Mold material selection is a very important link in the whole mold making process. Mold material selection needs to meet three principles, namely: the mold meets the requirements of working conditions such as wear resistance, strength and toughness; the mold meets the process performance requirements; the mold meets the economic requirements

(1) The mold meets the requirements of working conditions

1. Abrasion resistance
When the blank is plastically deformed in the mold cavity, it flows and slides along the surface of the cavity, causing severe friction between the surface of the cavity and the blank, resulting in the failure of the mold due to wear. Therefore, the wear resistance of the material is one of the most basic and important properties of the mold. Hardness is the main factor affecting wear resistance. In general, the higher the hardness of the mold parts, the smaller the amount of wear and the better the wear resistance. In addition, wear resistance is also related to the type, quantity, shape, size and distribution of carbides in the material.
2. Strong toughness
Most of the working conditions of the mold are very harsh, and some often bear large impact loads, resulting in brittle fracture. In order to prevent sudden brittle fracture of mold parts during work, the mold must have high strength and toughness. The toughness of the mold mainly depends on the carbon content, grain size and organizational state of the material.
3. Fatigue fracture performance
During the working process of the mold, under the long-term action of cyclic stress, it often leads to fatigue fracture. Its forms are: small energy multiple impact fatigue fracture, tensile fatigue fracture, contact fatigue fracture and bending fatigue fracture. The fatigue fracture performance of the mold mainly depends on its strength, toughness, hardness, and the content of inclusions in the material.
4. High temperature performance
When the working temperature of the mold is high, the hardness and strength will decrease, resulting in early wear or plastic deformation of the mold and failure. Therefore, the mold material should have high stability against tempering to ensure that the mold has high hardness and strength at working temperature.
5. Cold and heat fatigue resistance
Some molds are in the state of repeated heating and cooling during the working process, so that the surface of the cavity is subjected to variable stress such as tension and pressure, causing surface cracks and peeling, increasing friction, hindering plastic deformation, and reducing dimensional accuracy, thus lead to mold failure. Cold and heat fatigue is one of the main forms of failure of hot work dies, and such dies should have high resistance to cold and heat fatigue.
6. Corrosion resistance
Some molds, such as plastic molds, when working, due to the presence of chlorine, fluorine and other elements in the plastic, after heating, they decompose and decompose strong corrosive gases such as HCl and HF, which erode the surface of the mold cavity, increase its surface roughness, and aggravate wear invalidated.

(2) The mold meets the process performance requirements
     The manufacture of molds generally goes through several processes such as forging, cutting, and heat treatment. In order to ensure the manufacturing quality of the mold and reduce the production cost, the material should have good forgeability, machinability, hardenability, hardenability and grindability; it should also have small oxidation, decarburization sensitivity and quenching Deformation cracking tendency.
1. Malleability. It has low hot forging deformation resistance, good plasticity, wide forging temperature range, low tendency of forging cracking, cold cracking and precipitation of network carbides.
2. Annealing process. The spheroidizing annealing temperature range is wide, the annealing hardness is low and the fluctuation range is small, and the spheroidizing rate is high.
3. Machinability. The cutting amount is large, the tool loss is low, and the machined surface roughness is low.
4. Sensitivity to oxidation and decarburization. When heated at high temperature, it has good oxidation resistance, slow decarburization speed, insensitive to heating medium, and little pitting tendency.
5. Hardenability. After quenching, it has uniform and high surface hardness.
6. Hardenability. After quenching, a deep hardened layer can be obtained, and it can be hardened with a mild quenching medium.
7. Quenching deformation cracking tendency. The volume change of conventional quenching is small, the shape is warped, the distortion is slight, and the tendency of abnormal deformation is low. Conventional quenching has low cracking sensitivity and is insensitive to quenching temperature and workpiece shape.
8. Grindability. The grinding wheel is relatively small in loss, and the amount of grinding without burn limit is large. It is not sensitive to the quality of the grinding wheel and cooling conditions, and it is not easy to cause abrasion and grinding cracks.

(3) The mold meets the economic requirements
    When selecting mold materials, the principle of economy must be considered to reduce manufacturing costs as much as possible. Therefore, under the premise of satisfying the use performance, first choose the one with lower price, if carbon steel can be used, alloy steel is not used, and if domestic material can be used, imported material is not needed. In addition, when selecting materials, the production and supply conditions of the market should also be considered, and the selected steel types should be as few as possible and concentrated, and easy to purchase.