Endogenous nanoparticle reinforced die steel additive manufacturing powder and preparation method

Abstract

The invention provides endogenous nano-particle reinforced die steel additive manufacturing powder and a preparation method of the endogenous nano-particle reinforced die steel additive manufacturing powder. The preparation method of the endogenous nano-particle reinforced die steel additive manufacturing powder comprises the steps that Nb powder and BN powder are evenly mixed and then mixed with Fe powder according to the proportion of 75%-85%: 15%-25%, 55%-65%: 35%-45% and 45%-55%: 45%-55% to obtain three powder mixtures, the three powder mixtures are sequentially wrapped in aluminum foil, and wires with the powder mixtures distributed in a gradient mode are obtained after packaging is conducted through a wire wrapping machine. The method comprises the following steps: adding a wire material into a die steel melt under the protection of argon, continuously reacting a powder mixture under the action of high temperature to introduce generated nanoparticles into the melt, and carrying out vacuum casting to obtain an as-cast steel billet containing the nanoparticles. And then electroslag remelting treatment is carried out on the as-cast steel billet to obtain a melt, and argon is used for carrying out injection atomization and sedimentation treatment on the melt to obtain the endogenous nano-particle reinforced die steel additive manufacturing powder.

Description

Technical Field

[0001] The present invention relates to the technical field of additive manufacturing, and in particular to an additive manufacturing powder of an endogenous nanoparticle-reinforced die steel and a preparation method thereof. Background Art

[0002] Mold steel is an important industrial material, widely used in the fields of manufacturing molds, stamping parts and forming tools. In recent years, with the rapid development of additive manufacturing technology, researchers have used selective laser melting (SLM) technology to realize mold manufacturing and mold repair of complex structures, which has gradually become a research hotspot. However, in the SLM process, the characteristics of the powder play a key role in the performance of the final product. Traditional mold steel powder has problems such as poor fluidity, insufficient density and poor strength and plasticity after printing, which limit the application of mold steel in the field of additive manufacturing. Therefore, improving the fluidity and formability of powder to improve the strength and plasticity of powder after molding is an important task in the development of mold steel powder materials. The existing technology improves the formability of powder by optimizing printing process and parameters, increasing laser energy density, preheating printing substrates, etc., but the adjustment of related parameters is difficult and costly, and can cause problems such as reduced powder molding quality and reduced powder utilization. Therefore, improving powder fluidity, formability and improving the strength and plasticity of powder after molding are technical problems that need to be solved in the additive manufacturing process of mold steel. Summary of the invention

[0003] In order to solve the above technical problems, the present invention provides an endogenous nanoparticle reinforced mold steel additive manufacturing powder, and its preparation method comprises the following steps:

[0004] (1) Nb powder and BN powder are mixed in a mass ratio of 55-65%:35-45%, and mixed in a ball mill at a speed of 30-45 rpm for 120-180 minutes to obtain powder No. 1, and then powder No. 1 is mixed with Fe powder in mass ratios of 75-85%:15-25%, 55-65%:35-45%, and 45-55%:45-55% to obtain powder No. 2, powder No. 3, and powder No. 4, respectively;

[0005] The particle size of the Nb powder is 50-150 μm, the particle size of the BN powder is 20-100 μm, and the particle size of the Fe powder is 10-150 μm;

[0006] (2) adding powders No. 2, 3 and 4 obtained in step 1 to a strip of aluminum foil in a mass ratio of 5-15%: 15-25%: 65-75% in sequence, and packaging with a wire wrapping machine at a speed of 2-4 m / min to obtain a powder mixture gradient distribution wire;

[0007] (3) Under argon protection, heat the die steel at 1550 - 1700 °C for 40 - 80 min to obtain a melt, and uniformly mix the powder mixture gradient distribution wire obtained in step (2) with the melt at a mass ratio of 0.01% - 0.08%:1. Under argon protection, keep it at 1600 - 1800 °C. After the wire melts in the melt, obtain an as-cast steel billet containing nanoparticles through vacuum casting;

