(1) The mold meets the requirements of working conditions
1. Wear 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, which causes the mold to fail due to wear. Therefore, one of the most basic and important properties of the wear resistance mold of the material.
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, the wear resistance is also related to the type, number, form, size and distribution of carbides in the material.
2. Strong and tough
Most of the working conditions of the mold are very bad, and some often bear a large impact load, which leads to brittle fracture. In order to prevent the mold parts from being brittlely broken during work, the mold should have high strength and toughness.
The toughness of the mold mainly depends on the carbon content, grain size and microstructure of the material.
3. Fatigue fracture performance
In the process of mold work, under the action of cyclic stress, it often leads to fatigue fracture. Its forms are low 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 higher, 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 the working temperature.
5. Cold and heat fatigue resistance
Some molds are in the state of repeated heating and cooling during the work process, which causes the surface of the cavity to be pulled and the stress of the pressure changes, causing surface cracking and flaking, increasing friction, hindering plastic deformation, and reducing dimensional accuracy, resulting in Mold failure. Hot and cold fatigue is one of the main forms of hot work die failure, and help molds should have high resistance to cold and hot fatigue performance.
6. Corrosion resistance
When some molds such as plastic molds work, due to the presence of chlorine, fluorine and other elements in the plastic, after heating, the strong corrosive gases such as HCI and HF are resolved, eroding the surface of the mold cavity, increasing its surface roughness, and aggravating wear failure.
(B) The mold meets the process performance requirements
The manufacture of the mold generally goes through several processes such as forging, cutting, and heat treatment. In order to ensure the manufacturing quality of the mold and reduce production costs, the material should have good forgeability, cutting workability, hardenability, hardenability and grindability; it should also have small oxidation, decarburization sensitivity and quenching Deformation and cracking tendency.
1. Forgeability
It has low resistance to hot forging deformation, good plasticity, wide forging temperature range, low forging cracking and low tendency to precipitate network carbide.
2. Annealing processability
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
Large amount of cutting, low tool loss and low surface roughness.
4. Sensitivity to oxidation and decarburization
Antioxidation is good when heated at high temperature, the decarburization speed is slow, it is not sensitive to the heating medium, and the tendency to produce pitting is small.
5. Hardenability
After quenching, it has uniform and high surface hardness.
6. Hardenability
After quenching, a deeper hardened layer can be obtained, which can be hardened by using a mild quenching medium.
7. Cracking tendency of quenching deformation
Conventional quenching has small volume changes, slight warpage and distortion, and low tendency to abnormal deformation. Conventional quenching has low cracking sensitivity and is insensitive to quenching temperature and workpiece shape.
8. Grindability
The relative wear of the grinding wheel is small, the maximum amount of grinding without burns is large, and it is not sensitive to the quality of the grinding wheel and the cooling conditions, and it is not easy to cause scratches and grinding cracks.
(3) The mold meets the economic requirements
In the selection of materials for molds, the principle of economy must be considered to reduce manufacturing costs as much as possible. Therefore, on the premise of satisfying the use performance, first of all, the lower price is selected, and the carbon steel can be used without alloy steel, and the production material can be used without imported materials. In addition, the production and supply of the market should also be considered when selecting materials. The steel grades selected should be as few and concentrated as possible and easy to purchase.
