Surface treatment of die parts

The surface performance of die parts is very important to the working performance and service life, such as wear resistance, corrosion resistance, friction coefficient, fatigue performance, etc. It is very limited and uneconomical to rely solely on the improvement and enhancement of the matrix materials. However, through the surface treatment technology, we can get twice the result with half the effort. Therefore, the mold surface treatment technology has been developed rapidly.

This technology is a system engineering that changes the shape, chemical composition, structure and stress state of the die surface through surface coating, surface modification or composite treatment technology to obtain the required surface properties. The main surface treatment technologies used in die manufacturing are nitriding, carburizing and hardening film deposition.

(1) Nitriding process includes gas nitriding, ion nitriding, liquid nitriding, etc. Nitriding technology can form surface with excellent properties; The nitriding process is well coordinated with the quenching process of die steel; The nitriding temperature is low, no rapid cooling is required, and the deformation is very small. Therefore, the nitriding technology has been used earlier and most widely in mold surface strengthening.

(2) Die carburizing can improve the overall strength and toughness of the die, that is, the working surface of the die has high strength and wear resistance. The lower grade materials can be used to replace the higher grade materials by carburizing and quenching to reduce the manufacturing cost.

(3) At present, cvd (chemical vapor deposition) and pvd (physical vapor deposition) are the mature deposition technologies of hardened film. Hardened film deposition technology was first applied to tools (tools, cutting tools, measuring tools, etc.) with excellent results. Many tools have adopted the coating of hardened film as the standard process. Hardening film deposition equipment is expensive and only used in some precision and long-life molds.

This method has the characteristics that are urgently needed in mold manufacturing, such as prevention of heating oxidation and non decarburization, vacuum degassing or degassing, elimination of hydrogen embrittlement, small deformation, etc.

According to different cooling medium, vacuum quenching can be divided into vacuum oil cooling quenching, vacuum gas cooling quenching, vacuum water cooling quenching and vacuum nitrate isothermal quenching. The first three types are mainly used in mold vacuum heat treatment.

The successful development and application of computer simulation technology of vacuum heat treatment process (including tissue simulation and performance prediction technology) make it possible to intelligentize heat treatment of dies. In developed countries, such as the United States and Japan, the research on vacuum high-pressure gas quenching is mainly aimed at molds.