普通碳素鋼的淬火與回火英文翻譯

1、Hardening and Tempering of Plain Carbon SteelPlain carbon steel has been valued from early time because of certain properties. this soft silver-gray metal could be converted into a superhard substance that would cut glass and many other substance，sincluding itself when soft. Furthermore，its hardness

2、 could be controlled. This converting of carbon steel into a steel of useful hardnessis done with different heat treatments， two of the most important of which are hardening and tempering (drawing)，what s theapinl carbon steel and which you will investigate in this lesson.Plain Carbon SteelIn simple

3、 terms，a plain carbon steel may be said to be an alloy of iron and carbon containing less than 1.7% carbon. In practic，e however，these steels rarely contain more than about 1.4% carbon and other elements are also present， either as deliberate additions(e.g. manganese) or as impurities(e.g. sulphur a

4、nd phosphorus).Plain carbon steels may be classified into three main groups:1. Low carbon steel (mild steel) containing less than 0.3% carbon.2. Medium carbon steel containing 0.3% to 0.6% carbon.3. High carbon steel containing 0.6% to 1.4% carbon.Low carbon steelLow carbon steels may be sub-divided

5、 into:1. Dead mild steel containing 0.05% to 0.10% carbonIn the manufacture of this materia，l complete deoxidation is not carried out and it is made as rimming steel. It is produced as hot and cold worked she，etstrip，rod，wire and tube，and is available in the hot-worked or process annealed condition

6、for the deep drawing of sheet，but the strength is low. This type of steel is used for the manufacture of motorcar bodies，refrigerators，washing machines，office furniture ，pressings，rivets and nails.2. Carburising steels containing 0.1% to 0.2% carbonThe strength and hardness of these steels is lo，w b

7、ut a hard surface can be obtained by carburizing in order to combine a wear-resistant surface with tough core properties. The ductility makes rapid machining difficult unless the Mn and S content is increased by using a shlphur content of 0.2% to 0.3% with about 1% manganese.3. Constructional mild s

8、teels containing 0.2% to 0.3% carbonAs the carbon content is raised above 0.2% ，the strength increases into the range required for constructional purposes，but the ductility decreases. The fabrication qualities (working and welding characteristics) of this material are very good. The steel is hot-rol

9、led into plate for making boilers ，ships and vehicles，and also into sections (e. g. girders，beams， joists) for use in bridges and buildings. The steel is often used in the hot-rolled condition ，but the smaller sized material may be normalized.It has been estimated that about 90% (by weight) of all s

10、teel used is of this low carbon classification.Medium Carbon SteelsMedium carbon steels are often quenched-hardened and fully tempered to give good strength with maximum toughness, which are the properties required of components such as shafts, gears and connecting rods. Steels containing 0.4% to 0.

11、5% carbon may also be surface hardened by localized heating and quenching.High Carbon SteelHigh carbon steel are quench hardened and lightly tempered to give high hardness with only limited toughness. Material in this classification is mainly used for making fairly small, relatively inexpensive cutt

12、ing tools so that the group as a whole is known as carbon tool steel. Steels containing 0.6% to 0.8% carbon are used for making dies , springs , wire ropes and railway types . Many different kinds of tools are made form higher carbon steels as indicated below .Carbon%Type of tool0.81.0Cold chisels,

13、shear blades, punches, hammers1.01.2Files, axes, saws, knives1.21.4Razors, drills, wood-cutting and metal-cutting toolsLimitations of Plain Carbon SteelsPlain carbon steels have many limitations including the following:(1) If reasonable toughness and ductility are required, the maximum tensile stren

14、gth2 obtainable is about 700N/mm .(2) Large sections cannot be effectively hardened, thus restricting their use to relatively thin sections.(3) Water quenching is necessary for full hardening with consequent risk of distortion and cracking.(4) Rapid softening above about 300 Co limits their use for

15、high-speed metal cutting.(5) Poor resistance to corrosion and to oxidation at elevated temperatures.To overcome these limitations, additional elements are added to the steel to give alloy steels with specific properties. The main alloying elements include manganese, nickel, chromium, molybdenum, tun

16、gsten, vanadium, cobalt and silicon.Hardening of Plain Carbon SteelAs steel is heated above the lowed critical temperature of 1330F(72o1C)，the carbon that was in the from of layers of iron carbide in pearlite begins to dissolve in the iron and from a solid solution called austenite. When this soluti

