【正文】 質(zhì)性證據(jù)|實質(zhì)證據(jù)substantial order:大宗訂單|大訂單 amounts in engineering materials. The result is known as an alloy. The distinction between the descriptors “metal” and “alloy” is not clearcut. The term “metal” may be used to enpass both a mercially 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無論如何，不管怎樣, the chemical position of a metal or an alloy must be known and controlled within certain limits if consistent一致的 performance is to be achieved in service. Thus chemical position 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 produced and used in large quantities in engineering practice. The most important by far is iron鐵, on which are based the ubiquitous普遍的，無處不在的 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 uses (that is, for structures that are expected to carry loads) are aluminum鋁, copper, nickel, and titanium [tai39。Unit 1 Metals金屬 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 posed, about half are classified as metals. The distinction between a metal and a nonmetal is not always clearcut. The most basic definition centers around以…為中心 the type of bonding existing between the atoms of the element, and around the characteristics of certain of the electrons某種電子 associated with these atoms. In a more practical way, however, a metal can be defined as an element which has a particular package of properties. Metals are when in the solid state and, with few exceptions極少例外 (. mercury), are solid at ambient周圍環(huán)境的 temperatures. They are good conductors of heat and electricity and are opaque不透明的 to light. They usually have a paratively high density. Many metals are ductile柔軟的；易延展的that is, their shape can be changed permanently永久地，長期不變地 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 paratively high, although, the fracture forces is not nearly =far from,much less than as high 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 [,krist?39。teini?m, ti]n. [化]鈦（金屬元素）. Aluminum accounts for about % by weight of all metals produced, and copper about %, leaving only % for all other metals. As might be expected, the remainders are all used in rather相當(dāng) special applications. For example, nickel alloys are used principally主要地 in corrosionand heatresistant applications, while titanium is used extensively廣泛地 in the aerospace industry because its alloys have good binations of high strength and low density. Both nickel and titanium are used in highcost, highquality applications, and, indeed, it is their high cost that tends to restrict their application. We cannot discuss these more esotericadj. 秘傳的；限于圈內(nèi)人的；難懂的Esoteric Buddhism:密宗|密宗，特別是指西藏的喇嘛教。 it may have to be able to be fabricated by a particular process such as deep drawing, machining, or welding。金屬和非金屬之間的區(qū)別不是特別明顯。它們是熱和電的良導(dǎo)體，不透光。 從我們的觀點來看，在所有的特性中結(jié)晶性是最重要的。在工程實踐中應(yīng)用的金屬由大量的晶體組成，這些晶體稱之為晶粒。 絕對純凈的金屬從來也沒有被生產(chǎn)出來過。如果是有益的，它們被認(rèn)為是合金元素。金屬這個詞可以包括工業(yè)用純金屬和它的合金。 在50種左右的金屬元素里，工程實踐中只有少數(shù)金屬被大量生產(chǎn)和使用。在所有的金屬產(chǎn)量中，％，％，％。 我們不能在這里討論這些深奧的特性。 all are very similar in mechanical properties. Selection must be made on factors such as hardenability [,hɑ:d?n?39。 , 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 [mi39。不僅僅是因為這種鋼含有2％的合金元素另一種鋼含有1％而使前者具有了后者沒有的某些能力，或者是某種鋼具有神奇的名字。 therefore, not much can be done無論做什么都是 白費力，都改變不了既定的現(xiàn) 實 to improve its forgeability. Highercarbon steel is difficult to forge. Large grain size is best if subsequent heat treatment will refine the grain size.關(guān)于加工的考慮最后零件的特性（硬度、強度和可加工性）而不是鍛造特性決定了材料的選擇。Lowcarbon, nickelchromium(鉻) steels are just about幾乎，差不多j as plastic at high temperature under a single 520ftlb的沖擊下表現(xiàn)出與相同碳含量普通鋼幾乎同樣的塑性。 likewise（同樣地）, the steel must have sufficient（充足的） ductility to flow to the required shape without cracking. The force required depends on the yield point, because deformation starts in the plastic range above the yield point of steel. Workhardening also occurs here, progressively（日益增多地） stiffening（使變硬） the metal and causing difficulty, particularly（獨特的，顯著的） in the lowcarbon steels.成形鋼的冷成形是它的拉伸強度和延展性相結(jié)合的結(jié)果。It is quite interesting in this connection（關(guān)于這一點，就此而論） to discover that deep draws can sometimes be made in one rapid operation that could not possibly be done leisurely（緩慢地，從容不迫地） 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（換句話說）, if the piece is given time to workharden. This may not be a scientific statement, but it is actually what seems to happen.在這方面，相當(dāng)有趣的是你將發(fā)現(xiàn)有時可通過一次快速加載完成大拉伸，但以緩慢的方式兩三次加載卻不能實現(xiàn)。例如工件停止成型加工后會發(fā)生回彈，在隨后的熱處理后，工件會發(fā)生翹曲。經(jīng)過熱處理的工件像我們看到的那樣會發(fā)生嚴(yán)重的翹曲，但是我們?nèi)匀幌Ｍぜ蝗拥綗崽幚頎t中被處理，這樣好過它存在內(nèi)應(yīng)力的狀態(tài)。有兩點值得注意：吸收熱量的多少；移除速度。由于周圍金屬的較高溫度，當(dāng)焊接弧移開焊接點后，冷卻速度不會太快，產(chǎn)生了低速冷卻的結(jié)果?？杉庸ば允堑毒吆土慵慕Y(jié)合。s?lf?]（硫磺） in steel.加工性不僅僅只由硬度決定，它還由韌性，微觀結(jié)構(gòu)，化學(xué)成分和在冷加工下金屬所呈現(xiàn)的硬化特性所決定。柔軟的金屬往往會被加入合金從而犧牲它的延展性來提高加工性能。 In the machining of metal, the metal being cut, the cutting tool, the coolant, the process and type of machine tool（機床）, and the cutting conditions all influence the results. By changing any one of these factors, diffe