購(gòu)買設(shè)計(jì)請(qǐng)充值后下載，，資源目錄下的文件所見(jiàn)即所得，都可以點(diǎn)開(kāi)預(yù)覽，，資料完整，充值下載可得到資源目錄里的所有文件。。?！咀ⅰ浚篸wg后綴為CAD圖紙，doc,docx為WORD文檔，原稿無(wú)水印，可編輯。。。帶三維備注的都有三維源文件，由于部分三維子文件較多，店主做了壓縮打包，都可以保證打開(kāi)的，三維預(yù)覽圖都是店主用電腦打開(kāi)后截圖的，具體請(qǐng)見(jiàn)文件預(yù)覽，有不明白之處，可咨詢QQ:1304139763===========題目最后備注XX系列，只是店主整理分類，與內(nèi)容無(wú)關(guān)，請(qǐng)忽視
沈陽(yáng)理工大學(xué)學(xué)位論文
附錄A 英文原文
A.1 FORGING
Bulk defirnnation of metals refers to various processes, such as forging, rolling, or extruding, where there is a controlled plastic flow or working of metals into useful shapes. The most well known of these processes is forging where deformation is accomplished by means of pressure, impact blows, or a combination of both.
Hammer Forging
Hanuner forging consists of striking the hot metal with a large semiautomatic hammer. If no dies are involved, the forging will be dependent mainly on the skill of the operator. If closed or impression dies are used, one blow is struck for each of several (lie cavities. A- gain, productivity and quality depend to a large degree on the skill of the hanimer operator and the tooling.
Press Forging
Press forging is characterized by a slow squeezing action. Again, open or closed dies may be used. The open dies are used chiefly for large, simple-geometry parts that are later machined to shape. Closed-die forging relies less on operator skill awl more on the design of the preform and forging dies.2 As an example of the versatility of the process, newer developments have made it possible to produce bevel gears with straight or helical teeth. Rotation of the die (luring penetration will press bevel gears with spiral teeth.
Open-die Forging
Open-die forging is distinguished by the fact that the metal is never completely confined as it is shaped by various dies. Most open-die forgings are produced on flat, V, or swaging dies. Round swaging (lies and V dies are used in pairs or with a flat die. The top (lie is attached to the ram of the press, and the bottom die is attached to the hammer anvil or, in the case of press open-die forging, to the press bed.
As the workpiece is hammered or pressed, it is repeatedly manipulated between the dies until hot working forces the metal to the final dimensions, as-shown in Fig. 1. After forging, the part is rough- and finished-machined. As an example of the amount of material allowed for machining, a 6.5 in. diameter shaft would have to be forged to 7.4 in. dianieter.
In open-die forging of steel, a rule of thumb says that 50 lb of falling weight is required for each square inch of cross section.
Impression-die Forging
In the simplest example of impression-die forging, two dies are brought together, and the workpiece undergoes plastic deformation until its enlarged sides touch the side walls of the die (Fig. 2). A small amount of material is forced outside the die impression, forming flash that is gradually thinned. The flash cools rapidly and presents increased resistance to deformation, effectively becoming a part of the tool, and helps build up l)ressUre inside the bulk of the work- piece that aids material flow into unfilled impressions.
Closed-die forgings, a special form of impression-die forging, does not depend on the formation of flash to achieve complete filling of the (lie. Thus closed-die forging is considerably more demanding on die design. Since pressing is often completed in one stroke, careful control of the workpieee volume is necessaiy to achieve complete filling without generating extreme pressures in the dies from overfilling.
Extrusion Forging
As with upsetting, extrusion forging is often accomplished by cold working. Three principal types of metal displacement by plastic flow are involved. Backward and forward, tube, and impact extrusion are shown in Fig. 3. The metal is placed in a container and corn- pressed by a ram movement until pressure inside the metal reaches flow-stress levels. The workpiece completely fills the container, and additional pressure causes it to leave through an orifice and form the extruded product.
