機械設(shè)計制造及其自動化專業(yè)英語翻譯

1、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 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 existi ng betwee n 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 defi ned as an eleme nt which has a particular package of properties.M

3、etals are crystalline when in the solid state and, with few exceptions (e.g. mercury), are solid at ambient temperatures. They are good con ductors 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 cha

4、nged permanently by the application of a force without break ing. The forces required to cause this deformation and those required to break or fracture a metal are comparatively high,在人類社會的開展中，金屬的應(yīng)用 起著關(guān)鍵性的作用。構(gòu)成物質(zhì)的大約100種根本兀素中，大約有一半為金屬。金屬和非 金屬之間的區(qū)別不是特別明顯。最根本的定 義集中在元素原子間存在的連接形式和與這 些原子相關(guān)聯(lián)的電子的某些特性。然而，在 實

5、際應(yīng)用中，可以將具有某些特性集合金屬 定義為某種元素。除了少數(shù)例外金屬在常溫下是固態(tài) 的。它們是熱和電的良導(dǎo)體，不透光。它們 往往具有較咼的密度。 許多金屬具有延展性， 也就是說，在不被破壞的情況下它們的形狀 在外力的作用下可以發(fā)生變化。引起永久變 形所需的力和最終使金屬斷裂所需的力相當(dāng) 大，盡管發(fā)生斷裂所需的力遠沒有像所預(yù)期 的撕開金屬原子所需的力那么大。從我們的觀點來看，在所有的特性中結(jié) 晶性是最重要的。結(jié)晶體是這樣一種結(jié)構(gòu)， 組成它的原子定位在規(guī)那么的三維排列中，仿 佛位于三維棋盤的方格的角上。原子間距隨 著原子大小呈規(guī)律性變化，原子間距是金屬 的一種特性。三維排列的軸線決定了晶體在 空

6、間中的方向。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。在 大多數(shù)情況下，晶粒在空間中是自由排列的。 在原子范圍內(nèi)，晶粒之間相互接觸緊密結(jié)合。 晶粒之間連接區(qū)域被稱為晶界。although, the fracture forces is not nearly ashigh as would be expected from simplecon siderati on of the forces required to tear apartthe atoms of the metal.One of the more significant of these characteri

7、stics from our point of view is that of crystalli nity 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 of a three-dimensional chessboard The spaci ng ofthe atoms in the array is of the sa

8、me order as the size of the atoms, the actual spaci ng being a characteristic of the particular metal. The direct ions of the axes of the array defi ne the orientation of the crystal in space. The metalscommonly used in engineering practice are composed of a large number of such crystals, called gra

9、ins. In the most general case, the crystals of the various grains are randomly orie nted in space. The grains are everywhere in in timate con tact with one ano ther and joined together on an atomic scale. The region at which they join is known as a gra in boun dary.An absolutely pure metal (i.e. one

10、 composed of only one type of atom) has n ever bee n produced. Engin eers 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 inevitably contain small amounts of one or more foreign elements, either meta

11、llic or nonmetallic. These foreign elements may be detrimental , they may be beneficial, or they may have no in flue nee at all on a particular property. If disadva ntageous, the foreig n elements tend to be known as impurities . If advantageous, they tend to be known as allo yingeleme nts. Allo yin

12、geleme nts arecommonly 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 encompass both a commercially pure metal and its alloys. Perhaps 計 can be

13、 said that the more deliberately an allo ying additi on has bee n 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 of a metal or an alloy must be known and con trolled within certa in l

14、imits if con siste nt performa nee is to be achieved in service. Thus chemical compos it ion has to be taken into絕對純潔的金屬從來也沒有被生產(chǎn)出來 過。即使絕對純潔的金屬可以生產(chǎn)出來，工 程師們對它們也并不會特別感興趣，因為它 們很柔軟、脆弱。實際應(yīng)用中的金屬往往都 包含著一定數(shù)量的一種或多種外來金屬或非 金屬元素，這些外來元素可能是有害的也可 能是有益的或者它們對某種特定的屬性沒有 影響。如果是有害的，這些外來元素被認為 是雜質(zhì)。如果是有益的，它們被認為是合金 元素。在工程材料中

