1. Strengthening mechanism of blanking die steel structure
In the blanking of the plate, due to the larger unit load (≥200MPa), the stress state of the blanked material is more complicated, and the heat temperature of the cutting edge of the die is higher (200°C) during the separation process, so the die is durable In most cases, the requirements for sheet metal stamping cannot be met.
In order to improve the durability of the punching die, three new types of die steels have been developed. It is to increase the durability of the stamping die by increasing the number of carbide phases in the die steel and changing its type. However, due to the increased carbide inhomogeneity, the mechanical properties of the die steel may deteriorate at this time. Therefore, it is necessary to add certain active elements simultaneously in the die steel. For example, vanadium and molybdenum may improve the distribution of the elements in the structure. , And can improve the physical and mechanical properties of the mold steel and performance. Molybdenum can partially replace the chromium atoms in the carbides, while vanadium can reduce the total amount of cementite in the alloy, which can significantly reduce the chemical composition and carbide inhomogeneity in the microvolume of the mold steel.
The formation of carbide M7C3 is related to a significant amount of chromium (up to 8% to 9%), so that the effect of alloying is often reduced. To eliminate this phenomenon, 0.4% to 0.8% Ti must be added in the steel, so that the carbon content in the α solid solution can be reduced, the martensite transformation point temperature can be increased, and the retained austenite in the microstructure can be reduced. Quantity (up to 7% to 10%). In addition, reducing the amount of carbon can promote better toughness of the parent, and can lead to increased relaxation within the stress source, which is very important for the working process of die steel.
Based on the reasonable alloying of carbide-forming active elements (Mo, V, Ti, etc.), an effective mechanism for strengthening the structure was developed. It can ensure the improvement of the overall performance of the die steel, partially reduce the chemical composition inhomogeneity of the carbides in the steel, and can eliminate or make it difficult to transfer the chromium atoms from the solid solution into the carbides.
The insoluble carbides of the above elements are not dissolved at the quenching temperature t quenching = 1040 to 1080°C, which ensures that the austenite maintains finer grains and thus has a higher level of brittle fracture resistance and bending strength. In addition, increasing the volume fraction of the most dispersed MC type carbides during the r→α transformation can increase the number of martensite nucleation centers, thereby also promoting the increase of the martensitic transformation temperature M and M and the fineness of the grains. It is difficult for the metal of the cutting edge to flow when the mold is in use, thereby improving the wear resistance of the mold.
The starting temperature of the martensitic transformation M and the end temperature M end with the mold steel composition and quenching temperature curve
2. Chemical composition of blanking die steel
It has been determined that in mold steels containing 6% to 12% Cr, the active element, especially Ti (up to 0.7%), is optimally combined with Mn, Cr, and Mo, which can promote the formation of higher-quality microstructures and can improve The strength of die steel (σb≥3400MPa～3600MPa), wear resistance and heat resistance (t≥450～500°C). Containing 0.2% to 0.9% molybdenum can inhibit the precipitation of dispersed brittle particles along the martensite grain boundary, and can significantly improve the impact toughness of die steel after quenching and tempering. Vanadium and titanium can refine grains to increase the wear resistance of die steel. Vanadium and molybdenum, silicon can guarantee the satisfactory combination of various properties of die steel, and when titanium is added, their effect on the wear resistance can be improved.
The high chromium alloyed with the carbide forming active element is less sensitive to overheating during quenching, ensuring that the quench water temperature zone of the fine grain is significantly enlarged, thereby establishing that the chromium carbide and other elements are larger in austenite. Dissolved conditions.
The statistical data of chromium distribution shows that the addition of titanium can increase the concentration of chromium in the solid solution and shift it to the right. This proves that the free chromium in the process of forming carbides can increase the alloying degree of the die steel metal matrix.
Chromium Distribution After Quenching 1. Crl2MoV Steel 2.Cr5V3SiTi Steel 3.Cr12MOSiMi Steel 4.Cr3MnVTi Steel n.Cr Distribution Frequency Based on the above studies, the reasonable chemical composition of the three blanking die steels was developed. In Table 1.
Table 1 Chemical composition of die-die steel
Steel chemical element content (%)
C Mn Si Cr Mo V Ti
Cr3MnVTi 1.15∽1.25 1.0∽1.2 0.45∽0.52 2.8∽3.4 0.2∽0.3 1.0∽1.2 0.55∽0.08
Cr5V3SiTi 1.75∽1.85 ≥0.8 0.9∽1.2 4.6∽5.4 0.2∽0.4 2.3∽3.2 0.4∽0.7
Cr12MoSiTi 1.75∽1.85 0.3∽0.6 0.7∽1.0 441∽2.5 0.65∽0.95 0.3∽0.5 0.4∽0.7
3, the new mold steel mechanical properties
It has been determined that in the mold containing more than 3% chromium, the formation of the more active elements of carbide combined with manganese, chromium and molybdenum can improve the strength and wear resistance of the mold steel after heat treatment, as shown in Table 2.
Table 2 Best Practices for Heat Treatment and Mechanical Properties of Die Steels
Steel temperature (oC) Hardness (HRC) Flexural strength limit (MPa) Impact toughness (MJ/m3)
Quenching and tempering
Crl2MoV 1000~1020 200~220 61~62 2700~2900 0.35~0.4
Cr3MnVTi 980~1000 180~200 61~63 3200~3700 0.35~0.45
Cr5V3SiTi 1020~1060
In the blanking of the plate, due to the larger unit load (≥200MPa), the stress state of the blanked material is more complicated, and the heat temperature of the cutting edge of the die is higher (200°C) during the separation process, so the die is durable In most cases, the requirements for sheet metal stamping cannot be met.
