With the development of science and technology in recent years, the application of technology in die and mould industry is also constantly improving. Die and mould enterprises have been focusing on ways to improve the metallurgical quality of die steel. After years of efforts and exploration, at present, the main metallurgical production departments at home and abroad are committed to improving the metallurgical quality of die steel in the following aspects:
1. For high-quality die steel, refining outside furnace, vacuum treatment, vacuum smelting, powder spraying, electroslag remelting and other processes are widely used at home and abroad to reduce the content of harmful elements, oxygen, hydrogen and inclusions in steel, and to fine-tune the chemical composition and pouring temperature. Electroslag remelting can also effectively improve the macrostructure and density of steel and improve the isotropy of die steel. 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. 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 steels with special requirements, powder high speed steel and powder high alloy die steel produced by powder metallurgy process can better improve the structure and properties of steel.
2. On the basis of ensuring certain forging ratio, upsetting-drawing forging and cross-rolling are adopted as far as possible to improve the isotropy of die materials. In order to reduce the processing allowance and improve the utilization rate of materials, 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 for heat treatment and finishing of forging and rolling materials to avoid oxidative decarbonization. Some plastic die steels and hot work die steels should be pre-hardened by metallurgical departments. In order to further improve the properties of steel, especially isotropy, fine and uniform distribution of carbides can be obtained by pre-refinement of structure of some high-requirement hot-working die materials by metallurgical departments, eliminating coarse carbides and chain carbides in steel. According to some reports abroad, some hot-working die steels have been produced by electroslag remelting, multi-direction forging (rolling) and fine structure treatment. The transverse impact toughness of these steels can be more than 90% of the longitudinal impact toughness. Many steelmakers have named commodity brands for the steels produced by this process, such as ISODISC of Bole Steel Works in Austria, ISOTROPY of Hitachi Metal Company in Japan and MICROFINE of Gaozhou Steel Company in Japan. Many metallurgical production departments in China are also working on this work. In addition, considering the metallurgical quality of all parts of steel, attention should be paid to making the main working face of the die (such as cavity or edge) close to the surface of steel; because in general, the surface of steel is cleaner than that of steel, and the center of steel is the area where the low-magnification defects of steel are concentrated; especially in large section ledeburite steel, the steel in the center of the die is common. The inhomogeneity of crystalline carbides is 2-3 orders higher than that of surface areas. In addition, the direction of the main load bearing of the die should be in accordance with the deformation direction of the steel, so as to reduce the negative influence of the anisotropy of the steel on the die.
4. Thermal conductivity is also one of the main performance indicators of die steel, especially some hot-working die steel and plastic die steel. Die steel with good thermal conductivity can quickly transmit heat generated in the process and heat transmitted from the workpiece, so as 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, the moulds which are hoped to be pressed will be rapidly cooled and demoulded to improve productivity. In order to solve this problem, some die materials with better thermal conductivity than iron and steel, such as high strength copper alloy and high strength aluminum alloy, are sometimes selected.
5. Precision materials and products shorten the manufacturing cycle of the die. When choosing the die steel, the die manufacturing department should choose the fine materials and products, such as the fine steel after peeling, cold drawing or grinding, and the module after roughing, finishing or even finishing quenching and tempering. Mould manufacturing department can use these fine materials and products to assemble and use with the standard die base after a little processing. It can not only effectively shorten the manufacturing cycle of the die and meet the needs of the use Department of the die, but also because the production of concentrates and products in the previous stage is produced in high-efficiency mass production in metallurgical plants, which can reduce production costs and improve the utilization rate of materials.
When choosing die steel reasonably, other factors should be considered. According to the use conditions and requirements of the die, besides the above factors, especially the main properties of the die steel must be compatible with the requirements of the use conditions of the die, the price and versatility of the selected die steel should also be considered. Generally, when the production of large batches of work pieces and small size of the die, the share of die steel in the cost of die manufacturing is very small. The price of die steel can not be considered as the main index, and the more advanced and applicable die steel can be selected as far as possible. For large or super-large moulds with simple shapes, because the cost of die steel will account for a larger share of the total cost of the moulds, the lower-priced die steel can be selected according to the batch production of workpieces, or the lower-priced die steel can be selected for the main body of the moulds, while the insert or surfacing method is used in the key working parts of the moulds, such as the cavity or the edge. Insert advanced die steel