熱處理畢業(yè)論文外文翻譯

1、<p><b>　　附錄一</b></p><p><b>　　外文翻譯</b></p><p><b>　　原文：</b></p><p>　　Heat Treatment</p><p>　　The understanding of heat treatment

2、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. </p><p>　　Heat treatment is the operation of

3、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. &

4、lt;/p><p>　　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

5、because small percentages of certain elements, notably carbon, greatly affect the physical properties.</p><p>　　Alloy steel owe their properties to the presence of one or more elements other than carbon, na

6、mely 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.</p><

7、;p>　　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

8、above the critical range results in hard structure, whereas very slow cooling produces the opposite effect.</p><p>　　If we focus only on the materials normally known as steels, a simplified diagram is of

9、ten used. </p><p>　　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 t

10、he one in Fig.2.1, focuses on the eutectoid region and is quite useful in understanding the properties and processing of steel. </p><p>　　The key transition described in this diagram is the decomposition of

11、single-phase austenite(γ) to the two-phase ferrite plus carbide structure as temperature drops. </p><p>　　Control of this reaction, which arises due to the drastically different carbon solubility of austen

12、ite and ferrite, enables a wide range of properties to be achieved through heat treatment.</p><p>　　To begin to understand these processes, consider a steel of the eutectoid composition, 0.77% carbon, bei

13、ng 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 occ

14、ur simultaneously.</p><p>　　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. </p><p>　　The

15、 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.</p><p>　　Since this

16、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 solut

17、ion of nitric acid and alcohol reveal the lamellar structure of alternating plates that forms on slow cooling.</p><p>　　This structure is composed of two distinct phases, but has its own set of characteristi

18、c properties and goes by the name pearlite, because of its resemblance to mother- of- pearl at low magnification.</p><p>　　Steels having less than the eutectoid amount of carbon (less than 0.77%) are known

19、 as hypo-eutectoid steels. Consider now the transformation of such a material represented by cooling along line y-y’ in Fig.2.1. </p><p>　　At high temperatures, the material is entirely austenite, but upon

20、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.</p>

21、<p>　　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

22、 ferrite (ferrite that formed above the eutectoid reaction) and regions of pearlite.</p><p>　　Hypereutectoid steels are steels that contain greater than the eutectoid amount of carbon. When such steel cool

23、s, 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.</p><p>　　As the carbon-rich phase forms,

24、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.</p><

25、;p>　　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

26、in the reverse manner. </p><p>　　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 su

27、ch cases, the phase diagram is no longer a useful tool for engineering analysis.</p><p><b>　　Hardening</b></p><p>　　Hardening is the process of heating a piece of steel to a temper

28、ature within or above its critical range and then cooling it rapidly. </p><p>　　If the carbon content of the steel is known, the proper temperature to which the steel should be heated may be obtained by refe

29、rence 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. </p><p>　　A good procedure to

30、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

31、will be a marked change in hardness and other properties. </p><p>　　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.

32、If the steel is heated too fast, the outside becomes hotter than the interior and uniform structure cannot be obtained. </p><p>　　If a piece is irregular in shape, a slow rate is all the more essential to el

33、iminate warping and cracking. The heavier the section, the longer must be the heating time to achieve uniform results. </p><p>　　Even after the correct temperature has been reached, the piece should be held

34、at that temperature for a sufficient period of time to permit its thickest section to attain a uniform temperature.</p><p>　　The hardness obtained from a given treatment depends on the quenching rate, the ca

35、rbon 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 har

36、dness except in unhardened or partially hardened steels.</p><p>　　Steel with low carbon content will not respond appreciably to hardening treatment. As the carbon content in steel increases up to around 0.60

37、%, the possible hardness obtainable also increases. </p><p>　　Above this point the hardness can be increased only slightly, because steels above the eutectoid point are made up entirely of pearlite and cemen

38、tite in the annealed state. Pearlite responds best to heat-treating operations; and steel composed mostly of pearlite can be transformed into a hard steel. </p><p>　　As the size of parts to be hardened incre

39、ases, 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. </p><p>　　No matter how cool the quenching medi

40、um 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 surfac

41、e of the quenched part to its own temperature and maintaining it at or close to this temperature.</p><p>　　Under these circumstances there would always be some finite depth of surface hardening regardless of

42、 size. This is not true in oil quenching, when the surface temperature may be high during the critical stages of quenching.</p><p>　　Tempering </p><p>　　Steel that has been hardened by rapid que

43、nching 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．</p><p>　　As these properties are reduced th

44、ere 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 a

45、ny rate of cooling. </p><p>　　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 cau

46、se much decrease in hardness and are used principally to relieve internal strains. </p><p>　　Although this process softens steel, it differs considerably from annealing in that the process lends itself to cl

