Mold steel can be roughly divided into three categories: cold-rolled mold steel, hot-rolled mold steel and plastic mold steel, which are used for forging, stamping, cutting, and die casting. Due to the different uses of various molds and complex working conditions, the steel for molds should have high hardness, strength, wear resistance, sufficient toughness, and high hardenability and hardening according to the working conditions of the molds it manufactures. Rigid and other process properties. Due to different uses and complex working conditions, the performance requirements for mold steel are also different.

Cold-rolled dies include cold-punching dies, wire drawing dies, drawing dies, embossing dies, wire drawing dies, rolling boards, cold heading dies and cold extrusion dies. Cold working die steel should have high hardness, strength, abrasion resistance, sufficient toughness, and high hardenability, hardenability and other process properties according to the working conditions of the manufacturing. The alloy tool steel used for this purpose generally belongs to high-carbon alloy steel, with a carbon mass fraction of 0.80% or more. Chromium is an important alloying element of this type of steel, and its mass fraction is usually not more than 5%. However, for some wear resistance requirements, mold steel with small deformation after quenching, the highest chromium mass fraction can reach 13%, and in order to form a large number of carbides, the carbon mass fraction in the steel is also very high, up to 2.0% ~ 2.3%. Cold work die steel has a higher carbon content, and most of its structure belongs to hypereutectoid steel or lainite steel. Commonly used steels are high carbon low alloy steel, high carbon high chromium steel, chromium molybdenum steel, medium carbon chromium tungsten hafnium steel, and so on.

Hot rolling molds are divided into hammer forging, die forging, extrusion and die casting, including hot forging dies, press forging dies, stamping dies, hot extrusion dies and metal die casting dies. In addition to the huge mechanical stress, the hot deformed mold must withstand repeated heating and cooling during the work, which causes great thermal stress. In addition to the high hardness, strength, red hardness, wear resistance and toughness of hot work die steel, it should also have good high temperature strength, thermal fatigue stability, thermal conductivity and corrosion resistance. Hardenability to ensure consistent mechanical properties throughout the section. For steel for die-casting molds, it should also have the performance that the surface layer does not generate cracks after repeated heating and cooling, and that it can withstand the impact and erosion of liquid metal flow. This type of steel generally belongs to medium carbon alloy steel, with a carbon mass fraction of 0.30% ~ 0.60%, which belongs to hypoeutectoid steel, and some steels become eutectoid due to the addition of more alloying elements such as tungsten, molybdenum, vanadium, etc Hypereutectoid steel. Commonly used steels are chromium-manganese steel, chromium-nickel steel, and chromium-tungsten steel.

Plastic molds include thermoplastic molds and thermoset plastic molds. Steel for plastic molds requires certain properties such as strength, hardness, wear resistance, thermal stability, and corrosion resistance. In addition, good processability is required, such as small heat treatment deformation, good processability, good corrosion resistance, good grinding and polishing performance, good repair welding performance, high roughness, good thermal conductivity, and stable size and shape of working conditions, etc. . In general, hot-working die steel can be used for injection molding or extrusion molding; cold-working die steel can be used for thermosetting forming and molds requiring high wear resistance and high strength.