What is the heat treatment for Q345B plate?

The heat treatment process for Q345B plate generally includes three processes of heating, heat preservation and cooling, and sometimes only two processes of heating and cooling. These processes are interconnected and uninterrupted.
 
Heating is one of the important processes of heat treatment. There are many heating methods for metal heat treatment. The earliest uses charcoal and coal as heat sources, and then uses liquid and gas fuels. The use of electricity makes heating easy to control without environmental pollution. These heat sources can be used for direct heating, or indirect heating through molten salts or metals, or even floating particles.
When the Q345B 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 the steel part is reduced), which has a negative impact on the surface properties of the part after heat treatment. Therefore, the metal should usually be heated in a controlled atmosphere or a protective atmosphere, in molten salt and in a vacuum. It can also be protected by coating or packaging.
 
Heating temperature is one of the important process parameters of heat treatment process. Selecting and controlling the heating temperature is the main issue to ensure the quality of heat treatment. The heating temperature varies with the Q345B plate material being processed and the purpose of the heat treatment, but it is generally heated above the phase transition temperature to obtain a high-temperature structure. In addition, the transformation requires a certain time, so when the surface of the metal workpiece reaches the required heating temperature, it must be maintained at this temperature for a certain period of time to make the internal and external temperatures consistent and complete the transformation of the microstructure. This period is called the holding time. When high energy density heating and surface heat treatment are used, the heating speed is extremely fast, and generally there is no holding time, while the holding time of chemical heat treatment is often longer.
 
Cooling is also an indispensable step in the heat treatment process. The cooling method varies depending on the process, mainly to control the cooling rate. Generally, the cooling speed of annealing is the slowest, the cooling speed of normalizing is faster, and the cooling speed of quenching is faster. However, there are different requirements for different steel types. For example, hard steel can be quenched with the same cooling rate as normalizing.
 

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