Die Steel Quenching Cooling Technique
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.
3. Die steel isothermal quenching method
The mold steel workpiece heated to the austenitizing temperature is quenched into a hot bath at a temperature slightly higher than the Ms point of the quenched steel grade, and the phase transition is completed to obtain the lower bainite structure or the lower bainite and Markov. Body mixed tissue. The purpose of this method is to alleviate deformation and cracking, and the quenching stress is small. Has similar strength and toughness to tempered martensite.
4. Die steel single liquid quenching method
The mold steel or parts are heated to austenitizing and then quenched into water, oil or other cooling medium, and cooled for a certain period of time (cooled to a region below the pearlite type transition temperature or martensite transformation temperature) to take out the mold steel air cooling. Since the mold steel cooling process is completed in a single cooling medium, it is called a single liquid quenching method.
5. Die steel two-liquid quenching method
As the name implies, the quenching and cooling process of the die steel is done in two cooling media (most commonly water, oil). The cooling process is ideal, which is rapidly cooled in the pearlite transformation region and slowly cooled in the martensite transformation region. The specific method is to first quench the mold steel or parts heated to the austenitizing temperature into the high temperature region. a medium (usually water or a brine solution) to inhibit the pearlite transformation of supercooled austenite. When cooled to about 0 ℃, quickly remove the second medium that is transferred to the low temperature zone and slowly cooled (usually oil).
Since the martensite transformation is carried out under milder cooling conditions, it can effectively alleviate or prevent deformation and cracking, which is commonly referred to as water quenching and oil cooling. This method requires a high level of skill. Sometimes understood as three kinds of media, namely water first, after oil, and finally air.
Avoiding the deformation and cracking of the die steel during use, it is also necessary for the cooling of the die steel quenching process, which will make the die steel not easy to deform, have suitable viscosity under the use conditions, and are non-flammable and explosive. Non-toxic and so on.