[0008] The composition of the die steel is as follows by mass percentage: Cr: 4.85 - 5.05 wt.%; Mo: 2.85 - 3.05 wt.%; C: 0.50 - 0.54 wt.%; Si: 0.10 - 0.20 wt.%; Mn: 0.25 - 0.35 wt.%; V: 0.55 - 0.65 wt.%; P: ≤0.002 wt.%; S: ≤0.003 wt.%; the balance is Fe;

[0009] (4) Keep the as-cast steel billet containing nanoparticles obtained in step (3) at 1650 - 1800 °C for 40 - 80 min for electroslag remelting treatment to obtain a melt. Use argon gas with a gas pressure of 4 - 6 MPa to spray and atomize the melt, and then obtain the powder of die steel reinforced with in-situ nanoparticles after sedimentation treatment at room temperature;

[0010] The yield strength of the powder of die steel reinforced with in-situ nanoparticles after SLM treatment is ≥980 MPa, the tensile strength is ≥1482 MPa, and the fracture strain is ≥1.82%.

[0011] Furthermore, the particle size of the Nb powder in step (1) is 70 - 140 μm, the particle size of the BN powder is 40 - 90 μm, and the particle size of the Fe powder is 40 - 130 μm.

[0012] Furthermore, the composition of the die steel in step (3) is as follows by mass percentage: Cr: 4.9 - 5.0 wt.%; Mo: 2.9 - 3.0 wt.%; C: 0.51 - 0.53 wt.%; Si: 0.12 - 0.18 wt.%; Mn: 0.26 - 0.34 wt.%; V: 0.56 - 0.62 wt.%; P: ≤0.001 wt.%; S: ≤0.002 wt.%; the balance is Fe. Description of the Drawings

[0013] Figure 1 It is the room-temperature engineering stress-strain curve of the specimen obtained after SLM treatment of the powder of die steel reinforced with in-situ nanoparticles 1 in Example 1 of the present invention;

[0014] Figure 2 It is the room-temperature engineering stress-strain curve of the specimen obtained after SLM treatment of the powder of die steel reinforced with in-situ nanoparticles 2 in Example 2 of the present invention;

[0015] Figure 3 This is the room-temperature engineering stress-strain curve of the specimen obtained after SLM processing of the mold steel powder 3 containing endogenic nanoparticle reinforcement in Example 3 of the present invention;

[0016] Figure 4 This is the room-temperature engineering stress-strain curve of the specimen obtained after SLM processing of the mold steel powder 4 in Comparative Example 1 of the present invention. Detailed implementation manners

[0017] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Apparently, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0018] Example 1

[0019] The mold steel powder 1 containing endogenic nanoparticle reinforcement, and its preparation method steps are as follows:

[0020] (1) Mix Nb powder and BN powder according to a mass ratio of 60%:40%, put them into a ball milling device and mix for 150 minutes at a rotation speed of 30 revolutions per minute to obtain Powder No. 1, and then mix Powder No. 1 with Fe powder according to mass ratios of 80%:20%, 60%:40% and 50%:50% respectively to obtain Powder No. 2, Powder No. 3 and Powder No. 4;

[0021] The particle size of the Nb powder is 50 - 150 μm, the particle size of the BN powder is 20 - 100 μm, and the particle size of the Fe powder is 10 - 150 μm;

[0022] (2) Add the obtained Powders No. 2, 3 and 4 in step 1 to a strip-shaped aluminum foil in sequence according to mass ratios of 10%, 20% and 70%, and encapsulate them with a wire wrapping machine at a speed of 4 m / min to obtain a wire material with a gradient distribution of powder mixture;

[0023] (3) Under argon protection, heat the mold steel at 1550 °C for 80 min to obtain Melt 1, mix the wire material with a gradient distribution of powder mixture obtained in step (2) with Melt 1 according to a mass ratio of 0.02%:1, keep it warm at 1800 °C under argon protection, wait for the wire material to melt in the melt, and then obtain the as-cast steel billet 1 containing nanoparticles after vacuum casting;

[0024] By mass percentage, the composition of the die steel is as follows: Cr: 4.95 wt.%; Mo: 2.95 wt.%; C: 0.52 wt.%; Si: 0.16 wt.%; Mn: 0.31 wt.%; V: 0.60 wt.%; P: 0.0015 wt.%; S: 0.002 wt.%; the balance is Fe.

