High-strength and high-toughness steel based on laser rapid melting and additive manufacturing method of high-strength and high-toughness steel

Abstract

The invention provides high-strength and high-toughness steel based on laser rapid melting, and the alloy components of the high-strength and high-toughness steel comprise the following elements in percentage by mass: 0.1-0.3% of C, 0.1-2.6% of Mn, 0.1-1.5% of Ni, 0.1-4% of Mo, 1-4.5% of W, 0.1-1.2% of Si and the balance of Fe and inevitable impurity elements, in the impurity elements, P is less than or equal to 0.01%, and S is less than or equal to 0.02%; wherein the ratio of the sum of the mass percentages of Ni and Mn to the mass percentage of Si is not less than 1.572. Meanwhile, the invention further discloses an additive manufacturing method of the high-strength and high-toughness steel based on laser rapid melting. According to the high-strength and high-toughness steel, the influence of alloying elements on an Mf point and an Ac1 point is fully considered during design, it is ensured that all sedimentary structures are lath martensite, and the macrosegregation phenomenon in solidification structures is avoided through laser rapid melting; and then nanoscale film austenite is obtained on the two sides of the lath martensite through in-situ laser ultra-fast heat treatment or off-site infrared ultra-fast heat treatment, and the high yield strength of 1200 MPa and the ultrahigh Charpy V-shaped notch impact energy of 120 J are obtained.

Description

Technical Field

[0001] The present invention belongs to the technical field of metal additive manufacturing, and particularly relates to a high-strength and high-toughness steel based on laser rapid melting and solidification and an additive manufacturing method thereof. Background Art

[0002] High-strength and high-toughness steels are a class of metal materials with both high strength and excellent fracture toughness, and are widely used in fields with extremely high requirements for safety and reliability, such as aerospace, energy equipment, etc., such as load-bearing components of spacecraft, brackets for precision instruments, and lightweight components. However, there is often an inverse relationship between the strength and toughness of steel materials, which poses a huge challenge to the design of steel materials that take into account both high strength and high toughness. Existing research has shown that introducing an appropriate amount of austenite into steel plays an important role in improving the toughness of steel. However, the austenite introduced after traditional forging or heat treatment has problems such as large size and uneven distribution, which will have an adverse impact on the strength and toughness of the material; on the other hand, due to the influence of carbon content on the processability of additive manufacturing, there is basically no high-strength and high-toughness steel suitable for additive manufacturing.

[0003] Patent CN102644025A, titled "A High-Strength and High-Toughness Steel Plate and a Preparation Method Thereof". Its alloy composition by mass percentage includes C: 0.03 - 0.09%, Si: 0.2 - 0.35%, Mn: 0.80 - 1.60%, Nb: 0.06 - 0.08%, Cu: 1.00 - 1.35%, Ni: 1.00 - 1.80%, Al: 0.62 - 0.68%, P≤0.005%, P≤0.020%, S≤0.010%, and the balance is Fe and unavoidable impurity elements. This patent mainly utilizes the strengthening effect of Al in steel materials. However, this alloy composition contains Nb, Cu, and Al, and the yield strength of the high-strength and high-toughness steel in this invention is ≥650 MPa, the tensile strength is ≤900 MPa, and the Charpy V-notch impact energy is ≥90 J, and its comprehensive performance is far inferior to that of the high-strength and high-toughness steel in the present invention.

[0004] Patent CN119328159A, titled "Method for Improving the Impact Toughness of Martensitic Stainless Steel by Arc Additive Manufacturing through Nitrogen Alloying", although it belongs to the technical field of additive manufacturing like this patent, its alloy range is the martensitic stainless steel material system. This patent mainly uses nitrogen to refine grains and regulate the austenite and ferrite to improve the impact toughness of arc additive manufacturing martensitic stainless steel. However, the highest Charpy V-notch impact energy in this invention patent is only 45.765 J, which is much smaller than the performance of the high-strength and high-toughness steel in the present invention.

[0005] Therefore, there is an urgent need to develop a high-strength and high-toughness steel that can balance the strength and toughness of the material and give the corresponding preparation method. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a high-strength and tough steel based on laser rapid melting and solidification and its additive manufacturing method in view of the deficiencies of the above-mentioned prior art, so as to solve the problem of the mismatch between the strength and toughness of steel in the field of metal additive manufacturing.

