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1、 Unit 1 Metals 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 the type of bonding existing between the atoms of the element, and around the characteristics of certain of the electrons associated with these atoms. In a more practical way, however, a metal can be defined as an element which has a particular package of properties.Metal
3、s are crystalline when in the solid state and, with few exceptions (e.g. mercury), are solid at ambient temperatures. They are good conductors of heat and electricity and are opaque to light. They usually have a comparatively high density. Many metals are ductile-that is, their shape can be changed
4、permanently 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 as high as would be expected from simple consideration of the forces required
5、to tear apart the atoms of the metal.One of the more significant of these characteristics from our point of view is that of crystallinity. A crystalline solid is one in which the constituent atoms are located in a regular three-dimensional array as if they were located at the corners of the squares
6、of a three-dimensional chessboard. 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 directions of the axes of the array define the orientation of the crystal in space. The metals commonly used
7、in engineering practice are composed of a large number of such crystals, called grains. In the most general case, the crystals of the various grains are randomly oriented in space. The grains are everywhere in intimate contact with one another and joined together on an atomic scale. The region at wh
8、ich they join is known as a grain boundary.An absolutely pure metal (i.e. one composed of only one type of atom) has never been produced. Engineers would not be particularly interested in such a metal even if it were to be produced, because it would be soft and weak. The metals used commercially ine
9、vitably contain small amounts of one or more foreign elements, either metallic or nonmetallic. These foreign elements may be detrimental, they may be beneficial, or they may have no influence at all on a particular property. If disadvantageous, the foreign elements tend to be known as impurities. If
10、 advantageous, they tend to be known as alloying elements. Alloying elements are commonly added deliberately in substantial 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
11、encompass both a commercially pure metal and its alloys. 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, the chemical composition
12、 of a metal or an alloy must be known and controlled within certain limits if consistent 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 5
13、0 or so metallic elements, only a few are produced and used in large quantities in engineering practice. The most important by far is iron, on which are based the ubiquitous steels and cast irons (basically alloys of iron and carbon). They account for about 98% by weight of all metals produced. Next
14、 in importance for structural uses (that is, for structures that are expected to carry loads) are aluminum, copper, nickel, and titanium. 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 remain
15、ders are all used in rather special applications. For example, nickel alloys are used principally in corrosion-and heat-resistant applications, while titanium is used extensively in the aerospace industry because its alloys have good combinations of high strength and low density. Both nickel and tit
16、anium 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 esoteric properties here. Suffice it to say that a whole complex of properties in addition to structural strength is required of an alloy b
17、efore it will be accepted into, and survive in, engineering practice. It may, for example, have to be strong and yet have reasonable corrosion 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 recyclable
18、; and its cost and availability may be of critical importance.翻译如下： 第一单元 金属 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
19、。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
20、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
21、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（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