[0025] (4) The as-cast steel billet 1 containing nanoparticles obtained in step (3) was held at 1700 °C for 60 min and then subjected to electroslag remelting treatment to obtain melt 2. After the melt 2 was blown and atomized with argon gas at a gas pressure of 5 MPa, the as-cast steel powder 1 reinforced with in-situ nanoparticles was obtained after sedimentation treatment at room temperature.

[0026] In this example, the as-cast steel powder 1 reinforced with in-situ nanoparticles was prepared. The room-temperature engineering stress-strain curve of the specimen obtained after SLM treatment is as Figure 1 shown. The yield strength is 980 MPa, the tensile strength is 1519 MPa, and the fracture strain is 1.77%.

[0027] Example 2

[0028] The as-cast steel powder 2 reinforced with in-situ nanoparticles, and its preparation method steps are as follows:

[0029] (1) Mix Nb powder and BN powder according to a mass ratio of 55%:45%, put them into a ball milling device and mix for 170 minutes at a rotation speed of 35 revolutions per minute to obtain powder 1. Then, mix powder 1 with Fe powder according to mass ratios of 75%:25%, 55%:45%, and 45%:55% respectively to obtain powder 2, powder 3, and powder 4.

[0030] The particle size of the Nb powder is 50 - 150 μm, the particle size of the BN powder is 20 - 100 μm, and the particle size of the Fe powder is 10 - 150 μm.

[0031] (2) Add the obtained powders 2, 3, and 4 in step 1 to a strip-shaped aluminum foil in sequence according to a mass ratio of 15%, 20%, and 65%, and encapsulate them with a wire wrapping machine at a speed of 3 m / min to obtain a wire material with a gradient distribution of powder mixture.

[0032] (3) Under argon protection, heat the die steel at 1700 °C for 40 min to obtain melt 3. Mix the wire material with a gradient distribution of powder mixture obtained in step (2) with melt 3 according to a mass ratio of 0.04%:1. Under argon protection, hold at 1700 °C. After the wire material melts in the melt, vacuum casting is carried out to obtain the as-cast steel billet 2 containing nanoparticles.

[0033] By mass percentage, the composition of the die steel is: Cr: 4.95 wt.%; Mo: 2.95 wt.%; C: 0.52 wt.%; Si: 0.16 wt.%; Mn: 0.31 wt.%; V: 0.60 wt.%; P: 0.0015 wt.%; S: 0.002 wt.%; the balance is Fe.

[0034] (4) The as-cast steel billet 2 containing nanoparticles obtained in step (3) is held at 1750 °C for 40 min and then subjected to electroslag remelting treatment to obtain a melt 4. The melt 4 is spray atomized with argon gas at a gas pressure of 4 MPa, and then collected by sedimentation treatment at room temperature to obtain the in-situ nano-particle reinforced die steel powder 2.

[0035] In this example, the in-situ nano-particle reinforced die steel powder 2 is prepared. The engineering stress-strain curve of the specimen obtained after SLM treatment at room temperature is as Figure 2 shown. Its yield strength is 999 MPa, the tensile strength is 1766 MPa, and the fracture strain is 1.93%.

[0036] Example 3

[0037] The in-situ nano-particle reinforced die steel powder 3 is prepared, and its preparation method steps are as follows:

[0038] (1) Mix Nb powder and BN powder according to a mass ratio of 65%:35%, put them into a ball milling device and mix for 120 minutes at a rotation speed of 45 revolutions per minute to obtain the No. 1 powder. Then, mix the No. 1 powder and Fe powder according to mass ratios of 85%:15%, 55%:45%, and 55%:45% respectively to obtain the No. 2 powder, No. 3 powder, and No. 4 powder.

