What’s the difference between cold work tool steel and hot work tool steel?

Tool steel can be divided into these six groups: water-hardening, cold work, shock resisting, high-speed, hot work and special purpose according to its chemical composition and different applications. Cold work tool steel refers to the die steel used to deform or shape metal in cold conditions. It has high wear resistance, strength and toughness, strong bite resistance, softening ability under heat, etc. When cold working die steel is working, its working part is under great pressure, bending force, impact force and friction force due to great deformation resistance, so the failure of cold working die is usually because of the wear as well as the fracture, collapse force and deformation out of tolerance and failure in advance. Cold working tool steel includes die for cutting (blanking die, trimming die, punch, scissors), cold heading die and cold extrusion die, bending die and drawing die etc.

Hot work tool steel refers to the alloy tool steel maintain strength and hardness while exposed to prolonged elevated temperatures, such as hammer forging dies, hot extrusion dies and die-casting dies. Because the hot mold contact with hot metal directly, so there is a more severe demand requirement such as high strength, hardness and thermal stability, especially high thermal strength, thermal fatigue, toughness and wear resistance is required to ensure that the mold is enough to have a long service life. This is the main difference with cold mold working conditions. In addition, they differ from:

• Different operating temperature.

Cold working tool steel works at room temperature (below 100℃). Hot work tool steel is in contact with hot metal or even liquid metal, so the surface temperature of the mold is very high, generally 350 ~ 700℃.

• Different carbon and alloying elements

Cold tool steel usually has higher carbon content (1.45% ~ 2.30%) to meet the requirements of high hardenability and wear resistance. Medium carbon steel is sometimes used to improve the impact resistance and toughness of the die. Alloying elements such as Cr (11% ~ 13%), Mo, W, V are added to cold working die steels mainly to improve hardenability and wear resistance.

Hot-working die steel is medium carbon (0.3% ~ 0.6%). It has more requirements on red hardness, thermal conductivity and wear resistance, and the general requirements for hardness. Alloying elements such as Cr, Mn, Si, Ni, W, Mo, V can increase hardenability, oxidation resistance, wear-resistance and red hardness.

• Different applications

Cold working tool steel is mainly used for making blanking die (blanking die, trimming die, punch, scissors), cold heading die and cold extrusion die, bending die and drawing dies.  Hot-working tool steel is mainly used in die casting.

4.Different tool steel codes

The series “A”, “O”, “D” belong to cold working tool steel, while the “H” series(H13) is the hot worked tool steel.