1. Definition: metal heat treatment is a process of heating the metal workpiece in a certain medium to a suitable temperature and keeping it at this temperature for a certain time, then cooling it at different speeds.
2. Features: heat treatment generally does not change the shape and overall chemical composition of the workpiece, but endows or improves the service performance of the workpiece by changing the microstructure inside the workpiece or the chemical composition on the surface of the workpiece. Its characteristic is to improve the internal quality of the workpiece.
3. Process: heat treatment process generally includes heating, heat preservation and cooling, sometimes only heating and cooling.
The important process parameters of heating process are heating temperature and holding time. The heating temperature varies with the metal material being treated and the purpose of heat treatment, but it is generally heated above the phase change temperature to obtain high temperature structure. When the surface of the metal workpiece reaches the required heating temperature, it must be kept at this temperature for a certain period of time, so that the internal and external temperatures are the same, and the microstructure is completely transformed. This period of time is called the holding time. When high energy density heating and surface heat treatment are used, the heating speed is extremely fast, and there is generally no heat preservation time, while the heat preservation time of chemical heat treatment is often longer.
Cooling is mainly to control the cooling speed. Generally, the cooling speed of annealing is the slowest, that of normalizing is faster, and that of quenching is faster. But there are different requirements due to different kinds of steel. For example, air hardening steel can be quenched at the same cooling rate as normalizing.
On 2018-08-08 11:45:46