[0039] The particle size of the Nb powder is 50 - 150 μm, the particle size of the BN powder is 20 - 100 μm, and the particle size of the Fe powder is 10 - 150 μm.

[0040] (2) Add the No. 2, No. 3, and No. 4 powders obtained in step 1 to the strip-shaped aluminum foil in sequence according to mass ratios of 10%, 15%, and 75%, and encapsulate them with a wire wrapping machine at a speed of 2 m / min to obtain a wire material with a gradient distribution of powder mixture.

[0041] (3) Under argon protection, heat the die steel at 1600 °C for 60 min to obtain a melt 5. Mix the wire material with a gradient distribution of powder mixture obtained in step (2) and the melt 5 according to a mass ratio of 0.06%:1. Under argon protection, hold at 1600 °C. After the wire material melts in the melt, vacuum casting is carried out to obtain the as-cast steel billet 3 containing nanoparticles.

[0042] By mass percentage, the composition of the die steel is: Cr: 4.95 wt.%; Mo: 2.95 wt.%; C: 0.52 wt.%; Si: 0.16 wt.%; Mn: 0.31 wt.%; V: 0.60 wt.%; P: 0.0015 wt.%; S: 0.002 wt.%; the balance is Fe.

[0043] (4) The as-cast steel billet 3 containing nanoparticles obtained in step (3) is held at 1650 °C for 80 min and then subjected to electroslag remelting treatment to obtain a melt 6. The melt 6 is spray atomized with argon gas at a gas pressure of 5 MPa, and then collected by sedimentation treatment at room temperature to obtain the die steel powder body 3 reinforced with in-situ nanoparticles.

[0044] For the die steel powder body 3 reinforced with in-situ nanoparticles prepared in this example, the room-temperature engineering stress-strain curve of the specimen obtained after SLM treatment is as Figure 3 shown. Its yield strength is 985 MPa, its tensile strength is 1482 MPa, and its fracture strain is 1.73%.

[0045] Comparative Example 1

[0046] A die steel powder body 4, and its preparation method steps include the following:

[0047] (1) Under argon protection, the die steel is heated at 1600 °C for 60 min to obtain a melt 7, and then the as-cast steel billet 4 of the die steel is obtained through vacuum casting.

[0048] By mass percentage, the composition of the die steel is: Cr: 4.95 wt.%; Mo: 2.95 wt.%; C: 0.52 wt.%; Si: 0.16 wt.%; Mn: 0.31 wt.%; V: 0.60 wt.%; P: 0.0015 wt.%; S: 0.002 wt.%; the balance is Fe.

[0049] (2) The as-cast steel billet 4 of the die steel obtained in step (1) is held at 1650 °C for 80 min and subjected to electroslag remelting treatment to obtain a melt 8. The melt 8 is spray atomized with argon gas at a gas pressure of 6 MPa, and then collected by sedimentation treatment at room temperature to obtain the die steel additive manufacturing powder body 4.

[0050] For the die steel powder body 4 prepared in this example, the room-temperature engineering stress-strain curve of the specimen obtained after SLM treatment is as Figure 4 shown. Its yield strength is 950 MPa, its tensile strength is 1145 MPa, and its fracture strain is 1.04%.

[0051] The difference between Examples 1-3 of the present invention and Comparative Example 1 is that:

[0052] The yield strength of the specimen obtained after SLM treatment of the in-situ nano-particle reinforced die steel powder 1 prepared in Example 1 was 980 MPa, the tensile strength was 1519 MPa, and the fracture strain was 1.77%. Compared with Comparative Example 1, the yield strength (950 MPa), tensile strength (1145 MPa), and fracture strain (1.04%) were increased by 3.1%, 32.6%, and 70.6% respectively. Therefore, the mechanical properties of the specimen obtained after SLM treatment of the die steel powder obtained in this example were significantly better than those of Comparative Example 1.