[0007] To solve the above technical problems, the technical solution adopted by the present invention is: a high-strength and tough steel based on laser rapid melting and solidification, characterized in that the alloy composition of the high-strength and tough steel is composed of the following elements in mass percentages: C: 0.1-0.3%, Mn: 0.1-2.6%, Ni: 0.1-1.5%, Mo: 0.1-4%, W: 1-4.5%, Si: 0.1-1.2%, and the balance is Fe and unavoidable impurity elements, and in the impurity elements, P≤0.01%, S≤0.02%; among them, the ratio of the sum of the mass percentages of Ni and Mn to the mass percentage of Si is not less than 1.572; the yield strength of the high-strength and tough steel ≥1200 MPa, and the V-notch impact energy ≥120 J.

[0008] The present invention provides a reasonable design of the alloy composition of the laser rapid melting and solidification high-strength and tough steel based on A c1 and M f points. In terms of mass percentage, it is: A c1 =723-14×Mn%+22×Si%-14.4×Ni%+23.3×Cr%, M f =324-423×C%-30.4×Mn%-12.1×Cr%-17.7×Ni%-7.5×Mo%. The present invention regulates the composition range: on the one hand, because the M f point is lower than room temperature, which will lead to incomplete martensite transformation after laser rapid melting and solidification. Therefore, the present invention regulates the M f point to be higher than room temperature to obtain a non-segregated fully martensite structure; on the other hand, because too high Ac1 will lead to too large austenite nucleation driving force, and the thin-film austenite is prone to instability and grow into coarse austenite. Therefore, the present invention regulates the A c1 point temperature to match the subsequent heat treatment process to ensure specific tissue changes during the heat treatment process.

[0009] C in the present invention is the main strengthening element in steel, but the addition of C will increase the carbon equivalent, resulting in very large internal stress in the formed part during laser rapid melting and solidification (cooling rate 10 3-8 K / s), which is prone to cracking, and this cracking tendency increases with the increase of C content. On the other hand, excessive C content will form large-size carbides, deteriorating the material properties. Therefore, the present invention reasonably controls the C content within 0.1-0.3%, which not only ensures the strengthening effect but also avoids the cracking tendency, realizing high-quality forming with high density (>99%).

[0010] Si is usually substitutionally dissolved in steel, hindering dislocation movement and increasing the strength of steel. At the same time, Si can improve the fluidity of the molten pool during the laser rapid melting and solidification process, and improve the formability of steel by laser rapid melting and solidification. Si can effectively reduce the oxygen content in the original steel powder. However, Si will greatly increase the A c1 point temperature, which is not conducive to the formation of reverse transformation austenite during the heat treatment process. Therefore, in the present invention, the Si content range is controlled to be 0.1 - 1.2%, and subsequently, the addition of Mn and Ni is used to eliminate the influence of Si on A c1 point.

[0011] The addition of Mn in steel is beneficial to the formation by laser rapid melting and solidification. Since low-melting-point FeS easily causes hot cracking of steel during the laser rapid melting and solidification process, a certain amount of Mn is added so that Mn combines with S to form high-melting-point MnS, improving the quality of steel formed by laser rapid melting and solidification. The addition of Mn can lower the A c1 point temperature, which is conducive to the formation of reverse transformation austenite during the heat treatment process. Mn can improve hardenability, but excessive addition will cause the M f point to decrease significantly. If the M f point is lower than room temperature, it is not conducive to obtaining a fully martensitic structure during laser rapid melting and solidification. Therefore, considering all aspects, the Mn content range is controlled to be 0.1 - 2.6%.

[0012] Ni is dissolved in the matrix, which can produce a significant solid solution strengthening effect. At the same time, it can improve the hardenability of steel and effectively improve its strength and toughness. On the other hand, Ni has a very small impact on the C equivalent of steel, and its improvement of alloy toughness can effectively ensure the processability of laser rapid melting and solidification. Although Ni can effectively lower the A c1 point temperature, which is conducive to the formation of reverse transformation austenite during the heat treatment process; however, excessive Ni may cause the M f point temperature to be lower than room temperature, which is not conducive to obtaining a fully martensitic structure during laser rapid melting and solidification. Therefore, considering various aspects, the Ni content range is controlled within 0.1 - 1.5%. At the same time, in order to eliminate the influence of Si on A c1 point, it is also necessary to satisfy that the ratio of the sum of the mass percentages of (Ni + Mn) to the mass percentage of Si is not less than 1.572.

