Unit-13-Heat-Treatment-of-Metal-机电专业英语-图文课件

1、Unit 13 Heat Treatment of MetalContentsNew Words & Expressions Text & TranslationComplex Sentence AnalysisKey to ExercisesNew Words & Expressions forge f:d v. 铸造, 伪造transformation trnsfmein n. 变换，转换，相变eutectoid ju:tektid adj. 类似共熔体的，共析的austenite stinait n. 奥氏体pearlite p:lait n. 珠光体cementite simentai

2、t n. 渗碳体New Words & Expressions martensitic m:tnzaitik adj. 马氏体的stress relieving 消除应力，低温退火tempering tempri n. 回火normalizing n:mlaizi n.正火ferrous alloy 铁合金 still stil adj. 不动的，静止的full annealing 完全退火notably nutbli adv. 显著地, 特别是New Words & Expressions austenitize stinitaiz v. 奥氏体化，使成奥氏体denote dinut v.

3、指示，表示，概述machinability mi:nbiliti n. 切削加工性，机械加工性能facilitation fsilitein n. 容易化，助长，便于in-process pruses adj. (加工、处理) 过程中的qualification kwlifikein n. 资格, 条件, 限制, 限定quenching kwent n. 淬火New Words & Expressionsbrine brain n. 盐水caustic k:stik adj. 腐蚀性的, 碱性的aqueous eikwis adj. 水的, 水成的warp w:p n. 翘曲，变形fog qu

4、enching 喷雾淬火interrupted quenching 分级淬火selective quenching 局部淬火quench-hardened kwenth:dnd adj. 淬硬的process annealing 中间退火，工序间退火Text & TranslationThe generally accepted definition for heat treating metals and metal alloys is “heating and cooling a solid metal or alloy in a way so as to obtain specific

5、conditions and/or properties.” Heating for the sole purpose of hot working (as in forging operations) is excluded from this definition. Likewise，the types of heat treatment that are sometimes used for products such as glass or plastics are also excluded from coverage by this definition.Text & Transl

6、ation1.Transformation Curves Heat treatment bases on the timetemperaturetransformation curves or TTT curves; all the three parameters are plotted in a single diagram. Because of the shape of the curves，they are also sometimes called C-curves or S-curves. Fig.13.1 shows the isothermal decomposition d

7、iagram of T80 steel.Text & TranslationTo plot TTT curves，the particular steel is held at a given temperature and the structure is examined at predetermined intervals to record the amount of transformation taken place. 1It is known that the eutectoid steel(T80) under equilibrium conditions contains，a

8、ll austenite above 723 ,whereas below，it is pearlite. To form pearlite，the carbon atoms should diffuse to form cementite. The diffusion being a rate process，would require sufficient time for completing transformation of austenite to pearlite. From different samples，it is possible to note the amount

9、of the transformation taking place at any temperature. 2These points are then plotted on a graph with time and temperature as the axes. Through these points，transformation curves can be plotted as shown in Fig.13.1 for eutectoid steel. Text & TranslationThe curve at extreme left represents the time

10、required for the transformation of austenite to pearlite to start at any given temperature. Similarly，the curve at extreme right represents the time which is required for completing the transformation. The points representing partial transformation are between the two curves. The start and finish of

11、 martensitic transformation are represented by the horizontal lines Ms and Mf. Fig. 13-1 Isothermal Decomposition Diagram of T80 Steel Text & Translation2.Classification of Heat Treating Processes In some instances，heat treatment procedures are clear cut in terms of technique and application，while i

12、n other instances，descriptions or simple explanations are insufficient because the same technique frequently may be used to obtain different objectives. For example，stress relieving and tempering are often accomplished with the same equipment and by use of identical time and temperature cycles. The

13、objectives，however，are different for the two processes.The following descriptions of the principal heat treating processes are generally arranged according to their interrelationships.Text & Translation1)NormalizingNormalizing means heating a ferrous alloy to a suitable temperature (usually 50 F to

14、100 F or 28 C to 56 C) above its specific upper transformation temperature. 3This is followed by cooling in still air to at least some temperature well below its transformation temperature range. For low carbon steels，the resulting structure and properties are the same as those achieved by full anne

15、aling；for most ferrous alloys，normalizing and annealing are different. Text & TranslationNormalizing usually is used as a conditioning treatment，notably for refining the grains of steels that have been subjected to high temperatures for forging or other hot working operations. The normalizing proces

