Unit 1
?Types of Materials
材料的类型
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.
材料可以按多种方法分类。科学家常根据状态将材料分为：固体、液体或气体。他们也把材料分为有机材料(曾经有生命的)和无机材料(从未有生命的)。
For industrial purposes, materials are divided into engineering materials or nonengineering materials. Engineering materials are those used in manufacture and become parts of products.
就工业效用而言，材料被分为工程材料和非工程材料。那些用于加工制造并成为产品组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.
非工程材料则是化学品、燃料、润滑剂以及其它用于加工制造过程但不成为产品组成部分的材料。
Engineering materials may be further subdivided into: ①Metal ②Ceramics ③Composite ④Polymers, etc.
工程材料还能进一步细分为：①金属材料②陶瓷材料③复合材料④聚合材料，等等。
?Metals and Metal Alloys
金属和金属合金
Metals are elements that generally have good electrical and thermal conductivity. Many metals have high strength, high stiffness, and have good ductility.
金属就是通常具有良好导电性和导热性的元素。许多金属具有高强度、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.
某些金属能被磁化，例如铁、钴和镍。在极低的温度下，某些金属和金属化合物能转变成超导体。
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.
合金与纯金属的区别是什么？纯金属是在元素周期表中占据特定位置的元素。例如电线中的铜和制造烹饪箔及饮料罐的铝。
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.
合金包含不止一种金属元素。合金的性质能通过改变其中存在的元素而改变。金属合金的例子有：不锈钢是一种铁、镍、铬的合金，以及金饰品通常含有金镍合金。
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.
为什么要使用金属和合金？许多金属和合金具有高密度，因此被用在需要较高质量体积比的场合。
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.
某些金属合金，例如铝基合金，其密度低，可用于航空航天以节约燃料。许多合金还具有高断裂韧性，这意味着它们能经得起冲击并且是耐用的。
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.
金属有哪些重要特性？
密度定义为材料的质量与其体积之比。大多数金属密度相对较高，尤其是和聚合物相比较而言。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.
高密度材料通常由较大原子序数原子构成，例如金和铅。然而，诸如铝和镁之类的一些金属则具有低密度，并被用于既需要金属特性又要求重量轻的场合。
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.
断裂韧性可以描述为材料防止断裂特别是出现缺陷时不断裂的能力。金属一般能在有缺口和凹痕的情况下不显著削弱，并且能抵抗冲击。橄榄球运动员据此相信他的面罩不会裂成碎片。
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.
塑性变形就是在断裂前弯曲或变形的能力。作为工程师，设计时通常要使材料在正常条件下不变形。没有人愿意一阵强烈的西风过后自己的汽车向东倾斜。
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，有时我们也能利用塑性变形。汽车上压皱的区域在它们断裂前通过经历塑性变形来吸收能量。
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.
金属的原子连结对它们的特性也有影响。在金属内部，原子的外层阶电子由所有原子共享并能到处自由移动。由于电子能导热和导电，所以用金属可以制造好的烹饪锅和电线。
It is impossible to see through metals, since these valence electrons absorb any photons of light which reach the metal. No photons pass through.
因为这些阶电子吸收到达金属的光子，所以透过金属不可能看得见。没有光子能通过金属。
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.
合金是由一种以上金属组成的混合物。加一些其它金属能影响密度、强度、断裂韧性、塑性变形、导电性以及环境侵蚀。
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，往铝里加少量铁可使其更强。同样，在钢里加一些铬能减缓它的生锈过程，但也将使它更脆。
?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义为无机的非金属材料。照此定义，陶瓷材料也应包括玻璃；然而许多材料科学家添加了“陶瓷”必须同时是晶体物组成的约定。
A glass is an inorganic nonmetallic material that does not have a crystalline structure. Such materials are said to be amorphous.
玻璃是没有晶体状结构的无机非金属材料。这种材料被称为非结晶质材料。
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
高熔点、低密度、高强度、高刚度、高硬度、高耐磨性和抗腐蚀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.
许多陶瓷都是电和热的良绝缘体。某些陶瓷还具有一些特殊性能：有些是磁性材料，有些是压电材料，还有些特殊陶瓷在极低温度下是超导体。陶瓷和玻璃都有一个主要的缺点：它们容易破碎。
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。因为大多数陶瓷在从液态冷却时将会完全破碎(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, canno t be used for the production of crystalline ceramics. Instead, “sintering” or “firing” is the process typically used.
因此，所有用于玻璃生产的简单有效的—诸如浇铸和吹制这些涉及熔化的技术都不能用于由晶体物组成的陶瓷的生产。作为替代，一般采用“烧结”或“焙烧”工艺。
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.
在烧结过程中，陶瓷粉末先挤压成型然后加热到略低于熔点温度。在这样的温度下，粉末内部起反应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.
光导纤维有三层：核心由高折射指数高纯光传输玻璃制成，中间层为低折射指数玻璃，是保护核心玻璃表面不被擦伤和完整性不被破坏的所谓覆层，外层是聚合物护套，用于保护光导纤维不受损。
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.
为了使核心玻璃有比覆层大的折射指数，在其中掺入微小的、可控数量的能减缓光速而不会吸收光线的杂质或搀杂剂。
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数比覆层大，只要在全内反射过程中光线照射核心/覆层分界面的角度比临界角大，在核心玻璃中传送的光线将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.
全内反射现象与核心玻璃的高纯度一样，使光线几乎无强度损耗传递长距离成为可能。
?Composites 复合材料
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.
复合材料由两种或更多材料构成。例子有聚合物/陶瓷和金属/陶瓷复合材料。之所以使用复合材料是因为其全面性能优于组成部分单独的性能。
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/陶瓷复合材料具有比聚合物成分更大的模量，但又不像陶瓷那样易碎。
复合材料有两种：纤维加强型复合材料和微粒加强型复合材料。
Fiber-reinforced Composites
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.
纤维加强型复合材料
加强纤维可以是金属、陶瓷、玻璃或是已变成石墨的被称为碳纤维的聚合物。纤维能加强基材的模量。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.
沿着纤维长度有很强结合力的共价结合在这个方向上给予复合材料很高的模量，因为要损坏或拉伸纤维就必须破坏或移除这种结合。
Fibers are difficult to process into composites, making fiber-reinforced composites relatively expensive.
把纤维放入复合材料较困难，这使得制造纤维加强型复合材料相对昂贵。
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.
纤维加强型复合材料用于某些最先进也是最昂贵的运动设备，例如计时赛竞赛用自行车骨架就是用含碳纤维的热固塑料基材制成的。
Body parts of race cars and some automobiles are composites made of glass fibers (or fiberglass) in a thermoset matrix.
竞赛用汽车和某些机动车的车体部件是由含玻璃纤维(或玻璃丝)的热固塑料基材制成的。
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.
纤维在沿着其轴向有很高的模量，但垂直于其轴向的模量却较低。纤维复合材料的制造者往往旋转纤维层以防模量产生方向变化。
Particle-reinforced composites
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.
微粒加强型复合材料
用于加强的微粒包含了陶瓷和玻璃之类的矿物微粒，铝之类的金属微粒以及包括聚合物和碳黑的非结晶质微粒。
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、减少基材的渗透性和延展性。微粒加强型复合材料的一个例子是机动车胎，它就是在聚异丁烯人造橡胶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链的重复结构。这种重复结构产生链状大分子。由于重量轻、耐腐蚀、容易在较低温度下加工并且通常较便宜，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)、软化及熔化点、结晶度和结构。聚合材料的机械性能一般表现为低强度和高韧性。它们的强度通常可采用加强复合结构来改善。
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：单个聚合物分子一般分子量为10,000到1,000,000g/mol之间，具体取决于聚合物的结构—这可以比2,000个重复单元还多。
The mechanical properties of a polymer are significantly affected by the molecular weight, with better engineering properties at higher molecular weights.
