The weld is heat treated using ultrasonic induction heating equipment. How should the tempering temperature be selected?

The purpose of the weld tempering treatment of low-carbon low-alloy steel and micro-alloyed V, Nb, and Ti steel with a carbon content of less than 0.40% is to maintain the strength and toughness of the base material of the welded pipe body at the same level, and along the length of the pipe The mechanical properties of the weld area are stable. Therefore, choosing the appropriate weld tempering temperature is crucial. Today, the editor will tell you how to choose the tempering temperature when the weld is tempered by ultrasonic induction heating equipment.

(1) The relationship between weld induction heating tempering temperature and mechanical properties. After induction heating and quenching, the tempering temperature of the weld can be selected from medium temperature tempering 400-550℃ and high temperature tempering 600-700℃. The choice of medium temperature tempering or high temperature tempering is mainly based on the chemical composition of the weld and the requirements for the mechanical properties after tempering. We analyzed the relationship between the tempering temperature, tensile strength and impact value of the 16MnSi welded pipe weld after being quenched at 950°C by ultrasonic induction heating equipment and then tempered at high temperature. It can be seen that the impact of tempering temperature on the tensile strength and impact value of the weld metal is contradictory. As the tempering temperature increases, the tensile strength decreases and the impact value increases. Therefore, it should be considered to maintain a high impact value as much as possible while maintaining a certain strength of the weld, and choose 650-680°C tempering to make the weld have better overall performance. In short, the selection of weld tempering temperature should be based on the mechanical properties of the pipe base material. After tempering, the weld is cooled directly to normal temperature in the air.

(2) The stability of mechanical properties after weld tempering treatment. The mechanical properties of the metal materials in the weld area that have been quenched and tempered by induction heating should be at the same level as the properties of the base material of the pipe body. At the same time, they should be uniform and stable with a small fluctuation range.

We analyzed the distribution of the tensile strength and impact value of the metal in the weld zone along the length of the welded pipe (diameter 1020mm, wall thickness 10.5mm, length 8m) after quenching at 950°C and tempering at 650°C. After analysis, we can know that the fluctuation range of the tensile strength of the metal in the weld area after induction heating quenching and tempering treatment is 20MPa (666-686MPa), which is smaller than the fluctuation range of the pipe base material: the fluctuation range of the impact value is 4J.cm- 2. The strength of the weld meets the requirements of X80 steel grade in API standards.

In summary, the weld seam has high strength and toughness after quenching and tempering using local induction heating. By selecting appropriate quenching and tempering process parameters, the mechanical properties of the weld can be completely consistent with the base material of the pipe body, achieving "seamless welded pipe".

Whether the tempering temperature is appropriate is directly related to the heat treatment quality of the workpiece. Therefore, it is very necessary to choose the appropriate tempering temperature. This article briefly introduces how to choose the tempering temperature of the weld. Many manufacturers choose the tempering temperature according to the above method. The quality of the weld after heat treatment is good and meets the work needs.