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1、Metal heat treatmentA, annealingIn 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 increased to improve
2、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, including mater
3、ial 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 workpiece surface
4、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 condition, high h
5、ardness 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 slow cooling. To
6、precipitation of ferrite and pearlite bulky iron, steel in the soft, the strain of toughness and minimum, must slow cooling.Second, normalizingHow much is the fire of similar purposes, but not the annealing steel soft and fine pearlite state. Not bulky. Steel is refined grains, fire can release of s
7、tress, 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 to Ac3 respectively,
8、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 of austenitic to dissolve all
9、 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 annealingThrough the steel ball annealing can get minimum hardness and the biggest plastic, it can make the iron carbon
10、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 slightly low temperature preservation
11、) 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. Because of the heat treatment for a lo
12、ng time, so the cost is higher than that of ball annealing is common or annealing.Four, steel sclerosisThe 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 method - austenitic. YaGongXiGang h
13、eated 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 cooling in the nose produces isothermal
14、 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 ability of the sequence.High tempera
15、ture gradient produces high stress, deformation and cracking causes, 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 stick to end its vertical quenching, is insert
16、ed 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.With several special quenching method can reduce
17、 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 uniformity, at the beginning of forming bainite, t
18、hen 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 isothermal quenching (austenitic steel in salt bath)
19、, 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 hardness can be obtained when good impact toughness
20、.Five, temperingTo 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 micro stress, stress, low plasticity materials. To red
21、uce 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 piece.it is emphasized, method, but the reverse is
22、 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 temper
23、ature effect, so the choice is often sacrificed for the hardness and strength plasticity and toughness. Again, to quench heating to influence of carbon-steel, in between, structure, changes will occur in the above, the structure and properties of the significant changes. In the next time the tempera
