【正文】 assified into three major headings: (i) Physical, (ii) Chemical, (iii) Mechanical.Physical propertiesDensity or specific gravity, moisture [39。4 Cr 鉻在鋼中形成較穩(wěn)定的碳化物，提高碳化物在鋼中的溶解溫度，減慢溶解速度。2Mn 在鋼中形成MnS以代替FeS?！　?鋼的原始組織的粗細和分布對奧氏體的成分將有重大影響。鋼的淬透性是鋼材本身所固有的屬性，它只取決于其本身的內部因素，而與外部因素無關。 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, different results will be obtained. The criterion [krai39。s?lf?]（硫磺） in steel.加工性不僅僅只由硬度決定，它還由韌性，微觀結構，化學成分和在冷加工下金屬所呈現的硬化特性所決定。由于周圍金屬的較高溫度，當焊接弧移開焊接點后，冷卻速度不會太快，產生了低速冷卻的結果。經過熱處理的工件像我們看到的那樣會發(fā)生嚴重的翹曲，但是我們仍然希望工件被扔到熱處理爐中被處理，這樣好過它存在內應力的狀態(tài)。It is quite interesting in this connection（關于這一點，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，相當有趣的是你將發(fā)現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。lb的沖擊下表現出與相同碳含量普通鋼幾乎同樣的塑性。 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 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。 , 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。 我們不能在這里討論這些深奧的特性。 在50種左右的金屬元素里，工程實踐中只有少數金屬被大量生產和使用。如果是有益的，它們被認為是合金元素。在工程實踐中應用的金屬由大量的晶體組成，這些晶體稱之為晶粒。它們是熱和電的良導體，不透光。 it may have to be able to be fabricated by a particular process such as deep drawing, machining, or welding。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。 that a whole plex 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 corrosion resistance。 除了少數例外金屬在常溫下是固態(tài)的。三維排列的軸線決定了晶體在空間中的方向。如果是有害的，這些外來元素被認為是雜質。因此，當想了解決定金屬和合金性質的因素時，應充分考慮它們的化學組成。鎳合鈦有高成本和高質量的使用特性，事實上，它們高的成本限制了它們的應用。此量度考慮了產品的可靠性（多久會失效）和可用性（多久能被修復）。bil?ti]n. 切削性；機械加工性), 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。 neither has the method of manufacture any effect on highcarbon steel.在高溫下低碳，鎳鉻合金鋼在受到520ft與此同時，加工硬化也同時發(fā)生，金屬變得越來越硬，增加加工難度，尤其在低碳鋼中容易發(fā)生。如果存在內應力，工件會發(fā)生變形。例如當 被預熱至 或 時可以很好的焊接。krifais] n. 犧牲；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.（犧牲） in ductility. Examples are use of lead（鉛） in brass（黃銅） and of sulfur [39。b?ut?i?] n. 拉削；拉孔；推削；擴孔v. 鉆孔；開口（拉削）, and reaming（鉸）.機械加工性能是在指對工件材料使用刀具進行諸如車、鉆、銑、拉削、鉸加工時的難易程度。淬硬層深度越大，則鋼的淬透性越好。　　 在相同冷度條件下，奧氏體成分越均勻，珠光體的形核率就越低，轉變的孕育期增長，C曲線右移，臨界冷卻速度減慢，鋼的淬透性越高。一般高合金工具鋼含碳高，故具有變形抗力大，塑性差，碳化物不易被粉碎等特點。為了消除這種組織可采用鐓粗和拔長交錯進行，或在1000～1100℃下長時期擴散退火。Mo提高鋼的熱強性，提高變形抗力。ei??n]n. 偏差；誤差；背離average deviation:平均偏差|平均差|平均偏差，均差 thereafter, in the stressstrain curve.Within the elastic range, the limiting value of the stress up to which the stress and strain are proportional, is called the limit of proportionality. In this region, the metal obeys Hooke’s law, which states that the stress is proportional to strain in the elastic range of loading (the material pletely regains its original dimensions after the load is removed). In the actual plotting of the curve, the proportionality limit is obtained at a slightly lower value of the load than the elastic limit. This may be attributed to the timelag in the regaining of the original dimensions of the material. This effect is very frequently noticed in some noferrous有色金屬鐵的，含鐵的 metals.While iron and nickel exhibit[iɡ39。化學特性 許多化學特性都歸入到這個范疇。對于許多材料來說，上述情況發(fā)生的應力極限值稱為彈性極限。實際上依靠測試儀器的精確性可以使比例極限和彈性極限區(qū)分得更清晰。在這個塑性流動期間的應力應變關系表示為曲線上的QRST段。金屬拉伸越長它的直徑越小。 cylindrical and conical sections。Consider the shell of revolution of general shape shown in under a loading that is rotationally symmetric。Substitution in equations () and () gives: 代入方程（）和（）得： ()The maximum values will occur at 。一塊金屬則是成千上萬相聯(lián)晶體的集合體，而這些晶粒都沉浸在從晶體原子中脫離出來的帶負電的價電子云中。所有黑色金屬的基本成分都是鐵元素。 Metals are of