Steel with high thermal conductivity and molten aluminum corrosion resistance for aluminum alloy die-casting die and preparation method of steel

Abstract

The invention discloses aluminum alloy die-casting die steel with high thermal conductivity and molten aluminum corrosion resistance, which comprises the following components in percentage by mass: 1.4%-1.8% of C, 0.8%-1.2% of Si, 0.5%-1.0% of Mn, 1.5%-2.5% of Mo, not more than 0.02% of S, not more than 0.025% of P and the balance of Fe and inevitable impurities. The structure composition comprises a metal matrix and fine graphite nodules, the metal matrix is tempered sorbite or troostite, the diameter of the graphite nodules is not larger than 10 micrometers, and the density number of the graphite nodules is not smaller than 700 / mm < 2 >. The aluminum alloy die-casting die solves the problems that an existing aluminum alloy die-casting die is short in service life and high in die cost in aluminum alloy die-casting products.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of metal material preparation, and particularly relates to an aluminum alloy die casting die steel with high thermal conductivity and aluminum liquid corrosion resistance, and a preparation method of the aluminum alloy die casting die steel with high thermal conductivity and aluminum liquid corrosion resistance. BACKGROUND

[0002] With the rapid development of lightweight technology, it has promoted the rapid development and huge market demand of aluminum and its related industries, which are the main materials for lightweight manufacturing. According to the statistical data of China Nonferrous Metals Association, the primary aluminum output in China in 2023 was 4159 tons, with a production value of more than 800 billion yuan; the aluminum alloy output was 1218.3 tons, with a production value of nearly 300 billion yuan. The large-scale application of aluminum and its alloys has promoted the rapid development of aluminum and its alloy processing and manufacturing industry. For example, as the main tool for aluminum and its alloy forming, the die casting market for aluminum alloy forming is close to 100 billion yuan. As one of the main methods of aluminum alloy forming (for example, in automobiles, aluminum alloy die castings account for 77% of the total aluminum alloy consumption), the die casting market for aluminum alloy forming in 2023 has exceeded 50 billion yuan.

[0003] The existing aluminum alloy die casting die has been using hot deformed die steel, H13 steel. Although the aluminum alloy die casting die made of hot deformed die steel has excellent mechanical properties, good high-temperature performance and other advantages, it also has serious performance defects such as poor aluminum liquid melting resistance. Therefore, during the aluminum alloy die casting process, there is serious molten corrosion between the aluminum liquid and the die base material steel, and then high-brittle intermetallic compounds are generated on the surface of the die. The high-brittle intermetallic compounds, on the one hand, are subject to thermal fatigue, and then are subject to peeling under the action of aluminum alloy melt scouring and the friction force of the die casting, and finally form melting pits or develop into cracks on the surface of the die, resulting in premature failure of high-value dies. For example, the high-pressure aluminum alloy die casting die made of hot deformed die steel H13 of BYD has served for only 18,000 times (much lower than the service life of 150,000 times of magnesium alloy die casting die under the same working conditions), and the surface of the die cavity has formed a large number of corrosion pits and cracks due to the corrosion of the aluminum liquid, resulting in failure. The premature aging of high-value dies has become a bottleneck restricting the cost of the aluminum alloy manufacturing industry, and has become a pain point of the industry.

[0004] In addition, for the die casting die, the molten metal is quickly solidified to quickly form the required shape of the die casting, which is the key to improving the die casting production efficiency. The die casting die made of high thermal conductivity material can not only quickly remove the heat released during the solidification of the melt through high thermal performance to improve the die casting production efficiency, but also can accelerate the solidification speed and supercooling degree of the die casting, refine the microstructure of the die casting, thereby improving the mechanical properties and quality of the die casting, and finally improving the quality of the die casting. Therefore, improving the thermal conductivity of the die is not only the need to improve the die casting production efficiency, but also the need to prepare high-quality die castings.

[0005] Until now, improving the aluminum liquid corrosion resistance and thermal conductivity of the die, prolonging the service life of the aluminum alloy die casting die, reducing the manufacturing and use cost of the die, improving the production efficiency of the die casting and the production quality of the die casting, is still a difficult problem that needs to be solved in the industry. SUMMARY

[0006] The first object of the present application is to provide an aluminum alloy die casting die steel with high thermal conductivity and aluminum liquid corrosion resistance, which solves the problem of short service life of the existing aluminum alloy die casting die and high cost of the die in the aluminum alloy die casting product.

[0007] In order to achieve the above object, the technical scheme adopted by the present application is: an aluminum alloy die casting die steel with high thermal conductivity and aluminum liquid corrosion resistance, according to mass percentage, its composition is: C: 1.4%~1.8%, Si: 0.8%~1.2%, Mn: 0.5%~1.0%, Mo: 1.5%~2.5%, S: not more than 0.02%, P: not more than 0.025%, the rest is Fe and unavoidable impurities.

