UNIT 1 Advanced Engineering Materials

第一單元 先進(jìn)的工程材料

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Types of Materials ?
材料的類型

????????Materials may be grouped in several ways. Scientists often classify materials by their state: solid, liquid, or gas. They also separate them into organic (once living) and inorganic (never living) materials.

????????材料可以按多種方法分類?？茖W(xué)家常根據(jù)狀態(tài)將材料分為：固體、液體或氣體。他們也把材料分為有機(jī)材料(曾經(jīng)有生命的)和無機(jī)材料(從未有生命的)。

???????For industrial purposes, materials are divided into engineering materials or nonengineering materials. Engineering materials are those used in manufacture and become parts of products.

???????就工業(yè)效用而言，材料被分為工程材料和非工程材料。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。

Nonengineering materials are the chemicals, fuels, lubricants, and other materials used in the manufacturing process, which do not become part of the product.

非工程材料則是化學(xué)品、燃料、潤(rùn)滑劑以及其它用于加工制造過程但不成為產(chǎn)品組成部分的材料。

????????Engineering materials may be further subdivided into: ①M(fèi)etal ②Ceramics ③Composite ④Polymers, etc.

????????工程材料還能進(jìn)一步細(xì)分為：①金屬材料②陶瓷材料③復(fù)合材料?④聚合材料，等等。

Metals?and Metal Alloys
金屬和金屬合金

???????Metals are elements that generally have good electrical and thermal conductivity. Many metals have high strength, high stiffness, and have good ductility.

???????金屬就是通常具有良好導(dǎo)電性和導(dǎo)熱性的元素。許多金屬具有高強(qiáng)度、高硬度以及良好的延展性。

Some metals, such as iron, cobalt and nickel, are magnetic. At low temperatures, some metals and intermetallic compounds become superconductors.

某些金屬能被磁化，例如鐵、鈷和鎳。在極低的溫度下，某些金屬和金屬化合物能轉(zhuǎn)變成超導(dǎo)體。

???????What is the difference between an alloy and a pure metal? Pure metals are elements which come from a particular area of the periodic table. Examples of pure metals include copper in electrical wires and aluminum in cooking foil and beverage cans.

???????合金與純金屬的區(qū)別是什么？純金屬是在元素周期表中占據(jù)特定位置的元素。例如電線中的銅和制造烹飪箔及飲料罐的鋁。

Alloys contain more than one metallic element. Their properties can be changed by changing the elements present in the alloy. Examples of metal alloys include stainless steel which is an alloy of iron, nickel, and chromium; and gold jewelry which usually contains an alloy of gold and nickel.

合金包含不止一種金屬元素。合金的性質(zhì)能通過改變其中存在的元素而改變。金屬合金的例子有：不銹鋼是一種鐵、鎳、鉻的合金，以及金飾品通常含有金鎳合金。

?????????Why are metals and alloys used? Many metals and alloys have high densities and are used in applications which require a high mass-to-volume 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 metal alloys, such as those based on aluminum, have low densities and are used in aerospace applications for fuel economy. Many alloys also have high fracture toughness, which means they can withstand impact and are durable.

某些金屬合金，例如鋁基合金，其密度低，可用于航空航天以節(jié)約燃料。許多合金還具有高斷裂韌性，這意味著它們能經(jīng)得起沖擊并且是耐用的。

????????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 compared 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。大多數(shù)金屬密度相對(duì)較高，尤其是和聚合物相比較而言。

Materials with high densities often contain atoms with high atomic numbers, such as gold or lead. However, some metals such as aluminum or magnesium have low densities, and are used in applications that require other metallic properties but also require low weight.

高密度材料通常由較大原子序數(shù)原子構(gòu)成，例如金和鉛。然而，諸如鋁和鎂之類的一些金屬則具有低密度，并被用于既需要金屬特性又要求重量輕的場(chǎng)合。

????????Fracture toughness?can be described as a material’s ability to avoid fracture, especially when a flaw is introduced. Metals can generally contain nicks and dents without weakening very much, and are impact resistant. A football player counts on this when he trusts that his facemask won’t shatter.

???????斷裂韌性可以描述為材料防止斷裂特別是出現(xiàn)缺陷時(shí)不斷裂的能力。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。橄欖球運(yùn)動(dòng)員據(jù)此相信他的面罩不會(huì)裂成碎片。

????????Plastic deformation?is the ability of bend or deform before breaking. As engineers, we usually design materials so that they don’t deform under normal conditions. You don’t want your car to lean to the east after a strong west wind.

???????塑性變形就是在斷裂前彎曲或變形的能力。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。沒有人愿意一陣強(qiáng)烈的西風(fēng)過后自己的汽車向東傾斜。

However, sometimes we can take advantage of plastic deformation. The crumple zones in a car absorb energy by undergoing plastic deformation before they break.

然而，有時(shí)我們也能利用塑性變形。汽車上壓皺的區(qū)域在它們斷裂前通過經(jīng)歷塑性變形來吸收能量。

???????The atomic bonding of metals also affects their properties. In metals, the outer valence electrons are shared among all atoms, and are free to travel everywhere. Since electrons conduct heat and electricity, metals make good cooking pans and electrical wires.

???????金屬的原子連結(jié)對(duì)它們的特性也有影響。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)。由于電子能導(dǎo)熱和導(dǎo)電，所以用金屬可以制造好的烹飪鍋和電線。

It is impossible to see through metals, since these valence electrons absorb any photons of light which reach the metal. No photons pass through.

因?yàn)檫@些階電子吸收到達(dá)金屬的光子，所以透過金屬不可能看得見。沒有光子能通過金屬。

????????Alloys?are compounds consisting of more than one metal. Adding other metals can affect the density, strength, fracture toughness, plastic deformation, electrical conductivity and environmental degradation.

???????合金是由一種以上金屬組成的混合物。加一些其它金屬能影響密度、強(qiáng)度、斷裂韌性、塑性變形、導(dǎo)電性以及環(huán)境侵蝕。

For example, adding a small amount of iron to aluminum will make it stronger. Also, adding some chromium to steel will slow the rusting process, but will make it more brittle.

例如，往鋁里加少量鐵可使其更強(qiáng)。同樣，在鋼里加一些鉻能減緩它的生銹過程，但也將使它更脆。

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; however, many materials scientists add the stipulation that “ceramic” must also be crystalline.

???????陶瓷通常被概括地定義為無機(jī)的非金屬材料。照此定義，陶瓷材料也應(yīng)包括玻璃；然而許多材料科學(xué)家添加了“陶瓷”必須同時(shí)是晶體物組成的約定。

???????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)的無機(jī)非金屬材料。這種材料被稱為非結(jié)晶質(zhì)材料。

Properties of Ceramics and Glasses

????????Some of the useful properties of ceramics and glasses include high melting temperature, low density, high strength, stiffness, hardness, wear resistance, and corrosion resistance.

