機(jī)械設(shè)計(jì)制造及其自動(dòng)化專業(yè)英語翻譯超級(jí)大全x

1、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 basic definition c

2、enters around the type of bonding existing between the atoms of the element, and around the金屬在人類社會(huì)的發(fā)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種基本元素中, 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 基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(shí)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 高的密度。許多金屬具有延展性,char

3、acteristics of certain of也就是說，在不被破壞的情況下the electrons associated with它們的形狀在外力的作用下可以these atoms. In a more發(fā)生變化。引起永久變形所需的practical way, however, a力和最終使金屬斷裂所需的力相metal can be defined as an當(dāng)大，盡管發(fā)生斷裂所需的力遠(yuǎn)element which has a particular沒有像所預(yù)期的撕開金屬原子所package of properties.Metals are crystalline when in the so

4、lid 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 permanently by the application

5、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需的力那么大。從我們的觀點(diǎn)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

6、種結(jié)構(gòu)，組成它的原 子定位在規(guī)則的三維排列中，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 在空間中的方向。在工程實(shí)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。絕對(duì)純凈的金屬從來也沒有 被生產(chǎn)出來過。即使絕對(duì)純凈的 金屬可以生產(chǎn)出來，工程師們對(duì) 它們也并不會(huì)特別感興趣，因?yàn)?它們很柔軟、脆弱。實(shí)際應(yīng)用中 的金屬往往都包含著一定數(shù)量的required to tear apart the at

7、oms of the metal.Oneof 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 of a three-dimensiona

8、l 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 in 一種或多種外來金屬或非金屬元 素，這

9、些外來元素可能是有害的 也可能是有益的或者它們對(duì)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(rèn)為是雜 質(zhì)。如果是有益的，它們被認(rèn)為 是合金元素。在工程材料中往往 被特意地加入一定數(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(gè)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 元素越故意的被添加，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(shí)，應(yīng)充 分考慮它們的化

10、學(xué)組成。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

11、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

12、vitably contain small amounts of one or在50種左右的金屬元素里， 工程實(shí)踐中只有少數(shù)金屬被大量 生產(chǎn)和使用。到目前為止最重要 的是鐵，以它為基礎(chǔ)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)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、銀和鈦。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(duì)特殊的用途。例如，銀 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(qiáng)度和 低密度的綜合特性，鈦被廣泛應(yīng) 用于航空工業(yè)中。銀合鈦有高成 本

13、和高質(zhì)量的使用特性，事實(shí)上， 它們高的成本限制了它們的應(yīng) 用。我們不能在這里討論這些深 奧的特性。在合金材料被采用和more foreign elements, either應(yīng)用于工程實(shí)際之前，掌握其結(jié)metallic or nonmetallic. These foreign elements may be detrimental , they may be beneficial, or they mayhave no influence at all on a particular property. If disadvantageous, the foreign elements ten

14、d to be known as impurities . If 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.Th

15、e term “metal ” may be used to encompass both a構(gòu)強(qiáng)度和它的綜合性質(zhì)就夠了。舉例來說，它可以強(qiáng)度很高，并 且有好的耐磨性；它可以被例如 拉伸加工，機(jī)械加工，或焊接等 特殊工藝來加工出來；它可以被 循環(huán)利用；它的成本和實(shí)用性是 首要的。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 ad

16、dition, 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 controlled within certain limits if consistent performance is to be achieved in service. Thus chemical composition has to be taken into

17、 account when developing an understanding of the factors which determine the properties of metals and their alloys.Of the 50 or so metallicelements,onlya few areproduced and used in large quantities inengineeringpractice. The most important by far is iron , on which are based the ubiquitous steels a

18、nd 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) arealuminum,copper, nickel, and titanium.Aluminum accounts for about 0.8% by weight of al

19、l metals produced, and copper about 0.7%, leaving only 0.5% for all other metals. As might be expected, the remainders areall used in rather specialapplications. For example, nickel alloys are used principally in corrosion-and heat-resistant applications, while titanium is used extensively in the ae

20、rospace industry because its alloys have good combinations of high strength and low density. Both nickel and titanium are used in high-cost,high-qualityapplications, and, indeed, it is their high cost that tends to restrict their application.We cannot discuss these more esoteric properties here. Suf