[0008] As a preferred technical scheme of the present application, the organizational composition includes a metal matrix and fine graphite balls, wherein the metal matrix is tempered sorbite or troostite, the diameter of the graphite ball is not more than 10um, and the density of the graphite ball is not less than 700 / mm 2 .

[0009] The second object of the present application is to provide a preparation method of an aluminum alloy die casting die steel with high thermal conductivity and aluminum liquid corrosion resistance, which solves the problem of short service life of the existing aluminum alloy die casting die and high cost of the die in the aluminum alloy die casting product; at the same time, improves the production efficiency of the die casting and the quality of the die casting.

[0010] In order to achieve the above object, the technical scheme adopted by the present application is: a preparation method of an aluminum alloy die casting die steel with high thermal conductivity and aluminum liquid corrosion resistance, which is specifically implemented according to the following steps: Step 1, melt the molten steel according to the melting composition requirements of the die steel, and then cast the billet; Step 2: After hot forging the billet obtained in Step 1, a forging is obtained; Step 3: After graphitizing the forging obtained in Step 2, a sample is obtained; Step 4: Quench the sample obtained in Step 3. Step 5: Temper the sample obtained in step 4.

[0011] The technical solution of the present invention also has the following characteristics: As a preferred technical solution of the present invention, in step 2: the forging ratio during hot forging is 4~10.

[0012] As a preferred technical solution of the present invention, in step 3: the graphitization treatment includes high-temperature graphitization treatment and low-temperature graphitization treatment; in: The high-temperature graphitization treatment involves directly immersing the forging, still at a high temperature after hot forging, into a heating furnace at 950℃~1000℃ for 8~10 hours, with the carbon potential of the furnace not lower than 1.6. After the holding period, the billet is removed from the furnace and air-cooled to room temperature. After the high-temperature graphitization treatment, the carbides with a diameter not exceeding 10µm in the original forging billet are essentially transformed into graphite spheres with a diameter not exceeding 10µm. The low-temperature graphitization treatment involves heating the high-temperature graphitized sample to 700℃~750℃ at a heating rate of 100℃ / h~200℃ / h and holding it at that temperature for 15h~20h to complete the low-temperature graphitization treatment of the steel billet, achieving a graphite sphere diameter of no more than 10µm and a density of no less than 700 spheres / mm² in the microstructure. 2 .

[0013] As a preferred technical solution of the present invention, in step 4, the quenching is as follows: the graphitized sample is heated to 820℃~850℃ at a heating rate of 100℃ / h~200℃ / h and held for 1h~2h, and then quenched in a nitrate bath at 280℃~320℃ and held isothermally for 2h~4h to complete the isothermal quenching of the sample.

[0014] As a preferred technical solution of the present invention, in step 5, the tempering specifically involves: immediately sending the sample after quenching and isothermal holding into an air furnace, heating the sample to 500℃~550℃ at a heating rate of 100℃ / h~200℃ / h and holding it for 1h~2h, and after holding, removing it from the furnace and air-cooling it to room temperature to complete the tempering of the sample.

[0015] As a preferred technical solution of the present invention, in step 5, the tempered structure is tempered sorbite / troostite + graphite spheres, and the hardness of the structure after tempering is not less than HRC40.

[0016] The beneficial effects of this invention are: the aluminum alloy die-casting mold steel with high thermal conductivity and resistance to aluminum melt corrosion, and its preparation method, have a microstructure consisting of a metal matrix and a large number of fine graphite spheres. The metal matrix is ​​tempered sorbite or troostite; the graphite spheres have a diameter of less than 10 μm and a density of not less than 700 spheres / mm². 2 Because graphite spheroids possess excellent resistance to molten aluminum corrosion and high thermal conductivity, the presence of densely packed, fine graphite spheroids in the steel microstructure endows the die steel with good resistance to molten aluminum corrosion and excellent thermal conductivity, without excessively compromising the steel's mechanical properties, such as strength, toughness, and fatigue performance. Furthermore, the addition of appropriate amounts of Mo and Mn allows the steel to achieve the required thermal stability and high-temperature hardness at service temperatures. Therefore, compared to existing hot-work die steels for aluminum alloy die casting, this steel offers better resistance to molten aluminum corrosion and higher thermal conductivity while maintaining comparable mechanical properties and thermal stability. Compared to ductile iron aluminum alloy die casting molds, it exhibits better strength, toughness, and fatigue performance without compromising resistance to molten aluminum corrosion. Thus, it is a preferred steel for aluminum alloy die casting and provides important reference value for the development of high-performance, long-life aluminum alloy die casting molds. In addition, this invention has solved the problem of how to efficiently obtain a large amount of graphite in steel through solid phase transformation and achieve control over its morphology and size by optimizing the composition and exploring the heat treatment process, thus laying a technical foundation for the application of new steel for aluminum alloy die casting molds. Attached Figure Description

[0017] Appendix Figure 1 This is a metallographic image (uncorroded) of the steel used in the aluminum alloy die-casting mold obtained by this invention. The small black circles or dots in the image are graphite spheres. According to the scale in the image, the diameter of the graphite spheres is less than 10 μm.

