(1) Enough surface hardness and wear resistance: the hardness of plastic mold is usually below 50 ~ 60 HRC, and the mold after heat treatment should have enough surface hardness to ensure that the mold has enough rigidity. Because the filling and flow of plastic in the mold have to bear large compressive stress and friction, the mold is required to maintain the stability of shape accuracy and dimensional accuracy, so as to ensure that the mold has enough service life. The wear resistance of the die depends on the chemical composition and heat treatment hardness of the steel, so increasing the hardness of the die is conducive to improving its wear resistance.

(2) 良好的机械加工性能：要选用易于切削，且在加工后能得到高精度零件的钢种。为此，以中碳钢和中碳合金钢常用，这对大型模具尤其重要。对需要电火花加工的零件，还要求该钢种的烧伤硬化层较薄。

(2) Good machinability: choose the steel which is easy to cut and can get high precision parts after machining. For this reason, medium carbon steel and medium carbon alloy steel are most commonly used, which is especially important for large mold. For the parts that need EDM, the burn hardening layer of the steel is required to be thin.

(3) 优良的抛光性能：高品质的塑料制品，要求型腔表面的粗糙度值小。因此，注塑模具成型零件工作表面多需要抛光到镜面，Ra≤0.05μm，需要钢材硬度35~40 HRC 为宜，表面过硬会使抛光困难。为此，选用的钢材要求材料杂质少，显微组织应均匀致密，无纤维方向性，抛光时不应出现麻点或桔皮状缺陷。

(3) Excellent polishing performance: for high quality plastic products, the roughness of the cavity surface is required to be small. Therefore, the working surface of injection mold parts needs to be polished to the mirror surface, RA ≤ 0.05 μ m, and the steel hardness of 35 ~ 40 HRC is appropriate, which will make polishing difficult. For this reason, the selected steel should have less impurities, uniform and compact microstructure, no fiber orientation, and no pitting or orange peel defects during polishing.

(4) 良好的热稳定性：塑料注射模的零件形状往往比较复杂，淬火后难以加工，因此应尽量选用具有良好的热稳定性的材料，使得模具成型零件经热处理后线膨胀系数小，热处理变形小，温度差异引起的尺寸变化率小，金相组织和模具尺寸稳定，可减少或不再进行加工，从而保证模具尺寸精度和表面粗糙度要求。

(4)  Good thermal stability: the shape of plastic injection mold parts is often more complex, and it is difficult to process after quenching, so the materials with good thermal stability should be selected as far as possible, so that the linear expansion coefficient of mold parts after heat treatment is small, the heat treatment deformation is small, the size change rate caused by temperature difference is small, the metallographic structure and mold size are stable, and the processing can be reduced or stopped So as to ensure the dimensional accuracy and surface roughness of the die.

(5) 良好的耐磨性和抗疲劳性：注塑模具型腔不仅受高压塑料熔体冲刷，而且还受冷热交变的温度应力作用。一般的高碳合金钢可经热处理获得高硬度，但韧性差，易形成表面裂纹，不宜采用。所选钢种应使注塑模能减少抛光修模的次数，能长期保持型腔的尺寸精度，达到批量生产的使用寿命期限。

(5) Good wear resistance and fatigue resistance: the cavity of injection mold is not only scoured by high pressure plastic melt, but also affected by alternating temperature stress. General high carbon alloy steel can obtain high hardness by heat treatment, but its toughness is poor and surface crack is easy to form, so it is not suitable to use. The selected steel grade should be able to reduce the polishing times of injection mold, maintain the dimensional accuracy of cavity for a long time, and reach the service life of mass production.