There are four aspects to be aware of when mold steel is quenched and cooled. They are cooling medium problems, cooling equipment problems, clear mold surface covering problems, and manual operation technical problems.
1. Die steel spray quenching method
Large-scale complex, especially thick and thin workpieces and die steels, in order to avoid excessive quenching stress during cooling, control the cooling rate of different parts of different stages of the cooling process. There are spray (water or aqueous solution), spray (compressed air and water sprayed to different parts of the part by atomization), gas quenching, etc., which have the advantage of controlling different media or different flow rates, and controlling and adjusting the temperature by pressure. The cooling rate of the area; or changing the number and position of different nozzles; cooling evenly. At present, the most popular in mold heat treatment is vacuum high pressure gas quenching.
2. Die steel grade quenching method
The mold steel or workpiece heated to the austenitizing temperature is quenched into a cooling medium (usually a salt bath) whose temperature is near the martensite transformation temperature, and is left for a period of time, so that the surface of the workpiece and the center temperature gradually become uniform. The air cooling is taken out and the martensite transformation is completed at a lower cooling rate. This method can significantly reduce the deformation and improve the toughness of the mold steel, and is one of the commonly used quenching methods for the mold parts.
There are two choices for the temperature of the die steel quenching. One is to take the Markov transformation starting temperature (Ms point) of the steel of the workpiece to be processed by 10~30 °C; the other is to select 80~100 °C below the Ms point. The residence time of the classification should also be well mastered. If the temperature is too short, the temperature is not uniform enough to achieve the purpose of classification quenching; if it is too long, non-martensitic transformation may occur to reduce the hardness.