21、fice it to say that a whole complex of properties in addition to structural strength is required of an alloy before it will beaccepted into, and survive in,engineering practice. It may,for example, have to be strongand yethavereasonablecorrosionresistance;it mayhave to be ableto befabricatedby a par

22、ticularprocess such as deep drawing,machining, or welding; it mayhave to be readily recyclable;may be of criticaland its cost and availabilityimportance.Unit 2 Selection of Construction Materials工程材料的選擇There is not a great difference between "this " steel and “that ” steel; all are very si

23、milar in mechanical properties. Selection must be made on factors such as在鋼之間沒有太大的區(qū)別；所有的鋼在機(jī) 械性能方面都是近似的。它們的選取標(biāo)準(zhǔn)是諸 如脆硬性，價(jià)格，和可用性等。不僅僅是因?yàn)?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。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)同樣在 合金鋼中存在。hardenability, price, and availability , and not with theidea that "th

24、is ” steel can dosomething no other can do because it contains 2 percent instead of 1 percent of a certain alloying element, or because it hasmysterious （神秘的，不可思議的name. A tremendous rangeofproperties is available in anysteel after heat treatment; thisis particularly true ofalloysteels.Considerations

25、infabrication( 制造)The properties of the finalpart (hardness, strength,and關(guān)于加工的考慮最后零件的特性（硬度、強(qiáng)度和可加工性） 而不是鍛造特性決定了材料的選擇。可鍛性與材料的最后特性聯(lián)系不大；因此，提高金屬的可鍛造性價(jià)值不大。高碳鋼很難鍛造。如果在 隨后的熱處理過程進(jìn)行細(xì)化，大尺寸晶粒是最 好的。machinability ), ratherthanproperties required by forging,govern the selection of material.The properties required

26、forforging have very little relationto the final properties of thematerial; therefore, not muchcanbe done to improve itsforgeability.Higher-carbonsteel is difficult to forge. Large grain size is best if subsequent heat treatment will refine the grain size.Low-carbon,nickel-chromium（銘）steels are just

27、 about as plastic at high temperature under a single 520-ft - lb（1 ft lb=1.35582J） blow as plain steels of similar carbon content. Nickel decreases在高溫下 低碳，饃銘合金鋼在受到 520-ft - lb的沖擊下表現(xiàn)出與相同碳含量普 通鋼幾乎同樣的塑性。 饃減少了中碳鋼的可鍛 性，但對(duì)低碳鋼影響不大。銘在鍛造溫度下時(shí) 使鋼硬化，但鈕沒有明顯的效果；兩種加工方 法對(duì)高碳鋼沒有影響。forgeability of medium-carbonsteels,

28、 but has little effect on low-carbon steels. Chromiumseems to harden steel at forgingtemperatures, but vanadium（鋼）has no discernible（ 可辨另U 的）effect; neither has the method ofmanufacture any effect onhigh-carbon steel.Formability成形鋼的冷成形是它的拉伸強(qiáng)度和延展性相結(jié) 合的結(jié)果。拉伸強(qiáng)度和屈服點(diǎn)不能太高否則在丁一 一一1一一一.發(fā)生彎曲時(shí)需要做很多工作；與之相類似，鋼T

29、he cold-formability of steel應(yīng)該有高延展性，使其在沒有斷裂的情況下成.1./ 玨匕、 r , 形。加工力的大小取決于屈服點(diǎn)，因?yàn)殇撛谇?s a funct|on（功目匕）of |ts服點(diǎn)之上才開始變形。與此同時(shí)，加工硬化也 “同時(shí)發(fā)生，金屬變得越來越硬，增加加工難度，tensilestrengthcombined with尤其在低碳鋼中容易發(fā)生。ductility. The tensile strengthand yield point must not be high or too muchwork will be required in bending （彎曲）

30、;likewise （同 樣地）,the steel must have sufficient （充足的）ductility to flow to the required shape withoutcracking.The forcerequireddependson the yieldpoint,becausedeformationstarts 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