聚合物的分子量极大地影响其机械性能，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.
热转换性：聚合物的软化点(玻璃状转化温度)和熔化点决定了它是否适合应用。这些温度通常决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，许多工业上的重要聚合物其玻璃状转化温度接近水的沸点(100℃, 212℉)，它们被广泛用于室温下。而某些特别制造的聚合物能经受住高达300℃(572℉)的温度。
Crystallinity.Polymers can be crystalline or amorphous, but they usually have a combination of crystalline and amorphous structures (semi-crystalline).
结晶度：聚合物可以是晶体状的或非结晶质的，但它们通常是晶体状和非结晶质结构的结合物(半晶体)。
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.
原子链间的相互作用：聚合物的原子链可以自由地彼此滑动(热可塑性)或通过交键互相连接(热固性或弹性)。热可塑性材料可以重新形成和循环使用，而热固性与弹性材料则是不能再使用的。
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.
链内结构：原子链的化学结构对性能也有很大影响。根据各自的结构不同，聚合物可以是亲水的或憎水的(喜欢或讨厌水)、硬的或软的、晶体状的或非结晶质的、易起反应的或不易起反应的。
Unit 2
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.
对热处理的理解包含于对冶金学较广泛的研究。冶金学是物理学、化学和涉及金属从矿石提炼到最后产物的工程学。
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.
热处理是将金属在固态加热和冷却以改变其物理性能的操作。按所采用的步骤，钢可以通过硬化来抵抗切削和磨损，也可以通过软化来允许机加工。
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.
使用合适的热处理可以去除内应力、细化晶粒、增加韧性或在柔软材料上覆盖坚硬的表面。因为某些元素(尤其是碳)的微小百分比极大地影响物理性能，所以必须知道对钢的分析。
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.
合金钢的性质取决于其所含有的除碳以外的一种或多种元素，如镍、铬、锰、钼、钨、硅、钒和铜。由于合金钢改善的物理性能，它们被大量使用在许多碳钢不适用的地方。
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.
下列讨论主要针对被称为普通碳钢的工业用钢而言。热处理时冷却速率是控制要素，从高于临界温度快速冷却导致坚硬的组织结构，而缓慢冷却则产生相反效果。
? A Simplified Iron-carbon Diagram
简化铁碳状态图
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说的钢上，经常要用到简化铁碳状态图。
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.
铁碳状态图中靠近三角区和含碳量高于2%的那些部分对工程师而言不重要，因此将它们删除。如图2.1所示的简化铁碳状态图将焦点集中在共析区，这对理解钢的性能和处理是十分有用的。
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.
在此图中描述的关键转变是单相奥氏体(γ) 随着温度下降分解成两相铁素体加渗碳体组织结构。
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.
控制这一由于奥氏体和铁素体的碳溶解性完全不同而产生的反应，使得通过热处理能获得很大范围的特性。
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.
为了理解这些过程，考虑含碳量为0.77%的共析钢，沿着图2.1的x-x’线慢慢冷却。在较高温度时，只存在奥氏体，0.77%的碳溶解在铁里形成固溶体。当钢冷却到727℃(1341℉)时，将同时发生若干变化。
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.
铁需要从面心立方体奥氏体结构转变为体心立方体铁素体结构，但是铁素体只能容纳固溶体状态的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.
被析出的碳与金属化合物Fe3C形成富碳的渗碳体。本质上，共析体的基本反应是奥氏体0.77%的碳→铁素体0.02%的碳+渗碳体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.
由于这种碳成分的化学分离完全发生在固态中，产生的组织结构是一种细致的铁素体与渗碳体的机械混合物。通过打磨并在弱硝酸酒精溶液中蚀刻制备的样本显示出由缓慢冷却形成的交互层状的薄片结构。
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.
这种结构由两种截然不同的状态组成，但它本身具有一系列特性，且因与低倍数放大时的珠母层有类同之处而被称为珠光体。
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.
含碳量少于共析体(低于0.77%)的钢称为亚共析钢。现在来看这种材料沿着图2.1中y-y’ 线冷却的转变情况。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.
在较高温度时，这种材料全部是奥氏体，但随着冷却就进入到铁素体和奥氏体稳定状态的区域。由截线及杠杆定律分析可知，低碳铁素体成核并长大，剩下含碳量高的奥氏体。
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℉)时，奥氏体为共析组成(含碳量0.77%)，再冷却剩余的奥氏体就转化为珠光体。作为结果的组织结构是初步的共析铁素体(在共析反应前的铁素体)和部分珠光体的混合物。
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.
过共析钢是含碳量大于共析量的钢。当这种钢冷却时，就像图2.1的z-z’线所示，除了初步的共析状态用渗碳体取代铁素体外，其余类似亚共析钢的情况。
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. 随着富碳部分的形成，剩余奥氏体含碳量减少，在727℃(1341℉)时达到共析组织。就像以前说的一样，当缓慢冷却到这温度时所有剩余奥氏体转化为珠光体。
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.
应该记住由状态图描述的这种转化只适合于通过缓慢冷却的近似平衡条件。如果缓慢加热，则以相反的方式发生这种转化。
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，当快速冷却合金时，可能得到完全不同的结果。因为没有足够的时间让正常的状态反应发生，在这种情况下对工程分析而言状态图不再是有用的工具。
?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.
淬火就是把钢件加热到或超过它的临界温度范围，然后使其快速冷却的过程。
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.
如果钢的含碳量已知，钢件合适的加热温度可参考铁碳合金状态图得到。然而当钢的成分不知道时，则需做一些预备试验来确定其温度范围。
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.
要遵循的合适步骤是将这种钢的一些小试件加热到不同的温度后淬火，再通过硬度试验或显微镜检查观测结果。一旦获得正确的温度，硬度和其它性能都将有明显的变化。
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.
在任何热处理作业中，加热的速率都是重要的。热量以一定的速率从钢的外部传导到内部。如果钢被加热得太快，其外部比内部热就不能得到均匀的组织结构。
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.
如果工件形状不规则，为了消除翘曲和开裂最根本的是加热速率要缓慢。截面越厚，加热的时间就要越长才能达到均匀的结果。
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.
即使加热到正确的温度后，工件也应在此温度下保持足够时间以让其最厚截面达到相同温度。
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.
通过给定的热处理所得到的硬度取决于淬火速率、含碳量和工件尺寸。除了非淬硬钢或部分淬硬钢外，合金钢中合金元素的种类及含量仅影响钢的淬透性(工件被硬化到深层的能力)而不影响硬度。
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.
含碳量低的钢对淬火处理没有明显的反应。随着钢的含碳量增加到大约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.
高于此点，由于超过共析点钢完全由珠光体和退火状态的渗碳体组成，硬度增加并不多。珠光体对热处理作业响应最好；基本由珠光体组成的钢能转化成硬质钢。
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.
即使所有其它条件保持不变，随着要淬火的零件尺寸的增加其表面硬度也会有所下降。热量在钢中的传导速率是有限的。
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.
无论淬火介质怎么冷，如果在大工件中的热量不能比特定的临界速率更快散发，那它内部硬度就会受到明确限制。然而盐水或水淬火能够将被淬零件的表面迅速冷却至本身温度并将其保持或接近此温度。
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.
