（1） The die meets the requirements of working conditions
1. Wear resistance
When the blank is plastically denatured in the mold cavity, it flows and slides along the surface of the mold cavity, resulting in severe friction between the surface of the mold cavity and the blank, resulting in the failure of the mold due to wear. So the wear resistance of material is one of the basic and important properties of die.
Hardness is the main factor affecting wear resistance. In general, the higher the hardness of die parts, the smaller the wear, the better the wear resistance. In addition, the wear resistance is also related to the type, quantity, shape, size and distribution of carbides in the material.
2. Strength and toughness
Most of the working conditions of the dies are very bad, and some of them often bear large impact load, which leads to brittle fracture. In order to prevent the sudden brittle fracture of die parts, the die should have high strength and toughness.
The toughness of the die mainly depends on the carbon content, grain size and microstructure of the material.
3. Fatigue fracture property
In the working process of die, under the long-term action of cyclic stress, fatigue fracture is often caused. 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 die 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 die is higher, the hardness and strength will decrease, leading to early wear or plastic deformation and failure of the die. Because the die material should have high tempering stability, in order to ensure that the die has high hardness and strength at working temperature.
5. Cold and hot fatigue resistance
Some molds are in the state of repeated heating and cooling in the working process, which makes the cavity surface subject to tension and pressure stress, causes surface cracking and spalling, increases friction, hinders plastic deformation, reduces dimensional accuracy, and leads to mold failure. Cold and hot fatigue is one of the main failure modes of hot working dies. This kind of dies should have high cold and hot fatigue resistance.
6. Corrosion resistance
When some moulds, such as plastic moulds, work, because there are chlorine, fluorine and other elements in the plastics, they decompose and precipitate HCI, HF and other strong corrosive gases after heating, which erode the surface of the mould cavity, increase its surface roughness and aggravate the wear failure.
（2） The die meets the requirements of process performance
Mold manufacturing generally has to go through forging, cutting, heat treatment and other processes. In order to ensure the manufacturing quality of the die and reduce the production cost, the material should have good malleability, machinability, hardenability, hardenability and grindability, as well as small oxidation, decarbonization sensitivity and quenching deformation cracking tendency.
It has low hot forging deformation resistance, good plasticity, wide forging temperature range, low tendency of forging crack, cold crack and network carbide precipitation.
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.
Large cutting parameters, low tool loss and low surface roughness.
4. Oxidation and decarbonization sensitivity
When heated at high temperature, the oxidation resistance is good, the decarbonization speed is slow, and it is insensitive to the heating medium.
After quenching, it has uniform and high surface hardness.
After quenching, a deeper hardening layer can be obtained, which can be hardened by using mild quenching medium.
7. Quenching deformation and cracking tendency
Conventional quenching has small volume change, slight shape warpage and distortion, and low tendency of abnormal deformation. It is not sensitive to quenching temperature and workpiece shape.
It is not sensitive to the quality and cooling conditions of the grinding wheel, and is not easy to cause grinding damage and grinding cracks.
（3） The die meets the economic requirements
In selecting the material for the mould, we must consider the principle of economy to reduce the manufacturing cost as much as possible. Therefore, on the premise of meeting the service performance, the first choice is the lower price. If carbon steel can be used, alloy steel will not be used, and if domestic materials can be used, imported materials will not be used. In addition, the production and supply situation of the market should also be considered when selecting materials. The selected steel grades should be as few as possible, concentrated and easy to purchase.