外文翻譯--普通碳鋼的淬火

河南科技大學(xué)畢業(yè)論文 1 翻 譯 文 獻(xiàn) 原文： HARDDENING OF PLAIN CARBON STEELS Heat treatment is used to soften metal and relieve internal stresses (annealing), harden metal, and temper metal (to toughen certain parts). Hardening is a process of heating and cooling steel to increase its hardness and tensile strength , to reduce its ductility and to obtain a fine grain strength. Hardening increases the strength of pieces after they are temperature. It is accomplishd by heating the steel to some in air, oil, water, or brine. Only medium, high, and very high carbon steels can be hardened by this method. The temperature at which the steel must be heated varies with the steel used. The tendency of a steel to harden may or may not be desirable depending upon how it is going to be processed. For example, if it is to be welded, a strong tendency to harden will make a steel brittle and susceptible to cracking during the welding process. Special precautions such as preheating and a very careful control of heat input and cooling will be necessary to minimize this condition. During welding, an extremely high localized temperature differential exists between the molten metal of the weld and the soild, much colder metal being welded. The resulting structure if these areas is hard, brittle martensite. The greater the hardenability of a steel, the less severe the rate of heat extraction necessary to cause it to harden. This is one of the reasons that alloy and high carbon steels have to be welded with greater care than ordinary low carbon steels. The phase changes in plain carbon steels as the carbon content and the temperature vary. For a pure iron, the phase change from 河南科技大學(xué)畢業(yè)論文 2 body-centered cubic at lower temperatures to face-centered cubic austenite occurs at 1666F. The bcc state is termed ferrite. This ferrite phase is commonly found in carbon and alloy steels and cast irons. It can be considered to be pure iron, but in plain carbon steels it is actually a solution of 0.008% carbon in iron at room temperature (though iron can dissolve somewhat more carbon than this at higher temperatures).The carbon atoms are small enough (0.77A) to fit between the iron atoms in the body-centered cubic crystal lattice. But even an extra low-carbon stainless steel contains much more carbon than 0.008%, so that the carbon in steels must be in the steel in some form other than this. The irresistible chemical attraction between most metals and carbon has been a recurrent theme in this book: virtually all the carbon in steels denum, vanadium, titanium, and other metals. Here we come to the heart of the matter. We can heat-treat any steel that contains sufficient carbides. Pure iron cannot be heat-treated. Carbon steels with less than about 0.3% carbon have carbides insufficient for any significant heat treating to be possible. Thus the 300-series stainless steels, in which carbon is generally less than 0.15%, cannot be heat-treated. The martensitic stainless steels are enough carbon to produce sufficient carbides of iron and chromium for heat treating. The non-heat-treatable ferritic stainless steels must be discussed later. To heat-treat then, we need carbides plus one other steel characteristic-a phase transformation from austenite at higher the 300-series austenitic stainless steels do not have this second characteristic, but most steels do. Iron carbide, Fe3C, is called cementite. Like other carbides, it is hard, strong, and brittle, the hardest constituent in carbon steels. Cementite has a carbon content of 6.6%. At room temperature, all carbon steels are mixtures of ferrite and cementite. To harden a carbon