[0018] Appendix Figure 2 This is a metallographic image (corrosion) of the steel used for aluminum alloy die casting molds obtained in this invention. The image shows a sorbite structure.

[0019] Appendix Figure 3 This is a metallographic diagram (corrosion) of the steel forging used in the aluminum alloy die-casting mold obtained in this invention. The white granular or strip-shaped structures in the diagram are carbides. Referring to the scale in the diagram, the diameter or width of the carbides is less than 10 μm. Detailed Implementation

[0020] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0021] The present invention discloses a steel for aluminum alloy die-casting molds with high thermal conductivity and resistance to aluminum melt corrosion, the composition of which, by mass percentage, is as follows: C: 1.4%~1.8%, Si: 0.8%~1.2%, Mn: 0.5%~1.0%, Mo: 1.5%~2.5%, S: not more than 0.02%, P: not more than 0.025%, the remainder being Fe and unavoidable impurities; Its microstructure consists of a metallic matrix and fine graphite spheres, wherein the metallic matrix is ​​tempered sorbite or troostite, the graphite spheres have a diameter of no more than 10 μm, and the graphite sphere density is no less than 700 spheres / mm². 2 . Figure 1 This is a metallographic image (uncorroded) of the steel used in aluminum alloy die-casting molds according to the present invention. The small black circles or dots in the image are graphite spheres. According to the scale in the image, the diameter of the graphite spheres is less than 10 μm. Figure 2 This is a metallographic image (corrosion) of a steel used for aluminum alloy die casting molds according to the present invention. The image shows a sorbite structure.

[0022] The present invention discloses a method for preparing steel for aluminum alloy die casting molds with high thermal conductivity and resistance to aluminum melt corrosion, which is specifically implemented according to the following steps: Step 1: Melt molten steel according to the smelting composition requirements of mold steel, and then cast it into a billet; Step 2: After hot forging the billet obtained in Step 1, a forging is obtained; The billet needs to be hot forged to eliminate shrinkage cavities, porosity, coarse grains, and carbides present in the billet. The forging ratio of hot forging is 4~10, and high-temperature graphitization treatment is carried out directly after hot forging; after forging, the carbides in the microstructure are uniformly distributed and the diameter does not exceed 10um. Figure 3 This is a metallographic diagram (corrosion) of the steel forging process used in the aluminum alloy die-casting mold of this invention. The white granular or strip-shaped structures in the diagram are carbides. Referring to the scale in the diagram, the diameter or width of the carbides is less than 10 μm.

[0023] Step 3: After graphitizing the forging obtained in Step 2, a sample is obtained; Graphitization treatment includes high-temperature graphitization treatment and low-temperature graphitization treatment. in: The high-temperature graphitization treatment involves directly immersing the forging, still at a high temperature after hot forging, into a heating furnace at 950℃~1000℃ for 8~10 hours, with the carbon potential of the furnace not lower than 1.6. After the holding period, the billet is removed from the furnace and air-cooled to room temperature. After the high-temperature graphitization treatment, the carbides with a diameter not exceeding 10µm in the original forging billet are essentially transformed into graphite spheres with a diameter not exceeding 10µm. The low-temperature graphitization treatment involves heating the high-temperature graphitized sample to 700℃~750℃ at a heating rate of 100℃ / h~200℃ / h and holding it at that temperature for 15h~20h to complete the low-temperature graphitization treatment of the steel billet, achieving a graphite sphere diameter of no more than 10µm and a density of no less than 700 spheres / mm² in the microstructure. 2 .

[0024] Step 4: Quench the sample obtained in Step 3. Quenching is performed by heating the graphitized sample to 820℃~850℃ at a heating rate of 100℃ / h~200℃ / h and holding it at that temperature for 1h~2h, then quenching it in a nitrate bath at 280℃~320℃ and holding it isothermally for 2h~4h to complete the isothermal quenching of the sample.

[0025] Step 5: Temper the sample obtained in Step 4. Tempering is specifically performed as follows: after the quenching isothermal holding is completed, the sample is immediately sent into an air furnace and heated to 500℃~550℃ at a heating rate of 100℃ / h~200℃ / h and held for 1h~2h. After the holding is completed, the sample is taken out of the furnace and air-cooled to room temperature to complete the tempering of the sample. The tempered microstructure consists of tempered sorbite / troostite + graphite spheroids, and the hardness of the microstructure after tempering is not less than HRC40.