在这种情况下不管零件尺寸如何，其表面总归有一定深度被硬化。但油淬情况就不是如此，因为油淬时在淬火临界阶段零件表面的温度可能仍然很高。
?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．
快速淬火硬化的钢是硬而易碎的，不适合大多数场合使用。通过回火，硬度和脆性可以降低到使用条件所需要的程度。
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.
随着这些性能的降低，拉伸强度也降低而钢的延展性和韧性则会提高。回火作业包括将淬硬钢重新加热到低于临界范围的某一温度然后以任意速率冷却。
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.
虽然这过程使钢软化，但它与退火是大不相同的，因为回火适合于严格控制物理性能并在大多数情况下不会把钢软化到退火那种程度。回火完全淬硬钢得到的最终组织结构被称为回火马氏体。
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.
由于马氏体这一淬硬钢主要成分的不稳定性，使得回火成为可能。低温回火，300℉到400℉(150℃~205℃)，不会引起硬度下降很多，主要用于减少内部应变。
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.
随着回火温度的提高，马氏体以较快的速率分解，并在大约600℉(315℃)迅速转变为被称为回火马氏体的结构。回火作业可以描述为渗碳体析出和凝聚或聚结的过程。
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.
渗碳体的大量析出开始于600℉(315℃)，这使硬度下降。温度的上升会使碳化物聚结而硬度继续降低。
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.
在回火过程中，不但要考虑温度而且要考虑时间。虽然大多数软化作用发生在达到所需温度后的最初几分钟，但如果此温度维持一段延长时间，仍会有些额外的硬度下降。
Usual practice is to heat the steel to the desired temperature and hold it there only long enough to have it uniformly heated.
通常的做法是将钢加热到所需温度并且仅保温到正好使其均匀受热。
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.
两种采用中断淬火的特殊工艺也是回火的形式。这两种工艺中，淬硬钢在其被允许冷却前先在一选定的较低温度盐浴淬火。这两种分别被称为奥氏体回火和马氏体回火的工艺，能使产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坚硬的钢软化以便机加工或冷作。
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.
通常是非常缓慢地将钢加热到临界温度以上，并将其在此温度下保持到工件全部均匀受热，然后以受控的速率慢慢地冷却，这样使得工件表面和内部的温度近似相同。
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.
这过程被称为完全退火，因为它去除了以前组织结构的所有痕迹、细化晶粒并软化金属。退火也释放了先前在金属中的内应力。
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.
给定的钢其退火温度取决于它的成分；对碳钢而言可容易地从局部的铁碳合金平衡图得到。达到退火温度后，钢应当保持在此温度等到全部均匀受热。
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.
加热时间一般以工件的最大截面厚度计每英寸(25mm )大约需45min。为了得到最大柔软性和延展性冷却速率应该很慢，比如让零件与炉子一起冷下来。含碳量越高，冷却的速率必须越慢。
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.
加热的速率也应与截面的尺寸及均匀程度相协调，这样才能使整个零件尽可能均匀地加热。
?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.
正火处理包括先将钢加热到高于上临界区50℉到100℉(10℃~40℃)然后在静止的空气中冷却到室温。
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.
退火主要用于低碳钢、中碳钢及合金钢，使晶粒结构更均匀、释放内应力或获得所需的物理特性。大多数商业钢材在轧制或铸造后都要退火。
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.
球化是使渗碳体产生成类似球状分布结构的工艺。如果把钢缓慢加热到恰好低于临界温度并且保持较长一段时间，就能得到这种组织结构。
The globular structure obtained gives improved machinability to the steel. This treatment is particularly useful for hypereutectoid steels that must be machined.
所获得的球状结构改善了钢的可切削性。此处理方法对必须机加工的过共析钢特别有用。
?Surface Hardening
表面硬化
Carburizing
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.
渗碳
最早的硬化钢表面的方法是表面淬火或渗碳。铁在靠近并高于其临界温度时对碳具有亲合力。
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.
碳被吸收进金属与铁形成固溶体使外表面转变成高碳钢。碳逐渐扩散到零件内部。渗碳层的深度取决于热处理的时间和温度。
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. 固体渗碳的方法是将要处理的零件与木炭或焦炭这些含碳的材料一起放入密闭容器。这是一个较长的过程，用于产生深度为0.03到0.16 英寸(0.76~4.06mm)这么厚的硬化层。
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.
用于渗碳的一般是含碳量约为0.15%、本身不太适合热处理的低碳钢。在处理过程中外层转化为含碳量从
0.9%到1.2%的高碳钢。
A steel with varying carbon content and, consequently, different critical temperatures requires a special heat treatment.
含碳量变化的钢具有不同的临界温度，因此需要特殊的热处理。
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.
由于在较长的渗碳过程中钢内部会有些晶粒生长，所以工件应该加热到核心部分的临界温度再冷却以细化核心部分的组织结构。然后重新加热到高于外层转变温度再淬火以生成坚硬、细致的组织结构。
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.
由于恰好高于低临界温度通常使过共析钢奥氏体化而硬化，所以对外层采用较低的热处理温度。第三次回火处理可用于减少应变。
Carbonitriding
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.
碳氮共渗
碳氮共渗，有时也称为干法氰化或渗碳氮化，是一种表面硬化工艺。通过把钢放在高于临界温度的气体中，让它吸收碳和氮。
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.
可以使用任何富碳气体加氨气，能生成厚度从0.003到0.030英寸(0.08~ 0.76mm)的耐磨外层。碳氮共渗的优点之一是加入氮后外层的淬透性极大增加，为使用低价钢提供条件。
Cyaniding
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
氰化，有时称为液体碳氮共渗，也是一种结合了吸收碳和氮来获得表面硬度的工艺，它主要用于不适合通常热处理的低碳钢。
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没在略高于Ac1温度熔化的氰化钠盐溶液中，浸泡的持续时间取决于硬化层的深度。然后将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.
通过这样处理可以容易地获得0.005到0.015英寸(0.13~0.38mm)的硬化深度。氰化主要用于处理小零件。Nitriding
Nitriding is somewhat similar to ordinary case hardening, but it uses a different material and treatment to create the hard surface constituents.
渗氮
渗氮有些类似普通表面硬化，但它采用不同的材料和处理方法来产生坚硬表面成分。
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.
这种工艺中金属加热到约950℉(510℃)，然后与氨气接触一段时间。氨气中的氮进入钢内，形成细微分布于金属表面又十分坚固的氮化物。
Nitrogen has greater hardening ability with certain elements than with others, hence, special nitriding alloy steels have been developed.
氮与某些元素的硬化能力比其它元素大，因此开发了专用的渗氮合金钢。
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℃).
在钢中含铝1%到1.5%被证明特别合适，它能与氨气结合形成很稳定坚固的成分。其加热温度范围为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.
液体渗氮利用熔化的氰化物盐，就像气体渗氮，温度保持在低于转化范围内。液体渗氮时在氰化物溶液中加入比氰化及渗碳都较多的氮和较少的碳。
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.
液体渗氮可以获得厚度为0.001到0.012英寸(0.03~0.30mm)的硬化层，然而气体渗氮则能获得厚0.025英寸(0.64mm)的硬化层。一般而言两种渗氮方法的用途是类似的。
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.
渗氮在钢表面获得远远超出正常标准的硬度。其硬度范围为900到1,100布氏硬度，这远高于普通表面硬化所获得的硬度。
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.
由于渗氮钢的合金比例，它们比普通钢更强，也容易热处理。建议对这种钢在渗氮前先机加工和热处理，因为渗氮后没有剥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.
值得庆幸的是由于渗氮处理一点都不影响内部结构和性能，也无需淬火，所以几乎没有任何产生翘曲、裂缝及变化条件的趋势。这种表面能有效地抵御水、盐雾、碱、原油和天然气的腐蚀反应。
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.
