英文翻译第二章

The understanding of heat treatment is embraced by the broader study of metallurgy. Metallurgy is the physics, chemistry, and engineering related to metals from ore extraction to the final product.

Heat treatment is the operation of heating and cooling a metal in its solid state to change its physical properties. According to the procedure used, steel can be hardened to resist cutting action and abrasion, or it can be softened to permit machining.

With the proper heat treatment internal stresses may be removed, grain size reduced, toughness increased, or a hard surface produced on a ductile interior. The analysis of the steel must be known because small percentages of certain elements, notably carbon, greatly affect the physical properties.

Alloy steel owe their properties to the presence of one or more elements other than carbon, namely nickel, chromium, manganese, molybdenum, tungsten, silicon, vanadium, and copper. Because of their improved physical properties they are used commercially in many ways not possible with carbon steels.

The following discussion applies principally to the heat treatment of ordinary commercial steels known as plain carbon steels. With this process the rate of cooling is the controlling factor, rapid cooling from above the critical range results in hard structure, whereas very slow cooling produces the opposite effect.

? A Simplified Iron-carbon Diagram

If we focus only on the materials normally known as steels, a simplified diagram is often used.

Those portions of the iron-carbon diagram near the delta region and those above 2% carbon content are of little importance to the engineer and are deleted. A simplified diagram, such as the one in Fig.2.1, focuses on the eutectoid region and is quite useful in understanding the properties and processing of steel.

The key transition described in this diagram is the decomposition of single-phase austenite(γ) to the two-phase ferrite plus carbide structure as temperature drops.

Control of this reaction, which arises due to the drastically different carbon solubility of austenite and ferrite, enables a wide range of properties to be achieved through heat treatment.

To begin to understand these processes, consider a steel of the eutectoid composition, 0.77% carbon, being slow cooled along line x-x’ in Fig.2.1. At the upper temperatures, only austenite is present, the 0.77% carbon being dissolved in solid solution with the iron. When the steel cools to 727℃(1341℉), several changes occur simultaneously.

The iron wants to change from the FCC austenite structure to the BCC ferrite structure, but the ferrite can only contain 0.02% carbon in solid solution.

The rejected carbon forms the carbon-rich cementite intermetallic with composition Fe3C. In essence, the net reaction at the eutectoid is austen ite 0.77%C→ferrite 0.02%C+cementite 6.67%C.

Since this chemical separation of the carbon component occurs entirely in the solid state, the resulting structure is a fine mechanical mixture of ferrite and cementite. Specimens prepared by polishing and etching in a weak solution of nitric acid and alcohol reveal the lamellar structure of alternating plates that forms on slow cooling.

This structure is composed of two distinct phases, but has its own set of characteristic properties and goes by the name pearlite, because of its resemblance to mother- of- pearl at low magnification.

Steels having less than the eutectoid amount of carbon (less than 0.77%) are known as hypo-eutectoid steels. Consider now the transformation of such a material represented by cooling along line y-y’ in Fig.2.1.

At high temperatures, the material is entirely austenite, but upon cooling enters a region where the stable phases are ferrite and austenite. Tie-line and level-law calculations show that low-carbon ferrite nucleates and grows, leaving the remaining austenite richer in carbon.

At 727℃(1341℉), the austenite is of eutectoid composition (0.77% carbon) and further cooling transforms the remaining austenite to pearlite. The resulting structure is a mixture of primary or pro-eutectoid ferrite (ferrite that formed above the eutectoid reaction) and regions of pearlite.

Hypereutectoid steels are steels that contain greater than the eutectoid amount of carbon. When such steel cools, as shown in z-z’ of Fig.2.1 the process is similar to the hypo-eutectoid case, except that the primary or pro-eutectoid phase is now cementite instead of ferrite.

As the carbon-rich phase forms, the remaining austenite decreases in carbon content, reaching the eutectoid composition at 727℃(1341℉). As before, any remaining austenite transforms to pearlite upon slow cooling through this temperature.

t should be remembered that the transitions that have been described by the phase diagrams are for equilibrium conditions, which can be approximated by slow cooling. With slow heating, these transitions occur in the reverse manner.

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 analysis.

?Hardening

Hardening is the process of heating a piece of steel to a temperature within or above its critical range and then cooling it rapidly.

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 iron-iron carbide phase diagram. However, if the composition of the steel is unknown, a little preliminary experimentation may be necessary to determine the range.