17、on of iron and carbon is suddenly cooled or quenched，a new microstructure is formed. This is called martensite. Martensite is very hard and brittle ，having a much higher tensile strength than the steel with a pearlite microstructure. It is quite unstable，however，and must be tempered(drawn) to reliev

18、e internal stresses in order to have the ductility and toughness needed to be useful. AISIC1095， commonly known as water-hardening tool(W1) steel ，will begin to show hardness when quenched from a temperature just over 1330F(72o1C) but will not harden at all if quenched from a temperature lower than

19、1330F(721oC). This steel will become as hard as it can get when heated to 1450(78o8C) and quenched in water. This quenching temperature changes as the carbon content changes.It should be 50F(28oC) above the upper critical temperature for carbon steels containing less than 0.83 percent carbon. The re

20、ason carbon steel， less than eutectoid，should be heated above the upper critical temperature is that the ferrite is not all transformed into austenite below this point ， and when quenched，is retained in the martensitic structure. The retained ferrite causes brittleness even after tempering.Low carbo

21、n steels such as AISI1020 will no，t for all practical purposes，harden when they are heated and quenched. Oil-and air-hardening steels have a higher hardenability and do not have to be quenched as rapidly as plain carbon steels. Consequen，tlythey are deeper hardening than water hardening types，which

22、must be cooled to 200F(93oC) within 1 or 2 seconds. Plain carbon steels containing 0.83 percent carbon can get as hard (RC67) as any plain carbon steel containing more carbon.Tempering of Plain Carbon SteelTempering，or drawing，is a process of reheating a steel part that has been previously to transf

23、orm some of the hard martensite into softer structures. The higher the tempering temperature used， the more martensite is transformed，and the softer and tougher(less brittle) the piece becomes. Therefore，tempering temperatures are specified according to the strength and ductility desired. Mechanical

24、 properties charts， which may be found in steel manufacturers handbooks and catalog，s give these data for each type of alloy steel.temperature and holding it there for a length of time， then cooling it in air or water. A part can be tempered in a furnace or oven by bringing it to the required Some t

25、ool steels should be cooled rapidly after tempering to avoid temper brittleness.Tempering should be done as soon as possible after hardening. The part should not be allowed to cool completely ， since untempered it contains very high internal stresses and tends to split or crack. Tempering will relie

26、ve the internal stresses. A hardened part left overnight without tempering may develop cracks by itself.Classification of Heat Treating ProcessesIn some instances， heat treatment procedures are clear cut in terms of technique and application whereas in other instances， descriptions or simple explana

27、tions are insufficient because the same technique frequently may be used to obtain different objectivesFor example， stress relieving and tempering are often accomplished with the same equipment and by use of identical time and temperature cycles The objectives， however，are different for the two proc

28、essesThe following descriptions of the principal heat treating processesare generally arrangedNormalizing usually is used as a conditioning treatment， notably for refining the grains of steels that have been subjected to high temperatures forforging or other hot working Operations.The normalizing pr

29、ocess usually is succeeded by another heat treating operation such as austenitizing for hardenin，g annealing， or temperingAnnealing IS a generic term denoting a heat treatment that consisis of heating to and holding at a suitable temperature followed by cooling at a suitable rateIt is used primarily

30、 to soften metallic materials，but also to simultaneously produce desired changes in other properties or in microstructure.The purpose of such changes may be，but is not confined to， improvement Of machinability ， facilitation of cold work(known as in process annealing)， improvement of mechanical or e

31、lectrical properties， or to increase dimensional stabilityWhen applied solely to reIieve stresses，it commonly is called stressrelief annealing，synonymous with stress relievingWhen the term “ annealing a”pipslied to ferrous alloys without qualification,full annealing is implied This is achieved by he

32、ating above the alloy tisansformation temperature，then applying a cooling cycle which provides maximum softnessThis cycle may vaiy widely，depending on composition and chaiacteiistics of the specific alloyQuenching is the iapid cooling of a steel oi alloy fiom the austenitizing tempeiatuie byimmeisin

33、g the woikpiece in a liquid oi gaseous mediumQuenching media commonly used include watei，5%biine，5caustic in an aqueous solution，oil，polymei solutions， oi gas(usually aii oi nitiogen ).Selection of a quenching medium depends laigely on the haidennability of the mateiial and the mass of mateiial bein

34、g tieated (piincipally section thickness).The cooling capabilities of the above-listed quenching media vaiy gieatly. In selecting a quenching medium, it is best to avoid a solution that has moie cooling powei than is needed to achieve the iesults, thus minimizing the possibility of ciacking and waip

