1、Unit 1 Metals金属The use of metals has always been a key factor in the development of the social systems of man. Of the roughly 100 basic elements of which all matter is composed, about half are classified as metals. The distinction between a metal and a nonmetal is not always clear-cut. The most basi
2、c definition centers around以为中心 the type of bonding existing between the atoms of the element, and around the characteristics of certain of the electrons某种电子 associated with these atoms. In a more practical way, however, a metal can be defined as an element which has a particular package of properti
3、es.Metals are crystallineadj.晶体的 when in the solid state and, with few exceptions极少例外 (e.g. mercury), are solid at ambient周围环境的 temperatures. They are good conductors of heat and electricity and are opaque不透明的 to light. They usually have a comparatively high density. Many metals are ductile柔软的；易延展的-
4、that is, their shape can be changed permanently永久地，长期不变地 by the application of a force without breaking. The forces required to cause this deformation and those required to break or fracture a metal are comparatively high, although, the fracture forces is not nearly =far from,much less than as high
5、as would be expected from simple consideration of the forces required to tear apart the atoms of the metal.One of the more significant of these characteristics from our point of view is that of crystallinitycrystallinity ,kristlinti. A crystalline solid is one in which the constituent atoms are loca
6、ted in a regular three-dimensional array as if they were located at the corners of the squares of a three-dimensional chessboardn. 棋盘. The spacing of the atoms in the array is of the same order as the size of the atoms, the actual spacing being a characteristic of the particular metal. The direction
7、s of the axes of the array define the orientation of the crystal in space. The metals commonly used in engineering practice are composed of a large number of such crystals, called grains晶粒. In the most general case一般情况下, the crystals of the various grains are randomly oriented in space. The grains a
8、re everywhere in intimate contact with one another and joined together on an atomic scale. The region at which they join is known as a grain boundary.An absolutely pure metal (i.e.也就是 one composed of only one type of atom) has never been produced. Engineers would not be particularly interested in su
9、ch a metal even if it were to be produced, because it would be soft and weak. The metals used commercially inevitably不可避免地 contain small amounts of one or more foreign elements, either metallicmetallic mitlik, me-adj. 金属的，含金属的 or nonmetallic. These foreign elements may be detrimental有害的, they may be
10、 beneficial, or they may have no influence at all on a particular property. If disadvantageous, the foreign elements tend to be known as impurities杂质. If advantageous, they tend to be known as alloying elements合金元素. Alloying elements are commonly added deliberately故意地，蓄意地 in substantialadj. 大量的；实质的；
11、内容充实的substantial evidence:实（质）体证据|实质性证据|实质证据substantial order:大宗订单|大订单 amounts in engineering materials. The result is known as an alloy.The distinction between the descriptors “metal” and “alloy” is not clear-cut. The term “metal” may be used to encompass both a commercially pure metal and its allo
12、ys. Perhaps it can be said that the more deliberately an alloying addition has been made and the larger the amount of the addition, the more likely it is that the product will specifically be called an alloy. In any event无论如何，不管怎样, the chemical composition of a metal or an alloy must be known and co
13、ntrolled within certain limits if consistent一致的 performance is to be achieved in service. Thus chemical composition has to be taken into account when developing an understanding of the factors which determine the properties of metals and their alloys.Of the 50 or so metallic elements, only a few are
14、 produced and used in large quantities in engineering practice. The most important by far is iron铁, on which are based the ubiquitous普遍的，无处不在的 steels and cast irons (basically alloys of iron and carbon). They account for about 98% by weight of all metals produced. Next in importance for structural u
15、ses (that is, for structures that are expected to carry loads) are aluminum铝, copper, nickel, and titanium taiteinim, ti-n. 化钛（金属元素）. Aluminum accounts for about 0.8% by weight of all metals produced, and copper about 0.7%, leaving only 0.5% for all other metals. As might be expected, the remainders
16、 are all used in rather相当 special applications. For example, nickel alloys are used principally主要地 in corrosion-and heat-resistant applications, while titanium is used extensively广泛地 in the aerospace industry because its alloys have good combinations of high strength and low density. Both nickel and
17、 titanium are used in high-cost, high-quality applications, and, indeed, it is their high cost that tends to restrict their application.We cannot discuss these more esotericadj. 秘传的；限于圈内人的；难懂的Esoteric Buddhism:密宗|密宗，特别是指西藏的喇嘛教。 properties here. Suffice it to say1. Suffice it to say that you love me.
