1. Sufficient surface hardness and wear resistance
The hardness of plastic mold is usually below 50-60HRC. The mold after heat treatment should have enough surface hardness to ensure that the mold has enough stiffness. Mould in the work because of the plastic filling and flow to bear the greater compressive stress and friction force, requires the mold to maintain the stability of the shape accuracy and dimensional accuracy, to ensure that the mold has enough service life. The wear resistance of the die depends on the chemical composition of the steel and the hardness of the heat treatment, so improving the hardness of the die is beneficial to improving its wear resistance.
2. Good machinability
In addition to EMD processing, the majority of plastic moulds also need some cutting and fitter repair. In order to prolong the service life of the cutting tool, improve the cutting performance and reduce the surface roughness, the hardness of the steel used for plastic die must be appropriate.
3. Good polishing performance
High quality plastic products require small roughness value of the cavity surface. For example, the surface roughness of the injection mold cavity is required to be less than Ra0.1 ~ 0.25, and the optical surface is required to be Ra<0.01nm. The cavity must be polished to reduce the surface roughness value. For this use of steel material requirements less impurity, fine organization uniform, no fiber direction, polishing should not appear pit or orange peel defects.
4. Good thermal stability
Plastic injection mould parts shapes are more complex, difficult to process after quenching, so should choose as far as possible with good thermal stability, when the mould processing after the heat treatment for small linear expansion coefficient, heat treatment deformation is small, the size of the rate of change caused by the temperature difference is small, the microstructure and the mold size stability, can reduce or no longer carry on the processing, can guarantee the mold size accuracy and surface roughness requirements.