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Research Progress of Heat Treatment of Mold Materials and Dies in China

In the fifties, China's steel used in molds was entirely based on foreign steel grades. In the 1960s, in order to save raw materials and improve the accuracy of blanks, there were rapid developments in the absence of cutting processes and precision forming technologies. In order to increase production efficiency, many high-efficiency press processing equipment were used, and forging hammers were gradually replaced by presses. The performance of the original die steel often cannot meet the high performance requirements of the service conditions, which affects the service life of the die and the popularization and application of the new equipment for pressure processing. At the end of the 1970s, the use of precision and large-scale engineering plastic products became increasingly widespread. The demand for plastic mold steel increased sharply, and new requirements were also put forward for the performance of plastic mold steel. At that time, there was no steel for plastic molds in China.

Since the 1960s, with the support of the relevant ministries and commissions of the country, Chinese scientists and technicians have developed a number of new tool steels in combination with the national conditions. Some of the new steels with excellent performance and relatively good process performance have been subjected to the manufacture and use of molds. welcome. During this period, some foreign steel grades were also introduced. Some of the steel grades passed trial production and achieved good results. For some cold working die steels and hot die steels with better results, the relevant departments also organized performance comparison test studies and proposed suggestions for selection and application. In order to meet the needs of high wear-resisting and long-life molds, at the end of the 1950s, China's cemented carbides had rapid development. At the same time, a variety of steel-bonded hard alloys were also developed and used as molds to achieve good results.

This article is divided into cold work die steel, hot work die steel, plastic die steel, hard alloy and steel cemented carbide, mold heat treatment, outlook and recommendations in six parts.

Cold working die steel

At present, cold die steels commonly used in China are still the old steel grades of low alloy tool steel CrWMn and high carbon and high chromium tool steel Cr12MoV and Cr12. CrWMn steel has appropriate hardenability and wear resistance, heat treatment deformation is small, but CrWMn steel after forging needs to strictly control the cooling rate, and the use of appropriate heat treatment, so that the carbides were uniformly fine granular, distributed on the substrate, Otherwise it is easy to form network carbides, resulting in mold chipping and cracking in use. High-carbon high-chromium tool steel has high wear resistance, but its carbide segregation is more serious, leading to reduced directionality and toughness of deformation. Through repeated dialing, the degree of segregation can be improved to some extent.

In 1981, China introduced the internationally used high-carbon high-chromium tool steel D2 (Cr12Mo1V1). Compared with Cr12MoV steel, the carbide segregation of D2 steel is slightly improved compared with Cr12MoV, and the strength and toughness are slightly improved. The service life of D2 steel mold is also improved to varying degrees. High-speed steels (mainly W6Mo5Cr4V2 and W18Cr4V) have higher wear resistance and strength and are often used to make molds, but their toughness cannot meet the needs of molds with large and large impact loads.

In order to improve the toughness of these steels, China has developed new cold die steels such as:

1Low alloy cold working die steel

The main characteristics of this type of steel are good processability, low quenching temperature, small heat treatment distortion, good toughness, and appropriate wear resistance. Such as GD (6CrMnNiMoVSi), 7CrSiMnMoV (abbreviated CH), DS steel. GD steel is used to make cold stamping die with easy chipping and fracture, which has a high service life. The composition of CH steel is the same as that of Japan's SX105V steel. It is a flame-hardened steel and is often used to make mold parts for production lines such as automobiles. When the flame is quenched, the cutting edge of the mold edge is heated and hardened layer has a high toughness. The substrate is cushioned so that the mold has a high service life. DS steel is an impact cold working tool steel, its impact toughness is significantly better than the commonly used high toughness tool steel 6CrW2Si blade.

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Shandong Jining Qingfeng Machinery Hardware Co.,Ltd

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Tel: +86-537-3281595

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E-mail: info@qfmh.com

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