31、）the metal and causing difficulty, particularly（獨(dú)特的，顯著的）in thelow-carbon steels.It is quite interesting在這方面，相當(dāng)有趣的是你將發(fā)現(xiàn)有時(shí)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(shí)現(xiàn)。如果拉伸進(jìn)行了一this connection （關(guān)于這一點(diǎn),止匕而論）to discover that deep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(shí)間進(jìn)行加工硬化。 這不是 一種科學(xué)的敘述方法，但確實(shí)是發(fā)生了。draws can sometimes be madei

32、nonerapid operation that couldnotpossibly be done leisurely （緩慢 地，從容不迫地）in two or three.This may not be a scientific statement, but it is actually what seems to happen.Internal stressesCold forming is done above the yield point in the work-hardening range, so internal stresses can內(nèi)應(yīng)力在高于屈服點(diǎn)的加工硬化區(qū)進(jìn)行冷加

33、工很 容易產(chǎn)生內(nèi)應(yīng)力。例如工件停止成型加工后會(huì) 發(fā)生回彈，在隨后的熱處理后， 工件會(huì)發(fā)生翹 曲。即使是一個(gè)簡單的墊圈，由于打孔和隨后的平整加工中產(chǎn)生內(nèi)應(yīng)力，也會(huì)在熱處理中呈現(xiàn)嚴(yán)重的翹曲。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 work-harden.be built up easily. Evidence ofthis is the springback （回

34、彈）asthe work leaves the formingoperation and the warpage （翹曲，扭曲）in any （任何一種） subsequent heat treatment. Even a simple washer might, by virtue of（ 依靠）the internal stresses resulting from punching（沖壓）and then flattening（整平）,warp（彎曲）severely（嚴(yán)格地，激烈地） during heat treating.（virtue n.德行，美德，貞操，優(yōu) 點(diǎn)，功效，效力，英

35、勇believed in the virtue of prayer.相信祈禱的力量當(dāng)是否內(nèi)應(yīng)力會(huì)引起翹曲的懷疑存在時(shí)，可以通過將工件加工至 1100然后進(jìn)行冷卻來 驗(yàn)證。如果存在內(nèi)應(yīng)力，工件會(huì)發(fā)生變形。經(jīng) 過熱處理的工件像我們看到的那樣會(huì)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OWhen doubt exists as to （關(guān) 于） whether internal stresses will cause warpage, a piece can be checked by heating it to about1100 and then l

36、etting it cool. Ifthere are internal 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-treaterwas expected to put them through and bring them out better than they were in the first place.WeldingThe maximumcarbon content of

37、 plain carbon steel safeforwelding without preheatingorsubsequent heat treatmentis0.3%. higher-carbon steeliswelded every day, but only with proper preheating. There are two important factors: the amount of heats that is put in ; the rate at which it is removed.Welding at a slower rate puts in more

38、heat and heats a large volume of metal, so the cooling rate due to loss of heat to the base metal is decreased（ 減少）.A preheat will do the same thing.焊接不需要預(yù)熱或之后進(jìn)行熱處理就能安全焊 接的最高碳含量為 0.3%。高碳鋼通過合適的 預(yù)熱通常也可焊接。有兩點(diǎn)值得注意：吸收熱 量的多少；移除速度。低速焊接帶來了更多的熱量，這對(duì)金屬的大量體積進(jìn)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＠绠?dāng)被預(yù)熱至 或 時(shí)可以很好的焊接。由于周圍金

39、 屬的較高溫度，當(dāng)焊接弧移開焊接點(diǎn)后， 冷卻 速度不會(huì)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 和慢速焊接達(dá)到良好的焊接效果。For example, sae4150 steel, preheated to 600 or 800, can bewelded readily （容易地）.Whenthe 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

40、and slower cooling results. Even the most rapid air-hardening （風(fēng)硬鋼）steels are weldable if preheated and welded at a slow rate.MachinabilityMachinability means several可加工性可加工性意味著幾件事情。對(duì)于加工者來（機(jī)械加工性能）說，它意味著可以快速的移除金屬， 取得最好的加工效果，得到最長的刀具壽命?？杉庸ば?.十是刀具和零件的結(jié)合。things.Toproduction menit generally means being ab

41、le to remove metal at the fastest rate, leave the best possible finish, and obtain the longest possible tool life. Machinability applies to （應(yīng)用于） the tool-work （工具，零件） combination.以 _ _加工性不僅僅只由硬度決定，它還由韌性，1t is not determined by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hardness （硬度）alone, but by the to

42、ughness （韌 性） , microstructure,chemicalcomposition （成分）,and tendency（傾向）of a metal to hardenunder cold work. In the misleading expre ssion “too hard to machine” , the wor d “hard” is usually meant to be synonymous（同義的） with a difficult : Manytimes a material is actually too soft to machine readily.