35、age of the paits being tieated. Modifications of the teim quenching include diiect quenching, fog quenching, hot quenching, inteiiupted quenching selective quenching, spiay quenching, and time quenching.Tempeiing. In heat tieating of feiious alloys, tempeiing consists of ieheating the austenitized a

36、nd quench-haidenedsteel oi iion to some pieselectedtempeiatuie that is below the lowei tiansfoimation tempeiatuie (geneially below 1300 F oi 705). Tempeiing offeis a means of obtaining vaiious combinations of mechanical piopcities. Tempeiing tempeiatuies used foi haidened steels aie often no highei

37、than 300 F(150). The teim “tempeiings”hould not be confused with eithei piocess annealing oi stiess ielieving. Even though time and tempeiatuie cycles foi the thiee piocesses may be the same, the conditions of the mateiials being piocessed and the objectives may be diffeient.Stiess ielieving. Like t

38、empeiing, stiess ielieving is always done by heating to some tempeiatuie below the lowei tiansfoimation steels and iions. Foi nonfeiious metals, the temperature may vary form slightly above room temperature to several hundred degrees, depending on the alloy and the amount of stress relief that is de

39、sired.The primary purpose of stress relieving is to relieve stresses that have been imparted to the workpiece form such processesas forming, rolling, machining or welding. The usual procedure is to heat workpieces to the pre-established temperature long enough to reduce the residual stresses(this is

40、 a time-and temperature-dependentoperation) to an acceptable level; this is followed by cooling at a relatively slow rate to avoid creation of new stresses.普通碳素鋼的淬火與回火很久以前，普通碳素鋼就因其某些性能而受到重視，這種銀灰色的軟金屬能夠 轉(zhuǎn)變呈一種超硬的物質(zhì)，該物質(zhì)可以切削玻璃和許多其他物質(zhì)，包括處于軟狀態(tài)的 該金屬本身。此外，普通碳素鋼的硬度也可以控制。這種根據(jù)用途使碳鋼具有不同 硬度的轉(zhuǎn)變，可以有不同的熱處理來實現(xiàn)，其中兩種最

41、重要的熱處理方法就是淬火 和回火。什么是普通碳素鋼及其淬火和回火是本篇文章所要研究的內(nèi)容。普通碳素鋼簡單地說，普通碳素鋼是鐵與含量小于 1.7% 的碳組成的合金。然而，在實際生產(chǎn)中，碳鋼的含碳量很少超過 1.4% 。此外，碳鋼中還存在其它的元素，這些元素或 者是有意加入鋼中的（如錳） ，或者是雜質(zhì)元素（如硫與磷） 。普通碳素鋼可以被分為三個主要類別：（1）低碳鋼（軟鋼），含碳量低于 0.3% ；（2）中碳鋼，含碳量 0.3% 0.5% ；（3）高碳鋼，含碳量 0.6% 1.4% 。低碳鋼低碳鋼可再劃分為：1. 極軟低碳鋼，含碳 0.05% 0.10% 在制造過程中，這種材料沒有進(jìn)行彎曲脫氧，因

42、此，這種鋼是沸騰鋼。這種鋼 被制造成冷軋或熱軋的板材、 帶材、 棒材、線材和管材， 適宜在熱加工狀態(tài)下使用。 這類鋼有極好的塑性，這對于鋼板的拉伸非常重要。但這類鋼的強度低，常用于制 造汽車的車體、電冰箱、洗衣機、辦公設(shè)備、沖壓件、鉚釘和鐵釘?shù)取?. 滲碳鋼，含碳 0.1% 0.2% 這類鋼強度硬度低，但通過滲碳可以獲得一個硬的表面，從而表面耐磨，心部 韌性好。這類鋼的塑性使得對其快速切削加工變得困難， 除非通過加入 0.2% 0.3% 的硫和大約1%的錳，使Mn、S的含量增加，才可解決這一問題。3. 低碳結(jié)構(gòu)鋼，含碳 0.2% 0.3%當(dāng)含碳量增加至 0.2%以上時， 鋼的強度便增加至結(jié)構(gòu)件

