Die steel additive for die casting core formation and method of manufacturing the same

Abstract

The application discloses a die steel additive for die casting core forming and a manufacturing method thereof, and belongs to the field of laser advanced manufacturing technology, and comprises the following steps: mixing, coating, and pre-pressing Al powder, Ti powder, and boron carbide to obtain a briquette; heating and remelting the briquette to generate a combustion synthesis reaction to obtain TiC+TiB2 / Al intermediate alloy; heating and remelting die steel, adding the TiC+TiB2 / Al intermediate alloy to obtain steel liquid, and pouring the steel liquid to obtain a nano-particle die steel; heating and remelting the nano-particle die steel to obtain a nano-particle die steel solution, and atomizing the nano-particle die steel solution by introducing nitrogen to obtain nano-particle reinforced powder; and preparing the nano-particle reinforced powder by using selective laser melting to obtain the die steel additive; and the die steel additive has high compactness and high strength and toughness.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of laser advanced manufacturing technology, and particularly relates to a die steel additive for forming a die casting core and a manufacturing method thereof. BACKGROUND

[0002] "Modern industry, die leading", molds are widely used in the fields of automobiles, aviation, navigation, etc., and traditional methods for producing molds have a series of problems such as many processes, long cycle, difficult to process, etc., and cannot meet the development needs of modern industry. The development of SLM technology provides a new choice for forming molds, and the unique laser processing method of SLM can also produce unique microstructure and good mechanical properties. At present, there are few commercial die steel powders in China, mainly H13 and 18Ni300, and there are some problems in these die steels at present, such as poor high-temperature strength, poor cold-heat alternating fatigue resistance, etc., which leads to reduced mold life and causes premature failure of the mold. Therefore, it is of important practical significance to develop new high-performance die steel powder for SLM forming mold technology. SUMMARY

[0003] Nanoceramic particles have been proven to effectively improve the comprehensive performance of die steel. Research shows that the traditional method is to add external or in-situ ceramic particles, and a high volume fraction of ceramic particles is needed to resist load, but a high volume fraction of ceramic particles will have a bad effect on the toughness of the steel. Therefore, in the development process of new die steel powder, we propose to introduce trace nanoceramic particles by using intermediate alloy method to improve the strength and toughness of the die steel powder after forming, and develop a new high-performance hot work die steel powder.

[0004] In view of the deficiencies of the prior art, the application provides a die steel additive for forming a die casting core and a manufacturing method thereof.

[0005] A manufacturing method of a die steel additive for forming a die casting core comprises the following steps:

[0006] (1) Al powder, Ti powder and boron carbide are mixed, coated, pre-pressed to obtain a briquette, the briquette is heated to occur a combustion synthesis reaction to obtain a TiC+TiB2 / Al intermediate alloy;

[0007] (2) The die steel is heated and remelted, the TiC+TiB2 / Al intermediate alloy is added, a steel liquid is obtained, and the steel liquid is poured to obtain a nanometer particle die steel;

[0008] (3) The nanometer particle die steel is heated and remelted to obtain a nanometer particle die steel solution, nitrogen gas is introduced for atomization to obtain a nanometer particle reinforced powder;

[0009] (4) The nanometer particle reinforced powder is prepared by using selective laser melting to obtain a die steel additive.

[0010] Preferably, the combustion synthesis reaction environment is a vacuum environment.

[0011] Preferably, the temperature of the heating remelting in the step (2) and step (3) is 1650℃.

[0012] Preferably, the pressure of the nitrogen is 4MPa.

[0013] Preferably, the coated material is aluminum foil.

[0014] Preferably, the mass ratio of the Al powder, Ti powder and boron carbide is 24:6:70.

[0015] A die steel additive for die casting core forming, comprising the following mass percentages of chemical components: TiC and TiB2: 0.02-0.05wt.%; C: 0.48-0.53wt.% and Mo: 2.8-3.0wt.%.

[0016] Preferably, further comprising the following mass percentages of chemical components: Si: 0.3wt.%; Mn:

[0017] 0.20-0.40wt.%; P: 0.015wt.%; S: 0.002wt.%; Cr 4.5-5.0wt.%; V: 0.55-0.65wt.%; Cu: 0.05wt.% and Fe.

[0018] Application of the above die steel additive or the die steel additive prepared by the above manufacturing method in producing die casting cores.