陶瓷和玻璃的特性

???????高熔點(diǎn)、低密度、高強(qiáng)度、高剛度、高硬度、高耐磨性和抗腐蝕性是陶瓷和玻璃的一些有用特性。

Many ceramics are good electrical and thermal insulators. Some ceramics have special properties: some ceramics are magnetic materials; some are ?piezoelectric materials; 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。某些陶瓷還具有一些特殊性能：有些是磁性材料，有些是壓電材料，還有些特殊陶瓷在極低溫度下是超導(dǎo)體。陶瓷和玻璃都有一個(gè)主要的缺點(diǎn)：它們?nèi)菀灼扑椤?/span>

????????Ceramics are not typically formed from the melt. This is because most ceramics will crack extensively (i.e. form a powder) upon cooling from the liquid ?state.

???????陶瓷一般不是由熔化形成的。因?yàn)榇蠖鄶?shù)陶瓷在從液態(tài)冷卻時(shí)將會(huì)完全破碎(即形成粉末)。

Hence, all ?the simple and efficient manufacturing techniques used for glass production such as casting and blowing, which involve the molten state, cannot be used for the production of crystalline ceramics. Instead, “sintering” or “firing” is the process typically used.

因此，所有用于玻璃生產(chǎn)的簡(jiǎn)單有效的—諸如澆鑄和吹制這些涉及熔化的技術(shù)都不能用于由晶體物組成的陶瓷的生產(chǎn)。作為替代，一般采用“燒結(jié)”或“焙燒”工藝。

In sintering, ceramic powders are processed into compacted shapes and then heated to temperatures just below the melting point. At such temperatures, the powders react internally to remove porosity and fully dense articles can be obtained.

在燒結(jié)過程中，陶瓷粉末先擠壓成型然后加熱到略低于熔點(diǎn)溫度。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。

???????An optical fiber contains three layers: a core made of highly pure glass with a high refractive index for the light to travel, a middle layer of glass with a lower refractive index known as the cladding which protects the core glass from scratches and other surface imperfections, and an out polymer jacket to protect the fiber from damage. ?

???????光導(dǎo)纖維有三層：核心由高折射指數(shù)高純光傳輸玻璃制成，中間層為低折射指數(shù)玻璃，是保護(hù)核心玻璃表面不被擦傷和完整性不被破壞的所謂覆層，外層是聚合物護(hù)套，用于保護(hù)光導(dǎo)纖維不受損。

In order for the core glass to have a higher refractive index than the cladding, the core glass is doped with a small, controlled amount of an impurity, or dopant, which causes light to travel slower, but does not absorb the light.

為了使核心玻璃有比覆層大的折射指數(shù)，在其中摻入微小的、可控?cái)?shù)量的能減緩光速而不會(huì)吸收光線的雜質(zhì)或攙雜劑。

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。

The total internal reflection phenomenon, as well as ?the high ?purity of the core glass, enables light to travel ?long distances with little loss of intensity.

全內(nèi)反射現(xiàn)象與核心玻璃的高純度一樣，使光線幾乎無強(qiáng)度損耗傳遞長(zhǎng)距離成為可能。

Composites

復(fù)合材料

?????????Composites are formed from two or more types of materials. Examples include polymer/ceramic and metal/ceramic composites. Composites are used because overall properties of the composites are superior to ?those of the ?individual components.

???????復(fù)合材料由兩種或更多材料構(gòu)成。例子有聚合物/陶瓷和金屬/陶瓷復(fù)合材料。之所以使用復(fù)合材料是因?yàn)槠淙嫘阅軆?yōu)于組成部分單獨(dú)的性能。

For example: polymer/ceramic composites have a greater modulus than the polymer component, but aren’t as brittle as ceramics.

????????Two types of composites are: fiber-reinforced composites and particle-reinforced composites.

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。

???????復(fù)合材料有兩種：纖維加強(qiáng)型復(fù)合材料和微粒加強(qiáng)型復(fù)合材料。

Fiber-reinforced Composites

纖維加強(qiáng)型復(fù)合材料

?????????Reinforcing fibers can be made of metals, ceramics, glasses, or polymers that have been turned into graphite and known as carbon fibers. Fibers increase the modulus of the matrix material.

???????加強(qiáng)纖維可以是金屬、陶瓷、玻璃或是已變成石墨的被稱為碳纖維的聚合物。纖維能加強(qiáng)基材的模量。

The strong covalent bonds along the fiber’s length give them a very high modulus in this direction because to break or extend the fiber the bonds must also be broken or moved.

沿著纖維長(zhǎng)度有很強(qiáng)結(jié)合力的共價(jià)結(jié)合在這個(gè)方向上給予復(fù)合材料很高的模量，因?yàn)橐獡p壞或拉伸纖維就必須破壞或移除這種結(jié)合。

????????Fibers are difficult to process into composites, ?making fiber-reinforced composites relatively expensive.

???????把纖維放入復(fù)合材料較困難，這使得制造纖維加強(qiáng)型復(fù)合材料相對(duì)昂貴。

Fiber-reinforced composites are used in some of the most advanced, and therefore most expensive sports equipment, such as a time-trial racing bicycle frame which consists of carbon fibers in a thermoset polymer matrix.

纖維加強(qiáng)型復(fù)合材料用于某些最先進(jìn)也是最昂貴的運(yùn)動(dòng)設(shè)備，例如計(jì)時(shí)賽競(jìng)賽用自行車骨架就是用含碳纖維的熱固塑料基材制成的。

Body parts of race cars and some automobiles are composites made of glass fibers (or fiberglass) in a thermoset matrix.

競(jìng)賽用汽車和某些機(jī)動(dòng)車的車體部件是由含玻璃纖維(或玻璃絲)的熱固塑料基材制成的。

????????Fibers have a very high modulus along their axis, but have a low modulus ?perpendicular to their axis. Fiber composite 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。纖維復(fù)合材料的制造者往往旋轉(zhuǎn)纖維層以防模量產(chǎn)生方向變化。

Particle-reinforced composites

微粒加強(qiáng)型復(fù)合材料

????????Particles used for reinforcing include ?ceramics and glasses such as small ?mineral particles, metal particles such as ??aluminum, and amorphous materials, ???including polymers and carbon black.

???????用于加強(qiáng)的微粒包含了陶瓷和玻璃之類的礦物微粒，鋁之類的金屬微粒以及包括聚合物和碳黑的非結(jié)晶質(zhì)微粒。

????????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 particle-reinforced composites 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。微粒加強(qiáng)型復(fù)合材料的一個(gè)例子是機(jī)動(dòng)車胎，它就是在聚異丁烯人造橡膠聚合物基材中加入了碳黑微粒。

??Polymers ???聚合材料

????????A polymer has a repeating structure, ?usually based on a carbon backbone. The repeating structure results in large chainlike molecules. Polymers are useful because they are lightweight, corrosion resistant, easy to process at low ?temperatures and generally ?inexpensive.

???????聚合物具有一般是基于碳鏈的重復(fù)結(jié)構(gòu)。這種重復(fù)結(jié)構(gòu)產(chǎn)生鏈狀大分子。由于重量輕、耐腐蝕、容易在較低溫度下加工并且通常較便宜，聚合物是很有用的。

????????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 composite 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)。聚合材料的機(jī)械性能一般表現(xiàn)為低強(qiáng)度和高韌性。它們的強(qiáng)度通?？刹捎眉訌?qiáng)復(fù)合結(jié)構(gòu)來改善。

Important Characteristics of Polymers

聚合材料的重要特性

?????????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!

