Conventional overall quenching has been difficult to meet the high surface wear resistance and toughness requirements of the die-casting mold. Surface strengthening treatment can not only improve the wear resistance and other properties of the die-casting mold surface, but also maintain sufficient strength and toughness of the matrix, while preventing molten metal from sticking to the mold and eroding, which improves the overall performance of the die-casting mold and saves alloying elements. Dramatically reducing costs, realizing the full potential of materials, and making better use of new materials are all very effective.
Production practice shows that surface strengthening treatment is an important measure to improve the quality of die casting mold and prolong the service life of the molds. The surface strengthening treatment processes often used in die casting molds are: carburizing, nitriding, nitrocarburizing, boronizing, chromizing and aluminizing.
Carburizing is the most widely used chemical heat treatment method in the machinery industry. The process characteristics are: heating medium-low-high-carbon low-alloy die steel and medium-high-carbon high-alloy steel mold in a carburizing active medium (carburizing agent) to 900℃-930℃, so that carbon atoms penetrate into the surface of the mold. layer, followed by quenching and low temperature tempering, so that the surface and core of the mold have different compositions, structures and properties. Carburizing is further divided into solid carburizing, liquid carburizing and gas carburizing. Recently, it has developed into controlled atmosphere carburizing, vacuum carburizing and benzene ion carburizing.
The process of infiltrating nitrogen into the surface of steel is called nitriding of steel. Nitriding can enable mold parts to obtain higher surface hardness, wear resistance, fatigue properties, red hardness and corrosion resistance than carburizing. Because the nitriding temperature is low, the deformation of the mold parts after nitriding is small. Nitriding methods include solid nitriding, liquid nitriding and gas nitriding. At present, new technologies such as ion nitriding, vacuum nitriding, electrolytic catalytic nitriding and high-frequency nitriding are widely used, which shortens the nitriding time and obtains high-quality nitriding layers.
Nitrocarburizing is a low-temperature nitrocarburizing process in which nitrogen and carbon are simultaneously infiltrated into a medium containing activated carbon and nitrogen atoms. In the low-temperature nitrocarburizing process mainly based on nitriding, the brittleness of the nitrocarburizing layer is small, and the nitrocarburizing time is much shorter than the nitriding time. After the die-casting mold is nitrocarburized, its thermal fatigue properties can be significantly improved.
The harsh working conditions require the die-casting mold to have good high-temperature mechanical properties, cold and thermal fatigue resistance, liquid metal erosion resistance, oxidation resistance, and high hardenability and wear resistance. Heat treatment is the main manufacturing process that determines these properties.
The heat treatment of the die-casting mold is to change the structure of the steel, so that the surface of the mold can obtain high hardness and wear resistance, while the core still has sufficient strength and toughness, and at the same time effectively prevent the molten metal from sticking to the mold and erosion. Selecting the right heat treatment process can reduce scrap and significantly increase the service life of the mold.