铸造是一种将熔化的金属倒入或注入合适的铸模腔并且在其中固化的制造工艺。在冷却期间或冷却后，把铸件从铸模中取出，然后进行交付。
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.
铸造工艺和铸造材料技术从简单到高度复杂变化很大。材料和工艺的选择取决于零件的复杂性和功能、产品的质量要求以及成本预算水平。
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.
通过铸造加工，铸件可以做成很接近它们的最终尺寸。回溯6,000年历史，各种各样的铸造工艺就如同科技进步一样处于一个不断改进和发展的状态。
?Sand Casting 砂型铸造
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).
砂型铸造用于制造大型零件(具有代表性是铁，除此之外还有青铜、黄铜和铝)。将熔化的金属倒入由型砂(天然的或人造的)做成铸模腔。
The processes of sand casting are discussed in this section, including patterns, sprues and runners, design considerations, and casting allowance.
本节讨论砂型铸造工艺，包括型模、浇注口、浇道、设计考虑因素及铸造余量。
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(真实零件的近似复制品)构成的，型模一般为木制，有时也用金属制造。型腔整个包含在一个被放入称为砂箱的箱子里的组合体内。
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.
砂芯是插入铸模的砂型，用于生成诸如孔或内通道之类的内部特征。砂芯安放在型腔里形成所需形状的孔洞。砂芯座是加在型模、砂芯或铸模上的特定区域，用来在铸模内部定位和支撑砂芯。
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.
冒口是在铸模内部增加的额外空间，用于容纳过多的熔化金属。其目的是当熔化金属凝固和收缩时往型腔里补充熔化金属，从而防止在主铸件中产生孔隙。
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.
在典型砂型铸造的两箱铸模中，上半部分(包括型模顶半部、砂箱和砂芯)称为上型箱，下半部分称为下型箱，见图3.1所示。分型线或分型面是分离上下型箱的线或面。
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，并在靠近分型线处放置浇注系统。然后将上型箱与下型箱装配在
一起，再把型砂倒入上型箱盖住型模、砂芯和浇注系统。
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.
型砂通过振动和机械方法压实。然后从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坏型腔。
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.
通过设计拔模斜度—型模垂直相交表面的微小角度偏移量—来使取出型模变得容易。拔模斜度最小一般为1.5mm(0.060in.)，只能比此大。型模表面越粗糙，则拔模斜度应越大。
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.
熔化的金属从浇注杯注入型腔，浇注杯是浇注系统向型腔提供熔化金属的部分。
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.
将浇注系统的垂直部分与浇注杯连接的是浇注口，浇注系统的水平部分称为浇道，最后到多点把熔化金属导入型腔的称为闸道。
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，还有称为排放口的浇注系统延长段，它为合成气体和置换空气排放到大气提供通道。
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许在金属冷却到室温时收缩。这通过把型模做得大于所需尺寸来达到。为解决收缩效应，一般而言型模做得比所需尺寸大，必须考虑线性因素并作用于各个方向。
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.
收缩余量仅仅是近似的，因为准确的余量是由铸件的形状和尺寸决定的。另外，铸件的不同部分也可能需要不同的收缩余量。
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.
砂型铸件一般表面粗糙，有时还带有表面杂质和表面变异。对这类缺陷采用机加工(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，砂型铸造作业的典型阶段包括(如图3.2所示)：
1. 制作型模。做成用于在型砂中形成型腔的形状。
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. 同时还要制作砂芯。这些砂芯用粘结砂做成，等铸件完成后将被打碎取出。
3. 型砂与膨润土之类的添加剂充分地混合以增强连接及整体强度。
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. 型砂在型模周围成形，并根据需要安放闸道、浇道、冒口、排放口和浇注杯等。通常要采取压紧步骤来保证良好的覆盖和坚固的铸型。
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.
安放砂芯来制成铸件的凹形结构或内部特征。为了以后铸模匹配还要用到定位销。对大质量铸件可能需要加入冷却物来使其较快冷却。
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，将铸模烘焙以增加强度。
6. 匹配上下铸模，做好浇铸金属的准备。
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. 金属在熔炉或坩埚中预热到高于液化温度的一个合适范围内(不希望金属在浇铸完成前凝固)。确切的温度要根据应用场合严格控制。
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.
在此期间还要进行排气和其它处理步骤，例如去除杂质(即熔渣)。可以加入一定量原先是这种金属铸件的废料再融化—10%是适当的。
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. 将金属缓慢而连续地注满型模。
9. 随着熔化金属的冷却(几分钟到几天)，金属收缩体积减小。在此期间熔化金属可能从冒口回流供给零件以保持其形状不变。
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.
10. 在零件开始凝固其内部形成固态金属的小型树枝状结晶期间金属性能被确定，同时也产生了内应力。如果零件以恒定速率冷却得足够缓慢，最终零件将相对均质并释放内应力。
11. Once the part has completely solidified below the eutectic point it may be removed with no concern for final metal properties. At this point the sand is simply broken up, and the part removed. At this point the surface will have a quantity of sand adhering to the surface, and solid cores inside.
11. 一旦零件在共析点以下完全凝固，可以不考虑金属的最后性能而将其取出。这时可以简单地打碎砂型并取出零件，但零件表面会有大量型砂粘附着，内部还有实心的砂芯。
12. A bulk of the remaining sand and cores can be removed by mechanically striking the part. Other options are to use a vibrating table, sand/shot blaster, hand labor, etc.
12.大量的剩余型砂和砂芯要通过机械敲击零件来去除。其它的选择还有采用振动台、喷砂/喷丸机、手工作业等等。
13. The final part is cut off the runner gate system, and is near final shape using cutters, torches, etc. Grinding operations are used to remove any remaining bulk.
14. The part is taken down to final shape using machining operations. And cleaning operations may be used to remove oxides, etc.
13. 最后零件要用刀具、喷枪等切掉浇道闸道系统，这样就接近最终形状了。再用磨削作业去除多余的部分。
14. 通过机加工将零件切削到最终形状。可能还要用清洗作业去除氧化物等。
?Investment casting
熔模铸造
Investment casting is also known as the lost wax process. This process is one of the oldest manufacturing processes. The Egyptians used it in the time of the Pharaohs to make gold jewelry (hence the name Investment) some 5,000 years ago.
熔模铸造也称为失蜡加工。这是最古老的制造工艺之一。大约在5,000年前的法老王时代，埃及人就用它制造黄金饰品(因此而得名投资)。
Intricate shapes can be made with high accuracy. In addition, metals that are hard to machine or fabricate are good candidates for this process. It can be used to make parts that cannot be produced by normal manufacturing techniques, such as turbine blades that have complex shapes, or airplane parts that have to withstand high temperatures.
复杂的形状能被高精度地制造。另外较难机加工或制作的金属都能用此工艺。它还能用于生产一般制造技术无法生产的零件，例如有复杂形状的涡轮叶片或必须耐得住高温的飞机零件。
The mold is made by making a pattern using wax or some other material that can be melted away. This wax pattern is dipped in refractory slurry, which coats the wax pattern and forms a skin. This is dried and the process of dipping in the slurry and drying is repeated until a robust thickness is achieved.
制作铸型的型模采用石蜡或其它一些能被融化掉的材料做成。石蜡型模浸泡在耐热浆里，让它覆盖型模并形成外壳，然后使其变干。重复这个浸泡、变干的过程直至获得足够的厚度。
After this, the entire pattern is placed in an oven and the wax is melted away. This leads to a mold that can be filled with the molten metal. Because the mold is formed around a one-piece pattern (which does not have to be pulled out from the mold as in a traditional sand casting process), very intricate parts and undercuts can be made.
