Characteristics of various cold deformed die steels and the corresponding processing technology

Update:07-05-2021
Summary:

Low-hardenability cold-deformed die steels are mainly c […]

Low-hardenability cold-deformed die steels are mainly carbon tool steels, especially high-carbon complex steels GCr15 and 9Cr2Mo. Among them, GCr15 bearing steel and 9Cr2Mo are used to make various forming wheels and cold rolls. GCr15 steel has good wear resistance, but poor hardenability and large quenching deformation. As a small cold roll (φ≤200m/m), it can be heated as a whole or at a high temperature of 900-950℃ for rapid heating, quenching and cooling with brine→oil, Control the cooling time of the workpiece in salt water and then temper at 200-220℃. The surface hardness of the roll is controlled between Rc60-62, which can obtain a higher service life. If the hardness Rc≥62 is above, it is easy to cause the surface of the roll to be rolled during rolling. Surface spalling occurs. Various forming wheels made with GCr15 can be quenched in alkaline bath or quenched with dinitrate and trinitrate solution. The cooling time in the solution is controlled, and air cooling or oil cooling can be taken out to obtain high surface hardness. The effect of small deformation.

With the development of the processing industry and the massive development of the material restructuring industry, the corresponding high-speed multi-roll rolling steel 9Cr2Mo and German roll steel 86CrMoV7 must be based on industrial methods.

New breakthroughs must be made in strengthening and toughening treatment, and new breakthroughs must be made in the use of new roll steel. At present, D2 (Cr12MOv; Cr12Movco) and 5H12 (5Cr5MovSi) are used in the work rolls and transmission rolls of high-speed rolling mills. The material of the work roll should be selected from the viewpoint of contact extrusion fatigue stress and friction and wear, and the material of the transmission roll should be selected with the ability to resist accidents caused by breakage.

Low-deformation die steel

1) Mn-Cr-W series, which is a representative steel with excellent comprehensive performance commonly used in various countries, with CrMn as the representative steel. This steel has the characteristics of small heat treatment deformation, high wear resistance, and high hardenability and toughness. The mold made of CrWMn steel, such as using a reasonable heat treatment process, well controlled and adjusted, can completely replace the blanking mold made of Cr12 commonly used in the factory by reducing the thermal stress and structural stress caused by quenching, and reducing deformation.

2) Mn series, 9Mn2V is a substitute steel for CrWMn, 9CrSi, etc. in my country, which can be used to make cold punching dies, blanking dies, scissors, and bending dies.

3) The SiMnMo series graphite steel is characterized by high Si content. Under the action of the strong graphitization element Si, part of the carbon is in a graphitized state, which makes the steel self-lubricating and has high seizure resistance. Machinability and wear resistance, heat treatment deformation is small, and the size is stable. SiMnMo steel is used to make bending, stretching and shaping dies with strict surface quality requirements, which can significantly improve the quality of the stamping parts.

High wear-resistant micro-deformation cold-deformed die steel is represented by Cr12Mov type, which is the most widely used high-performance cold-deformed die steel at home and abroad. Cr12Mov is an improved Cr12 steel. The carbon content is too high, causing serious unevenness of large carbides. Cr12Mov steel is characterized by high wear resistance and hardenability. It is the main material of micro-deformed cold blanking die and cold heading die. At present, Cr12 steel is still widely used in general factories. The modified material has high hardness and high wear resistance. It has high hardness, high hardenability, especially small deformation after heat treatment, and good filing performance during pliers processing. It is still widely used in punching forming dies, drawing dies and other molds. However, the Cr12 material has serious uneven carbides and the formation of large blocks of carbides, which become the root cause of premature failure of the mold caused by collapse, cracking, and fracture during use. According to the author's practical experience, if some blanking punch dies use a mixed structure of bainite and paraffinic carbide, the service life will be significantly improved.

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