1. The quenching equipment is a high-pressure, high-flow, open air quenching furnace.
(1) Before quenching: Use the thermal balance method to improve the overall consistency of mold heating and cooling. All thin-walled holes, grooves, cavities, etc. that affect this point must be filled and sealed to ensure that the mold can be heated and cooled evenly; also, pay attention to the furnace loading method to avoid the die-casting mold being damaged due to high temperatures. Deformation caused by self-respect.
(2) Heating of the mold: During the heating process, it is necessary to heat slowly (use 200°C/h to increase the temperature), and use a two-stage preheating method to prevent rapid heating from causing excessive temperature differences between the inside and outside of the mold and causing excessive thermal stress. , and also reduces the phase change stress.
(3) Quenching cooling: Use pre-cooling method, and adjust the air pressure and wind speed to effectively control the cooling rate to maximize the ideal cooling. That is: after pre-cooling to 850°C, increase the cooling rate and quickly pass through the nose of the "C" curve. When the mold temperature is below 500°C, the cooling rate will gradually decrease. When the mold temperature is below the Ms point, a cooling method similar to isothermal transformation will be used. Minimize quenching deformation. When the mold cools to about 150°C, turn off the cooling fan and allow the mold to cool naturally.
(4) Quenching temperature and holding time: The lower limit of quenching heating temperature should be selected, and the soaking time should not be too short or too long. The soaking time is generally determined by the wall thickness and hardness.
2. When the tempered and quenched mold is cooled to about 100°C, it must be tempered immediately to avoid continued deformation or even cracking. The tempering temperature is determined by the hardness of the workpiece, and usually three temperings are required.
3. Annealing includes spheroidizing annealing after casting and stress relief annealing during the mold manufacturing process. Its main purpose: to improve the crystal structure in the raw material stage; to facilitate processing and reduce hardness; to prevent deformation and quenching cracks after processing and remove internal stress.
(1) Stress relief annealing. If the mold steel with residual stress is machined, deformation will occur after processing. If there is still stress after machining, large deformation or quenching cracks will occur during quenching.
(2) Spheroidizing annealing. After the mold steel is cast, the internal structure of the steel becomes unstable crystals, making it difficult to cut with high hardness. Moreover, steel in this state has large internal stress, is prone to deformation and quenching cracks after processing, and has poor mechanical properties. In order to crystallize carbides Spheroidizing annealing is required to form a spheroidized stable structure.
4. Nitriding treatment: Normal die-casting molds can be used after quenching and tempering. However, in order to improve the wear resistance, corrosion resistance and oxidation resistance of the mold, prevent mold sticking and extend the life of the mold, nitriding treatment must be carried out. . The depth of the nitride layer is generally 0.15~0.2mm. After nitriding, it needs to be polished and the white bright layer removed.