15、往往被特意地參加一定 數(shù)量的合金元素。得到的物質(zhì)被叫做合金。金屬和合金區(qū)別不大。金屬這個詞可以 包括工業(yè)用純金屬和它的合金。也許可以這 樣說，合金元素越成心的被添加，被添加的 合金元素的量越大，那么生產(chǎn)出來的產(chǎn)品越 傾向于被稱之為合金。不管怎樣，如果想使 一種金屬或合金在使用中表現(xiàn)出穩(wěn)定一致的 特性，在其中添加何種化學(xué)成分，它的量多 大都應(yīng)該在控制范圍之內(nèi)。因此，當(dāng)想了解 決定金屬和合金性質(zhì)的因素時，應(yīng)充分考慮 它們的化學(xué)組成。在50種左右的金屬兀素里， 工程頭踐中 只有少數(shù)金屬被大量生產(chǎn)和使用。到目前為account when developing an understanding ofth

16、e factors which determine the properties ofmetals and their alloys.Of the 50 or so metallic elements, only a few are produced and used in large qua ntities inengin eeri ng practice. The most importa nt by far is iron , on which are based the ubiquitous steels and cast irons (basically alloys of iron

17、 and carb on). They acco unt for about 98% by weight of all metals produced. Next in importanee for structural uses (that is, for structures that are expected to carry loads) are aluminum , copper, nickel, and titanium% for all other metals. As might be expected, the rema in ders are all used in rat

18、her special applications. For example, nickel alloys are used principally in corrosion-and heat-resistant applicati ons, while tita nium is used exte nsively in the aerospace industry because its alloys have good comb in ati ons of high stre ngth and low den sity. Both ni ckel and tita nium are used

19、 in high-cost, high-qualityapplications, and,in deed, it is their high cost that tends to restrict their applicati on.We cannot discuss these more esoteric properties here. Suffice it to say that a whole complex of properties in addition to structural止最重要的是鐵，以它為根底構(gòu)成了處處可 見的鋼和鑄鐵。主要由鐵和碳構(gòu)成的合金 它們的重量占所有生產(chǎn)

20、出來的金屬重量的 98%。在結(jié)構(gòu)應(yīng)用也就是說，可以承受載 荷的結(jié)構(gòu)中居于其次位置的是鋁、銅、鎳 和鈦。在所有的金屬產(chǎn)量中，鋁占0.8%，銅占0.7%，剩下的占0.5%。剩下的金屬用于 相對特殊的用途。例如，鎳合金主要用于抗 磨損和耐高溫的用途，由于鈦合金具有高強 度和低密度的綜合特性，鈦被廣泛應(yīng)用于航 空工業(yè)中。鎳合鈦有咼本錢和咼質(zhì)量的使用 特性，事實上，它們高的本錢限制了它們的 應(yīng)用。我們不能在這里討論這些深奧的特性。 在合金材料被米用和應(yīng)用于工程實際之前， 掌握其結(jié)構(gòu)強度和它的綜合性質(zhì)就夠了。舉 例來說，它可以強度很咼，并且有好的耐磨 性；它可以被例如拉伸加工，機械加工，或 焊接等特殊工藝

21、來加工出來；它可以被循環(huán) 利用；它的本錢和實用性是首要的。stre ngth is required of an alloy before it will be accepted in to, and survive in. engin eeri ngpractice. It may, for example, have to be stro ng and yet have reas on able corrosi on resista nee; it may have to be able to be fabricated by a particular process such as de

22、ep drawing, machining, or welding; it may have to be readily recyclable; and its cost and availability may be of critical importa nee.Unit 2 Selection of Construction Materials工程材料的選擇There is not a great differenee between “ this steel and “ that steel; all are very similar in mecha nical properties

23、. Select ion must be made on factors such as harde nability, price, and availability , and not with the idea that“can do something no other can do because it contains 2 perce nt in stead of 1 perce nt of a certa in alloying element, or because it has a mysterious (神 在鋼之間沒有太大的區(qū)別；所有的鋼在機 械性能方面都是近似的。 它們

24、的選取標(biāo)準(zhǔn)是諸 如脆硬性，價格，和可用性等。不僅僅是因為 這種鋼含有2%的合金元素另一種鋼含有1%:hW使前者ee有了后者沒有的某些能力，或者是某種鋼具有神奇的名字。經(jīng)過熱處理后，任何 一種鋼都具有大范圍的特性；這種性質(zhì)冋樣在 合金鋼中存在。秘的，不可思議的 n ame. A treme ndous range of properties is available in any steel after heat treatme nt; this is particularly true of alloy steels.Con siderati ons in fabricati on制造The