[0026] This invention leverages the excellent mechanical properties, forgeability, and heat treatment performance of steel. Through composition design and optimization, and process optimization, it has developed a new type of aluminum alloy die-casting mold steel with a significantly higher number and smaller diameter of graphite spheres compared to ductile iron, while maintaining mechanical properties comparable to high-carbon die steel. This mold steel not only exhibits far superior resistance to molten aluminum erosion and higher thermal conductivity than H13, a commonly used hot-work die steel for aluminum alloy die casting, but also demonstrates superior mechanical and fatigue properties compared to aluminum alloy die-casting mold steel made from ductile iron. It is an aluminum alloy die-casting mold steel with exceptionally high resistance to molten aluminum erosion, thermal conductivity, and mechanical and fatigue properties. The invention of this steel will significantly improve the service performance and service life of aluminum alloy die-casting molds (according to our installation tests, the service life of aluminum alloy die-casting molds made of this steel is 50% longer than that of traditional H13 molds; its thermal conductivity is also increased from about 25.0 W / (m·k) at room temperature of H13 to more than 35 W / (m·k), and the die-casting production cycle is shortened by 2-4 s), thereby significantly reducing the proportion of mold costs in the manufacturing of aluminum alloy die-casting parts and improving the production efficiency of die casting, which has obvious significance for reducing the manufacturing cost of the aluminum industry.

[0027] Example 1 The present invention discloses a steel for aluminum alloy die-casting molds with high thermal conductivity and resistance to aluminum melt corrosion, the composition of which, by mass percentage, is as follows: C: 1.4%, Si: 0.8%, Mn: 0.5%, Mo: 1.5%, S: 0.02%, P: 0.025%, with the remainder being Fe and unavoidable impurities; Its microstructure consists of a metallic matrix and fine graphite spheres, wherein the metallic matrix is ​​tempered sorbite or troostite, the graphite spheres have a diameter of no more than 10 μm, and the density of graphite spheres is 865 spheres / mm². 2 .

[0028] The present invention discloses a method for preparing steel for aluminum alloy die casting molds with high thermal conductivity and resistance to aluminum melt corrosion, which is specifically implemented according to the following steps: Step 1: Melt molten steel according to the smelting composition requirements of mold steel, and then cast it into a billet; Step 2: After hot forging the billet obtained in Step 1, a forging is obtained; The billet needs to be hot forged to eliminate shrinkage cavities, porosity, coarse grains, and carbides present in the billet. The forging ratio of hot forging is 4, and high-temperature graphitization treatment is carried out directly after hot forging; after forging, the distribution of carbides in the microstructure is uniform, and the diameter does not exceed 10 μm.

[0029] Step 3: After graphitizing the forging obtained in Step 2, a sample is obtained; Graphitization treatment includes high-temperature graphitization treatment and low-temperature graphitization treatment. in: The high-temperature graphitization treatment involves directly immersing the forging, which is still at a high temperature after hot forging, into a heating furnace at 950℃ and holding it for 10 hours, with the carbon potential of the furnace not lower than 1.6. After holding, the billet is removed from the furnace and air-cooled to room temperature. After the high-temperature graphitization treatment, the carbides with a diameter not exceeding 10 μm in the original forging billet are basically transformed into graphite spheres with a diameter not exceeding 10 μm. The low-temperature graphitization treatment involves heating the high-temperature graphitized sample to 700℃ at a heating rate of 100℃ / h and holding it at that temperature for 20 hours to complete the low-temperature graphitization treatment of the steel billet. This process achieves a graphite sphere diameter of no more than 10 μm and a density of 865 spheres / mm² in the microstructure. 2 .

[0030] Step 4: Quench the sample obtained in Step 3. The quenching process is as follows: the graphitized sample is heated to 820℃ at a heating rate of 100℃ / h and held for 2h, then quenched in a 280℃ nitrate bath and held isothermally for 4h to complete the isothermal quenching of the sample.

[0031] Step 5: Temper the sample obtained in Step 4. Tempering is specifically performed as follows: after the quenching isothermal holding is completed, the sample is immediately sent into an air furnace and heated to 500℃ at a heating rate of 100℃ / h and held for 2 hours. After the holding is completed, the sample is taken out of the furnace and air-cooled to room temperature to complete the tempering of the sample. The tempered microstructure consists of tempered sorbite / troostite + graphite spheroids, and the hardness of the microstructure after tempering is HRC43.5.

