In mold production costs, material costs generally account for 10% to 20%, while machining, heat treatment, assembly and management costs account for more than 80%. Therefore, the process performance of mold materials is the main factor affecting mold production costs and ease of manufacture. one.

Machinability

——Hot workability means thermoplasticity, processing temperature range, etc .;

——Cold working performance refers to cutting, grinding, polishing, cold drawing and other processing properties.

Most of the cold work die steels are hypereutectoid steels and bainitic steels. The hot working and cold working properties are not very good, so the process parameters of hot working and cold working must be strictly controlled to avoid defects and scrap. On the other hand, by improving the purity of the steel, reducing the content of harmful impurities, and improving the structure state of the steel, the hot and cold working properties of the steel are improved, thereby reducing the production cost of the mold.

In order to improve the cold workability of mold steel, since the 1930s, research into adding S, Pb, Ca, Te and other free-cutting processing elements or the graphitization of carbon in mold steel has been developed. Cutting die steel to further improve its cutting and grinding performance, reduce tool abrasive consumption and reduce costs.

Hardenability and hardenability

Hardenability mainly depends on the chemical composition of the steel and the original state of the structure before quenching; hardenability mainly depends on the carbon content of the steel. For most cold work die steels, hardenability is often one of the main considerations. For hot work mold steel and plastic mold steel, the general mold size is large, especially for manufacturing large molds, the hardenability is more important. In addition, for various molds with complex shapes that are prone to heat treatment deformation, in order to reduce quenching deformation, a quenching medium with a weak cooling capacity, such as air cooling, oil cooling, or salt bath cooling, is often used as much as possible in order to obtain the required hardness and hardened layer. Depth, it is necessary to use a mold steel with better hardenability.

Quenching temperature and heat treatment deformation

In order to facilitate production, the quenching temperature range of mold steel is required to be as wide as possible, especially when the mold is locally quenched by flame heating, because it is difficult to accurately measure and control the temperature, a wider quenching temperature range is required for mold steel.

During the heat treatment of the mold, especially during the quenching process, volume changes, shape warping, distortion, etc. must occur. In order to ensure the quality of the mold, the heat treatment deformation of the mold steel is required to be small, especially for precision molds with complex shapes that are difficult to trim after quenching. For more severe requirements on heat treatment deformation, micro-deformation die steel should be used.

Oxidation and decarburization sensitivity

During the heating process of the mold, if oxidation and decarburization occur, its hardness, wear resistance, serviceability and service life will be reduced; therefore, the sensitivity of the mold steel to oxidation and decarburization is required. For mold steels with high molybdenum content, special heat treatments such as vacuum heat treatment, controlled atmosphere heat treatment, and salt bath heat treatment are required due to their strong sensitivity to oxidation and decarburization.

other factors

When selecting the mold steel, in addition to the use performance and process performance, the versatility of the mold steel and the price of the steel must also be considered. Generally speaking, the amount of mold steel is not large. In order to facilitate the preparation of materials, the generality of steel should be considered as much as possible, and general-purpose mold steel produced in large quantities should be used as much as possible to facilitate procurement, material preparation and material management. In addition, a comprehensive analysis must be carried out economically, considering the manufacturing cost of the mold, the production batch of the workpiece, and the cost of the mold allocated to each workpiece. Comprehensive analysis from technical and economic aspects, in order to finally select a reasonable mold material.