The main performance requirements for cold working die materials are: good wear resistance, sufficient strength and toughness, high fatigue life, good scratch resistance and bite resistance, and good process performance.
Before 1990s, the commonly used cold-working die steels in China are: carbon tool steel T 1OA, alloy tool steel 9SiCr, 9Mn2V, CrWMn, Cr6WV, Cr 12, Cr 12MoV, 5crw2si; ; High speed tool steel w18cr4v; Bearing steel gcr15; ; Spring steel 60Si2Mn, carburized steel 20Cr,12crni3a; ; Stainless steel 3Crl3, etc. The most commonly used ones are C r 12, Cr 12MoV, T 10A, CrWMn, 9SiCr, 9Mn2V, GCr 15, 60Si2Mn, W 18Cr4V.
In order to meet the production requirements, a series of new cold-working die steels have been developed in China.
1, low alloy cold working die steel
Among the low-alloy cold-working die steels developed in China, 7CrSiMnMoV (code name CH),
6crmnmimovsi (code GD), 6CrMnNiMoVWSi(DS), CrNiWMoV, etc. These steels have good hardenability, low quenching temperature, small heat treatment deformation, low price and good combination of strength and toughness, and are suitable for manufacturing molds with complex precision.
7CrSiMnMoV, code name CH, can be quenched at 820 ~ 1000℃, and its hardness can be higher than HRC60. It is an air-quenched micro-deformation steel, which can be hardened by flame heating and air cooling. Although the wear resistance of this steel is worse than Cr 12MoV, it is better than 9Mn2V and T 10A. Bending strength, compressive strength and impact toughness are better than Cr 12MoV and 9Mn2V. The deformation after heat treatment is equivalent to that of Cr 12MoV, Cr2Mn2SiWMoV, Cr4W2MoV and other commonly used steels. CH steel has good strength and toughness and good manufacturability, and can be used to replace cold-working dies with high requirements on strength and toughness, such as T 10A, 9Mn2V, CrWMn, GCr 15, Cr 12MoV, such as punching punches and trimming and blanking dies for medium and thin steel plates (2 ~ 5 mm thick). Because this steel can be hardened by flame heating and air cooling, it is also used to manufacture some automobile molds that need surface flame quenching. 6 crmnnimovski, code GD, increases Ni by about 0.85% compared with CH steel, further strengthening and toughening the matrix. The steel has a wide quenching temperature range, good hardenability, good strength and toughness, and can also be quenched by flame heating and air cooling. When used to make cold die tools that are easy to collapse, the life of the die is longer.
2, high toughness wear-resistant steel
Cr 12 series cold-working die steel is widely used, which has good hardenability and wear resistance, but its carbide segregation is serious, its toughness is poor, and its abnormal deformation is large after quenching. In order to make up for the performance defects of this kind of steel, some high-strength and toughness wear-resistant steels have been developed in China, such as 7 Cr7Mo2V2Si (code name L D), 8WMOV3Si (code name ER5), 9 Cr6W3Mo2V2 (code name GM), 80Cr7Mo3W2V and so on. Compared with Cr 12 and Cr 12MoV, this kind of steel has lower carbon and chromium content, which improves the heterogeneity and toughness of carbide. Properly increase the content of alloying elements such as W, Mo and V to enhance the secondary hardening ability and improve the wear resistance. Therefore, this kind of steel not only has good strength and toughness, but also has excellent wear resistance and comprehensive properties, and is mainly used to manufacture all kinds of cold working dies that bear large stress and require high strength, toughness and wear resistance.
7Cr7Mo2V2Si, code-named LD, was originally developed for cold heading dies. Its carbon content is lower than the' equilibrium carbon' law recommended by G. Steven, which makes the steel have high hardness and good toughness; Adding Cr, Mo and V elements is beneficial to secondary hardening and ensures high hardness, high strength and good wear resistance of steel. A certain amount of Si is added to strengthen the matrix and improve the tempering stability. The common heat treatment process of LD steel is1100 ~1150℃ quenching and tempering at 530 ~ 570℃, and the hardness after tempering is HRC 57 ~ 63. After quenching at 1 100℃, the microstructure is fine needle martensite, with ten residual austenite and ten residual carbides, and the grain size is 10.5. L 100℃ quenching +000℃ tempering, the microstructure is tempered martensite+residual carbide. LD steel has been widely used to manufacture cold-working dies which bear great impact and bending stress and require wear resistance, such as cold forging, cold stamping, cold pressing and cold bending.
Cr8MoWV3Si, code name ER5, has high strength and toughness and outstanding wear resistance. The special carbide dispersed during tempering of this steel is an important reason why ER5 has higher strength, toughness and wear resistance than Crl2 steel. ER5 steel is suitable for manufacturing cold working dies such as precision cold stamping and heavy cold stamping with high impact resistance and high impact speed.
9Cr6W3Mo2V2, code-named GM, is also a high wear-resistant cold-working die steel with the main purpose of improving wear resistance. The steel has the best secondary hardening ability and wear resistance by reasonably proportioning carbide-forming elements such as Cr, W, Mo and V, and distributing carbon according to the law of carbon balance, while maintaining high toughness and good cold and hot workability. It is suitable for manufacturing precision and high wear-resistant cold working dies such as stamping, cold extrusion, cold forging, cold shearing, high-strength bolts and rollers.