Quenching Explained – Definition, Process, Benefits and More

热处理过程are crucial to obtain desired properties from different metals and make them suitable for various applications。通过热处理，可以改变许多机械性能而不会改变金属的化学成分。

热处理中有许多不同的过程。其中最常用的是淬火过程。让我们讨论它是什么。

什么是淬火？

Quenching is a rapid cooling process that alters specific properties of materials by manipulating the cooling rate. The material is heated above the recrystallisation temperature but below the melting point to allow grain restructuring followed by controlled cooling to a predetermined temperature.

在淬火期间加热碳钢的温度可以从iron-carbon phase diagram。For hypoeutectic steels (0,2…0,8% C) it is 30-50°C over Ac3 and for hypereutectic steels (C > 0,8%) over 30-50°C over Ac1.

The intention of quenching is to transform the austenitic phase into martensite, which is an exceptionally hard phase of steel. To achieve this, the material is exposed to a cooling media and the cooling time is reduces.

当在AC1而不是AC3上加热高压钢钢时，淬火后仍将某些铁氧体保留在结构中，这种降低的硬度。对于过度的钢钢，将钢加热到AC1和ACM相极限之间的温度是最佳的，因此，次级水泥岩将保留在马氏体旁边的结构中。在过ACM时，淬火后存在粗粒结构形成的风险，这使钢非常脆。

总的来说,淬火过程会导致增加hardness and reduced ductility of the material. But the brittleness also increases and thus, to avoid unwanted side effects such as cracking and distortion, choosing a suitable cooling rate is essential.

淬火和tempering processesare often used in sequence to restore some of the lost ductility and reduce hardness to suitable levels. Tempering also reduces brittleness.

Annealing偶尔也会进行减少淬灭钢的硬度。

When Is Quenching Used?

当需要增加硬度时，使用淬火。许多应用，例如建筑，采矿，重型机械，军事等，都需要具有硬表面的金属。一种可以抵抗磨损，划痕并影响撞击的人。淬火的硬度增加能够提供这些品质。

可以为多种材料进行淬火，但钢是最常见的淬火金属。淬火钢显示出极端硬度。

Quenching Process

The quenching process may happen in one of two ways: spray quenching or bath quenching.

在喷雾淬火过程中，金属的热表面通过喷洒在金属上的淬火剂的撞击效果来冷却。该方法的传热速率高于淬火。

The bath quenching process is, however, more common. In bath quenching, the material to be cooled is placed in a bath of liquid or gas. As the quenchant surrounds the material, it is rapidly cooled.

But even this rapid cooling occurs at different rates from the time quenching begins until it ends. Let us look at these different stages in the next section.

淬火阶段

During the bath quenching process, the material undergoes three distinct cooling stages. These stages are:

• 蒸气阶段

• 沸腾阶段

• 对流阶段

蒸气阶段

As soon as the material is placed in the quenching media, the vapour stage begins. Since the temperature of the hot material is above the boiling point of the quenching media, the media turns to vapour and thus, a stable vapour blanket is formed around the material.

适当的淬火加快了冷却过程，导致其进入沸腾阶段。

沸腾阶段

我n the boiling stage, the vapour blanket stops forming. The cooling medium comes into contact with the metal surface, but since the metal is still above the quenchant’s boiling point, it evaporates and rises.

周围的液体取代其位置，过程不断重复。在三个淬火阶段中，此阶段的传热率最高。一旦金属的温度落在淬灭剂的沸腾温度以下，淬火过程就进入第三阶段。

对流阶段

第三阶段是对流阶段。冷却介质不再在金属表面上蒸发。但是，它吸收了金属的热量并增加。周围液体取代其位置，并设置对流过程。

This stage has the lowest heat transfer rates. This is also the stage where the distortion of the material occurs.

淬灭媒体

淬灭培养基是指在淬火过程中吸收金属热量的材料。我们可以选择许多淬火媒介。每种媒介都提供其独特的优势和局限性。

所选淬火介质的类型取决于所需的冷却速率，材料特性，成本，可重复使用性和环境影响等因素。

We can choose from the following quenching media:

• Air

• Oil

• 淡水

• Brine (salt water)

• 聚合物

Air

Air isn’t too popular when it comes to quenching but in some cases, it is still used. It takes the longest time among all media to cool down a metal part. With this method, forced air flows over the metal surface and absorbs its heat.

Forced air cools faster than still air and may either be provided through a compressed air source or through various mechanical means such as a fan. The rate of cooling depends on the air pressure and the exposed area of the part.

空qeende材料可以更高地控制冷却速率和最终硬度。他们也有更好mechanical properties。但是，由于冷却速率较低，与其他淬火介质相比，硬度水平较低。

如果仍将空气用于缓慢冷却，则该过程称为normalising而不是淬火。

惰性气体也用于淬火。例如，氮淬灭是一种具有成本效益的方法，因为它可以在现场生成。

Oil

淬火可提供比空气更好的淬火速率，但小于水和盐水。油是易燃的，但可以帮助防止缺陷，例如失真和破裂。

Quenching oils are highly versatile and adjustable depending on the application. Nowadays, the most common quenching oil is mineral oil.

淡水

我n this method, the heated metal is immersed in a water bath. Cooling occurs faster than air as well as oil. Water is non-flammable which gives it an advantage over oil. It is also a cheap and pollution-free alternative.

但是，如果该工艺不能很好地控制，水会扭曲或破裂金属。

盐水（盐水）

盐水或盐水是最有效的淬火介质之一。它的淬火速率比石油，水和空气更高。这是因为它可以防止空气球和蒸气毯的形成。

The salts may either be nitrate-based or chlorine-based. Rapidly cooling metal in brine or salt water, however, makes it more susceptible to warping.

聚合物

当材料对石油淬火良好反应时，通常会使用聚合物淬火。它提供的冷却速率低于新鲜或盐水，但比空气更高。聚合物淬火可以容纳中断的淬火。这意味着可以将金属拆除中间量化，以减少失真的机会而不会冒火风险。

Benefits of Quenching

The quench-hardening process provides the following benefits:

1. Maximumhardnessamong all heat treatment processes

2. Retention of more beneficial crystal structure

3. 增加韧性

4. 更对齐的晶粒结构

5. 增加的抵抗力wear, vibrations and abrasion.