18、只要说你爱我就够了。2. Suffice it to say that the gun was his.只需说这枪是他的就够了。 that a whole complex of properties in addition to structural strength is required of an alloy before it will be accepted into, and survive in, engineering practice. It may, for example, have to be strong and yet have reasonable corrosi
19、on resistance; it may have to be able to be fabricated by a particular process such as deep drawing, machining, or welding; it may have to be readily容易地 recyclable; and its cost and availability may be of critical importance.在人类社会的发展中，金属的应用起着关键性的作用。构成物质的大约100种基本元素中，大约有一半为金属。金属和非金属之间的区别不是特别明显。最基本的定义集
20、中在元素原子间存在的连接形式和与这些原子相关联的电子的某些特性。然而，在实际应用中，可以将具有某些特性集合金属定义为某种元素。除了少数例外金属在常温下是固态的。它们是热和电的良导体，不透光。它们往往具有较高的密度。许多金属具有延展性，也就是说，在不被破坏的情况下它们的形状在外力的作用下可以发生变化。引起永久变形所需的力和最终使金属断裂所需的力相当大，尽管发生断裂所需的力远没有像所预期的撕开金属原子所需的力那么大。从我们的观点来看，在所有的特性中结晶性是最重要的。结晶体是这样一种结构，组成它的原子定位在规则的三维排列中，仿佛位于三维棋盘的方格的角上。原子间距随着原子大小呈规律性变化，原子间距是金
21、属的一种特性。三维排列的轴线决定了晶体在空间中的方向。在工程实践中应用的金属由大量的晶体组成，这些晶体称之为晶粒。在大多数情况下，晶粒在空间中是自由排列的。在原子范围内，晶粒之间相互接触紧密结合。晶粒之间连接区域被称为晶界。绝对纯净的金属从来也没有被生产出来过。即使绝对纯净的金属可以生产出来，工程师们对它们也并不会特别感兴趣，因为它们很柔软、脆弱。实际应用中的金属往往都包含着一定数量的一种或多种外来金属或非金属元素，这些外来元素可能是有害的也可能是有益的或者它们对某种特定的属性没有影响。如果是有害的，这些外来元素被认为是杂质。如果是有益的，它们被认为是合金元素。在工程材料中往往被特意地加入一定
22、数量的合金元素。得到的物质被叫做合金。金属和合金区别不大。金属这个词可以包括工业用纯金属和它的合金。也许可以这样说，合金元素越故意的被添加，被添加的合金元素的量越大，那么生产出来的产品越倾向于被称之为合金。不管怎样，如果想使一种金属或合金在使用中表现出稳定一致的特性，在其中添加何种化学成分，它的量多大都应该在控制范围之内。因此，当想了解决定金属和合金性质的因素时，应充分考虑它们的化学组成。在50种左右的金属元素里，工程实践中只有少数金属被大量生产和使用。到目前为止最重要的是铁，以它为基础构成了处处可见的钢和铸铁。（主要由铁和碳构成的合金）它们的重量占所有生产出来的金属重量的98%。在结构应用（
23、也就是说，可以承受载荷的结构）中居于其次位置的是铝、铜、镍和钛。在所有的金属产量中，铝占0.8，铜占0.7，剩下的占0.5。剩下的金属用于相对特殊的用途。例如，镍合金主要用于抗磨损和耐高温的用途，由于钛合金具有高强度和低密度的综合特性，钛被广泛应用于航空工业中。镍合钛有高成本和高质量的使用特性，事实上，它们高的成本限制了它们的应用。我们不能在这里讨论这些深奥的特性。在合金材料被采用和应用于工程实际之前，掌握其结构强度和它的综合性质就够了。举例来说，它可以强度很高，并且有好的耐磨性；它可以被例如拉伸加工，机械加工，或焊接等特殊工艺来加工出来；它可以被循环利用；它的成本和实用性是首要的。Unit
24、2 Selection of Construction Materials工程材料的选择There is not a great difference between “this” steel and “that” steel; all are very similar in mechanical properties. Selection must be made on factors such as hardenability ,h:dnbiltin. 可硬化性；淬硬性, price, and availability ,veilbilti是产品在被调用时能够运行（即未处于失效或修复状态）
25、的概率。此量度考虑了产品的可靠性（多久会失效）和可用性（多久能被修复）。 , and not with the idea that “this” steel can do something no other can do because it contains 2 percent instead of 1 percent of a certain alloying element, or because it has a mysterious mistirisadj. 神秘的；不可思议的；难解的(神秘的，不可思议的) name. A tremendousadj. 极大的，巨大的；惊人的 ra
26、nge of properties is available in any steel after heat treatment; this is particularly true of alloy steels.在钢之间没有太大的区别；所有的钢在机械性能方面都是近似的。它们的选取标准是诸如脆硬性，价格，和可用性等。不仅仅是因为这种钢含有2的合金元素另一种钢含有1而使前者具有了后者没有的某些能力，或者是某种钢具有神奇的名字。经过热处理后，任何一种钢都具有大范围的特性；这种性质同样在合金钢中存在。Considerations in fabrication(制造)The properties o
27、f the final part (hardness, strength, and machinability m,i:nbiltin. 切削性；机械加工性), rather than properties required by forging, govern the selection of material. The properties required for forging have very little relation to the final properties of the material; therefore, not much can be done无论做什么都是
28、 白费力，都改变不了既定的现 实 to improve its forgeability. Higher-carbon steel is difficult to forge. Large grain size is best if subsequent heat treatment will refine the grain size.关于加工的考虑最后零件的特性（硬度、强度和可加工性）而不是锻造特性决定了材料的选择。可锻性与材料的最后特性联系不大；因此，提高金属的可锻造性价值不大。高碳钢很难锻造。如果在随后的热处理过程进行细化，大尺寸晶粒是最好的。Low-carbon, nickel-ch