[0019] The die steel additive of the present application has the following beneficial effects:

[0020] The SLM formed nano-particle strengthened hot work die steel is subjected to the combined action of laser and nano-particles in the forming process, and the grain size thereof is found to be much smaller than that of the die steel obtained by conventional methods, so that the grain boundary is increased, which hinders the dislocation movement in the material, thereby improving the strength of the material; the existence of nano-particles accelerates the dispersion precipitation of fine carbides, but due to the difference in thermal expansion coefficient between the carbides and nano-particles and the hot work die steel, a larger stress is generated around the carbides in the SLM forming process, resulting in a large number of geometric dislocations around the carbides, thereby producing thermal mismatch strengthening; in the SLM forming process of the nano-particle strengthened die steel, laser processing belongs to fast cooling processing, and fine and dispersed precipitated phases are generated in the processing process, which pin the dislocations and hinder the slip of dislocations, and the die of the present application has high strength, high oxidation resistance and thermal fatigue resistance. BRIEF DESCRIPTION OF DRAWINGS

[0021] In order to more clearly illustrate the technical solutions in the embodiments of the present disclosure or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, for those skilled in the art, other drawings can also be obtained based on these drawings without any creative effort.

[0022] Figure 1 Morphology of the die steel powder in Example 1.

[0023] Figure 2 Metallographic photo of the die steel in Example 1.

[0024] Figure 3 Laser absorption rate of the die steel powder in Example 1.

[0025] Figure 4 Room temperature tensile curve of each embodiment.

[0026] Figure 5 High temperature tensile curve of each embodiment. DETAILED DESCRIPTION

[0027] The technical solutions in the embodiments of the present disclosure will be described clearly and completely below with reference to the drawings in the embodiments of the present disclosure. Obviously, the described embodiments are only a part of the embodiments of the present disclosure, rather than all the embodiments. Based on the embodiments in the present disclosure, all other embodiments obtained by those skilled in the art without any creative effort fall within the protection scope of the present disclosure.

[0028] Example 1:

[0029] Designing nanoparticle reinforced die steel additive powder: preparing a nanoparticle intermediate alloy, mixing Al powder, Ti powder and boron carbide according to a mass ratio of 24:6:70, putting the mixed powder into a high-energy ball mill, uniformly mixing at a speed of 40 r / min for 48 hours, and using aluminum foil to coat the mixed powder.

[0030] Pre-pressing on a hydraulic testing machine to obtain a cold briquette, and then putting the cold briquette into a graphite mold to perform a combustion synthesis reaction in a vacuum sintering furnace to finally obtain a TiC+TiB2 / Al intermediate alloy.

[0031] The chemical composition and mass percentage of the high-performance die steel are as follows: C: 0.48wt.%; Si: 0.30wt.%; Mn: 0.4wt.%; P: 0.015wt.%; S: 0.002wt.%; Cr: 4.5wt.%; Mo: 3.0wt.%; V: 0.55wt.%; Cu: 0.05wt.%; and the balance is Fe.

[0032] The high-performance die steel is cut into blocks according to 2 kg, and is remelted in the hearth of the intermediate frequency induction furnace. The TiC+TiB2 / Al intermediate alloy cut in advance is added into the intermediate frequency induction furnace to obtain molten steel. When the molten steel is tapped at about 1650 ℃, the molten steel is uniformly injected into the ladle at about 1500 ℃, the nano TiC+TiB2 particles are dispersed in the molten steel with the boiling of the molten steel, the Al acts as an oxygen scavenger to generate aluminum oxide floating above the molten steel, and then the molten steel is poured into a sand mold to obtain a TiC and TiB2 strengthened die steel with a content of 0.02wt.%.

[0033] Preparation of nano-particle reinforced powder:

[0034] The nano-particle strengthened die steel is remelted in the hearth of the intermediate frequency induction furnace, the nano-particle strengthened die steel is heated to a liquid state, and after being kept at 1650 ℃ for 2 min, a nano-particle strengthened die steel melt is obtained.

[0035] The obtained melt is transferred to the tundish under a nitrogen environment, the melt flows downward from the opening at the bottom of the tundish at a diameter of about 4 mm, and then enters the sealed channel. Nitrogen gas with a pressure of about 4 MPa is introduced, which can blow away the downwardly flowing molten metal to realize the nitrogen atomization process. After free fall, the atomized melt is cooled at the bottom to form a nano-particle reinforced powder.

[0036] The obtained powder is then sieved into two parts, and the sieving requirements are 15-53 μm and 53-150 μm, respectively.

