金属的热处理外文翻译

附录 1

英文及翻译

Heat Treating of metals

Heating

For this discussion, I will take you through the hardening process that I use on a high carbon steel blade, but first a few asides. When you place the steel in the fire it begins to gain heat. The steel will begin to give off visible color just above 900F it will continue to pick up color until it reaches a point where it seems to hang. It is still gaining heat, but it is undergoing an internal transformation from its cold structure into a metastable condition called austenite. This point at which it seems to hang is called decalescence and it represents the bottom of the critical temperature. It usually begins around 1335F

In carbon steel depending on the carbon content. Once it passes through this point, the crystal structure of the steel changes as the ferrite reacts with some of the carbide and begins to pool into austenite. As the temperature increases more of the austenite will begin to form in other places and continue until it reaches a point 10 or 15 degrees above the critical temperature where all of the ferrite should be consumed. At this point the steel should consist of austenite and undissolved carbides. The austenite grains start from a small nucleus and continue to grow until they impinge on other growing grains. The initial grain size is established at this point and if the excess carbide is in large quantities it will maintain this size with little increase, pinned by the carbide.

You can see this transformation if you watch the steel carefully and bring the steel up slowly. The Japanese talked about watching the shadows on the blade and quenching when the shadows turned to liquid. If you take the blade out of the fire at this point and watch the colors drop, you will notice a point where the steel will brighten even as it is cooling. On a tapered cross section like a knife blade it will appear to travel up from the edge to the spine of the blade. This is call

recalescenceand represents the transformation from austenite back to pearlite. After I am done forging a blade, I cycle the blade just above critical and down to dark heat at least three times. I watch for these two points to establish critical in my mind and to set up a very fine grain pearlite structure in the steel.

After reaching critical temperature, the steel should be fully austenized, but the carbides will continue to dissolve. It may be necessary to soak at temperature to fully dissolve all the carbides. In some steels it may be necessary to continue to raise the temperature for this to be accomplished especially in the presence of alloying elements that retard the transformation.

Once the steel is above critical and austenite, it may be quenched and hardened. The structure of the steel can be established by carefully controlling the time it takes the steel drop from critical through the various temperature sensitive points.

Transformations on Cooling

Annealing, normalizing, quenching

The structure and hardness of the steel is established by the rate of cooling from the austenitic condition. If brought down slowly the steel will be annealed and soft. The structure will be mostly ferrite and cementite, carbides. This can be done in a temperature controlled furnace by dropping the temperature through a known rate over a set period of time dependent on the type of steel. Another method is to preheat a heavy bar of low carbon to the same temperature as critical for the steel and bury both of them together in vermiculite. It will slow the cooling rate down so that the blade will still be hot to the touch the next day. For most of the carbon steels this will be enough to anneal the piece.

If allowed to air cool it will be normalized, a tougher condition comprised of fine pearlite and carbides. Blades can be prepared for heat treatment in either normalized or annealed states. Another treatment that is particularly effective for workability and for dimensional stability is called sphereodizing. With the steel in a normalized

condition you reheat, usually in salt to inhibit oxidization, to a temperature just below lower critical, 1300F and hold for at least an hour. What occurs is that the carbides will begin to aglomulate or pool into larger more evenly spaced particles in a ferrite matrix. It makes handfinishing much easier.

It is important to precondition your blades not only because it helps workability, but also to stress relieve the steel after forging. This will reduce chances of cracking and warping in the quench. It is helpful to think of the forging stage as the beginning of the heat treatment and to pay careful attention to the heats especially in the final forging. My last heats are always at critical. When the blade is finally shaped, I cycle the blade just above critical and down to almost black heat at least three times, cooling between by moving it back and forth in the air gently.

Hardening

You have a lot of options when it comes to hardening carbon steel. Even the slightest change in alloy content can make a remarkable difference in the hardening characteristics of the steel, so I would again encourage you to study the steels you will be using.