[0032] Example 2 The present invention discloses a steel for aluminum alloy die-casting molds with high thermal conductivity and resistance to aluminum melt corrosion, the composition of which, by mass percentage, is as follows: C: 1.8%, Si: 1.2%, Mn: 1.0%, Mo: 2.5%, S: 0.01%, P: 0.02%, with the remainder being Fe and unavoidable impurities; Its microstructure consists of a metallic matrix and fine graphite spheres, wherein the metallic matrix is ​​tempered sorbite or troostite, the graphite spheres have a diameter of no more than 10 μm, and the density of graphite spheres is 938 spheres / mm². 2 .

[0033] The present invention discloses a method for preparing steel for aluminum alloy die casting molds with high thermal conductivity and resistance to aluminum melt corrosion, which is specifically implemented according to the following steps: Step 1: Melt molten steel according to the smelting composition requirements of mold steel, and then cast it into a billet; Step 2: After hot forging the billet obtained in Step 1, a forging is obtained; The billet needs to be hot forged to eliminate shrinkage cavities, porosity, coarse grains, and carbides present in the billet. The forging ratio of hot forging is 10, and high-temperature graphitization treatment is carried out directly after hot forging; after forging, the distribution of carbides in the microstructure is uniform, and the diameter does not exceed 10 μm.

[0034] Step 3: After graphitizing the forging obtained in Step 2, a sample is obtained; Graphitization treatment includes high-temperature graphitization treatment and low-temperature graphitization treatment. in: The high-temperature graphitization treatment involves directly immersing the forging, which is still at a high temperature after hot forging, into a heating furnace at 1000℃ and holding it for 8 hours, with the carbon potential of the furnace not lower than 1.6. After holding, the billet is removed from the furnace and air-cooled to room temperature. After the high-temperature graphitization treatment, the carbides with a diameter not exceeding 10 μm in the original forging billet are basically transformed into graphite spheres with a diameter not exceeding 10 μm. The low-temperature graphitization treatment involves heating the high-temperature graphitized sample to 750℃ at a heating rate of 200℃ / h and holding it at that temperature for 15 hours to complete the low-temperature graphitization treatment of the steel billet. This process achieves a graphite sphere diameter of no more than 10 μm and a density of 938 spheres / mm² in the microstructure. 2 .

[0035] Step 4: Quench the sample obtained in Step 3. The quenching process is as follows: the graphitized sample is heated to 850℃ at a heating rate of 200℃ / h and held for 1h, then quenched in a 320℃ nitrate bath and held isothermally for 2h to complete the isothermal quenching of the sample.

[0036] Step 5: Temper the sample obtained in Step 4. The tempering process is as follows: After the quenching isothermal holding is completed, the sample is immediately sent into an air furnace and heated to 500℃ at a heating rate of 200℃ / h and held for 1 hour. After the holding is completed, the sample is taken out of the furnace and air-cooled to room temperature to complete the tempering of the sample. The tempered microstructure consists of tempered sorbite / troostite + graphite spheroids, and the hardness of the microstructure after tempering is HRC41.

[0037] Example 3 The present invention discloses a steel for aluminum alloy die-casting molds with high thermal conductivity and resistance to aluminum melt corrosion, the composition of which, by mass percentage, is as follows: C: 1.6%, Si: 1%, Mn: 0.75%, Mo: 2%, S: 0.01%, P: 0.15%, with the remainder being Fe and unavoidable impurities; Its microstructure consists of a metallic matrix and fine graphite spheres, wherein the metallic matrix is ​​tempered sorbite or troostite, the graphite spheres have a diameter of no more than 10 μm, and the density of graphite spheres is 731 spheres / mm². 2 .

[0038] The present invention discloses a method for preparing steel for aluminum alloy die casting molds with high thermal conductivity and resistance to aluminum melt corrosion, which is specifically implemented according to the following steps: Step 1: Melt molten steel according to the smelting composition requirements of mold steel, and then cast it into a billet; Step 2: After hot forging the billet obtained in Step 1, a forging is obtained; The billet needs to be hot forged to eliminate shrinkage cavities, porosity, coarse grains, and carbides present in the billet. The forging ratio of hot forging is 5, and high-temperature graphitization treatment is carried out directly after hot forging; after forging, the distribution of carbides in the microstructure is uniform, and the diameter does not exceed 10 μm.

[0039] Step 3: After graphitizing the forging obtained in Step 2, a sample is obtained; Graphitization treatment includes high-temperature graphitization treatment and low-temperature graphitization treatment. in: The high-temperature graphitization treatment involves directly immersing the forging, which is still at a high temperature after hot forging, into a heating furnace at 960℃ and holding it for 9 hours, with the carbon potential of the furnace not lower than 1.6. After holding, the billet is removed from the furnace and air-cooled to room temperature. After the high-temperature graphitization treatment, the carbides with a diameter not exceeding 10 μm in the original forging billet are basically transformed into graphite spheres with a diameter not exceeding 10 μm. The low-temperature graphitization treatment involves heating the high-temperature graphitized sample to 725℃ at a heating rate of 150℃ / h and holding it at that temperature for 16 hours to complete the low-temperature graphitization treatment of the steel billet. This process achieves a graphite sphere diameter of no more than 10 μm and a density of 731 spheres / mm² in the microstructure. 2 .

