Surface treatment technology of casting moulds indicates that surface properties are crucial to working performance and service life of moulds, in addition to the required enough strength and toughness of mould base. Surface properties include wear-resistant property, corrosion-resistant property, coefficient of friction, fatigue property, etc.
The improvement of these surface properties is very limited and uneconomical, merely depending on the improved materials of mould base. Nevertheless, it will be remarkable through the surface treatment technology. For this reason, surface treatment technology develops rapidly.
Surface treatment technology of
casting moulds is such a technology of changing form, chemical composition, microstructure and stress state of mould surface through surface coating, surface modification and combined treatment techniques to achieve the required surface properties.
The surface treatment methods include chemical method, physical method, physical-chemical method and mechanical method. Technologies like nitriding, carburization and sedimentation of hardened film are widely used in the manufacture of molds, in spite of the constant emergence of new techniques of improving mould surface properties.
Nitriding process can be classified into gas nitriding method, plasma nitriding method and liquid nitriding method and so on. For each nitriding method, several nitriding techniques can be used to meet requirements of different steel grades and different artifacts.
As an early application of nitriding techniques, the surface strengthening of casting mould is also the most widely applied technology. Moulds being manufactured through this method undergo little deformation. Good surface properties can be achieved by nitriding techniques while it harmonizes with the quenching process of die steels. What is more, on account of low temperature during the process, high intensity cooling is unwanted after nitriding.