[0037] The selected laser additive powder has a size of 15-53 μm and an absorption rate of 36.43% in the 1064 laser band, as shown in Figure 3 The laser selective melting technology is used for preparation, the fixed laser power is 200 W, the scanning speed is 900 mm / s, the powder layer thickness is fixed at 30 μm, the laser scanning spacing is fixed at 100 μm, the laser scanning strategy is interlayer rotation of 70°, and the component realizes high-density forming.

[0038] The performance of the finally prepared die steel is shown in Table 1. The Rockwell hardness of the sample is measured by a Rockwell hardness tester (300HRSS-150) of Laizhou Huayin Test Instrument Co., Ltd. Before testing, the sample is polished smooth to ensure that the upper and lower surfaces are parallel. During the test, the experimental force is 150 kgf, the experimental force is maintained for 5 s, and the hardness of eight random points on the sample is measured. After removing the maximum and minimum values, the average value is taken as the final hardness value of the sample. The room temperature hardness measured by the Rockwell hardness tester is 56.87 HRC. The sample is made into a standard tensile specimen size, the surface is polished smooth with sandpaper, and a servo-hydraulic material testing system is used for tensile test. The tensile speed is 10 -4 s -1a tensile strength of 1766 MPa, a yield strength of 999 MPa at room temperature (20°C) and a tensile strength of 1471 MPa, a yield strength of 1413 MPa at high temperature (550°C).

[0039] Example 2:

[0040] Designing nanoparticle reinforced die steel additive powder: prepare nanoparticle intermediate alloy, mix Al powder, Ti powder and boron carbide according to the mass ratio of 24:6:70, put the mixed powder into a high-energy ball mill, mix uniformly at a speed of 40 r / min for 36 hours, and then wrap the mixed powder with aluminum foil.

[0041] Pre-pressing on a hydraulic testing machine to obtain a cold briquette, then the cold briquette is put into a graphite mold to undergo a combustion synthesis reaction in a vacuum sintering furnace to finally obtain a TiC+TiB2 / Al intermediate alloy.

[0042] The chemical composition and mass percentage of the high-performance die steel are as follows: C: 0.53wt.%; Si: 0.3wt.%; Mn: 0.2wt.%; P: 0.015wt.%; S: 0.002wt.%; Cr: 5.0wt.%; Mo: 2.8wt.%; V: 0.65wt.%; Ti: 0.005wt.%; Cu: 0.05wt.%; and the balance is Fe.

[0043] The high-performance die steel is cut into blocks of 1 kg and remelted in the hearth of a medium-frequency induction furnace. The pre-cut TiC+TiB2 / Al intermediate alloy is added to the medium-frequency induction furnace to obtain molten steel. When the molten steel is tapped at a temperature of about 1650°C, it is poured into a ladle at a uniform speed at a temperature of about 1500°C. The nano TiC+TiB2 particles are dispersed in the molten steel as it boils, and Al acts as a deoxidizer to form aluminum oxide that floats above the molten steel. Then the molten steel is poured into a sand mold to obtain a die steel containing 0.05wt.% TiC and TiB2.

[0044] Preparation of nanoparticle reinforced powder:

[0045] The nanoparticle reinforced die steel is placed in the hearth of a medium-frequency induction furnace for remelting. The nanoparticle reinforced die steel is heated to a liquid state and maintained at 1600°C for 3 min to obtain a nanoparticle reinforced die steel melt.

[0046] The obtained melt is transferred to a tundish under a nitrogen environment. The melt flows downward freely from the opening at the bottom of the tundish, and then enters a sealed channel. Nitrogen gas with a pressure of about 4 MPa is introduced into the channel to blow away the downwardly flowing molten metal, achieving a nitrogen atomization process. The atomized melt forms a nanoparticle reinforced powder after free fall and cooling at the bottom.

[0047] The obtained powder is then sieved into two parts, and the sieving requirements are 15-53 pm and 53-150 pm, respectively.

[0048] The selected laser additive powder has a size of 15-53 pm, and is prepared by using selective laser melting technology, with a fixed laser power of 200 W, a scanning speed of 1000 mm / s, a fixed powder layer thickness of 30 pm, a fixed laser scanning pitch of 100 pm, and a laser scanning strategy of interlayer rotation of 70°, so that the component realizes high-density forming.