22、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。Reading Material 1 Stainless Steel Stainless steels do not rust in the atmosphere as most other steels do. The term stainless implies a resistance to stai
23、ning, rusting, and pitting in the air, moist and polluted as it is, and generally defines a chromium content in excess of 11 % but less than 30%. And the fact that the stuff is steel means that the base is iron. Stainless steels have room-temperature yield strengths that range from 205 MPa (30 ksi)
24、to more than 1725 MPa (250 ksi). Operating temperatures around 750 C (1400 F) are reached. At the other extreme of temperature some stainless steels maintain their toughness down to temperatures approaching absolute zero.With specific restrictions in certain types, the stainless steels can be shaped
25、 and fabricated in conventional ways. They can be produced and used in the as-cast condition; shapes can be produced by powder-metallurgy techniques; cast ingots can be rolled or forged (and this accounts for the greatest tonnage by far). The rolled product can be drawn, bent, extruded, or spun. Sta
26、inless steel can be further shaped by machining, and it can be joined by soldering, brazing, and welding. It can be used as an integral cladding on plain carbon or low-alloy steels.The generic term stainless steel covers scores of standard compositions as well as variations bearing company trade nam
27、es and special alloys made for particular applications. Stainless steels vary in their composition from a fairly simple alloy of, essentially, iron with 11% chromium, to complex alloys that include 30% chromium, substantial quantities of nickel, and half a dozen other effective elements. At the high
28、-chromium, high-nickel end of the range they merge into other groups of heat-resisting alloys, and one has to be arbitrary about a cutoff point. If the alloy content is so high that the iron content is about half, however, the alloy falls outside the stainless family. Even with these imposed restric
29、tions on composition, the range is great, and naturally, the properties that affect fabrication and use vary enormously. It is obviously not enough to specify simply a stainless steel.”Classification the various specifying bodies categorize stainless steels according to chemical composition and othe
30、r properties. However, all the stainless steels, whatever specifications they conform to, can be conveniently classified into six major classes that represent three distinct types of alloy constitution, or structure. These classes are ferritic, martensitic, austenitic, manganese-substituted austenit
31、ic, duplex austenitic ferritic, and precipitation-hardening. Each class is briefly described below. Ferrous stainless steels: This class is so named because the crystal structure of the steel is the same as that of iron at room temperature. The alloys in the class are magnetic at room temperature an
32、d up to their Curie temperature (about 750 C; 1400 F). Common alloys in the ferrous class contain between 11% and 29% chromium, no nickel, and very little carbon in the wrought condition. Martensitic stainless steels: Stainless steels of this class, which necessarily contain more than 11 % chromium,
33、 have such a great hardenability that substantial thickness will harden during air cooling, and nothing more drastic than oil quenching is ever required. The hardness of the as-quenched martensitic stainless steel depends on its carbon content. However, the development of mechanical properties throu
34、gh quenching and tempering is inevitably associated with increased susceptibility to corrosion. Austenitic stainless steels: The traditional and familiar austenitic stainless steels have a composition that contains sufficient chromium to offer corrosion resistance, together with nickel to ensure aus
35、tenite at room temperature and below. The basic austenitic composition is the familiar l8% chromium, 8% nickel alloy. Both chromium and nickel contents can be increased to improve corrosion resistance, and additional elements (most commonly molybdenum) can be added to further enhance corrosion resis