24、ture of the A1 heat will produce and process of ball annealing of similar structures.In industry, usually avoid to scope, because the tempering within the scope of tempering steel often produced unexplained brittleness or plastic loss. Some alloy in to scope, also can produce temper brittleness, esp
25、ecially from (or by) the temperature range slow cooling will appear. When these steel heat temper, they must usually heated to rapid cooling and above. Of course, from the temperature of cold wont produce sclerosis, fast because no austenitic.金属热处理一、退火在前面描述冷拔加工材料的软化并重新获得塑性的热处理方法时，就已使用退火这个词，该词具有相似的意义
26、。完全退火的目的是降低硬度、增加塑性，有时也提高高碳钢的切削性能，否则这种钢很难加工。这种热处理方法也用来减少应力，细化晶粒，提高整个材料的结构均匀性。退火不总是能提高切削加工性，切削加工性一词用来描述几个相关因素，包括材料切削时获得好的光洁度（即较小的表面粗糙度译者）的能力。当完全退火时，普通低碳钢硬度较低，强度较小，对切削的阻力较小，但通常由于塑性和韧性太大以至切屑离开工件表面时会划伤表面，工件表面质量比较差，导致较差的切削加工性。对这类钢，退火可能不是最合适的处理方法。许多高碳钢和大多数合金钢的切削加工性通常可经退火大大改善，因为除在最软条件下，它们的硬度和强度太高而不宜加工。亚共析刚的
27、退火方法是将钢缓慢加热到线以上大约，保温一段时间，使整个材料温度相同，形成均匀奥氏体，然后随炉或埋在石灰或其它绝缘材料中缓慢冷却。要析出粗大铁素体和珠光体，使钢处于最软、最韧和应变最小的状态，必须缓慢冷却。二、正火正火的目的多少类似于退火，但钢不是最软状态且珠光体是细匀而不粗大。钢的正火能细化晶粒，释放内应力，改善结构均匀性同时恢复一些塑性，得到高的韧性。这种方法经常用来改进切削加工性，减少应力，减少因部分切削加工或时效产生的变形。正火方法是将亚析钢或过共析钢分别缓慢加热到Ac3线或Accm线上约，保温一段时间以便形成奥氏体，并在静止空气中缓冷。要注意，含碳量超过共析成分的钢要加热到Accm线
28、以上，而不是退火时的Ac1线以上。正火的目的是在奥氏体化过程中试图溶解所有渗碳体，从而尽可能减少晶界上的硬脆铁碳化合物，而得到小晶粒的细珠光体、最小自由铁素体和自由渗碳体。三、球化退火通过球化退火可使钢得到最小的硬度和最大的塑性，它可使铁碳化合物以小球状分布在铁素体基体上。为了使小颗粒球化更容易，通常对正火钢进行球化退火。球化退火可用几种不同的方法，但所有方法都需要在A1线温度附近（通常略低）保温很长时间，使铁碳化合物形成更稳定，能级较低的小圆球。球化退火方法的主要目的是改进高碳钢的切削加工性，并对淬硬钢进行预处理，使其淬火后结构更均匀。因为热处理时间长，因此成本高，球化退火不如退火或正火常用
29、。四、钢的硬化钢的大多数热处理硬化方法是基于产生高比例的马氏体。因此，第一步用的似乎大多数其他热处理常用的方法产生奥氏体。亚共析钢加热到Ac1线温度以上大约，进行保温，使温度均布，奥氏体均匀。过共析钢Ac1线温度以上大约时保温，钢中仍残留部分铁碳化合物。第二步是快速冷却，力图避免在等温曲线鼻部产生珠光体转变。冷却速度取决于温度和淬火时淬火介质从钢表面带走热量的能力以及钢本身传热的能力。表11-1是一些常用介质和冷却方法，按冷却能力降低的顺序排列。高的温度梯度产生高应力，会引起变形和开裂，所以淬火只有在非常需要产生特定结构时才使用。淬火时必须小心，使热量均匀扩散以减少热应力。比如，一根细长棒需端
30、部淬火，即将它垂直插进冷却介质中，这样整个截面同时产生温度变化。如果这种形状的工件的某一边比另一边早降温，尺寸变化很可能引起很高的应力，产生塑性流动和永久变形。用几种特殊的淬火方法可减小淬火应力，减小变形开裂倾向。一中称为分级淬火，其方法是：将奥氏体钢放入温度高于马氏体转变起始温度（Ms）的盐浴中，放置一定的时间直到温度均匀，在开始形成贝氏体之前取出，然后放在空气中冷却，产生与从高温开始淬火时同样硬的马氏体，而导致开裂和翘曲的高的热应力或淬火应力已经被消除。在略高一点温度下的类似方法称为等温淬火，这时，将（奥氏体）钢放在盐浴中，保持很长时间，等温处理的结果是形成贝氏体。贝氏体结构不如在同样成分
31、时形成的马氏体硬，但除了减少钢在正常淬火时受到的热冲击外，不必要进一步处理，就可获得在高硬度时好的冲击韧性。五、回火调整淬硬钢以便使用的第三步通常是回火。除了等温淬火钢通常在淬火状态下使用外，大多数钢都不能在淬火状态下使用。为产生马氏体而采取的激冷使钢很硬，产生宏观内应力和微观内应力，使材料塑性很低，脆性极大。为减少这种危害，可通过将钢再加热到A1线（低温转变）以下某一温度。淬火钢回火时产生的结构变化是时间和温度的函数，其中温度是最重要的。必须要强调，回火不是硬化方法，而是刚好相反。回火钢是将经热处理硬化的钢，通过回火时的再加热，来释放应力、软化和提高塑性。回火引起的结构变化和性能改变取决于钢重新加热的温度。温度越高，效果越大，所以温度的选择通常取决于牺牲硬度和强度换取塑性和韧性的程度。重新加热到以下，对淬火普碳钢影响不大，在到之间，结构会发生某些变化，在以上，结构和性能显著变化。在紧靠着A1温度以下的长时间加热会产生与球化退火过程类似的球化结构。在工业上，通常要避免在到范围内回火，因为这个范围内回火的钢经常会产生无法解释的脆性或塑性丧失现象。一些合金钢在到范围内，也会产生“回火脆性”，特别是从（或通过）这个温度范围缓慢冷却时会出现。当这些钢必须高温回火时，它们通常加热到以上并快速冷却。当然，从这个温度快冷不会产生硬化，因为没有进行奥氏体化。