[0049] The properties of the finally prepared die steel are shown in Table 1. The Rockwell hardness of the sample is measured by using a Rockwell hardness tester (300HRSS-150) of Laizhou Huayin Test Instrument Co., Ltd. Before testing, the sample is polished smooth to ensure that the upper and lower surfaces are parallel. During the test process, the experimental force is 150 kgf, the experimental force is maintained for 5 s, and the hardness of eight random points on the sample is measured. After removing the maximum and minimum values, the average value is taken as the final hardness value of the sample. The room temperature hardness measured by the Rockwell hardness tester is 56.79 HRC. The sample is made into a standard tensile specimen size, the surface is polished smooth using sandpaper, and a servo-hydraulic material testing system is used for tensile test. The tensile speed is 10 -4 s -1 The tensile strength at room temperature (20°C) is 1482 MPa, the yield strength is 985 MPa, and the tensile strength at high temperature (550°C) is 1414 MPa, and the yield strength is 1257 MPa.

[0050] Example 3:

[0051] Designing nanoparticle reinforced die steel additive powder: prepare a nanoparticle intermediate alloy, mix Al powder, Ti powder and boron carbide according to a mass ratio of 24:6:70, put the mixed powder into a high-energy ball mill, uniformly mix at a speed of 40 r / min for 48 hours, and wrap the mixed powder with aluminum foil.

[0052] Pre-pressing is performed on a hydraulic testing machine to obtain a cold compact, and then the cold compact is put into a graphite mold to perform a combustion synthesis reaction in a vacuum sintering furnace, and finally obtain a TiC+TiB2 / Al intermediate alloy.

[0053] The chemical composition and mass percentage of the high-performance die steel are as follows: C: 0.50wt.%; Si: 0.3wt.%; Mn: 0.3wt.%; P: 0.015wt.%; S: 0.002wt.%; Cr: 4.8wt.%; Mo: 2.9wt.%; V: 0.59wt.%; Cu: 0.05wt.%; and the balance is Fe.

[0054] The high-performance die steel is cut into blocks according to 2 kg, and is remelted in the hearth of the medium-frequency induction furnace. The TiC+TiB2 / Al intermediate alloy cut in advance is added into the medium-frequency induction furnace to obtain molten steel. When the molten steel is tapped at about 1650 ℃, the molten steel is injected into the ladle at about 1500 ℃ at a uniform speed. The nano TiC+TiB2 particles are dispersed in the molten steel by boiling, and the Al acts as an oxygen scavenger to generate aluminum oxide floating above the molten steel. Subsequently, the molten steel is poured into a sand mold to obtain a die steel containing 0.02 wt.% TiC and TiB2.

[0055] The nano-particle reinforced powder is prepared as follows:

[0056] The nano-particle reinforced die steel is remelted in the hearth of the medium-frequency induction furnace. The nano-particle reinforced die steel is heated to a liquid state, and after being kept at 1650 ℃ for 2 min, a nano-particle reinforced die steel melt is obtained.

[0057] The obtained melt is transferred to a tundish under a nitrogen environment. The melt flows downward from the opening at the bottom of the tundish at a diameter of about 4 mm, and then enters a sealed channel. Nitrogen gas with a pressure of about 4 MPa is introduced into the sealed channel. The nitrogen gas can blow away the downwardly flowing metal melt to realize the nitrogen gas atomization process. After free fall, the atomized melt is cooled at the bottom to form a nano-particle reinforced powder.

[0058] Subsequently, the obtained powder is sieved into two parts, and the sieving requirements are 15-53 μm and 53-150 μm, respectively.

[0059] Subsequently, the laser additive powder with a size of 15-53 μm is selected, and a selective laser melting technology is used for preparation. The fixed laser power is 200 W, the scanning speed is 900 mm / s, the powder layer thickness is fixed at 30 μm, the laser scanning spacing is fixed at 100 μm, the laser scanning strategy is interlayer rotation of 70°, and the component realizes high-density forming.

[0060] The printed high-density forming die steel is subjected to tempering heat treatment to eliminate internal residual stress. The tempering heat treatment steps are as follows: the formed die steel is placed in a heat treatment furnace, the heating rate is set to 12 ℃ / min, the temperature is raised to 625 ℃, and after being kept for 120 min, the sample is taken out and air-cooled to room temperature.

[0061] The properties of the finally prepared die steel are shown in Table 1. The Rockwell hardness of the sample is measured by a Rockwell hardness tester (300HRSS-150) of Laizhou Huayin Test Instrument Co., Ltd. Before testing, the sample is polished smooth to ensure that the upper and lower surfaces are parallel. During the test, the experimental force is 150 kgf, the experimental force is maintained for 5 s, and the hardness of eight random points on the sample is measured. The average value after removing the maximum and minimum values is the final hardness value of the sample. The room temperature hardness measured by the Rockwell hardness tester is 56.87 HRC. The sample is prepared into a standard tensile specimen size, the surface is polished smooth using sandpaper, and a servo-hydraulic material testing system is used for tensile test. The tensile speed is 10 -4 s -1 The tensile strength at room temperature (20°C) is 1766 MPa, the yield strength is 999 MPa, and the tensile strength at high temperature (550°C) is 1471 MPa, and the yield strength is 1413 MPa.