25、properties of the final part hardness, stre ngth, and mach in ability , rather tha n 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 to improve its

26、 forgeability. Higher-carb on steel is difficult to forge. Large grain size is best if subseque nt heat treatme nt 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?？慑懶耘c材料的最后特性聯(lián)系不大；因此，提高金屬的可鍛造性價值不大。 咼碳鋼很難鍛造。如果在 隨后的熱處理過程進行細化， 大尺寸晶粒是最 好的。Low-carb on, n ickel-chromium鉻steels are just

27、about as plastic at high temperature under a single 520-ft lb1 ft lb=1.35582J blow as plai n steels of similar carb on content. Nickel decreases forgeability of medium-carb on steels, but has little effect on low-carb on steels. Chromium seems to harden steel at forging temperatures, but vanadium 釩h

28、as no discernible可區(qū)分的effect; neither has the method of manufacture any effect on high-carb on steel.在高溫下低碳，鎳鉻合金鋼在受到 520-ft lb的沖擊下表現(xiàn)出與相冋碳含量普通 鋼幾乎同樣的塑性。鎳減少了中碳鋼的可鍛 性，但對低碳鋼影響不大。鉻在鍛造溫度下時使鋼硬化，但釩沒有明顯的效果；兩種加工方 法對高碳鋼沒有影響。FormabilityThe cold-formability of steel is a function功 能of its ten sile stre ngth comb

29、ined with ductility. The tensile strength and yield point must not be high or too much work will be required in bending彎曲;likewise冋樣地,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

30、in the plastic range above the yield point of steel. Work-hardening also occurs here, progressively日益增多地 stiffening使 變硬the metal and caus ing difficulty, particularly獨特的，顯著的in the low-carb on 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。拉伸強度和屈服點不能太高否那么在 發(fā)生彎曲時需要做很多工作； 與之相類似，鋼 應(yīng)該有咼延展性，使其在沒有斷裂的情況下成 形。加工力的大小取決于屈服點，

31、因為鋼在屈服點之上才開始變形。 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。It is quite in terest ing in this connection 關(guān)于 這一點，就此而論to discover that deep drawscan sometimes be made in one rapid operati on that could not possibly be done leisurely 緩慢地，從 容不迫地in two or three. If a draw is half madeand the n stopped,

32、it may be n ecessary to ann eal退 火before proceeding, that is換句話說，if the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)。如果拉伸進行了一 半就停止了，那么在再加工之前應(yīng)先退火，也 就是說工件是否有時間進行加工硬化。這不是一種科學(xué)的表達方法，但確頭是發(fā)生了。piece is given time to work-harden. This may not be a scientific statement, but it is actually what seems to h

33、appe n.Internal stressesCold forming is done above the yield point in the work-hardening range, so internal stressescan be built up easily. Evidenee of this is the springback回彈 as the work leaves the forming operation and the warpage翹曲，扭曲in any任何一種subseque nt heat treatme nt. Even asimple washer mig

34、ht, by virtue of依靠the internal stresses result ing from pun chi ng沖壓and then flattening整平，warp彎曲 severely 嚴(yán)格地，劇烈地duri ng heat treat in g. virtue n.德行，美德，貞操，優(yōu)點，成效，效力，英勇 believed in the virtue of prayer.相信祈禱的力量內(nèi)應(yīng)力在咼于屈服點的加工硬化區(qū)進行冷加工很 容易產(chǎn)生內(nèi)應(yīng)力。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。即使是一個簡單的墊圈，由于打孔和隨后 的平整加工中

35、產(chǎn)生內(nèi)應(yīng)力，也會在熱處理中呈現(xiàn)嚴(yán)重的翹曲。When doubt exists as to關(guān)于whetherinternal stresses will cause warpage，a piece can be checked by heating it to about 1100 and then letting it cool. If there are internal stresses，the piece is likely to可能deform. Pieces that will warpseverely while being heated have been seen，yet 然而

36、the heat-treater was expected to put them through and bring them out better than they were in the first place.當(dāng)是否內(nèi)應(yīng)力會引起翹曲的疑心存在時， 可以通過將工件加工至1100然后進行冷卻來驗證。如果存在內(nèi)應(yīng)力，工件會發(fā)生變形。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?理爐中被處理，這樣好過它存在內(nèi)應(yīng)力的狀 態(tài)。Weldi ng%. higher-carb on steel is welded every day，but only with