[0013] The addition of Mo and W can improve the hardenability and thermal strength of steel, and help to improve the material hardness, wear resistance and high-temperature stability. When the steel contains elements such as Cr, Mn, and Ni that are prone to segregation at grain boundaries during heat treatment and cause temper brittleness, the addition of Mo and W can inhibit the temper brittleness caused by such elements, thereby improving the toughness of steel. However, excessive Mo will cause the M f point to be lower than room temperature, which is not conducive to the control of the structure during laser rapid melting and solidification. Compared with Mo, W has a smaller impact on the M fThe influence of points is relatively small. Therefore, considering from the aspects of tissue control and performance regulation, the content range of Mo in the present invention is controlled at 0.1-4%, and the content range of W is controlled at 1-4.5%.

[0014] By adding the above elements, the strengthening effect of alloy elements is ensured, and the cracking problem that is prone to occur during the laser rapid melting and solidification forming process of carbon steel is avoided; the M point is regulated between 92-306 °C to obtain a non-segregated fully martensitic structure; the A point is regulated between 667-723 °C, and the corresponding heat treatment process is matched, and a unique ultra-fast and precise heat treatment method is adopted to generate uniformly distributed nano-scale thin-film austenite. f point is between 92-306 °C to obtain a non-segregated fully martensitic structure; regulate the A C1 point is between 667-723 °C, and match the corresponding heat treatment process, and adopt a unique ultra-fast and precise heat treatment method to generate uniformly distributed nano-scale thin-film austenite.

[0015] Preferably, there is no macroscopic segregation in the microstructure of the high-strength and high-toughness steel, and it is composed of lath martensite and nano-scale austenite, wherein the content of thin-film austenite is 3-7% by volume percentage.

[0016] Preferably, the alloy composition of the high-strength and high-toughness steel is composed of the following elements in mass percentages: C: 0.19%, Mn: 1.2%, Ni: 1.4%, Mo: 3.28%, W: 3.53%, Si: 0.5%, and the balance is Fe and inevitable impurity elements. Among the impurity elements, P≤0.01% and S≤0.02%.

[0017] The present invention also provides an additive manufacturing method for high-strength and high-toughness steel based on laser rapid melting and solidification. This manufacturing method includes the following steps: Step 1: Take the alloy powder of high-strength and high-toughness steel and lay powder on the substrate to obtain the first layer of metal powder, then through laser rapid melting and solidification forming, and then perform in-situ laser ultra-fast heat treatment to obtain the first layer of high-strength and high-toughness steel; during the laser rapid melting and solidification forming process, the laser power is 260-320 W, the scanning speed is 600-900 mm / s, the scanning spacing is 0.08-0.11 mm, the surface energy density is 2.63-6.67 J / mm 2 , the powder laying layer thickness is 0.03-0.06 mm, and the substrate is preheated to a temperature not exceeding 80 °C; the laser power of the in-situ laser rapid heat treatment is 10-30 W, the scanning speed is 1000-1300 mm / s, the scanning spacing is 0.08-0.11 mm, and the surface energy density is 0.07-0.375 J / mm 2 ; Step 2: Lay powder on the first layer of high-strength and high-toughness steel obtained in Step 1, and then perform in-situ laser ultra-fast heat treatment and in-situ laser ultra-fast heat treatment in sequence to obtain the second layer of high-strength and high-toughness steel; repeat the above powder laying, in-situ laser ultra-fast heat treatment and in-situ laser ultra-fast heat treatment until high-strength and high-toughness steel with the required height is obtained.

[0018] The present invention also provides an additive manufacturing method for high-strength and tough steel based on laser rapid melting and solidification, and the manufacturing method includes the following steps: Step 1: Take alloy powder of high-strength and tough steel and spread the powder on a substrate, and then obtain a formed part of high-strength and tough steel through a layer-by-layer forming method of laser rapid melting and solidification; during the laser rapid melting and solidification forming process, the laser power is 260-320 W, the scanning speed is 600-900 mm / s, the scanning spacing is 0.08-0.11 mm, and the surface energy density is 2.63-6.67 J / mm 2 , the powder spreading layer thickness is 0.03-0.06 mm, and the substrate is preheated to a temperature not exceeding 80 °C in advance; Step 2: Take the formed part of high-strength and tough steel obtained in Step 1 and perform off-site infrared ultra-rapid heat treatment to finally obtain high-strength and tough steel; the process of the off-site infrared ultra-rapid heat treatment is: rapidly heat the formed part of high-strength and tough steel to 750-800 °C at a rate of not less than 100 °C / s, then hold for 3-5 min and take it out for air cooling to obtain high-strength and tough steel.

