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附錄1 譯文 金屬熱處理 保羅博士 現(xiàn)代塑料（45-48頁） 1999年6月 金屬熱處理包含在廣義的冶金學(xué)研究領(lǐng)域里。冶金學(xué)是綜合化學(xué)，物理和從礦石提取到最后產(chǎn)品相關(guān)的金屬工程的一門學(xué)科。熱處理是對固態(tài)金屬進(jìn)行加熱和冷卻處理來改變金屬物理性能的一種工藝。根據(jù)使用的場合的，提高鋼的強(qiáng)度可以它的耐切削性和耐磨性，或者使鋼軟化以便于機(jī)械加工。正確的熱處理可以去掉內(nèi)應(yīng)力，減小晶粒大小，韌性增加或者在較好的材料表面給形成一個高強(qiáng)度的表面。分析鋼的成分是很有必要的，因?yàn)樾“俜直鹊哪撤N元素就會對鋼的物理性能產(chǎn)生很大的影響，特別地，碳這種元素。 合金鋼的性質(zhì)取決于含有的除碳以外的其它的一種或幾種元素，如：鎳，鉻，錳，鉬，鎢，硅，釩和銅。改善了性能的鋼可以有很多的商業(yè)用途，碳鋼是不能比的。 下面主要介紹普通商業(yè)用鋼像總所周知的普通碳素鋼的熱處理。在這個過程中冷卻速率是關(guān)鍵因素，在臨界溫度以上時快速冷卻可得到堅固的結(jié)構(gòu)，然而，非常慢的冷卻會有相反的影響。一張簡化的鐵-碳相圖 我們經(jīng)常用一張簡單的相圖來研究鋼這種材料，對工程人員來說，鐵-碳相圖中的近鐵素體區(qū)和含碳量大于2%的部分并不重要，所以這兩部分被刪掉。如表2-1 所示；它表述的是共析區(qū)，這張圖對研究鋼的性能和鋼的結(jié)晶過程是相當(dāng)有用的。 這張圖表明，一個重要的轉(zhuǎn)變是隨著溫度的降低，單相的奧氏體分解成兩相的鐵素體和碳化物?？刂七@個反應(yīng)，可以是奧氏體和鐵素體的C 溶解性有很大的不同，這樣通過熱處理就可以得到一系列的機(jī)械性能。 首先研究這個過程，在圖2-1 中，在含碳0.77%沿著線x-x’降低溫度，考慮鋼的共析化合物。在高溫時，只有奧氏體，溶0.77%的碳是溶解在溶體狀態(tài)鐵中。當(dāng)溫度下降到7270C(13410F)時，數(shù)個反應(yīng)同時發(fā)生。鐵需要從面心立方奧氏體轉(zhuǎn)變成體心立方鐵素 體結(jié)構(gòu)，但是鐵素體只能容納固溶體狀態(tài)0.02%的碳。析出的碳形成碳較富裕的滲碳體，也就是形成合成物Fe3C。基本上，這個共析轉(zhuǎn)變是： 奧氏體——〉鐵素體+ 滲碳體 0.77%C 0.02%C 6.67%C 在固體狀態(tài)里，碳的成分發(fā)生化學(xué)分離，形成了有好的機(jī)械性能混合物，鐵素體和滲碳體。這種結(jié)構(gòu)由兩種截然不同的狀態(tài)組成，但它本身有一系列特性，且因與低倍放大時的珠母層有類同之處而被稱為珠光體。 亞共析鋼比共析鋼含碳量要少的多，亞共析鋼含碳量少于0.77%?，F(xiàn)在考慮沿y-y’降溫材料特征的轉(zhuǎn)化。在高溫時，成分是奧氏體，但在冷卻線上進(jìn)入一個有鐵素體和滲碳體組成的穩(wěn)定的區(qū)域。由截線和杠桿定理分析可知，低碳鐵素體成核并不斷長大，余下含碳量高的奧氏體。溫度在7270C(13410F)時，奧氏體發(fā)生共析轉(zhuǎn)變，繼續(xù)降溫，奧氏體轉(zhuǎn)化成珠光體。最終的產(chǎn)物是鐵素體和珠光體的混合物。 過共析鋼含碳量比共析鋼多。沿z-z’線冷卻，和亞共析過程差不多。只是其中一相現(xiàn)在是滲碳體而不是鐵素體。達(dá)到共析溫度7270C 的時候，隨著富碳相的形成，奧氏體含碳量減少。同樣的余下的奧氏體在通過這個溫度是都要轉(zhuǎn)化成珠光體。 相圖中表示的轉(zhuǎn)化需要平衡條件，就是近似看作需要緩慢冷卻。隨著慢慢加熱，過程是相反的。然而，合金冷卻迅速，將得到完全不同的產(chǎn)物，因?yàn)闆]有足夠的時間完成正常的相轉(zhuǎn)化，在這種情況下，相圖就不再適用于這個工程分析了。 淬火是把鋼溫度升到臨界溫度或以上并迅速冷卻這樣一個過程。如果知道了碳含量，就可以用鐵-鐵碳化合物相圖來選擇正確的淬火溫度。然而，如果不知道鋼的成分，可以用逐步實(shí)驗(yàn)的方法來確定溫度范圍。好的處理工藝是通過對大量試件在各種溫度下進(jìn)行實(shí)驗(yàn)，然后對結(jié)果進(jìn)行分析得到的，分析的方式可以是強(qiáng)度測試也可以用精密的測試。用合適的溫度對鋼進(jìn)行熱處理后，鋼的強(qiáng)度和其它的機(jī)械性能都有很大的改善。 熱處理效率在熱處理中是非產(chǎn)重要的。熱以一定的速率從外部傳到內(nèi)部。如果鋼將加熱的太快，零件的外面比里面溫度高，將得不到一致的晶體結(jié)構(gòu)。如果零件的形狀是不規(guī)則的，考慮到零件的扭曲變形，就要用慢速加熱的方式。質(zhì)量越大的部分，越需要多的時間來加熱，從而得到成分均勻的產(chǎn)物。當(dāng)溫度達(dá)到恰當(dāng)?shù)臏囟群螅３肿銐虻囊欢螘r間，使零件最厚的部的溫度是一致的。 淬火的速率，含碳量和零件的尺寸決定了淬火獲得的硬度。對合金鋼來說，金屬元素的量和種類決定淬硬的深度（淬透性）。除了未變硬和部分淬硬的鋼，不影響硬度。 低碳鋼的淬硬性好，在含碳量低于0.6%時，隨著含碳量的升高，淬硬性也在升高。含碳量高于這個點(diǎn)，淬硬性增加不顯著，因?yàn)楣参鰷囟纫陨系匿撛谠谕嘶饡r是由珠光體和滲碳體組成。珠光體的熱處理性比較好，包括珠光體在內(nèi)的多數(shù)鋼都可以轉(zhuǎn)化成硬鋼。 隨著零件尺寸的增大，即使所有的條件都一樣，表面硬度要降低。鋼的熱傳遞速率是有限的。無論冷卻液溫度有多低，大零件內(nèi)部的冷卻速度比可能快于臨界冷卻速度，內(nèi)部硬度有一定的限制。然而，鹽水或水冷卻液可以迅速把淬火零件表面的溫度降低到冷卻液的溫度，保持或逼近它。在這種環(huán)境下，不管零件尺寸大小淬硬的深度是有限制的。在用油淬火時，就是在臨界淬火期間 表面溫度可能較高這種情況就不正確了。 回火：快速淬火得到的鋼是脆的，大部分情況不適合直接使用。通過回火，可以降低硬度和脆性來達(dá)到使用要求。隨著這些性能的降低，強(qiáng)度降低，鋼的延展性和柔韌性增加.回火就是把淬硬的鋼加熱到零界溫度以下，然后以任一速率冷卻。盡管回火可以使鐵變軟，但它與退火不同。退火是使鋼盡量靠近控制物理性能，并且多數(shù)情況下沒有把鋼變軟到退火本應(yīng)達(dá)到的程度。淬 硬的鋼完全回火后得到的組織叫回火馬氏體。 回火可以消除馬氏體的不穩(wěn)定。3000F-4000F(1500C -2050C)低溫回火,不降低鋼的硬度又可以釋放內(nèi)應(yīng)力。隨著回火溫度的升高，馬氏體加速分解。.在大約6000F（3150C）淬火鋼組織快速向回火馬氏體轉(zhuǎn)化?；鼗疬^程就是快速結(jié)合或滲碳體化合。滲碳體在6000F（3150C）迅速形成，它的硬度有所降低。溫度升高時，隨著碳化合物持續(xù)形成，硬度在降低。 回火時，還要考慮溫度以外的其它事情。盡管在到達(dá)回火溫度的前幾分鐘完成軟化，但是如果溫度的延續(xù)時間太長，硬度會降低的更多。通常的做法是把鋼的溫度升高到期望值，并保持一段合適的時間，均勻的加熱。 用局部淬火方法的兩種特別的工藝是回火的一種形式。在這兩個過程中，用鹽水淬火的鋼在冷卻之前要先保持一段時間的低溫。這些工藝,眾所周知等溫回火可以得到想要的物理性能。 