High alloy die steel has high chromium and medium chromium tool steel, high-speed steel, matrix steel, etc.. These steels contain more alloying elements, with good hardenability, high wear resistance and quenching deformation and other characteristics, widely used for bearing large loads, large production batch, high wear resistance requirements and complex shape of the mold. (1) High-carbon high-chromium steel The composition of such steel is characterized by high chromium amount, high carbon amount, is the most widely used in cold work die steel, the largest number. Representative steel grades are Crl2, Crl2MoV, Crl2MolVl (D2), Crl2W, etc.. This type of steel forging is usually used after spheroidal annealing treatment, annealing hardness of 207 ~ 255 HB. commonly used quenching process for. (1) lower temperature quenching Crl2 steel heated to 960 ~ 980 ℃, oil cooling, quenching hardness of 62HRC or more. For Crl2MoV steel, quenching temperature of 1020 ~ 1050 ℃, oil cooling, quenched hardness of 62HRC or more. Using this method can make the steel to obtain high hardness, high wear resistance and high precision size, used to make cold stamping dies. (2) higher temperature quenching and multiple high-temperature tempering for Crl2 steel, heated to 1050 ~ 1100 ℃, oil-cooled, quenched hardness of 42 ~ 50 HRC. for Crl2MoV steel, quenching temperature of 1100 ~ 1150 ℃, oil-cooled, quenched hardness of 42 ~ 50 HRC. higher temperature quenching plus multiple high-temperature tempering, you can make the steel to obtain high red hardness and wear resistance, used to making molds that work at high temperatures. Crl2 type steel should be tempered promptly after quenching, and the tempering temperature can be determined according to the required hardness. For cold stamping dies requiring high hardness, the tempering temperature is between 150~170℃, and the hardness after tempering is above 60HRC. For cold stamping dies requiring high strength, hardness and certain toughness, the tempering temperature is 250~270℃, and the hardness is 58~60HRC after tempering. for cold stamping dies requiring high impact toughness and certain hardness, the tempering temperature can be increased to about 450℃, and the hardness is 55~58HRC after tempering, Crl2 steel should avoid the tempering brittle zone of 275~375℃. (2)High carbon medium chromium steel Mainly Cr6WV steel, Cr4W2MoV steel, Cr6MolV steel. (3)High-speed steel Copper or aluminum parts when cold extrusion, the die is not too violent forces, you can generally use Crl2 type die steel. But the ferrous metal cold extrusion, the force is intense, the working conditions are very harsh, the die put forward higher requirements. Therefore, it is necessary to use more advanced die steel, such as high-speed steel to manufacture dies. High-speed steel heat treatment with high hardness and compressive strength, good wear resistance, can meet the more demanding cold extrusion conditions. Commonly used cold extrusion high-speed steel are W6 Mo5 Cr4 V2 steel, Wl8Cr4V steel, 6W6Mo5Cr4V steel. Wl8Cr4V steel has good red hardness, at 600 ℃ still has a high hardness and good toughness, but its carbide is coarse, strength and toughness with size increases and decreases. W6Mo5Cr4V2 steel has good red hardness and toughness, after quenching the surface hardness can reach 64 ~ 66 HRC, is a Mo low W high-speed steel, its carbide particles are relatively small, distributed More uniform, strength and toughness than Wl8Cr4V steel is good. Most of the HSS made of cold extrusion (including cold heading) die, can be quenched at a temperature slightly lower than the quenching temperature of HSS tools, such as Wl8Cr4V steel with 1240 ~ 1250 ℃, W6 Mo5 Cr4 V2 steel with 1180 ~ 1200 ℃, and then tempered at 560 ℃ for three times. For some slender or thin-walled mold, requiring high toughness, it can further reduce the quenching temperature to improve its service life. However, after low-temperature quenching, high-speed steel compressive strength is reduced, can not be used for high-load molds, but also make wear resistance reduced. Table 9.1.3 commonly used cold extrusion high-speed steel hardness and impact toughness after quenching and tempering heat treatment at different temperatures.  

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