Heat treatment process generally includes three processes: heating, heat preservation and cooling. Sometimes there are only two processes: heating and cooling. These processes are interconnected and uninterrupted.

加热是热处理的重要工序之一。金属热处理的加热方法很多，是采用木炭和煤作为热源，近而应用液体和气体燃料。电的应用使加热易于控制，且无环境污染。利用这些热源可以直接加热，也可以通过熔融的盐或金属，以浮动粒子进行间接加热。

Heating is one of the important processes of heat treatment. There are many heating methods for metal heat treatment. Charcoal and coal are used as heat sources, and liquid and gas fuels are used recently. The application of electricity makes heating easy to control and no environmental pollution. These heat sources can be used for direct heating or indirect heating through molten salt or metal or even floating particles.

金属加热时，工件暴露在空气中，常常发生氧化、脱碳(即钢铁零件表面碳含量降低)，这对于热处理后零件的表面性能有很不利的影响。因而金属通常应在可控气氛或保护气氛中、熔融盐中和真空中加热，也可用涂料或包装方法进行保护加热。

When the metal is heated, the workpiece is exposed to the air, and oxidation and decarburization often occur (that is, the carbon content on the surface of steel parts is reduced), which has a very adverse impact on the surface properties of parts after heat treatment. Therefore, metals should usually be heated in controlled atmosphere or protective atmosphere, molten salt and vacuum, or protected by coating or packaging.

加热温度是热处理工艺的重要工艺参数之一，选择和控制加热温度，是保证热处理质量的主要问题。加热温度随被处理的金属材料和热处理的目的不同而异，但一般都是加热到相变温度以上，以获得高温组织。

Heating temperature is one of the important process parameters of heat treatment process. Selecting and controlling heating temperature is the main problem to ensure the quality of heat treatment. The heating temperature varies with the treated metal materials and the purpose of heat treatment, but it is generally heated above the phase transformation temperature to obtain high-temperature microstructure.

另外转变需要一定的时间，因此当金属工件表面达到要求的加热温度时，还须在此温度保持一定时间，使内外温度一致，使显微组织转变完全，这段时间称为保温时间。采用高能密度加热和表面热处理时，加热速度快，一般就没有保温时间，而化学热处理的保温时间往往较长。

In addition, the transformation takes a certain time. Therefore, when the metal workpiece surface reaches the required heating temperature, it must be maintained at this temperature for a certain time to make the internal and external temperatures consistent and complete the transformation of microstructure. This period of time is called holding time. When high-energy density heating and surface heat treatment are adopted, the heating speed is fast, and generally there is no holding time, while the holding time of chemical heat treatment is often longer.

冷却也是热处理工艺过程中不可缺少的步骤，冷却方法因工艺不同而不同，主要是控制冷却速度。一般退火的冷却速度慢，正火的冷却速度较快，淬火的冷却速度更快。但还因钢种不同而有不同的要求，例如空硬钢就可以用正火一样的冷却速度进行淬硬。

Cooling is also an indispensable step in the process of heat treatment. The cooling method varies with different processes, mainly controlling the cooling rate. Generally, the cooling speed of annealing is slow, the cooling speed of normalizing is faster, and the cooling speed of quenching is faster. However, there are different requirements due to different steel types. For example, air hardening steel can be hardened at the same cooling rate as normalizing.