【正文】 A preheat will do the same thing. For example, sae4150 steel, preheated to 600 or 800, can be welded readily（容易地）. When the flame or arc is taken away from the weld, the cooling rate is not so great, owing to the higher temperature of the surrounding metal and slower cooling results. Even the most rapid airhardening（風(fēng)硬鋼） steels are weldable if preheated and welded at a slow rate.低速焊接帶來(lái)了更多的熱量，這對(duì)金屬的大量體積進(jìn)行了加熱，所以冷卻速度降低。WeldingThe maximum carbon content of plain carbon steel safe for welding without preheating or subsequent heat treatment is %. highercarbon steel is welded every day, but only with proper preheating. There are two important factors: the amount of heats that is put in 。即使是一個(gè)簡(jiǎn)單的墊圈，由于打孔和隨后的平整加工中產(chǎn)生內(nèi)應(yīng)力，也會(huì)在熱處理中呈現(xiàn)嚴(yán)重的翹曲。如果拉伸進(jìn)行了一半就停止了，那么在再加工之前應(yīng)先退火，也就是說(shuō)工件是否有時(shí)間進(jìn)行加工硬化。拉伸強(qiáng)度和屈服點(diǎn)不能太高否則在發(fā)生彎曲時(shí)需要做很多工作；與之相類似，鋼應(yīng)該有高延展性，使其在沒(méi)有斷裂的情況下成形。鎳減少了中碳鋼的可鍛性，但對(duì)低碳鋼影響不大。lb(1 ft可鍛性與材料的最后特性聯(lián)系不大；因此，提高金屬的可鍛造性價(jià)值不大。經(jīng)過(guò)熱處理后，任何一種鋼都具有大范圍的特性；這種性質(zhì)同樣在合金鋼中存在。sti?ri?s]adj. 神秘的；不可思議的；難解的(神秘的，不可思議的) name. A tremendousadj. 極大的，巨大的；驚人的 range of properties is available in any steel after heat treatment。bil?ti]n. 可硬化性；淬硬性, price, and availability [?,veil?39。在合金材料被采用和應(yīng)用于工程實(shí)際之前，掌握其結(jié)構(gòu)強(qiáng)度和它的綜合性質(zhì)就夠了。剩下的金屬用于相對(duì)特殊的用途。到目前為止最重要的是鐵，以它為基礎(chǔ)構(gòu)成了處處可見(jiàn)的鋼和鑄鐵。也許可以這樣說(shuō)，合金元素越故意的被添加，被添加的合金元素的量越大，那么生產(chǎn)出來(lái)的產(chǎn)品越傾向于被稱之為合金。在工程材料中往往被特意地加入一定數(shù)量的合金元素。即使絕對(duì)純凈的金屬可以生產(chǎn)出來(lái)，工程師們對(duì)它們也并不會(huì)特別感興趣，因?yàn)樗鼈兒苋彳?、脆弱。在大多?shù)情況下，晶粒在空間中是自由排列的。結(jié)晶體是這樣一種結(jié)構(gòu)，組成它的原子定位在規(guī)則的三維排列中，仿佛位于三維棋盤的方格的角上。它們往往具有較高的密度。最基本的定義集中在元素原子間存在的連接形式和與這些原子相關(guān)聯(lián)的電子的某些特性。 it may have to be readily容易地 recyclable。 properties here. Suffice it to say1. Suffice it to say that you love me.只要說(shuō)你愛(ài)我就夠了。lin?ti]. A crystalline solid is one in which the constituent atoms are located in a regular threedimensional array as if they were located at the corners of the squares of a threedimensional chessboardn. 棋盤. The spacing of the atoms in the array is of the same order as the size of the atoms, the actual spacing being a characteristic of the particular metal. The directions of the axes of the array define the orientation of the crystal in space. The metals monly used in engineering practice are posed of a large number of such crystals, called grains晶粒. In the most general case一般情況下, the crystals of the various grains are randomly oriented in space. The grains are everywhere in intimate contact with one another and joined together on an atomic scale. The region at which they join is known as a grain boundary. An absolutely pure metal ( one posed of only one type of atom) has never been produced. Engineers would not be particularly interested in such a metal even if it were to be produced, because it would be soft and weak. The metals used mercially inevitably不可避免地 contain small amounts of one or more foreign elements, either metallicmetallic [mi39。t230。2. Suffice it to say that the gun was his.只需說(shuō)這槍是他的就夠了。 and its cost and availability may be of critical importance. 在人類社會(huì)的發(fā)展中，金屬的應(yīng)用起著關(guān)鍵性的作用。然而，在實(shí)際應(yīng)用中，可以將具有某些特性集合金屬定義為某種元素。許多金屬具有延展性，也就是說(shuō)，在不被破壞的情況下它們的形狀在外力的作用下可以發(fā)生變化。原子間距隨著原子大小呈規(guī)律性變化，原子間距是金屬的一種特性。在原子范圍內(nèi)，晶粒之間相互接觸緊密結(jié)合。