材料成型及控制工程专业英语PPT学习教案

1、会计学1 材料成型及控制工程专业英语材料成型及控制工程专业英语PPT课件课件 - - 2 2 - - 任何热处理的目的都是（通过）将金属加热到一定的温度并( 随后)冷却,以使金属组织产生所需变化。 第1页/共52页 - - 3 3 - - 因此，热处理的主要因素是温度和时间，所以任何热处理工艺 都以用温度-时间为坐标轴进行表示。 第2页/共52页 - - 4 4 - - Heat treatment conditions are characterized by the following parameters: heating temperature tmax, i.e. the maxim

2、um temperature to which an alloy metal is heated; time of holding at the heating temperature ; heating rate and cooling rate . 第3页/共52页 - - 5 5 - - If heating (or cooling) is made at a constant rate, the temperature-time relationship will be described by a straight line with a respective angle of in

3、cline . Respective分别的, 各自的 第4页/共52页 - - 6 6 - - With a varying heating ( or cooling) rate. the actual rate should be attributed to the given temperature ,more strictly, to an infinite change of temperature and time: that is the first derivative of temperature in time . Infinite无限的东西(如空间、时间), 数无穷大 第5

4、页/共52页 - - 7 7 - - Heat treatment may be a complex process, including multiple heating stages . interrupted or stepwise heating ( cooling) , cooling to subzero temperatures, etc . Any process of heat treatment can he described by a diagram in temperature-time coordinates . interrupt中断stepwise楼梯式的, 逐

5、步的subzero- 零度以 下的（温度） 第6页/共52页 - - 8 8 - - 根据Fe-C相图，在平衡临界点缓慢加热，珠光体转变为奥氏体 。一般条件下，转变会延迟导致guore，即转变温度略高于Fe- C相图中的指定温度。 The transformation of pearlite into austenite can only take place at the equilibrium critical point on a very slow heating as follows from the Fe-C constitutional diagram. Under common

6、 conditions, the transformation is retarded and results in overheating, i. e. occurs at temperatures slightly higher than those indicated in the Fe-C diagram. Constitutional diagram相图(构成的, 增强体质的, 宪法的）pearlite 珠光体 retard延迟, 使减速, 阻止, 妨碍, 阻碍 第7页/共52页 - - 9 9 - - When overheated above the critical point

7、, pearlite transform into austenite， the rate of transformation being dependent on the degree of overheating . 第8页/共52页 - - 1010 - - The time of transformation at various temperatures (depending on the degree of overeating) shows that the transformation takes place faster (in a shorter time) at a hi

8、gher temperature and occurs at a higher temperature on a quicker heating . 第9页/共52页 - - 1111 - - For instance, on quick heating and holding at 780， the pearlite to austenite transformation is completed in 2 minutes and on holding at 740C, in 8 minutes . centigrade 第10页/共52页 - - 1212 - - 转变结束是以奥氏体形成和

9、珠光体(F+渗碳体)消失为标记 的。然而，即使在单个晶粒中奥氏体的也不均匀。 The end of the transformation is characterized by formation of austenite and the disappearance of pearlite ( ferrite +cementite) . This austenite is however inhomogeneous even in the volume of a single grain. 第11页/共52页 - - 1313 - - 早期形成的片状(或li状)珠光体渗碳体，其含碳量高于片 状

10、铁素体，这就是奥氏体（成分）不均匀的原因。 lamellae薄片状的, 薄层状的 In places earlier occupied by lamellae (or grains) of a pearlitic cementite, the content of carbon is greater than in places of ferritic lamellae . This is why the austenite just formed is inhomogeneous . 第12页/共52页 - - 1414 - - In order to obtain homogeneous

11、austenite, it is essential on heating not only to pass through the point of the end of pearlite to austenite transformation, but also to overheat the steel above that point and to allow a holding time to complete the diffusion processes in austenitic grains 第13页/共52页 - - 1515 - - 奥氏体均匀化的速度主要依赖与钢的原始组

12、织，特别是渗 碳体的分布及晶粒形状。当渗碳体颗粒细小均匀，总表面 积较大时，相转变更快。 The rate of homogenization of austenite appreciably depends on the original structure of the steel, in particular on the dispersion and particle shape of cementite . The transformations described occur more quickly when cementite particles are fine and, t

