機械設(shè)計制造及其自動化專業(yè)英語_Unit 02 Selection of Construction Materials

1、word availability 可用性 veilbiliti fabrication 制造 fbrikein forgeability 可鍛性 f:dblt nickle 鎳 nikl chromium 鉻 kroumjm vanadium 釩 vneidim discernible 可辨別得出的；可看出的 disnbl ductility 延(展)性；韌性 dktiliti cracking 開裂；裂紋 krkiSelection of Construction Materials1word Work-harden 加工硬化；冷作硬化 anneal 退火 ni:l warp 翹曲；變形

2、w:rp preheat 預熱 prihit microstructure 顯微結(jié)構(gòu) makrostrkt mislead 使誤解；誤導 msli:d ream 鉸孔 rim arbitrary 任意的 :rbitrri Selection of Construction Materials2Selection of Construction Materials There is not a great difference between “this” steel and “that” steel; all are very similar in mechanical properties.

3、 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。3Selection of Construction Materials Selection 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 2 percent instead of 1 percent of a certain alloying eleme

4、nt, or because it has a mysterious mistiris name. 它們的選取標準是諸如脆硬性，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。4Selection of Construction Materials A tremendous range of properties is available in any steel after heat treatment; this is particularly true of alloy steels. 經(jīng)過熱處理后，任何一種

5、鋼都具有大范圍的特性；這種性質(zhì)同樣在合金鋼中存在。5Considerations in fabrication The properties of the final part (hardness, strength, and machinability), rather than properties required by forging, govern the selection of material. 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。6Considerations in fabrication The properties required fo

6、r 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，提高金屬的可鍛造性價值不大。 Higher-carbon steel is difficult to forge. Large grain size is best if subsequent heat treatment will refine the grain size. 高碳鋼

7、很難鍛造。如果后續(xù)的熱處理會細化晶粒尺寸，那么大的晶粒尺寸是最好的。7Considerations in fabrication Low-carbon, nickel-chromium steels are just about as plastic at 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 li

8、ttle 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，但對低碳鋼影響不大。8Considerations in fabrication Chromium 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.

9、 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。9Formability The cold-formability 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 f

10、low to the required shape without cracking. 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則在發(fā)生彎曲時需要做很多工作；相似地，鋼應(yīng)該有高延展性，使其在沒斷裂的情況下成形。10Formability The 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, progr

11、essively stiffening the metal and causing difficulty, particularly in the low-carbon steels. 加工力的大小取決于屈服點，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。11Formability It is quite interesting in this connection to discover that deep draws can sometimes be made in one rapid operation that c

12、ould not possibly be done leisurely leli in two or three. 在這方面，相當有趣的是你將發(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)。12Formability If 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 scientific stateme

13、nt, but it is actually what seems to happen. 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，如果工件已經(jīng)有時間被加工硬化。這不是一種科學的敘述方法，但確實是發(fā)生了。13Internal stresses Cold forming is done above the yield point in the work-hardening range, so internal stresses can be built up easily. Evidence of this is the springback as the work lea

14、ves the forming operation and the warpage in any subsequent heat treatment. 在高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。14Internal stresses Even a simple washer might, by virtue of the internal stresses resulting from punching and then flattening, warp severely during heat treating.

15、即使是一個簡單的墊圈，由于打孔和隨后的平整加工中產(chǎn)生內(nèi)應(yīng)力，也會在熱處理中呈現(xiàn)嚴重的翹曲。15Internal stresses When doubt exists as to whether internal stresses will cause warpage, a piece can be checked by heating it to about 1100 and then letting it cool. 當是否內(nèi)應(yīng)力會引起翹曲的懷疑存在時，可以通過將工件加工至1100 然后進行冷卻來驗證。16Internal stresses If there are internal str

16、esses, 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 out better than they were in the first place. 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)。17We

17、lding The maximum carbon content of plain carbon steel safe for welding without preheating or subsequent heat treatment is 0.3%. higher-carbon steel is welded every day, but only with proper preheating. 不需要預熱或之后進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熱通常也可焊接。18Welding There are two important factors: the amo

18、unt 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 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. 有兩點值得注意：吸收熱量的多少；熱量移除速度。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，由于基

19、體金屬熱損失的減少因此冷卻速度降低。預熱可以取得與之相當?shù)男Ч?9Welding For example, SAE 4,150 steel, preheated to 600 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

20、most rapid air-hardening steels are weldable if preheated and welded at a slow rate. 例如當SAE 4,150鋼被預熱至600 或800 時可以很好的焊接。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(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熱和慢速焊接達到良好的焊接效果。20Machinability Machinability means several things. To production men it generally means being able t

21、o remove metal at the fastest rate, leave the best possible 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。對于加工者來說，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?？杉庸ば允堑毒吆土慵慕Y(jié)合。21Machinability It is not determined by hardness alone, but by the to

22、ughness, microstructure, chemical 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

23、義。22Machinability Many 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 sacrifice in ductility. Examples are use of lead in brass and of sulfur in steel. 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，使金屬在完成切削前流動至刀具前端。本質(zhì)上柔軟而堅韌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。如黃銅中加入鉛鋼中加入硫磺。23Machinability Machinability is a term used to indicate the r