完成后把整个型模放在烤箱里融化石蜡。这样就做成了能填充熔化金属的铸型。由于这种铸型是环绕整块型模形成
的(无需像传统的砂型铸造工艺那样拔模)，能制作十分复杂的零件和浮雕。
The wax pattern itself is made by duplicating using a stereo lithography or similar model—which has been fabricated using a computer solid model master.
石蜡型模本身能用立体制版或类似的模型复制—这可以采用计算机立体模型原版制作。
The materials used for the slurry are a mixture of plaster, a binder and powdered silica, a refractory, for low temperature melts. For higher temperature melts, sillimanite or alumina-silicate is used as a refractory, and silica is used as a binder.
对较低熔化温度而言，用于耐热浆的材料是石膏作粘合剂和用粉末状硅石作耐温材料的混合物。对较高熔化温度而言，则采用硅线石或氧化铝硅酸盐作耐温材料、无水硅酸作粘合剂。
Depending on the fineness of the finish desired additional coatings of sillimanite and ethyl silicate may be applied. The mold thus produced can be used directly for light castings, or be reinforced by placing it in a larger container and reinforcing it more slurry.
根据最后所需光洁度也可采用硅线石和乙烷基硅酸盐。这样生成的铸模可直接用于薄壁铸件或通过将其放在较大容器内用更多耐热浆加强。
Just before the pour, the mold is pre-heated to about 1,000℃(1,832℉) to remove any residues of wax, harden the binder. The pour in the pre-heated mold also ensures that the mold will fill completely.
在正要浇铸之前，将型模预热到约1,000℃(1,832℉)以去除剩余石蜡、硬化粘合剂。在预热的型模中浇铸也能保证型模完全充满。
Pouring can be done using gravity, pressure or vacuum conditions. Attention must be paid to mold permeability when using pressure, to allow the air to escape as the pour is done.
浇铸可采用重力、压力或真空条件来实现。当使用压力时必须注意渗透性，以便在浇铸的同时让空气逸出。
Tolerances of 0.5% of length are routinely possible, and as low as 0.15% is possible for small dimensions. Castings can weigh from a few grams to 35kg (0.1oz to 80lb), although the normal size ranges from 200g to about 8kg(7oz to 15 lb). Normal minimum wall thicknesses are about 1mm to about 0.5mm(0.040~ 0.020 in.) for alloys that can be cast easily.
一般公差可能为长度的0.5%，小尺寸可能低到0.15%。虽然通常尺寸的铸件重量范围为200g到约8kg(7oz 到15lb)，但实际可从几克到35kg (0.1oz to 80lb)。对容易铸造的合金而言，通常壁厚约为1mm到0.5mm(0.040~ 0.020 in.)。
The types of materials that can be cast are aluminum alloys, bronzes, tool steels, stainless steels, stellite, hastelloys, and precious metals. Parts made with investment castings often do not require any further machining, because of the close tolerances that can be achieved.
可以用于铸造的材料类型有：铝合金、青铜、工具钢、不锈钢、钨铬钴合金、镍基合金和贵金属。采用熔模铸造的零件常常不需要进一步加工，因为熔模铸造能达到精密的公差。
?Centrifugal Casting
离心铸造
Centrifugal casting (Fig.3.3) as a category includes centrifugal casting, semi-centrifugal casting and centrifuging. In centrifugal casting, a permanent mold is rotated about its axis at high speeds (300 to 3,000rpm) as the molten metal is poured.
离心铸造(图3.3)作为一个种类包括了离心铸造、半离心铸造和离心法铸造。离心铸造中，永久性的型模在熔化金属浇铸时以较高速度(300到3,000rpm)绕其轴线旋转。
The molten metal is centrifugally thrown towards the inside mold wall, where it solidifies after cooling. The casting is usually a fine grain casting with a very fine-grained outer diameter, which is resistant to atmospheric corrosion, a typical situation with pipes. The inside diameter has more impurities and inclusions, which can be machined away.
受离心力作用熔化金属被抛向型模的内壁，在那里冷却后固化。这种铸件通常为外径处晶粒非常细小的细晶粒铸件，能耐大气腐蚀，典型的情况是管子。内径处则有较多的杂质和内含物，但可用机加工去除。
Only cylindrical shapes can be produced with this process. Size limits are up to 3m(10feet) diameter and 15m(50 feet) length. Wall thickness can be 2.5mm to 125mm(0.1~5.0in.). The tolerances that can be held on the OD can be as good as 2.5mm (0.1in.) and on the ID can be 3.8mm(0.15in.). The surface finish ranges from 2.5mm to 12.5mm(0.1~0.5in.) rms(root-mean-square).
只有圆柱形才能用此工艺生产。尺寸限制为直径大到3m(10feet)、长度大到15m(50feet)。壁厚为2.5mm到125mm(0.1~5.0in.)。外径公差保持在2.5mm(0.1in.)以内，内径公差保持在3.8mm(0.15in.)以内。表面粗糙度的有效值(均方根)范围为2.5mm到12.5mm(0.1~0.5in.)。
Typical materials that can be cast with this process are iron, steel, stainless steels, and alloys of aluminum, copper and nickel. Two materials can be cast by introducing a second material during the process. Typical parts made by this process are pipes, boilers, pressure vessels, flywheels, cylinder liners and other parts that are axis-symmetric.
可用此工艺铸造的典型材料有：铁、钢、不锈钢以及铝、铜和镍的合金。通过在生产过程中加入第二种材料能进行两种材料铸造。采用这种工艺制造的典型零件有：管子、锅炉、压力容器、飞轮、汽缸衬垫和其它轴对称零件。
Semi-centrifugal casting. The molds used can be permanent or expendable, can be stacked as necessary. The rotational speeds are lower than those used in centrifugal casting.
半离心铸造：型模可以是永久性的或是消耗性的，可根据需要叠加。它的旋转速度比离心铸造低。
The center axis of the part has inclusion defects as well as porosity and thus is suitable only for parts where this can be machined away. This process is used for making wheels, nozzles and similar parts where the axis of the part is removed by subsequent machining.
零件的中心轴附近存在缺陷和孔隙，因此仅适用于能将这些机加工去除的零件。这种工艺被用于制造车轮、管嘴及类似的随后可用机加工去除中心轴部分的零件。
Centrifuging.Centrifuging is used for forcing metal from a central axis of the equipment into individual mold cavities that are placed on the circumference. This provides a means of increasing the filling pressure within each mold and allows for reproduction of intricate details. This method is often used for the pouring of investment casting pattern.
离心法铸造：离心法铸造用于迫使金属从设备的中心轴进入分布在圆周上的单独型腔。它为每个型腔提供了一种增加填充压力方法并允许再现复杂细节。这种方法常用于浇铸熔模铸型。
Full-mold casting is a technique similar to investment casting, but instead of wax as the expendable material, polystyrene foam is used as the pattern. The foam pattern is coated with a refractory material. The pattern is encased in a one-piece sand mold. As the metal is poured, the foam vaporizes, and the metal takes its place.
实型铸造是与熔模铸造类似的技术，但它用做型模的消耗材料是聚苯乙烯泡沫而不是石蜡。泡沫型模用难熔材料覆盖。型模装入整体砂模中。当金属浇入时，泡沫材料蒸发，金属取代其位置。
This can make complex shaped castings without any draft or flash. However, the pattern cost can be high due to the expendable nature of the pattern. Minimum wall thicknesses are 2.5mm, tolerances can be held to 0.3% on dimensions. Surface finish can be held from 2.5μm to 25μm(0.1μin. to 1.0μin.) rms(root-mean-square).