[0019] Preferably, the yield strength of the high-strength and tough steel is ≥1200 MPa, and the V-notch impact energy is ≥120 J.

[0020] The present invention has the following advantages compared with the prior art: 1. For the high-strength and tough steel based on laser rapid melting and solidification provided by the present invention, while ensuring the strengthening effect of alloy elements on the material, the cracking problem that is prone to occur during the laser rapid melting and solidification forming process is avoided; by designing an orthogonal experiment to perform high-throughput screening to obtain a suitable laser rapid melting and solidification forming process window, forming with a high density (>99%) is realized.

[0021] 2. In the additive manufacturing method provided by the present invention, the heat treatment method realizes specific microstructural changes during the heat treatment process by precisely controlling the temperature and time, including in-situ laser ultra-rapid heat treatment during the laser rapid melting and solidification process or off-site infrared ultra-rapid heat treatment after laser melting and solidification forming. Such changes include retaining non-segregated martensite and generating uniformly distributed nano-scale thin-film austenite structure, and the volume fraction of austenite is 3-7%. This fine and uniformly distributed combination of hard and soft structures ensures that the prepared steel has extremely outstanding impact toughness (CVN≥120 J) without losing strength (yield strength≥1200 MPa).

[0022] The technical solution of the present invention will be further described in detail below with reference to the drawings and embodiments. Description of the Drawings

[0023] Figure 1 It is the SEM diagram of the formed part of high-strength and tough steel in Example 2; Figure 2 XRD patterns of the formed part, high-strength and tough steel in Example 2, and high-strength and tough steel in Example 3; Figure 3 TEM image of the high-strength and tough steel in Example 3; Figure 4 Room-temperature tensile curve of the high-strength and tough steel in Example 2; Figure 5 Room-temperature tensile curve of the high-strength and tough steel in Example 3; Figure 6 Comparison chart of the strength and impact toughness between the high-strength and tough steel in the present invention and the steel in the existing additive manufacturing field; Detailed implementation manners

[0024] The experiments involved in the present invention were strictly carried out in accordance with "GB / T 228.1-2021 Metallic materials - Tensile testing - Part 1: Method of test at room temperature" and "GB / T 229—2020 Metallic materials - Charpy pendulum impact test method". Examples

[0025] Alloy powders of high-strength and tough steel were prepared using a gas atomization powder-making device according to the designed target composition, and their actual chemical compositions, powder properties, and powder morphologies were detected. The results are shown in Table 1 and Table 2.

[0026] Table 1 Chemical composition (mass percentage) of the alloy powders of the prepared high-strength and tough steel C Mn Mo W Si Ni P S Fe 0.19 1.2 3.28 3.53 0.5 1.4 0.005 0.004 Bal. Table 2 Particle size distribution, density, and fluidity of the alloy powders of the high-strength and tough steel in Example 1 D10 (μm) D50 (μm) D90 (μm) <![CDATA[Bulk density (g / cm 3 )]]> <![CDATA[Tap density (g / cm 3 )]]> Hall flow rate (s / 50g) 18.02 33.37 55.65 4.04 4.73 17.4 Examples

[0027] The alloy powders of the high-strength and tough steel prepared in Example 1 were taken and experiments were carried out using a BLT-A320 device. To avoid oxidation of the alloy powders after being melted by the laser, the entire forming process was carried out in a closed forming chamber under argon protection, including the following steps: Step 1: Take the alloy powders of the high-strength and tough steel prepared in Example 1 and lay the powder on the substrate, and then obtain a formed part of high-strength and tough steel through a laser rapid melting and solidification layer-by-layer forming method.

