Strength performance (1) The hardness is the main technical index of the mold steel. The mold must maintain a sufficiently high hardness under the action of high stress to maintain its shape and size. Cold work die steel at room temperature to maintain the general hardness of about HRC60, hot work die steel according to their working conditions, the general requirements remain in HRC40 ~ 55 range. For the same type of steel, within a certain range of hardness values, hardness and deformation resistance is proportional to; but with the same hardness and composition of different steel grades, the plastic deformation resistance may be significantly different. (2) Red Hardness Hot working molds that operate at high temperatures require the maintenance of their microstructure and properties to maintain their high enough hardness, a property known as red hardness. Carbon tool steels and low-alloy tool steels generally maintain this behavior over the temperature range of 180-250 ° C. Chromium-molybdenum hot-work tool steels generally maintain this behavior over the 550-600 ° C temperature range. The red hardness of steel depends mainly on the chemical composition of steel and heat treatment process.
(3) Compression yield strength and compressive bending strength Die in the use of the process often by the higher strength of the pressure and bending, and therefore require the mold material should have a certain compressive strength and bending strength. In many cases, the compression test and bending test conditions are close to the actual working conditions of the mold (for example, the measured compressive yield strength of the die steel is in good agreement with the deformation resistance exhibited by the punch during working) . Another advantage of the flexural test is that the absolute value of the strain is large and can more sensitively reflect the difference in deformation resistance between different steels and between different heat treatments and microstructures.
In the course of work, the mold bear the impact of the load, in order to reduce the use of the process of fracture, collapse and other forms of damage, require the mold steel has a certain toughness. Die steel chemical composition, grain size, purity, carbide and inclusions such as the number, shape, size and distribution, as well as the heat treatment of mold steel and heat treatment obtained after the microstructure and other factors on the steel Toughness brought great influence. In particular, the steel's purity and hot working distortion have more pronounced effects on its transverse toughness. Steel toughness, strength and wear resistance are often contradictory. Therefore, the reasonable choice of steel chemical composition and the use of reasonable refining, thermal processing and heat treatment process to make the mold material wear resistance, strength and toughness to achieve the best match. Impact toughness is the total energy absorbed by the sample throughout the fracture during a single impact. However, many tools are fatigue fracture under different working conditions, therefore, conventional impact toughness can not fully reflect the fracture properties of die steel. Experimental techniques of small energy multiple impact fracture work or multiple fracture life and fatigue life are being used.