【正文】 This process is principally used with low and mediumcarbon steels as well as alloy steels to make the grain structure more uniform, to re。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(xié)調，這樣才能使整個零件盡可能均勻地加熱。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。達到退火溫度后，鋼應當保持在此溫度等到全部均勻受熱。 The temperature to which a given steel should be heated in annealing depends on its position。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。 ? 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。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。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。 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。 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。 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。 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。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(shù)情況下不會把鋼軟化到退火那種程度。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。? Tempering 回火 Steel that has been hardened by rapid quenching is brittle and not suitable for most uses. By tempering or drawing, the hardness and brittleness may be reduced to the desired point for service conditions． 快速淬火硬化的鋼是硬而易碎的，不適合大多數(shù)場合使用。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。No matter how cool the quenching medium may be, if the heat inside a large piece cannot escape faster than a certain critical rate, there is a definite limit to the inside hardness. However, brine or water quenching is capable of rapidly bringing the surface of the quenched part to its own temperature and maintaining it at or close to this temperature.無論淬火介質怎么冷，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。 As the size of parts to be hardened increases, the surface hardness decreases somewhat even though all other conditions have remained the same. There is a limit to the rate of heat flow through steel. 即使所有其它條件保持不變，隨著要淬火的零件尺寸的增加其表面硬度也會有所下降。 and steel posed mostly of pearlite can be transformed into a hard steel. 高于此點，由于超過共析點鋼完全由珠光體和退火狀態(tài)的滲碳體組成，硬度增加并不多。%，可能得到的硬度也增加。除了非淬硬鋼或部分淬硬鋼外，合金鋼中合金元素的種類及含量僅影響鋼的淬透性(工件被硬化到深層的能力)而不影響硬度。Even after the correct temperature has been reached, the piece should be held at that temperature for a sufficient period of time to permit its thickest section to attain a uniform temperature.即使加熱到正確的溫度后，工件也應在此溫度下保持足夠時間以讓其最厚截面達到相同溫度。If a piece is irregular in shape, a slow rate is all the more essential to eliminate warping and cracking. The heavier the section, the longer must be the heating time to achieve uniform results. 如果工件形狀不規(guī)則，為了消除翹曲和開裂最根本的是加熱速率要緩慢。熱量以一定的速率從鋼的外部傳導到內部。一旦獲得正確的溫度，硬度和其它性能都將有明顯的變化。然而當鋼的成分不知道時，則需做一些預備試驗來確定其溫度范圍。? Hardening 淬火 Hardening is the process of heating a piece of steel to a temperature within or above its critical range and then cooling it rapidly. 淬火就是把鋼件加熱到或超過它的臨界溫度范圍，然后使其快速冷卻的過程。However, when alloys are cooled rapidly, entirely different results may be obtained, because sufficient time is not provided for the normal phase reactions to occur, in such cases, the phase diagram is no longer a useful tool for engineering analysis.
然而，當快速冷卻合金時，可能得到完全不同的結果。 It should be remembered that the transitions that have been described by the phase diagrams are for equilibrium conditions, which can be approximated by slow cooling. With slow heating, these transitions occur in the reverse manner. 應該記住由狀態(tài)圖描述的這種轉化只適合于通過緩慢冷卻的近似平衡條件。As the carbonrich phase forms, the remaining austenite decreases in carbon content, reaching the eutectoid position at 727℃(1341℉). As before, any remaining austenite transforms to pearlite upon slow coolin