1. strength performance
(1) hardness and hardness are the main technical indexes of die steel. The die must be of high hardness in order to keep its shape and size under high stress. Cold working die steel at room temperature, the general hardness of about HRC60, hot working die steel according to its working conditions, general requirements remain in the range of HRC40~55. For the same grade, in a certain range of hardness, hardness and deformation resistance is proportional; but with the same hardness and different steel composition and microstructure, the plastic deformation resistance may have obvious difference.
(2) the red hot working die in the high temperature condition, the request maintains its organization and the performance stability, thus maintains the enough high hardness, this kind of performance is called the red rigid. Carbon tool steels and low-alloy tool steels are generally able to maintain this performance at a temperature range of 180~250 degrees Celsius. Chromium - molybdenum hot work die steels generally maintain this performance at a temperature range of 550~600 degrees C. The red hardness of steel depends mainly on the chemical composition and heat treatment process of steel.
(3) the compressive strength and compressive bending strength are often affected by the higher strength and bending of the die during use. Therefore, the die material should have a certain compressive strength and flexural strength. In many cases, the conditions of the compression test and the bending test are close to the actual working conditions of the die
In the course of work, the die is subjected to impact loading, and in order to reduce the damage in the course of use, such as broken, broken edge and other forms, die steel is required to have certain toughness.
The chemical composition, mould steel, grain size, purity, quantity, carbides and inclusions such as morphology, size and distribution, bring great impact and heat treatment system and heat treatment of die steel after the microstructure factors on toughness of steel. In particular, the purity of steel and the deformation of hot working have more obvious influence on its lateral toughness. The toughness, strength and wear resistance of steel are often contradictory.
3. wear resistance
The most important factor determining the service life of the die is the wear resistance of the mold material. The die is subjected to considerable compressive stress and friction at work, requiring the die to retain its dimensional accuracy under severe friction. The wear of mould mainly consists of three types: mechanical wear, oxidation wear and melting wear. In order to improve the wear resistance of die steel, it is necessary to keep the die steel with high hardness, and to ensure the composition, appearance and distribution of carbides or other hardening phases in the steel. For heavy load, high speed wear mold under the condition of service requirements, die steel surface to form a thin and dense oxide film with good adhesion, maintain lubrication, reduce the melt viscosity bite, welding and other wear between the mold and the workpiece, and can reduce the oxidation caused by oxidation wear die surface. Therefore, the working conditions of the die have great influence on the wear of the steel.
4. thermal fatigue resistance
Hot die steel under service conditions in addition to the periodic change of the load bearing and also by high temperature and periodic thermal shock effect, therefore, the thermal mechanical fatigue fracture resistance of mould steel materials for thermal evaluation should pay attention to. Thermal mechanical fatigue is a comprehensive performance index, which includes three aspects: thermal fatigue property, mechanical fatigue, crack growth rate and fracture toughness.
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