37、proper preheating. There are two important factors: the amount of heats that is put in ; the rate at which it is removed.焊接不需要預(yù)熱或之后進行熱處理就能平安焊 接的取咼碳含里為 0.3%。咼碳鋼通過適宜的 預(yù)熱通常也可焊接。有兩點值得注意：吸收熱 量的多少；移除速度。Weldi ng at a slower rate puts in more heat and heats a large volume of metal，so the cooling rate due to

38、 loss of heat to the base metal is decreased減 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 take n away from the weld, the cooli ng rate is not so great, owing to the higher temperature of the surro unding me

39、tal and slower cooli ng results. Even the most rapid air-harde ning 風(fēng)硬鋼 steels are weldable if preheated and welded at a slow rate.低速焊接帶來了更多的熱量，這對金屬的 大量體積進行了加熱，所以冷卻速度降低。預(yù) 熱可以取得與之相當(dāng)?shù)男Ч?。例如?dāng)被預(yù)熱至或 時可以很好的焊接。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。 即使 是冷作硬化速度最快的金屬也可以通過預(yù)熱 和慢速焊接到達良好的焊接效果。Machi nability

40、Mach in ability機械加工性冃能means severalthin gs. To product ion men it gen erally mea ns being可加工性可加工性意味著幾件事情。對于加工者來 說，它意味著可以快速的移除金屬，取得最好able to remove metal at the fastest rate, leave the best possible fini sh, and obta in the Ion gest possible tool life. Mach in ability applies to應(yīng)用于thetool-work 工具，零件c

41、omb in atio n.的加工效果，得到最長的刀具壽命。 可加工性 是刀具和零件的結(jié)合。It is not determined by hardness硬度 alone, but by the toughness韌性，microstructure,chemical composition成分，and tendency傾 向 of a metal to harden under cold work. In the misleading expression “ tochard to machine the word “ hard is usually meant to be synonymo

42、us 同義的 with “difficult . Many times a mat is actually too soft to mach ine readily. Softn ess and tough ness may cause the metal to tear撕裂 and flow ahead of the cutting tool rather than cut clea nly. Metal that are in here ntly天性地,固有地 soft and tough are sometimes alloyed to improve their mach in abi

43、lity at some sacrifice犧牲inductility. Examples are use of lead 鉛 in brass 黃銅and of sulfur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。在容易混淆的表示“難加 工中，“ hard與“ difficult 同義。許多時 候，因為材料過軟而難于穩(wěn)定加工。材料柔軟性和韌性能夠產(chǎn)生金屬撕裂，使金屬在完成切 e削前流動至刀具前端。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。 如黃銅中參加鉛鋼中參加硫磺。Mach in abili

44、ty is a term used to in dicate the relative比擬的ease不費力with which amaterial can be machined by sharp cutting tools in operations such as turning 車,drilling 鉆, milling銃，broaching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、銃、拉削、鉸加工時的難易 程度。In the mach ining of metal, the metal being cut, the cutt ing tool

45、, the coola nt, the process and type of machine tool機床，and the cutting conditions all in flue nee the results. By cha nging any one of these factors, different results will be obtained. The criterion 標(biāo)準(zhǔn)upon which the ratinas 等級listed are based等級評定的標(biāo)準(zhǔn) is the relative在對金屬進行加工時，被切削的金屬，切 肖U刀具，冷卻液，使用的機床的

46、種類，切削條 件均影響著切削效果。改變?nèi)魏我环N均會產(chǎn)生 不同的切削效果。切削效果評定的準(zhǔn)那么是：車 削時在固疋的切削條件下產(chǎn)生一疋量的刀具 磨損時，被加工試件相應(yīng)的材料去除量。volume of various不同種 materials that may beremoved by turning under fixed conditions toJJproduce an arbitrary任意的fixed amount of1J' 1J -tool wear淬透性：指在規(guī)定條件下，決定鋼材淬硬深度和硬度分布的特性。即鋼淬火時得到 淬硬層深度大小的能力，它表示鋼接受淬火的能力。鋼材淬透性

