Cold work die steel is mainly used for stamping, blanking, forming, bending, cold extrusion, cold drawing, powder metallurgy dies, etc. It requires high hardness, high wear resistance and sufficient toughness. Generally divided into two categories: general type and special type. For example, the general-purpose cold work die steel in the United States usually includes four steel grades: 01, A2, D2, and D3. The comparison of the steel grades of general-purpose cold work alloy die steel in various countries is shown in Table 4. According to the Japanese JIS standard, the main types of cold work die steel that can be used are SK series, including SK series carbon tool steel, 8 SKD series alloy tool steels, and 9 SKHMO series high-speed steels, for a total of 24 steel grades. China’s GB/T1299-2000 alloy tool steel standard includes a total of 11 steel types, forming a relatively complete series. With the changes in processing technology, processed materials and demand for molds, the original basic series cannot meet the needs. Japanese steel mills and major European tool and die steel manufacturers have developed special-purpose cold work die steel, and gradually formed Respective cold work die steel series, the development of these cold work die steels is also the development direction of cold work die steel.
Low alloy air quenching cold work die steel
With the development of heat treatment technology, especially the wide application of vacuum quenching technology in the mold industry, in order to reduce quenching deformation, some low-alloy air-quenched micro-deformation steels have been developed at home and abroad. This type of steel requires good hardenability and heat treatment It has small deformation, good strength and toughness, and has certain wear resistance. Although standard high-alloy cold work die steel (such as D2, A2) has good hardenability, it has high alloy content and is expensive. Therefore, some low-alloy micro-deformation steels have been developed at home and abroad. This type of steel generally contains alloy elements Cr and Mn alloy elements to improve hardenability. The total content of alloy elements is generally <5%. It is suitable for manufacturing precision parts with small production batches. Complex molds. Representative steel grades include A6 from the United States, ACD37 from Hitachi Metals, G04 from Daido Special Steel, AKS3 from Aichi Steel, etc. Chinese GD steel, after quenching at 900°C and tempering at 200°C, can maintain a certain amount of retained austenite and has good strength, toughness and dimensional stability. It can be used to make cold stamping dies that are prone to chipping and fracture. High service life.
Flame quenched mold steel
In order to shorten the mold manufacturing cycle, simplify the heat treatment process, save energy and reduce the manufacturing cost of the mold. Japan has developed some special cold work die steels for flame quenching requirements. Typical ones include Aichi Steel’s SX105V (7CrSiMnMoV), SX4 (Cr8), Hitachi Metal’s HMD5, HMD1, Datong Special Steel Company’s G05 steel, etc. China has developed 7Cr7SiMnMoV. This type of steel can be used to heat the blade or other parts of the mold using an oxyacetylene spray gun or other heaters after the mold is processed and then air-cooled and quenched. Generally, it can be used directly after quenching. Due to its simple process, it is widely used in Japan. The representative steel type of this type of steel is 7CrSiMnMoV, which has good hardenability. When φ80mm steel is oil quenched, the hardness at a distance of 30mm from the surface can reach 60HRC. The difference in hardness between the core and the surface is 3HRC. When flame quenching, After preheating at 180~200°C and heating to 900-1000°C for quenching with a spray gun, the hardness can reach over 60HRC and a hardened layer over 1.5mm can be obtained.
High toughness, high wear resistance cold work die steel
In order to improve the toughness of cold work die steel and reduce the wear resistance of the steel, some major foreign mold steel production companies have successively developed a series of cold work die steels with both high toughness and high wear resistance. This type of steel generally contains about 1% carbon and 8% Cr. With the addition of Mo, V, Si and other alloying elements, its carbides are fine, evenly distributed, and its toughness is much higher than that of Cr12 type steel, while its wear resistance is similar. . Their hardness, flexural strength, fatigue strength and fracture toughness are high, and their anti-tempering stability is also higher than Crl2 type mold steel. They are suitable for high-speed punches and multi-station punches. The representative steel types of this type of steel are Japan’s DC53 with low V content and CRU-WEAR with high V content. DC53 is quenched at 1020-1040°C and the hardness can reach 62-63HRC after air cooling. It can be tempered at low temperature (180 ~200℃) and high temperature tempering (500~550℃), its toughness can be 1 times higher than D2, and its fatigue performance is 20% higher than D2; after CRU-WEAR forging and rolling, it is annealed and austenitized at 850-870℃. Less than 30℃/hour, cooled to 650℃ and released, the hardness can reach 225-255HB, the quenching temperature can be selected in the range of 1020~1120℃, the hardness can reach 63HRC, tempered at 480~570℃ according to the use conditions, with obvious secondary The hardening effect, wear resistance and toughness are better than D2.
Base steel（High-speed steel）
High-speed steel has been widely used abroad to manufacture high-performance, long-life cold work molds due to its excellent wear resistance and red hardness, such as Japan’s general standard high-speed steel SKH51 (W6Mo5Cr4V2). In order to adapt to the requirements of the mold, the toughness is often improved by reducing the quenching temperature, quenching hardness or reducing the carbon content in high-speed steel. Matrix steel is developed from high-speed steel, and its chemical composition is equivalent to the matrix composition of high-speed steel after quenching. Therefore, the number of residual carbides after quenching is small and evenly distributed, which greatly improves the toughness of the steel compared to high-speed steel. The United States and Japan studied base steels with grades VascoMA, VascoMatrix1 and MOD2 in the early 1970s. Recently, DRM1, DRM2, DRM3, etc. have been developed. Generally used for cold work molds that require higher toughness and better anti-tempering stability. China has also developed some base steels, such as 65Nb (65Cr4W3Mo2VNb), 65W8Cr4VTi, 65Cr5Mo3W2VSiTi and other steels. This type of steel has good strength and toughness and is widely used in cold extrusion, thick plate cold punching, thread rolling wheels, impression dies, cold heading dies, etc., and can be used as warm extrusion dies.
Powder metallurgy mold steel
LEDB-type high-alloy cold work die steel produced by conventional processes, especially large-section materials, has coarse eutectic carbides and uneven distribution, which seriously reduces the toughness, grindability and isotropy of the steel. In recent years, major foreign special steel companies that produce tool and die steel have concentrated on developing a series of powder metallurgy high-speed steel and high-alloy die steel, which has led to the rapid development of this type of steel. Using the powder metallurgy process, the atomized steel powder cools quickly and the carbides formed are fine and uniform, which significantly improves the toughness, grindability and isotropy of the mold material. Due to this special production process, the carbides are fine and uniform, and the machinability and grinding performance are improved, allowing higher carbon and vanadium content to be added to the steel, thus developing a series of new steel types. For example, Japan’s Datong’s DEX series (DEX40, DEX60, DEX80, etc.), Hitachi Metal’s HAP series, Fujikoshi’s FAX series, UDDEHOLM’s VANADIS series, France’s Erasteel’s ASP series, and the American CRUCIBLE company’s powder metallurgy tool and die steel are developing rapidly. Forming a series of powder metallurgy steels such as CPMlV, CPM3V, CPMlOV, CPM15V, etc., their wear resistance and toughness are significantly improved compared to tool and die steel manufactured by ordinary processes.
Post time: Apr-02-2024