實(shí)際應(yīng)用中的金屬往往都包含著一定數(shù)量的一種或多種外來(lái)金屬或非金屬元素，這些外來(lái)元素可能是有害的也可能是有益的或者它們對(duì)某種特定的屬性沒(méi)有影響。得到的物質(zhì)被叫做合金。不管怎樣，如果想使一種金屬或合金在使用中表現(xiàn)出穩(wěn)定一致的特性，在其中添加何種化學(xué)成分，它的量多大都應(yīng)該在控制范圍之內(nèi)。（主要由鐵和碳構(gòu)成的合金）它們的重量占所有生產(chǎn)出來(lái)的金屬重量的98%。例如，鎳合金主要用于抗磨損和耐高溫的用途，由于鈦合金具有高強(qiáng)度和低密度的綜合特性，鈦被廣泛應(yīng)用于航空工業(yè)中。舉例來(lái)說(shuō)，它可以強(qiáng)度很高，并且有好的耐磨性；它可以被例如拉伸加工，機(jī)械加工，或焊接等特殊工藝來(lái)加工出來(lái)；它可以被循環(huán)利用；它的成本和實(shí)用性是首要的。bil?ti]是產(chǎn)品在被調(diào)用時(shí)能夠運(yùn)行（即未處于失效或修復(fù)狀態(tài)）的概率。 this is particularly true of alloy steels.在鋼之間沒(méi)有太大的區(qū)別；所有的鋼在機(jī)械性能方面都是近似的。Considerations in fabrication(制造)The properties of the final part (hardness, strength, and machinability [m?,?i:n?39。高碳鋼很難鍛造。lb=) blowat a single blow= at one blowat a single blow:一下子|一舉|一擊 as plain steels of similar carbon content. Nickel decreases forgeability of mediumcarbon steels, but has little effect on lowcarbon steels. Chromium seems to harden steel at forging temperatures, but vanadium(釩) has no discernible(可辨別的) effect。鉻在鍛造溫度下時(shí)使鋼硬化，但釩沒(méi)有明顯的效果；兩種加工方法對(duì)高碳鋼沒(méi)有影響。加工力的大小取決于屈服點(diǎn)，因?yàn)殇撛谇c(diǎn)之上才開(kāi)始變形。這不是一種科學(xué)的敘述方法，但確實(shí)是發(fā)生了。When doubt exists as to（關(guān)于） whether internal stresses will cause warpage, a piece can be checked by heating it to about 1100 and then letting it cool. If there are internal stresses, the piece is likely to（可能） deform. Pieces that will warp severely while being heated have been seen, yet （然而）the heattreater熱處理爐 was expected to有望做某事；被期待做某事 put them throughput through 完成 and bring them out better than they were in the first place.當(dāng)是否內(nèi)應(yīng)力會(huì)引起翹曲的懷疑存在時(shí)，可以通過(guò)將工件加工至1100然后進(jìn)行冷卻來(lái)驗(yàn)證。 the rate at which it is removed.焊接％。預(yù)熱可以取得與之相當(dāng)?shù)男Ч?。MachinabilityMachinability（機(jī)械加工性能） means several things. To production men it generally means being able to remove metal at the fastest rate, leave the best possible finish, and obtain the longest possible tool life. Machinability applies to（應(yīng)用于） the toolwork（工具，零件） bination.可加工性可加工性意味著幾件事情。s230。許多時(shí)候，因?yàn)椴牧线^(guò)軟而難于穩(wěn)定加工。Machinability is a term used to indicate the relative（比較的） ease（不費(fèi)力） with which a material can be machined by sharp cutting tools in operations such as turning（車）, drilling（鉆）, milling（銑）, broaching[39。改變?nèi)魏我环N均會(huì)產(chǎn)生不同的切削效果。鋼材淬透性好與差，常用淬硬層深度來(lái)表示。淬透性好的鋼材，可使鋼件整個(gè)截面獲得均勻一致的力學(xué)性能以及可選用鋼件淬火應(yīng)力小的淬火劑，以減少變形和開(kāi)裂。但晶粒粗大將增大鋼的變形、開(kāi)裂傾向和降低韌性?？慑懶?forgeability)金屬具有熱塑性，在加熱狀態(tài)(各種金屬要求溫度不同)，可以進(jìn)行壓力加工，稱為具有可鍛性。所有碳化物都有硬度高、塑性低、熔點(diǎn)高的特點(diǎn)，但滲碳體型碳化物在加熱到鍛造溫度時(shí)經(jīng)適當(dāng)保溫可大部分或全部溶入固溶體中，而合金碳化物較難溶入固溶體中，對(duì)鋼的可鍛性影響最大。錳對(duì)鋼的過(guò)熱性（粗晶）很敏感，鋼錠加熱溫度過(guò)高，易生粗晶，使鍛造困難。珠光體Ni鋼在鍛造時(shí)易形成片狀破裂和帶狀組織。高鉻鋼在空氣中冷卻即能淬火，常在表面生裂，所以不易鍛造。這些鋼在空冷時(shí)間淬火，要防止冷裂。sid?ti] n. 酸度；酸性；酸過(guò)多；胃酸過(guò)多 or alkalinity[,230。sis?] n. [數(shù)]橫坐標(biāo)；橫線) in a tensile test. A material tends to change or changes its dimensions when it is loaded, depending upon the magnitude大小 of the load. When the load is removed it can be seen that the deformation disappear s. For many materials this occurs up to一直到；相當(dāng)于；忙于，在做；由決定的 a certain value of the stress called the elastic limit. This is depicted by the straight line relationship and a small deviation[,di:vi39。the diminishing[di39。物理特性 密度或特定的重力，濕度等都屬于此范疇。力學(xué)特性 力學(xué)特性包括諸如拉伸，壓縮，剪切，扭