47、好與差，常用淬硬層深 度來表示。淬硬層深度越大， 那么鋼的淬透性越好。 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(nèi)部因素，而與外部因素?zé)o關(guān)。鋼的淬透性主要取決于它的化學(xué)成 分，特別是含增大淬透性的合金元素及晶粒度，加熱溫度和保溫時間等因素有關(guān)。淬透 性好的鋼材，可使鋼件整個截面獲得均勻一致的力學(xué)性能以及可選用鋼件淬火應(yīng)力小的 淬火劑，以減少變形和開裂。淬透性主要取決于其臨界冷卻速度的大小，而臨界冷卻速度那么主要取決于過冷奧氏體的穩(wěn)定性，影響奧氏體的穩(wěn)定性主要是：1.化學(xué)成分的影響碳的影響是主要的，當(dāng)C%小于1.2 %時，隨著奧氏體中碳濃度的提高，顯著降低臨界冷卻速度，C曲線右移，

48、鋼的淬透性增大；當(dāng)C %大于時, 鋼的冷卻速度反而升高， C 曲線左移，淬透性下降。其次是合金元素的影響，除鈷外，絕大多數(shù)合金元素溶入奧氏體后，均使 C 曲線右移，降低臨界冷卻速度， 從而提高鋼的2. 奧氏體晶粒大小的影響 大的奧氏體晶粒能使 C 曲線右移，形、開裂傾向和降低韌性。3. 奧氏體均勻程度的影響核率就越低，轉(zhuǎn)變的孕育期增長，4. 鋼的原始組織的影響淬透性。奧氏體的實際晶粒度對鋼的淬透性有較大的影響，粗降低了鋼的臨界冷卻速度。 但晶粒粗大將增大鋼的變在相同冷度條件下， 奧氏體成分越均勻， 珠光體的形 C 曲線右移，臨界冷卻速度減慢，鋼的淬透性越高。 鋼的原始組織的粗細和分布對奧氏體的

49、成分將有重大 影響。5.局部元素，例如 Mn ， Si 等元素對提高淬透性能起到一定作用，但同時也會對鋼 材帶來其他不利的影響?？慑懶?forgeability金屬具有熱塑性，在加熱狀態(tài)各種金屬要求溫度不同 ，可以進行壓力加工，稱為具有可鍛性?？慑懶裕褐附饘俨牧显趬毫庸r，能改變形狀而不產(chǎn)生裂紋的性能。它包括 在熱態(tài) 或 冷態(tài)下能夠進行錘鍛，軋制，拉伸，擠壓等加工。可鍛性的好壞主要與金屬 材料的化學(xué)成分有關(guān)討論 元素在鋼中的形成物對可鍛性的影響1C與Fe形成滲碳體Fe3C,與其它合金元素形成合金滲碳體FeM3C或合金碳化物。所有碳化物都有硬度高、 塑性低、 熔點高的特點， 但滲碳體型碳化物在

50、加熱到鍛造溫度時經(jīng) 適當(dāng)保溫可大局部或全部溶入固溶體中， 而合金碳化物較難溶入固溶體中， 對鋼的可鍛性影 響最大。 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。2Mn 在鋼中形成 MnS以代替FeS。因MnS熔點高1620C，且呈斷續(xù)分布，不像 FeS 熔點988C,呈網(wǎng)狀分布在晶界，所以可減少熱脆。錳對鋼的過熱性粗晶很敏感，鋼錠加熱溫度過高，易生粗晶，使鍛造困難。錳對珠光體 鋼的可鍛性影響較小，奧氏體錳鋼臨界點將降低。3 Ni 煉鋼時有 Ni 極易吸收氫形成大量氣泡，鍛造時引起開裂。 Ni 與 Mn 的作用相反， 它促使硫化物成網(wǎng)狀分布于晶界，使鍛造時開裂

51、，所以不宜在含硫的爐氣中加熱。珠光體 Ni 鋼在鍛造時易形成片狀破裂和帶狀組織。為了消除這種組織可采用鐓粗和拔長交錯進行，或在10001100 C下長時期擴散退火。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。 鉻能促進使鑄錠生成大晶粒，冷卻時沿晶界形成內(nèi)裂。高鉻鋼在空氣中冷卻即能淬火，常在外表生裂，所以不易鍛造。5 V與碳形成穩(wěn)定碳化物V 能使鋼生成細晶組織，阻止過熱，適當(dāng)參加對鍛性有利。6 Mo 鉬的熔點高，能降低鋼的過熱傾向它和 Ni 一樣，使硫化物以網(wǎng)狀分布在晶界。 含有 0.7%C， 25%Mo 的鉬鋼，鍛造時無特殊困難。這些鋼在空冷時間淬火，要防止