A good procedure to follow is to heat-quench a number of small specimens of the steel at various temperatures and observe the result, either by hardness testing or by microscopic examination. When the correct temperature is obtained, there will be a marked change in hardness and other properties.

In any heat-treating operation the rate of heating is important. Heat flows from the exterior to the interior of steel at a definite rate. If the steel is heated too fast, the outside becomes hotter than the interior and uniform structure cannot be obtained.

If a piece is irregular in shape, a slow rate is all the more essential to eliminate warping and cracking. The heavier the section, the longer must be the heating time to achieve uniform results. 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 temperature.

he hardness obtained from a given treatment depends on the quenching rate, the carbon content, and the work size. In 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 steels.

Steel with low carbon content will not respond appreciably to hardening treatment. As the carbon content in steel increases up to around 0.60%, the possible hardness obtainable also increases.

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 state. Pearlite responds best to heat-treating operations; and steel composed mostly of pearlite can be transformed into a hard steel.

As the size of parts to be hardened increases, the surface hardness decreases somewhat even though all other conditions have remained the same. There is a limit to the rate of heat flow through steel.

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 hardness. However, 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 temperature.

Under these circumstances there would always be some finite depth of surface hardening regardless of size. This is not true in oil quenching, when the surface temperature may be high during the critical stages of quenching.

?Tempering

Steel that has been hardened by rapid quenching is brittle and not suitable for most uses. By tempering or drawing, the hardness and brittleness may be reduced to the desired point for service conditions．

As these properties are reduced there is also a decrease in tensile strength and an increase in the ductility and toughness of the steel. The operation consists of reheating quench-hardened steel to some temperature below the critical range followed by any rate of cooling.

Although this process softens steel, it differs considerably from annealing in that the process lends itself to close control of the physical properties and in most cases does not soften the steel to the extent that annealing would. The final structure obtained from tempering a fully hardened steel is called tempered martensite.

Tempering is possible because of the instability of the martensite, the principal constituent of hardened steel. Low-temperature draws, from 300℉ to 400℉ (150℃~205℃), do not cause much decrease in hardness and are used principally to relieve internal strains.

As the tempering temperatures are increased, the breakdown of the martensite takes place at a faster rate, and at about 600℉(315℃) the change to a structure called tempered martensite is very rapid. The tempering operation may be described as one of precipitation and agglomeration or coalescence of cementite.

A substantial precipitation of cementite begins at 600℉(315℃), which produces a decrease in hardness. Increasing the temperature causes coalescence of the carbides with continued decrease in hardness.

In the process of tempering, some consideration should be given to time as well as to

temperature. Although most of the softening action occurs in the first few minutes after the temperature is reached, there is some additional reduction in hardness if the temperature is maintained for a prolonged time.

Usual practice is to heat the steel to the desired temperature and hold it there only long enough to have it uniformly heated.

Two special processes using interrupted quenching are a form of tempering. In both, the hardened steel is quenched in a salt bath held at a selected lower temperature before being allowed to cool. These processes, known as austempering and martempering, result in products having certain desirable physical properties.

?Annealing

The primary purpose of annealing is to soften hard steel so that it may be machined or cold worked.

This is usually accomplished by heating the steel too slightly above the critical temperature, holding it there until the temperature of the piece is uniform throughout, and then cooling at a slowly controlled rate so that the temperature of the surface and that of the center of the piece are approximately the same.

This process is known as full annealing because it wipes out all trace of previous structure, refines the crystalline structure, and softens the metal. Annealing also relieves internal stresses previously set up in the metal.

The temperature to which a given steel should be heated in annealing depends on its composition; for carbon steels it can be obtained readily from the partial iron-iron carbide equilibrium diagram. When the annealing temperature has been reached, the steel should be held there until it is uniform throughout.

This usually takes about 45min for each inch(25mm) of thickness of the largest section. For maximum softness and ductility the cooling rate should be very slow, such as allowing the parts to cool down with the furnace. The higher the carbon content, the slower this rate must be.

The heating rate should be consistent with the size and uniformity of sections, so that the entire part is brought up to temperature as uniformly as possible.

?Normalizing and Spheroidizing

The process of normalizing consists of heating the steel about 50℉to 100℉(10℃~40℃) above the upper critical range and cooling in still air to room temperature.

This process is principally used with low- and medium-carbon steels as well as alloy steels to make the grain structure more uniform, to relieve internal stresses, or to achieve desired results in physical properties. Most commercial steels are normalized after being rolled or cast.

