機(jī)械設(shè)計(jì)制造及其自動(dòng)化專(zhuān)業(yè)英語(yǔ)-Unit-02-Selection-of-Construction-Materials分解課件

1、wordavailability 可用性veilbilitifabrication 制造 fbrikeinforgeability 可鍛性f:dbltnickle 鎳 niklchromium 鉻kroumjmvanadium 釩vneidimdiscernible 可辨別得出的；可看出的 disnblductility 延(展)性；韌性 dktiliticracking 開(kāi)裂；裂紋 krkiSelection of Construction Materials1wordavailability 可用性veilwordWork-harden 加工硬化；冷作硬化 anneal 退火 ni:lwa

2、rp 翹曲；變形w:rppreheat 預(yù)熱 prihit microstructure 顯微結(jié)構(gòu) makrostrktmislead 使誤解；誤導(dǎo) msli:d ream 鉸孔 rimarbitrary 任意的:rbitrriSelection of Construction Materials2wordWork-harden 加工硬化；冷作硬化 SSelection of Construction MaterialsThere is not a great difference between “this” steel and “that” steel; all are very simi

3、lar in mechanical properties. 在鋼之間沒(méi)有太大的區(qū)別；所有的鋼在機(jī)械性能方面都是近似的。3Selection of Construction MateSelection of Construction MaterialsSelection must be made on factors such as hardenability, price, and availability, and not with the idea that “this” steel can do something no other can do because it contains

4、2 percent instead of 1 percent of a certain alloying element, or because it has a mysterious mistiris name.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)檫@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(méi)有的某些能力，或者是某種鋼具有神奇的名字。4Selection of Construction MateSelection of Construction MaterialsA tremendous range of properties is available in

5、any steel after heat treatment; this is particularly true of alloy steels. 經(jīng)過(guò)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。5Selection of Construction MateConsiderations in fabricationThe properties of the final part (hardness, strength, and machinability), rather than properties required by forging, govern the

6、selection of material. 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。6Considerations in fabricationTConsiderations in fabricationThe properties required for forging have very little relation to the final properties of the material; therefore, not much can be done to improve its forgeability. 可鍛性與材料的最后特性聯(lián)系不大；因此

7、，提高金屬的可鍛造性?xún)r(jià)值不大。Higher-carbon steel is difficult to forge. Large grain size is best if subsequent heat treatment will refine the grain size.高碳鋼很難鍛造。如果后續(xù)的熱處理會(huì)細(xì)化晶粒尺寸，那么大的晶粒尺寸是最好的。7Considerations in fabricationTConsiderations in fabricationLow-carbon, nickel-chromium steels are just about as plastic at

8、high temperature under a single 520-ftlb(1 ftlb=1.35582J) blow as plain steels of similar carbon content. Nickel decreases forgeability of medium-carbon steels, but has little effect on low-carbon steels.在高溫下低碳，鎳鉻合金鋼在受到520-ftlb的沖擊下表現(xiàn)出與相同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(duì)低碳鋼影響不大。8Considerations in fabricat

9、ionLConsiderations in fabricationChromium seems to harden steel at forging temperatures, but vanadium has no discernible effect; neither has the method of manufacture any effect on high-carbon steel.鉻在鍛造溫度下時(shí)使鋼硬化，但釩沒(méi)有明顯的效果；兩種加工方法對(duì)高碳鋼沒(méi)有影響。9Considerations in fabricationCFormabilityThe cold-formability

10、of steel is a function of its tensile strength combined with ductility. The tensile strength and yield point must not be high or too much work will be required in bending; likewise, the steel must have sufficient ductility to flow to the required shape without cracking.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

11、點(diǎn)不能太高否則在發(fā)生彎曲時(shí)需要做很多工作；相似地，鋼應(yīng)該有高延展性，使其在沒(méi)斷裂的情況下成形。10FormabilityThe cold-formabilitFormabilityThe force required depends on the yield point, because deformation starts in the plastic range above the yield point of steel. Work-hardening also occurs here, progressively stiffening the metal and causing dif

12、ficulty, particularly in the low-carbon steels.加工力的大小取決于屈服點(diǎn)，因?yàn)殇撛谇c(diǎn)之上才開(kāi)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(lái)越硬，增加加工難度，尤其在低碳鋼中容易發(fā)生。11FormabilityThe force required FormabilityIt is quite interesting in this connection to discover that deep draws can sometimes be made in one rapid operation that could not possibly

13、 be done leisurely leli in two or three.在這方面，相當(dāng)有趣的是你將發(fā)現(xiàn)有時(shí)可通過(guò)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)。12FormabilityIt is quite interesFormabilityIf a draw is half made and then stopped, it may be necessary to anneal before proceeding, that is, if the piece is given time to work-harden. This may not be a scienti