退火：退火的主要目的就是使鋼變軟，以至于可以用來機(jī)械加工或冷加工。把溫度緩慢加熱到臨界溫度以上一點(diǎn)，保持一定的時間以確保整個零件的溫度是一致的，然后慢慢冷卻，以保證零件內(nèi)外的溫度幾乎保持一致。這個過程叫完全退火過程，它 轉(zhuǎn)化了以前形成的組織，又重新形成了晶體組織。并且使鋼變軟了。退火也可釋放金屬內(nèi)部的內(nèi)應(yīng)力。 退火溫度由給定碳鋼的成分決定。碳鋼在鐵碳平衡圖上很容易得到。在確定加熱速率時要要考慮零件尺寸和形狀，這樣來確保整個零件溫度盡可能同步上升。達(dá)到退火溫度后，要把溫度保持到整個零件都被加熱。零件最厚部分每英寸45mm 處常有這樣的情況。為了得到最軟和柔韌性最好的鋼，冷卻速率應(yīng)該非常慢，讓零件隨爐子一起冷卻。零件含碳量越高，冷卻速度必須越低。 正火和球化處理：正火處理過程就是把鋼加熱到500F-1000F(100C -400C)在上臨界溫度以上，然后空冷到室溫。正火主要用于低碳鋼和中碳鋼，來細(xì)化并均勻晶粒，釋放內(nèi)應(yīng)力或得到理想的機(jī)械性能。多數(shù)商業(yè)用鋼在滾壓或鑄造后都要正火處理。 球化處理產(chǎn)生一種組織，滲碳體在該組織中以球狀存在。如果鋼緩慢加熱到零界溫度以下，保持一段時間，就能得到這種組織。球狀組織能改善鋼的機(jī)械加工性能。球化處理用來處理需要加工的過共析鋼是非常有用的。 附錄2 原文 HEAT TREATMENT OF METALS Dr. Paul Engelmann MODERN PLASTICS 45 June 1999—48 June 1999 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. 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. 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. Alloy steels 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. The following discussion applies principally to the heat treatment of ordinary commercial steel 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. A Simplified Iron-carbon Diagram If we focus only on the materials normally known as steels, a simplified diagram is often used. 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. 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. Control of this reaction, which arises due to the drastically different carbon solubilities of austenite and ferrite, enables a wide range of properties to be achieved through heat treatment. 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 727oC (1341oF), several changes occur simultaneously. The iron wants to change from the fcc austenite structure to the bcc ferrite structure, but ferrite can only contain 0.02% carbon in solid solution. The rejected carbon forms the carbon-rich cementite intermetallic with composition Fe3C. In essence, the net reaction at the eutectoid is Austenite → ferrite + cementite 0.77%C????? 0.02%C???? 6.67%C 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. 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. Steels having less than the eutectoid amount of carbon (less than 0.77%) are known as hypoeutectoid steels. Consider now the transformation of such a material represented by cooling along line y-y′ in Fig.2.1. 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 lever-law calculations show that low-carbon ferrite nucleates and grows, leaving the remaining austenite richer in carbon. At 727oC (1341oF), 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. Hypereutectoid steels are steels that contain greater than the eutectoid amount of carbon. When such a steel cools, as in z-z′ of Fig.2.1, the process is similar to the hypoeutectoid case, except that the primary or proeutectoid phase is now cementite instead of ferrite. As the carbon-rich phase forms, the remaining austenite decreases in carbon content, reaching the eutectoid composition at 727oC (1341oF). As before, any remaining austenite transforms to pearlite upon slow cooling through this temperature. 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. 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. Hardening Hardening is the process of heating a piece of steel to a temperature within or above its critical range and then cooling it rapidly. 