????????尺寸：單個(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。

The ?mechanical properties of a polymer are ?significantly affected by the molecular weight, with better engineering properties at higher molecular weights.

聚合物的分子量極大地影響其機(jī)械性能，分子量越大，工程性能也越好。

?????????Thermal ?transitions.?The softening ?point (glass transition temperature) and the melting ?point of a polymer will determine which it will be suitable for applications. These temperatures usually determine the upper limit for which a polymer can be used.

???????熱轉(zhuǎn)換性：聚合物的軟化點(diǎn)(玻璃狀轉(zhuǎn)化溫度)和熔化點(diǎn)決定了它是否適合應(yīng)用。這些溫度通常決定聚合物能否使用的上限。

For example, many industrially important polymers have glass transition temperatures near the boiling point of water (100℃, 212℉), and they are most useful for room temperature applications. Some specially engineered polymers can withstand temperatures as high as 300℃(572℉).

例如，許多工業(yè)上的重要聚合物其玻璃狀轉(zhuǎn)化溫度接近水的沸點(diǎn)(100℃, 212℉)，它們被廣泛用于室溫下。而某些特別制造的聚合物能經(jīng)受住高達(dá)300℃(572℉)的溫度。

????????Crystallinity.?Polymers can be ?crystalline or amorphous, but they usually ?have a combination of crystalline and amorphous structures (semi-crystalline).

???????結(jié)晶度：聚合物可以是晶體狀的或非結(jié)晶質(zhì)的，但它們通常是晶體狀和非結(jié)晶質(zhì)結(jié)構(gòu)的結(jié)合物(半晶體)。

????????Interchain interactions.?The polymer chains can be free to slide past one another (thermo-plastic) or they can be connected to each other with crosslinks (thermoset or elastomer). Thermo-plastics can be reformed and recycled, while thermosets and elastomers are not reworkable.

???????原子鏈間的相互作用：聚合物的原子鏈可以自由地彼此滑動(dòng)(熱可塑性)或通過交鍵互相連接(熱固性或彈性)。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。

????????Intrachain structure.?The chemical structure of the chains also has a tremendous effect on the properties. Depending on the structure the polymer may be hydrophilic or hydrophobic (likes ?or hates water), stiff or flexible, crystalline or amorphous, reactive or unreactive.

???????鏈內(nèi)結(jié)構(gòu)：原子鏈的化學(xué)結(jié)構(gòu)對(duì)性能也有很大影響。根據(jù)各自的結(jié)構(gòu)不同，聚合物可以是親水的或憎水的(喜歡或討厭水)、硬的或軟的、晶體狀的或非結(jié)晶質(zhì)的、易起反應(yīng)的或不易起反應(yīng)的

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UNIT 2 Heat treatment of metals

金屬的熱處理

??????????The understanding of heat treatment is embraced by the broader study of metallurgy. Metallurgy is the physics, chemistry, and engineering related to metals from ore extraction to the final product.

???????對(duì)熱處理的理解包含于對(duì)冶金學(xué)較廣泛的研究。冶金學(xué)是物理學(xué)、化學(xué)和涉及金屬?gòu)牡V石提煉到最后產(chǎn)物的工程學(xué)。

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。按所采用的步驟，鋼可以通過硬化來抵抗切削和磨損，也可以通過軟化來允許機(jī)加工。

With the proper heat treatment internal stresses may be removed, grain size reduced, toughness increased, or a hard surface produced on a ductile interior. The analysis of the steel must be known because small percentages of certain ?elements, notably carbon, greatly affect the physical properties.

使用合適的熱處理可以去除內(nèi)應(yīng)力、細(xì)化晶粒、增加韌性或在柔軟材料上覆蓋堅(jiān)硬的表面。因?yàn)槟承┰?/span>(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。

???????Alloy steel owe their properties to the presence of one or more elements other than carbon, namely nickel, chromium, manganese, molybdenum, tungsten, silicon, vanadium, and copper. Because of their improved physical properties they are used commercially in many ways not possible with carbon steels.

???????合金鋼的性質(zhì)取決于其所含有的除碳以外的一種或多種元素，如鎳、鉻、錳、鉬、鎢、硅、釩和銅。由于合金鋼改善的物理性能，它們被大量使用在許多碳鋼不適用的地方。

???????The following discussion applies principally to the heat treatment of ordinary commercial steels known as plain carbon steels. With this process the rate of ?cooling is the controlling factor, rapid cooling from above the critical range ?results in hard structure, whereas very ?slow cooling produces the opposite effect.

???????下列討論主要針對(duì)被稱為普通碳鋼的工業(yè)用鋼而言。熱處理時(shí)冷卻速率是控制要素，從高于臨界溫度快速冷卻導(dǎo)致堅(jiān)硬的組織結(jié)構(gòu)，而緩慢冷卻則產(chǎn)生相反效果。

A Simplified Iron-carbon Diagram

簡(jiǎn)化的鐵碳狀態(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的鋼上，經(jīng)常要用到簡(jiǎn)化的鐵碳狀態(tài)圖。

Those portions of the iron-carbon diagram near the delta region and those above 2% carbon content are of little importance to the engineer and are deleted. A simplified diagram, such as the one in Fig.2.1, focuses on the eutectoid region and is quite useful in understanding the properties and processing of steel.

鐵碳的狀態(tài)圖中靠近三角區(qū)和含碳量高于2%的那些部分對(duì)工程師而言不重要，因此將它們刪除。如圖2.1所示的簡(jiǎn)化的鐵碳狀態(tài)圖將焦點(diǎn)集中在共析區(qū)，這對(duì)理解鋼的性能和處理是十分有用的。

????????The key transition described in this diagram is the decomposition of single-phase austenite(γ) to the two-phase ?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)。

Control of this reaction, which arises due to the drastically different carbon solubility of austenite and ferrite, enables a wide range of properties to be achieved through heat treatment.

控制這一由于奧氏體和鐵素體的碳溶解性完全不同而產(chǎn)生的反應(yīng)，使得通過熱處理能獲得很大范圍的特性。

?????????To begin to understand these ?processes, consider a steel of the ?eutectoid composition, 0.77% carbon, being slow cooled along line x-x’ in Fig.2.1. ?At the upper temperatures, only austenite is present, the 0.77% carbon being dissolved in solid solution with the iron. When the steel cools to 727℃(1341℉), several changes occur simultaneously.

???????為了理解這些過程，考慮含碳量為0.77%的共析鋼，沿著圖2.1的x-x’線慢慢冷卻。在較高溫度時(shí)，只存在奧氏體，0.77%的碳溶解在鐵里形成固溶體。當(dāng)鋼冷卻到727℃?(1341℉)時(shí)，將同時(shí)發(fā)生若干變化。

??????The iron wants to change from the FCC austenite structure to the BCC ferrite structure, but the ferrite can only contain 0.02% carbon in solid solution.

???????鐵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)，但是鐵素體只能容納固溶體狀態(tài)的0.02%的碳。

The rejected carbon forms the carbon-rich cementite intermetallic with composition Fe3C. In essence, the net reaction at the eutectoid is austenite 0.77%C→ferrite 0.02%C+cementite 6.67%C.

