The hot forging die steel bears great impact when it works. The die cavity contacts with high-temperature metal, and is heated and cooled repeatedly. Its service conditions are extremely poor. In order to meet the use requirements of hot work dies, hot work die steel shall have the following basic characteristics:

(1) High temperature strength and good toughness. Hot working dies, especially hot forging dies, bear great impact force when working, and the impact frequency is very high. If the die does not have high strength and good toughness, it is easy to crack.

(2) Good wear resistance. In addition to friction and wear caused by blank deformation, hot work die steel is also subject to high-temperature oxidation corrosion and grinding of oxidized iron filings, so hot work die steel is required to have high hardness and adhesion resistance.

(3) High thermal stability. Thermal stability refers to the ability of steel to maintain its mechanical properties at room temperature for a long time at high temperature. When the hot working die works, it contacts the hot metal, even the liquid metal, so the surface temperature of the die is very high, generally 400 ~ 700 ℃. This requires that the hot working die steel should not be heated at high temperature and have high thermal stability, otherwise the die will be plastic deformed, causing collapse and failure.

(4) Excellent heat fatigue resistance. The working characteristics of hot working dies are that they are repeatedly heated and cooled. The dies are heated and expanded at one time and cooled and contracted at the other time, forming a large thermal stress. Moreover, this thermal stress is generated alternately in the opposite direction. Under the action of repeated thermal stress, a network of cracks (cracks) will be formed on the surface of the die. This phenomenon is called thermal fatigue. The premature fracture of the die due to thermal fatigue is one of the main reasons for the failure of the hot working die. Therefore, hot work die steel must have good thermal fatigue.

(5) High hardenability. Hot working dies are generally large in size, especially hot forging dies. In order to make the mechanical properties of the whole die section uniform, hot working die steel is required to have high hardenability.

(6) Good thermal conductivity. In order to prevent excessive heat accumulation of the die, resulting in the decline of mechanical properties, it is necessary to reduce the die surface temperature as much as possible and reduce the temperature difference inside the die, which requires that the hot work die steel should have good heat conduction performance.

(7) Good forming process performance to meet the needs of processing and forming.