To begin, it is important to establish the proper operating temperature for the heating system.
It is essential to standardize the working temperature for the heat treatment of galvanized pipes to obtain a uniform and tiny austenite crystallization. This helps in the formation of martensite structure after the heat treatment process. The temperature of the heat treatment process for galvanized pipes should be determined based on the zero boundary point of the pipe. For eutectoid steel pipes, the galvanized pipe is heated to 30-50℃ above Ac1, while for high carbon steel pipes, it is heated to slightly lower Ac3 points. If the heat treatment process temperature is between Ac1 and Ac3, it may affect the strength and tensile properties of the seamless pipe.
For eutectoid galvanized steel pipes, electric heater temperature is limited to 30-50℃ above Ac1 to ensure that the desired crystalline martensite and granular pearlite structure is obtained. The heat treatment process for hypereutectoid steel pipes should not exceed Accm to prevent reduction in strength and wear resistance of the pipe fitting. It is not recommended to apply high temperature heat treatment process to austenitic crystalline stainless steel as it can cause passivation of the material. Additionally, high carbon composition can lead to the formation of small and coarse martensite containing cracks after heat treatment process, which will reduce the ductility of the seamless tube. Moreover, high temperature heat treatment process can cause thermal stress, oxidation, and nitriding, which will make the seamless pipe more susceptible to deformation and cracking.
To ensure the effectiveness of galvanized pipe heat treatment, it is important to establish the appropriate temperature based on the zero boundary point Ac1 or Ac3, taking into account the various metal material elements involved. For more efficient austenitizing, a higher heat treatment temperature may be utilized, typically 50~100℃ above Ac1 or Ac3. For high carbon tool steel pipes, a high passivation temperature due to strong pearlite elements may demand a higher heat treatment temperature. Conversely, galvanized pipes with elevated carbon and manganese content should employ lower heat treatment temperatures to avoid unintended passivation of austenitic crystalline stainless steel.