Mold material selection is a very important part in the whole process of die making.
The mold material selection needs to meet the three principles, die to meet the needs of wear resistance, toughness and other work, die to meet the process requirements, while the mold should meet the economic applicability.
Condition requirements

1, wear resistance
When the billet is plastic degeneration in the mold cavity, the surface of the mould is both flowing and sliding, which makes the surface of the mold cavity and the blank to produce the intense friction, which leads to the failure of the die due to abrasion. So material wear resistance is one of the most basic and most important properties.
Hardness is the main factor affecting the wear resistance. Under normal circumstances, the higher the hardness of the mold parts, the smaller the wear, the better the wear resistance. In addition, the wear resistance is related to the type, quantity, shape, size and distribution of carbides in the material.

2 strong toughness
Mold working conditions are mostly very poor, and some often bear a larger impact load, which leads to brittle fracture. In order to prevent the mold parts in the work of brittle fracture, the mold must have high strength and toughness.
The toughness of the mould is mainly determined by the carbon content, grain size and microstructure of the material.

3 fatigue fracture behavior
During the working process of the mould, the fatigue fracture is often caused by the long term effect of the cyclic stress. The form has small energy multiple impact fatigue fracture, tensile fatigue fracture contact fatigue fracture and bending fatigue fracture.
The fatigue fracture behavior of the mold mainly depends on its strength, toughness, hardness, and the content of the inclusions in the material.

4 high temperature performance
When the working temperature of the mold is higher, the hardness and strength decrease, leading to the early wear of the die or the failure of the plastic deformation. Therefore, the mold material should have high tempering stability, in order to ensure that the mold at the working temperature, with high hardness and strength.

5 resistance to cold and hot fatigue
Some molds in the working process in the repeated heating and cooling of the state, the cavity surface tension and stresses the role of, cause cracking and peeling off the surface, increase the friction, hinder plastic deformation, size accuracy is reduced, resulting in die failure. Cold and hot fatigue is one of the main forms of failure of hot die, which should have high resistance to cold and hot fatigue.

6 corrosion resistance
Some molds, such as plastic mold at work, due to the presence of chlorine, fluorine plastic, after heat decomposition of precipitation HCI, HF, and other strong erosion of gas, the mold cavity surface erosion, increase the surface roughness of intensified wear failure.
Process performance
Mold manufacturing generally through forging, machining, heat treatment and other processes. In order to ensure the quality of mould manufacturing and reduce the production cost, the material should be with good can be forging, machinability, quench hardening, permeability and grinding; also has a small oxidation and decarbonization and quenching deformation and cracking tendency.

1 malleable
With low hot forging deformation resistance, good plasticity, wide forging temperature range, cold forging, cold cracking and carbide tendency of precipitation is low.

2 annealing process
The annealing temperature range is wide, the hardness is low and the fluctuation range is small, the rate of the ball is high.

3 machinability
The cutting quantity is big, the cutting tool loss is low, the processing surface roughness is low.

4 oxidation and decarburization sensitivity
When heated to high temperature oxidation with good decarburization rate is slow, not sensitive to the heating medium, produce pitting tendency.

5 quenching hardness
After quenching, the surface hardness is uniform and high.

6 quenching property
The hardened layer can be obtained after quenching, and the quenching medium can be hardened by quenching.

7 quenching deformation and cracking tendency
The conventional quenching volume change is small, the shape is warped, the distortion is slight, and the abnormal deformation tendency is low. The quenching cracking sensitivity is low, which is not sensitive to the quenching temperature and the shape of the workpiece.

8 grinding ability
Grinding wheel loss is relatively small, no limit of burn grinding dosage, not sensitive to wheel quality and cooling condition. It's not easy to change rubs and grinding cracks.