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Vacuum Heat Treating Cold Work Tooling

Cr12 mold steel is a high-carbon, high-chromium cold work mold steel with good hardenability and wear resistance. However, due to its high carbon content, it is easy to form uneven eutectic carbides, so its impact toughness is poor. Easily brittle. After the vacuum quenching process, Cr12 mold steel usually contains a large amount of dense residual austenite and network eutectic carbides. However, a large number of common carbides in steel are unevenly distributed, and severe segregation of carbides will reduce the strength and toughness of the mold, causing the mold blade to collapse, fracture or collapse. During the solidification process of Cr12 mold steel, a large number of coarse eutectic carbides distributed in a continuous network are easily formed at the grain boundaries. The effects of different matrix strengthening and toughening vacuum heat treatment processes on the microstructure and mechanical properties of Cr12Mo1V1 cold work die steel were studied. It was found that the cyclic phase transformation multiple austenitization process can effectively improve Cr12Mo1V1 steel by refining the grain size and carbides. The strength and toughness, cycle number and austenitization temperature have a significant impact on its mechanical properties. A study on the structure and properties of Cr12 mold steel under the secondary hardening process (vacuum quenching + high temperature tempering) found that the secondary hardening uses a higher quenching temperature to obtain austenite with high alloying degree, which is beneficial to improving the tempering softening resistance of martensite. It plays an important role in the precipitation strengthening of alloy carbides in martensite and retained austenite and the secondary quenching strengthening of retained austenite. When vacuum quenched at 1050°C, the hardening peak of Cr12 steel is between 520 and 550°C.

Taking Cr12 cold work die steel treated with different vacuum heat treatment processes as the main research material, the physical phase, metallographic phase, hardness and impact toughness were analyzed to obtain the effects of different heat treatment processes on the microstructure and mechanical properties of Cr12 die steel. Impact, the following main conclusions are drawn:

1) The vacuum heat treatment process has a great influence on the microstructure, hardness and impact toughness of Cr12 cold work die steel. The sample after vacuum quenching at 1020℃ has a maximum hardness value of 63.6 HRC, after vacuum quenching at 950℃ and vacuum tempering at 520℃ The sample has the maximum impact energy of 25.10J.
2) After vacuum annealing, the microstructure of Cr12 is uniformly distributed pearlite and granular carbides. After vacuum annealing and vacuum quenching, the size of the carbides becomes smaller.
3) At the same quenching temperature, as the tempering effect and tempering temperature increase, the hardness of Cr12 mold steel will decrease.
4) The quenching effect, tempering effect, and increase in tempering temperature (210~520 ℃) can all improve the impact toughness of Cr12.
5) After a comparative study of 7 samples, it was found that the heat treatment process of sample 4 is the optimal process. The specific plan is: 860°C vacuum annealing + 980°C vacuum quenching + 520°C vacuum tempering.
6) In the metallographic structure of the best process, there are a large number of fine grained tempered sorbite, in which the carbon and alloying elements will re-form carbides, disperse and precipitate evenly, with high strength and toughness.