The transformation temperatures and times are described using a chart that shows the Ae1 line, the temperature at which austenite begins to form and the Msline, the temperature at which martensite starts to form from austenite.The time line at the bottom of the chart is in seconds and side bars give temperature. This is called an "S" curve chart and it is very useful in determining the quench speeds for each steel. The top curve of the "S" is known as the nose of the curve. When quenching from critical, the temperature of the steel must drop below the nose of the curve within a precise amount of time in order for the steel to harden to martensite. In this case, it must get below 900F in under five seconds to form martensite.

Marquenching

If the steel is quenched to below the Ms, martensite will be the predominate structure, however if the blade is quenched to a point slightly above the Ms point, say around 500F and held until it has stabilized at that temperature, the steel has the promise to form martensite, but will not set up until it drops below Ms. This is called marquenching and is commonly used because it is less stressful particularly in difficult cross sections like we encounter in knife blades. When the blade is removed from the quench it is still above the Ms point and has very unusual properties. It can be easily bent or straightened and isstill quite soft. As it cools however, it begins to setup martensite and will harden at room temperature. Again, you need to look at the chart for each steel you will be using because the Mf,or martensite finish point can be well below room temperature on some highly alloyed steels. These steels benefit from sub zero quenching because the colder temperatures are necessary to complete the austenite transformation and to reach the martensite finish. Care must be taken that the blade is not chilled by placing on a cold surface or even by being placed in a breeze or draft. The safest method is to allow it to cool in still air. The blade should be tempered after it has cooled to the point where it can be handled with bare hands.

Austempering

If the steel is quenched from Ae3, critical, to a point between the Ms and the nose of the curve, say 600F and held at temperature for a long time, the austenite will convert to banite. Banite is a much tougher structure than martensite and will maintain the hardness of the steel as tempered to that temperature. This process requires a salt bath and good controls, but makes an really tough spring and is being used by some makers on steels like 52100.

Quenchants

The method of controlling the speed of cooling is the quenchant. The quench rate is determined by how quickly the quenchant can remove the heat from the steel.

When a piece of hot steel enters the quenchant the area surrounding the blade absorbs heat from the blade until it is heated itself.

金属的热处理

加热

加热这种讨论,我将以高碳钢为例向你介绍其硬化过程.首先，你把钢铁放在火上加热时。当超过900F时钢铁的颜色开始显著的增加，其颜色还在继续增加直到达到一个平衡点，这时它还在蓄积热能。但这个由冷态结构转变成奥氏体状态的过程称为奥氏体转变。这个临界温度,看起来很复杂，它代表了加热的临界温度。1335f碳素钢。通常依靠碳含量来决定。它通常徘徊在1335F左右。

碳钢的性能取决于含碳量的高低，如果高于这一值,晶体结构里的铁素体将会和碳反应变成奥氏体。随着温度的上升越来越多的奥氏体更将会在其他地方形成并持续直到达到或超过临界温度10到15度,所有的铁素体都消失。此时钢的奥氏体组织开始形核心长大并和其他长大的晶体连到一起。原始晶粒的增长是建立在以碳核为中心的一点点的凝结上.最初的长大是建立在那些碳凝结核上，如果含碳量很高，那么晶粒围着碳核长大量会很小。

如果你把钢铁缓慢加热并仔细观察，你能看到其转变过程。日本人介绍了他们看到的叶状组织上的一点点变化，并且在淬火时转变成液体。如果你在这点从火中取出叶片并且看颜色下降，你将注意到在其冷却过程中有一个亮点。它看起来是从边缘逐渐移动到刀刃或刀刀刃口的横断面上。这个过程被称为再结晶转变，描述其从奥氏体转变成珠光体。后来我锻打了一个叶状块,将其加热到临界温度并冷却到奥氏体以下温度状态至少三次以上，我留意这两个临界点在我的脑海里建立临界点这一概念，并获得了很细的珠光体组织。

达到临界温度后应使钢充分奥氏体化,但碳化物将会继续分解。可能必须完全加热到一定温度碳化物才能全部消失。有些钢可能需要继续提高温度,这是因为合金元素阻碍了奥氏体转变，一旦刚被加热到高于临界温度并被奥氏体化，就可以淬火硬化，其组织结构可以通过精确控制从临界点降温的各个温度段的保温时间来实现。