Extruded products may be either solid or hollow shapes. Tube extrusion is used to produce hollow shapes such as containers and pipes. Reverse-impact extrusion is used for mass production of aluminum cans. The ram hits a slug of metal in the die at high impact, usually 15 times the yield strength of the metal, which causes it to flow instantaneously up the walls of the die. Other common hollow extrusion products are aerosol cans, lipstick cases, flashlight cases, and vacuum bottles. Secondary operations, such as heading, thread rolling, dimpling, and machining, are often needed to complete the items.
Generally steel impacts are limited to 2.5 times the punch diameter. Hydraulic presses are used for loads of over 2000 tons because they have a greater variation in stroke length, speed, and other economic advantages. Tolerances vary with materials arid design, hut production runs calling for 0.002- to 0.005-in, tolerance are regularly made.
Roll Forging
Roll forging in its simplest form consists of a heated billet passing between a pair of rolls that deform it along its length (Fig. 8-4). Compared to conventional rolling processes, the rolls are relatively small in diameter and serve as an arbor into which the forging tools are secured. The active surface of the tool occupies only a portion (usually half) of the roll circumference to accommodate the full cross section of the stock.
The reduction of the cross section obtainable in one pass is limited by the tendency of the material to spread and form an undesirable flash that may be forged into the surface as a defect in the subsequent operations. The workpiece is int roduced repeatedly with rota- tion between passes.
Ring Rolling
Ring rolling offers a homogeneous circumferential grain flow, ease of fabrication and machining, and versatility of material size . Manu- facture of a rolled ring starts with a sheared blank, which is forged to a pancake, punched, and pierced.
There is no limit to the size of the rolled rings, ranging from roller-bearing sleeves to Fig. 4 Roll forging rings 25 ft in diameter with face heights of 80 in. Various profiles may be rolled by suitably shaping the driven, idling rolls.
CAD/CAM in Forging
CAD/CAM is being increasingly applied to frging. Using the three-dimensional description of a machined part, which may have been computer designed, it is possible to generate the geometry of the associated forging. Thus the forging sections can be obtained from a common (laiR base. Using well-known techniques, forging loads and stresses can be obtained and flash dimensions can be selected for each section where metal flow is approximated as ro dimensional (plane strain or axisymmetric ). In some relatively simple section geomethes, computer simulation can be conducted to evaluate initial guesses on preform sections. Once the preform geometry has been developed to the designer?ˉs satisfaction, this geometric data base can utilized to write NC part programs to obtain the NC tapes or disks for machining.
A.2 HEAT TREATMENT OF METAL
Annealing
The word anneal has been used before to describe heat-treating processes for softening and regaining ductility in connection with cold working of material. It has a similar meaning when used in connection with the heat treating of allotropic materials. The purpose of full annealing is to decrease hardness, increase ductility, and sometimes improve machinability of high carbon steels that might otherwise be difflcult to cut. The treatment is also used to relieve stresses, refine grain size, and promote uniformity of structure throughout the material.
Machinability is not always improved by annealing. The word machinability is used to describe several interrelated factors, including the ability of a material to be cut with a good surface finish. Plain low carbon steels, when fully annealed, are soft and relatively weak, offering little resistance to cutting, but usually having sufficient ductility and toughness that a cut chip tends to puli and tear the surface from which it is removed, leaving a comparatively poor quality surface, which results in a poor machinability rating. For such steels annealing may not be the most suitable treatment. The machinability of many of the higher plain carbon and most of the alloy steels can usually be greatly improved by annealing, as they are often too hard and strong to be easily cut at any but their softest condition .
The procedure for annealing hypoeutectoid steel is to heat slowly to approximately 60 above the Ac3 line, to soak for a long enough period that the temperature equalizes throughout the material and homogeneous austenite is formed, and then to allow the steel to cool very slowly by cooling it in the furnace or burying it in lime or some other insulating material. The slow cooling is essential to the precipitation of the maximum ferrite and the coarsest pearlite to place the steel in its softest, most ductile, and least strained condition.