被析出的碳與金屬化合物Fe3C形成富碳的滲碳體。本質(zhì)上，共析體的基本反應(yīng)是奧氏體0.77%的碳→鐵素體0.02%的碳+滲碳體6.67%的碳。

???????Since this chemical separation of the carbon component 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。通過打磨并在弱硝酸酒精溶液中蝕刻制備的樣本顯示出由緩慢冷卻形成的交互層狀的薄片結(jié)構(gòu)。

This structure is composed of two distinct phases, but has its own set of characteristic properties and goes by the name pearlite, because of its resemblance to mother- of- pearl at low magnification.

這種結(jié)構(gòu)由兩種截然不同的狀態(tài)組成，但它本身具有一系列特性，且因與低倍數(shù)放大時(shí)的珠母層有類同之處而被稱為珠光體。

????????Steels having less than the eutectoid amount of carbon (less than 0.77%) are known as hypo-eutectoid steels. Consider now the transformation of such a material represented by cooling along line y-y’ in Fig.2.1.

???????含碳量少于共析體(低于0.77%)的鋼稱為亞共析鋼?，F(xiàn)在來看這種材料沿著圖2.1中y-y’ 線冷卻的轉(zhuǎn)變情況。

At high temperatures, the material is entirely austenite, but upon cooling enters a region where the stable phases are ferrite and austenite. Tie-line and level-law calculations show that low-carbon 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。由截線及杠桿定律分析可知，低碳鐵素體成核并長(zhǎng)大，剩下含碳量高的奧氏體。

At 727℃(1341℉), the austenite is of eutectoid composition (0.77% carbon) ?and further cooling transforms the remaining austenite to pearlite. The resulting structure is a mixture of primary or pro-eutectoid ferrite (ferrite that formed ?above the eutectoid reaction) and regions ?of pearlite.

在727℃(1341℉)時(shí)，奧氏體為共析組成(含碳量0.77%)，再冷卻剩余的奧氏體就轉(zhuǎn)化為珠光體。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。

????????Hypereutectoid steels are steels that contain greater than the eutectoid amount of carbon. When such steel cools, as shown in z-z’ of Fig.2.1 the process is similar to the hypo-eutectoid case, except that the primary or pro-eutectoid phase is now cementite instead of ferrite.

???????過共析鋼是含碳量大于共析量的鋼。當(dāng)這種鋼冷卻時(shí)，就像圖2.1的z-z’線所示，除了初步的共析狀態(tài)用滲碳體取代鐵素體外，其余類似亞共析鋼的情況。

As the carbon-rich phase forms, the remaining austenite decreases in carbon content, reaching the eutectoid composition at 727℃(1341℉). As before, any remaining austenite transforms to pearlite upon slow cooling through this temperature.

隨著富碳部分的形成，剩余奧氏體含碳量減少，在727℃(1341℉)時(shí)達(dá)到共析組織。就像以前說的一樣，當(dāng)緩慢冷卻到這溫度時(shí)所有剩余奧氏體轉(zhuǎn)化為珠光體。

????????It should be remembered that the transitions that have been described by the phase diagrams are for equilibrium conditions, which can be approximated by slow cooling. With slow heating, these transitions occur in the reverse ?manner.

???????應(yīng)該記住由狀態(tài)圖描述的這種轉(zhuǎn)化只適合于通過緩慢冷卻的近似平衡條件。如果緩慢加熱，則以相反的方式發(fā)生這種轉(zhuǎn)化。

However, when alloys are cooled rapidly, entirely different results may be obtained, because sufficient time is not provided for the normal phase reactions to occur, in ?such cases, the phase diagram is no ?longer a useful tool for engineering ?analysis.

然而，當(dāng)快速冷卻合金時(shí)，可能得到完全不同的結(jié)果。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。

??Hardening

??淬火

????????Hardening is the process of heating a piece of steel to a temperature within or above its critical range and then cooling it rapidly.

???????淬火就是把鋼件加熱到或超過它的臨界溫度范圍，然后使其快速冷卻的過程。

If the carbon content of the steel is known, the proper temperature to which the steel should be heated may be obtained by reference to the iron-iron carbide phase diagram. However, if the composition of the steel is unknown, a little preliminary experimentation may be necessary to determine the range.

如果鋼的含碳量已知，鋼件合適的加熱溫度可參考鐵碳合金狀態(tài)圖得到。然而當(dāng)鋼的成分不知道時(shí)，則需做一些預(yù)備試驗(yàn)來確定其溫度范圍。?

A good procedure to follow is to heat-quench a number of small specimens of the steel at various temperatures and observe the result, either by hardness testing or by microscopic examination. When the correct temperature is obtained, there will be a marked change in hardness and other properties.

要遵循的合適步驟是將這種鋼的一些小試件加熱到不同的溫度后淬火，再通過硬度試驗(yàn)或顯微鏡檢查觀測(cè)結(jié)果。一旦獲得正確的溫度，硬度和其它性能都將有明顯的變化。?

????????In any heat-treating operation the rate of heating is important. Heat flows from the exterior to the interior of steel at a definite rate. If the steel is heated too fast, the outside becomes hotter than the interior and uniform structure cannot be obtained.

???????在任何熱處理作業(yè)中，加熱的速率都是重要的。熱量以一定的速率從鋼的外部傳導(dǎo)到內(nèi)部。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)。

If a piece is irregular in shape, a slow rate is all the more essential to eliminate warping and cracking. The heavier the section, the longer must be the heating time to achieve uniform results.

如果工件形狀不規(guī)則，為了消除翹曲和開裂最根本的是加熱速率要緩慢。截面越厚，加熱的時(shí)間就要越長(zhǎng)才能達(dá)到均勻的結(jié)果。

Even after the correct temperature has been reached, the piece should be held at that temperature for a sufficient period of time to permit its thickest section to attain a uniform temperature.

即使加熱到正確的溫度后，工件也應(yīng)在此溫度下保持足夠時(shí)間以讓其最厚截面達(dá)到相同溫度。

????????The hardness obtained from a given treatment depends on the quenching rate, the carbon ?content, and the work size. In alloy steels the kind and amount of alloying element influences only the hardenability (the ability of the workpiece to be hardened to depths) of the steel and does not affect the hardness except in unhardened or partially hardened steels.

???????通過給定的熱處理所得到的硬度取決于淬火速率、含碳量和工件尺寸。除了非淬硬鋼或部分淬硬鋼外，合金鋼中合金元素的種類及含量?jī)H影響鋼的淬透性(工件被硬化到深層的能力)而不影響硬度。

?????????Steel with low carbon content will not respond appreciably to hardening treatment. As the carbon content in steel increases up to around 0.60%, the possible hardness obtainable also increases.

???????含碳量低的鋼對(duì)淬火處理沒有明顯的反應(yīng)。隨著鋼的含碳量增加到大約0.60%，可能得到的硬度也增加。

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 heat-treating operations; and steel composed mostly of pearlite can be transformed into a hard steel.