47、ose 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.<

48、/p><p>　　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. Th

49、e tempering operation may be described as one of precipitation and agglomeration or coalescence of cementite. </p><p>　　A substantial precipitation of cementite begins at 600℉(315℃), which produces a decrea

50、se in hardness. Increasing the temperature causes coalescence of the carbides with continued decrease in hardness.</p><p>　　In the process of tempering, some consideration should be given to time as well as

51、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

52、. </p><p>　　Usual practice is to heat the steel to the desired temperature and hold it there only long enough to have it uniformly heated.</p><p>　　Two special processes using interrupted quench

53、ing 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 pr

54、oducts having certain desirable physical properties.</p><p>　　Annealing </p><p>　　The primary purpose of annealing is to soften hard steel so that it may be machined or cold worked.</p>

55、<p>　　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 controll

56、ed rate so that the temperature of the surface and that of the center of the piece are approximately the same.</p><p>　　This process is known as full annealing because it wipes out all trace of previous stru

57、cture, refines the crystalline structure, and softens the metal. Annealing also relieves internal stresses previously set up in the metal.</p><p>　　The temperature to which a given steel should be heated in

58、 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

59、until it is uniform throughou</p><p>　　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

60、 allowing the parts to cool down with the furnace. The higher the carbon content, the slower this rate must be.</p><p>　　The heating rate should be consistent with the size and uniformity of sections, so th

61、at the entire part is brought up to temperature as uniformly as possible.</p><p>　　Normalizing and Spheroidizing</p><p>　　The process of normalizing consists of heating the steel about 50℉ to 10

62、0℉ (10℃~40℃) above the upper critical range and cooling in still air to room temperature.</p><p>　　This process is principally used with low- and medium-carbon steels as well as alloy steels to make the gra

63、in 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.</p><p>　　Spheroidizing is the

64、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 struct

65、ure will be obtained. </p><p>　　The globular structure obtained gives improved machinability to the steel. This treatment is particularly useful for hypereutectoid steels that must be machined.</p>&l

66、t;p>　　Carburizing</p><p>　　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 f

67、or carbon.</p><p>　　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 par

68、t. The depth of the case depends on the time and temperature of the treatment.</p><p>　　Pack carburizing consists of placing the parts to be treated in a closed container with some carbonaceous material such

69、 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.</p><p>　　Steel for carburizing is usually a low-carbon steel of about 0.15% c

70、arbon 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.</p><p>

71、;　　A steel with varying carbon content and, consequently, different critical temperatures requires a special heat treatment. </p><p>　　Because there is some grain growth in the steel during the prolonged car

72、burizing 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

73、 case and quenched to produce a hard, fine structure.</p><p>　　The lower heat-treating temperature of the case results from the fact that hypereutectoid steels are normally austenitized for hardening just a

74、bove the lower critical point. A third tempering treatment may be used to reduce strains.</p><p>　　Carbonitriding</p><p>　　Carbonitriding, sometimes known as dry cyaniding or nicarbing, is a ca

75、se-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.</p><p>　　Any carbon-rich gas with ammonia can be u

76、sed. 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, p

77、ermitting the use of low-cost steels.</p><p><b>　　Cyaniding</b></p><p>　　Cyaniding, or liquid carbonitriding as it is sometimes called, is also a process that combines the absorption

78、 of carbon and nitrogen to obtain surface hardness in low-carbon steels that do not respond to ordinary heat treatment. </p><p>　　The part to be case hardened is immersed in a bath of fused sodium cyanide sa

79、lts 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. </p><p>　　Case depths of 0.0

80、05 to 0.015in. (0.13~0.38mm) may be readily obtained by this process. Cyaniding is used principally for the treatment of small parts.</p><p><b>　　Nitriding</b></p><p>　　Nitriding is

81、somewhat similar to ordinary case hardening, but it uses a different material and treatment to create the hard surface constituents. </p><p>　　In this process the metal is heated to a temperature of around 9

82、50℉(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.</p>

83、<p>　　Nitrogen has greater hardening ability with certain elements than with others, hence, special nitriding alloy steels have been developed. </p><p>　　Aluminum in the range of 1% to 1.5% has proved t

84、o 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℃).</p><p>　　Liquid nitriding uti

85、lizes 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. <

86、;/p><p>　　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.&

87、lt;/p><p>　　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. </p>&

88、lt;p>　　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

89、, because there is no scale or further work necessary after this process.</p><p>　　Fortunately, the interior structure and properties are not affected appreciably by the nitriding treatment and, because no q

90、uenching 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.&

91、lt;/p><p><b>　　譯文：</b></p><p><b>　　熱處理</b></p><p>　　對(duì)熱處理的理解包含于對(duì)冶金學(xué)較廣泛的研究。冶金學(xué)是物理學(xué)、化學(xué)和涉及金屬?gòu)牡V石提煉到最后產(chǎn)物的工程學(xué)。</p><p>　　熱處理是將金屬在固態(tài)加熱和冷卻以改變其物理性能的操作。按所采用的步驟