Normalizing
The purpose of normalizing is somewhat similar to that of annealing with the exceptions that the steel is not reduced to its softest condition and the pearlite is left rather fine instead of coarse. Refinement of grain size, relief of internal stresses, and improvement of structural uniformity together with recovery of some ductility provide high toughness qualities in normalized steel. The process is frequently used for improvement of machinability and for stress nlief to reduce distortion that might occur with partial machining or aging.
The procedure for normalizing is to austenitize by slowly heating to approximately above the Ac3 or Accm3 temperature for hypoeutectoid or hypereuteetoid steels, respectively; providing soaking time for the formation of austenite; and cooling slowly in still air. Note that the steels with more carbon than the eutectoid composition are heated above the Aom instead of the Ac used for annealing. The purpose of normalizing is to attempt to dissolve all the cementite during austenitization to eliminate, as far as possible, the settling of hani, brittle iron carbide in the grain boundaries. The desired decomposition products are smallgrained, fine pearlite with a minimum of free ferrite and free cementite.
Spheroidizing
Minimum hardness and maximum ductility of steel can he produced by a process called spheroidizing, which causes the iron carbide to form in small spheres or nodules in a ferrite matrix, in order to start with small grains that spheroid ize more readily, the process is usually performed on normalized steel. Several variations of processing am used, but all reqllin the holding of the steel near the A1 temperature (usually slightly below) for a number of hours to allow the iron carbide to form on its more stable and lower energy state of small, rounded glohules.
The main need for the process is to improve the machinability quality of high carbon steel and to pretreat hardened steel to help produce greater structural uniformity after quenching. Because of the lengthy treatment time and therefore rather high cost, spheroidizing is not performed nearly as much as annealing or normalizing.
Hardening of Steel
Most of the heat treatment hardening processes for steel are basel on the production of high pereentages of martensite. The first step. therefore, is that used for most of the other heat-treating processes-treatment to produce austenite. Hypoeutectoid steels are heated to approximately 60CC above the Ac3 temperature and allowed to soak to obtain temperature unifonnity and austenite homogeneity. Hypereutectoid steels are soaked at about 60CC above the A1 temperature, which leaves some iron carbide present in the material.
The second step involves cooling rapidly in an attempt to avoid pearlite transformation by missing the nose of the i-T curve. The cooling rate is determined by the temperature and the ability of the quenching media to carry heat away from the surface of the material being quenched and by the conduction of heat through the material itself. Table1 shows some of the commonly used media and the method of application to remove heat, arranged in order of decreasing cooling ability.
High temperature gradients contribute to high stresses that cause distortion and cracklug, so the quench should only as extreme as is necessary to produce the desired structure. Care must be exercised in quenching that heat is removed uniformly to minimize thermal stresses. For example, a long slender bar should be end-quenched, that is, inserted into the quenching medium vertically so that the entire section is subjected to temperature change at one time. if a shape of this kind were to be quenched in a way that caused one side to drop in temperature before the other, change of dimensions would likely cause high stresses producing plastic flow and permanent distortion.
Several special types of quench are conducted to minimize quenching stresses and decrease the tendency for distortion and cracking. One of these is called martempering and consists of quenching an austenitized steel in a salt at a temperature above that needed for the start of martensite formation (Ms). The steel being quenched is held in this bath until it is of uniform temperature but is removed before there is time for fonnation of bainite to start. Completion of the cooling in air then causes the same hard martensite that would have formed with quenching from the high temperature, but the high thermal or ?°quench?± stresses that are the primary source of cracks and warping will have been eliminated.