高于此點(diǎn)，由于超過共析點(diǎn)鋼完全由珠光體和退火狀態(tài)的滲碳體組成，硬度增加并不多。珠光體對(duì)熱處理作業(yè)響應(yīng)最好；基本由珠光體組成的鋼能轉(zhuǎn)化成硬質(zhì)鋼。

?????????As the size of parts to be hardened increases, the surface hardness decreases somewhat even though all other conditions have remained the same. There is a limit to the rate of heat flow through steel.

???????即使所有其它條件保持不變，隨著要淬火的零件尺寸的增加其表面硬度也會(huì)有所下降。熱量在鋼中的傳導(dǎo)速率是有限的。

No matter how cool the quenching medium may be, if the heat inside a large piece cannot escape faster than a certain critical rate, there is a definite limit to the inside hardness. However, brine or water quenching is capable of rapidly bringing the surface of the quenched part to its own temperature and maintaining it at or close to this temperature.

無論淬火介質(zhì)怎么冷，如果在大工件中的熱量不能比特定的臨界速率更快散發(fā)，那它內(nèi)部硬度就會(huì)受到明確限制。然而鹽水或水淬火能夠?qū)⒈淮懔慵谋砻嫜杆倮鋮s至本身溫度并將其保持或接近此溫度。

Under these circumstances there would always be some finite depth of surface hardening regardless of size. This is not true in oil quenching, when the surface temperature may be high during the critical stages of quenching.

在這種情況下不管零件尺寸如何，其表面總歸有一定深度被硬化。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。

??Tempering ??

???回火

????????Steel that has been hardened by rapid quenching is brittle and not suitable for most uses. By tempering or drawing, the hardness and brittleness may be reduced to the desired point for service conditions．

???????快速淬火硬化的鋼是硬而易碎的，不適合大多數(shù)場(chǎng)合使用。通過回火，硬度和脆性可以降低到使用條件所需要的程度。

As these properties are reduced there is also a decrease in tensile strength and an increase in the ductility and toughness of the steel. The operation consists of reheating quench-hardened steel to some temperature below the critical range followed by any rate of cooling.

隨著這些性能的降低，拉伸強(qiáng)度也降低而鋼的延展性和韌性則會(huì)提高?；鼗鹱鳂I(yè)包括將淬硬鋼重新加熱到低于臨界范圍的某一溫度然后以任意速率冷卻。

Although this process softens steel, it differs considerably from annealing in that the process lends itself to close control of the physical properties and in most cases does not soften the steel to the extent that annealing would. The final structure obtained from tempering a fully hardened steel is called tempered martensite.

雖然這過程使鋼軟化，但它與退火是大不相同的，因?yàn)榛鼗疬m合于嚴(yán)格控制物理性能并在大多數(shù)情況下不會(huì)把鋼軟化到退火那種程度?；鼗鹜耆阌蹭摰玫降淖罱K組織結(jié)構(gòu)被稱為回火馬氏體。

????????Tempering is possible because of the instability of the martensite, the principal constituent of hardened steel. Low-temperature draws, from 300℉?to 400℉?(150℃~205℃), do not cause much decrease in hardness and are used principally to relieve internal strains.

???????由于馬氏體這一淬硬鋼主要成分的不穩(wěn)定性，使得回火成為可能。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。?

As the tempering temperatures are increased, the breakdown of the martensite takes place at a faster rate, and at about 600℉(315℃) the change to a structure called tempered martensite is very rapid. The tempering operation may be described as one of precipitation and agglomeration or coalescence of ?cementite.

隨著回火溫度的提高，馬氏體以較快的速率分解，并在大約600℉(315℃)迅速轉(zhuǎn)變?yōu)楸环Q為回火馬氏體的結(jié)構(gòu)。回火作業(yè)可以描述為滲碳體析出和凝聚或聚結(jié)的過程。?

A substantial precipitation of cementite begins at 600℉(315℃), which produces a decrease in hardness. Increasing the temperature causes coalescence of the carbides with continued decrease in hardness.

滲碳體的大量析出開始于600℉(315℃)，這使硬度下降。溫度的上升會(huì)使碳化物聚結(jié)而硬度繼續(xù)降低。

????????In the process of tempering, some consideration should be given to time as well as to temperature. Although most of the softening action occurs in the first few minutes after the temperature is reached, there is some additional reduction in hardness if the temperature is maintained for a prolonged time.

???????在回火過程中，不但要考慮溫度而且要考慮時(shí)間。雖然大多數(shù)軟化作用發(fā)生在達(dá)到所需溫度后的最初幾分鐘，但如果此溫度維持一段延長(zhǎng)時(shí)間，仍會(huì)有些額外的硬度下降。

Usual practice is to heat the steel to the desired temperature and hold it there only long enough to have it uniformly heated.

通常的做法是將鋼加熱到所需溫度并且僅保溫到正好使其均勻受熱。

???????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。這兩種工藝中，淬硬鋼在其被允許冷卻前先在一選定的較低溫度鹽浴淬火。這兩種分別被稱為奧氏體回火和馬氏體回火的工藝，能使產(chǎn)品具有特定所需的物理性能。?

??Annealing ???

??退火

??????The primary purpose of annealing is to soften hard steel so that it may be machined or cold worked.

???????退火的主要目的是使堅(jiān)硬的鋼軟化以便機(jī)加工或冷作。

This is usually accomplished by heating the steel too slightly above the critical temperature, holding it there until the ?temperature of the piece is uniform ?throughout, and then cooling at a slowly controlled rate so that the temperature of the surface and that of the center of the piece are approximately the same.

通常是非常緩慢地將鋼加熱到臨界溫度以上，并將其在此溫度下保持到工件全部均勻受熱，然后以受控的速率慢慢地冷卻，這樣使得工件表面和內(nèi)部的溫度近似相同。

This process is known as full annealing because it wipes out all trace of previous structure, refines the crystalline structure, and softens the metal. Annealing also ?relieves internal stresses previously set up in the metal.

這過程被稱為完全退火，因?yàn)樗コ艘郧敖M織結(jié)構(gòu)的所有痕跡、細(xì)化晶粒并軟化金屬。退火也釋放了先前在金屬中的內(nèi)應(yīng)力。

???????The temperature to which a given steel should be heated in annealing depends on its composition; for carbon steels it can be obtained readily from the partial iron-iron 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衡圖得到。達(dá)到退火溫度后，鋼應(yīng)當(dāng)保持在此溫度等到全部均勻受熱。

This usually takes about 45min for each inch(25mm) of thickness of the largest section. For maximum softness and ductility the cooling rate should be very slow, such as allowing the parts to cool down with the furnace. The higher the ?carbon content, the slower this rate must be.

加熱時(shí)間一般以工件的最大截面厚度計(jì)每英寸(25mm )大約需45min。為了得到最大柔軟性和延展性冷卻速率應(yīng)該很慢，比如讓零件與爐子一起冷下來。含碳量越高，冷卻的速率必須越慢。

The heating rate should be consistent with the size and uniformity of sections, so that the entire part is brought up to temperature as uniformly as possible.

加熱的速率也應(yīng)與截面的尺寸及均勻程度相協(xié)調(diào)，這樣才能使整個(gè)零件盡可能均勻地加熱。

Normalizing and Spheroidizing
正火和球化

????????The process of normalizing consists of heating the steel about 50℉?to 100℉??(10℃~40℃) above the upper critical range and cooling in still air to room temperature.