冷却转变

退火、正火、淬火

钢的结构和硬度是通过控制奥氏体的冷却速度获得的。如果降温缓慢，钢将获得很好的塑性和韧性。结构将主要是铁素体、铁渗碳体和碳化物。不同类型的钢可以通过控制炉温以一个已知的速率跨过一个阶段获得。另一种方法是预热低碳钢到同样的临界温度使碳和钢互渗。加热后正火处理，将冷却速度慢下来,以便热量能够保持到第二天. 对大部分的碳钢都可以完全退火处理。

空冷将是一个获得珠光体和渗碳体更加良好的条件,可以通过正火火退火进行热处理. 另一尤为有效和可行的处理叫做淬火处理. 在正常的情况下对钢进行加热,通常用抑制氧化盐的办法,使温度低略低于临界温度1300f并保温至少一小时。在这个过程中，炭化物开始汇集成较大的奥氏体颗粒或间隔，更大的亚铁盐矩阵。它使热处理容易得多。

对片状件的预处理很重要，不仅是因为可使用性，而且减少锻造残余应力，这将减少淬火变形和裂缝的机会。这将使我们想到锻造尤其终锻就是热处理的开始阶段。我加热总是到临界点，状件片最后成形的时候,我将刀片在临界温度冷却循环热处理至少三次，冷却方式是来回的在空气中移动。

硬化

碳素钢硬化有很多方式,稍有改变合金成分能显著的得到不同的硬度特征,所以我再次鼓励你们学习那些你有用的部分。

转变温度和时间是用图表中的Ae1线来描述的，这个温度是奥氏体和马氏体的相转变线，在这一刻马氏体开始从奥氏体中形成。时间线在图表的底部温度线旁边以秒为单位，被称为“S”曲线，这个在确定每个钢淬火钢的速度方面非常有用。最高曲线" S"称为鼻型曲线，淬火时当温度从临界温度下降时，必须在很短暂的时间内降低到低于鼻形曲线的范围，钢开始变硬变成马氏体组织。必须在5秒内使温度降低900F的条件下才能形成马氏体。

马氏体淬火

如果低于钢淬火M s ,马氏体是主要结构,但如果是加热点略高于M s,并在500f附近举行,直至稳定在这个温度,钢材已形成马氏体结构,但也不会稳定,直到低于这个温度。这叫马氏体淬火这种方法很常用因为它很普遍，特别在困难的横剖面如我们经常见到的刀片里。当刀片从停止加热仍在临界温度之上并且有非常异常的产物产生。可以轻易弯曲或拉直,还是相当柔软。但是因为冷却后,开始马氏体转变,在室温下硬化. 再次,要看看你的每一个钢号,你将因为使用M F 马氏体点可以完成或低于室温下的硬度不钨钢高一些而自豪。这得益于钢的零气温骤冷,是因为要彻底改造,实现了马氏体的绝大部分转变。必须注意的是不能绝对完成的,将冷冻冷藏表面甚至被放在一个冷库里. 最安全的方法还是把它放进冷却机。在锻炼后冷却,就能处理的很好。

奥氏体化

如钢铁是从火 Ae3 临界点开始，达到M s 和鼻曲线之间，例如600F并在此温度保持很长时间，奥氏体将转变为板条马氏体。板条马氏体的结构比马氏体更大，并保留了钢的锻炼硬度,温度，盐浴,这需要盐浴和一个好的过程控制，但得到的非常严格的要求,正在使用的一些钢号如钢52100。

淬火介质

控制冷却速度的方法是控制淬火介质的冷却速度，介质的冷却速度快慢要看其从钢铁上转移热量的快慢。当一块热钢开始淬火，周围环境开始从它上面吸收热量直到温度平衡。是由可消除热量的介质钢在一片热水器淬火介质进入附近的区域开始吸热,和淬火介质温度相等。