92、，鋼可以通過(guò)硬化來(lái)抵抗切削和磨損，也可以通過(guò)軟化來(lái)允許機(jī)加工。</p><p>　　使用合適的熱處理可以去除內(nèi)應(yīng)力、細(xì)化晶粒、增加韌性或在柔軟材料上覆蓋堅(jiān)硬的表面。因?yàn)槟承┰?尤其是碳)的微小百分比極大地影響物理性能，所以必須知道對(duì)鋼的分析。</p><p>　　合金鋼的性質(zhì)取決于其所含有的除碳以外的一種或多種元素，如鎳、鉻、錳、鉬、鎢、硅、釩和銅。由于合金鋼改善的物理性能，它們被大量使

93、用在許多碳鋼不適用的地方。</p><p>　　下列討論主要針對(duì)被稱(chēng)為普通碳鋼的工業(yè)用鋼而言。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。</p><p>　　如果只把注意力集中于一般所說(shuō)的鋼上，經(jīng)常要用到簡(jiǎn)化鐵碳狀態(tài)圖。</p><p>　　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(duì)工程師而言不重要，因此

94、將它們刪除。如圖2.1所示的簡(jiǎn)化鐵碳狀態(tài)圖將焦點(diǎn)集中在共析區(qū)，這對(duì)理解鋼的性能和處理是十分有用的。</p><p>　　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)。</p><p>　　控制這一由于奧氏體和鐵素體的碳溶解性完全不同而產(chǎn)生的反應(yīng)，使得通過(guò)熱處理能獲得很大范圍的特性。</p><p>　　為了理解這些過(guò)程，考慮

95、含碳量為0.77%的共析鋼，沿著圖2.1的x-x’線慢慢冷卻。在較高溫度時(shí)，只存在奧氏體，0.77%的碳溶解在鐵里形成固溶體。當(dāng)鋼冷卻到727℃ (1341℉)時(shí)，將同時(shí)發(fā)生若干變化。</p><p>　　鐵需要從面心立方體奧氏體結(jié)構(gòu)轉(zhuǎn)變?yōu)轶w心立方體鐵素體結(jié)構(gòu)，但是鐵素體只能容納固溶體狀態(tài)的0.02%的碳。</p><p>　　被析出的碳與金屬化合物Fe3C形成富碳的滲碳體。本質(zhì)上，共析體

96、的基本反應(yīng)是奧氏體0.77%的碳→鐵素體0.02%的碳+滲碳體6.67%的碳。</p><p>　　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。通過(guò)打磨并在弱硝酸酒精溶液中蝕刻制備的樣本顯示出由緩慢冷卻形成的交互層狀的薄片結(jié)構(gòu)。</p><p>　　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(lèi)同

97、之處而被稱(chēng)為珠光體。</p><p>　　在較高溫度時(shí)，這種材料全部是奧氏體，但隨著冷卻就進(jìn)入到鐵素體和奧氏體穩(wěn)定狀態(tài)的區(qū)域。由截線及杠桿定律分析可知，低碳鐵素體成核并長(zhǎng)大，剩下含碳量高的奧氏體。</p><p>　　在727℃(1341℉)時(shí)，奧氏體為共析組成(含碳量0.77%)，再冷卻剩余的奧氏體就轉(zhuǎn)化為珠光體。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

98、混合物。</p><p>　　過(guò)共析鋼是含碳量大于共析量的鋼。當(dāng)這種鋼冷卻時(shí)，就像圖2.1的z-z’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(lèi)似亞共析鋼的情況。</p><p>　　隨著富碳部分的形成，剩余奧氏體含碳量減少，在727℃(1341℉)時(shí)達(dá)到共析組織。就像以前說(shuō)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。</p><p>　　應(yīng)該

99、記住由狀態(tài)圖描述的這種轉(zhuǎn)化只適合于通過(guò)緩慢冷卻的近似平衡條件。如果緩慢加熱，則以相反的方式發(fā)生這種轉(zhuǎn)化。</p><p>　　然而，當(dāng)快速冷卻合金時(shí)，可能得到完全不同的結(jié)果。因?yàn)闆](méi)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(duì)工程分析而言狀態(tài)圖不再是有用的工具。</p><p><b>　　淬火</b></p><p>　　淬火就是把鋼件加熱

100、到或超過(guò)它的臨界溫度范圍，然后使其快速冷卻的過(guò)程。</p><p>　　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。然而當(dāng)鋼的成分不知道時(shí)，則需做一些預(yù)備試驗(yàn)來(lái)確定其溫度范圍。</p><p>　　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(guò)硬度試驗(yàn)或顯微鏡檢查觀測(cè)結(jié)果。一旦獲得正確的溫度，硬度和其它性能都將有明顯的變化。 </p>