43、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 machinabilityatsome sacrifice（犧牲）inductility. Examples are use of lead （鉛）in brass （黃銅）and of工&q

44、uot;中，"hard"與"difficult ”同義。許 多時(shí)候，因?yàn)椴牧线^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，使金屬在完成切削前流動(dòng)至刀具前端。柔軟的金屬往往會(huì) 被加入合金從而犧牲它的延展性來提高加工 性能。如黃銅中加入鉛鋼中加入硫磺。sulfur （硫磺）in steel.Machinability is a term usedto indicate the relative （比較的）機(jī)械加工性能是在指對(duì)工件材料使用刀具 進(jìn)行諸如車、鉆、銃、拉削、錢加工時(shí)的難易 程度。ease （不 費(fèi)力） with which a material ca

45、n be machined by sharp cutting tools in operations suchas turning （車）,drilling （鉆）milling （銃），broaching （拉削）， and reaming （較）.In the machining of metal, the metal being cut, the cutting tool, the coolant, the process在對(duì)金屬進(jìn)行加工時(shí)，被切削的金屬，切 削刀具，冷卻液，使用的機(jī)床的種類，切削條 件均影響著切削效果。改變?nèi)魏我环N均會(huì)產(chǎn)生 不同的切削效果。 切削效果評(píng)定的準(zhǔn)則是： 車

46、削時(shí)在固定的切削條件下產(chǎn)生一定量的刀具 磨損時(shí)，被加工試件相應(yīng)的材料去除量。and type of machine tool （機(jī)床）and the cutting conditions allinfluence the results. By changing any one of these factors, different results willbe obtained. The criterion（標(biāo)準(zhǔn)）upon which the ratings（等級(jí)）listed are based（等級(jí)評(píng)定的標(biāo)準(zhǔn) ） is the relative volume of various（不同不

47、中） materials that may beremoved by turning under fixed conditions to produce anarbitrary (任意的)fixed amountof 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(shí)得 到淬硬層深度大小的能力，它表示鋼接受淬火的能力。鋼材淬透性好與差，常用淬硬 層深度來表示。淬硬層深度越大，則鋼的淬透性越好。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

48、保溫時(shí)間等因 素有關(guān)。淬透性好的鋼材，可使鋼件整個(gè)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，而臨界冷卻速度則主要取決于過 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(shí)，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，鋼的淬透性增大；當(dāng) C%大于時(shí)，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，除鉆外，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 提高鋼的淬透性。2 .奧氏體晶粒大小的影響奧氏體的

49、實(shí)際晶粒度對(duì)鋼的淬透性有較大的影響，粗大的奧氏體晶粒能使 C曲線右移，降低了鋼的臨界冷卻速度。但晶粒粗大將增大鋼 的變形、開裂傾向和降低韌性。3 .奧氏體均勻程度的影響 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(zhuǎn)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4 .鋼的原始組織的影響 鋼的原始組織的粗細(xì)和分布對(duì)奧氏體的成分將有重 大影響。5 .部分元素，例如 Mn, Si等元素對(duì)提高淬透性能起到一定作用，但同時(shí)也會(huì)對(duì) 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(jìn)行壓力加工，稱為具 有可鍛性。

50、可鍛性：指金屬材料在壓力加工時(shí)，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(jìn)行錘鍛，軋制，拉伸，擠壓等加工?？慑懶缘暮脡闹饕?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(duì)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(FeM)3c或合金碳化物。所有碳化物都有硬度高、塑性低、熔點(diǎn)高的特點(diǎn)，但滲碳體型碳化物在加熱到鍛造溫度時(shí)經(jīng)適當(dāng)保溫可大部分或全部溶入固溶體中， 而合 金碳化物較難溶入固溶體中，對(duì)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(diǎn)。2Mn在鋼中形成 MnS以代替FeSo因MnS熔點(diǎn)高（162

