Induction Heat Treatment

March 13, 2023
Induction Heat Treatment
Heat treatment refers to a metal thermal processing process in which materials are heated, kept warm and cooled in a solid state to obtain the desired structure and properties. 
Metal heat treatment processes can be roughly divided into three categories: overall heat treatment, surface heat treatment and chemical heat treatment. According to the difference of heating medium, heating temperature and cooling method, each big class can be divided into some different heat treatment processes again. The same metal adopts different heat treatment processes to obtain different structures and thus have different properties.
Thermal treatment process generally comprises heating, insulation, three processes of cooling, has only two processes of heating and cooling sometimes. These processes are connected with each other and cannot be interrupted.
Overall heat treatment is a metal heat treatment process that heats the workpiece as a whole and then cools it at an appropriate rate to obtain the required metallographic structure to change its overall mechanical properties. The overall heat treatment of steel generally has four basic processes: annealing, normalizing, quenching and tempering.
Surface heat treatment is a metal heat treatment process that only heats the surface of the workpiece to change the mechanical properties of the surface. The main methods of surface heat treatment are flame quenching and High frequency induction heating machine heating heat treatment. The commonly used heat sources are flames such as oxyacetylene or oxypropane, induced current, laser and electron beam.
Chemical heat treatment is a metal heat treatment process that changes the chemical composition, structure and properties of the workpiece surface. The difference between chemical heat treatment and surface heat treatment is that the former changes the chemical composition of the workpiece surface.
Induction heating heat treatment is to put the workpiece into the inductor, which is generally a hollow copper tube that inputs medium frequency or high frequency alternating current (300HZ-300KHz or higher). Generate an alternating magnetic field to generate an induced current of the same frequency in the workpiece. The distribution of this induced current on the workpiece is uneven, strong on the surface, but weak inside. Using this skin effect, the surface of the workpiece can be heated rapidly , within a few seconds the surface temperature rises to the temperature required for heat treatment.
Selection of induction heating frequency: select the frequency according to the requirements of heat treatment and heating depth, the higher the frequency, the shallower the heating depth. The heating depth of high-frequency (above 10KHZ) is 0.5-2.5mm, which is generally used for heating small and medium-sized parts, such as small modulus gears and small and medium-sized shaft parts. Medium frequency (1~10KHZ) heating depth is 2-10mm, generally used for heating shafts with large diameter and gears with large and medium modulus.
Induction heating surface quenching has the advantages of good surface quality, low brittleness, hardened surface is not easy to oxidize and decarburize, and has small deformation, so induction heating equipment has been widely used in metal surface heat treatment.