13、herefore ,have a large total surface area . Particle 粒子, 点, 极小量, 微粒 Appreciably 1.有一点儿的; 可以感到的; 2.可观的, 值得重视的 第14页/共52页 - - 1616 - - At the beginning of pearlite to austenite transformation. The first grains of austenite form at the boundaries between the ferrite and cementite the two structural cons

14、tituents of pearlite. Since these boundaries are very developed, the transformation starts from formation of a multitude of fine grains. 第15页/共52页 - - 1717 - - Therefore, at the end of the transformation the austenite will be composed of a great multitude of fine grains whose size characterizes what

15、 is called the original austenite grain size. 第16页/共52页 - - 1818 - - Further heating ( or holding) upon the transformation will cause coarsening of austenitic grains. The process of grain coarsening is spontaneous, since the total surface area of grains diminishes ( the surface energy decreases) and

16、 a high temperature can only accelerate the rate of this process. 第17页/共52页 - - 1919 - - In that connection, two types of steels are distinguished: inherent fine grained and inherent coarse grained, the former being less liable to grain coarsening than the latter. The size of grains formed in a stee

17、l by heat treatment is called the actual grain size. 第18页/共52页 - - 2020 - - Thus , a distinction should be made between: (1) original grain, i.e. the size of austenitic grains immediately after the pearlite to austenite transformation; (2) inherent ( natural) grain, i.e. the liability of austenite t

18、o grain coarsening; and (3) actual grain, i.e. the size of austenitic grains under given particular conditions. 第19页/共52页 - - 2121 - - 奥氏体转变为珠光体时珠光体晶粒的大小决定于奥氏体形成时 的晶粒大小。奥氏体仅在加热时长大（冷却时不细化），因为 奥氏体区的最高温度和固有晶粒度决定了最终晶粒尺寸。 The size of pearlitic grains at same temperature of the austenite to pearlite trans

19、formation depends on that of the austenitic grains from which they have formed. Austenitic grains grow only during heating ( but are not refined in subsequent cooling), because of which the highest temperature a steel is heated to in the austenitic state and the inherent grain size of that steel det

20、ermine the final grain size. 第20页/共52页 - - 2222 - - 钢的性能仅仅由最终晶粒大小而不是固有晶粒大小决定。具有 相同等级的两种钢(一是固有粗晶粒，另一是细晶粒)根据不容 温度的热处理，将有相同的实际晶粒尺寸，它们的性质也将相 同。否则，两种钢的许多性能将不同。 The properties of a steel are affected only by the actual grain size and not by the inherent grain size. If two steels of the same grade (one inh

21、erently coarse grained, the other fine grained) have the same actual grain size upon heat treatment at different temperatures, their properties will also be the same; if otherwise, many properties of the two steels will also be different. 第21页/共52页 - - 2323 - - 奥氏体向珠光体转变本质是奥氏体分解为近乎纯的铁 素体和渗碳体。 The au

22、stenite to pearlite transformation is essentially the decomposition of austenite into almost pure ferrite and cementite. 第22页/共52页 - - 2424 - - 在平衡温度时，不发生转变，因为初始奥氏体的自由能等于最 终产物珠光体的自由能。 At the equilibrium temperature, the transformation is impossible, since the free energy of the original austenite is

23、 equal to that of the final product, pearlite. 第23页/共52页 - - 2525 - - 只有珠光体(铁素体和碳化物的混合物)的自由能低于奥氏体， 在一定的过冷度下，转变才发生。 The transformation can only start at a certain undercooling when the free energy of the ferrite carbide mixture (pearlite) is lower than that of austenite. 第24页/共52页 - - 2626 - - 转变温度越低

24、、过冷度越大，自由能差越大，转变速 度越快。 The lower the transformation temperature, the higher the degree of undercooling and the greater the difference in free energies and the transformation proceeds at a higher rate. 第25页/共52页 - - 2727 - - 在珠光体转变中，新相的成分与原始相完全不同，铁 素体几乎不含碳，渗碳体含碳6.67。， in the pearlite transformation,

