1、毕业设计说明书 27 Metal heat treatment A, annealing In front of the description lengba processing materials and softening plastic treatment methods, it has been used the word, the word annealing with similar meanings. The purpose is to reduce completely annealing, hardness, plastic, sometimes also increase
2、d to improve the cutting performance, high this steel is difficult to processing. This method is used to reduce heat stress, refined grains, improve the structure of the material. Annealing is not always can improve the cutting machining, cutting processing a word used to describe several factors, i
3、ncluding material cutting when good finish (i.e. smaller surface roughness - the ability of the translator. When fully annealing, ordinary low hardness, low intensity of cutting resistance smaller, less, but usually due to the plasticity and toughness is too big to chip away when the surface of work
4、piece surface of workpiece surface quality, scratch, leads to poor cutting processing. For this kind of steel, annealing may not be the most appropriate treatment. Many of the most high and cutting steel processing usually can be greatly improved by annealing except in the soft, because of their con
5、dition, high hardness and strength for processing. And the annealing method is GongXi just slow to the steel wire, insulation above about for a period of time, make the same temperature uniformity, forming materials, then the austenitic or buried with furnace lime or other insulating materials in sl
6、ow cooling. To precipitation of ferrite and pearlite bulky iron, steel in the soft, the strain of toughness and minimum, must slow cooling. Second, normalizing How much is the fire of similar purposes, but not the annealing steel soft and fine pearlite state. Not bulky. Steel is refined grains, fire
7、 can release of stress, improve structural homogeneity and restore some plastic, high toughness. This method is often used to improve cutting machining, reduce stress, reduce part machining or limitation of deformation. Is the fire will chromatography method is GuoGongXiGang steel or slow heated 毕业设
8、计说明书 28 to Ac3 respectively, Accm line or on-line insulation for a period of time to form, and in the austenitic stationary air slow cooling. Should notice more, GongXi composition of carbon steel needs to be heated to Accm line above, not Ac1 line above the annealing. The purpose is in the process
9、of austenitic to dissolve all cementite, thus to minimize the boundaries on hard and brittle iron carbon compounds, and get little grain of ferrite pearlite, minimum free cementite and freedom. Third, the ball annealing Through the steel ball annealing can get minimum hardness and the biggest plasti
10、c, it can make the iron carbon compounds with small globular distribution in ferritic matrix. In order to make the ball easier small particles, usually for fire steel ball annealing. Ball annealing available in several different methods, but all the methods are needed in A1 line near (usually slight
11、ly low temperature preservation) for a long time, make the iron carbon compounds formed more stable, low level of small ball. Ball annealing method of the main objective is to improve the cutting processing, and drawing of hardened steel pretreatment, make it more uniform structure quenching. Becaus
12、e of the heat treatment for a long time, so the cost is higher than that of ball annealing is common or annealing. Four, steel sclerosis The most hardened steel heat treatment method is based on the production of martensite high. Therefore, the first step to most other treatment with commonly used m
13、ethod - austenitic. YaGongXiGang heated to Ac1 liquidus temperature, heat preservation, more about that temperature uniformly, austenitic evenly. GuoGongXiGang Ac1 above liquidus temperature preservation in steel, while about still remain iron carbon compounds. The second step is to avoid rapid cool
14、ing in the nose produces isothermal curve transformation pearlite. The cooling speed depends on the temperature and hardened steel quenching medium heat can be taken away from the surface of the ability of heat transfer and steel itself. Table 1-11 is some common medium and cooling method, cooling a
15、bility of the sequence. High temperature gradient produces high stress, deformation and cracking causes, 毕业设计说明书 29 so only in the very need to produce quenching specific structures are used. When the quenching heat uniform, care must be taken to reduce the heat stress diffusion. For example, a thin
16、 stick to end its vertical quenching, is inserted into the cooling medium, so whole section and temperature changes. If the shape of a side of the workpiece cooling, and on the other side of the earlier than size change is likely to cause high stress, produce plastic flow and permanent deformation.
17、With several special quenching method can reduce stress, deformation and cracking quenching decreases. One called hierarchical quenching, the method is: will the austenitic steel in temperature is higher than that of martensite transformation temperature (Ms), salt bath time until the temperature un
18、iformity, at the beginning of forming bainite, then put before air cooling, heat generated from the start when the same hardware quenching cracking, martensite and warpage cause of high thermal stress or eliminate stress have been quenched. In a similar method of temperature, then, is called the iso
19、thermal quenching (austenitic steel in salt bath), keep for a long time, the result is formed with the isothermal bainite. Bainite structure in the same ingredients as the formation of martensite hard, but in normal hardened steel, reduce the heat shock, by further processing, unnecessary in high ha
20、rdness can be obtained when good impact toughness. Five, tempering To adjust hardened steel used the third step is often backfire. Besides the isothermal quenching steel quenching condition usually used in most all can use in production. To produce martensite steel to quench make hard, macro and mic
21、ro stress, stress, low plasticity materials. To reduce the harm that can be heated to steel again by low-temperature shift (A1) below a certain temperature. Hardened steel structure change of tempering time and temperature is the function of temperature, which is the most important. Must be hardened
22、 piece.it is emphasized, method, but the reverse is true. Steel is tempered by heat treatment of hardened steel, through the tempering of heating, to release stress again, soften and improve plastic. The structural change and tempering causes change depending on performance of the heating temperature steel back. The higher the temperature, the temperature