A similar process performed at a slightly higher temperature is called austempering. In this case the steel is held at the bath temperarnre for a longer period, and the result of the isothermal treatment is the formation of bainite. The bainite structure is not as hard as the martensite that could be formed from the same composition, but in addition to reducing the thermal shock to which the steel would be subjected under normal hardening procedures, ii is unnecessary to perform any further treatment to develop good impact resistance in the high hardness range
Tempering
A third step usually required to condition a hardened steel for service is tempering, or as it is sometimes referred to, drawing. With the exception of austempered steel, which is frequently used in the as-hardened condition, most steels are not serviceable “as quenched”. The drastic cooling to produce martensite causes the steel to be very hard and to contain both macroscopic and microscopic internal stresses with the result that the material has little ductility and extreme brittleness. Reduction of these faults is accomplished by reheating the steel to some point below the A1 (lower transformation) temperature. The stnictural changes caused by tempering of hardened steel are functions of both time and temperature, with temperature being the most important. It should be emphasized that tempering is not a hardening process, but is, instead, the reverse. A tempered steel is one that has been hardened by heat treatment and then stress relieved, softened, and provided with increased ductility by reheating in the tempering or drawing procedure.
The magnitude of the structural changes and the change of properties caused by tempering depend upon the temperature to which the steel is reheated. The higher the ternperatun, the greater the effect, so the choice of temperature will generally depend on willingness to sacrifice hardness and strength to gain ductility and toughness. Reheating