???????正火處理包括先將鋼加熱到高于上臨界區(qū)50℉到100℉(10℃~40℃)然后在靜止的空氣中冷卻到室溫。

This process is principally used with low- and medium-carbon steels as well as alloy steels to make the grain structure more uniform, to relieve internal stresses, or to achieve desired results in physical properties. Most commercial steels are normalized after being rolled or cast.

退火主要用于低碳鋼、中碳鋼及合金鋼，使晶粒結(jié)構(gòu)更均勻、釋放內(nèi)應(yīng)力或獲得所需的物理特性。大多數(shù)商業(yè)鋼材在軋制或鑄造后都要退火。

????????Spheroidizing is the process of producing a structure in which the cementite is in a spheroidal distribution. If steel is heated slowly to a temperature just below the critical range and held there for a prolonged period of time, this structure will be obtained.

???????球化是使?jié)B碳體產(chǎn)生成類似球狀分布結(jié)構(gòu)的工藝。如果把鋼緩慢加熱到恰好低于臨界溫度并且保持較長(zhǎng)一段時(shí)間，就能得到這種組織結(jié)構(gòu)。

The globular structure obtained gives improved machinability to the steel. This treatment is particularly useful for hypereutectoid steels that must be machined.

所獲得的球狀結(jié)構(gòu)改善了鋼的可切削性。此處理方法對(duì)必須機(jī)加工的過共析鋼特別有用。

Surface Hardening

表面硬化

Carburizing滲碳

????????The oldest known method of producing a hard surface on steel is case hardening or carburizing. Iron at temperatures close to and above its critical temperature has an affinity for carbon.

???????最早的硬化鋼表面的方法是表面淬火或滲碳。鐵在靠近并高于其臨界溫度時(shí)對(duì)碳具有親合力。

The carbon is absorbed into the metal to form a solid solution with iron and converts the outer surface into high-carbon steel. The carbon is gradually diffused to the interior of the part. The depth of the case depends on the time and temperature of the treatment.

碳被吸收進(jìn)金屬與鐵形成固溶體使外表面轉(zhuǎn)變成高碳鋼。碳逐漸擴(kuò)散到零件內(nèi)部。滲碳層的深度取決于熱處理的時(shí)間和溫度。

Pack carburizing consists of placing the parts to be treated in a closed container with some carbonaceous material such as charcoal or coke. It is a long process and used to produce fairly thick cases of from 0.03 to 0.16 in.(0.76~4.06mm) in depth.

固體滲碳的方法是將要處理的零件與木炭或焦炭這些含碳的材料一起放入密閉容器。這是一個(gè)較長(zhǎng)的過程，用于產(chǎn)生深度為0.03到0.16 英寸(0.76~4.06mm)這么厚的硬化層。?

???????Steel for carburizing is usually a low-carbon steel of about 0.15% carbon that would not in itself responds appreciably to heat treatment. In the course of the process the outer layer is converted into high-carbon steel with a content ranging from 0.9% to 1.2% carbon.

???????用于滲碳的一般是含碳量約為0.15%、本身不太適合熱處理的低碳鋼。在處理過程中外層轉(zhuǎn)化為含碳量從0.9%到1.2%的高碳鋼。?

????????A steel with varying carbon content and, consequently, different critical temperatures requires a special heat treatment.

???????含碳量變化的鋼具有不同的臨界溫度，因此需要特殊的熱處理。

Because there is some grain growth in the steel during the prolonged carburizing treatment, the work should be heated to the critical temperature of ?the core and then cooled, thus refining the core structure. The steel should then be reheated to a point above the transformation range of the case and ?quenched to produce a hard, fine structure.

由于在較長(zhǎng)的滲碳過程中鋼內(nèi)部會(huì)有些晶粒生長(zhǎng)，所以工件應(yīng)該加熱到核心部分的臨界溫度再冷卻以細(xì)化核心部分的組織結(jié)構(gòu)。然后重新加熱到高于外層轉(zhuǎn)變溫度再淬火以生成堅(jiān)硬、細(xì)致的組織結(jié)構(gòu)。

???????The lower heat-treating temperature of the case results from the fact that hypereutectoid steels are normally austenitized for hardening just above the lower critical point. A third tempering treatment may be used to reduce strains.

???????由于恰好高于低臨界溫度通常使過共析鋼奧氏體化而硬化，所以對(duì)外層采用較低的熱處理溫度。第三次回火處理可用于減少應(yīng)變。

Carbonitriding

碳氮共滲

??????Carbonitriding, sometimes known as dry cyaniding or nicarbing, is a case-hardening process in which the steel is held at a temperature above the critical range in a gaseous atmosphere from which it absorbs carbon and nitrogen.

???????碳氮共滲，有時(shí)也稱為干法氰化或滲碳氮化，是一種表面硬化工藝。通過把鋼放在高于臨界溫度的氣體中，讓它吸收碳和氮。

Any carbon-rich gas with ammonia can be used. The wear-resistant case produced ?ranges from 0.003 to 0.030 inch(0.08~ 0.76mm) in thickness. An advantage of carbonitriding is that the hardenability of the case is significantly increased when nitrogen is added, permitting the use of low-cost steels.

可以使用任何富碳?xì)怏w加氨氣，能生成厚度從0.003到0.030英寸(0.08~ 0.76mm)的耐磨外層。碳氮共滲的優(yōu)點(diǎn)之一是加入氮后外層的淬透性極大增加，為使用低價(jià)鋼提供條件。

Cyaniding

氰化

?????????Cyaniding, or liquid carbonitriding as it is sometimes called, is also a process that combines the absorption of carbon and nitrogen to obtain surface hardness in low-carbon steels that do not respond to ordinary heat treatment.

???????氰化，有時(shí)稱為液體碳氮共滲，也是一種結(jié)合了吸收碳和氮來獲得表面硬度的工藝，它主要用于不適合通常熱處理的低碳鋼。

The part to be case hardened is immersed in a bath of fused sodium cyanide salts at a temperature slightly above the Ac1?range, the duration of soaking depending on the depth of the case. The part is then quenched in water or oil to obtain a hard surface.

需表面硬化的零件浸沒在略高于Ac1溫度熔化的氰化鈉鹽溶液中，浸泡的持續(xù)時(shí)間取決于硬化層的深度。然后將零件在水或油中淬火。

Case depths of 0.005 to 0.015in. (0.13~0.38mm) may be readily obtained by this process. Cyaniding is used principally for the treatment of small parts.

通過這樣處理可以容易地獲得0.005到0.015英寸(0.13~0.38mm)的硬化深度。氰化主要用于處理小零件。

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Nitriding

滲氮

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????????Nitriding is somewhat similar to ordinary case hardening, but it uses a different material and treatment to create the hard surface constituents.

???????滲氮有些類似普通表面硬化，但它采用不同的材料和處理方法來產(chǎn)生堅(jiān)硬表面成分。

In this process the metal is heated to a temperature of around 950℉(510℃) and held there for a period of time in contact with ammonia gas.?Nitrogen from the gas ?is introduced into the steel, forming very ?hard nitrides that are finely dispersed through the surface metal.

