Process specification for heat treatment of automobile leaf springs with ultrasonic induction heating power supply

Automotive leaf springs are elastic components that need to withstand huge friction and impact loads during operation. In order to make automobile leaf springs work better, we often use ultrasonic induction heating power to heat treat automobile springs to improve their working performance and service life.

The material selected for automobile leaf springs is 60Si2Mn. The heat treatment process is: preheating, heating, cooling, and medium temperature tempering. The required hardness is 42~45HRC. After quenching, the leaf spring must be tempered in time. The tempering temperature is generally 440 ~520℃, the metallographic structure is tempered troostite.

(1) Heating process parameters. In order to achieve heat treatment of automobile spring steel plates, they should be heated to the austenitizing temperature. The preferred temperature is 865~875°C. The austenitizing temperature is important for the quenching martensite (metallographic structure) of the steel plate. Under the influence of quenching, flake martensite is obtained after quenching below 860°C, while lath martensite is obtained above 880°C. The higher the temperature, the amount of lath martensite increases, the size gradually grows, and the residual The amount of austenite increases. When the temperature is lower than 900°C, the retained austenite is distributed in blocks between the lath martensite. When it reaches 920°C, strip-shaped retained austenite is obviously formed, and along the lath martensite body distribution.

The heat treatment heating equipment used includes oil furnaces, controlled atmosphere mesh belt furnaces or coal-fired reverberatory furnaces. According to the production process, the single leaf spring can complete the heating process in a continuous heating furnace (hydraulic stepping type) or a periodic operating furnace. , the continuous heating furnace has the characteristics of uniform furnace temperature, stable composition, and high thermal efficiency. The steel plate is fed into the furnace from one end by a conveyor belt and cooled out from the other end. The relationship between the thickness of the automobile leaf spring and the heating time is that the thickness of the leaf spring is 6.5mm, the holding time is 2 minutes, the thickness is 8mm, the holding time is 3 minutes, the thickness of the leaf spring is 8.5-10mm, the holding time is 4 minutes. If the thickness of the steel plate is 12mm, the holding time needs to be 5 minutes.

(2) Cooling process requirements. After the holding time of the spring steel plate in the heating furnace is over, the spring steel plate is automatically clamped and formed on the quenching machine using a chain plate conveyor chain, or the heated steel plate is moved by a manipulator to the hydraulic automatic bending quenching machine for oil injection cooling, and then enters the quenching machine. The oil cools and swings left and right, automatically unloading the pieces, and then delivers the quenching oil pool through the conveyor belt. The cooling medium in the quenching oil pool is 5# mechanical oil, and the oil temperature is between 20 and 80°C. The purpose of quenching is to increase the hardness of the steel plate. The martensite level after quenching is around level 5, and the matrix hardness after quenching is ≥ 63HRC.

(3) Tempering process parameters. The tempering of automobile leaf springs should be carried out within the range of 460~540℃ to obtain the tempered troostite structure. It should be noted that the carbides have not grown significantly at this time and have stress distribution characteristics. The matrix phase only undergoes a recovery process, maintaining the martensitic needle state and a certain strengthening effect. The tempered troostite has a higher elastic limit. Water cooling after tempering can prevent the occurrence of the second type of temper brittleness, generate residual compressive stress on the surface of the steel plate, and improve the fatigue strength. The hardness is 42~45HRC. The relationship between the thickness of automobile leaf springs and the tempering and holding time is shown in the table below:

The relationship between automobile leaf spring thickness and tempering and heat preservation time:

As an important part of the car, the quality of automobile leaf springs is directly related to the overall operation of the car. The ultrasonic induction heating equipment produced by Zhengzhou Gou's is specially used for heat treatment of automobile leaf springs. It has many advantages such as fast heating speed, uniform quenching layer, and less surface decarburization. If you want to have such a device, if you want to know more about the heat treatment of automobile leaf springs. We welcome your inquiries.