to below lOOt has little noticeable effect on hardened plain carbon steel. Between lO(YC and 200T, there is evidence of some structural changes. Above 200T marked changes in structure and properties appear. Prolonged heating at just under the A1 temperature will result in a spheroidized structure similar to that produced by the spheroidizing process.
In commercial tempering the temperature range of 25O-425 is usually avoided because of an unexplained embrittlement, or loss of ductility, that often occun with steels ternpered in this range. Certain alloy steels also develop a ?°temper brittleness?± in the tempera- ture range of 425-600, particularly when cooled slowly from or through this range of temperature. When high temperature tempering is necessary for these steels, they are usually heated to above 600 and quenched for rapid cooling. Quenches from this temperature, of course, do not cause hardening because austenitization has not been accomplished.
附錄B 漢語(yǔ)翻譯
B.1 鍛造
金屬變形方法有多種，比如通過(guò)鍛造、滾壓或擠壓，使金屬的塑性流動(dòng)或加工受到控制而得到有用的形狀。這些方法中最廣為人知的是鍛造，它通過(guò)壓力、沖擊或兩者的組合使材料變形。
錘鍛
錘鍛是用大的半自動(dòng)鍛錘鍛打熱金屬，如果不用模具，鍛造主要取決于操作者的技巧。如使用封閉模或型腔模，對(duì)幾個(gè)模膛的每一個(gè)模膛都要錘打一次。同樣地，生產(chǎn)率和質(zhì)量在很大程度上取決于錘鍛操作者的技巧和所用工具。
鍛壓
鍛壓具有緩慢加壓的特點(diǎn)，同樣可用開(kāi)?；蚍忾]模。開(kāi)模主要用于大型的形狀簡(jiǎn)單的零件，鍛壓后再加工成形。封閉模鍛造很少依賴操作者的技巧，而更多地取決于預(yù)成形模和鍛模的設(shè)計(jì)。例如，目前能用直齒或螺旋齒加工錐齒輪，加工過(guò)程中旋轉(zhuǎn)的模具用螺旋齒擠壓出錐齒輪。
開(kāi)模鍛
開(kāi)模鍛的顯著特征是：用不同模具成形時(shí)，金屬?zèng)]有被完全限制。大多數(shù)開(kāi)模鍛使用平砧、V 形砧或U 型砧模一圓形砧和V 形砧成對(duì)使用或和一個(gè)平砧一起使用，上模裝在壓力機(jī)的壓頭上，下模裝在錘砧上，開(kāi)模壓力鍛時(shí)裝在壓力機(jī)床身上。
錘鍛或壓鍛時(shí)，將工件在模具間重復(fù)鍛打，直至金屬達(dá)到最終尺寸，如圖l 所示。鍛打后，零件再粗加工和精加工，作為一個(gè)加工余量的實(shí)例，一根直徑6 . 5 英寸的軸的鍛打直徑為7 . 4 英寸。
在鋼的開(kāi)模鍛中，一個(gè)經(jīng)驗(yàn)數(shù)據(jù)是每平方英寸橫截面需50 磅鍛擊力。
型腔模鍛
型腔模鍛的最簡(jiǎn)單實(shí)例是，將兩個(gè)模具相互靠攏，其間的工件經(jīng)受塑性變形直至其周邊充滿模具為止（圖2 ）。少量材料被壓出型模膛，形成薄薄的飛邊。飛邊迅速冷卻，增加了變形阻力，變成了模具的一部分，幫助在工件內(nèi)部產(chǎn)生壓力，使材料流至未填充的型腔。
封閉模鍛是一種特殊的型腔模鍛，不依賴飛邊的形成，叮完整充填模具。因此，封閉模鍛更多地依賴于模具設(shè)計(jì)。因壓鍛經(jīng)常在一次沖程中完成，因此應(yīng)仔細(xì)控制工件體積，做到既能完全充填，在模具中又不產(chǎn)生多余壓力，使材料滋出。
