The performance requirement of die steel
Wear resistance The most important factor in determining the life span of die is the wearability of die materials. The mold is subjected to considerable stress and friction at work, and it is required that the mould can maintain its dimension accuracy under intense friction. The wear and tear of the mould are mainly of mechanical wear, oxidation and wear and tear. In order to improve the wear resistance of steel, will be die steel with high hardness, and to ensure that the carbide in steel or other composition, morphology and distribution of hardening phase is quite reasonable. Serving for overloading, high-speed wear under the condition of the mold, the steel surface to form a thin and dense oxide film with good sex of adhesion, lubrication, reducing between die and workpiece stick bite, welding, melting and wear, and can reduce the mold surface oxidation caused by oxidation wear and tear. So the working conditions of the mould have a large effect on the wear and tear of steel. The test method of abrasion resistance can be used to measure the relative wear-resisting index, as a parameter of the resistance level of different chemical constituents and tissues. In order to present the life of the pre-burring height, it reflects the wear-resisting level of various kinds of steel. The test was based on Cr12MoV steel.
toughness In the process of work, mold under impact load, in order to reduce the broken in the using process, the collapse edge form of damage, such as requirements die steel has a certain toughness. Die steel chemical composition, grain size, purity, the number of carbide and inclusion, morphology, size and distribution, as well as the system of heat treatment of steel and heat treatment microstructure of factors have great influence on the toughness of steel. In particular, the net degree of steel and the deformation of thermal machining are more obvious to the lateral toughness. Steel's toughness, strength and abrasion are often contradictory. Therefore, to reasonably select steel chemical composition and adopt reasonable refining, hot working and heat treatment process, in order to make the wear resistance of die material, with the strength and toughness to best. The total energy absorbed by the test sample during the whole fracture process during the shock process is the impact toughness system. But many tools are broken under different working conditions, so the conventional impact toughness does not fully reflect the fracture properties of the mold steel. Experimental techniques such as multiple impact fracture work or multiple fracture life and fatigue life are being adopted.
Compressive yield strength and compressive strength of bending strength mould in use process is often high pressure and bending effect, so the mold material should have certain compressive strength and bending strength. In many cases, the compression test and bending test conditions close to the actual working conditions of mould (for example, measured by the steel compressive yield strength and deformation resistance of punch work was coincident). Another advantage of the bending test is the absolute value of the dependent variable is large, can be more sensitive to reflect the different steel grade and condition in different heat treatment and organizations between the difference of deformation resistance.
Red hardness Work under high temperature condition of hot-work die to maintain the stability of the organization and performance, to maintain a high enough hardness, this performance is called red hardness. Carbon tool steel, low alloy tool steel can often in 180 ~ 250 ℃ temperature range of this kind of performance, chrome molybdenum steel is in commonly 550 ~ 600 ℃ temperature range this performance. The red hardness of steel mainly depends on the chemical composition of the steel and the process of heat treatment.
The hardness is the main technical indicator of the mold steel, the mould is in high stress to keep its shape and size constant, it must have high hardness. Cold is a mold steel which is generally hard at room temperature under the condition of HRC60, the heat is made of steel according to its working condition, the general requirement is kept in the HRC40 ~ 55 range. In the case of the same steel, the hardness is proportional to the deformation resistance in a certain degree of hardness. However, there may be significant differences in the plasticity resistance of the steel species with the same hardness value and different tissue.
