The properties of plastic mould steel should be determined according to the type of plastic, the use of products, the forming method and the production batch size. Generally, it requires simple heat treatment process, little or no deformation, good cutting performance in pre hardened state, excellent mirror polishing performance and pattern etching performance, low surface roughness and long service life.

①切削加工性能

① Machinability

对于大型、复杂和精密的挤压和注射模具，通常预硬化到28-35HRC之间，再进行切削和磨削加工所要求的尺寸和精度后，直接投入使用，从而避免了热处理变形、氧化和脱碳的缺陷。加入易切削元素S、Co和稀土，用以改善硬钢的切削加工性能。

For large, complex and precise extrusion and injection moulds, they are usually pre hardened to 28-35hrc, then cut and ground to the required size and accuracy, and then directly put into use, so as to avoid the defects of heat treatment deformation, oxidation and decarburization. Free cutting elements s, CO and re are added to improve the machinability of hard steel.

②镜面加工性能

② Mirror processing performance

激光盘和塑料透镜等塑料制品的表面粗糙度要求很高，主要由模具型腔的粗糙度来保证，一般模具型腔的粗糙度要比塑料制品的高一级。模具钢的镜面加工性能与钢的纯洁度、组织、硬度和镜面加工技术有关。硬度高、显微组织细小而均匀、非金属夹杂少，均有利于提高镜面抛光性。镜面抛光性要求高的塑料模具钢常采用真空熔炼或真空除气。

The surface roughness of plastic products such as laser disk and plastic lens is very high, which is mainly guaranteed by the roughness of mold cavity. Generally, the roughness of mold cavity is one level higher than that of plastic products. The mirror finishing performance of die steel is related to the purity, microstructure, hardness and mirror finishing technology of the steel. High hardness, fine and uniform microstructure, less non-metallic inclusions are conducive to improve the mirror polishing. Vacuum melting or degassing is often used for plastic mould steel with high requirement of mirror polishing.

③图案蚀刻性能

③ Pattern etching performance

某些塑料制品表面要求呈现清晰而丰满的图案花纹，还有皮革工业中的大型皮纹压花版，都要求模具钢有良好的图案光刻性能，图案光刻性能对材质的要求与镜面抛光性能相似，钢的纯洁订要高，组织要致密，硬度要高。

The surface of some plastic products is required to present clear and full patterns, and the large-scale leather embossing plate in the leather industry requires the mold steel to have good pattern lithography performance. The requirements of pattern lithography performance for materials are similar to mirror polishing performance. The purity of steel should be high, the structure should be compact, and the hardness should be high.

④耐蚀性能

④ Corrosion resistance

含氯和氟的树脂以及在ABS树脂中添加抗燃剂时，在成型过程中将释放出有腐蚀性的气体。对于这类塑料模具要选用耐蚀塑料模具钢或表面镀铬或采用镍磷非晶态表面涂层。

The corrosive gas will be released in the molding process when the resin containing chlorine and fluorine and the flame retardant is added to ABS resin. For this kind of plastic mould, corrosion-resistant plastic mould steel or chromium plating or nickel phosphorus amorphous surface coating should be selected.