A brief discussion on the specific process of heat treatment of broaches using ultrasonic induction quenching equipment

The broach is a tool for cutting inner and outer holes at low speed. It is a high-efficiency and high-precision cutting tool. It needs to withstand high friction during work and is required to have high wear resistance and red hardness. In order to meet the needs of its work, we usually use ultrasonic induction quenching equipment to perform some simple heat treatment on the broach.

1. Technical requirements for heat treatment of broaches. Broaches are generally made of high-speed tool steel (W18Cr4V, W9M03Cr4V or W6MoCr4V2). After heat treatment, the hardness of the blade is required to reach 63~66HRC, the handle is 40~45HRC, and the bending deformation after heat treatment is ≤0.30mm. The grain size is controlled at level 9~10, and the metallographic examination shows that the tempering is sufficient, there is no overheating or overburning, and there is no corrosion, bumps or cracks on the surface.

The general heat treatment process flow of broaches is: loading - primary preheating - secondary preheating - heating - cooling - thermal straightening - cleaning - tempering - thermal straightening - tempering (3 to 4 times) - handle treatment - cleaning - inspection - surface preparation.

2. Broach ultrasonic heat treatment process:

1. Preheat. The broach has a high content of alloy elements, poor thermal conductivity, and a large diameter. According to different diameters, it can be divided into one, two or three preheatings. The purpose is to reduce the temperature difference between the surface and the core of the broach during heating and reduce the heat. stress and tissue stress to make the internal and external temperatures consistent, thereby reducing the tendency of deformation and cracking caused by the thermal stress of the broach. The two temperatures are 550~600℃ and 800~850℃ respectively. One of the preheating should be in the box-type resistor It is carried out in the furnace, and the preheating time is 3 times and 2 times of the final heating time respectively, that is, there must be sufficient holding time for preheating. Whether the broach is being heated or cooled, it must be suspended in order to reduce the bending deformation of the broach. When the broach is heated to above 880°C, austenite transformation will occur, which can reduce the phase transformation stress during quenching heating, shorten the subsequent quenching heating time, and prevent excessive oxidation and decarburization of the broach.

2. Quenching and heating. When the broach is subjected to ultrasonic quenching, the grain size should be controlled at level 9 to 10, and the usual heating coefficient is 10 to 15 s/mm.

3. Quenching and cooling. Usually classification or isothermal quenching is used, and the classification temperature is 580~620℃. When the surface temperature reaches 650~700℃, it is transferred to nitrate salt at 220~250℃ and kept for 30~40 minutes.

4. Clean and temper. Boil the residual salt on the surface of the broach in a boiling water tank. Insert the broach vertically upward into the circular tempering basket and squeeze it for tempering. The medium is 100% KN03. The temperature is 540~560℃, keep warm for 80-100min, and temper three times.

Broach is an important cutting tool. After heat treatment, the hardness of its cutting teeth and precision cutting teeth must reach 63-66HRC. If you want to know more about the heat treatment of broaches, you can call us freely.