What are the process properties of mold steel?
Process Performance of Die Steel
Workability
① Hot workability, refers to thermoplasticity, processing temperature range, etc.
② Cold workability, refers to cutting, grinding, polishing, cold heading and other processing properties.
Most cold-work die steels belong to hypereutectoid steel and ledeburite steel, and their hot and cold workability are generally not good. Therefore, it is necessary to strictly control the process parameters of hot and cold working to avoid defects and rejects. On the other hand, by increasing the purity of the steel, reducing the content of harmful impurities, and improving the microstructure of the steel, the hot and cold workability of the steel can be improved, thereby reducing the production cost of the die.
To improve the cold workability of die steel, since the 1930s, research began on adding free-cutting elements such as S, Pb, Ca, Te, or elements that cause the graphitization of carbon in the die steel, which led to the development of various types of free-cutting die steels to further improve their cutting and grinding properties, reduce abrasive consumption, and lower costs.
Hardenability and Hardening Capacity
Hardenability mainly depends on the chemical composition of the die steel and the original microstructure before quenching; hardening capacity mainly depends on the carbon content in the steel. For most cold-work die steels, hardening capacity is often one of the main factors considered. For hot-work die steels and plastic mould steels, the die size is generally larger, especially for manufacturing large-scale dies, where hardenability is more critical. In addition, for various dies with complex shapes that are prone to quenching deformation, cooling media with weaker cooling capacity, such as air cooling, oil cooling, or salt bath cooling, are often adopted as much as possible to reduce quenching deformation. To obtain the required hardness and deep hardened depth, die steel with good hardenability is required.
Quenching Temperature and Heat Treatment Deformation
For the convenience of production, the quenching temperature range of die steel should be broadened as much as possible, especially when the die uses flame heating for localized quenching. Since it is difficult to accurately measure and control the temperature, die steel is required to have a wider quenching temperature range.
During the heat treatment of dies, especially during the quenching process, volume changes, shape warping, and distortion will occur. To ensure the quality of the die, the heat treatment deformation of the die steel is required to be small, especially for precision dies with complex shapes that are difficult to correct after quenching. The requirements for the degree of heat treatment deformation are even more stringent, and micro-deformation die steel should be selected for manufacturing.
Oxidation and Decarburization Sensitivity
If oxidation or decarburization occurs during the heating process of a die, its hardness, wear resistance, service performance, and service life will be reduced. Therefore, die steel is required to have good resistance to oxidation and decarburization. For die steels with higher molybdenum content, special heat treatments, such as vacuum heat treatment, controlled atmosphere heat treatment, or salt bath heat treatment, are required due to their strong sensitivity to oxidation and decarburization.