36、tance. Manganese-substituted austenitic stainless steels: The austenitic structure can be encouraged by elements other than nickel, and the substitution of manganese and nitrogen produces a c1ass that we believe is sufficiently different in its properties to be separated from the chromium-nickel aus
37、tenitic class just described. The most important difference lies in the higher strength of the manganese-substituted alloys. Duplex austenitic-ferrous stainless steels: The structure of these steels is a hybrid of the structures of ferrite and austenite; and the mechanical properties likewise combin
38、e qualities of each component steel type. The duplex steels combine desirable corrosion and mechanical properties, and their use is as a result increasing in both wrought and cast form. Precipitation-hardening stainless steels: Stainless steels can be designed so that their composition is amenable t
39、o precipitation hardening. This class cuts across two of the other c1asses, to give us martensitic and austenitic precipitation-hardening stainless steels. In this class we find stainless steels with the greatest useful strength as well as the highest useful operating temperature.Properties In selec
40、tion of stainless steels, three kinds of properties have to be considered: (1) Physical properties: density, thermal conductivity, electrical resistivity, and so on; (2) Mechanical properties: strength, ductility, hardness, creep resistance, fatigue, and so on; and (3) corrosion-resistant properties
41、. Note that properties of stainless steels are substantially influenced by chemica1 composition and microstructure. Hence specifications include chemical composition, or, more correctly, an analysis of the most important elements (traces of unreported elements also may be present) as well as a heat
42、treatment that provides the optimum structure.Applications Since stainless steels were first used in cutlery industry, the number of applications has increased dramatically. The relative importance of the major fields of application for flat and long stainless steel products is shown in Table 1. Che
43、mical and power engineering is the largest market for both long and flat products. It began in about 1920 with the nitric acid industry. Today, it includes an extremely diversified range of service conditions, including nuclear reactor vessels, heat exchangers, oil industry tubular, components for t
44、he chemical processing and pulp and paper industries, furnace parts, and boilers used in fossil fuel electric power plants. 翻译如下阅读材料1 不锈钢 不锈钢就像其他大多数的钢在空气中不会生锈，“不锈的”这个术语暗示了在空气中抵抗污点，生锈和腐蚀，还具有抵抗潮湿和腐蚀。通常含铬量大于11%且小于30%.实际上叫钢的材料就是铁。不锈钢在室温下的屈服强度的变化范围是从205MPa（30ksi)到1725MPa(250ksi).工作温度可达到750C（1400F)，一些不锈钢能
45、维持其韧性当温度达到绝对零度。由于特定的类型有特殊的限制，不锈钢可以通过常规方法成型和制造。它们可以在铸造状态下制造和运用。其成型可以通过粉冶金技术，铸造锭可以轧或者锻造（这是至今为止最大的吨位）。轧制产品可以取出，弯曲，挤压或旋转。不锈钢可以被进一步用机械加工塑造成型，它可以加入锡焊，铜焊和焊接。还可以用于普通钢和低合金钢的整体电镀。一般术语上说的“不锈钢”包括数十种标准组成部分，还包括变更轴承公司交易名称和特殊合金的独特应用。不锈钢的合成成分各不相同，本质上，从单一的合金，如含11%铬的铁到含30%铬和大量镍的与五六种其他有效成分的复杂合金。高含量的铬和镍最后组成其他好的热稳定性的合金，并
46、且分界点必定的任意的。然而，如果合金含量太高，铁的含量达到一半左右，该合金就不再是不锈家族了。即使这加强成分的限制，但是范围很大，很自然，其性能将很大影响制造和应用。显然，不能单纯地指定某一“不锈钢”。划分多种指定机体种类的不锈钢要根据它们的化学成分和其他性质。但是，全部的不锈钢，不论它们属于哪种规格，都可以被分为六大类，代表着三种不同的合金宪法或结构。这类别是铁素体，马氏体，奥氏体，锰代铬奥氏体，奥氏体-铁素体双相和沉淀硬化型，每种类别简述如下：铁素体不锈钢:这种类被这样命名是因为钢的晶体结构在室温下和铁的相同。该类里的合金在室温到居里温度(about750 C; 1400 F)间具有磁性。
47、普通的合金在铁素体类别里含有11%到29%的铬元素，没有镍，在锻造条件中含有极少的碳。 马氏体不锈钢：这种类别的不锈钢，需要含量超过11%的铬，在巨大的淬透性下和冷空气下将大幅度变硬，有时候要在比油淬更激烈的情况下进行。淬火马氏体不锈钢的硬度取决于它的碳含量。然而，机械性能通过淬火、回火而形成和增加金属易感性的腐蚀有着必然的联系。 奥氏体不锈钢：传统和熟悉的奥氏体不锈钢成分中拥有充分的铬同时含有镍元素保证奥氏体在室温下或更低温度的抗腐蚀性，奥氏体基本的成分是熟悉的18%铬和8%镍的合金。增加铬和镍的含量可以提高抗腐蚀性，额外的元素（大多是钼)能进一步加强抗腐蚀性。 锰代铬奥氏体不锈钢：奥氏体结
48、构被鼓励通过描述和我们相信它充分的不同性能从铬镍奥氏体中分离出来，通过加进其他元素如镍、锰的替代物和氮的方法。最重要的区别在于高强度的锰代铬合金。 奥氏体-铁素体双相不锈钢： 这种结构的钢是铁素体和奥氏体的混合体；机械性能也相似于组成的钢的质量的结合。双重钢结合想要的腐蚀性和机械性能，它们的用途使锻造和铸造形式更加困难。 沉淀硬化型不锈钢：不锈钢可以被设计使它们的成分服从沉淀硬化。这种类跨过其他两种类别，给我们马氏体和奥氏体沉淀硬化型不锈钢。在这种类型我们发现不锈钢有最多有用的强度和最高有用的操作温度。 性能 在选择不锈钢时，三种性能必须加以考虑：（1）物理性能：密度，导热系数，电阻率等；（2
49、)机械性能：强度，韧性，硬度，蠕变阻力，疲劳度等；（3）抗腐蚀性能：要认识到化学成分和微观结构在本质上影响不锈钢的性能。因此规格包括化学构成，或者更准确地说，一种最重要的成分（没被公布的成分的踪迹会被呈现）的分析和热疗将提供最适宜的结构。 应用 自从不锈钢第一次被应用于餐具，刀剑工业，到现在应用的数量戏剧性的增加。对单位和长期不锈钢商品的相对重要的主要应用领域如表1所示。化学和电力是单位和长期不锈钢商品的最大市场。它开始与约1920年的硝酸工业。如今，它包括极其多种多样的服务条件，包括核反应船舶，热交换器，石油工业管道，部分化学加工，纸浆和造纸工业，熔炉部件和化石燃料发电厂使用的锅炉。 Unit 2 Selection of Construction Materials There is not a great