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Application of Vacuum High Pressure Gas Quenching Furnace in Heat Treatment of Casting Die

With the continuous enhancement of people’s awareness of environmental protection, behaviors that endanger the environment are gradually restricted or prohibited. Because vacuum heat treatment is pollution-free, it has developed very rapidly in my country in recent years. At present, the 6bar vacuum air quenching furnace has been widely used in the heat treatment of small molds. When heat treating large molds, vacuum air quenching furnaces with higher gas quenching pressure are generally used. This is because the cooling rate is not ideal, which will have a great impact on the impact toughness and service life of the mold.

1.Disadvantages of traditional craft methods

When the die-casting mold is quenched, in order to prevent the surface oxidative decarburization, deformation and cracking, the traditional process is to use a barium chloride high-temperature salt bath with good deoxidation, or to heat it in a protective atmosphere electric furnace, or to heat it in an ordinary box-type electric furnace after packaging and protection.

We used to use high temperature salt bath heating, there are many problems

①The heat treatment is labor-intensive and the working environment is harsh. The gas released during heating, the waste slag, salt, and old electric furnaces cause pollution to the environment, and the salt bath treatment has been restricted.

②The surface of the workpiece after salt bath quenching is easy to be corroded by the salt bath. Even if the workpiece is cleaned and ground, it is easy to rust during use, which will reduce the service life of the workpiece.

③ Salt bath treatment due to the fast heating speed and large temperature difference of the workpiece section, the deformation caused by thermal stress increases.

④Uneven cooling in the salt bath quenching process easily causes soft spots, resulting in uneven hardness and reduced service life.

2.Advantages of vacuum heat treatment

Vacuum heat treatment has the following advantages:

①High efficiency. Low energy consumption, no pollution, low labor intensity and high product quality.

② The workpiece has no oxidation, no decarburization, can be degreased, can be degassed (especially the harmful gas hydrogen inside the mold, etc.) in vacuum heating, the surface is clean and bright, and the surface properties are also significantly improved, which can improve wear resistance and fatigue strength. Wait.

③In vacuum heating, the heating rate is controllable, the temperature difference of the die section is small, and the deformation caused by thermal stress is small, which is about 70% smaller than that of salt bath quenching. During quenching, the cooling gas can spray and cool the workpiece within a range of 360 degrees, the cooling is relatively uniform, the workpiece will not appear soft spots, and the quenching hardness is uniform.

3.Difficulties in handling die casting molds

The life of a die casting mold depends on many factors, such as the chemical composition of the material, the smelting process, the metallographic structure, the design and machining of the mold, the mold specification, the use and maintenance of the mold, as well as the forging process, heat treatment process, etc.

There are two main failure modes of die casting molds:

① Thermal cracking. The typical cracks of thermal cracking are moiré-like cracks distributed in a network, and there are also small cracks generated at high temperature and stress concentration parts.

② Serious cracking. Severe cracking occurs suddenly during mold use. The crack source is often initiated at the stress concentration on the surface of the mold, and finally cracks suddenly with brittle fracture, causing the mold to be scrapped.

Practical experience has proved that the length of mold life mainly depends on the quality of material properties, and excellent mold materials should have the ability to delay the initiation and expansion of cracks. The key to improving mold life is:

① The ability of the material to resist plastic deformation at high temperature, that is, the high temperature yield strength and the tempering resistance of the material at high temperature, and the hardness is not easy to decrease.

②Good thermal conductivity and low thermal expansion.

③ The ability to absorb plastic deformation is high, that is, high ductility, good impact toughness and fracture toughness.

4.Selection of vacuum furnace equipment:

The RVGQ high-pressure vacuum air quenching furnace produced by SIMUWU is a single-chamber horizontal vacuum furnace which is heated by graphite tubes and insulated by graphite hard felt heat shields. The equipment is composed of a pressure furnace body, a heating chamber, an air cooling system, a convection heating device, a vacuum system, an air charging system, a pneumatic system, a water cooling system, an out-of-furnace material truck and an electrical control system. It is mainly suitable for vacuum bright quenching of alloy steel such as air-cooled tool and die steel, and can also be used for other vacuum heat treatments such as vacuum tempering, annealing, solution treatment, etc.

RVGQ series is a high-quality product for vacuum heat treatment of tools and molds. Good temperature control accuracy and uniformity of temperature control ensure the effective progress of the vacuum heat treatment process. SIMUWU specializes in the manufacture of vacuum furnaces, has more than ten years of relevant experience, and has a good reputation in the field of vacuum furnace manufacturing. The product line includes vacuum air quenching furnace, vacuum oil quenching furnace, vacuum brazing furnace, etc., which are widely sold in developed and developing countries.

5.Heat treatment process:

The process curve is shown below. The RVGQ furnace type has good heating performance. The furnace load is about 1000kg, the heating time is 10-12h, and the holding time is about 2h. Its cooling performance is relatively high, the cooling time from 1040°C to 800°C is about 12-20min, and the cooling time from 1040°C to 200°C is generally about 1.5h, and the cooling curve can be adjusted and set according to needs to meet different needs mold requirements.