29、romium(铬) steels are just about几乎，差不多j as plastic at high temperature under a single 520-ftlb(1 ftlb=1.35582J) blowat a single blow= at one blowat a single blow:一下子|一举|一击 as plain steels of similar carbon content. Nickel decreases forgeability of medium-carbon steels, but has little effect on low-ca
30、rbon steels. Chromium seems to harden steel at forging temperatures, but vanadium(钒) has no discernible(可辨别的) effect; neither has the method of manufacture any effect on high-carbon steel.在高温下低碳，镍铬合金钢在受到520-ftlb的冲击下表现出与相同碳含量普通钢几乎同样的塑性。镍减少了中碳钢的可锻性，但对低碳钢影响不大。铬在锻造温度下时使钢硬化，但钒没有明显的效果；两种加工方法对高碳钢没有影响。Forma
31、bilityThe cold-formability of steel is a function(功能) of its tensile strength combined with ductility. The tensile strength and yield point must not be high or too much work will be required in bending（弯曲）; likewise（同样地）, the steel must have sufficient（充足的） ductility to flow to the required shape wi
32、thout cracking. The force required depends on the yield point, because deformation starts in the plastic range above the yield point of steel. Work-hardening also occurs here, progressively（日益增多地） stiffening（使变硬） the metal and causing difficulty, particularly（独特的，显著的） in the low-carbon steels.成形钢的冷成
33、形是它的拉伸强度和延展性相结合的结果。拉伸强度和屈服点不能太高否则在发生弯曲时需要做很多工作；与之相类似，钢应该有高延展性，使其在没有断裂的情况下成形。加工力的大小取决于屈服点，因为钢在屈服点之上才开始变形。与此同时，加工硬化也同时发生，金属变得越来越硬，增加加工难度，尤其在低碳钢中容易发生。It is quite interesting in this connection（关于这一点，就此而论） to discover that deep draws can sometimes be made in one rapid operation that could not possibly b
34、e done leisurely（缓慢地，从容不迫地） in two or three. If a draw is half made and then stopped, it may be necessary to anneal（退火） before proceeding, that is（换句话说）, if the piece is given time to work-harden. This may not be a scientific statement, but it is actually what seems to happen.在这方面，相当有趣的是你将发现有时可通过一次快
35、速加载完成大拉伸，但以缓慢的方式两三次加载却不能实现。如果拉伸进行了一半就停止了，那么在再加工之前应先退火，也就是说工件是否有时间进行加工硬化。这不是一种科学的叙述方法，但确实是发生了。Internal stressesCold forming is done above the yield point in the work-hardening range, so internal stresses can be built up easily. Evidence of this is the springback（回弹） as the work leaves the forming ope
36、ration and the warpage（翘曲，扭曲） in any（任何一种） subsequent heat treatment. Even a simple washer might, by virtue of由于，凭借(依靠) the internal stresses resulting from punching（冲压） and then flattening（整平）, warp（弯曲） severely（严格地，激烈地） during heat treating. （virtue n.德行, 美德, 贞操, 优点, 功效, 效力, 英勇 believed in the vir
37、tue of prayer.相信祈祷的力量内应力在高于屈服点的加工硬化区进行冷加工很容易产生内应力。例如工件停止成型加工后会发生回弹，在随后的热处理后，工件会发生翘曲。即使是一个简单的垫圈，由于打孔和随后的平整加工中产生内应力，也会在热处理中呈现严重的翘曲。When doubt exists as to（关于） whether internal stresses will cause warpage, a piece can be checked by heating it to about 1100 and then letting it cool. If there are interna
38、l stresses, the piece is likely to（可能） deform. Pieces that will warp severely while being heated have been seen, yet （然而）the heat-treater热处理炉 was expected to有望做某事；被期待做某事 put them throughput through 完成 and bring them out better than they were in the first place.当是否内应力会引起翘曲的怀疑存在时，可以通过将工件加工至1100然后进行冷却来