擠壓鍛造
如同冷墩，擠壓常通過(guò)冷加工完成。擠壓鍛主要有三種形式的金屬塑性流動(dòng)，即正與反擠壓、管擠壓和沖擊擠壓，如圖3 所示：將金屬置于容器中，通過(guò)壓頭移動(dòng)加壓直至金屬內(nèi)部壓力達(dá)到流動(dòng)應(yīng)力。金屬完全填滿容器，進(jìn)一步加壓導(dǎo)致金屬通過(guò)小孔流出，形成擠壓產(chǎn)品。
擠壓產(chǎn)品既可以是實(shí)心件也可以是空心件。管擠壓用來(lái)制造空心產(chǎn)品，如容器和管道。反向沖擊擠壓用于鋁罐的大批量生產(chǎn)，壓頭高速?zèng)_擊模具中的金屬原料，通常，應(yīng)力是金屬屈服強(qiáng)度的巧倍，這使金屬瞬間成形。其他常用的空心擠出產(chǎn)品是氣霧罐，唇膏筒，電筒殼和真空瓶，它們經(jīng)常需要進(jìn)一步的加工，比如卷邊，螺紋滾壓，做出波紋和機(jī)加工來(lái)完成產(chǎn)品制作。
通常，鋼的沖擊限制在沖頭直徑的2 . 5 倍以內(nèi)。由于行程長(zhǎng)度、速度等其有較大的變化范圍及其他經(jīng)濟(jì)優(yōu)點(diǎn)，液壓機(jī)用于載荷超過(guò)2000噸場(chǎng)合。公差隨材料和設(shè)計(jì)而變，但生產(chǎn)上通常需要0.002——0.005 英寸的公差.
輥軋鍛造
最簡(jiǎn)單的輥軋鍛造是將· 根加熱的棒通過(guò)一對(duì)軋輥，使其沿長(zhǎng)度方向變形（圖8 一4 ）與傳統(tǒng)棍軋過(guò)程相比，輥軋鍛造的軋輥直徑較小，相當(dāng)于安裝鍛打工具的心軸。工具的工作表面只占軋輥圓周的一部分（通常一半），來(lái)容納棒料的整個(gè)橫截面。
棒料輥鍛一次的橫截面減少量受到材料擴(kuò)展和形成不必要的毛邊的限制，毛邊可能被壓進(jìn)鍛件表面，在后續(xù)操作中形成缺陷，，工件每重復(fù)送進(jìn)軋輥一次，都要轉(zhuǎn)90度。
環(huán)狀軋制
環(huán)狀軋制可得到均質(zhì)的周向纖維流，易于制造和加工，可用于多種尺寸。要將原材料制成一個(gè)，先要卜料，鍛成盤形，再?zèng)_孔和貫穿。
對(duì)環(huán)型坯料的尺寸沒(méi)有限制，小至軸承套，大到直徑25 英尺、面高8 0英寸的圓環(huán)。適當(dāng)?shù)爻尚伪粍?dòng)軋輥和空轉(zhuǎn)軋輥可軋制出不同輪廓的制品。
鍛造中的CAD/CAM
CAD/CAM 已日益應(yīng)用于鍛造之中。利用計(jì)算機(jī)設(shè)計(jì)的被加工零件的三維描述，就能生成相關(guān)鍛件的幾何形狀。因此，鍛件橫截面叮通過(guò)一個(gè)通用數(shù)據(jù)庫(kù)獲得。使用眾所周知的方法，可獲得鍛擊力和應(yīng)力，對(duì)每種截面可選擇飛邊尺寸，這里金屬的流動(dòng)近似為二維（平面應(yīng)變和軸對(duì)稱）。對(duì)相對(duì)簡(jiǎn)單的截面形狀，可用計(jì)算機(jī)仿真來(lái)評(píng)價(jià)對(duì)預(yù)成形橫截面的最初設(shè)想：一旦預(yù)成形的幾何形狀修改到符合設(shè)計(jì)者的要求，可用兒何數(shù)據(jù)庫(kù)來(lái)書(shū)寫(xiě)數(shù)控加工程序，得到數(shù)控加工紙帶或磁盤。
B.2 金屬的熱處理
退火
在前面描述冷拔加工材料的軟化并重新獲得塑性的熱處理方法時(shí)，就已經(jīng)用退火這個(gè)詞。當(dāng)用于同素異晶材料的熱處理時(shí)，該詞具有相似的意義。完全退火的目的是降低硬度、增加塑性，有時(shí)也提高高碳鋼的切削加工性，否則這種鋼很難加工。這種熱處理方法也用來(lái)減少應(yīng)力，細(xì)化晶粒，提高整個(gè)材料的結(jié)構(gòu)均勻性。
退火不總是能提高切削加工性，切削加工性一詞用來(lái)描述幾個(gè)相關(guān)因素，包括材料切削時(shí)獲得好的表面光潔度（即較小的表面粗糙度值― 譯者）的能力。，當(dāng)完全退火時(shí)，普通低碳鋼硬度較低，強(qiáng)度較小，對(duì)切削的阻力較小，但通常由于塑性和韌性太大以致切屑離開(kāi)工件表面時(shí)會(huì)劃傷表面，工件表面質(zhì)量比較差，導(dǎo)致較差的切削加工性。對(duì)這類鋼，退火可能不是最合適的處理方法。許多高碳鋼和大多數(shù)合金鋼的切削加工性通?？山?jīng)退火大大改善，因?yàn)槌谧钴洍l件下，它們的硬度和強(qiáng)度太高而不易加工。
