【正文】 此處理方法對必須機(jī)加工的過共析鋼特別有用。如果把鋼緩慢加熱到恰好低于臨界溫度并且保持較長一段時(shí)間，就能得到這種組織結(jié)構(gòu)。大多數(shù)商業(yè)鋼材在軋制或鑄造后都要退火。? 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。含碳量越高，冷卻的速率必須越慢。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。 for carbon steels it can be obtained readily from the partial ironiron carbide equilibrium diagram. When the annealing temperature has been reached, the steel should be held there until it is uniform throughout.給定的鋼其退火溫度取決于它的成分；對碳鋼而言可容易地從局部的鐵碳合金平衡圖得到。退火也釋放了先前在金屬中的內(nèi)應(yīng)力。This is usually acplished 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。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。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。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時(shí)間，仍會(huì)有些額外的硬度下降。溫度的上升會(huì)使碳化物聚結(jié)而硬度繼續(xù)降低?；鼗鹱鳂I(yè)可以描述為滲碳體析出和凝聚或聚結(jié)的過程。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。回火完全淬硬鋼得到的最終組織結(jié)構(gòu)被稱為回火馬氏體。回火作業(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。通過回火，硬度和脆性可以降低到使用條件所需要的程度。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。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。熱量在鋼中的傳導(dǎo)速率是有限的。珠光體對熱處理作業(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。Above this point the hardness can be increased only slightly, because steels above the eutectoid point are made up entirely of pearlite and cementite in the annealed state. Pearlite responds best to heattreating operations。Steel with low carbon content will not respond appreciably to hardening treatment. As the carbon content in steel increases up to around %, the possible hardness obtainable also increases.含碳量低的鋼對淬火處理沒有明顯的反應(yīng)。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。截面越厚，加熱的時(shí)間就要越長才能達(dá)到均勻的結(jié)果。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)。In any heattreating 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 bees 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。A good procedure to follow is to heatquench 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)或顯微鏡檢查觀測結(jié)果。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 ironiron carbide phase diagram. However, if the position 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。因?yàn)闆]有足夠的時(shí)間讓正常的狀態(tài)反應(yīng)發(fā)生，在這種情況下對工程分析而言狀態(tài)圖不再是有用的工具。如果緩慢加熱，則以相反的方式發(fā)生這種轉(zhuǎn)化。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。當(dāng)這種鋼冷卻時(shí)，’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。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。由截線及杠桿定律分析可知，低碳鐵素體成核并長大，剩下含碳量高的奧氏體?！?線冷卻的轉(zhuǎn)變情況。This structure is posed 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。Since this chemical separation of the carbon ponent occurs entirely in the solid state, the resulting structure is a fine mechanical mixture of ferrite and cementite. Specimens prepared by polishing and etching in a weak solution of nitric acid and alcohol reveal the lamellar structure of alternating plates that forms on slow cooling.由于這種碳成分的化學(xué)分離完全發(fā)生在固態(tài)中，產(chǎn)生的組織結(jié)構(gòu)是一種細(xì)致的鐵素體與滲碳體的機(jī)械混合物。The rejected carbon forms the carbonrich cementite intermetallic with position Fe3C. In essence, the net reaction at the eutectoid is austenite %C→ferrite %C+cementite %C.被析出的碳與金屬化合物Fe3C形成富碳的滲碳體。當(dāng)鋼冷卻到727℃ (1341℉)時(shí)，將同時(shí)發(fā)生若干變化。To begin to understand these processes, consider a steel of the eutectoid position, % carbon, being slow cooled along line xx’ in . At the upper temperatures, only austenite is present, the % 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，%的共析鋼，’線慢慢冷卻。The key transition described in this diagram is the deposition of singlephase austenite(γ) to the twophase ferrite plus carbide structure as temperature drops.在此圖中描述的關(guān)鍵轉(zhuǎn)變是單相奧氏體(γ) 隨著溫度下降分解成兩相鐵素體加滲碳體組織結(jié)構(gòu)。Those portions of the ironcarbon 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 , focuses on the eutectoid region and is quite useful in understanding the properties and processing of steel.鐵碳狀態(tài)圖中靠近三角區(qū)和含碳量高于2%的那些部分對工程師而言不重要，因此將它們刪除。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。由于合