Characteristics of hot working die

Date:2014-07-29

Hot work die mainly comprises a hammer forging die, hot extrusion mold and die casting mold three class. The main characteristics of hot work die working conditions is in contact with the hot metal phase, which is associated with the cold work die working conditions of the main I don't. Therefore, will bring the following two problems.

(1) die cavity surface heating in metal hammer forging die work, usually of the mold cavity surface temperature of 300 to 400 DEG C, hot extrusion die can reach 500 to 800 DEG C, die-casting mold cavity temperature and casting material type and pouring temperature on. Such as die casting ferrous metal die temperature can reach more than 1000 DEG C, this high temperature will make the mold cavity surface hardness and strength decreased significantly, therefore, is the hot plastic deformation resistance of high performance for the basic requirements of die steel for hot, including high hardness and high temperature strength, high thermal plastic deformation resistance that is also the tempering stability. While the addition of Cr, W, Si and other alloy elements, by alloying method, can improve the stability of tempering steel.

(2) die cavity surface metal Gelau (Gui Lie) hot die at work are intermittent, every time the hot metal forming are required to surface water, oil, air cooling medium cavity. Therefore, the work is repeated heating and cooling of the die cavity repeatedly, thus the surface of metal have repeated thermal expansion and contraction, repeated tension and compression under the action of alternating stress. The result will cause cracking appearance surface of the mold cavity, the phenomenon known as thermal fatigue, therefore, the requirements of hot work die steel has higher thermal fatigue resistance. The main factors which influence the thermal fatigue resistance of steel are as follows.

Thermal conductivity of steel: thermal conductivity is higher, can minimize heat the metal mold surface, thereby reducing the tendency of thermal fatigue of steel. Is generally believed that the thermal conductivity of steel and carbon content, carbon content of high thermal conductivity is low, and the carbon content is too low, will lead to a decline in the steel hardness and strength. Therefore, in the production of medium carbon steel is usually used to do hot working die.

The influence of the critical point of steel: usually the critical point of steel (Ac1 steel) higher, the lower the tendency of thermal fatigue. Therefore, generally by the addition of alloying elements Cr, W, Si by enhancing the critical point of steel, to improve the thermal fatigue resistance of steel to.