In order to improve the durability of the punching die, three new types of die steels have been developed. It is to increase the durability of the stamping die by increasing the number of carbide phases in the die steel and changing its type. However, due to the increased carbide inhomogeneity, the mechanical properties of the die steel may deteriorate at this time. Therefore, it is necessary to add certain active elements simultaneously in the die steel. For example, vanadium and molybdenum may improve the distribution of the elements in the structure. , And can improve the physical and mechanical properties of the mold steel and performance. Molybdenum can partially replace the chromium atoms in the carbides, while vanadium can reduce the total amount of cementite in the alloy, which can significantly reduce the chemical composition and carbide inhomogeneity in the microvolume of the mold steel.
The formation of carbide M7C3 is related to a significant amount of chromium (up to 8% to 9%), so that the effect of alloying is often reduced. To eliminate this phenomenon, 0.4% to 0.8% Ti must be added in the steel, so that the carbon content in the α solid solution can be reduced, the martensite transformation point temperature can be increased, and the retained austenite in the microstructure can be reduced. Quantity (up to 7% to 10%). In addition, reducing the amount of carbon can promote better toughness of the parent, and can lead to increased relaxation within the stress source, which is very important for the working process of die steel.
Based on the reasonable alloying of carbide-forming active elements (Mo, V, Ti, etc.), an effective mechanism for strengthening the structure was developed. It can ensure the improvement of the overall performance of the die steel, partially reduce the chemical composition inhomogeneity of the carbides in the steel, and can eliminate or make it difficult to transfer the chromium atoms from the solid solution into the carbides.
The insoluble carbides of the above elements are not dissolved at the quenching temperature t quenching = 1040 to 1080°C, which ensures that the austenite maintains finer grains and thus has a higher level of brittle fracture resistance and bending strength. In addition, increasing the volume fraction of the most dispersed MC type carbides during the r→α transformation can increase the number of martensite nucleation centers, thereby also promoting the increase of the martensitic transformation temperature M and M and the fineness of the grains. It is difficult for the metal of the cutting edge to flow when the mold is in use, thereby improving the wear resistance of the mold.
The starting temperature of the martensitic transformation M and the end temperature M end with the mold steel composition and quenching temperature curve
2. Chemical composition of blanking die steel
It has been determined that in mold steels containing 6% to 12% Cr, the active element, especially Ti (up to 0.7%), is optimally combined with Mn, Cr, and Mo, which can promote the formation of higher-quality microstructures and can improve The strength of die steel (σb≥3400MPa～3600MPa), wear resistance and heat resistance (t≥450～500°C). Containing 0.2% to 0.9% molybdenum can inhibit the precipitation of dispersed brittle particles along the martensite grain boundary, and can significantly improve the impact toughness of die steel after quenching and tempering. Vanadium and titanium can refine grains to increase the wear resistance of die steel. Vanadium and molybdenum, silicon can guarantee the satisfactory combination of various properties of die steel, and when titanium is added, their effect on the wear resistance can be improved.
The high chromium alloyed with the carbide forming active element is less sensitive to overheating during quenching, ensuring that the quench water temperature zone of the fine grain is significantly enlarged, thereby establishing that the chromium carbide and other elements are larger in austenite. Dissolved conditions.
The statistical data of chromium distribution shows that the addition of titanium can increase the concentration of chromium in the solid solution and shift it to the right. This proves that the free chromium in the process of forming carbides can increase the alloying degree of the die steel metal matrix.
Chromium Distribution After Quenching 1. Crl2MoV Steel 2.Cr5V3SiTi Steel 3.Cr12MOSiMi Steel 4.Cr3MnVTi Steel n.Cr Distribution Frequency Based on the above studies, the reasonable chemical composition of the three blanking die steels was developed. In Table 1.
Table 1 Chemical composition of die-die steel
Steel chemical element content (%)
C Mn Si Cr Mo V Ti
Cr3MnVTi 1.15∽1.25 1.0∽1.2 0.45∽0.52 2.8∽3.4 0.2∽0.3 1.0∽1.2 0.55∽0.08
Cr5V3SiTi 1.75∽1.85 ≥0.8 0.9∽1.2 4.6∽5.4 0.2∽0.4 2.3∽3.2 0.4∽0.7
Cr12MoSiTi 1.75∽1.85 0.3∽0.6 0.7∽1.0 441∽2.5 0.65∽0.95 0.3∽0.5 0.4∽0.7
3, the new mold steel mechanical properties
It has been determined that in the mold containing more than 3% chromium, the formation of the more active elements of carbide combined with manganese, chromium and molybdenum can improve the strength and wear resistance of the mold steel after heat treatment, as shown in Table 2.
Table 2 Best Practices for Heat Treatment and Mechanical Properties of Die Steels
Steel temperature (oC) Hardness (HRC) Flexural strength limit (MPa) Impact toughness (MJ/m3)
Quenching and tempering
Crl2MoV 1000~1020 200~220 61~62 2700~2900 0.35~0.4
Cr3MnVTi 980~1000 180~200 61~63 3200~3700 0.35~0.45
Cr5V3SiTi 1020~1060
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