16、s usually is succeeded by another heat treating operation such as austenitizing for hardening，annealing，or tempering. Text & Translation2)AnnealingAnnealing is a generic term denoting a heat treatment that consists of heating to and holding at a suitable temperature followed by cooling at a suitable

17、 rate. It is used primarily to soften metallic materials，but also to simultaneously produce desired changes in other properties or in microstructure. The purpose of such changes may be，but is not confined to，improvement of machinability，facilitation of cold work (known as in process annealing)，impro

18、vement of mechanical or electrical properties，or to increase dimensional stability. When applied solely to relieve stresses，it commonly is called stress relief annealing，synonymous with stress relieving.When the term “annealing” is applied to ferrous alloys without qualification，it means full anneal

19、ing. This is achieved by heating above the alloys transformation temperature，then applying a cooling cycle which provides maximum softness. This cycle may vary widely，depending on composition and characteristics of the specific alloy.Text & Translation3)QuenchingQuenching is the rapid cooling of a s

20、teel or alloy from the austenitizing temperature by immersing the workpiece in a liquid or gaseous medium. Quenching media commonly used include water，5% brine，5% caustic in an aqueous solution，oil，polymer solutions，or gas (usually air or nitrogen).Selection of a quenching medium depends largely on

21、the hardenability of the material and the mass of the material being treated (principally section thickness). Text & TranslationThe cooling capabilities of the above listed quenching media differs a lot. In selecting a quenching medium，it is best to avoid a solution that has more cooling power than

22、is needed to achieve the results，thus minimizing the possibility of cracking and warp of the parts being treated. Modifications of the term quenching include direct quenching，fog quenching，hot quenching，interrupted quenching，selective quenching，spray quenching，and time quenching.Text & Translation4)

23、TemperingIn heat treating of ferrous alloys，tempering consists of reheating the austenitized and quench hardened steel or iron to some preselected temperature that is below the lower transformation temperature (generally below 1 300 F or 705 C). Tempering offers a means of obtaining various combinat

24、ions of mechanical properties. Tempering temperatures used for hardened steels are often no higher than 300 F(150 C). The term “tempering” should not be confused with either process annealing or stress relieving. Even though time and temperature cycles for the three processes may be the same，the con

25、ditions of the materials being processed and the objectives may be different.Text & Translation5)Stress relievingLike tempering，stress relieving is always done by heating to some temperature below the lower transformation temperature for steels and irons. For nonferrous metals，the temperature may va

26、ry from slightly above room temperature to several hundred degrees，depending on the alloy and the amount of stress relief that is desired.Text & TranslationThe primary purpose of stress relieving is to relieve stresses that have been imparted to the workpiece from such processes as forming，rolling，m

27、achining or welding. The usual procedure is to heat workpieces to the preestablished temperature long enough to reduce the residual stresses (this is a time and temperature dependent operation) to an acceptable level；this is followed by cooling at a relatively slow rate to avoid creation of new stre

28、sses.Text & Translation普遍认同的对金属及合金热处理的定义是，以一定的方式加热或和冷却固态金属或合金以达到一定的条件和/或获得某些性能。以热加工(如锻造)为目的的加热，不在此定义之列。同样地，有时用于生产诸如玻璃或塑料制品的热处理也不属于该定义的范畴。Text & Translation1.相变曲线 热处理的基础分别是时间-温度-相变曲线，即TTT 曲线，3 个参数都绘制在一个图中。根据曲线的形状特点，分别称为C曲线或S曲线。如图13-1所示为共析钢的等温转变曲线图。Text & Translation为了绘制TTT 曲线，将特定的钢置于给定温度下，以预先确定的时间间隔检

29、查其结构，记录发生相变的量。我们知道共析钢(C80)在平衡条件下，在723 以上时全为奥氏体，而低于此温度，则为珠光体。为了形成珠光体，碳原子将产生扩散形成渗碳体。扩散是一种渐进过程，需要足够的时间完成奥氏体向珠光体的转变。对于不同的样品，可以记录下在任一温度时产生相变的量。然后把这些点绘制在一条以时间和温度为坐标轴的曲线上。通过这些点就可以得到图13-1所示的共析钢的相变曲线。左边的曲线表示任一给定温度下奥氏体开始转变为珠光体所需要的时间。类似地，右边的曲线表示相变完成所需要的时间。两条曲线之间是表示部分相变的点。两条水平线Ms 和 Mf 表示马氏体转变的开始和结束。Text & Trans