[0028] Step 2: Take the high-strength and high-toughness steel formed part obtained in Step 1 for off-site infrared ultra-rapid heat treatment to finally obtain high-strength and high-toughness steel. The specific steps are as follows: rapidly heat the high-strength and high-toughness steel formed part to 780 °C, then hold it for 3 minutes and take it out for air cooling, where the heating rate is 130 °C / s. By reasonably designing the heating rate of the rapid heat treatment and precisely controlling the holding temperature and time, the uniform generation of nano-scale reverse transformed austenite is achieved while avoiding the influence of coarse grains after traditional heat treatment on the properties of the steel, ensuring a specific microstructure of non-segregated martensite + nano-scale thin-film austenite in the steel, thereby guaranteeing the high strength and high toughness of the steel.

[0029] In this embodiment, process parameters such as laser power (P), scanning spacing (h), and scanning speed (v) during the laser rapid melting and solidification forming process in Step 1 will all affect the forming quality, and these parameters interact with each other. Since the alloy powder composition of the laser rapid melting and solidification high-strength and high-toughness steel is a self-designed formula, the present invention uses the surface energy density model (E = P / (h∙v)) to comprehensively consider the influence of each parameter, designs an orthogonal experiment to high-throughput screen the appropriate forming process window for the laser rapid melting and solidification high-strength and high-toughness steel, so that the high-strength and high-toughness steel formed part has a high density. In this embodiment, the density of the high-strength and high-toughness steel formed parts prepared under various process parameters is measured by the Archimedes drainage method. The substrate preheating temperature will also affect obtaining a fully martensitic structure during laser rapid melting and solidification forming. Excessive temperature will cause insufficient cooling. To ensure that the as-deposited material is a fully martensitic structure, the substrate preheating temperature is set to 80 °C. The specific process parameters during the laser rapid melting and solidification forming process in this embodiment are shown in Table 3.

[0030] Table 3 Different laser rapid melting and solidification forming process parameters in Example 2 Number Laser power (W) Scanning speed (mm / s) Scanning spacing (mm) <![CDATA[Surface energy density (J / mm 2 ).]]> Layer thickness of powder spreading (mm) Substrate preheating temperature (°C) Relative density (%) 1 260 600 0.08 5.417 0.04 80 99.94 2 260 600 0.09 4.815 0.04 80 99.97 3 260 600 0.10 4.333 0.04 80 99.75 4 260 600 0.11 3.939 0.04 80 99.69 5 280 700 0.08 5.000 0.04 80 99.98 6 280 700 0.09 4.444 0.04 80 99.95 7 280 700 0.10 4.000 0.04 80 99.75 8 280 700 0.11 3.636 0.04 80 99.78 9 300 800 0.08 4.688 0.04 80 99.97 10 300 800 0.09 4.167 0.04 80 99.98 11 300 800 0.10 3.750 0.04 80 99.78 12 300 800 0.11 3.409 0.04 80 99.67 13 320 900 0.08 4.444 0.04 80 99.88 14 320 900 0.09 3.951 0.04 80 99.99 15 320 900 0.10 3.556 0.04 80 99.97 16 320 900 0.11 3.232 0.04 80 99.88 As can be seen from Table 3, the density of the high-strength and high-toughness steel prepared in this embodiment under each selected laser rapid melting and solidification forming process parameter is above 99%, indicating that the high-strength and high-toughness steel has a large laser rapid melting and solidification forming process window and is suitable for additive manufacturing. The process parameter with the highest density is No. 14, and the density is 99.99%. Figure 1 This is the secondary electron morphology photo of the high-strength and high-toughness steel formed under process parameter No. 14 observed under a scanning electron microscope, showing typical melt pool characteristics. Figure 2 This is the XRD phase composition analysis of the high-strength and high-toughness steel formed part and the high-strength and high-toughness steel. It can be seen that the high-strength and high-toughness steel formed part is a fully martensitic structure, and the high-strength and high-toughness steel is composed of a martensite and austenite dual phase. Further calculation shows that the austenite volume fraction is 3.5%. Figure 3 This is the transmission electron microscopic analysis of the high-strength and high-toughness steel, and it is proved by the selected area electron diffraction technique that the matrix structure after laser rapid melting and solidification + off-site infrared ultra-rapid heat treatment is lath martensite, and nano-scale thin-film austenite is evenly distributed on both sides of the lath martensite.