[0062] Example 4:

[0063] Designing nanoparticle reinforced die steel additive powder: prepare a nanoparticle intermediate alloy, mix Al powder, Ti powder and boron carbide in a mass ratio of 24:6:70, put the mixed powder into a high-energy ball mill, mix uniformly at a speed of 40 r / min for 48 hours, and wrap the mixed powder with aluminum foil.

[0064] Pre-pressing is performed on a hydraulic testing machine to obtain a cold briquette, and then the cold briquette is placed into a graphite mold to perform a combustion synthesis reaction in a vacuum sintering furnace to finally obtain a TiC+TiB2 / Al intermediate alloy.

[0065] The chemical composition and mass percentage of the high-performance die steel are as follows: C: 0.50wt.%; Si: 0.3wt.%; Mn: 0.3wt.%; P: 0.015wt.%; S: 0.002wt.%; Cr: 4.8wt.%; Mo: 2.9wt.%; V: 0.59wt.%; Cu: 0.05wt.%; and the balance is Fe.

[0066] The high-performance die steel is cut into blocks of 2 kg and remelted in the hearth of a medium-frequency induction furnace. The pre-cut TiC+TiB2 / Al intermediate alloy is added to the medium-frequency induction furnace to obtain molten steel. When the molten steel is tapped at a temperature of about 1650°C, the molten steel is uniformly injected into the ladle at a temperature of about 1500°C. The nano TiC+TiB2 particles are dispersed in the molten steel by boiling, and Al acts as an oxygen scavenger to generate aluminum oxide that floats above the molten steel. Then the molten steel is poured into a sand mold to obtain a die steel containing 0.02wt.% TiC and TiB2.

[0067] Preparation of nanoparticle reinforced powder:

[0068] The nanoparticle reinforced mold steel is placed in the hearth of a medium-frequency induction furnace for remelting, the nanoparticle reinforced mold steel is heated to a liquid state, and after being kept at 1650 °C for 2 min, a nanoparticle reinforced mold steel melt is obtained.

[0069] The obtained melt is transferred to a tundish under a nitrogen environment, the melt flows downward from the opening at the bottom of the tundish at a diameter of about 4 mm, and then enters a sealed channel, nitrogen gas with a pressure of about 4 MPa is introduced, the nitrogen gas can blow away the downwardly flowing metal melt, and the atomized melt is cooled to form a nanoparticle reinforced powder after free fall.

[0070] The obtained powder is then sieved into two parts, and the sieving requirements are 15-53 μm and 53-150 μm, respectively.

[0071] The selected laser additive powder has a size of 15-53 μm, and is prepared by using a selective laser melting technology, the fixed laser power is 200 W, the scanning speed is 900 mm / s, the powder layer thickness is fixed at 30 μm, the laser scanning spacing is fixed at 100 μm, the laser scanning strategy is interlayer rotation of 70°, and the component realizes high-density forming.

[0072] The printed high-density forming mold steel is subjected to tempering heat treatment to eliminate internal residual stress, and the tempering heat treatment steps are as follows: the formed mold steel is placed in a heat treatment furnace, the heating rate is set to 10 °C / min, the temperature is raised to 600 °C, and after being kept for 120 min, the sample is taken out and air-cooled to room temperature.

[0073] The properties of the finally prepared mold steel are shown in Table 1, the Rockwell hardness of the sample is measured by using a Rockwell hardness tester (300HRSS-150) of Laizhou Huayin Test Instrument Co., Ltd., the sample is polished smooth before testing to ensure that the upper and lower surfaces are parallel, the experimental force is 150 kgf during testing, the experimental force is kept for 5 s, the hardness of eight random points on the sample is measured, and the average value after removing the maximum and minimum values is taken as the final hardness value of the sample. The room temperature hardness measured by the Rockwell hardness tester is 58.65 HRC. The sample is made into a standard tensile specimen size, the surface is polished smooth using sandpaper, and a servo-hydraulic material testing system is used for tensile test, the tensile speed is 10 -4 s -1 , the tensile strength at room temperature (20 °C) is 2380 MPa, the yield strength is 1766 MPa, and the tensile strength at high temperature (550 °C) is 1671 MPa, and the yield strength is 1450 MPa.