Spheroidizing is the process of producing a structure in which the cementite is in a spheroidal distribution. If steel is heated slowly to a temperature just below the critical range and held there for a prolonged period of time, this structure will be obtained.

The globular structure obtained gives improved machinability to the steel. This treatment is particularly useful for hypereutectoid steels that must be machined.

?Surface Hardening

Carburizing

The oldest known method of producing a hard surface on steel is case hardening or carburizing. Iron at temperatures close to and above its critical temperature has an affinity for carbon.

The carbon is absorbed into the metal to form a solid solution with iron and converts the outer surface into high-carbon steel. The carbon is gradually diffused to the interior of the part. The depth of the case depends on the time and temperature of the treatment.

Pack carburizing consists of placing the parts to be treated in a closed container with some carbonaceous material such as charcoal or coke. It is a long process and used to produce fairly thick cases of from 0.03 to 0.16 in.(0.76~4.06mm) in depth.

Steel for carburizing is usually a low-carbon steel of about 0.15% carbon that would not in itself responds appreciably to heat treatment. In the course of the process the outer layer is converted into high-carbon steel with a content ranging from 0.9% to 1.2% carbon.

A steel with varying carbon content and, consequently, different critical temperatures requires a special heat treatment.

Because there is some grain growth in the steel during the prolonged carburizing treatment, the work should be heated to the critical temperature of the core and then cooled, thus refining the core structure. The steel should then be reheated to a point above the transformation range of the case and quenched to produce a hard, fine structure.

The lower heat-treating temperature of the case results from the fact that hypereutectoid steels are normally austenitized for hardening just above the lower critical point. A third tempering treatment may be used to reduce strains.

Carbonitriding

Carbonitriding, sometimes known as dry cyaniding or nicarbing, is a case-hardening process in which the steel is held at a temperature above the critical range in a gaseous atmosphere from which it absorbs carbon and nitrogen.

Any carbon-rich gas with ammonia can be used. The wear-resistant case produced ranges from 0.003 to 0.030 inch(0.08~ 0.76mm) in thickness. An advantage of carbonitriding is that the hardenability of the case is significantly increased when nitrogen is added, permitting the use of low-cost steels.

Cyaniding

Cyaniding, or liquid carbonitriding as it is sometimes called, is also a process that combines the absorption of carbon and nitrogen to obtain surface hardness in low-carbon steels that do not respond to ordinary heat treatment.

The part to be case hardened is immersed in a bath of fused sodium cyanide salts at a temperature slightly above the Ac1 range, the duration of soaking depending on the depth of the case. The part is then quenched in water or oil to obtain a hard surface.

Case depths of 0.005 to 0.015in. (0.13~0.38mm) may be readily obtained by this process. Cyaniding is used principally for the treatment of small parts.

Nitriding

Nitriding is somewhat similar to ordinary case hardening, but it uses a different material and treatment to create the hard surface constituents.

In this process the metal is heated to a temperature of around 950℉(510℃) and held there for a period of time in contact with ammonia gas. Nitrogen from the gas is introduced into the steel, forming very hard nitrides that are finely dispersed through the surface metal.

Nitrogen has greater hardening ability with certain elements than with others, hence, special nitriding alloy steels have been developed.

Aluminum in the range of 1% to 1.5% has proved to be especially suitable in steel, in that it combines with the gas to form a very stable and hard constituent. The temperature of heating ranges from 925℉ to 1,050℉(495℃~565℃).

Liquid nitriding utilizes molten cyanide salts and, as in gas nitriding, the temperature is held below the transformation range. Liquid nitriding adds more nitrogen and less carbon than either cyaniding or carburizing in cyanide baths.

Case thickness of 0.001 to 0.012in.(0.03~0.30mm) is obtained, whereas for gas nitriding the case may be as thick as 0.025 in.(0.64mm). In general the uses of the two-nitriding processes are similar.

Nitriding develops extreme hardness in the surface of steel. This hardness ranges from 900 to 1,100 Brinell, which is considerably higher than that obtained by ordinary case hardening.

Nitriding steels, by virtue of their alloying content, are stronger than ordinary steels and respond readily to heat treatment. It is recommended that these steels be machined and heat-treated before nitriding, because there is no scale or further work necessary after this process.

Fortunately, the interior structure and properties are not affected appreciably by the nitriding treatment and, because no quenching is necessary, there is little tendency to warp, develop cracks, or change condition in any way. The surface effectively resists corrosive action of water, saltwater spray, alkalies, crude oil, and natural gas.

