机械设计制造及其自动化专业英语_Unit 02 Selection of Construction Materials讲解

1、word availability 可用性 veilbiliti fabrication 制造 fbrikein forgeability 可锻性 f:dblt nickle 鎳 nikl chromium 铬 kroumjm vanadium 钒 vneidim discernible 可辨别得出的；可看出的 disnbl ductility 延(展)性；韧性 dktiliti cracking 开裂；裂纹 krki Selection of Construction Materials 1 word Work-harden 加工硬化；冷作硬化 anneal 退火 ni:l warp 翘曲；

2、变形 w:rp preheat 预热 prihit microstructure 显微结构 makrostrkt mislead 使误解；误导 msli:d ream 铰孔 rim arbitrary 任意的 :rbitrri Selection of Construction Materials 2 Selection of Construction Materials There is not a great difference between “this” steel and “that” steel; all are very similar in mechanical proper

3、ties. 在钢之间没有太大的区别；所有的钢在机械 性能方面都是近似的。 3 Selection 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 alloyi

4、ng element, or because it has a mysterious mistiris name. 它们的选取标准是诸如脆硬性，价格，和可 用性等。不仅仅是因为这种钢含有2的合 金元素另一种钢含有1而使前者具有了后 者没有的某些能力，或者是某种钢具有神奇 的名字。 4 Selection of Construction Materials A tremendous range of properties is available in any steel after heat treatment; this is particularly true of alloy steel

5、s. 经过热处理后，任何一种钢都具有大范围的 特性；这种性质同样在合金钢中存在。 5 Considerations 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、强度和可加工性） 而不是锻造特性决定了材料的选择。 6 Considerations in fabrication The pr

6、operties required for forging have very little relation to the final properties of the material; therefore, not much can be done to improve its forgeability. 可锻性与材料的最后特性联系不大；因此， 提高金属的可锻造性价值不大。 Higher-carbon steel is difficult to forge. Large grain size is best if subsequent heat treatment will refin

7、e the grain size. 高碳钢很难锻造。如果后续的热处理会细化 晶粒尺寸，那么大的晶粒尺寸是最好的。 7 Considerations 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-c

8、arbon steels, but has little effect on low-carbon steels. 在高温下低碳，镍铬合金钢在受到520-ftlb 的冲击下表现出与相同碳含量普通钢几乎同 样的塑性。镍减少了中碳钢的可锻性，但对 低碳钢影响不大。 8 Considerations in fabrication Chromium seems to harden steel at forging temperatures, but vanadium has no discernible effect; neither has the method of manufacture any

9、 effect on high-carbon steel. 铬在锻造温度下时使钢硬化，但钒没有明显 的效果；两种加工方法对高碳钢没有影响。 9 Formability 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 mus

10、t have sufficient ductility to flow to the required shape without cracking. 钢的冷成形是它的拉伸强度和延展性相结合 的结果。拉伸强度和屈服点不能太高否则在 发生弯曲时需要做很多工作；相似地，钢应 该有高延展性，使其在没断裂的情况下成形。 10 Formability The force required depends on the yield point, because deformation starts in the plastic range above the yield point of steel. W

11、ork-hardening also occurs here, progressively stiffening the metal and causing difficulty, particularly in the low- carbon steels. 加工力的大小取决于屈服点，因为钢在屈服 点之上才开始变形。与此同时，加工硬化也 同时发生，金属变得越来越硬，增加加工难 度，尤其在低碳钢中容易发生。 11 Formability It is quite interesting in this connection to discover that deep draws can some

12、times be made in one rapid operation that could not possibly be done leisurely leli in two or three. 在这方面，相当有趣的是你将发现有时可通 过一次快速加载完成大拉伸，但以缓慢的方 式两三次加载却不能实现。 12 Formability 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 wo

13、rk-harden. This may not be a scientific statement, but it is actually what seems to happen. 如果拉伸进行了一半就停止了，那么在再加 工之前应先退火，也就是说，如果工件已经 有时间被加工硬化。这不是一种科学的叙述 方法，但确实是发生了。 13 Internal stresses Cold forming is done above the yield point in the work-hardening range, so internal stresses can be built up easily

14、. Evidence of this is the springback as the work leaves the forming operation and the warpage in any subsequent heat treatment. 在高于屈服点的加工硬化区进行冷加工很容 易产生内应力。例如工件停止成型加工后会 发生回弹，在随后的热处理后，工件会发生 翘曲。 14 Internal stresses Even a simple washer might, by virtue of the internal stresses resulting from punching

15、and then flattening, warp severely during heat treating. 即使是一个简单的垫圈，由于打孔和随后的 平整加工中产生内应力，也会在热处理中呈 现严重的翘曲。 15 Internal 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. 当是否内应力会引起翘曲的怀疑存在时，可 以通过将工件加

16、工至1100 然后进行冷却 来验证。 16 Internal stresses If 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 out better than they were in the first place. 如果存在内应力，工件会发生变形。

17、经过热 处理的工件像我们看到的那样会发生严重的 翘曲，但是我们仍然希望工件被扔到热处理 炉中被处理，这样好过它存在内应力的状态。 17 Welding 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. 不需要预热或之后进行热处理就能安全焊接 的最高碳含量为

18、0.3。高碳钢通过合适的预 热通常也可焊接。 18 Welding 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 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

19、 do the same thing. 有两点值得注意：吸收热量的多少；热量移除 速度。低速焊接带来了更多的热量，这对金属 的大量体积进行了加热，由于基体金属热损失 的减少因此冷却速度降低。预热可以取得与之 相当的效果。 19 Welding 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 h

20、igher 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. 例如当SAE 4,150钢被预热至600 或800 时可 以很好的焊接。由于周围金属的较高温度，当焊接 弧移开焊接点后，冷却速度不会太快，产生了低速 冷却的结果。即使是冷作硬化速度最快的金属也可 以通过预热和慢速焊接达到良好的焊接效果。 20 Machinability

21、 Machinability means several things. To production men it generally means being able to 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. 可加工性意味着几件事情。对于加工者来说， 它意味着可以快速的移除金属，取得最好的 加工效果，得到最长的

22、刀具寿命。可加工性 是刀具和零件的结合。 21 Machinability It is not determined by hardness alone, but by the toughness, 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 “dif

23、ficult”. 加工性不仅仅只由硬度决定，它还由韧性， 微观结构，化学成分和在冷加工下金属所呈 现的硬化特性所决定。在容易混淆的表示 “难加工”中，“hard”与“difficult”同义。 22 Machinability 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 a

24、re 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. 许多时候，因为材料过软而难于稳定加工。材料柔 软性和韧性能够产生金属撕裂，使金属在完成切削 前流动至刀具前端。本质上柔软而坚韧的金属往往 会被加入合金从而牺牲它的延展性来提高加工性能。 如黄铜中加入铅钢中加入硫磺。 23 Machinability Machinability is a term used to indicate the rel