Ultra cold treatment process and properties of tools and dies
(1) After quenching and tempering, the ultra cold treatment process tools and dies are cooled to – 160 ~ – 180 ℃ and cold holding time Tmin = k * D. the empirical formula D is the effective diameter or thickness of workpiece mm * k = 0.8 ~ 1.0min/mm, the upper limit is square workpiece, and the lower limit is circular workpiece ~ reheating.
(2) The change of properties of W18Cr4V and Cr12MoV steel after super cooling treatment.
The red hardness (thermal hardness) of W18Cr4V Steel after super cooling treatment is increased to a certain extent, which can increase the cutting speed and improve the machining efficiency. In addition, the surface roughness of tool and die is reduced after grinding. Because of the change of the internal microstructure of the tool after super cooling treatment, the strength and toughness of the tool are improved, resulting in the decrease of the surface roughness of the tool after grinding. On the contrary, there are more retained austenite in the interior with low strength and easy fatigue spalling under the action of periodic stress, resulting in carbide particles hanging in the microstructure, rapidly separating from the matrix, resulting in spalling pits and forming a surface with larger roughness. The real contact area between the tool and the workpiece is only carried out on a very small surface area. The relative sliding between the tool with a certain surface roughness and the workpiece occurs in the so-called boundary lubrication area under the boundary lubrication state. When the load is applied, enough surface area produces metal plastic flow to bear the load. Due to the continuous sliding and plastic deformation, the lubricating film breaks and the metal adheres. The smaller the surface roughness, the more conducive to expand the boundary lubrication, reduce the dry friction area, reduce the friction coefficient, reduce the generation and effect of friction heat, maintain a good lubrication state, and improve the wear resistance of the tool.
Production application examples and conclusions
In recent years, in more than 20 enterprises, the author has applied this technology to dozens of kinds of cutting tools, such as drill bits, reamers, various milling cutters, boring cutters, spline broaches, circular hole expanding cutters, machine taps, gear cutters, automobile sample cutters, thread rolling dies, disc rolling shears, etc., and the service life is increased by 1.0 times to 3.8 times. There are M12 nut cold upsetting die and other cold and hot stamping dies. The service life is increased by 1.0 ~ 6.0 times.
1. As a follow-up process in the process of tool and die manufacturing, super cooling treatment improves the manufacturing process. Further tapping the potential of materials can save a lot of Limited earth resources for the society, and the social and economic benefits are very significant.
2. The modification mechanism of ultra cold treatment of tools and dies has not been fully understood by human beings, and it needs to be further explored and studied to continuously improve the manufacturing process of tools and dies.
3. Theory and practice have proved that this new technology can be used not only for carbon tool steel and alloy tool steel, but also for cutting tools and dies made of cemented carbide, and the service life has been greatly improved, which is worthy of popularization and application.