【正文】 ions show that lowcarbon ferrite nucleates and grows, leaving the remaining austenite richer in carbon.在較高溫度時(shí)，這種材料全部是奧氏體，但隨著冷卻就進(jìn)入到鐵素體和奧氏體穩(wěn)定狀態(tài)的區(qū)域。 The iron wants to change from the FCC austenite structure to the BCC ferrite structure, but the ferrite can only contain % carbon in solid solution. 鐵需要從面心立方體奧氏體結(jié)構(gòu)轉(zhuǎn)變?yōu)轶w心立方體鐵素體結(jié)構(gòu)，%的碳。? A Simplified Ironcarbon Diagram簡(jiǎn)化鐵碳狀態(tài)圖 If we focus only on the materials normally known as steels, a simplified diagram is often used. 如果只把注意力集中于一般所說(shuō)的鋼上，經(jīng)常要用到簡(jiǎn)化鐵碳狀態(tài)圖。Heat treatment is the operation of heating and cooling a metal in its solid state to change its physical properties. According to the procedure used, steel can be hardened to resist cutting action and abrasion, or it can be softened to permit machining. 熱處理是將金屬在固態(tài)加熱和冷卻以改變其物理性能的操作。而某些特別制造的聚合物能經(jīng)受住高達(dá)300℃(572℉)的溫度。 Some important characteristics of polymers include their size (or molecular weight), softening and melting points, crystallinity, and structure. The mechanical properties of polymers generally include low strength and high toughness. Their strength is often improved using reinforced posite structures. 聚合材料具有一些重要特性，包括尺寸(或分子量)、軟化及熔化點(diǎn)、結(jié)晶度和結(jié)構(gòu)。 Fibers have a very high modulus along their axis, but have a low modulus perpendicular to their axis. Fiber posite manufacturers often rotate layers of fibers to avoid directional variations in the modulus. 纖維在沿著其軸向有很高的模量，但垂直于其軸向的模量卻較低。For example: polymer/ceramic posites have a greater modulus than the polymer ponent, but aren’t as brittle as ceramics. Two types of posites are: fiberreinforced posites and particlereinforced posites.例如：聚合物/陶瓷復(fù)合材料具有比聚合物成分更大的模量，但又不像陶瓷那樣易碎。在這樣的溫度下，粉末內(nèi)部起反應(yīng)去除孔隙并得到十分致密的物品。 and a few special ceramics are superconductors at very low temperatures. Ceramics and glasses have one major drawback: they are brittle.許多陶瓷都是電和熱的良絕緣體。? Ceramics and Glasses陶瓷和玻璃 A ceramic is often broadly defined as any inorganic nonmetallic material． By this definition, ceramic materials would also include glasses。在金屬內(nèi)部，原子的外層階電子由所有原子共享并能到處自由移動(dòng)。金屬一般能在有缺口和凹痕的情況下不顯著削弱，并且能抵抗沖擊。 Why are metals and alloys used? Many metals and alloys have high densities and are used in applications which require a high masstovolume ratio. 為什么要使用金屬和合金？許多金屬和合金具有高密度，因此被用在需要較高質(zhì)量體積比的場(chǎng)合。Some metals, such as iron, cobalt and nickel, are magnetic. At low temperatures, some metals and intermetallic pounds bee superconductors.某些金屬能被磁化，例如鐵、鈷和鎳?？茖W(xué)家常根據(jù)狀態(tài)將材料分為：固體、液體或氣體。2那些用于加工制造并成為產(chǎn)品組成部分的就是工程材料。例如電線中的銅和制造烹飪箔及飲料罐的鋁。 What are some important properties of metals? Density is defined as a material’s mass divided by its volume. Most metals have relatively high densities, especially pared to polymers. 金屬有哪些重要特性？ 密度定義為材料的質(zhì)量與其體積之比。作為工程師，設(shè)計(jì)時(shí)通常要使材料在正常條件下不變形。沒有光子能通過(guò)金屬。 A glass is an inorganic nonmetallic material that does not have a crystalline structure. Such materials are said to be amorphous. 玻璃是沒有晶體狀結(jié)構(gòu)的無(wú)機(jī)非金屬材料。 