[0040] Step 4: Quench the sample obtained in Step 3. The quenching process is as follows: the graphitized sample is heated to 825℃ at a heating rate of 150℃ / h and held at that temperature for 1.5h. Then, it is quenched in a 300℃ nitrate bath and held isothermally for 3h to complete the isothermal quenching of the sample.

[0041] Step 5: Temper the sample obtained in Step 4. The tempering process is as follows: After the quenching isothermal holding is completed, the sample is immediately sent into an air furnace and heated to 525℃ at a heating rate of 150℃ / h and held for 1.5h. After the holding is completed, the sample is taken out of the furnace and air-cooled to room temperature to complete the tempering of the sample. The tempered microstructure consists of tempered sorbite / troostite + graphite spheroids, and the hardness of the microstructure after tempering is HRC40.

[0042] Example 4 The present invention discloses a steel for aluminum alloy die-casting molds with high thermal conductivity and resistance to aluminum melt corrosion, the composition of which, by mass percentage, is as follows: C: 1.5%, Si: 0.9%, Mn: 0.7%, Mo: 1.8%, S: 0.02%, P: 0.025%, with the remainder being Fe and unavoidable impurities; Its microstructure consists of a metallic matrix and fine graphite spheres, wherein the metallic matrix is ​​tempered sorbite or troostite, the graphite spheres have a diameter of no more than 10 μm, and the density of graphite spheres is 769 spheres / mm². 2 .

[0043] The present invention discloses a method for preparing steel for aluminum alloy die casting molds with high thermal conductivity and resistance to aluminum melt corrosion, which is specifically implemented according to the following steps: Step 1: Melt molten steel according to the smelting composition requirements of mold steel, and then cast it into a billet; Step 2: After hot forging the billet obtained in Step 1, a forging is obtained; The billet needs to be hot forged to eliminate shrinkage cavities, porosity, coarse grains, and carbides present in the billet. The forging ratio of hot forging is 5, and high-temperature graphitization treatment is carried out directly after hot forging; after forging, the distribution of carbides in the microstructure is uniform, and the diameter does not exceed 10 μm.

[0044] Step 3: After graphitizing the forging obtained in Step 2, a sample is obtained; Graphitization treatment includes high-temperature graphitization treatment and low-temperature graphitization treatment. in: The high-temperature graphitization treatment involves directly immersing the forging, which is still at a high temperature after hot forging, into a heating furnace at 960℃ and holding it for 9 hours, with the carbon potential of the furnace not lower than 1.6. After holding, the billet is removed from the furnace and air-cooled to room temperature. After the high-temperature graphitization treatment, the carbides with a diameter not exceeding 10 μm in the original forging billet are basically transformed into graphite spheres with a diameter not exceeding 10 μm. The low-temperature graphitization treatment involves heating the high-temperature graphitized sample to 730℃ at a heating rate of 160℃ / h and holding it at that temperature for 17 hours to complete the low-temperature graphitization treatment of the steel billet. This process achieves a graphite sphere diameter of no more than 10 μm and a density of 769 spheres / mm² in the microstructure. 2 .

[0045] Step 4: Quench the sample obtained in Step 3. The quenching process is as follows: the graphitized sample is heated to 830℃ at a heating rate of 120℃ / h and held for 1h, then quenched in a 290℃ nitrate bath and held isothermally for 2h to complete the isothermal quenching of the sample.

[0046] Step 5: Temper the sample obtained in Step 4. The tempering process is as follows: After the quenching isothermal holding is completed, the sample is immediately sent into an air furnace and heated to 510℃ at a heating rate of 120℃ / h and held for 2 hours. After the holding is completed, the sample is taken out of the furnace and air-cooled to room temperature to complete the tempering of the sample. The tempered microstructure consists of tempered sorbite / troostite + graphite spheroids, and the hardness of the microstructure after tempering is not less than HRC41.9.

[0047] Example 5 The present invention discloses a steel for aluminum alloy die-casting molds with high thermal conductivity and resistance to aluminum melt corrosion, the composition of which, by mass percentage, is as follows: C: 1.4%, Si: 1.2%, Mn: 0.5%, Mo: 2.5%, S: 0.01%, P: 0.01%, with the remainder being Fe and unavoidable impurities; Its microstructure consists of a metallic matrix and fine graphite spheres, wherein the metallic matrix is ​​tempered sorbite or troostite, the graphite spheres have a diameter of no more than 10 μm, and the density of graphite spheres is 836 spheres / mm². 2.

