(1) Metallurgical quality Metallurgical quality has a g […]
(1) Metallurgical quality Metallurgical quality has a great influence on the performance of die steel. Only with good metallurgical quality can the various properties of die steel be fully utilized. Metallurgical quality generally includes the following aspects: smelting quality, rolling and forging process performance, heat treatment and finishing performance, thermal conductivity and the degree of fine material and productization.
The general consumption of die steel is not large, and there are many varieties and specifications. In order to facilitate market procurement and material preparation, the versatility of materials should be considered. In addition to special requirements, a large number of general-purpose die steels should be used as much as possible. This is because the general-purpose die steel is applied technology More mature. Selecting high-quality, high-performance, high-precision mold steel concentrates and products, high-efficiency, high-speed, low-cost production of high-quality molds, has become the main development trend of mold manufacturing in industrial developed countries.
(2) Machinability The machinability of die steel includes: the cold workability of the mold, such as cutting, grinding, polishing, cold extrusion, cold drawing processability, and the hot workability includes thermoplasticity and hot working range temperature. Good workability is one of the important conditions for the selection of die steel.
(3) The quenching temperature range and quenching deformation require a wide quenching temperature range and smaller quenching deformation for die steel. (4) Hardenability and hardenability The hardenability depends on the carbon content of the steel, and the hardenability mainly depends on the chemical composition of the steel, the content of alloying elements and the microstructure before quenching. Most cold work molds that require high hardness have higher requirements for hardenability; while most hot work molds and plastic molds have relatively low hardness requirements, and often pay attention to hardenability; especially for some large cross-sectional deep For cavity molds, in order to obtain a good structure and uniform hardness in the core of the mold, mold steels with good hardenability are required.
(4) Oxidative decarburization of sensitive molds during the heating process will change the surface shape and performance of the mold, which will affect the hardness, wear resistance and service life of the mold, and cause early failure of the mold. Through special heat treatment processes such as vacuum heat treatment, oxidative decarburization can be avoided.
(5) Hardness Hardness is the main technical performance index of mold steel. In order to keep the shape and size of the mold stable and unchanged, the mold must have a sufficiently high hardness when it is in the role of high response side. Cold work die steel should generally maintain its hardness at around 60HRC at room temperature. Hot work die steel generally requires a hardness of 40~55HRc according to its working conditions. For the same steel grade in a certain range of hardness value, the hardness is proportional to the deformation resistance; but the plastic deformation resistance may be significantly different between steel grades with the same hardness value but different compositions and structures.
The hardness of steel is closely related to the chemical composition and metallographic structure. A wide range of hardness changes can be obtained through heat treatment. The hardness of die steel mainly depends on the carbon content or nitrogen content dissolved in martensite. For example, the new mold steels 012A1 and CG2 can be tempered at low temperature and the hardness is 60~62HRC respectively, and the hardness after high temperature tempering is 50~52HRC. Therefore, they can be used to make cold work or hot work molds with different hardness requirements.
(6) Red hardness hot work molds that work at high temperatures require the stability of their structure and performance to maintain a sufficiently high hardness. This performance is called red hardness. Red hardness is also the ability to maintain its hardness and structural stability, and resist softening. It is an important performance index of hot work die steel and part of heavy load cold work die steel. Carbon tool gongs and low-alloy tool steels can generally maintain this performance in the temperature range of 180~250~C, and chromium molybdenum hot work die steels generally maintain this performance in the temperature range of 550~600℃. The red hardness of steel mainly depends on the chemical composition of the steel and the heat treatment process adopted.
(7) Strength Strength refers to the ability of steel to resist deformation and fracture during service. For the mold, it is the ability of the entire forming surface or each part to resist tensile force, compression force, bending force, torsion force or comprehensive force during service.
The commonly used method to measure the strength of steel is to conduct a tensile test. For molds that work under compression, the compressive strength is often given to m. For die steel, especially cold work die steel with high carbon content, because of its poor plasticity, tensile strength is generally not used as a practical indicator. The stress state produced by the bending test is very similar to the state of Yue Yue force produced on the working surface of many molds, and it can relatively * reflect the influence of the material composition and organizational factors on the performance. The bending test can reflect a certain degree of plasticity even for extremely brittle materials.