這種工藝中金屬加熱到約950℉(510℃)，然后與氨氣接觸一段時(shí)間。氨氣中的氮進(jìn)入鋼內(nèi)，形成細(xì)微分布于金屬表面又十分堅(jiān)固的氮化物。

????????Nitrogen has greater hardening ability with certain elements than with others, hence, special nitriding alloy steels have been developed.

???????氮與某些元素的硬化能力比其它元素大，因此開發(fā)了專用的滲氮合金鋼。

Aluminum in the range of 1% to 1.5% has proved to be especially suitable in steel, in that it combines with the gas to form a very stable and hard constituent. The temperature of heating ranges from 925℉?to 1,050℉(495℃~565℃).

在鋼中含鋁1%到1.5%被證明特別合適，它能與氨氣結(jié)合形成很穩(wěn)定堅(jiān)固的成分。其加熱溫度范圍為925℉到1,050℉?(495℃~565℃)。

????????Liquid nitriding utilizes molten cyanide salts ?and, as in gas nitriding, the temperature is held below the transformation range. Liquid nitriding adds more nitrogen and less carbon than either cyaniding or carburizing in cyanide baths.

???????液體滲氮利用熔化的氰化物鹽，就像氣體滲氮，溫度保持在低于轉(zhuǎn)化范圍內(nèi)。液體滲氮時(shí)在氰化物溶液中加入比氰化及滲碳都較多的氮和較少的碳。

Case thickness of 0.001 to 0.012in.(0.03~0.30mm) is obtained, whereas for gas nitriding the case may be ?as thick as 0.025 in.(0.64mm). In general the uses of the two-nitriding processes are similar.

液體滲氮可以獲得厚度為0.001到0.012英寸?(0.03~0.30mm)的硬化層，然而氣體滲氮?jiǎng)t能獲得厚0.025英寸(0.64mm)的硬化層。一般而言兩種滲氮方法的用途是類似的。

????????Nitriding develops extreme hardness in the surface of steel. This hardness ranges from 900 to 1,100 Brinell, which is considerably higher than that obtained by ordinary case hardening.

???????滲氮在鋼表面獲得遠(yuǎn)遠(yuǎn)超出正常標(biāo)準(zhǔn)的硬度。其硬度范圍為900到1,100布氏硬度，這遠(yuǎn)高于普通表面硬化所獲得的硬度。

Nitriding steels, by virtue of their alloying content, are stronger than ordinary steels and respond readily to heat treatment. It is ?recommended that these steels be machined and heat-treated before nitriding, because there is no scale or further work necessary after this process.

由于滲氮鋼的合金比例，它們比普通鋼更強(qiáng)，也容易熱處理。建議對(duì)這種鋼在滲氮前先機(jī)加工和熱處理，因?yàn)闈B氮后沒有剝落并不需要更多的加工。

Fortunately, the interior structure and properties are not affected appreciably by the nitriding treatment and, because no quenching is necessary, there is little tendency to ?warp, develop cracks, or change condition in any way. The surface effectively resists corrosive action of water, saltwater spray, alkalies, crude oil, and natural gas.

值得慶幸的是由于滲氮處理一點(diǎn)都不影響內(nèi)部結(jié)構(gòu)和性能，也無需淬火，所以幾乎沒有任何產(chǎn)生翹曲、裂縫及變化條件的趨勢(shì)。這種表面能有效地抵御水、鹽霧、堿、原油和天然氣的腐蝕反應(yīng)。

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UNIT3 Casting Processes 鑄造工藝

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??Casting is a manufacturing process in which molten metal is poured or injected and allowed to solidify in a suitably shaped mold cavity. During or after ?cooling, the cast part is removed from the mold and then processed for delivery.

???????鑄造是一種將熔化的金屬倒入或注入合適的鑄模腔并且在其中固化的制造工藝。在冷卻期間或冷卻后，把鑄件從鑄模中取出，然后進(jìn)行交付。

???????Casting processes and cast-material technologies vary from simple to highly complex. Material and process selection depends on the part’s complexity and function, the product’s quality specifications, and the projected cost ?level.

???????鑄造工藝和鑄造材料技術(shù)從簡(jiǎn)單到高度復(fù)雜變化很大。材料和工藝的選擇取決于零件的復(fù)雜性和功能、產(chǎn)品的質(zhì)量要求以及成本預(yù)算水平。

????????Castings are parts that are made close to their final dimensions by a casting process. With a history dating back 6,000 ?years, the various casting processes are ?in a state of continuous refinement and evolution as technological advances are being made.

???????通過鑄造加工，鑄件可以做成很接近它們的最終尺寸?；厮?/span>6,000年歷史，各種各樣的鑄造工藝就如同科技進(jìn)步一樣處于一個(gè)不斷改進(jìn)和發(fā)展的狀態(tài)。

??Sand Casting ??

???砂型鑄造

??????????Sand casting is used to make large parts (typically iron, but also bronze, brass, aluminum). Molten metal is poured into a mold cavity formed out of sand (natural or synthetic).

???????砂型鑄造用于制造大型零件(具有代表性是鐵，除此之外還有青銅、黃銅和鋁)。將熔化的金屬倒入由型砂(天然的或人造的)做成鑄模腔。

The processes of sand casting are discussed in this section, including patterns, sprues and runners, design considerations, and casting allowance.

本節(jié)討論砂型鑄造工藝，包括型模、澆注口、澆道、設(shè)計(jì)考慮因素及鑄造余量。

?????????The cavity in the sand is formed by using a pattern (an approximate duplicate of the real part), which are typically made out of wood, sometimes metal. The cavity is contained in an aggregate housed in a box called the flask.

???????砂型里的型腔是采用型模(真實(shí)零件的近似復(fù)制品)構(gòu)成的，型模一般為木制，有時(shí)也用金屬制造。型腔整個(gè)包含在一個(gè)被放入稱為砂箱的箱子里的組合體內(nèi)。

Core is a sand shape inserted into the mold to produce the internal features of the part such as holes or internal passages. Cores are placed in the cavity to form holes of the desired shapes. Core print is the region added to the pattern, core, or mold that is used to locate and support the core within the mold.

砂芯是插入鑄模的砂型，用于生成諸如孔或內(nèi)通道之類的內(nèi)部特征。砂芯安放在型腔里形成所需形狀的孔洞。砂芯座是加在型模、砂芯或鑄模上的特定區(qū)域，用來在鑄模內(nèi)部定位和支撐砂芯。

A riser is an extra void created in the mold to contain excessive molten material. The purpose of this is to feed the molten metal to the mold cavity as the molten metal solidifies and shrinks, and thereby prevents voids in the main casting.

冒口是在鑄模內(nèi)部增加的額外空間，用于容納過多的熔化金屬。其目的是當(dāng)熔化金屬凝固和收縮時(shí)往型腔里補(bǔ)充熔化金屬，從而防止在主鑄件中產(chǎn)生孔隙。

???????In a two-part mold, which is typical of sand ?castings, the upper half, including the top half of the pattern, flask, and core is called cope and ?the lower half is called drag, as shown in Fig.3.1. The parting line or the parting surface is line or surface that separates the cope and drag.

