Conventional overall quenching has been difficult to meet the high surface wear resistance of the die casting mold and the toughness requirements of the matrix.
The surface strengthening treatment not only improves the wear resistance and other properties of the surface of the die-casting mold, but also maintains the matrix with sufficient toughness and at the same time prevents the molten metal from sticking and etching, which improves the overall performance of the die-casting mold and saves alloying elements. Significant cost reductions, the full potential of materials, and 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 molds and extend the service life of the molds. The surface strengthening treatment processes commonly used in die-casting molds include carburizing, nitriding, nitrocarburizing, boronizing, chromizing and aluminizing.
Carburizing is currently the most widely used chemical heat treatment method in the mechanical industry. The process features: low-alloy high-carbon low-alloy mold steel and medium-high-carbon high-alloy steel mold in a carbon-enriched active medium (carburizing agent), heated to 900 ° C -930 ° C, so that carbon atoms penetrate the mold surface The layer, followed by quenching and low temperature tempering, gives the surface and core of the mold different compositions, textures 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 steel surface is called nitriding of steel. Nitriding enables mold parts to achieve higher surface hardness, wear resistance, fatigue properties, red hardness and corrosion resistance than carburization. Because of the lower nitriding temperature (500-570 ° C), the mold parts are less deformed after nitriding.
Nitriding methods include solid nitriding, liquid nitriding, and gas nitriding. At present, new technologies such as ion nitriding, vacuum nitriding, electrolytic nitriding and high-frequency nitriding are being widely used, the nitriding time is shortened, and a high-quality nitriding layer can be obtained.
Nitrocarburizing is a low-temperature nitrocarburizing process (530 ° C - 580 ° C) in which nitrogen and carbon are simultaneously infiltrated in a medium containing activated carbon and nitrogen atoms, and nitriding is mainly used. The nitrocarburizing layer has little brittleness, and the osmosis time is much shorter than the nitriding time. The die-casting mold can significantly improve its thermal fatigue performance after nitrocarburizing.
Poor working conditions require good high temperature mechanical properties, resistance to cold and heat fatigue, resistance to liquid metal erosion, oxidation resistance and high hardenability and wear resistance. Heat treatment is the main factor determining these properties. Manufacturing process.
The heat treatment of the die-casting mold is to change the microstructure of the steel to obtain high hardness and wear resistance of the mold surface, while the core still has sufficient strength and toughness, and at the same time effectively prevent the molten metal from sticking and etching. The use of an appropriate heat treatment process reduces waste and significantly increases mold life.