In the production process of mold steel, many manufacturers strictly control the hot and cold processing to avoid defective products. They also improve the purity of the steel to reduce harmful impurities, improve the purity of the mold steel, and improve its process performance. So what is the process performance of mold steel? Let us tell you.
From the 1930s, various easy-to-cut mold steels have been developed by adding appropriate elements such as S, Pb, Ca, and rare earth metals to the steel or elements that can promote the graphitization of C in the mold steel.
It was later discovered that some harmful inclusions (such as iron sulfide) would be produced in the mold steel after adding certain easy-to-cut elements, resulting in a decrease in mechanical properties, especially transverse plasticity and toughness. Therefore, in the late refining stage, the steel liquid is subjected to modification treatment, and a modifier is added to form a calcium-rich sulfide or rare earth sulfide, which can suppress the adverse effects of sulfur on the mechanical properties of steel, retain and exert its favorable effect on the cutting and grinding properties of steel, and further develop easy-to-cut mold steels.
Some mold steel material, such as high-vanadium high-speed steel and high-vanadium high-alloy mold steel, have poor grinding properties and low grinding ratio, which are not suitable for grinding processing.
In recent years, powder metallurgy has been used to produce mold steel, which can make the carbide in the steel small and uniform, completely eliminating the large particle carbides in high-vanadium mold steel produced by ordinary processes. This not only greatly improves the grinding properties of this kind of steel, but also improves the plasticity, toughness, and other properties of the steel, making it suitable for promotion and application in mold manufacturing.
It has relatively high strength, hardness, and impact toughness at temperatures of 400℃-600℃, so as to have greater deformation capacity and good wear resistance. Impact toughness is the basic performance of forging dies. For die steel used in hammer forging molds, the impact toughness should be ≧30J/㎝2. In order to prevent or delay crack propagation, it is also required to have a high fracture limit.
It has good resistance to thermal fatigue and can withstand working conditions of cold and hot exchange. If it has good thermal conductivity and low thermal expansion coefficient, its thermal fatigue resistance will be high, which can delay the formation of thermal fatigue cracks. It has good tempering stability, which prevents the hardness from decreasing due to heating during forging work, resulting in a decrease in wear resistance.
It has good hardenability, small shape distortion during heat treatment, stable size, and uniform mechanical properties throughout the mold. For hot forging dies with large dimensions, the entire cross-section of the mold requires uniform and consistent mechanical properties. If the center is not hardened, it may form bainite or other tissues, resulting in premature mold failure.
In summary, when the mold steel is sold in the market, a modifier can be added to make the sulfide particles spheroidized, which can suppress the adverse effects on mechanical properties and improve the toughness of mold steel.
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