39、验证。如果存在内应力，工件会发生变形。经过热处理的工件像我们看到的那样会发生严重的翘曲，但是我们仍然希望工件被扔到热处理炉中被处理，这样好过它存在内应力的状态。WeldingThe maximum carbon content of plain carbon steel safe for welding without preheating or subsequent heat treatment is 0.3%. higher-carbon steel is welded every day, but only with proper preheating. There are two im
40、portant factors: the amount of heats that is put in ; the rate at which it is removed.焊接不需要预热或之后进行热处理就能安全焊接的最高碳含量为0.3。高碳钢通过合适的预热通常也可焊接。有两点值得注意：吸收热量的多少；移除速度。Welding at a slower rate puts in more heat and heats a large volume of metal, so the cooling rate due to loss of heat to the base metal is decre
41、ased(减少). A preheat will do the same thing. For example, sae4150 steel, preheated to 600 or 800, can be welded readily（容易地）. When the flame or arc is taken away from the weld, the cooling rate is not so great, owing to the higher temperature of the surrounding metal and slower cooling results. Even
42、the most rapid air-hardening（风硬钢） steels are weldable if preheated and welded at a slow rate.低速焊接带来了更多的热量，这对金属的大量体积进行了加热，所以冷却速度降低。预热可以取得与之相当的效果。例如当 被预热至 或 时可以很好的焊接。由于周围金属的较高温度，当焊接弧移开焊接点后，冷却速度不会太快，产生了低速冷却的结果。即使是冷作硬化速度最快的金属也可以通过预热和慢速焊接达到良好的焊接效果。MachinabilityMachinability（机械加工性能） means several things.
43、To production men it generally means being able to remove metal at the fastest rate, leave the best possible finish, and obtain the longest possible tool life. Machinability applies to（应用于） the tool-work（工具，零件） combination.可加工性可加工性意味着几件事情。对于加工者来说，它意味着可以快速的移除金属，取得最好的加工效果，得到最长的刀具寿命。可加工性是刀具和零件的结合。It is
44、 not determined by hardness（硬度） alone, but by the toughness（韧性）, microstructure, chemical composition（成分）, and tendency（倾向） of a metal to harden under cold work. In the misleading expression “too hard to machine”, the word “hard” is usually meant to be synonymous（同义的） with “difficult”. Many times a
45、material is actually too soft to machine readily. Softness and toughness may cause the metal to tear（撕裂） and flow ahead of the cutting tool rather than cut cleanly. Metal that are inherently（天性地，固有地） soft and tough are sometimes alloyed to improve their machinability at some sacrifice skrifais n. 牺牲
46、；祭品；供奉All gains are made at some sacrifice.Most people might choose to divert the course of the train, and sacrifice only one child.（牺牲） in ductility. Examples are use of lead（铅） in brass（黄铜） and of sulfur slf（硫磺） in steel.加工性不仅仅只由硬度决定，它还由韧性，微观结构，化学成分和在冷加工下金属所呈现的硬化特性所决定。在容易混淆的表示“难加工”中，“hard”与“diffic
47、ult”同义。许多时候，因为材料过软而难于稳定加工。材料柔软性和韧性能够产生金属撕裂，使金属在完成切削前流动至刀具前端。柔软的金属往往会被加入合金从而牺牲它的延展性来提高加工性能。如黄铜中加入铅钢中加入硫磺。Machinability is a term used to indicate the relative（比较的） ease（不费力） with which a material can be machined by sharp cutting tools in operations such as turning（车）, drilling（钻）, milling（铣）, broachi
48、ngbuti n. 拉削；拉孔；推削；扩孔v. 钻孔；开口（拉削）, and reaming（铰）.机械加工性能是在指对工件材料使用刀具进行诸如车、钻、铣、拉削、铰加工时的难易程度。In the machining of metal, the metal being cut, the cutting tool, the coolant, the process and type of machine tool（机床）, and the cutting conditions all influence the results. By changing any one of these factors, different results will be obtained. The criterion kraitirinn. （批评判断的）标准；准则；规范；准据（标准） upon which the ratings（等级） listed are based(等级评定的标准) is the relativeadj. 相对的；
