How to modify the surface of die-casting mold

Carburizing and carbonitriding

The carburizing process is used in cold, hot work and surface strengthening of plastic molds, which can improve the life of the mold. For example, the die-casting mold made of 3Cr2W8V steel is first carburized, then quenched at 1140~1150℃, and tempered twice at 550℃. The surface hardness can reach HRC56~61, which increases the die life of die-casting non-ferrous metals and their alloys by 1.8~3.0 times. . When carburizing, the main process methods include solid powder carburizing, gas carburizing, vacuum carburizing, ion carburizing, and carbonitriding formed by adding nitrogen to the carburizing atmosphere. Among them, vacuum carburizing and ion carburizing are technologies developed in the past 20 years. This technology has the characteristics of fast carburization, uniform carburization, smooth carbon concentration gradient, and small deformation of the workpiece. It will be on the surface of the mold, especially the precision mold. Play an increasingly important role in surface treatment.

Nitriding and related low-temperature thermal expansion technology

This type includes nitriding, ion nitriding, carbonitriding, oxygen nitriding, sulphur nitriding and ternary sulphur carbonitriding, oxygen, nitrogen and sulfur. These methods have simple processing technology, strong adaptability, low diffusion temperature (usually 480 ~ 600 ℃), small deformation of the workpiece, especially suitable for surface strengthening of precision molds, and high hardness of the nitride layer, good wear resistance, and better Good anti-sticking performance.

3Cr2W8V steel die-casting mold, after quenching and tempering, 520~540℃ nitriding, the service life is 2~3 times longer than that of non-nitriding molds. Many die-casting molds made of H13 steel in the United States need to be nitrided, and nitriding is used instead of one-time tempering. The surface hardness is as high as HRC65~70, and the core of the mold has low hardness and good toughness, so as to obtain an excellent synthesis. Mechanical properties. Nitriding process is a commonly used process for surface treatment of die-casting molds, but when a thin and brittle white layer appears in the nitrided layer, it cannot resist the effect of alternating thermal stress, and it is easy to produce micro-cracks and reduce thermal fatigue resistance. Therefore, in the nitriding process, the process must be strictly controlled to avoid the formation of brittle layers.

Recently, foreign countries have proposed the use of secondary and multiple nitriding processes. The method of repeated nitriding can decompose the white bright nitride layer that is easy to produce micro-cracks during service, increase the thickness of the nitriding layer, and at the same time make the mold surface have a thick residual stress layer, so that the life of the mold can be significantly improved. In addition, there are methods such as salt bath carbonitriding and salt bath sulphur nitrocarburizing. These processes are widely used in foreign countries and rarely seen in China. For example, the TFI+ABI process is immersed in an alkaline oxidizing salt bath after nitrocarburizing in a salt bath. The surface of the workpiece is oxidized and appears black, and its wear resistance, corrosion resistance and heat resistance have been improved. The life of the aluminum alloy die-casting die treated by this method is increased by hundreds of hours. Another example is the oxynit process developed in France for nitriding after nitrocarburizing, which is more characteristic when applied to non-ferrous metal die-casting molds.