With the development of science and technology in recent years, the technology application of mould industry is also rising. Mold enterprises have been focusing on improving the metallurgical quality of die steels. After years of hard work and exploration, at present, the main metallurgical production departments at home and abroad are committed to improving the metallurgical quality of die steel mainly in the following aspects:
1. The smelting quality of high-quality die steel is widely used at home and abroad, such as furnace refining, vacuum treatment, vacuum smelting, powder spraying treatment, electroslag remelting and so on, to reduce the harmful elements, oxygen, hydrogen and inclusions in the steel, and to fine-tune the chemical composition and pouring temperature. Through ESR, the microstructure and density of the steel can be improved effectively, and the isotropy of the die steel can be improved. The tests in some domestic factories show that the transverse impact toughness of 4Cr5MoSiV1 steel produced by electric arc furnace is only 31% of the longitudinal impact toughness, and the transverse impact toughness of 4Cr5MoSiV1 steel produced by electroslag remelting is 70% of the longitudinal impact toughness, which can be increased by more than one time. For die steel with special requirements, powder high speed steel and powder high alloy die steel produced by powder metallurgy process can better improve the microstructure and properties of the steel.
2. On the basis of ensuring a certain forging ratio, forging and rolling processes of upsetting-drawing-length and cross rolling are adopted as far as possible to improve the isotropy of die materials. In order to reduce machining allowance and improve material utilization, precision forging machine, fast forging hydraulic press and high precision continuous rolling mill are widely used to produce high precision steel to meet the needs of die manufacturing.
3. Controllable atmosphere or vacuum heat treatment should be adopted in heat treatment and finishing forging and rolling heat treatment to avoid oxidative decarbonization. Some plastic die steels and hot-working die steels should be pre-hardened by metallurgical departments. Some high demand hot working die materials should be refined by Metallurgical Department in advance to eliminate coarse carbides and chain-like carbides in the steel and obtain fine and uniform carbide structure to further improve the properties of steel, especially isotropy. According to some reports abroad, some hot-working die steels have been produced by electroslag remelting-multidirectional forging (rolling) and microstructure refinement, and their transverse impact toughness can be more than 90% of the longitudinal impact toughness. Many steelmakers named the steel produced by this process as ISODISC of Berle Steel Works in Austria, ISOTROPY of Hitachi Metal Company in Japan and MICROFINE of Kaozhobo Steel Company in Japan. Many metallurgical production departments in China are also devoted to this work. In addition, considering the metallurgical quality of each part of the steel, attention should be paid to the main working surface (such as the cavity or edge) of the mold to choose the position close to the surface of the steel, because in general, the surface of the steel is the cleaner part of the steel, and the center of the steel is the area where the defects of the steel are concentrated. The unevenness of eutectic carbide in the center part of the steel is 2-3 grade higher than that in the surface part, especially in the large cross-section ledeburite steel. In addition, the direction of the main bearing load of the die can be chosen in accordance with the deformation direction of the steel, so as to reduce the adverse effect of the anisotropy of the steel on the die.4. Thermal conductivity is also one of the main performance indexes of mold steel, especially some hot-working mold steel and plastic mold steel. Die steel with good thermal conductivity can quickly transfer heat generated in processing and heat transferred from the workpiece to avoid overheating on the working surface of the die and improve the working conditions of the die. For some thermoplastic moulds and some die-casting moulds, in order to speed up the production rhythm and increase the productivity, some die materials with better thermal conductivity than steel, such as high strength copper alloy and high strength aluminum alloy, are sometimes selected.
5. Fine materials and products have shortened the mold manufacturing cycle. When choosing mold steels, mold manufacturing departments should choose fine materials and products, such as fine steels processed by peeling, cold drawing or grinding, and even hardening and tempering modules processed roughly, finely or even finely. The mold manufacturing department can use these fine materials and products for a little processing to be assembled with standard mold bases. It can effectively shorten the mold manufacturing cycle to meet the needs of the mold use department, and because the production of concentrate and products in the previous stage is high-efficiency mass production in metallurgical plants, it can reduce production costs and improve material utilization.
When choosing die steel reasonably, other factors should be considered. According to the service conditions and requirements of die steel, all the above factors must be considered, especially the main properties of die steel must be compatible with the service conditions of die steel, and the price and pass of die steel should also be considered. Use sex. In general, when the production of large batches of work pieces, mold size is small, mold steel in the mold manufacturing costs accounted for a very small share, the price of mold steel can not be considered as a major indicator, you can try to choose more advanced applicable mold steel. For large or super-large molds with simple shapes, the cost of mold steel will account for a larger share of the total cost of the mold, so the lower price mold steel can be selected according to the batch production of the workpiece, or the lower price mold steel can be used for the mold itself, while the key parts of the mold, such as Inserting or surfacing high-grade die steel at the cavity or edge can improve the service life of the die and reduce the material cost. The versatility of mould steels is also a factor that must be considered when selecting die steels. Die steel is generally used in a small amount, a lot of varieties, specifications, in order to facilitate the market procurement and material preparation, should consider the versatility of materials. In addition to special requirements, as far as possible to use a large number of production of general mold steel, general mold steel technology is more mature, accumulated production process and use experience more, performance data is more complete, convenient for reference in the design and manufacturing process. In addition, the general die steel can be selected to facilitate procurement, material preparation and material management.