[0074] Example 5:

[0075] Designing Nanoparticle Reinforced Die Steel Additive Powder: Prepare nanoparticle intermediate alloy, mix Al powder, Ti powder and boron carbide according to the mass ratio of 24:6:70, put the mixed powder into a high-energy ball mill, mix uniformly at a speed of 40 r / min for 48 hours, and then wrap the mixed powder with aluminum foil.

[0076] Pre-pressing on a hydraulic testing machine to obtain a cold briquette, then the cold briquette is placed into a graphite mold to undergo a combustion synthesis reaction in a vacuum sintering furnace to obtain a TiC+TiB2 / Al intermediate alloy.

[0077] The chemical composition and mass percentage of the high-performance die steel are as follows: C: 0.50wt.%; Si: 0.3wt.%; Mn: 0.3wt.%; P: 0.015wt.%; S: 0.002wt.%; Cr: 4.8wt.%; Mo: 2.9wt.%; V: 0.59wt.%; Cu: 0.05wt.%; and the balance is Fe.

[0078] The high-performance die steel is cut into blocks of 2 kg and remelted in the hearth of a medium-frequency induction furnace. The pre-cut TiC+TiB2 / Al intermediate alloy is added to the medium-frequency induction furnace to obtain molten steel. When the molten steel is tapped at a temperature of about 1650°C, it is poured into a ladle at a temperature of about 1500°C. The nano TiC+TiB2 particles are dispersed in the molten steel as it boils. Al acts as a deoxidizer to form aluminum oxide that floats above the molten steel. Then the molten steel is poured into a sand mold to obtain a die steel containing 0.02% TiC and TiB2.

[0079] Preparation of Nanoparticle Reinforced Powder:

[0080] The obtained nanoparticle reinforced die steel is remelted in the hearth of a medium-frequency induction furnace. The nanoparticle reinforced die steel is heated to a liquid state and maintained at 1650°C for 2 min to obtain a nanoparticle reinforced die steel melt.

[0081] The obtained melt is transferred to a tundish under a nitrogen atmosphere. The melt flows freely downward from the opening at the bottom of the tundish, and then enters a sealed channel. Nitrogen gas with a pressure of about 4 MPa is introduced into the channel. The nitrogen gas can disperse the downwardly flowing molten metal, achieving a nitrogen atomization process. The atomized melt is cooled to form nanoparticle reinforced powder after free fall.

[0082] The obtained powder is then sieved into two parts, with the sieving requirements being 15-53 μm and 53-150 μm, respectively.

[0083] The subsequently selected laser additive powder size is 15-53 μm, and is prepared by using selective laser melting technology, the fixed laser power is 200 W, the scanning speed is 900 mm / s, the powder layer thickness is fixed at 30 μm, the laser scanning interval is fixed at 100 μm, and the laser scanning strategy is interlayer rotation of 70°, and the component realizes high density forming.

[0084] The printed high-density forming die steel is subjected to tempering heat treatment to eliminate internal residual stress, and the tempering heat treatment steps are as follows: the forming die steel is placed in a heat treatment furnace, the heating rate is set to 12 ℃ / min, heated to 650 ℃, and after holding for 120 min, the sample is taken out and air cooled to room temperature.

[0085] The performance of the finally prepared die steel is shown in Table 1, the Rockwell hardness of the sample is measured by using a Rockwell hardness tester (300HRSS-150) of Laizhou Huayin Test Instrument Co., Ltd., the sample is polished smooth before testing to ensure that the upper and lower surfaces are parallel, the experimental force is 150 kgf during testing, the experimental force is maintained for 5 s, the hardness of eight random points on the sample is measured, and the average value after removing the maximum and minimum value is taken as the final hardness value of the sample, the room temperature hardness measured by the Rockwell hardness tester is 48.1 HRC. The sample is made into a standard tensile specimen size, the surface is polished smooth using sandpaper, and a servo-hydraulic material testing system is used for tensile test, the tensile speed is 10 -4 s -1 , the tensile strength at room temperature (20 ℃) is 1640 MPa, the yield strength is 1368 MPa, and the tensile strength at high temperature (550 ℃) is 957 MPa, and the yield strength is 871 MPa.

[0086] Table 1 Performance index of die steel prepared in Examples 1-5

[0087]

[0088]

[0089] As can be seen from the experimental data in Table 1, the density of each example is more than 99%, which indicates that the powder has good powder densification forming property, the printed state of the powder forming also has good strength before tempering, and by selecting a laser forming parameter, the strength will decrease with the increase of the tempering temperature, but the plasticity and toughness will increase with the increase of the tempering temperature.