[0053] The yield strength of the specimen obtained after SLM treatment of the in-situ nano-particle reinforced die steel powder 2 prepared in Example 2 was 999 MPa, the tensile strength was 1766 MPa, and the fracture strain was 1.93%. Compared with Comparative Example 1, the yield strength (950 MPa), tensile strength (1145 MPa), and fracture strain (1.04%) were increased by 5.1%, 54.2%, and 85.5% respectively. Therefore, the mechanical properties of the specimen obtained after SLM treatment of the die steel powder obtained in this example were significantly better than those of Comparative Example 1.

[0054] The yield strength of the specimen obtained after SLM treatment of the in-situ nano-particle reinforced die steel powder 3 prepared in Example 3 was 985 MPa, the tensile strength was 1482 MPa, and the fracture strain was 1.73%. Compared with Comparative Example 1, the yield strength (950 MPa), tensile strength (1145 MPa), and fracture strain (1.04%) were increased by 3.6%, 29.4%, and 66.3% respectively. Therefore, the mechanical properties of the specimen obtained after SLM treatment of the die steel powder obtained in this example were significantly better than those of Comparative Example 1.

[0055] Comparative Example 2

[0056] In the article "Numerical and experimental evaluation of a conformally cooled H13 steel injection mould manufactured with selective laser melting" published in the *International Journal of Advanced Manufacturing Technology*, Volume 93, Pages 881 - 900 in 2017, Maciej Mazur et al. first heated the substrate to 200 °C, and then performed SLM treatment on the H13 steel powder to obtain an H13 steel specimen. The tensile strength of this specimen was 1370 MPa and the elongation was 1.7%; for the specimen obtained by directly performing SLM treatment on the H13 steel powder without heating the substrate, the tensile strength was 1260 MPa and the elongation was 1.6%. This comparative example improved the mechanical properties of the powder after forming by adding the process of substrate heating; by mass percentage, the chemical composition of H13 steel in Comparative Example 2 was: Cr: 5.22 wt.%; Mo: 1.5 wt.%; C: 0.42 wt.%; Si: 0.85 wt.%; V: 1.04 wt.%; S: 0.01 wt.%; P: 0.01 wt.%; the balance was Fe. The technical inspiration given by Comparative Example 2 is that the combination of substrate preheating process and SLM can help improve the mechanical properties and plasticity of die steel.

[0057] Table 1 Room temperature mechanical properties of die steel powder after SLM forming in comparative examples and each example

[0058]

[0059] The strength and plasticity of the die steel obtained in Examples 1 - 3 of the present invention are superior to those of the die steel obtained by the prior art. In addition, the components, ratios and process parameters used in Examples 1 - 3 of the present invention are all different. Among them, the strength and plasticity of the die steel powder obtained after SLM forming in Example 2 are the highest among all examples, but the component ratio used in this example is not the highest. This shows that the most excellent properties of the die steel obtained in the present invention are not determined by a certain component or process parameter, but are achieved through the synergistic regulation of components, component ratios, processes and process parameters.

