Extending the service life of metal cutting tools and dies, improving labor productivity and machining quality of parts and components, and obtaining greater economic benefits for enterprises are important research topics in the machinery industry. In the 1970s, the ultra cold treatment technology initiated by the United States has greatly improved the service life of tools and moulds, obtained extensive use and achieved great social and economic benefits. In the 1980s, Chinese scientists and technicians also carried out experiments on similar principles. Our scientific research group has carried out systematic research on the principle of super cooling treatment of tools and moulds, design and manufacture of equipment, process methods, strengthening mechanism and Tribology of tools and dies. We have successively tried on dozens of cutting tools and cold and hot working dies in more than 20 domestic enterprises, which has improved the service life and achieved remarkable benefits.
Update the traditional manufacturing process of tools and moulds
(1) The limitation of the traditional hot working technology of tools and moulds, so far, the final performance of tools and moulds is given by quenching and tempering process. As we all know, the internal structure of steel is finally determined after quenching to room temperature, including: residual austenite volume; the size and quantity of carbon; the thickness of matrix structure, etc. Some retained austenite often remains in tool steel after quenching. Can martensitization be continued at lower temperature? Can carbides with larger dispersion be precipitated in tempering structure at lower temperature? Can microstructure of tempered structure appear at lower temperature? What changes will happen to tool and die properties under these changes?
With the development of low temperature technology, people pay attention to the feasibility of making the tool and die realize the above transformation under the temperature of – 160 ~ – 196 ℃. If it can be realized, the performance of the tool and die can be changed, and its strength, toughness and wear resistance can be further improved, and the service life of the tool and die will be greatly improved.
(2) Rationality of the new process of super cooling – 160 ~ – 180 ℃
In the 1970s, the United States first invented patents. After quenched and tempered tools and dies were treated at – 160 low temperature, it was found that most of retained austenite was martensitized, and carbide particles with high dispersion were precipitated in the martensite. With the microstructure of the matrix becoming finer, the wear resistance of the tools and dies was improved and the service life was prolonged. The authors have studied W18Cr4V high speed steel and Cr12MoV die steel, and confirmed the existence of the above transformation law. This transformation can not be explained by traditional metallurgic and phase transition theory. These transitions can not be carried out in the form of atomic diffusion. At – 160 ~ – 180 ℃, atoms lose the ability of diffusion, which can only be explained by the viewpoint of physical energy. At present, the mechanism of this transformation has not been studied clearly and needs to be explored.
After traditional cold and hot working, and then super cooling treatment, the microstructure of tool and die steel can be completely changed, a large number of high dispersion carbides precipitate, and the matrix is micronized, which improves the strength, toughness and wear resistance of the steel. The use potential of tools and moulds can be really tapped out.