14、fic statement, but it is actually what seems to happen.如果拉伸進(jìn)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(shuō)，如果工件已經(jīng)有時(shí)間被加工硬化。這不是一種科學(xué)的敘述方法，但確實(shí)是發(fā)生了。13FormabilityIf a draw is half mInternal stressesCold forming is done above the yield point in the work-hardening range, so internal stresses can be built up easily. Evidence of

15、 this is the springback as the work leaves the forming operation and the warpage in any subsequent heat treatment.在高于屈服點(diǎn)的加工硬化區(qū)進(jìn)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(huì)發(fā)生回彈，在隨后的熱處理后，工件會(huì)發(fā)生翹曲。14Internal stressesCold forming Internal stressesEven a simple washer might, by virtue of the internal stresses resulting from

16、 punching and then flattening, warp severely during heat treating. 即使是一個(gè)簡(jiǎn)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。15Internal stressesEven a simpleInternal stressesWhen doubt exists as to whether internal stresses will cause warpage, a piece can be checked by heating it to about 1100 and then letting i

17、t cool. 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(guò)將工件加工至1100 然后進(jìn)行冷卻來(lái)驗(yàn)證。16Internal stressesWhen doubt exInternal stressesIf there are internal stresses, the piece is likely to deform. Pieces that will warp severely while being heated have been seen, yet the heat-treater was expected to put them through and bring them ou

18、t better than they were in the first place. 如果存在內(nèi)應(yīng)力，工件會(huì)發(fā)生變形。經(jīng)過(guò)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蝗拥綗崽幚頎t中被處理，這樣好過(guò)它存在內(nèi)應(yīng)力的狀態(tài)。17Internal stressesIf there are WeldingThe maximum carbon content of plain carbon steel safe for welding without preheating or subsequent heat treatment is 0.3%. higher-carbon ste

19、el is welded every day, but only with proper preheating. 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(guò)合適的預(yù)熱通常也可焊接。18WeldingThe maximum carbon contWeldingThere 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 heat and heats a

20、large volume of metal, so the cooling rate due to loss of heat to the base metal is decreased. A preheat will do the same thing. 有兩點(diǎn)值得注意：吸收熱量的多少；熱量移除速度。低速焊接帶來(lái)了更多的熱量，這對(duì)金屬的大量體積進(jìn)行了加熱，由于基體金屬熱損失的減少因此冷卻速度降低。預(yù)熱可以取得與之相當(dāng)?shù)男Ч?9WeldingThere are two importantWeldingFor example, SAE 4,150 steel, preheated to 600

21、 or 800 , can be welded readily. When the 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 and slower cooling results. Even the most rapid air-hardening steels are weldable if preheated and welded at a slow rate.例如當(dāng)S

22、AE 4,150鋼被預(yù)熱至600 或800 時(shí)可以很好的焊接。由于周?chē)饘俚妮^高溫度，當(dāng)焊接弧移開(kāi)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(guò)預(yù)熱和慢速焊接達(dá)到良好的焊接效果。20WeldingFor example, SAE 4,150 MachinabilityMachinability means several things. To production men it generally means being able to remove metal at the fastest rate, leave the best possible

23、finish, and obtain the longest possible tool life. Machinability applies to the tool-work combination. 可加工性意味著幾件事情。對(duì)于加工者來(lái)說(shuō)，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(zhǎng)的刀具壽命?？杉庸ば允堑毒吆土慵慕Y(jié)合。21MachinabilityMachinability meaMachinabilityIt is not determined by hardness alone, but by the toughness, microstructure, chemic

24、al composition, and tendency of a metal to harden under cold work. In the misleading expression “too hard to machine”, the word “hard” is usually meant to be synonymous with “difficult”. 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。22MachinabilityIt is not dete

25、rmiMachinabilityMany times a material is actually too soft to machine readily. Softness and toughness may cause the metal to tear and flow ahead of the cutting tool rather than cut cleanly. Metal that are inherently soft and tough are sometimes alloyed to improve their machinability at some sacrific

26、e in ductility. Examples are use of lead in brass and of sulfur in steel. 許多時(shí)候，因?yàn)椴牧线^(guò)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。本質(zhì)上柔軟而堅(jiān)韌的金屬往往會(huì)被加入合金從而犧牲它的延展性來(lái)提高加工性能。如黃銅中加入鉛鋼中加入硫磺。23MachinabilityMany times a mateMachinabilityMachinability is a term used to indicate the relative ease with which a materia