它能制造没有拔模斜度和缝脊的复杂形状铸件。然而由于型模的消耗特性，型模成本可能较高。最小壁厚为2.5mm，公差能保持在尺寸的0.3% 之内。表面粗糙度的有效值(均方根)能保持在2.5μm至25μm(0.1μin.至1.0μin.)之间。Size limits are from 400g(1lb) to several tons. No draft allowance is required. Typical materials that can be cast with this process are aluminum, iron, steel, nickel alloys, copper alloys. Types of parts that can be made using these processes are pump housings, manifolds, and auto brake components.
重量限制从400g(1lb)到数吨。无需留拔模余量。这种工艺所用的典型材料有：铝、铁、钢、镍合金、铜合金。可以采用这些工艺制造的零件类型有泵壳、复式接头和自动刹车部件。
Unit 6
?Introduction 引言
Forging is an important hot-forming process. It is used in producing components of all shapes and sizes, from quite small items to large units weighing several tons.
锻造是一种重要的热成型工艺。它能用于生产各种形状和尺寸、从很小到重量数吨的零件。
Forging is the process by which metal is heated and is shaped by plastic deformation by suitably applying compressive force. Usually the compressive force is in the form of hammer blows using a power hammer or a press, as shown in Fig.4.1.
在锻造过程中先将金属加热，然后施加合适的压力使其塑性变形。通常压力都是以由如图4.1所示的动力锤或压力机提供的锤击形式出现。
Hand forging tools comprise variously shaped hammers. The base on which the work is supported during forging is the anvil.
手工锻造工具包括各种不同形状的锤子。在锻造中用于支撑工件的基础是铁砧。
For the semimechanized forging of small to medium-sized components, forging hammers powered by various means are employed. The feature common to all of them is that, like the hand forging hammer, they utilize the energy of a falling weight to develop the pressure needed for shaping the metal.
对小到中等尺寸零件的半机械化锻造而言，锻锤可采用多种动力。就其一般特性而言，都象手工锻锤一样，
它们均利用落重能量来产生金属成型所需的压力。
Larger components are forged by means of forging presses operated by steam or compressed air or by hydraulic or electric power. Largely automatic forging machines are used for the quantity production of engineering parts.
锻造大零件则要用到蒸汽、压缩空气、液力或电力驱动的锻压机。大型的自动化锻机用于工程零件的批量生产。
A distinction may be made between open-die forging, usually in the form of hammer forging, and closed-die forging. In hammer forging, the component is shaped by hammer blows aided by relatively simple tools. These may include open dies i.e., dies that do not completely enclose the metal to be shaped.
锤锻中常用的开式模锻与闭式模锻是有区别的。在锤锻中零件通过锤击辅之以相对简单的工具成型。其中包括开式锻模，就是不完全封闭被成型金属的模具。
One of the basic operations of hammer forging is the elongation of a piece of metal by stretching with hammer blows, causing it to become thinner and longer. In hand forging the work-piece is usually turned 90°after each blow, in order to forge it thoroughly and prevent its lateral expansion.
锤锻的基本操作之一就是通过锤击使金属伸长，促成其变细变长。手工锻造时一般在每次锤击后都转过90°以充分锻打工件并防止横向膨胀。
The opposite of elongation is upsetting, which produces compressive shortening. For example, the diameter of a bar can be increased by heating and hammering axially.
与伸长相反的是镦粗，即产生压缩性缩短。例如，棒料的直径可以通过加热和轴向锤击而增大。
More important is closed-die forging, very widely used for mass production in industry, in which the metal is shaped by pressing between a pair of forging dies. The upper die is usually attached to the ram of a forging press or a forging hammer, while the lower die is stationary.
更重要的是闭式模锻，在工业上广泛用于规模生产。闭式模锻中金属在一对锻模之间挤压成型。顶模通常放在锻压机的撞头或锻锤上，而底模则是固定的。
Together they form a closed die. Closed-die forging can produce components of greater complexity and accuracy, with a better surface finish than the more traditional methods not using closed dies. The dies are made of special heat-resistant and wear-resistant tool steels.
两者合在一起形成闭式锻模。闭式模锻能生产高度复杂和精确的零件，而且表面光洁度要比不用闭式锻模的更传统方法好。闭式锻模采用特殊的耐热、耐磨工具钢制成。
A piece of hot metal sufficient to slightly overfill the die shape is placed in the bottom die, and the top die is forced against it, so that the metal takes the internal shape of the die.
将一块大小足以充填模腔并能稍有溢出的加热金属放入底模，并将顶模加压合拢，这块金属便获得该模腔的形状。Closed-die forging is used for the rapid production of large numbers of fairly small parts and also for very large components. For the latter, e.g., modern jet-aircraft components, giant hydraulically operated presses are used, which can develop forces of 50,000 tons and more.
闭式模锻用于相当小的零件大批量快速生产，也可用于很大的零件。对后者而言，例如现代喷气飞机零件，使用能产生50,000吨以上压力的巨型液力锻压机。
One valuable feature of forging is that it improves the strength of the metal by refining the structure and making it uniform; so for heavy forgings, such as marine propeller shafts, an immensely powerful hydraulic press squeezes the metal with a force sometimes as great as 10,000 tonnes.
锻造有价值的特性之一是它通过使金属组织均匀而改善强度，因此对诸如船舶螺旋桨轴之类的重型锻件，要用能达10,000吨压力的庞大而有力的液压机来挤压金属。
Although the hydraulic forging press is a more expensive piece of equipment than a drop-forge, it has advantages beside those of giving greater strength and more uniform structure to large components. On account of the high pressure and squeezing action, it operates with less noise and vibration than a drop-forge.
虽然这种液压锻机比落锤锻造要昂贵得多，但它除了能给予大零件较高的强度和更均匀的组织外还有其它优点。由于较高的压力和挤压作用，它比落锤锻造噪声及振动都小得多。
As ingots of steel weighing 30 tonnes or more are forged in this way, manual operation is impossible and it is essential that all the manipulation of the ingot is done mechanically.
由于这种情况下被锻钢坯重量大于30吨，人工操作是不可能的，钢坯的所有操作都必须是机械化的。
Forging refines the grain structure and improves physical properties of the metal. With proper design, the grain flow can be oriented in the direction of principal stresses encountered in actual use.
铸造细化金属的晶粒组织、改善其物理性能。通过适当的设计，可以使晶粒流动方向与实际使用时的主应力方向一致。
As shown in Fig.4.2, grain flow is the direction of the pattern that the crystals take during plastic deformation. Physical properties (such as strength, ductility and toughness) are much better in a forging than in the base metal, which has
crystals randomly oriented.
如图4.2所示，晶粒流动的方向就是在塑性变形期间结晶排列的方向。锻件的物理性能(如强度、延展性和韧性)远好于基础金属，因为基础金属的晶粒是无序排列的。
Forgings are consistent from piece to piece, without any of the porosity, voids, inclusions and other defects. Thus, finishing operations such as machining do not expose voids, because there aren’t any. Also coating operations such as plating or painting are straightforward due to a good surface, which needs very little preparation.
锻件各部分是连贯一致的，没有孔隙、空洞、杂质及其它缺陷。因此像机加工之类的精加工工序不会受空洞的影响，因为根本就不存在。另外由于锻件良好的表面，像电镀或油漆之类的涂装工序就很简单，几乎不需要做准备工作。
Forgings yield parts that have high strength to weight ratio, thus are often used in the design of aircraft frame members.