[0048] The present invention discloses a method for preparing steel for aluminum alloy die casting molds with high thermal conductivity and resistance to aluminum melt corrosion, which is specifically implemented according to the following steps: Step 1: Melt molten steel according to the smelting composition requirements of mold steel, and then cast it into a billet; Step 2: After hot forging the billet obtained in Step 1, a forging is obtained; The billet needs to be hot forged to eliminate shrinkage cavities, porosity, coarse grains, and carbides present in the billet. The forging ratio of hot forging is 8, and high-temperature graphitization treatment is carried out directly after hot forging; after forging, the distribution of carbides in the microstructure is uniform, and the diameter does not exceed 10 μm.

[0049] Step 3: After graphitizing the forging obtained in Step 2, a sample is obtained; Graphitization treatment includes high-temperature graphitization treatment and low-temperature graphitization treatment. in: The high-temperature graphitization treatment involves directly immersing the forging, which is still at a high temperature after hot forging, into a heating furnace at 1000℃ and holding it for 8 hours, with the carbon potential of the furnace not lower than 1.6. After holding, the billet is removed from the furnace and air-cooled to room temperature. After the high-temperature graphitization treatment, the carbides with a diameter not exceeding 10 μm in the original forging billet are basically transformed into graphite spheres with a diameter not exceeding 10 μm. The low-temperature graphitization treatment involves heating the high-temperature graphitized sample to 700℃ at a heating rate of 200℃ / h and holding it at that temperature for 20 hours to complete the low-temperature graphitization treatment of the steel billet. This process achieves a graphite sphere diameter of no more than 10 μm and a density of 836 spheres / mm² in the microstructure. 2 .

[0050] Step 4: Quench the sample obtained in Step 3. The quenching process is as follows: the graphitized sample is heated to 820℃ at a heating rate of 200℃ / h and held for 2h, then quenched in a 320℃ nitrate bath and held isothermally for 4h to complete the isothermal quenching of the sample.

[0051] Step 5: Temper the sample obtained in Step 4. The tempering process is as follows: After the quenching isothermal holding is completed, the sample is immediately sent into an air furnace and heated to 550°C at a heating rate of 200°C / h and held for 1 hour. After the holding is completed, the sample is taken out of the furnace and air-cooled to room temperature to complete the tempering of the sample. The tempered microstructure consists of tempered sorbite / troostite + graphite spheroids, and the hardness of the microstructure after tempering is not less than HRC42.8.

[0052] Example 6 The present invention discloses a steel for aluminum alloy die-casting molds with high thermal conductivity and resistance to aluminum melt corrosion, the composition of which, by mass percentage, is as follows: C: 1.7%, Si: 1.2%, Mn: 0.7%, Mo: 2.5%, S: 0.02%, P: 0.005%, with the remainder being Fe and unavoidable impurities; Its microstructure consists of a metallic matrix and fine graphite spheres, wherein the metallic matrix is ​​tempered sorbite or troostite, the graphite spheres have a diameter of no more than 10 μm, and the density of graphite spheres is 793 spheres / mm². 2 .

[0053] The present invention discloses a method for preparing steel for aluminum alloy die casting molds with high thermal conductivity and resistance to aluminum melt corrosion, which is specifically implemented according to the following steps: Step 1: Melt molten steel according to the smelting composition requirements of mold steel, and then cast it into a billet; Step 2: After hot forging the billet obtained in Step 1, a forging is obtained; The billet needs to be hot forged to eliminate shrinkage cavities, porosity, coarse grains, and carbides present in the billet. The forging ratio of hot forging is 9, and high-temperature graphitization treatment is carried out directly after hot forging; after forging, the distribution of carbides in the microstructure is uniform, and the diameter does not exceed 10 μm.

[0054] Step 3: After graphitizing the casting obtained in Step 2, a sample is obtained; Graphitization treatment includes high-temperature graphitization treatment and low-temperature graphitization treatment. in: The high-temperature graphitization treatment involves directly immersing the forging, which is still at a high temperature after hot forging, into a heating furnace at 970℃ and holding it for 9 hours, with the carbon potential of the furnace not lower than 1.6. After holding, the billet is removed from the furnace and air-cooled to room temperature. After the high-temperature graphitization treatment, the carbides with a diameter not exceeding 10 μm in the original forging billet are basically transformed into graphite spheres with a diameter not exceeding 10 μm. The low-temperature graphitization treatment involves heating the high-temperature graphitized sample to 740℃ at a heating rate of 180℃ / h and holding it at that temperature for 19 hours to complete the low-temperature graphitization treatment of the steel billet. This process achieves a graphite sphere diameter of no more than 10 μm and a density of 793 / mm². 2 .

