Process analysis and implementation key points of heat treatment of broaches with ultrasonic induction heating equipment

The broach is a tool for cutting inner and outer holes at low speed. It is a multi-edged stepped toothed tool. Each tooth has an independent cutting effect. It is a high-efficiency and high-precision cutting tool. It has to withstand high friction during work, requiring high wear resistance and red hardness, as well as high mechanical properties. In order to meet this working requirement of the broach, we usually use ultrasonic induction heating equipment for heat treatment, and the effect is very good. Today, the editor will analyze the heat treatment process and implementation points of the broach.

(1) The cooling method of broach quenching is closely related to the bending, cracking and ease of straightening of the broach. For large-diameter broaches, secondary classification and short-term isothermal cooling can be used, which can control residual austenite, shell The relative amounts of martensite and martensite are corrected using phase transformation plasticity.

Isothermal air cooling in a nitrate salt bath at 240-280°C can transform part of the retained austenite into lower bainite. This structure improves the toughness of the broach and effectively reduces the tendency of bending deformation. Through subsequent high temperatures, Tempering can obtain higher hardness and red hardness.

In fact, strictly controlling the quenching heating temperature and holding time of the ultrasonic induction heating equipment can effectively prevent and avoid the occurrence of overheating or overburning of the broach. Therefore, in order to reduce the bending deformation of the broach, on the premise of meeting the requirements, adopt Lower heating temperature and heating time. However, in order to ensure that there is sufficient carbon and alloying elements in the martensite after the broach is quenched, a large number of dispersed alloy carbides are precipitated during tempering, and to ensure that the broach has good red hardness and wear resistance, a slightly High quenching temperature.

(2) If there are no conditions for grading or isothermal, oil cooling can also be used, but it is necessary to master the temperature of the quenching oil from the salt bath furnace to the quenching oil. Generally, the broach temperature is cooled to 1050-1200°C and quenched at 80 In hot oil at -120°C, the oil will be released when cooled to about 350°C. When air-cooled to 200°C, the guide part should be immersed in a medium-temperature salt bath and heated for a few minutes to reduce cracking of the ejector pin hole.

(3) The broach is tempered three times to ensure that the residual austenite (accounting for 20%-25%) after quenching is transformed into the tempered martensite structure, stabilizing the structure and size, and improving the hardness and wear resistance. Things to note Yes, the air cooling should be slowly cooled in the basket after each tempering. Do not force cooling (spray, water cooling, etc.). The next tempering can only be carried out after cooling to room temperature.

The tempering of the broach can fully eliminate the quenching stress of the material and precipitate a large amount of dispersed alloy carbides, which not only improves the strength and toughness of the broach, but also ensures that the broach has sufficient hardness and red hardness to improve the wear resistance of the broach. 

(4) The quenching of the handle can be carried out using ultrasonic induction heating equipment (heating temperature is 870-900°C, cooling in oil or 230-300°C nitrate salt bath, equivalent to annealing treatment), the hardness can be ensured in 40-45HRC.

(5) The straightening of the broach after quenching is carried out immediately after graded quenching, and then high-temperature tempering is carried out after shaping. There are two isothermal transformation zones above the martensite temperature transformation temperature range of high-speed steel: the product in the high-temperature transformation zone (650-760°C) is pearlite, and the transformation product in the medium-temperature transformation zone (220-350°C) is bainite. The area between the two (350-650°C) is the stable area of supercooled austenite, and its stability is used for thermal alignment.

(6) Regarding the annealing after forging of the broach, the purpose is to reduce the hardness, facilitate the elimination of machining and forging stress, and prepare for quenching. Isothermal annealing is usually used. The advantage is that it can ensure the annealing quality and shorten the annealing time. 

This article briefly introduces the analysis and implementation points of the heat treatment process of the broach. When operating the heat treatment process, everyone should be very serious and careful to avoid defects in the broach that affect its service life.