Three processes in the heat treatment of carbon steel pipes

Heat treatment involves heating metal materials to an appropriate temperature, maintaining that temperature, and then cooling them in various ways. This process alters the metallographic structure of the metal, imparting the desired structural properties. The heat treatment of metal materials typically includes overall heat treatment, surface heat treatment, and chemical heat treatment. For carbon seamless steel tubes, the overall heat treatment is generally employed.

During heat treatment, steel pipes undergo basic processes such as heating, heat preservation, and cooling. These processes can introduce quality defects such as unqualified structure and performance, dimensional inaccuracies, surface cracks, scratches, severe oxidation, decarburization, and overheating or overburning.

The heat treatment of carbon steel pipes comprises three main processes:

Heating:

Heating can occur at two different temperature ranges: below the critical point Ac1 or Ac3, or above these critical points.

Heating below Ac1 or Ac3 stabilizes the steel structure and relieves internal stress. Heating above Ac1 or Ac3 austenitizes the steel, changing its structural properties significantly.

Heat Preservation:

The purpose of this process is to equalize the temperature throughout the steel pipe, ensuring a uniform structure. This stage helps in achieving the desired metallurgical transformation initiated during heating.

Cooling:

This is the critical stage that determines the final metallographic structure and mechanical properties of the steel pipe. Various cooling methods can be employed, including furnace cooling, air cooling, oil cooling, polymer cooling, and water cooling. Each method influences the final properties of the steel pipe differently.

By following these processes, carbon steel pipes can be treated to meet specific structural and performance requirements, ensuring their quality and suitability for various applications.