[0090] In the description of the specification, the description of the terms "one embodiment", "an example", "a specific example" and the like means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any appropriate way in one or more embodiments or examples.

[0091] The basic principles, main features and advantages of the present application are shown and described above. Those skilled in the art should understand that the present application is not limited by the above embodiments, and the above embodiments and descriptions in the specification are only to illustrate the principles of the present application. Without departing from the spirit and scope of the present application, various changes and improvements can be made to the present application, and these changes and improvements all fall within the scope of the claimed present application.

Claims

1. A method for manufacturing a die steel additive for die casting core formation, characterized in that: The following steps are involved: Design of nanoparticle-reinforced mold steel additive powder: Prepare nanoparticle master alloy by mixing Al powder, Ti powder, and boron carbide in a mass ratio of 24:6:

70. Place the mixed powder in a high-energy ball mill and mix it uniformly at 40 rpm for 48 hours. The mixed powder is then coated with aluminum foil. Pre-pressing is performed on a hydraulic testing machine to obtain a cold pressed block, which is then placed in a graphite mold and heated in a vacuum sintering furnace to undergo combustion synthesis reaction, ultimately obtaining TiC+ / Al master alloy; The chemical composition and mass percentage of high performance die steel are: C: 0.48wt.%; Si: 0.30wt.%; Mn: 0.4wt.%; P: 0.015wt.%; S: 0.002wt.%; Cr: 4.5wt.%; Mo: 3.0wt.%; V: 0.55wt.%; Cu: 0.05wt.%; the balance is Fe; High-performance mold steel is cut into blocks of 2 kg and placed in the furnace of a medium-frequency induction furnace for remelting; pre-cut TiC+ / Al master alloy is added into the medium frequency induction furnace to obtain molten steel. When the steel is tapped at 1650℃, the molten steel is uniformly injected into the ladle at 1500℃. Nano-TiC+ The particles disperse in the molten steel as it boils, and Al acts as a deoxidizer to generate aluminum oxides that float above the molten steel. The molten steel is then poured into a sand mold to obtain a TiC content of 0.02wt.% and Strengthened mold steel; Preparation of nanoparticle-reinforced powders: The obtained nanoparticle-reinforced mold steel is placed in a medium-frequency induction furnace for remelting, and the nanoparticle-reinforced mold steel is heated to a liquid state and maintained at 1650°C for 2 minutes to obtain a nanoparticle-reinforced mold steel melt; Under a nitrogen environment, the obtained molten metal is transferred to a tundish. The molten metal flows freely downward from the opening at the bottom of the tundish with a diameter of 4 mm. Then, nitrogen gas at a pressure of 4 MPa is introduced into the sealed channel. The nitrogen gas can blow away the freely flowing molten metal downward, realizing the nitrogen atomization process. After the atomized molten metal falls freely, it cools at the bottom to form nanoparticle-reinforced powder. The obtained powder is then sieved and divided into two parts for sieving, and the sieving requirements are 15-53μm and 53-150μm respectively; The laser additive powder size selected subsequently was: 15-53μm, the absorption rate of the 1064 laser band was 36.43%, and it was prepared using selective laser melting technology, with a fixed laser power of 200W, a scanning speed of 900mm / s, a powder layer thickness of 30μm, a laser scanning spacing of 100μm, and a laser scanning strategy of 70° interlayer rotation, so that the components can be formed with high density.

2. A method for manufacturing a die steel additive for die casting core formation, characterized in that: The following steps are involved: Design of nanoparticle-reinforced mold steel additive powder: Prepare nanoparticle master alloy by mixing Al powder, Ti powder, and boron carbide in a mass ratio of 24:6:

70. Place the mixed powder in a high-energy ball mill and mix it uniformly at 40 rpm for 36 hours. The mixed powder is then coated with aluminum foil. Pre-pressing is performed on a hydraulic testing machine to obtain a cold pressed block, which is then placed in a graphite mold and heated in a vacuum sintering furnace to undergo combustion synthesis reaction, ultimately obtaining TiC+ / Al master alloy; The chemical composition and mass percentage of high performance die steel are: C: 0.53wt.%; Si: 0.3wt.%; Mn: 0.2wt.%; P: 0.015wt.%; S: 0.002wt.%; Cr: 5.0wt.%; Mo: 2.8wt.%; V: 0.65wt.%; Ti: 0.005wt.%; Cu: 0.05wt.%; the balance is Fe; High-performance mold steel is cut into blocks of 1 kg and placed in the furnace of a medium-frequency induction furnace for remelting; pre-cut TiC+ / Al master alloy is added into the medium frequency induction furnace to obtain molten steel. When the steel is tapped at 1650℃, the molten steel is uniformly injected into the ladle at 1500℃. Nano-TiC+ The particles disperse in the molten steel as it boils, and Al acts as a deoxidizer to generate aluminum oxides that float above the molten steel. The molten steel is then poured into a sand mold to obtain a TiC content of 0.05wt.% and Strengthened mold steel; Preparation of nanoparticle-reinforced powders: The obtained nanoparticle-reinforced mold steel is placed in a medium-frequency induction furnace for remelting, and the nanoparticle-reinforced mold steel is heated to a liquid state and maintained at 1600°C for 3 minutes to obtain a nanoparticle-reinforced mold steel melt; Under a nitrogen environment, the obtained molten metal is transferred to a tundish. The molten metal flows freely downward from the opening at the bottom of the tundish with a diameter of 4 mm. Then, nitrogen gas at a pressure of 4 MPa is introduced into the sealed channel. The nitrogen gas can blow away the freely flowing molten metal downward, realizing the nitrogen atomization process. After the atomized molten metal falls freely, it cools at the bottom to form nanoparticle-reinforced powder. The obtained powder is then sieved and divided into two parts for sieving, and the sieving requirements are 15-53μm and 53-150μm respectively; The size of the laser additive powder selected subsequently was: 15-53μm, and it was prepared using selective laser melting technology. The laser power was fixed at 200W, the scanning speed was 1000mm / s, the powder layer thickness was fixed at 30μm, the laser scanning spacing was fixed at 100μm, and the laser scanning strategy was a 70° interlayer rotation, so that the components achieved high-density forming.

3. A method for manufacturing a die steel additive for die casting core formation, characterized in that: The following steps are involved: Design of nanoparticle-reinforced mold steel additive powder: Prepare nanoparticle master alloy by mixing Al powder, Ti powder, and boron carbide in a mass ratio of 24:6:

70. Place the mixed powder in a high-energy ball mill and mix it uniformly at 40 rpm for 48 hours. The mixed powder is then coated with aluminum foil. Pre-pressing is performed on a hydraulic testing machine to obtain a cold pressed block, which is then placed in a graphite mold and heated in a vacuum sintering furnace to undergo combustion synthesis reaction, ultimately obtaining TiC+ / Al master alloy; The chemical composition and mass percentage of high performance mold steel are: C: 0.50wt.%; Si: 0.3wt.%; Mn: 0.3wt.%; P: 0.015wt.%; S: 0.002wt.%; Cr: 4.8wt.%; Mo: 2.9wt.%; V: 0.59wt.%; Cu: 0.05wt.%; the balance is Fe; High-performance mold steel is cut into blocks of 2 kg and placed in the furnace of a medium-frequency induction furnace for remelting; pre-cut TiC+ / Al master alloy is added into the medium frequency induction furnace to obtain molten steel. When the steel is tapped at 1650℃, the molten steel is uniformly injected into the ladle at 1500℃. Nano-TiC+ The particles are dispersed in the molten steel as it boils. Al acts as a scavenger, and the generated aluminum oxide floats above the molten steel. The molten steel is then poured into a sand mold with a content of 0.02wt.% TiC and Strengthened mold steel; Preparation of nanoparticle-reinforced powders: The obtained nanoparticle-reinforced mold steel is placed in a medium-frequency induction furnace for remelting, and the nanoparticle-reinforced mold steel is heated to a liquid state and maintained at 1650°C for 2 minutes to obtain a nanoparticle-reinforced mold steel melt; Under a nitrogen environment, the obtained molten metal is transferred to a tundish. The molten metal flows freely downward from the opening at the bottom of the tundish with a diameter of 4 mm. Then, nitrogen gas at a pressure of 4 MPa is introduced into the sealed channel. The nitrogen gas can blow away the freely flowing molten metal downward, realizing the nitrogen atomization process. After the atomized molten metal falls freely, it cools at the bottom to form nanoparticle-reinforced powder. The obtained powder is then sieved and divided into two parts for sieving, and the sieving requirements are 15-53μm and 53-150μm respectively; The size of the laser additive powder selected subsequently was: 15-53μm, and it was prepared using selective laser melting technology. The laser power was fixed at 200W, the scanning speed was 900mm / s, the powder layer thickness was fixed at 30μm, the laser scanning spacing was fixed at 100μm, and the laser scanning strategy was a 70° interlayer rotation, so that the components achieved high-density forming.

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