A forged metal can result in the following:
锻造生产的零件具有较高的强度重量比，所以常被用在飞机结构零件的设计中。
锻造金属可以导致下列结果：
?Increase length, decrease cross-section, called drawing out the metal.
?Decrease length, increase cross-section, called upsetting the metal.
?Change length, change cross-section, by squeezing in closed impression dies.
This results in favorable grain flow for strong parts.
●增加长度、减小横截面，称为延伸金属。
●减小长度、增加横截面，称为镦粗金属。
●通过用封闭锻模挤压，改变长度和横截面。
这导致有利的晶粒流使零件坚固。
?Common Forging Processes
常用的锻造工艺
The metal can be forged hot (above recrystallization temperatures) or cold.
金属既可热锻(高于再结晶温度)也可冷锻。
Open die forgings/Hand forgings. Open die forgings or hand forgings are made with repeated blows in an open die, where the operator manipulates the workpiece in the die. The finished product is a rough approximation of the die. This is what a traditional blacksmith does, and is an old manufacturing process.
开式模锻/手工锻：开式模锻或手工锻就是操作者操纵工件在开式锻模中反复击打。完成的产品是锻模的粗糙近似物。这就是传统铁匠干的活，是较古老的制造工艺。
Impression die forgings/Precision forgings.Impression die forgings and precision forgings are further refinements of the blocker forgings. The finished part more closely resembles the die impression.
压模锻/精密锻：压模锻和精密锻是雏形模锻的进一步改进。完成的零件与模膛更相似。
Press forgings. Press forgings use a slow squeezing action of a press, to transfer a great amount of compressive force to the workpiece. Unlike an open-die forging where multiple blows transfer the compressive energy to the outside of the product, press forging transfers the force uniformly to the bulk of the material.
压锻：压锻通过压力机缓慢的挤压动作将巨大的压力传递给工件。不像开式模锻那样需要多次击打把压缩能量传递到零件外表面，压锻能将力均匀地传递给材料的主体。
This results in uniform material properties and is necessary for large weight forgings. Parts made with this process can be quite large as much as 125kg(260lb) and 3m(10 feet) long.
这使材料性能一致，对大重量锻件而言是十分必要的。采用此工艺生产的零件重量可达125kg(260lb)而长度可达3m(10 feet)。
Upset forgings. Upset forging increases cross-section by compressing the length, this is used in making heads on bolts and fasteners, valves and other similar parts.
顶锻：顶锻通过压缩长度增加横截面，用于在螺栓等紧固件、柱塞及类似零件上制造头部。
Roll forgings.In roll forging, a bar stock, round or flat is placed between die rollers which reduces the cross-section and increases the length to form parts such as axles, leaf springs etc. This is an essential form of draw forging.
滚锻：在滚锻时，圆的或是扁平的棒料放在模辊之间缩小横截面增加长度制成诸如轮轴、板簧之类的零件。这是轧锻的基本形式。
Swaging. Swaging—a tube or rod is forced inside a die and the diameter is reduced as the cylindrical object is fed. The die hammers the diameter and causes the metal to flow inward causing the outer diameter of the tube or the rod to take the shape of the die.
型锻：型锻—将圆管或圆棒强制压入锻模，随着圆柱形物体的被压入其直径减小。锻模锤击横断面使金属向内流动导致圆管或圆棒的外径变为锻模的形状。
Net shape/Near-net shape forging.In net shape or near-net shape forging, forging results in wastage of material in the form of material flash and subsequent machining operations, as shown in Fig.4.3. This wastage can be as high as 70% for gear blanks, and even 90% in the case of aircraft structural parts.
纯型/近似纯型锻：采用纯型锻或近似纯型锻，产生材料损耗的主要形式是飞边以及随后的机加工，如图4.3所示。齿轮毛坯材料损耗为70% ，而飞机结构零件的材料损耗甚至达90% 。
Net-shape and near-net-shape processes minimize the waste by making precision dies, producing parts with very little draft angle (less than 1°). These types of processes often eliminate or reduce machining.
纯型锻和近似纯型锻工艺通过制作精密模具并生产锻模斜角很小(小于1°)的零件能使材料损耗最小化。此类工艺通常可以省去或减少机加工。
The processes are quite expensive in terms of tooling and the capital expenditure required. Thus, these processes can be only justified for current processes that are very wasteful where the material savings will pay for the significant increase in tooling costs.
从模具的角度而言这些工艺是相当昂贵的，需要资金投入。因此这些工艺只有对目前很浪费的生产过程，在材料节约足以补偿模具成本的大量增加时才是合理的。
?Die Design Consideration
锻模设计的考虑因素
?Parting surface should be along a single plane if possible, else following the contour of the part. The parting surface should be through the center of the part, not near the upper or lower edges.
?如果可能分模面应沿着单一平面，否则就顺着零件轮廓方向。分模面应经过零件中心，而不要靠近上下边缘。
If the parting line cannot be on a single plane, then it is good practice to use symmetry of the design to minimize the side thrust forces. Any point on the parting surface should be less than 75°from the principal parting plane.
如果分模面不能在单一平面，利用设计的对称性来减小侧向推力不失为一种好方法。分模面上任意点与主分模面的夹角应小于75°。
?As in most forming processes, use of undercuts should be avoided as these will make the removal of the part difficult, if not impossible.
?如同大多数成型工艺，如果不是非用不可，尽量避免采用凹槽，因为凹槽会使零件难以取出。
?Generous fillets and radius should be provided to aid in material flow during the forging process. Sharp corners are stress-risers in the forgings, as well as make the dies weak in service.
?Ribs should not be high or narrow; this makes it difficult for the material to flow.
?应提供尽可能大的倒角和半径以帮助材料在锻造过程中流动。锐角会增加锻件中的应力，同时在使用时削弱锻模。
?加劲肋不要过高、过窄，因为这会造成材料流动困难。
?Tolerances 公差
?Dimension tolerances are usually positive and are approximately 0.3% of the dimension, rounded off to the next higher 0.5mm(0.020in.).
?尺寸公差通常为正，大约取为该尺寸的0.3%，并圆整到较大的0.5mm(0.020in.)。
?Die wear tolerances are lateral tolerances (parallel to the parting plane) and are roughly +0.2% for copper alloys to +0.5% for aluminum and steel.
?锻模磨损公差为侧向公差(平行于分模面)，对铜合金大约为+0.2% ，对铝和钢大约为+0.5%。
?Die closure tolerances are in the direction of opening and closing, and range from 1mm(0.040in.) for small forgings, die projection area＜150cm2(23in.2), to 6.25mm(0.25in.) for large forgings, die projection area＞6,500cm2(100in.2).
?锻模的闭合公差处于开闭的方向上，范围从对较小锻件[其投影面积＜150cm2(23in.2)]取为1mm(0.040in.)，到较大锻件[其投影面积＞6,500cm2(100in.2)]取为6.25mm(0.25in.)。
?Die match tolerances are to allow for shift in the upper die with respect to the lower die.
?锻模的配合公差是为了允许上模能根据下模替换。
A proper lubricant is necessary for making good forgings. The lubricant is useful in preventing sticking of the workpiece to the die, and also acts as a thermal insulator to help reduce die wear.
制造良好的锻件必须有合适的滑润剂。滑润剂对防止工件粘住锻模很有用，还可以作为绝热体帮助减少锻模磨损。
Powder metallurgy(Fig.5.1) uses sintering process for making various parts out of metal powder. The metal powder is compacted by placing in a closed metal cavity (the die) under pressure.
