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Vacuum Heat Treatment Furnace

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Large complex mold vacuum heat treatment process

In the design of large and complex molds, those who can design the mold as a whole will design the mold as a whole, and with the development of automobile molds, the shape of automobile molds will also become larger and thicker.

The influence of the thickness and size of mold parts on heat treatment is a very large and very dangerous thing, especially when the thickness is greater than 250mm, due to heating and cooling, etc., there are poor hardenability and incomplete core structure transformation. If you do not pay attention to the control of the heat treatment process, instant cracking will occur, or there will be a certain structural stress, resulting in early cracking during use.

1 Selection of vacuum heat treatment process

The conventional heat treatment method is to heat to the austenitizing temperature through ordinary equipment, and after holding for a certain period of time, direct oil cooling at high temperature is adopted. Due to the complex shape of the mold and the thickness greater than 250mm, direct cooling, the surface cooling is too fast, and the core cooling is too slow. There are also phenomena of too fast and too slow tissue transformation, large thermal stress and tissue stress will appear, and the generation of internal and external stress is very risky, and it is extremely easy to cause deformation and cracking of parts.

Vacuum heat treatment method, 6.0~9.5bar, after preheating, heating to the austenitizing temperature, after holding for a certain period of time, adopting air cooling, the initial pressure is high, the temperature is high, and the surface cooling speed is not bad, but when cooled to a certain time , the cooling rate begins to slow down. Although the surface temperature begins to drop, the temperature of the core is far from cooling down. If the cooling rate is too slow, products such as pearlite and bainite will be produced, which seriously affects the mechanical properties of the workpiece. Lead to early cracking in use. Above 10bar is ultra-high pressure gas quenching. Although the speed of oil cooling can be achieved, there is also the risk of excessive temperature difference and rapid structural transformation.

According to the above situation, the control of vacuum heat treatment for parts with a thickness greater than 250mm is particularly critical, and it is even more important to choose the cooling method of vacuum quenching.

2 vacuum heat treatment process

For the cooling of mold parts with a thickness of more than 250mm, after preheating, the method of air-to-oil cooling is adopted. First, the workpiece is cooled from high-pressure air to the surface temperature of the workpiece is about 750°C, then transferred out of the vacuum furnace, and then slowly cooled and isothermal in the air through the detection of a temperature measuring gun and a thermocouple. When the temperature difference between the core and the surface is ≤90°C When the isothermal temperature is over, it is transferred to an oil bath furnace with an oil temperature of 130°C for cooling, and after cooling to 60°C on the surface of the workpiece, the first vacuum tempering is carried out.

Air cooling to 750°C by 10bar pressure first, lowering the high temperature of 1030°C, and reducing the thermal stress of the high and low temperature difference (at 750°C isothermal, according to the CCT diagram of the material, it is still an austenite structure, and has not yet developed into pearlite and bainite. temperature of microstructure transformation), and then rapidly cooled by oil, avoiding the transition point of C-curve (C-curve nose), directly supercooling to the martensitic transformation zone, reducing the risk of poor hardenability; direct supercooling to In the martensite transformation zone, although the surface structure has begun to transform to martensite structure, the core still has a certain temperature, the plasticity is good, and it will not be affected by the stress of the structure to cause cracking. In this way, the thermal stress and structural stress are controlled and reduced, greatly avoiding the risk of direct cracking during quenching, and obtaining a larger amount of quenched martensite. After correct vacuum tempering, early failure in use is avoided.

Through all aspects of measurement and numerical inspection, they all meet the acceptance indicators and fully meet the use of the mold. After several years of practice and verification, the cracking of the mold during the heat treatment process is zero.

Vacuum heat treatment equipment selection: In order to manufacture excellent large-scale mold products, heat treatment equipment must have the necessary performance indicators. The vacuum furnace manufactured by SIMUWU has extremely high temperature control accuracy and temperature uniformity. By determining the control range of each parameter, a good process curve is obtained, thereby ensuring good product quality. The vacuum furnace produced by SIMUWU is an excellent product for handling large mold processing processes.