It is necessary for the stainless steel electric heating tube to customize the correct heat treatment process before the operation. The stainless steel electric heating tube is subject to the limitation of the heating conditions during the induction heating process. Therefore, we should give full play to our subjective initiative and adopt a reasonable process to control and reduce the heat treatment to prevent workpieces. What measures should be taken to prevent distortion and cracking?
Let's take a look at the normalizing heat treatment process of ductile iron in the stainless steel electric heating tube:
The purpose of normalizing ductile iron is to obtain the pearlite structure, refine the grains and make the structure uniform, thereby improving the strength, hardness and wear resistance of the parts, and can be used as a pre-heat treatment for surface quenching.
Normalizing can be divided into two types: high temperature normalizing and low temperature normalizing:
(1) High-temperature normalizing: The high-temperature normalizing process is to heat the casting to above the eutectoid temperature range, generally 900~950℃, hold for 1~3h, make the matrix structure all austenitized, and then air-cooled out of the furnace to make it in In the eutectoid temperature range, if the pearlite matrix is obtained due to rapid cooling to thick-walled castings with high silicon content, air cooling or spray cooling should be used to ensure higher quality after normalizing.
(2) Low-temperature normalizing: The low-temperature normalizing process is to heat the casting to the eutectoid temperature range, that is, 820~860℃, hold for 1~4h, make the matrix structure partly austenitized, and then get out of the furnace after air cooling and low temperature normalizing. Pearlite and dispersed ferrite ductile iron can improve the toughness and plasticity of castings.
Due to the poor thermal conductivity of ductile cast iron and the larger elastic modulus, there is greater internal stress in the castings after normalizing. Therefore, most factories also perform a stress relief annealing (commonly called tempering) after normalizing, that is, heating Keep it at 550~600℃, keep it for 3~4h, and then air-cool it out of the furnace. Timely and correct tempering is particularly important for high-carbon steels and alloy steels with complex shapes.
In this heat treatment process, we need to control the heating speed: because the stainless steel electric heating tube heats up too fast, the workpiece generates excessive thermal stress. Generally, it must be preheated or limited the heating speed to achieve as uniform heating as possible.