steel, the steel is first heated to just above its critical temperature into 河南科技大學(xué)畢業(yè)論文 3 the austenite phase. It is held at this temperature long enough for cementite and other carbides to dissolve in the austenite. The steel in then cooled at a rapid rate. This fast cooling is obtained by quenching the hot steel in water or oil, or, in the case of a weld, the cooling is fast. Because of the rapid cooling, the austenite does not have time to dissociate into the usual ferrite and cementite. What comes down with drastic cooling is a supersaturated solution of carbon trapped in a body-centered tetragonal (i.e., rectangular) crystal structure, this frozen solution being given the name martensite. The transformation from austenite to martensite does not occur at the transformation temperature between ferrite and austenite. Instead, the martensite transformation occurs over a range of temperature. Austenite may begin to transform to martensite at 80 F in a low-alloy steel. As the temperature contiues to fall, more martensite is formed , until at room temperature the structure of the steel may be 99% martensite. With added alloy ingredients the mertensite transformation begins at a lower temperature, and the transformation is also less complete. In a high-speed steel, martensite may not begin to appear until a temperature of 600 F is reached, and perhaps only 80% of the austenite will have transformed when room temperature is reached. The untransformed fraction will still be austenite. All these changes teke place only during a fast quench of an alloy steel or a carbon steel of 0.3% carbon or more. Martensite is hard, brittle, and nonductile, so that the denger of cracking due to thermal stresses is ever present. Worse still, there is a vonlume expansion when martensite appears. The part of the steel that is merely cooling is contracting, while the fraction that is transforming is expanding. This makes the cracking possibilities even greater. In carbon steels, the brittle martensitie condition is obtainable only with a very rapid cooling rate. Additions of any alloying 河南科技大學(xué)畢業(yè)論文 4 ingredients affect this cooling rate. The greater the proportion of these ingredients in a steel, the slower the cooling rate that will still give a martensite condition. This statement holds true whether the alloying metals are carbideformers. Like tungsten and molybdenum or those that dissolve in ferrite, such as nickel and manganese. 翻譯 ： 普通碳鋼的淬火 熱處理是使金屬變軟，消除內(nèi)應(yīng)力（退火）和使金屬淬硬及回火（使某些部分變韌）。 淬火是把鋼加熱然后冷卻以提高其硬度得，抗拉強度， 降低其韌性并獲得細(xì)晶粒組織的方法。 在工件制好以后進(jìn)行淬火能提高其硬度淬火是把鋼加熱到再結(jié)臨界溫度以上的某個溫度然后使之在空氣中，油中，水中或鹽水中迅速冷卻來完成的。只有中碳鋼，高碳鋼以及很高的碳鋼才能用這種方法來硬化。鋼加熱到的溫度因鋼種的不同而不同。 鋼淬硬這一特定，是不是合乎需要，取決于何種加工。例如：如果進(jìn)行焊接加工過程中，強烈的淬硬趨勢是使鋼容易變脆或者開裂。必須采用專門的措施把這種情況降低到最低限度，例如進(jìn)行預(yù)熱，非常小心的控制輸入熱量以及冷卻。在焊接過程中當(dāng)焊逢熔化了的金屬和被 焊接的，固態(tài)的，溫度低的多的金屬存在著極大的局部溫差。涼的母體金屬對焊逢金屬及其附近已經(jīng)加熱到的臨界溫度上限以上的金屬起著一種淬火劑的作用。這些區(qū)域最后產(chǎn)生的結(jié)構(gòu)是脆硬的馬氏體。鋼的可淬性越高，使鋼淬火所必須的吸熱率的劇烈程度就越低。這是高碳鋼和合金鋼焊接時必須比低碳鋼更加小心的原因之一。 普通碳鋼的相，隨含碳量和溫度的變化而變化。對于純鐵，其相變從較低溫度的體心立方結(jié)構(gòu)到 1666 F 出現(xiàn)面心立方奧氏體。體心立方狀態(tài)時叫做鐵素體。通常在碳鋼，合金鋼和鑄鐵種都有這種鐵素體相?？梢园谚F素體河南科技大學(xué)畢業(yè)論文 5 相看成是純鐵，但是在普 通碳鋼種鐵素體相實際上是在室溫下溶有 0.008%的碳的鐵（雖然在溫度更高的情況下鐵所能溶解的碳還要多些）。碳原子是很小的（ 0.77），足以嵌在體心立方晶格種的鐵原子之間。 然而，就是超低碳不銹鋼的含碳量也大大超過 0.008%，因此，鋼種的碳必然以不同于溶入鐵素體的某種其他形式存在于鋼種。關(guān)于大多數(shù)金屬和碳之間不可抗拒的親和力已經(jīng)是本書種多次重復(fù)談到的問題。實際上鋼中所有的碳都與鐵 .鎢 .鉻 .鉬 .釩 .鈦和其他金屬化合成這些元素的碳化物。這里談到了問題的核心。我們能對含有足量碳化物的任何一種鋼進(jìn)行熱處理 。純鐵是不能熱處理的。含碳量低于 0.3%左右的碳鋼所含有的碳化物都不足以進(jìn)行任何有效的熱處理。因此含碳量通常低于 0.15%的 300 系列的不銹鋼是不能熱處理的。馬氏體不銹鋼含有足量的碳以形成足以進(jìn)行熱處理的碳化鐵和碳化鉻。不能熱處理的鐵素體不銹鋼將在以后討論。 因此為了進(jìn)行熱處理，我們需要碳化物再加上鋼的另一種特性即從較高溫度下的奧氏體轉(zhuǎn)變到較低溫度下的其他相的相變。而 300