[0060] In summary, compared with the prior art, through the synergistic regulation of components, ratios, processes, and process parameters, the present invention enables the obtained die steel powder to have more excellent strength and plasticity after being formed by SLM without adopting processes such as increasing the laser energy density and preheating the printing substrate. The specific advantages include: compared with the uneven particle distribution and agglomeration phenomena that occur when two powders are blended by the traditional external addition method, the present invention introduces nano-particles into the die steel by using the in-melt generation method, making the nano-particles evenly distributed in the die steel, and the size range of the introduced nano-particles is 70-140 nm. And this method effectively synchronously improves the strength and plasticity of the die steel powder after forming. And compared with the traditional external addition method that requires adding a high content of nano-particles (usually ≥0.1 wt.%), only a trace amount of nano-particles (≤0.1 wt.%) needs to be added in this paper to achieve the strengthening and toughening effect achieved by the previous technology, with obvious cost advantages. At the same time, avoiding the use of pre-heat treatment and high-energy laser density in the early stage reduces the cost, breaks through the bottleneck that it is difficult to synchronously improve the strength and plasticity of the powder formed parts in the prior art, that is, when the strength of the powder formed parts is increased, the plasticity of the powder formed parts will be reduced; in addition, the bottleneck that the prior art can only be prepared in the laboratory and it is difficult to realize the industrial production of enhanced die steel can be overcome through the synergistic regulation of the interaction between components, component ratios, processes, and process parameters, and the industrial stable production of high-strength and high-plasticity die steel powder materials can be realized.

Claims

1. An endogenous nanoparticle-reinforced die steel additive manufacturing powder, characterized in that: Its preparation method comprises the following steps: (1) Nb powder and BN powder are mixed in a mass ratio of 55-65%:35-45%, and mixed in a ball mill at a speed of 30-45 rpm for 120-180 minutes to obtain powder No. 1, and then powder No. 1 is mixed with Fe powder in mass ratios of 75-85%:15-25%, 55-65%:35-45%, and 45-55%:45-55% to obtain powder No. 2, powder No. 3, and powder No. 4, respectively; The particle size of the Nb powder is 50-150 μm, the particle size of the BN powder is 20-100 μm, and the particle size of the Fe powder is 10-150 μm; (2) adding powders No. 2, 3 and 4 obtained in step 1 to a strip of aluminum foil in a mass ratio of 5-15%: 15-25%: 65-75% in sequence, and packaging with a wire wrapping machine at a speed of 2-4 m / min to obtain a powder mixture gradient distribution wire; (3) Under argon protection, the mold steel is heated at 1550-1700° C. for 40-80 min to obtain a melt, and the powder mixture gradient distribution wire obtained in step (2) is uniformly mixed with the melt at a mass ratio of 0.01%-0.08%:1; Under the protection of argon, the temperature is kept at 1600-1800°C, and after the wire material is melted in the melt, a cast steel billet containing nanoparticles is obtained by vacuum casting; The mold steel composition is calculated by mass percentage as follows: Cr: 4.85-5.05wt.%; Mo: 2.85-3.05wt.%; C: 0.50-0.54wt.%; Si: 0.10-0.20wt.%; Mn: 0.25-0.35wt.%; V: 0.55-0.65wt.%; P: ≤0.002wt.%; S: ≤0.003wt.%; the balance is Fe; (4) subjecting the as-cast steel billet containing nanoparticles obtained in step (3) to electroslag remelting treatment at 1650-1800° C. for 40-80 min to obtain a melt, spraying and atomizing the melt using argon gas at a gas pressure of 4-6 MPa, and then subjecting the melt to sedimentation treatment at room temperature to obtain a mold steel powder containing endogenous nanoparticles reinforced; The yield strength of the mold steel powder containing endogenous nanoparticles reinforced after SLM treatment is ≥980MPa, the tensile strength is ≥1482MPa, and the fracture strain is ≥1.82%.

2. The endogenous nanoparticle-reinforced die steel additive manufacturing powder according to claim 1, characterized in that: The particle size of the Nb powder in step (1) is 70-140 μm, the particle size of the BN powder is 40-90 μm, and the particle size of the Fe powder is 40-130 μm.

3. The endogenous nanoparticle-reinforced die steel additive manufacturing powder according to claim 1, characterized in that: The mold steel composition described in step (3) is, in terms of mass percentage, Cr: 4.9-5.0wt.%; Mo: 2.9-3.0wt.%; C: 0.51-0.53wt.%; Si: 0.12-0.18wt.%; Mn: 0.26-0.34wt.%; V: 0.56-0.62wt.%; P: ≤0.001wt.%; S: ≤0.002wt.%; and the balance is Fe.

Images