52、冷裂。Mo 提高鋼的熱強性，提高變形抗力。7 W 與碳形成穩(wěn)定的碳化物 提高鋼的熱強性，增大變形抗力8 Cu 銅在鋼中可溶于鐵素體中，也可沿晶界析出游離銅銅中含0.15%Cu時，加熱不當(dāng)，外表易生裂紋，高溫軋制時易產(chǎn)生熱脆9 B硼能細化晶粒，能溶解在丫和a固溶體中，與Fe化合成Fe2B鋼中含B > 0.007%時，鍛造易裂10 S在鋼中形成硫化物或共晶體，如FeS、Fe的熔點為985C,且成網(wǎng)狀布于晶界顯著降低可鍛性紅脆11 P促成偏析，使晶粒粗大，容易引起鍛件外表龜裂降低可鍛性Unit 3 Mecha ni cal Properties of MaterialsThe material

53、properties can be classifiedinto three major headi ngs:(i) Physical, (ii) Chemical,(iii) Mecha ni cal.Physical propertiesDen sity or specificgravity, moisture content,etc., can be classified underthis category.Chemical properties Many chemical properties come un der this category. These in clude aci

54、dity or alkali nity, reactivity and corrosi on.The most importa nt of材料特性主要分為三類：(i)物理特性，(ii)化學(xué)特性，(iii)力學(xué)性能。物理特性密度或特定的重力，濕 度等都屬于此范疇?；瘜W(xué)特性許多化學(xué)特性都歸入到 這個范疇。其中包括酸性 或堿性，活性和耐腐蝕性。 而在這其中最重要的是耐 腐蝕性，通俗的解釋是材 料在特定大氣中長期使用 時，抵抗腐蝕的能力。these is corrosi on which can be expla ined inlayman ' s terms as the resistanc

55、e of the material to decay while in continu ous use in a particular atmosphere.Mecha ni cal properties Mecha ni cal properties in clude the stre ngth properties like ten sile, compressi on, shear torsi on, impact, fatigue and creep. The ten sile stre ngth of a material is obtai ned by dividi ng the

56、maximum load, which the specime n bears by the area of cross-section of the specime n.This is a curve plotted betwee n the stress力學(xué)特性力學(xué)特性包括諸如拉 伸，壓縮，剪切，扭轉(zhuǎn)， 沖擊，疲勞和蠕變等強度 特性。一種材料的拉伸強 度由試件承載的最大載何 除以試件的橫截面積得 至嘰7如下列圖為在拉伸試驗中 沿著X軸橫軸的應(yīng)變 和沿著丫軸縱軸的應(yīng) 力之間的關(guān)系曲線。材料 在加載時，隨著載荷大小 的變化，尺寸會發(fā)生改變。 當(dāng)卸載時，變形消失。對 于許多材料來說，上述情 況發(fā)

57、生的應(yīng)力極限值稱為 彈性極限。在應(yīng)力-應(yīng)變曲along the Y-axis(ord in ate) and the stra in along the X-axis(abscissa) in a ten sile test. A material tends to cha nge or cha nges its dime nsions whe n it is loaded, depe nding upon the magn itude of the load.Whe n the load is removed it can be see n that the deformati on disappear s. For many materials this occurs up to a certain value線中，直線關(guān)系和隨后的 小小的彎曲描述了上述的 加載和卸載。!在彈性范圍內(nèi)，應(yīng)力應(yīng) 變成比例的應(yīng)力極限值稱 為比例極限。在這個區(qū)域 中，金屬服從胡克定律一 闡述了在加載的彈性范圍 內(nèi)，應(yīng)力和應(yīng)變成比例關(guān) 系材料在卸載后，能夠 完全回復(fù)它原來的尺寸。 在曲線的實際繪制中，比 例極限值要稍微比彈性極 限值低。這可能是由于材 料回復(fù)原尺寸需要的時間 延遲。這種現(xiàn)象在一些有 色金屬中常常出現(xiàn)。of the stress called the elastic limit-Th