The heat treatment process of medium frequency induction heating machine for screw quenching

As an important part of machine tools and lathes, the screw must withstand huge friction during the heat treatment process. Therefore, the screw is generally required to have high hardness, wear resistance and service life. In order to meet the working requirements of the screw, the screw can only be quenched and heat treated. Nowadays, the most commonly used equipment for screw quenching is the medium frequency induction heating machine. Today, the editor will tell you about the medium frequency quenching process of the screw.

There are many types of screws due to their different applications. Therefore, the editor took it upon himself to tell you about the medium-frequency induction heat treatment process of the precision hardened screw of the M8650A lathe.

SM8650A lathe precision hardened screw, the commonly used material is T12A steel. The total length of the screw is 6486mm, and the threaded part is 5460mm long. The threaded part adopts 14 sections, each section is 392mm long. Due to the superb splicing technology, the joints are tightly sealed. After quenching, the workpiece hardness is 56~61HRC, and the radial circular runout is ≤0.15mm. Its induction heat treatment process is as follows:

1. Spheroidizing annealing. The function of spheroidizing annealing is to spheroidize the carbides in the steel. The difference from ordinary spheroidizing annealing is to shorten the spheroidizing annealing cycle, so that the distribution structure and hardness of the workpiece along the cross-section after annealing are more uniform. Spheroidizing isothermal annealing is particularly suitable for large alloy steel castings and forgings.

2. Quenching and low temperature tempering. It gives the T12A steel joint screw the ultimate performance, namely high hardness, high strength, high wear resistance, high precision, while reducing brittleness and internal stress. The medium frequency induction heating furnace is used for heating, using the salt water-oil double liquid quenching method, cooling in oil to about 50°C, and then immediately sending it to the tempering furnace for low-temperature tempering. After quenching and low-temperature tempering, the hardness is 56~61HRC, and the radial runout tolerance is 0.15mm. The T12A steel joint screw is a relatively precision part, so when quenching, you must pay attention to strict process specifications and operate it. Especially the quenching method - double liquid quenching (water quenching and oil cooling) method, that is, the heated workpiece is first quenched in a salt solution and then cooled for a certain period of time to ensure that the high-temperature austenite does not undergo martensitic transformation. When the workpiece is cooled to a slightly higher temperature At the Ms point, immediately take it out and transfer it to oil for cooling, so that the workpiece can be cooled slowly in the martensitic transformation zone. This method is an effective method that can not only ensure the hardening of the workpiece, but also reduce deformation and cracking. This method is mostly used for carbon steel workpieces with complex shapes or certain low-alloy steel large-section workpieces.