51、0C）,且呈斷續(xù)分布，不像FeS熔點(diǎn)988C,呈網(wǎng)狀分布在晶界，所以可減少 熱脆。鎰對(duì)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。鎰對(duì)珠光體鋼的可鍛性影響較小，奧氏體鎰鋼臨界點(diǎn)將降 低。3 Ni煉鋼時(shí)有Ni極易吸收氫形成大量氣泡，鍛造時(shí)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(shí)開 裂，所以不宜在含硫的爐氣中加熱。珠光體Ni鋼在鍛造時(shí)易形成片狀破裂和帶狀組織。為了消除這種組 織可采用鍛粗和拔長交錯(cuò)進(jìn)行，或在10001100c下長時(shí)期擴(kuò)散退火。4 Cr銘在鋼中形成較穩(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。銘能促進(jìn)使鑄錠生成大晶粒，

52、冷卻時(shí)沿晶界形成內(nèi)裂。高銘鋼在空氣中冷卻即能淬火，常在表面生裂，所以不易鍛造。5V與碳形成穩(wěn)定碳化物V能使鋼生成細(xì)晶組織，阻止過熱，適當(dāng)加入對(duì)鍛性有利。6 Mo鋁的熔點(diǎn)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%Q 25%M0勺鋁鋼，鍛造時(shí)無特殊困難。這些鋼在空冷時(shí)間淬火，要防止冷裂。Mo提高鋼的熱強(qiáng)性，提高變形抗力。7W與碳形成穩(wěn)定的碳化物提高鋼的熱強(qiáng)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(shí)，加熱不當(dāng)，表面易生裂紋，高溫軋制時(shí)易產(chǎn)生熱脆9 B硼能細(xì)化晶粒，能溶解在丫和口固溶體中，與Fe化合成Fe2B鋼中含B&

53、gt; 0.007%寸，鍛造易裂10 S在鋼中形成硫化物或共晶體，如 FeS Fe的熔點(diǎn)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，容易引起鍛件表面龜裂降低可鍛性Unit 3 Mechanical Properties of Materialsmajor物理特性，（ii）化學(xué)特性，（iii）The material properties can be classified into three材料特性主要分為三類：headings: (i) Physical, (ii) Chemical, (iii) Mechanical.Physical proper

54、tiesDensity or specific gravity,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?xì)w入到這個(gè)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(shí)， 抵抗腐蝕的能力。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(qiáng)度特性。一種材料的拉伸強(qiáng)度由試件承載的最大載荷除以試件的橫截面積得到。如圖所示為在拉伸試驗(yàn)中沿著X軸（橫軸）的應(yīng)變和沿著 Y軸（縱軸）的應(yīng)力之間的關(guān)系曲線。材料在加載時(shí)，隨著載荷大 小的變化，尺寸會(huì)發(fā)生改變。當(dāng) 卸載時(shí)，變形消失。對(duì)于許多材

55、料來說，上述情況發(fā)生的應(yīng)力極 限值稱為彈性極限。在應(yīng)力-應(yīng)變 曲線中，直線關(guān)系和隨后的小小moisture content, etc., can be classified under this category. Chemical properties Many chemical properties come under this category. These include acidity or alkalinity, reactivity and corrosion. The most important of these is corrosion which can be expl

56、ained in layman' s terms as the resistance of the material to decay while in continuous use in a particular atmosphere.Mechanical properties Mechanical properties include the strength properties like tensile, compression, shear, torsion, impact, fatigue and creep. The tensile strength of a mater

57、ial is obtained bydividing the maximum load, which the specimen bears by the area of cross-section of the specimen.This is a curve plotted between the stress along the Y-axis(ordinate) and the strainalongtheX-axis(abscissa) in a tensile test. A material tends to change or changes its dimensions when it is loaded, depending upon the magnitude of the load. When the load is removed it can be seen that the deformation disappear s. For many materials this occurs up to a certain value of th