30、lation图13-1 共析钢的等温转变曲线图Text & Translation2.热处理工艺的分类 在某些场合热处理过程可以根据其工艺和应用明确地区分开来。而在另一些场合，因为同样的工艺常常可以用来达到不同的目的，因此对该术语的说明和简单的解释是不够的。例如：消除应力的热处理和回火处理常常使用同样的设备、同样的时间和温度循环来实现，但这两种工艺的目的是不同的。下面对主要热处理工艺的描述大体上是按其相互关系来安排的。Text & Translation1）正火把铁类合金加热到指定的相变温度上限以上(通常50100F 或2856C) 的合适温度。接下来在不流动的空气中冷却到至少比相变温度低得多

31、的某一温度。对于低碳钢，得到的结构和性能与完全退火相同。而对于大多数铁类合金，正火和退火意义不同。正火一般作为起调节作用的热处理工艺，特别是用于细化在锻造或其他热加工工艺中经受了高温的钢的晶粒。正火处理之后通常还要接着进行淬火、退火或回火等进行奥氏体化。Text & Translation2）退火热处理的一个通用术语，指的是加热到一定温度并保温，然后以合适的速度冷却，主要用于降低金属材料的硬度，同时在其他性能或显微组织方面产生一些理想的变化。这种变化的目的是改善其机械加工性、便于冷加工(被称为中间退火)，改善机械或电性能，或增加工件的尺寸稳定性，但也不仅仅局限于此。如果仅仅用于消除应力，就叫做

32、去应力退火，与应力消除(stress relieving )热处理是同义词。Text & Translation当“退火”这个术语用于铁类合金而又无其他限制条件时，指的是完全退火。这种处理是把合金加热到其相变温度以上，再进行循环冷却以使硬度下降最大。冷却过程的变化范围较大，要看具体合金的成分和特性。3）淬火把钢或合金浸没在液体或气体介质中，从奥氏体化温度下快速冷却。常用的淬火介质有水、5%的盐水、5%的碱性水溶液、油、聚合物溶液或气体(常为空气或氮气)。对淬火介质的选择主要取决于材料的淬透性以及被处理的材料的质量(主要是淬火部分的厚度)。Text & Translation上面列出的各种淬火介

33、质的冷却能力有很大的区别。在选择淬火介质时，最好避免选择比达到预期效果所需的冷却能力更强的溶液，从而尽量降低处理零件开裂或变形的可能性。淬火包括直接淬火、喷雾淬火、热淬火、分级淬火、局部淬火、喷射淬火和限时淬火。4）回火在铁类合金的热处理中，回火指的是把奥氏体化和淬硬的钢或铁再加热到预先设定的相变温度下限以下的某一温度(通常低于1300 F 或705 C) 。回火提供了获得各种综合机械性能的方法。用于淬硬钢的回火温度通常低于300 F(150 C) 。不要把回火与中间退火或去应力退火混淆。即使3 种处理方法的时间和温度循环可能相同，但是被处理的材料的状态和目的可能是不同的。Text & Tra

34、nslation5）去应力退火与回火相似，去应力退火总是把钢和铁加热到相变温度下限以下的某一温度。对于有色金属，这个温度可以是稍高于室温，也可以达到几百度，取决于合金的种类和期望去除的应力的大小。去应力退火的主要目的是消除在模铸、轧制、机加工、焊接等过程中在工件中产生的应力。通常这一过程是把工件加热到预先设定的温度并保持足够长的时间来降低残留的应力(这是一个与时间和温度有关的工序)。接下来，以比较慢的速度冷却以避免产生新的应力。Complex Sentence Analysis1 It is known that the eutectoid steel (T80) under equilibr

35、ium conditions contains，all austenite above 723，whereas below，it is pearlite我们知道共析钢(T80)在平衡条件下，在723 以上时全为奥氏体，而低于此温度，则为珠光体。 that：引导主语从句，it is known that 译为“我们知道”。 eutectoid steel ：共析钢 below：指低于723。 whereas below 句是个省略句，完整的句子为 whereas it is below 723。Complex Sentence Analysis2 These points are then plott