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. A good procedure to follow is to heat-quench a number of small specimens of the steel at various temperatures and observe the results, 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. 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. 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. 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. 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. Steel with low carbon content will not respond appreciably to hardening treatments. As the carbon content in steel increases up to around 0.60%, the possible hardness obtainable also increases. 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; any steel composed mostly of pearlite can be transformed into a hard steel. 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. 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. 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. Tempering 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. 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. 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. Tempering is possible because of the instability of the martensite, the principal constituent of hardened steel. Low-temperature draws, from 300o to 400oF (150o-250oC), do not cause much decrease in hardness and are used principally to relieve internal strains. As the tempering temperatures are increased, the breakdown of the martensite takes place at a faster rate, and at about 600oF (315oC) 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. A substantial precipitation of cementite begins at 600oF (315oC), which produces a decrease in hardness. Increasing the temperature causes coalescence of the carbides with continued decrease in hardness. In the process of tempering, some consideration should be given to time as well as 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. Usual practice is to heat the steel to the desired temperature and hold it there only long enough to have it uniformly heated. 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. Annealing The primary purpose of annealing is to soften hard steel so that it may be machined or cold worked. This is usually accomplished by heating the steel to 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. 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. 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. 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. When the annealing temperature has been reached, the steel should be held there until it is uniform throughout. This usually takes about 45 min 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. Normalizing and Spheroidizing The process of normalizing consists of heating the steel about 50o to 100oF (10o-40oC) above the upper critical range and cooling in still air to room temperature. 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. Spheroidizing is the process of producing a structure in which the cementite is in a spheroidal distribution. If a 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. The globular structure obtained gives improved machinability to the steel. This treatment is particularly useful for hypereutectoid steels that must be machined.