Die steel is used to make cold stamping die, hot forging die and die-casting die. Mould is the main processing tool for manufacturing parts in the industrial departments of machinery manufacturing, radio instruments, motors, electrical appliances, etc. The quality of the die directly affects the quality of the pressure processing technology, the precision output of the product and the production cost, while the quality and service life of the die are mainly affected by the die material and heat treatment besides the reasonable structure design and processing precision. Die steel can be divided into hot die steel, cold die steel, plastic die steel and plastic die steel.

Die steel can be roughly divided into three categories: cold-rolled die steel, hot-rolled die steel and plastic die steel, which are used for forging, stamping, cutting, die-casting, etc. Due to the different purposes and complex working conditions of various moulds, the steel used for moulds shall have high hardness, strength, wear resistance, enough toughness, as well as high hardenability, hardenability and other technological properties according to the working conditions of the moulds. Because of the different uses and complex working conditions, the performance requirements of die steel are also different.

Plastic mold includes thermoplastic mold and thermosetting plastic mold. The steel used for plastic mould should have certain strength, hardness, wear resistance, thermal stability and corrosion resistance. In addition, it is also required to have good processability, such as smaller heat treatment, better processing performance, good corrosion resistance, good grinding and polishing performance, good repair welding performance, high roughness, good thermal conductivity and stable working condition size and shape.

In general, hot die steel can be used for injection molding or extrusion molding; thermosetting forming and high wear-resistant and high-strength cold rolling die include cold stamping die, drawing die, drawing die, stamping die, rolling die, rolling plate, cold heading die and cold extrusion die, etc. The cold working die has steel. According to the working conditions of the tool, it should have high hardness, strength, wear resistance, enough toughness, as well as high hardenability, hardenability and other technological properties. The alloy tool steel used for this purpose is generally high carbon alloy steel, with carbon content of more than 0.80%. Chromium is an important alloy element of this kind of steel, and its mass content is usually no more than 5%. However, for some die steels with small deformation after quenching, the highest chromium content is 13%. In order to form a large amount of carbides, the carbon content in the steel is also very high, the highest is 2.0% ~ 2.3%.

The carbon content of cold working die steel is high, and most of its structure belongs to hypereutectoid steel or ledeburite steel. Hot rolling dies of high carbon low alloy steel, high carbon high chromium steel, chromium molybdenum steel and carbon chromium tungsten plutonium steel are divided into hammer forging, die forging, extrusion and die casting, including hot forging die, press forging die, stamping die, hot extrusion die and metal die casting die. In addition to the great mechanical stress, the hot deformation die also bears the repeated heating and cooling, which causes great thermal stress. In addition to high hardness, strength, red hardness, wear resistance and toughness, cold working die steel can also be used for dies with good high temperature strength, thermal fatigue stability and thermal conductivity. And corrosion resistance, in addition to the requirements of high hardenability, to ensure that the entire section has the same mechanical properties. For die-casting die steel, it should also have the properties that the surface layer will not crack after repeated heating and cooling, and will withstand the impact and erosion of liquid metal flow.

This kind of steel generally belongs to medium carbon alloy steel, with carbon content of 0.30% ~ 0.60%. It belongs to hypoeutectoid steel, and some steels become eutectoid or hypereutectoid due to adding more alloy elements (such as tungsten, molybdenum, vanadium, etc.). Commonly used steels include chromium manganese steel, chromium nickel steel, chromium tungsten steel, etc.