25、the new phase sharply differ in their composition from the initial phase; they are ferrite which is almost free of carbon, and cementite which contains 6.67 percent carbon. 第26页/共52页 - - 2828 - - 因此奥氏体转变为珠光体伴随着碳的扩散和重新分布 。随着温度的降低，扩散率显著降低，因此，转变需 在较高的过冷下，转变会被延迟。 For this reason the austenite to pearlit

26、e transformation is accompanied with the diffusion, redistribution of carbon. The rate of diffusion sharply diminishes with decreasing temperature, therefore, the transformation should be retarded at a greater undercooling. 第27页/共52页 - - 2929 - - 因此，可得出一重要结论：过冷（较低的转变温度） 对转变速率可以产生两种相反的影响。 thus, we ha

27、ve come to an important conclusion that undercooling (lowering the transformation temperature) may have two opposite effects on the rate of transformation. 第28页/共52页 - - 3030 - - 一方面，温度较低，过冷较大，使奥氏体和珠光体自 由能差较大，因此加速相变，另一方面，它降低了碳 扩散的速率，又减慢了相转变。 On one hand, a lower temperature (greater undercooling ) g

28、ives a greater difference in free energy of austenite and pearlite, thus accelerating the transformation; on the other hand, it diminishes the rate of carbon diffusion, and thus slows down the transformation. 第29页/共52页 - - 3131 - - 整个影响就是：随着过冷度的增加，转变率增加到某 一最大值后，随着进一步的过冷而降低. The combined effect is th

29、at the rate of transformation first increase as undercooling is increased to a certain maximum and then decreases with further undercooling. 第30页/共52页 - - 3232 - - 在727和低于200时，转变率为0，因为727时自由 能差为0，低于200时，C的扩散率为0.（更严格的来 讲，温度太低，转变难以进行。） at 727 (A1) and below 200, the rate of transformations is zero, si

30、nce at 727 the free energy difference is zero and below 200 the rate of carbon diffusion is zero (more strictly, too low for the transformation to proceed). 第31页/共52页 - - 3333 - - 珠光体的形成是珠光体形核和珠光体晶粒长大的过程，这一点 首先由I.L.Mirkin 在1939年提出，并由R.F.Mehl 在1941年加以 完善。 As has been first indicated by I.L.Mirkin in

31、1939 and then developed by R.F.Mehl in 1941, the formation of pearlite is the process of nucleation of pearlite and growth of pearlitic crystals. 第32页/共52页 - - 3434 - - 因此，在不同过冷程度下珠光体的转变速率不同,(这)主要是因 为过冷度影响形核率N和晶核长大速率G。在A1和200以下， N和G都等于0，并在在150200时过冷度最大. Therefore, the different rate of the pearlite

32、transformation at various degrees of undercooling is due to the fact that undercooling differently affects the rate of nucleation N and the rate of crystal growth G. At temperature A1 and below 200, both parameters of crystallization N and G are equal to zero and have a maximum at an undercooling of

33、 150200. 第33页/共52页 - - 3535 - - 如前所述，当条件允许，例如奥氏体过冷到A1点以下，C的扩 散速率不为0，则产生形核中心，继而形成晶粒。随时间变化 产生的这一过程可用动力学转变曲线表示，该曲线中会显示从 转变开始后，随时间变化，珠光体的形成量。 It follows from the forgoing that as soon as the conditions are favorable, i.e. austenite is undercolled below A1, the diffusion of carbon is not zero, centers of

34、 crystallization appear, which give rise to crystals. This process occurs with time and can be represented in the form of so called kinetic curve of transformation, which shows the quantity of pearlite that has formed during the time elapsed from the beginning of the transformation. 第34页/共52页 - - 36

35、36 - - 初始阶段，转变速率非常慢，称之为孕育期。转变进程中，速 率加快，当大约有50%的奥氏体转变为珠光体时，转变速率达 到最大。然后转变速率减小并停止。 The initial stage is characterized by a very low rate of transformation; this is what is called incubation period. The rate of transformation increases with progress in the transformation. Its maximum approximately corr