???????在典型砂型鑄造的兩箱鑄模中，上半部分(包括型模頂半部、砂箱和砂芯)稱為上型箱，下半部分稱為下型箱，見圖3.1所示。分型線或分型面是分離上下型箱的線或面。

The drag is first filled partially with sand, and the core ?print, the cores, and the gating system are ?placed near the parting line. The cope is then assembled to the drag, and the sand is poured on the cope half, covering the pattern, core and the gating system.

首先往下型箱里部分地填入型砂和砂芯座、砂芯，并在靠近分型線處放置澆注系統(tǒng)。然后將上型箱與下型箱裝配在一起，再把型砂倒入上型箱蓋住型模、砂芯和澆注系統(tǒng)。

The sand is compacted by vibration and mechanical means. Next, the cope is removed from the drag, and the pattern is carefully removed. The object is to remove the pattern without breaking the mold cavity.

型砂通過振動(dòng)和機(jī)械方法壓實(shí)。然后從下型箱上撤掉上型箱，小心翼翼地取出型模。其目的是取出型模而不破壞型腔。

This is facilitated by designing a draft, a slight angular offset from the vertical to the vertical surfaces of the pattern. This is usually a minimum of 1.5mm(0.060in.), whichever is greater. The rougher the surface of the pattern, the more the draft to be provided.

通過設(shè)計(jì)拔模斜度—型模垂直相交表面的微小角度偏移量—來使取出型模變得容易。拔模斜度最小一般為1.5mm(0.060in.)，只能比此大。型模表面越粗糙，則拔模斜度應(yīng)越大。

????????The molten material is poured into the pouring cup, which is part of the gating system that supplies the molten material to the mold cavity.

???????熔化的金屬?gòu)臐沧⒈⑷胄颓?，澆注杯是澆注系統(tǒng)向型腔提供熔化金屬的部分。

The vertical part of the gating system connected to the pouring cup is the sprue, and the horizontal portion is called the runners and finally to the multiple points where it is introduced to the mold cavity called the gates.

將澆注系統(tǒng)的垂直部分與澆注杯連接的是澆注口，澆注系統(tǒng)的水平部分稱為澆道，最后到多點(diǎn)把熔化金屬導(dǎo)入型腔的稱為閘道。

Additionally there are extensions to the gating system called vents that provide the path for the built-up gases and the displaced air to vent to the atmosphere.

除此之外，還有稱為排放口的澆注系統(tǒng)延長(zhǎng)段，它為合成氣體和置換空氣排放到大氣提供通道。

?????????The cavity is usually made oversize to allow for the metal contraction as it cools down to room temperature. This is achieved by making the pattern oversize. To account for shrinking, the pattern must be made oversize by these factors on the average. These are linear factors and apply in each direction.

???????型腔通常大于所需尺寸以允許在金屬冷卻到室溫時(shí)收縮。這通過把型模做得大于所需尺寸來達(dá)到。為解決收縮效應(yīng)，一般而言型模做得比所需尺寸大，必須考慮線性因素并作用于各個(gè)方向。

These shrinkage allowances are only approximate, because the exact allowance is determined by the shape and size of the casting. In addition, different ?parts of the casting might require different shrinkage allowances.

收縮余量?jī)H僅是近似的，因?yàn)闇?zhǔn)確的余量是由鑄件的形狀和尺寸決定的。另外，鑄件的不同部分也可能需要不同的收縮余量。

Sand castings generally have a rough surface sometimes with surface impurities, and surface variations. A machining (finish) allowance is made for this type of defect.

砂型鑄件一般表面粗糙，有時(shí)還帶有表面雜質(zhì)和表面變異。對(duì)這類缺陷采用機(jī)加工(最后一道工序)的余量。

???????In general, typical stages of sand casting operation include (as shown in Fig.3.2):

1. Patterns are made. These will be the shape used to form the cavity in the sand.

???????一般而言，砂型鑄造作業(yè)的典型階段包括(如圖3.2所示)：

1. 制作型模。做成用于在型砂中形成型腔的形狀。

2. Cores may also be made at this time. These cores are made of bonded sand that will be broken out of the cast part after it is complete.

3. Sand is mulled (mixed) thoroughly with ?additives such as bentonite to increase ?bonding and overall strength.

2. 同時(shí)還要制作砂芯。這些砂芯用粘結(jié)砂做成，等鑄件完成后將被打碎取出。

3. 型砂與膨潤(rùn)土之類的添加劑充分地混合以增強(qiáng)連接及整體強(qiáng)度。

4. Sand is formed about the patterns, and gates, runners, risers, vents and pouring cups are added as needed. A compaction stage is typically used to ensure good coverage and solid molds.

4. 型砂在型模周圍成形，并根據(jù)需要安放閘道、澆道、冒口、排放口和澆注杯等。通常要采取壓緊步驟來保證良好的覆蓋和堅(jiān)固的鑄型。

Cores may also be added to make concave or internal features for the cast part. Alignment pins may also be used for mating the molds later. Chills may be added to cool large masses faster.

安放砂芯來制成鑄件的凹形結(jié)構(gòu)或內(nèi)部特征。為了以后鑄模匹配還要用到定位銷。對(duì)大質(zhì)量鑄件可能需要加入冷卻物來使其較快冷卻。

5. The patterns are removed, and the molds may be put through a baking stage to increase strength.

6. Mold halves are mated and prepared for pouring metal.

5. 取走型模，將鑄模烘焙以增加強(qiáng)度。

6. 匹配上下鑄模，做好澆鑄金屬的準(zhǔn)備。

7. Metal is preheated in a furnace or crucible until is above the liquidus temperature in a suitable range (we don’t want the metal solidifying before the pour is complete). The exact temperature may be closely controlled depending upon the application.

7. 金屬在熔爐或坩堝中預(yù)熱到高于液化溫度的一個(gè)合適范圍內(nèi)(不希望金屬在澆鑄完成前凝固)。確切的溫度要根據(jù)應(yīng)用場(chǎng)合嚴(yán)格控制。

Degassing, and other treatment ?processes may be done at this time, such ?as removal of impurities (i.e. slag). Some ?portion of this metal may be remelted scrap from previously cast parts—10% is reasonable.

在此期間還要進(jìn)行排氣和其它處理步驟，例如去除雜質(zhì)(即熔渣)。可以加入一定量原先是這種金屬鑄件的廢料再融化—10%是適當(dāng)?shù)摹?/span>

8. The metal is poured slowly, but continuously into the mold until the mold ?is full.

9. As the molten metal cools (minutes to days), ?the metal will shrink and the volume will decrease. During this time molten metal may backflow from the molten risers to feed the part and maintain the same shape.

8. 將金屬緩慢而連續(xù)地注滿型模。

9. 隨著熔化金屬的冷卻(幾分鐘到幾天)，金屬收縮體積減小。在此期間熔化金屬可能從冒口回流供給零件以保持其形狀不變。

10. Once the part starts to solidify small dendrites of solid material form in the part. During this time metal properties are being determined, and internal stresses are being generated. If a part is allowed to cool slowly enough at a constant rate then the final part will be relatively homogenous and stress free.