对热处理的理解包含于对冶金学较广泛的研究。冶金学是物理学、化学和涉及金属从矿石提炼到最后产物的工程学。

热处理是将金属在固态加热和冷却以改变其物理性能的操作。按所采用的步骤，钢可以通过硬化来抵抗切削和磨损，也可以通过软化来允许机加工。

使用合适的热处理可以去除内应力、细化晶粒、增加韧性或在柔软材料上覆盖坚硬的表面。因为某些元素(尤其是碳)的微小百分比极大地影响物理性能，所以必须知道对钢的分析。

合金钢的性质取决于其所含有的除碳以外的一种或多种元素，如镍、铬、锰、钼、钨、硅、钒和铜。由于合金钢改善的物理性能，它们被大量使用在许多碳钢不适用的地方。

下列讨论主要针对被称为普通碳钢的工业用钢而言。热处理时冷却速率是控制要素，从高于临界温度快速冷却导致坚硬的组织结构，而缓慢冷却则产生相反效果。

简化铁碳状态图

如果只把注意力集中于一般所说的钢上，经常要用到简化铁碳状态图。

铁碳状态图中靠近三角区和含碳量高于2%的那些部分对工程师而言不重要，因此将它们删除。如图2.1所示的简化铁碳状态图将焦点集中在共析区，这对理解钢的性能和处理是十分有用的。

在此图中描述的关键转变是单相奥氏体(γ) 随着温度下降分解成两相铁素体加渗碳体组织结构。控制这一由于奥氏体和铁素体的碳溶解性完全不同而产生的反应，使得通过热处理能获得很大范围的特性。

为了理解这些过程，考虑含碳量为0.77%的共析钢，沿着图2.1的x-x’线慢慢冷却。在较高温度时，只存在奥氏体，0.77%的碳溶解在铁里形成固溶体。当钢冷却到727℃ (1341℉) 时，将同时发生若干变化。

铁需要从面心立方体奥氏体结构转变为体心立方体铁素体结构，但是铁素体只能容纳固溶体状态的0.02%的碳。

被析出的碳与金属化合物Fe3C形成富碳的渗碳体。本质上，共析体的基本反应是奥氏体0.77%的碳→铁素体0.02%的碳+渗碳体6.67%的碳。

由于这种碳成分的化学分离完全发生在固态中，产生的组织结构是一种细致的铁素体与渗碳体的机械混合物。通过打磨并在弱硝酸酒精溶液中蚀刻制备的样本显示出由缓慢冷却形成的交互层状的薄片结构。

这种结构由两种截然不同的状态组成，但它本身具有一系列特性，且因与低倍数放大时的珠母层有类同之处而被称为珠光体。

含碳量少于共析体(低于0.77%)的钢称为亚共析钢。现在来看这种材料沿着图 2.1中y-y’线冷却的转变情况。

在较高温度时，这种材料全部是奥氏体，但随着冷却就进入到铁素体和奥氏体稳定状态的区域。由截线及杠杆定律分析可知，低碳铁素体成核并长大，剩下含碳量高的奥氏体。

在727℃(1341℉)时，奥氏体为共析组成(含碳量0.77%)，再冷却剩余的奥氏体就转化为珠光体。作为结果的组织结构是初步的共析铁素体(在共析反应前的铁素体)和部分珠光体的混合物。