Ceramics are not typically formed from the melt. This is because most ceramics will crack extensively (. form a powder) upon cooling from the liquid state. 陶瓷一般不是由熔化形成的。Because the refractive index of the core glass is greater than that of the cladding, light traveling in the core glass will remain in the core glass due to total internal reflection as long as the light strikes the core/cladding interface at an angle greater than the critical angle. 由于核心玻璃的折射指數(shù)比覆層大，只要在全內(nèi)反射過(guò)程中光線照射核心/覆層分界面的角度比臨界角大，在核心玻璃中傳送的光線將仍保留在核心玻璃中。纖維能加強(qiáng)基材的模量。 Particles are used to increase the modulus of the matrix, to decrease the permeability of the matrix, to decrease the ductility of the matrix. An example of particlereinforced posites is an automobile tire which has carbon black particles in a matrix of polyisobutylene elastomeric polymer. 微粒用于增加基材的模量、減少基材的滲透性和延展性。Important Characteristics of Polymers Size. Single polymer molecules typically have molecular weights between 10,000 and 1,000,000g/mol—that can be more than 2,000 repeating units depending on the polymer structure! 聚合材料的重要特性 尺寸：?jiǎn)蝹€(gè)聚合物分子一般分子量為10,000到1,000,000g/mol之間，具體取決于聚合物的結(jié)構(gòu)—這可以比2,000個(gè)重復(fù)單元還多。熱可塑性材料可以重新形成和循環(huán)使用，而熱固性與彈性材料則是不能再使用的。因?yàn)槟承┰?尤其是碳)的微小百分比極大地影響物理性能，所以必須知道對(duì)鋼的分析。 The key transition described in this diagram is the deposition of singlephase austenite(γ) to the twophase ferrite plus carbide structure as temperature drops. 在此圖中描述的關(guān)鍵轉(zhuǎn)變是單相奧氏體(γ) 隨著溫度下降分解成兩相鐵素體加滲碳體組織結(jié)構(gòu)。 Since this chemical separation of the carbon ponent occurs entirely in the solid state, the resulting structure is a fine mechanical mixture of ferrite and cementite. Specimens prepared by polishing and etching in a weak solution of nitric acid and alcohol reveal the lamellar structure of alternating plates that forms on slow cooling. 由于這種碳成分的化學(xué)分離完全發(fā)生在固態(tài)中，產(chǎn)生的組織結(jié)構(gòu)是一種細(xì)致的鐵素體與滲碳體的機(jī)械混合物。作為結(jié)果的組織結(jié)構(gòu)是初步的共析鐵素體(在共析反應(yīng)前的鐵素體)和部分珠光體的混合物。因?yàn)闆]有足夠的時(shí)間讓正常的狀態(tài)反應(yīng)發(fā)生，在這種情況下對(duì)工程分析而言狀態(tài)圖不再是有用的工具。如果鋼被加熱得太快，其外部比內(nèi)部熱就不能得到均勻的組織結(jié)構(gòu)。Above this point the hardness can be increased only slightly, because steels above the eutectoid point are made up entirely of pearlite and cementite in the annealed state. Pearlite responds best to heattreating operations。但油淬情況就不是如此，因?yàn)橛痛銜r(shí)在淬火臨界階段零件表面的溫度可能仍然很高。低溫回火， 300℉到400℉(150℃~205℃)，不會(huì)引起硬度下降很多，主要用于減少內(nèi)部應(yīng)變。 Two special processes using interrupted quenching are a form of tempering. In both, the hardened steel is quenched in a salt bath held at a selected lower temperature before being allowed to cool. These processes, known as austempering and martempering, result in products having certain desirable physical properties. 兩種采用中斷淬火的特殊工藝也是回火的形式。 for carbon steels it can be obtained readily from the partial ironiron carbide equilibrium diagram. When the annealing temperature has been reached, the steel should be held there until it is uniform throughout. 給定的鋼其退火溫度取決于它的成分；對(duì)碳鋼而言可容易地從局部的鐵碳合金平