Annealing of straight seam steel pipe is to heat the steel pipe to a certain temperature and keep it warm at this temperature and then slowly cool it to room temperature. Annealing includes complete annealing, spheroidizing annealing, and stress relief annealing.

1. Heating the steel pipe to a predetermined temperature, holding it for a period of time, and then cooling it slowly with the furnace is called complete annealing. The purpose is to reduce the hardness of the steel and eliminate the uneven structure and internal stress in the steel.

2. Heating the steel pipe to 750 degrees, keeping it warm for a period of time, slowly cooling it to 500 degrees, and finally cooling it in the air is called spheroidizing annealing. The purpose is to reduce the hardness of steel and improve cutting performance, mainly for high-carbon steel.

• 1. Steel pipe stress-removing annealing is also called low-temperature annealing. The steel is heated to 500-600 degrees, kept for a period of time, slowly cooled to below 300 degrees with the furnace, and then cooled at room temperature. During the annealing process, the structure does not change, and the internal stress of the metal is mainly eliminated.

• 2. Normalizing The heat treatment process of heating the steel pipe to 30-50°C above the critical temperature, holding it for an appropriate time, and then cooling it in still air is called normalizing. The main purpose of normalizing is to refine the structure, improve the performance of steel, and obtain a structure close to the equilibrium state. Compared with the annealing process, the main difference between normalizing and annealing is that the cooling rate of normalizing is slightly faster, so the production cycle of normalizing heat treatment is shorter. Therefore, when annealing and normalizing can also meet the performance requirements of parts, normalizing should be selected as much as possible.

• 3. Quenching Heat the steel pipe to a certain temperature above the critical point (quenching temperature for No. The heat treatment process of cooling in (oil) to obtain martensite or bainite structure is called quenching. The main difference between quenching, annealing, and normalizing is that the cooling rate is fast, and the purpose is to obtain a martensitic structure. Martensite structure is an unbalanced structure obtained after the quenching of steel. It has high hardness, but poor plasticity and toughness. The hardness of martensite increases with the carbon content of the steel.

• 4. After the tempered steel pipe is hardened, it is heated to a certain temperature below the critical temperature, held for a certain period of time, and then cooled to room temperature. The heat treatment process is called tempering. Quenched steel parts generally cannot be used directly, and must be tempered before use. Because of the high hardness and high brittleness of quenched steel, brittle fracture often occurs when it is used directly. Tempering can eliminate or reduce internal stress, reduce brittleness, and improve toughness; on the other hand, it can adjust the mechanical properties of quenched steel to achieve the performance of steel. According to the tempering temperature, tempering can be divided into three types: low-temperature tempering, medium-temperature tempering, and high-temperature tempering. A low temperature tempering 150 ~ 250. Reduce internal stress, and brittleness, maintain high hardness and wear resistance after quenching. B medium temperature tempering 350 ~ 500; improve elasticity, and strength. C high temperature tempering 500 ~ 650; tempering of quenched steel parts above 500 ℃ is called high-temperature tempering. Quenched steel parts have good comprehensive mechanical properties after high-temperature quenching (both certain strength and hardness, but also certain plasticity and toughness). Therefore, generally medium carbon steel and medium carbon alloy steel are often treated with high-temperature tempering after quenching. Shaft parts are the most widely used. Quenching + high-temperature tempering is called quenching and tempering treatment.