Wednesday, April 8, 2020

Several ways to improve the metallurgical quality of die steel in China

With the development of science and technology in recent years, the application of technology in the mold industry is constantly improving. Mold companies have been focusing on the research of ways to improve the metallurgical quality of mold steel. After years of hard work and exploration, at present, the main metallurgical production departments at home and abroad are committed to improving the quality of mold steel metallurgy mainly in the following aspects:
Several ways to improve the metallurgical quality of die steel in China

1. Smelting quality For high-quality mold steels, domestic and foreign extensive use of external refining, vacuum treatment, vacuum smelting, powder spraying, electroslag remelting and other processes to reduce harmful elements, oxygen, hydrogen and inclusions in steel Content, fine-tuning the chemical composition and pouring temperature. Electroslag remelting can also effectively improve the low-power structure and density of steel, and improve the isotropy of mold steel. Tests by some domestic manufacturers have shown that the transverse impact toughness value of 4Cr5MoSiV1 steel produced by electric arc furnace is only 31% of the longitudinal direction, and the transverse impact toughness value of 4Cr5MoSiV1 steel after electroslag remelting can be equivalent to 70% of the longitudinal direction Increase more than 1 times. For mold steel with special requirements, powder high-speed steel and powder high-alloy mold steel produced by powder metallurgy process can better improve the structure and performance of steel.

2. On the basis of guaranteeing a certain forging ratio, the forging rolling process adopts upsetting and drawing long forging and cross rolling processes as much as possible to improve the isotropy of the mold material. In order to reduce the processing margin and improve the utilization rate of materials, precision forging machines, fast forging hydraulic presses, and high-precision continuous rolling machines are widely used to provide high-precision steel products to meet the needs of mold manufacturing.

3. Heat treatment and heat treatment of forged and rolled materials should use controlled atmosphere or vacuum heat treatment to avoid oxidative decarburization. Some plastic mold steels and hot work mold steels should be pre-hardened by the metallurgy department. For some high-demand hot work die materials, the metallurgical department should pre-organize and refine the structure to eliminate coarse carbides and chain-like carbides in the steel to obtain a fine and uniformly distributed carbide structure to further improve the steel Various properties, especially isotropy. According to some foreign reports, some hot work die steels are electroslag remelted—multidirectional forging (rolling) —structure refinement treatment to produce high quality and isotropic die steels, the transverse impact toughness value of which can be comparable More than 90% of the vertical. Many steel mills have named trade names for the steel produced by this process, such as ISODISC of Bole Steel in Austria; ISOTROPY of Hitachi Metals in Japan; MICROFINE of Japan High Frequency Steel Co., Ltd., etc. this work. In addition, considering the metallurgical quality of each part of the steel, when manufacturing the mold, care should be taken to select the main working surface of the mold (such as the cavity or blade) to be close to the surface of the steel; because the surface of the steel is generally a clean part of the steel The core of the steel is the area where the low-magnification defects of the steel are concentrated; especially in the large-section Leidenite steel, the eutectic carbide unevenness of the steel in the central part will be 2 to 3 higher than the surface part. Also, the main load bearing direction of the mold can be selected to be consistent with the deformation direction of the steel to reduce the adverse effect of the anisotropy of the steel on the mold.

4. Thermal conductivity Thermal conductivity is also one of the main performance indicators of mold steel, especially some hot work mold steel and plastic mold steel. The mold steel with good thermal conductivity can quickly transfer the heat generated during processing and the heat transferred from the processed workpiece to avoid overheating on the working surface of the mold and improve the working conditions of the mold. For some thermoplastic forming molds and some die casting molds, in order to speed up the production rhythm, it is hoped that the pressed workpieces will be quickly cooled and demolded to improve productivity. In order to solve this problem, sometimes some mold materials with better thermal conductivity than steel are used, such as High strength copper alloy, high strength aluminum alloy, etc.

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