【正文】 e %C+cementite %。本質(zhì)上，%的碳→%的碳+%的碳。Since this chemical separation of the carbon ponent occurs entirely in the solid state, the resulting structure is a fine mechanical mixture of ferrite and prepared by polishing and etching in a weak solution of nitric acid and alcohol reveal the lamellar structure ofalternating plates that forms on slow ，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)。This structure is posed of two distinct phases, but has its own set of characteristic properties and goes by the name pearlite, because of its resemblance to motherofpearl at low ，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)同之處而被稱(chēng)為珠光體。Steels having less than the eutectoid amount of carbon(less than %)are known as hypoeutectoid now the transformation of such a material represented by cooling along line yy’ in (%)的鋼稱(chēng)為亞共析鋼。’ 線冷卻的轉(zhuǎn)變情況。At high temperatures, the material is entirely austenite, but upon cooling enters a region where the stable phases are ferrite and and levellaw calculations show that lowcarbon ferrite nucleates and grows, leaving the remaining austenite richer in ，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。At 727℃(1341℉), the austenite is of eutectoid position(% carbon)and further cooling transforms the remaining austenite to resulting structure is a mixture of primary or proeutectoid ferrite(ferrite that formed above the eutectoid reaction)and regions of ℃(1341℉)時(shí)，奧氏體為共析組成(%)，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)和部分珠光體的混合物。Hypereutectoid steels are steels that contain greater than the eutectoid amount of such steel cools, as shown in zz’ of the process is similar to the hypoeutectoid case, except that the primary or proeutectoid phase is now cementite instead of 。當(dāng)這種鋼冷卻時(shí)，’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。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 cooling through this ，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。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 slow heating, these transitions occur in the reverse 。如果緩慢加熱，則以相反的方式發(fā)生這種轉(zhuǎn)化。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 ，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。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 ，然后使其快速冷卻的過(guò)程。If the carbon content of the steel is known, the proper temperature to which the steel should be heated may be obtained by reference to the ironironcarbide phase , if the position of the steel is unknown, a little preliminary experimentation may be necessary to determine the ，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。A good procedure to follow is to heatquench a number of small specimens of the steel at various temperatures and observe the result, either by hardness testing or by microscopic the correct temperature is obtained, there will be a marked change in hardness and other ，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。In any heattreating operation the rate of heating is flows from the exterior to the interior of steel at a definite the steel is heated too fast, the outside bees hotter than the interior and uniform structure cannot be ，加熱的速率都是重要的。熱量以一定的速率從鋼的外部傳導(dǎo)到內(nèi)部。如果鋼被加熱得太快，其外部比內(nèi)部熱就不能得到均勻的組織結(jié)構(gòu)。If a piece is irregular in shape, a slow rate is all the more essential to eliminate warping and heavier the section, the longer must be the heating time to achieve uniform ，為了消除翹曲和開(kāi)裂最根本的是加熱速率要緩慢。截面越厚，加熱的時(shí)間就要越長(zhǎng)才能達(dá)到均勻的結(jié)果。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 ，工件也應(yīng)在此溫度下保持足夠時(shí)間以讓其最厚截面達(dá)到相同溫度。The hardness obtained from a given treatment depends on the quenching rate, the carbon content, and the work 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 hardness except in unhardened or partially hardened 、含碳量和工件尺寸。除了非淬硬鋼或部分淬硬鋼外，合金鋼中合金元素的種類(lèi)及含量?jī)H影響鋼的淬透性(工件被硬化到深層的能力)而不影響硬度。Steel with low carbon content will not respond appreciably to hardening the carbon content in steel increases up to around %, the possible hardness obtainable also 。%，可能得到的硬度也增加。Above this point the hardness can be increased only slightly, because steels above the eutectoid point are made up entirely of pearlite and cementite in the annealed responds best to heattreating operations。and steel posed mostly of pearlite can be transformed into a hard ，由于超過(guò)共析點(diǎn)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。珠光體對(duì)熱處理作業(yè)響應(yīng)最好；基本由珠光體組成的鋼能轉(zhuǎn)化成硬質(zhì)鋼。As the size of parts to be hardened increases, the surface hardness decreases somewhat even though all other conditions have remained the is a limit to the rate of heat flow through ，隨著要淬火的零件尺寸的增加其表面硬度也會(huì)有所下降。熱量在鋼中的傳導(dǎo)速率是有限的。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 , 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 ，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(nèi)部硬度就會(huì)受到明確限制。然而鹽水或水淬火能夠?qū)⒈淮懔慵谋砻嫜杆倮鋮s至本身溫度并將其保持或接近此溫度。Under these circumstances there would always be some finite depth of surface hardening regardless of is not true in oil quenching, when the surface temperature may be high during the critical stages of ，其表面總歸有一定深度被硬化。但油淬情況就不是如此，因?yàn)橛痛銜r(shí)在淬火臨界階段零件表面的溫度可能仍然很高。Tempering 回火