What are the forms of heat treatment for powder metallurgy materials?

What are the forms of heat treatment for powder metallurgy materials?

Powder metallurgy is a new type of net near-molding technology, which uses melting, heating, injection and pressing of metal powder to carry out the required mold molding. For some special materials such as refractory metals, refractory metals, high alloy and so on. What are the forms of heat treatment for powder metallurgy materials? The following is the share of zhongwei precision editor.

The form is as follows:

1. Quenching heat treatment process

Due to the existence of pores, the heat transfer rate of powder metallurgy materials is lower than that of dense materials, so the hardenability is relatively poor during quenching. In addition, during quenching, the sintering density of the powder material is directly proportional to the thermal conductivity of the material; Due to the difference between the sintering process and the dense material, the internal structure uniformity of powder metallurgy materials is better than that of the dense material, but there is a small heterogeneity in the micro-area. Therefore, the complete austenitizing time is 50% longer than the corresponding forging. When adding alloy elements, the complete austenitizing temperature will be higher and the time will be longer.

2. Chemical heat treatment process

Chemical heat treatment generally includes three basic processes: decomposition, absorption and diffusion. For example, the reaction of carburizing heat treatment is as follows:

2CO ≈ [C]+CO2 (exothermic reaction)

CH4 ≈ [C]+2H2 (endothermic reaction)

After the carbon is decomposed, it is absorbed by the metal surface and gradually diffused to the interior. After obtaining sufficient carbon concentration on the surface of the material, the quenching and tempering treatment can improve the surface hardness and hardening depth of the powder metallurgy material. Due to the existence of pores in powder metallurgy materials, activated carbon atoms infiltrate from the surface into the interior to complete the process of chemical heat treatment. However, the higher the material density, the weaker the pore effect, and the less obvious the effect of chemical heat treatment. Therefore, the reducing atmosphere with higher carbon potential should be used for protection. According to the pore characteristics of powder metallurgy materials, the heating and cooling speed is lower than that of dense materials, so the holding time shall be extended and the heating temperature shall be increased during heating.

Chemical heat treatment of powder metallurgy materials includes carburizing, nitriding, sulfurizing and multi-element co-carburizing. In chemical heat treatment, the hardening depth is mainly related to the density of the material. Therefore, corresponding measures can be taken in the heat treatment process, for example, during carburization, when the material density is greater than 7g/cm3, the time should be appropriately extended. The wear resistance of the material can be improved by chemical heat treatment. The uneven austenitic carburizing process of powder metallurgy materials can make the carbon content of the treated surface of the carburized layer of the material reach more than 2%, and the carbides are uniformly distributed on the surface of the carburized layer, which can well improve the hardness and wear resistance

3. Steam treatment

Steam treatment is to oxidize the surface of materials by heating steam, and form oxide film on the surface of materials, thus improving the properties of powder metallurgy materials. Especially for the corrosion prevention of the surface of powder metallurgy materials, the effective period is more obvious than that of bluing treatment, and the hardness and wear resistance of the treated materials are significantly increased.

4. Special heat treatment process

Special heat treatment process is the product of scientific and technological development in recent years, including induction heating quenching, laser surface hardening, etc. Induction heating quenching is under the influence of high-frequency electromagnetic induction eddy current. The heating temperature increases rapidly, which has a significant effect on the increase of surface hardness. However, soft spots are prone to occur. Generally, intermittent heating can be used to extend the austenitizing time; Laser surface hardening technology uses laser as the heat source to rapidly heat up and cool the metal surface, so that the substructure inside the austenite grain can not recover and recrystallize in time to obtain ultra-fine structure.

The above is the form of heat treatment of powder metallurgy materials. I hope this article will help you. If you need more information, please pay attention to the official website of zhongwei Precision.