43、所需要的范圍內(nèi)， 但鋼 的塑性降低。這類鋼的制造屬性（加工性和焊接性）很好。這類鋼可熱軋成用于制 造鍋爐、船舶和汽車的板材，也可熱軋成用于建筑橋梁和樓宇的型材（如桁架鋼、 梁架鋼、工字鋼）。這類鋼常在熱軋狀態(tài)下使用， 但對尺寸較小的材料可以進(jìn)行正火處理據(jù)估計，在使用的所有鋼中，約有 90% （重量）屬于低碳鋼。中碳鋼 中碳鋼通過淬火和高溫回火獲得高強度與最大的韌性，這些性能是軸、齒輪、 連桿等零件所需的。含碳 0.4%0.5%的鋼也可用于局部加熱淬火的方法使表面硬 化。高碳鋼 高碳鋼通過淬火與低溫回火獲得高硬度和有限的韌性。這類材料主要用于制造 尺寸很小、價格不貴的切削工具。 所以，整個這組鋼

44、稱為碳素工具鋼。 含碳量在 0.6% 0.8%范圍內(nèi)的高碳鋼用于制造模具、彈簧、線纜、火車輪轂等。許多不同種類的 工具用更高含碳量的高碳鋼來制造，如下表所示：C%工具類型0.81.0鑿子、剪切刀片、沖頭、錘子1.0 1.2銼刀、斧頭、鋸條、刀1.2 1.4剃刀、鉆頭、木工切削刀具和金屬切削刀具普通碳素鋼的局限性普通碳素鋼有很多局限性，例如：2（1）如果需要合理的韌性和塑性，可獲得的最大抗拉強度只有約 700N/ mm2（2）大截面的工件不能被有效的淬硬，這就使普通碳素鋼限用于較小截面的 工件。（3）為了完全淬硬，必須水淬，這就伴有變形和開裂的危險。（4）超過300 oC后迅速軟化，使這類鋼不能

45、用于高速切削金屬。（ 5 ）在較高溫度下，耐蝕性和抗氧化性差。為了克服這些局限性，可在鋼中加入合金元素，從而獲得具有特殊性能的合金 鋼。主要合金元素體有錳、鎳、鉻、鉬、鎢、釩、鈷和硅。普通碳素鋼的淬火當(dāng)鋼加熱到臨界溫度1330F（721oC）以上時，在珠光體中以片層狀鐵碳化合物形式存在的碳開始溶解到鐵中，形成稱為奧氏體的固溶體。當(dāng)該鐵碳固溶體突然 冷卻淬火時，便形成一種新的顯微組織，稱為馬氏體。馬氏體阻止非常硬脆，比珠 光體組織具有更高的抗拉強度。然而，馬氏體相當(dāng)不穩(wěn)定，必須對其回火來減少內(nèi) 應(yīng)力，獲得所需的塑性和韌性。對 AISI C1095 鋼(通常也稱為水硬工具鋼 W1)， 當(dāng)從剛剛高于

46、1330F (721oC)的溫度進(jìn)行淬火時，這種鋼已表現(xiàn)出硬度的提高， 但如果從1330F 一下某一溫度進(jìn)行激冷，將不能使鋼硬化。將該鋼加熱到1450F(788 oC)，然后在水中淬火，則該鋼能夠獲得它所能達(dá)到的最高硬度。含碳量的變化使淬 火溫度也隨之改變。對含碳量低于 0.83% 的碳鋼，必須將其加熱到上臨界溫度 50F(28 oC)。將低于共析成分的碳鋼加熱到上臨界溫度以上的原因是：若加熱溫度 低于這一數(shù)值，鋼中的鐵素體就沒有全部轉(zhuǎn)變成奧氏體，淬火以后，鐵素體也就保 留在馬氏體組織中。殘留的鐵素體會引起脆性，甚至在回火以后還有脆性。從實際用途看，像 AISI1020 這樣的低碳鋼，在加熱和淬火后，不能使其硬化。 油硬鋼和空氣硬化鋼具有較高的淬透性，它們淬火時不必像普通碳素鋼那樣迅速的 冷卻，同時，它們的淬硬深度也比水硬鋼高，水硬鋼淬火時，必須在一至兩秒內(nèi)冷 卻至200F(93 oC)。含碳量為0.83%的普通碳素鋼能夠達(dá)到任何含碳量更高的普通 碳素鋼所能達(dá)到的硬度( RC67 ) 。普通碳素鋼的回火 回火是將已經(jīng)進(jìn)行過淬火處理的鋼件重新加熱，使部分硬馬氏體組織轉(zhuǎn)變呈較 軟組織的過程?；鼗饻囟仍礁撸D(zhuǎn)變的馬氏體數(shù)量就越多，工件就越軟，韌性也越 好(即脆性越低)。因此，回火溫