[0055] Step 4: Quench the sample obtained in Step 3. The quenching process is as follows: the graphitized sample is heated to 840℃ at a heating rate of 190℃ / h and held for 2 hours, then quenched in a 310℃ nitrate bath and held isothermally for 3 hours to complete the isothermal quenching of the sample.

[0056] Step 5: Temper the sample obtained in Step 4. The tempering process is as follows: after the quenching isothermal holding is completed, the sample is immediately sent into an air furnace and heated to 540℃ at a heating rate of 190℃ / h and held for 2 hours. After the holding is completed, the sample is taken out of the furnace and air-cooled to room temperature to complete the tempering of the sample. The tempered microstructure consists of tempered sorbite / troostite + graphite spheroids, and the hardness of the microstructure after tempering is not less than HRC43.3.

Claims

1. A steel for aluminum alloy die-casting molds with high thermal conductivity and resistance to aluminum melt corrosion, characterized in that, Its composition, by mass percentage, is as follows: C: 1.4%~1.8%, Si: 0.8%~1.2%, Mn: 0.5%~1.0%, Mo: 1.5%~2.5%, S: not more than 0.02%, P: not more than 0.025%, the remainder being Fe and unavoidable impurities.

2. The aluminum alloy die-casting mold steel with high thermal conductivity and resistance to aluminum melt corrosion as described in claim 1, characterized in that, Its microstructure consists of a metallic matrix and fine graphite spheres, wherein the metallic matrix is ​​tempered sorbite or troostite, the graphite spheres have a diameter of no more than 10 μm, and the graphite sphere density is no less than 700 spheres / mm². 2 .

3. A method for preparing steel for aluminum alloy die-casting molds with high thermal conductivity and resistance to aluminum melt corrosion, characterized in that, The specific steps are as follows: Step 1: Melt molten steel according to the smelting composition requirements of mold steel, and then cast it into a billet; Step 2: After hot forging the billet obtained in Step 1, a forging is obtained; Step 3: After graphitizing the forging obtained in Step 2, a sample is obtained; Step 4: Quench the sample obtained in Step 3. Step 5: Temper the sample obtained in step 4.

4. The method for preparing aluminum alloy die-casting mold steel with high thermal conductivity and resistance to aluminum melt corrosion according to claim 3, characterized in that, In step 2, the forging ratio during hot forging is 4 to 10.

5. The aluminum alloy die-casting mold steel with high thermal conductivity and resistance to molten aluminum corrosion as described in claim 4, characterized in that, In step 3: the graphitization process includes high-temperature graphitization and low-temperature graphitization. in: The high-temperature graphitization treatment is as follows: the forgings that are still at high temperature after hot forging are directly placed into a heating furnace at a temperature of 950℃~1000℃ and held for 8h~10h, wherein the carbon potential of the heating furnace is not lower than 1.6; after the holding period, the billet is removed from the furnace and air-cooled to room temperature; after the high-temperature graphitization treatment, the carbides with a diameter of no more than 10um in the original forging billet are basically transformed into graphite spheres with a diameter of no more than 10um. The low-temperature graphitization treatment involves heating the high-temperature graphitized sample to 700℃~750℃ at a heating rate of 100℃ / h~200℃ / h and holding it at that temperature for 15h~20h to complete the low-temperature graphitization treatment of the steel billet, achieving a graphite sphere diameter of no more than 10µm and a density of no less than 700 spheres / mm² in the microstructure. 2 .

6. The aluminum alloy die-casting mold steel with high thermal conductivity and resistance to molten aluminum corrosion as described in claim 5, characterized in that, In step 4, the quenching is performed by heating the graphitized sample to 820℃~850℃ at a heating rate of 100℃ / h~200℃ / h and holding it at that temperature for 1h~2h, then quenching it in a nitrate bath at 280℃~320℃ and holding it isothermally for 2h~4h to complete the isothermal quenching of the sample.

7. The aluminum alloy die-casting mold steel with high thermal conductivity and resistance to molten aluminum corrosion as described in claim 6, characterized in that, In step 5, the tempering process is as follows: the sample after quenching and isothermal holding is immediately sent into an air furnace, and the sample is heated to 500℃~550℃ at a heating rate of 100℃ / h~200℃ / h and held for 1h~2h. After the holding is completed, the sample is taken out of the furnace and air-cooled to room temperature to complete the tempering of the sample.

8. The aluminum alloy die-casting mold steel with high thermal conductivity and resistance to molten aluminum corrosion as described in claim 7, characterized in that, In step 5, the tempered microstructure is tempered sorbite / troostite + graphite spheroids, and the hardness of the microstructure after tempering is not less than HRC40.

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