36、esponds to the moment when roughly 50 percent of austenite has transformed into pearlie. The rate of transformation then diminishes and finally stops. 第35页/共52页 - - 3737 - - 转变速率依赖于过冷度，过冷度过低和过高都使转变进程变慢 ，这是由于N、G比较小，前者是由于自由能差过低，后者是 因为原子扩散慢，在转变速率最大处，动力学曲线上有峰值， 在较短的时间间隔里，转变结束。 The rate of transformation

37、 depends on undercooling. At low and high degrees of undercooling the transformation proceeds slowly, since N and G are low: in the former case, owing to a low difference in free energy, and in the later, due to a low diffusion mobility of atoms. At the maximum rate of transformation the kinetic cur

38、ves have sharp peaks, and the transformation is finished in a short time interval. 第36页/共52页 - - 3838 - - 在高温时（即过冷度小），转变速度慢，孕育期和完全转变的 时间较长，在较低的温度转变，及过冷度较大，转变速率变大 ，转变时间和孕育期较短。 At a high temperature (slightly undercooling), the transformation proceeds slowly and the incubation period and the time of t

39、he transformation proper are long. At a lower temperature of the transformation, i.e. a deeper undercooling, the rate of transformation is greater, and the time of the incubation period and of the transformation is shorter. 第37页/共52页 第38页/共52页 - - 4040 - - 已经确定了奥氏体想珠光体转变开始的时间（孕育期）和各种 过冷度下转变结束的时间，我们可

40、以绘制一幅图，图左边的曲 线代表转变开始的时间，即：过冷态下，奥氏体仍然存在的时 间，从纵坐标轴到曲线的部分来度量其（奥氏体）的稳定性。 Having determined the time of the beginning of austenite to pearlite transformation ( incubation period ) and the time of the end of transformation at various degrees of undercooling, we can construct a diagram in which the left ha

41、nd curve determines the time of the beginning of the transformation, i.e. the time during which austenite still exists in the undercooling state, and the section from the axis of ordinates to the curve is the measure of its stability. 第39页/共52页 - - 4141 - - 在温度500600 时，这部分区间最短，即：在此温 度下转变在最短时间内开始。 Th

42、is section is shortest at a temperature of 500600 , i.e. the transformation begins in a shortest time at that temperature. 第40页/共52页 - - 4242 - - 右边曲线表示在给定过冷度下，完全转变所需的时间，这时在 同一温度下（500600 ）所用时间最短。注意图中的横坐标 是对数形式。这样做是为了更方便，因为珠光体形成速率明显 不同（在临界点A1点附近为上千秒，在曲线弯曲处只要一两 秒。） The right hand-curve shows the time

43、needed to complete the transformation at a given degree of undercolling. This time is the shortest at the same temperature (500600 ). Note that the abscissa of the diagram is logarithmic. This is done for more convenience, since the rates of formation of pearlite appreciably differ ( thousands of se

44、conds near the critical point A1 and only one or two seconds at the bend of the curve). 第41页/共52页 - - 4343 - - 图中曲线下的水平线代表无扩散马氏体转变温度，马 氏体有不同的转变机制，稍后讨论。 The horizontal line below the curves in the diagram determines the temperature of the diffusionless matensite transformation. The martensite transfo

45、rmation occurs by a different mechanism and will be discussed later. 第42页/共52页 - - 4444 - - 我们讨论的图通常称为TTT（时间温度转变）图，或 者C曲线，这主要因为曲线特殊的形状。奥氏体分解产 物的组织和性能取决于转变发生的温度。 Diagrams of the type we discussed are usually called TTT diagrams ( time temperature transformation), or C curve, owing to the specific sha

46、pe of the curves, the structure and properties of the products of austenite decomposition depends on the temperature at which the transformation has taken place. 第43页/共52页 - - 4545 - - 高温时，即：过冷度小，形成铁素体和渗碳体混合的 粗大晶粒，这可以在显微镜下区分。这种组织称为珠 光体。 At high temperatures, i.e. low degrees of undercooling, a coarse grained mixture of ferrite and cementite is formed which is easily distinguished in the microscope. This structure is called pearlite. 第44页/共52页 - - 4646 - - 温度继续降低，过冷度较大，铁素体和渗碳体的混合 片状组织更弥散、坚硬，这种组织只能在电子显微镜 下观察到，