过共析钢是含碳量大于共析量的钢。当这种钢冷却时，就像图2.1的z-z’线所示，除了初步的共析状态用渗碳体取代铁素体外，其余类似亚共析钢的情况。

随着富碳部分的形成，剩余奥氏体含碳量减少，在727℃(1341℉)时达到共析组织。就像以前说的一样，当缓慢冷却到这温度时所有剩余奥氏体转化为珠光体。

应该记住由状态图描述的这种转化只适合于通过缓慢冷却的近似平衡条件。如果缓慢加热，则以相反的方式发生这种转化。

然而，当快速冷却合金时，可能得到完全不同的结果。因为没有足够的时间让正常的状态反

应发生，在这种情况下对工程分析而言状态图不再是有用的工具。

淬火

淬火就是把钢件加热到或超过它的临界温度范围，然后使其快速冷却的过程。

如果钢的含碳量已知，钢件合适的加热温度可参考铁碳合金状态图得到。然而当钢的成分不知道时，则需做一些预备试验来确定其温度范围。

要遵循的合适步骤是将这种钢的一些小试件加热到不同的温度后淬火，再通过硬度试验或显微镜检查观测结果。一旦获得正确的温度，硬度和其它性能都将有明显的变化。

在任何热处理作业中，加热的速率都是重要的。热量以一定的速率从钢的外部传导到内部。如果钢被加热得太快，其外部比内部热就不能得到均匀的组织结构。

如果工件形状不规则，为了消除翘曲和开裂最根本的是加热速率要缓慢。截面越厚，加热的时间就要越长才能达到均匀的结果。

即使加热到正确的温度后，工件也应在此温度下保持足够时间以让其最厚截面达到相同温度。

通过给定的热处理所得到的硬度取决于淬火速率、含碳量和工件尺寸。除了非淬硬钢或部分淬硬钢外，合金钢中合金元素的种类及含量仅影响钢的淬透性(工件被硬化到深层的能力)而不影响硬度。

含碳量低的钢对淬火处理没有明显的反应。随着钢的含碳量增加到大约0.60%，可能得到的硬度也增加。

高于此点，由于超过共析点钢完全由珠光体和退火状态的渗碳体组成，硬度增加并不多。珠光体对热处理作业响应最好；基本由珠光体组成的钢能转化成硬质钢。

即使所有其它条件保持不变，随着要淬火的零件尺寸的增加其表面硬度也会有所下降。热量在钢中的传导速率是有限的。

无论淬火介质怎么冷，如果在大工件中的热量不能比特定的临界速率更快散发，那它内部硬度就会受到明确限制。然而盐水或水淬火能够将被淬零件的表面迅速冷却至本身温度并将其保持或接近此温度。

在这种情况下不管零件尺寸如何，其表面总归有一定深度被硬化。但油淬情况就不是如此，因为油淬时在淬火临界阶段零件表面的温度可能仍然很高。

回火

快速淬火硬化的钢是硬而易碎的，不适合大多数场合使用。通过回火，硬度和脆性可以降低到使用条件所需要的程度。

随着这些性能的降低，拉伸强度也降低而钢的延展性和韧性则会提高。回火作业包括将淬硬钢重新加热到低于临界范围的某一温度然后以任意速率冷却。

虽然这过程使钢软化，但它与退火是大不相同的，因为回火适合于严格控制物理性能并在大多数情况下不会把钢软化到退火那种程度。回火完全淬硬钢得到的最终组织结构被称为回火马氏体。

由于马氏体这一淬硬钢主要成分的不稳定性，使得回火成为可能。低温回火， 300℉到400℉(150℃~205℃)，不会引起硬度下降很多，主要用于减少内部应变。

随着回火温度的提高，马氏体以较快的速率分解，并在大约600℉(315℃)迅速转变为被称为回火马氏体的结构。回火作业可以描述为渗碳体析出和凝聚或聚结的过程。

渗碳体的大量析出开始于600℉(315℃)，这使硬度下降。温度的上升会使碳化物聚结而硬度继续降低。

在回火过程中，不但要考虑温度而且要考虑时间。虽然大多数软化作用发生在达到所需温度后的最初几分钟，但如果此温度维持一段延长时间，仍会有些额外的硬度下降。

通常的做法是将钢加热到所需温度并且仅保温到正好使其均匀受热。

两种采用中断淬火的特殊工艺也是回火的形式。这两种工艺中，淬硬钢在其被允许冷却前先在一选定的较低温度盐浴淬火。这两种分别被称为奥氏体回火和马氏体回火的工艺，能使产品具有特定所需的物理性能。

退火

退火的主要目的是使坚硬的钢软化以便机加工或冷作。

通常是非常缓慢地将钢加热到临界温度以上，并将其在此温度下保持到工件全部均匀受热，然后以受控的速率慢慢地冷却，这样使得工件表面和内部的温度近似相同。

这过程被称为完全退火，因为它去除了以前组织结构的所有痕迹、细化晶粒并软化金属。退火也释放了先前在金属中的内应力。

给定的钢其退火温度取决于它的成分；对碳钢而言可容易地从局部的铁碳合金平衡图得到。达到退火温度后，钢应当保持在此温度等到全部均匀受热。

加热时间一般以工件的最大截面厚度计每英寸(25mm )大约需45min。为了得到最大柔软性和延展性冷却速率应该很慢，比如让零件与炉子一起冷下来。含碳量越高，冷却的速率必须越慢。加热的速率也应与截面的尺寸及均匀程度相协调，这样才能使整个零件尽可能均匀地加热。

