Introduction to the Development of Cold Work Die Steel

Early cold-formed molds accounted for the highest output in the mold manufacturing industry. In recent years, due to the rapid development of plastic molds, the output of cold-formed molds has dropped to second place in many developed countries, but still accounts for about 1/3 of the total mold output. The largest user of molds, the automotive industry, saw a decline in car sales in 2018, but demand is expected to remain at a high level in the future.

Cold-formed molds are widely used in the automotive industry, and with the continuous increase in new car models, their introduction is becoming faster and faster. This puts higher and more demanding requirements on the performance, quality, and variety of cold-formed molds, making the development of cold work die steels particularly important.

Development status of cold work die steels

Cold work die steels are mainly used for stamping, blanking, forming, bending, cold extrusion, cold drawing, powder metallurgy molds, etc. They require high hardness, wear resistance, and sufficient toughness. They are generally divided into two categories: general-purpose and special-purpose. For example, the general-purpose cold work die steels in the United States usually include 01, A2, D2, D3, and the steel number comparison of general-purpose cold-formed alloy mold steels in various countries is shown in Table 4. The main cold work die steels that can be used in Japanese JIS standards are the SK series, which include SK series carbon tool steels, alloy tool steelsSKD series 8 steels, SKHMO series high-speed steels 9 steels, a total of 24 steel grades.

With changes in processing technology, materials being processed, and demand for molds, the original basic series cannot meet the needs of the market. Japanese steel mills and major European mold steel producers have developed special-purpose cold work die steels and gradually formed their own series of cold work die steels. The development of these cold work die steels is also the direction of the development of cold work die steels.

Classification of cold work die steels

Cold work tool steel can be broadly divided into: low alloy cold work tool steel, medium alloy cold work tool steel, high alloy cold work tool steel and in recent years the rapid development of the latest standard new cold work tool steel.

Low-alloy cold work tool steel, represented by Cr WMn, has a high cost performance, so it is commonly used. But the main defect is the carbide segregation is serious, hot processing is easy to form a network of carbide, toughness is poor, seriously affect the life of the mold.

Medium alloy cold work die steel, Cr5Mo1V (A2) as a representative, A2 steel and D2 steel compared to reduce the content of carbon chromium, carbide uniformity improved, its wear resistance is slightly lower and higher toughness, high hardenability, can be air-cooled quenching, heat treatment deformation is small, used in the manufacture of high wear resistance, but also to withstand a certain impact load of cold work die.

High alloy cold work die steel, to Cr12Mo1V1 (D2) as the representative, the traditional Cr12 series cold work die steel such as Cr12MoV, Cr12Mo1V1 is the most commonly used cold work die steel in China at the end of the 20th century, heat treatment deformation is small, high wear resistance, high load-bearing capacity, has long been widely used in China's large and medium-sized cold work die.

However, as Lainitic steel, there is a large amount of excess eutectic carbide in its solidification organization, and serious segregation, although good wear resistance, but its toughness is poor, and often caused by carbide segregation after heat treatment fracture.

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