On 2018-08-08 14:48:54
Important process of vacuum heat treatment
Heating and cooling are important processes of vacuum heat treatment
According to the vacuum heat treatment plant, the heating temperature is one of the important parameters of the vacuum heat treatment process. The heating temperature varies with the purpose of the metal being treated and the vacuum heat treatment, but is generally heated above the phase transition temperature to obtain high-temperature microstructure. In addition, the transformation needs a certain time, so when the surface of the metal workpiece reaches the required heating temperature, it must be kept at this temperature for a certain time, so that the internal and external temperature is the same, so that the microstructure changes completely, this period of time is called the holding time. When density heating and surface vacuum heat treatment are adopted, the heating speed is fast and there is generally no holding time, while the holding time of chemical vacuum heat treatment is often longer.
Cooling is also an indispensable step in the process of vacuum heat treatment. In general, the cooling rate of annealing is slow, the cooling rate of normalizing is fast, and the cooling rate of quenching is fast. However, there are also different requirements for different types of steel, such as hollow steel can be quenched with normalized cooling rate.
The steel is heated to a certain temperature and kept warm for a period of time. Annealing of steel is a vacuum heat treatment method in which steel is heated to the temperature at which phase transition or partial phase transition occurs and then slowly cooled after heat preservation. The purpose of annealing is to eliminate microstructure defects, optimize microstructure, homogenize composition and refine grain, increase mechanical properties of steel, and reduce residual stress. At the same time can reduce the hardness, increase the plasticity and toughness, optimize the cutting performance. Therefore, annealing is not only to eliminate and optimize the tissue defects and internal stress left by the previous process, but also to prepare for the subsequent process, so annealing is a semi-finished product vacuum heat treatment, also known as pre-vacuum heat treatment.