment of iron and steel has four basic processes: annealing, normalizing, quenching and tempering. Process means annealing is to heat the workpiece to an appropriate temperature, adopt different holding time according to the material and the size of the workpiece, and then slowly cool it, so as to make the internal structure of the metal reach or approach the equilibrium state, obtain good process performance and service performance, or prepare the structure for further quenching. Normalization is to heat the workpiece to a suitable temperature and then cool it in the air. The effect of normalization is similar to that of annealing, except that the obtained structure is finer, which is often used to improve the cutting performance of materials and sometimes used as the final heat treatment for some parts with low requirements. Quenching means that the workpiece is heated and insulated, and then rapidly cooled in quenching media such as water, oil or other inorganic salts, organic water solution, etc. After quenching, steel parts become hard but brittle at the same time. In order to eliminate brittleness in time, it is generally necessary to temper in time. In order to reduce the brittleness of steel parts