The automobile piston is like the central part of the automobile engine. It plays an extremely important role when the engine is started. It is used to withstand gas pressure and allows the connecting rod to drive the crankshaft to rotate through the piston pin. Therefore, during the operation of the car, the piston has to bear huge friction. For this reason, many manufacturers use medium-frequency induction heating equipment to heat treat the piston, which has very good results and improves its surface wear resistance. Today, the editor will take the vanadium steel piston as an example to briefly introduce the medium-frequency heat treatment process.
The heat treatment of vanadium steel piston includes four processes: pre-quenching, spheroidizing annealing, quenching and low-temperature tempering. Today, we will focus on its pre-quenching and low-temperature tempering process.
1. Pre-quenching is to prepare the structure for subsequent spheroidizing annealing to obtain good spheroidized pearlite, which is convenient for cutting. Medium frequency induction heating equipment is used for quenching heat treatment. The quenching preheating temperature is 720-735°C. This is to shorten the heating and holding time above the phase transformation point in order to obtain more lath martensite structure and meet the surface wear resistance need.
2. The selection of cooling medium is very important. The piston is a thin-shell part, so a medium that is beneficial to preventing quenching cracks should be used. 10% salt water or a mixed aqueous solution of sodium nitrite and sodium carbonate has the properties in the martensitic transformation temperature range. Due to the slow cooling rate, these two cooling media are usually used.
3. According to the relationship curve between the mechanical properties of vanadium steel and tempering temperature, when the tempering temperature is around 210°C, the bending strength, normal breaking resistance, plasticity and toughness of vanadium steel are in a better state, so at this temperature Tempering improves the service life of the piston.
4. It should be noted that to ensure uniform hardness on the inner and outer surfaces of the piston, all surfaces should exhibit residual stress. The premise is that the inner hole and outer surface of the piston should be quenched at the same time, so specially obtained quenching nozzles are often used for cooling to ensure uniform cooling of all parts of the piston.
The quality of the piston is directly related to the operation of the car, so we have very high quality requirements for it. This article briefly introduces the medium-frequency heat treatment process of vanadium steel piston. The hardness and wear resistance of the vanadium steel piston produced according to the above process are greatly improved, which meets its working requirements.
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GS-ZP-1200