正火和球化

正火处理包括先将钢加热到高于上临界区50℉到100℉(10℃~40℃)然后在静止的空气中冷却到室温。

退火主要用于低碳钢、中碳钢及合金钢，使晶粒结构更均匀、释放内应力或获得所需的物理特性。大多数商业钢材在轧制或铸造后都要退火。

球化是使渗碳体产生成类似球状分布结构的工艺。如果把钢缓慢加热到恰好低于临界温度并且保持较长一段时间，就能得到这种组织结构。

所获得的球状结构改善了钢的可切削性。此处理方法对必须机加工的过共析钢特别有用。表面硬化

渗碳

最早的硬化钢表面的方法是表面淬火或渗碳。铁在靠近并高于其临界温度时对碳具有亲合力。碳被吸收进金属与铁形成固溶体使外表面转变成高碳钢。碳逐渐扩散到零件内部。渗碳层的深度取决于热处理的时间和温度。

固体渗碳的方法是将要处理的零件与木炭或焦炭这些含碳的材料一起放入密闭容器。这是一个较长的过程，用于产生深度为0.03到0.16 英寸(0.76~4.06mm)这么厚的硬化层。

用于渗碳的一般是含碳量约为0.15%、本身不太适合热处理的低碳钢。在处理过程中外层转化为含碳量从0.9%到1.2%的高碳钢。

含碳量变化的钢具有不同的临界温度，因此需要特殊的热处理。

由于在较长的渗碳过程中钢内部会有些晶粒生长，所以工件应该加热到核心部分的临界温度再冷却以细化核心部分的组织结构。然后重新加热到高于外层转变温度再淬火以生成坚硬、细致的组织结构。

由于恰好高于低临界温度通常使过共析钢奥氏体化而硬化，所以对外层采用较低的热处理温度。第三次回火处理可用于减少应变。

碳氮共渗

碳氮共渗，有时也称为干法氰化或渗碳氮化，是一种表面硬化工艺。通过把钢放在高于临界温度的气体中，让它吸收碳和氮。

可以使用任何富碳气体加氨气，能生成厚度从0.003到0.030英寸(0.08~ 0.76mm)的耐磨外层。碳氮共渗的优点之一是加入氮后外层的淬透性极大增加，为使用低价钢提供条件。

氰化

氰化，有时称为液体碳氮共渗，也是一种结合了吸收碳和氮来获得表面硬度的工艺，它主要用于不适合通常热处理的低碳钢。

需表面硬化的零件浸没在略高于Ac1温度熔化的氰化钠盐溶液中，浸泡的持续时间取决于硬化层的深度。然后将零件在水或油中淬火。

通过这样处理可以容易地获得0.005到0.015英寸(0.13~0.38mm)的硬化深度。氰化主要用于处理小零件。

渗氮

渗氮有些类似普通表面硬化，但它采用不同的材料和处理方法来产生坚硬表面成分。这种工艺中金属加热到约950℉(510℃)，然后与氨气接触一段时间。氨气中的氮进入钢内，形成细微分布于金属表面又十分坚固的氮化物。

氮与某些元素的硬化能力比其它元素大，因此开发了专用的渗氮合金钢。

在钢中含铝1%到1.5%被证明特别合适，它能与氨气结合形成很稳定坚固的成分。其加热温度范围为925℉到1,050℉ (495℃~565℃)。

液体渗氮利用熔化的氰化物盐，就像气体渗氮，温度保持在低于转化范围内。液体渗氮时在氰化物溶液中加入比氰化及渗碳都较多的氮和较少的碳。

液体渗氮可以获得厚度为0.001到0.012英寸 (0.03~0.30mm)的硬化层，然而气体渗氮则能获得厚0.025英寸(0.64mm)的硬化层。一般而言两种渗氮方法的用途是类似的。

渗氮在钢表面获得远远超出正常标准的硬度。其硬度范围为900到1,100布氏硬度，这远高于普通表面硬化所获得的硬度。

由于渗氮钢的合金比例，它们比普通钢更强，也容易热处理。建议对这种钢在渗氮前先机加工和热处理，因为渗氮后没有剥落并不需要更多的加工。

值得庆幸的是由于渗氮处理一点都不影响内部结构和性能，也无需淬火，所以几乎没有任何产生翘曲、裂缝及变化条件的趋势。这种表面能有效地抵御水、盐雾、碱、原油和天然气的腐蚀反应。