機械工程英語課文翻譯-資料下載頁

　　

【正文】 l the quenching medium may be, if the heat inside a large piece cannot escape faster than a certain critical rate, there is a definite limit to the inside hardness. However, brine or water quenching is capable of rapidly bringing the surface of the quenched part to its own temperature and maintaining it at or close to this temperature.無論淬火介質怎么冷，如果在大工件中的熱量不能比特定的臨界速率更快散發(fā)，那它內部硬度就會受到明確限制。然而鹽水或水淬火能夠將被淬零件的表面迅速冷卻至本身溫度并將其保持或接近此溫度。Under these circumstances there would always be some finite depth of surface hardening regardless of size. This is not true in oil quenching, when the surface temperature may be high during the critical stages of quenching.在這種情況下不管零件尺寸如何，其表面總歸有一定深度被硬化。但油淬情況就不是如此，因為油淬時在淬火臨界階段零件表面的溫度可能仍然很高。? Tempering 回火 Steel that has been hardened by rapid quenching is brittle and not suitable for most uses. By tempering or drawing, the hardness and brittleness may be reduced to the desired point for service conditions． 快速淬火硬化的鋼是硬而易碎的，不適合大多數場合使用。通過回火，硬度和脆性可以降低到使用條件所需要的程度。As these properties are reduced there is also a decrease in tensile strength and an increase in the ductility and toughness of the steel. The operation consists of reheating quenchhardened steel to some temperature below the critical range followed by any rate of cooling. 隨著這些性能的降低，拉伸強度也降低而鋼的延展性和韌性則會提高。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。Although this process softens steel, it differs considerably from annealing in that the process lends itself to close control of the physical properties and in most cases does not soften the steel to the extent that annealing would. The final structure obtained from tempering a fully hardened steel is called tempered martensite.雖然這過程使鋼軟化，但它與退火是大不相同的，因為回火適合于嚴格控制物理性能并在大多數情況下不會把鋼軟化到退火那種程度。回火完全淬硬鋼得到的最終組織結構被稱為回火馬氏體。 Tempering is possible because of the instability of the martensite, the principal constituent of hardened steel. Lowtemperature draws, from 300℉ to 400℉ (150℃~205℃), do not cause much decrease in hardness and are used principally to relieve internal strains. 由于馬氏體這一淬硬鋼主要成分的不穩(wěn)定性，使得回火成為可能。低溫回火， 300℉到400℉(150℃~205℃)，不會引起硬度下降很多，主要用于減少內部應變。 As the tempering temperatures are increased, the breakdown of the martensite takes place at a faster rate, and at about 600℉(315℃) the change to a structure called tempered martensite is very rapid. The tempering operation may be described as one of precipitation and agglomeration or coalescence of cementite. 隨著回火溫度的提高，馬氏體以較快的速率分解，并在大約600℉(315℃)迅速轉變?yōu)楸环Q為回火馬氏體的結構。回火作業(yè)可以描述為滲碳體析出和凝聚或聚結的過程。 A substantial precipitation of cementite begins at 600℉(315℃), which produces a decrease in hardness. Increasing the temperature causes coalescence of the carbides with continued decrease in hardness.滲碳體的大量析出開始于600℉(315℃)，這使硬度下降。溫度的上升會使碳化物聚結而硬度繼續(xù)降低。 In the process of tempering, some consideration should be given to time as well as to temperature. Although most of the softening action occurs in the first few minutes after the temperature is reached, there is some additional reduction in hardness if the temperature is maintained for a prolonged time. 在回火過程中，不但要考慮溫度而且要考慮時間。雖然大多數軟化作用發(fā)生在達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間，仍會有些額外的硬度下降。Usual practice is to heat the steel to the desired temperature and hold it there only long enough to have it uniformly heated.通常的做法是將鋼加熱到所需溫度并且僅保溫到正好使其均勻受熱。 Two special processes using interrupted quenching are a form of tempering. In both, the hardened steel is quenched in a salt bath held at a selected lower temperature before being allowed to cool. These processes, known as austempering and martempering, result in products having certain desirable physical properties. 兩種采用中斷淬火的特殊工藝也是回火的形式。這兩種工藝中，淬硬鋼在其被允許冷卻前先在一選定的較低溫度鹽浴淬火。這兩種分別被稱為奧氏體回火和馬氏體回火的工藝，能使產品具有特定所需的物理性能。 ? Annealing 退火 The primary purpose of annealing is to soften hard steel so that it may be machined or cold worked. 退火的主要目的是使堅硬的鋼軟化以便機加工或冷作。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部的溫度近似相同。This process is known as full annealing because it wipes out all trace of previous structure, refines the crystalline structure, and softens the metal. Annealing also relieves internal stresses previously set up in the metal.這過程被稱為完全退火，因為它去除了以前組織結構的所有痕跡、細化晶粒并軟化金屬。退火也釋放了先前在金屬中的內應力。 The temperature to which a given steel should be heated in annealing depends on its position。 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。達到退火溫度后，鋼應當保持在此溫度等到全部均勻受熱。This usually takes about 45min for each inch(25mm) of thickness of the largest section. For maximum softness and ductility the cooling rate should be very slow, such as allowing the parts to cool down with the furnace. The higher the carbon content, the slower this rate must be.加熱時間一般以工件的最大截面厚度計每英寸(25mm )大約需45min。為了得到最大柔軟性和延展性冷卻速率應該很慢，比如讓零件與爐子一起冷下來。含碳量越高，冷卻的速率必須越慢。The heating rate should be consistent with the size and uniformity of sections, so that the entire part is brought up to temperature as uniformly as possible.加熱的速率也應與截面的尺寸及均勻程度相協調，這樣才能使整個零件盡可能均勻地加熱。? Normalizing and Spheroidizing正火和球化 The process of normalizing consists of heating the steel about 50℉ to 100℉ (10℃~40℃) above the upper critical range and cooling in still air to room temperature. 正火處理包括先將鋼加熱到高于上臨界區(qū)50℉到100℉(10℃~40℃)然后在靜止的空氣中冷卻到室溫。This process is principally used with low and mediumcarbon steels as well as alloy steels to make the grain structure more uniform, to relieve interna