(1) Good wear resistance
The surface roughness and dimension accuracy of the parts are directly related to the wear resistance of the die surface. For example, forming thermosetting resins and plastics with glass fiber, it requires the die to have high wear resistance. The surface hardness of the die is high, so it has good wear resistance and long service life.
(2) Better hardenability
In addition to high surface hardness, the die also requires sufficient core strength, such as the injection mold to withstand large injection pressure and clamping pressure, so the core strength of the die must be taken into account, that is, the steel is required to have good hardenability
(3) Good corrosion resistance
Plastics and additives have chemical corrosion effect on the surface of steel (such as PVC for telephone and joints and resin with flame retardant), so corrosion-resistant steel should be selected or treated with chromium and nickel plating on the surface of cavity.
(4) Good processability
After heat treatment, the deformation is small and the processing is good, which can ensure the shape and dimension accuracy of the die. At the same time, because the shape of the die parts is often complex, the processing after quenching is difficult, or it is impossible to process at all, so when choosing the die material, the steel with small deformation after heat treatment should be chosen as far as possible. Some die parts can be roughened first and then tempered. However, hardness after quenching and tempering should not be higher than 300HB. Its purpose is to facilitate mechanical processing and benchmarking. In this case, the material deformation after heat treatment does not matter, even if it is larger, because the semi-finished roughcast after roughing has to be finished.
(5) Good polishing performance
Parts often require good gloss and surface condition, so the die cavity must be polished well, so the selected steel should not contain rough impurities and pore, etc. Secondly, surface decorative pattern processing is needed. Metal mould is required to have good decorative grain processing performance, such as automobile and household electrical appliances.
There are some contradictions between the above performances, such as machinability, wear resistance, corrosion resistance and so on. Therefore, comprehensive consideration should be made according to the use requirements and manufacturing conditions of the die.
