The heat treatment of the mold has a great influence on the service life

The heat treatment of the mold has a great influence on the service life.

Most of the mold damages that we often come into contact with are caused by improper heat treatment. According to statistics, mold failure due to improper heat treatment accounts for more than 50% of the total failure rate. For the heat treatment of foreign molds, more and more vacuum furnaces, semi-vacuum furnaces and non-oxidizing protective atmosphere furnaces are used.

The heat treatment process of the mold includes the strengthening and toughening of the matrix and the surface strengthening treatment.

(1) The strengthening and toughening of the matrix is u200bu200bto improve the strength and toughness of the matrix and reduce the fracture and deformation. Therefore, its conventional heat treatment must be carried out in strict accordance with the process.

(2) Surface strengthening treatment, its main purpose is to improve the wear resistance, corrosion resistance and lubrication performance of the mold surface. There are many surface strengthening treatment methods, mainly carburizing, nitriding, sulphurizing, boronizing, nitrocarburizing, metalizing and so on.

The use of different surface strengthening treatment processes can increase the service life of the mold several times or even dozens of times. In recent years, some surface strengthening processes have appeared, such as the following three processes:

1. Ion Nitriding

In order to improve the corrosion resistance, wear resistance, thermal fatigue resistance and anti-adhesion properties of the mold, ion nitriding can be used.

The outstanding advantage of ion nitriding is that the nitriding time is significantly shortened, the structure of the nitriding layer can be controlled by adjusting different gas components, the surface brittleness of the nitriding layer is reduced, the deformation is small, and the hardness distribution curve of the nitriding layer is relatively stable. It is not easy to produce peeling and thermal fatigue. The permeable matrix material is wider than gas nitriding, non-toxic, non-explosive, and safe in production. However, for molds with complex shapes, it is difficult to obtain uniform heating and uniform infiltration layer, and the infiltration layer is shallow, the transition layer is steeper, and the temperature The measurement and temperature uniformity still need to be resolved.

Ion nitriding temperature is 450-520℃. After 6-9 hours of treatment, the depth of the nitriding layer is about 0.2-0.3mm. If the temperature is too low, the seepage layer is too thin; if the temperature is too high, the surface layer is prone to loose layer, which reduces the anti-sticking ability. The thickness of the ion nitriding layer is preferably 0.2-0.3mm. The worn ion nitriding mold can be put into use after repairing and ion nitriding again, which can greatly increase the total service life of the mold.

2. Nitrocarburizing

The temperature of the nitrocarburizing process is low (560～570℃), the deformation is small, the surface hardness of the processed mold steel is as high as 900-1000HV, the wear resistance is strong, the corrosion resistance is strong, and the high temperature hardness It can be used for die-casting molds, cold heading molds, cold extrusion molds, hot extrusion molds, high-speed forging molds and plastic molds. The service life can be increased 1-9 times. However, it often deforms after gas nitrocarburizing, and the expansion amount accounts for about 25% of the compound thickness, which is not suitable for precision molds. It must be annealed and eliminated before treatment.

For example: Cr12MoV steel plate spring hole punching die, after gas nitrocarburizing and salt bath vanadium infiltration treatment, the die life can be increased by 3 times. Another example: 60Si2 steel refrigerated heading screw punch, using pre-nitriding, short-term carbonitriding, direct oil quenching, low temperature quenching and higher temperature tempering treatment processes, which can improve the toughness of the heart and increase the life of the cold heading punch More than 2 times.

3. Carbon, nitrogen and boron ternary permeation

The ternary co-infiltration can be carried out in a nitriding furnace. The permeating agent is a boron-containing organic permeating agent and ammonia, the ratio is 1:7, the co-infiltration temperature is 600℃, the co-infiltration time is 4h, and the compound layer is co-infiltrated. The thickness is 3-4μm, the depth of the diffusion layer is 0.23mm, and the surface hardness is HV011050. After the co-infiltration treatment, the life of the mold is significantly improved.