粉末冶金(图5.1)采用烧结工艺将金属粉末制成各种各样的零件。金属粉末放在封闭的金属腔(模具)中在压力下被压实。
This compacted material is placed in an oven and sintered in a controlled atmosphere at high temperatures and the metal powders coalesce and form a solid. A Second pressing operation, repressing, can be done prior to sintering to improve the compaction and the material properties.
被压实的材料置于炉内烧结，在高温下炉内环境可控，金属粉末熔合形成固体。在烧结前可以进行二次挤压作业(再挤压)以改善压实状态和材料性能。
Powder metallurgy is a highly developed method of manufacturing reliable ferrous and nonferrous parts. Made by mixing elemental or alloy powders and compacting the mixture in a die, the resultant shapes are then sintered or heated in a controlled atmosphere furnace.
粉末冶金是一种高度发达的制造可靠铁或非铁零件的方法。通过混合元素或合金粉末并在模具中压实混合物，再烧结或在环境可控炉内加热制成最终形状。
?Material 材料
The majority of the structural components produced by fixed die pressing are iron-based. The powders are elemental, pre-alloyed, or partially alloyed.
大多数用固定模压制的结构件都是铁基的。粉末可以是单一元素、预先合金或部分合金。
Elemental powders, such as iron and copper, are easy to compress to relatively high densities, produce pressed compacts with adequate strength for handling during sintering, but do not produce very high strength sintered parts.
诸如铁、铜之类的单一元素粉末较容易被压得相对密度较高、生产具备足够强度的压制物供烧结处理，但是无法制造出很高强度的烧结零件。
Pre-alloyed powders are harder, less compressible and hence require higher pressing loads to produce high density compacts. However, they are capable of producing high strength sintered materials.
预先合金粉末比较硬、不容易压实，因此需要较高的挤压力来产生高密度的压制物。然而它们能生成高强度烧结材料。
Pre-alloying is also used when the production of a homogeneous material from elemental powders requires very high temperatures and long sintering times. The best examples are the stainless steels, whose chromium and nickel contents have to be pre-alloyed to allow economic production by powder metallurgy.
如果用单一元素粉末生产均匀材料需要很高温度和较长烧结时间，也可用预先合金。最好的例子是不锈钢，因含有铬和镍成分，所以粉末冶金必须用预先合金才经济。
Partially alloyed powders are a compromise approach. Elemental powders, e.g. iron with 2wt.% copper, are mixed to produce an homogeneous blend which is then partially sintered to attach the copper particles to the iron particles without producing a fully diffused powder but retaining the powder form.
部分合金粉末是一种折衷的方法。单一元素粉末，例如铁与2%的铜(重量百分比) 混合均匀，经部分烧结后铜微粒粘附到铁微粒上而没有产生充分扩散的粉末却保留了粉末的形态。
In this way the compressibilities of the separate powders in the blend are maintained and the blend will not segregate during transportation and use.
用这种方法混合物中单独粉末的可压缩性得以维持，在运送和使用期间结合将不会分离。
A similar technique is to “glue” the small percentage of alloying element onto the iron powder. This “glueing” technique is successfully used to introduce carbon into the blends, a technique which prevents carbon segregation and dusting, producing so-called “clean” powders.
另一种类似的技术是把小百分比的合金元素“粘合”到铁微粒上。这种“粘合”技术已成功用于将碳引入结合物，一种防止碳分离并起尘的技术，生产所谓的“清洁”粉末。
?Powder Consolidation
粉末合成
Components or articles are produced by forming a mass of powder into a shape, then consolidating to form inter-particle metallurgical bonds.
通过将大量的粉末放入模具成型为零件或物品，然后合成为内有微粒的冶金结合物。
An elevated temperature diffusion process referred to as sintering, sometimes assisted by external pressure, accomplishes this. The material is never fully molten, although there might be a small volume fraction of liquid present during the sintering process. Sintering can be regarded as welding the particles present in the initial useful shape.
提升温度扩散工艺被称为烧结，有时还辅之以外界的压力来达到目的。虽然在烧结过程中可能会有少量液态出现，但材料决不是全熔化。烧结可以被看作是把微粒焊接成初始的有用形状。
As a general rule both mechanical and physical properties improve with increasing density. Therefore the method selected for the fabrication of a component by powder metallurgy will depend on the level of performance required from the part. Many components are adequate when produced at 85~90% of theoretical full density whist others require full density for satisfactory performance.
作为普遍规律，随着密度的增加机械和物理性能均改善。因此选择何种粉末冶金方法来制作零件取决于其所需的性能级别。许多零件只需理论全密度的85~90%而其它的则需全密度才能满足要求。
Some components, in particular bush type bearings often made from copper and its alloys, are produced with significant and controlled levels of porosity, the porosity being subsequently filled with a lubricant.
Fortunately there is a wide choice of consolidation techniques available.
有些零件，尤其是衬套式轴承常用铜及其合金制作，控制多孔性程度的意义重大，因为这些孔随后要填充润滑剂。
还好有多种合成技术可供选择。
Cold Uniaxial Pressing
Elemental metal, or an atomized pre-alloyed powder is mixed with a lubricant, typically lithium stearate(0.75 wt.%), and pressed at pressures of say, 600MPa (87,000lb/in.2) in metal dies.
冷单向挤压
单一元素金属，或极小颗粒的预先合金粉末与润滑剂(一般是锂硬脂酸盐，重量百分比0.75%)混合，然后在金属模具中施加压力[比如600MPa (87,000lb/in.2)]挤压。
Cold compaction ensures that the as-compacted, or “green”, component is dimensionally very accurate, as it is moulded precisely to the size and shape of the die.
冷挤压能保证被压制或“未加工”的零件尺寸十分精确，因为它被精确地按模具的尺寸和形状成型。
One disadvantage of this technique is the differences in pressed density that can occur in different parts of the component due to particle/particle and die wall/particle frictional effects. Typical as-pressed densities for soft iron components would be 7.0g/cc, i. e. about 90% of theoretical density.
这种技术的缺点之一是由于微粒/微粒和模壁/微粒间的摩擦效应，零件不同部位的压实密度存在差异。典型的软铁零件压制密度为7.0g/cc，即大约是理论密度的90%。
Compaction pressure rises significantly if higher as-pressed densities are required, and this practice becomes uneconomic due to higher costs for the larger presses and stronger tools to withstand the higher pressures.
如果需要较高的压实密度则压实压力要显著提高，因为大型压力机成本较高并且在较高压力下模具强度要更高这样就不合算。
Cold Isostatic Pressing
Metal powders are contained in an enclosure e.g. a rubber membrane or a metallic can that is subjected to isostatic, which is uniform in all directions, external pressure. As the pressure is isostatic the as-pressed component is of uniform density.
冷均衡挤压
金属粉末装入均衡受压的橡胶膜或金属罐内，其所受外压力在各个方向都是均匀的。由于压力是均衡的，所以压制零件密度是均匀的。
Irregularly shaped powder particles must be used to provide adequate green strength in the as-pressed component. This will then be sintered in a suitable atmosphere to yield the required product.
必须采用不规则形状粉末微粒为压制零件提供足够的未加工强度。然后放入合适的环境中烧结成所需产品。
Normally this technique is only used for semi-fabricated products such as bars, billets, sheet, and roughly shaped components, all of which require considerable secondary operations to produce the final, accurately dimensioned component.
通常这种技术只用于制作诸如棒料、坯段、薄板及粗糙成型零件之类的半成品，所有这些都需要大量进一步加工才能生产出最终尺寸精确的零件。
Again, at economical working pressures, products are not fully dense and usually need additional working such as hot