Seamless pipe (SMLS) is a kind of pipe widely used in petroleum, natural gas, chemical industry, electric power and other fields, because of its high strength, corrosion resistance, high temperature resistance and other characteristics, it needs to be heat treated in the production process. The heat treatment of seamless steel pipes mainly includes quenching, tempering and other tempering processes, and the application of these processes can further improve the mechanical properties and corrosion resistance of seamless steel pipes to meet the requirements of different fields. This paper will introduce the process and principle of seamless pipe heat treatment in detail.
In the process of seamless pipe heat treatment, the heating speed, heating temperature, holding time and other parameters of the steel pipe have an important impact on the performance of the steel pipe. In order to obtain the best performance of the steel pipe, it is necessary to develop a reasonable heat treatment process.

When manufacturing seamless pipes, high temperature quenching and tempering heat treatment is usually required. Quenching is to heat the steel pipe to a certain temperature and hold it for a certain time, so that it is fully austenitic, and then quickly cool, so that the austenite into martensite. Tempering is to heat the steel pipe to a certain temperature and hold it for a certain time, so that the martensite is gradually transformed into tempered bainite. Tempered bainite structure has high hardness and strength, but also has a certain toughness. Quenching:
Quenching is an important process of seamless pipe heat treatment, the purpose of which is to heat the seamless steel pipe to a certain temperature and then quickly cool it to obtain higher hardness and strength. During the quenching process, the seamless steel pipe is heated to above the austenitizing temperature, and the internal structure of the steel pipe is transformed from the original pearlite and cementite to austenite, with high hardness and strength. In the rapid cooling process, austenite is rapidly transformed into martensite, which is a high-strength, high-hardness structure that can further improve the mechanical properties of seamless steel pipes.
The following points should be noted during the quenching process:
1, heating temperature: seamless steel pipe in the quenching process needs to be heated to a certain temperature, the determination of this temperature needs to consider the material, specifications, wall thickness and other factors of the seamless steel pipe to ensure that the internal organization of the seamless steel pipe is fully austenitic. Generally speaking, the quenching temperature of carbon steel is between 800 and 900 ° C, and the quenching temperature of alloy steel will be higher.
2, cooling speed: The quenching process needs to choose the appropriate cooling speed to ensure that the internal structure of the seamless steel pipe is fully and evenly changed. Generally speaking, the faster the cooling speed, the more complete the internal organization of the seamless steel pipe, but it will also increase the risk of deformation and cracking of the seamless steel pipe. Therefore, it is necessary to choose the appropriate cooling speed according to the material, specifications, wall thickness and other factors of the seamless steel pipe.

3, medium selection: The quenching process needs to choose the appropriate cooling medium to avoid cracks, deformation and other problems in the cooling process of seamless steel pipe. The commonly used cooling media are water, oil, salt bath, etc., which needs to be selected according to the material and specifications of the seamless steel pipe. Temper:
Tempering is another important process of seamless pipe heat treatment. The purpose is to reheat the quenched seamless steel pipe to a certain temperature, and cool it to room temperature after holding for a certain time, thereby reducing the hardness and strength of the seamless steel pipe and improving its toughness and corrosion resistance. In the tempering process, the quenched martensite structure gradually decomposes, transforming from high-strength and high-hardness martensite into low-carbon alloy steel structure with good hardness and plasticity in low carbon steel. This kind of structure has good toughness and corrosion resistance, which can further improve the service life and safety of seamless steel pipes.
The following points should be noted during the tempering process:
1、 heating temperature: seamless steel pipe in the tempering process needs to be heated to a certain temperature, the determination of this temperature needs to consider the material, specifications, wall thickness and other factors of seamless steel pipe, to ensure that the internal organization of seamless steel pipe is fully and evenly changed. In general, the higher the tempering temperature, the lower the strength and hardness of the seamless steel pipe, the better the toughness.
2、 holding time: in the tempering process, it is necessary to hold heat for a certain time at a certain temperature to ensure that the internal organization of the seamless steel pipe is fully and evenly changed. The determination of the holding time needs to consider the material, specifications, wall thickness and other factors of the seamless steel pipe to ensure that the seamless steel pipe has a good comprehensive performance during use.
3、 cooling speed: the cooling speed needs to be controlled during the tempering process to ensure that the internal organization of the seamless steel pipe is fully and evenly changed. Generally speaking, the slower the cooling rate, the lower the strength and hardness of the seamless steel pipe, the better the toughness.