As a processed mold product, this type of product has a very good effect in use, but we should also find in the production that there will be some problems in the processing of hot work mold steel. How should it be handled? Here is a simple analysis for you.
Usually, when the hammer forging die is working, the surface temperature of the die cavity can reach above 300-400℃. For example, when die casting ferrous metal, the cavity temperature can reach more than 1000 ℃.
Such a high use temperature will significantly reduce the surface hardness and strength of the cavity, and it is prone to stacking during use. For this reason, the basic performance requirements for hot work die steel are high thermoplastic deformation resistance, including high temperature hardness and high temperature strength. High thermoplastic deformation resistance actually reflects the high tempering stability of the steel.
From this, a way to alloy hot die steel can be found, that is, adding alloying elements such as Cr, W, Si, etc., can improve the tempering stability of the steel.
The working characteristics of the hot work die are intermittent. After each time the hot metal is formed, the surface of the die cavity must be cooled with water, oil, air and other media. Therefore, the working state of the hot mold is repeated heating and cooling, so that the metal on the surface of the mold cavity undergoes repeated thermal expansion and contraction, that is, repeated tensile and compressive stress. As a result, cracks appear on the surface of the mold cavity, which is called thermal fatigue phenomenon. Therefore, the basic performance requirements for hot mold steel are put forward, that is, high thermal fatigue resistance.
Generally speaking, the main factors that affect the thermal fatigue resistance of steel are:
1. Thermal conductivity of steel
The high thermal conductivity of steel can reduce the heating degree of the metal on the surface of the mold, thereby reducing the thermal fatigue tendency of the steel. It is generally believed that the thermal conductivity of steel is related to the carbon content. When the carbon content is high, the thermal conductivity is low, so high carbon steel should not be used for hot work die steel. In production, medium carbon steel (C0.3% 5-0.6%) is usually used with too low carbon content, which will lead to a decrease in the hardness and strength of the steel, which is also unfavorable.
2. The critical point effect of steel
Generally, the higher the critical point (Acl) of the steel, the lower the thermal fatigue tendency of the steel. Therefore, the critical point of steel is generally increased by adding alloying elements Cr, W, and Si. Thereby improving the thermal fatigue resistance of die steel.
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