亞共析鋼的退火方法是將鋼緩慢加熱到Ac3 線以上大約60 ℃ ，保溫一段時(shí)間，使整個(gè)材料溫度相同，形成均勻奧氏體，然后隨爐或埋在石灰或其他絕緣材料中緩慢冷卻。要析出粗大鐵素體和珠光體，使鋼處于最軟、最韌和應(yīng)變最小的狀態(tài)，必須緩慢冷卻。
正火
正火的目的多少類似于退火，但鋼不是最軟狀態(tài)且珠光體是細(xì)勻而不粗大。鋼的正火能細(xì)化晶粒，釋放內(nèi)應(yīng)力，改善結(jié)構(gòu)均勻性同時(shí)恢復(fù)一些塑性，得到高的韌性。這種方法經(jīng)常用來(lái)改進(jìn)切削加工性，減少應(yīng)力，減少因部分切削加工或時(shí)效產(chǎn)生的變形。
正火方法是將業(yè)析鋼或過(guò)共析鋼分別緩慢加熱到Ac3 線或Accm 線上約80 ℃ ，保溫一段時(shí)間以便形成奧氏體，并在靜止空氣中緩冷。要注意，含碳量超過(guò)共析成分的鋼要加熱到Accm 線以上，而不是退火時(shí)的線以下。正火的目的是在奧氏體化過(guò)程中試圖溶解所有滲碳體，從而盡可能減少晶界上的硬脆鐵碳化合物，而得到小晶粒的細(xì)珠光體、最小白由鐵素體和自由滲碳體。
球化退火
通過(guò)球化退火可使鋼得到最小的硬度和最大的塑性，它可使鐵碳化合物以小球狀分布在鐵素體基體上。為了使小顆粒球化更容易，通常對(duì)正火鋼進(jìn)行球化退火。球化退火可用幾種不同的方法，但所有方法都需在線溫度附近（通常略低）保溫很長(zhǎng)時(shí)間，使鐵碳化合物形成更穩(wěn)定，能級(jí)較低的小圓球。
球化退火方法的主要目的是改進(jìn)高碳鋼的切削加性，并對(duì)淬硬鋼進(jìn)行預(yù)處理，使其淬火后結(jié)構(gòu)更均勻。因?yàn)闊崽幚頃r(shí)間長(zhǎng)，因此成本高，球化退火不如退火或正火常用。
鋼的硬化
鋼的大多數(shù)熱處理硬化方法是基于產(chǎn)生高比例的馬氏體。因此，第一步用的是大多數(shù)其他熱處理用的方法—— 產(chǎn)生奧氏體。亞共析鋼加熱到溫度以下大約60 ℃ ，進(jìn)行保溫，使溫度均布，奧氏體均勻。過(guò)共析鋼在線溫度以上大約60℃ 時(shí)保溫，鋼中仍殘留部分鐵碳化合物。
第二步是快速冷卻，力圖避免在等溫曲線鼻部產(chǎn)生珠光休轉(zhuǎn)變。冷卻速度取決于溫度和淬火時(shí)淬火介質(zhì)從鋼表面帶走熱量的能力以及鋼本身傳熱的能力表11 一1 是一些常用介質(zhì)和冷卻方法，按冷卻能力降低的順序排列。
高的溫度梯度產(chǎn)生高應(yīng)力，會(huì)引起變形和開(kāi)裂，所以淬火只有在非常需要產(chǎn)生特定結(jié)構(gòu)時(shí)才使用。淬火時(shí)必須小心，使熱量均勻擴(kuò)散以減小熱應(yīng)力。比如，一根細(xì)長(zhǎng)棒需端部淬火，即將它垂直插進(jìn)冷卻介質(zhì)中，這樣整個(gè)截面同時(shí)產(chǎn)生溫度變化。如果這種形狀的工件的某一邊比另一邊早降溫，尺寸變化很可能引起很高的應(yīng)力，產(chǎn)生塑性流動(dòng)和永久變形。
用幾種特殊的淬火方法可減小淬火應(yīng)力，減小變形開(kāi)裂傾向，：一種稱為分級(jí)淬火，其方法是：將奧氏體鋼放人溫度高于馬氏體轉(zhuǎn)變起始溫度（Ms ）的鹽浴中，放置一定的時(shí)間直到溫度均勻，在開(kāi)始形成貝氏休之前取出，然后放在空氣中冷卻，產(chǎn)生與從高溫開(kāi)始淬火時(shí)同樣硬的馬氏休，而導(dǎo)致開(kāi)裂和翹曲的高的熱應(yīng)力或淬火應(yīng)力已經(jīng)被消除。
在略高一點(diǎn)溫度下的類似方法稱為等溫淬火，這時(shí)，將（奧氏體）鋼放在鹽浴中，保持很長(zhǎng)時(shí)間，等溫處理的結(jié)果是形成貝氏體。貝氏體結(jié)構(gòu)不如在同樣成分時(shí)形成的馬氏休硬，但除了減少鋼在正常淬火時(shí)受到的熱沖擊外，不必要進(jìn)一步處理，就可獲得在高硬度時(shí)好的沖擊韌性。
回火
調(diào)整淬硬鋼以便使用的第三步通常是回火。除了等溫淬火鋼通常在淬火狀態(tài)下使用外，大多數(shù)鋼都不能在淬火