[0031] Afterwards, a room temperature tensile test and a room temperature Charpy V-notch impact test were carried out on the high-strength and high-toughness steel prepared with process parameter No. 1 in this embodiment, and the test results are shown in Figure 4 , Table 7. Example

[0032] Take the alloy powder of the high-strength and high-toughness steel in Example 1 and conduct experiments using the BLT-A320 equipment. In order to avoid oxidation of the metal powder after being melted by the laser, the entire forming process is carried out in a sealed forming chamber under argon protection, including the following steps: Step 1: Take the alloy powder of the high-strength and high-toughness steel and spread it on the substrate to obtain the first layer of metal powder, then perform laser rapid melting and solidification forming, and then perform in-situ laser ultra-rapid heat treatment to obtain the first layer of high-strength and high-toughness steel; Step 2: Continue to spread the powder on the first layer of high-strength and high-toughness steel obtained in Step 1, and then perform in-situ laser ultra-rapid heat treatment and in-situ laser ultra-rapid heat treatment in sequence to obtain the second layer of high-strength and high-toughness steel; Repeat the above powder spreading, in-situ laser ultra-rapid heat treatment and in-situ laser ultra-rapid heat treatment until a high-strength and high-toughness steel sample block with a height of 5 cm is obtained.

[0033] In this embodiment, the laser rapid melting and solidification forming adopts various process parameters, and the specific process parameters are shown in Table 4. The in-situ laser ultra-rapid heat treatment adopts various process parameters, and the specific process parameters are shown in Table 5. The process parameters selected for laser rapid melting and solidification forming and in-situ laser ultra-rapid heat treatment correspond one by one according to the numbers.

[0034] Table 4 Process parameters of different laser rapid melting and solidification forming in Example 3 Number Laser power (W) Scanning speed (mm / s) Scanning spacing (mm) <![CDATA[Surface energy density (J / mm 2 ).]]> Layer thickness of powder spreading (mm) Substrate preheating temperature (°C) 1 260 600 0.08 5.417 0.04 70 2 260 600 0.09 4.815 0.04 70 3 260 600 0.10 4.333 0.04 70 4 260 600 0.11 3.939 0.04 70 5 280 700 0.08 5.000 0.04 70 6 280 700 0.09 4.444 0.04 70 7 280 700 0.10 4.000 0.04 70 8 280 700 0.11 3.636 0.04 70 9 300 800 0.08 4.688 0.04 70 10 300 800 0.09 4.167 0.04 70 11 300 800 0.10 3.750 0.04 70 12 300 800 0.11 3.409 0.04 70 13 320 900 0.08 4.444 0.04 70 14 320 900 0.09 3.951 0.04 70 15 320 900 0.10 3.556 0.04 70 16 320 900 0.11 3.232 0.04 70 Table 5 Process parameters of corresponding different in-situ laser ultra-rapid heat treatment after laser rapid melting in Example 3 Number Laser power (W) Scanning speed (mm / s) Scanning spacing (mm) <![CDATA[Surface energy density (J / mm 2 )]]> Relative density (%) 1 10 1000 0.08 0.125 99.97 2 10 1000 0.09 0.111 99.99 3 10 1000 0.10 0.100 99.87 4 10 1000 0.11 0.091 99.90 5 20 1100 0.08 0.227 99.86 6 20 1100 0.09 0.202 99.96 7 20 1100 0.10 0.182 99.94 8 20 1100 0.11 0.165 99.77 9 10 1200 0.08 0.104 99.96 10 10 1200 0.09 0.093 99.97 11 10 1200 0.10 0.083 99.77 12 10 1200 0.11 0.076 99.66 13 20 1300 0.08 0.192 99.92 14 20 1300 0.09 0.171 99.93 15 20 1300 0.10 0.154 99.92 16 20 1300 0.11 0.140 99.91 It can be seen from Table 4 and Table 5 that the process parameter with the highest relative density is No. 2, and the relative density is 99.99%. An XRD test was carried out on the high-strength and high-toughness steel prepared with the process parameter corresponding to No. 2 in this embodiment, and the XRD phase composition analysis is shown in Figure 2 , and it can be seen that it is composed of a duplex structure of martensite and austenite, and further calculation shows that the austenite volume fraction is 4.7%.

[0035] In this embodiment, the mechanical properties of the high-strength and high-toughness steel prepared with the process parameter corresponding to No. 2 are shown in Figure 5 , as shown in Table 7. Example

[0036] Take the alloy powder of the high-strength and high-toughness steel in Example 1, and perform forming according to the laser rapid melting and solidification process parameters of No. 14 in Example 2 to obtain a high-strength and high-toughness steel formed part. Then, perform off-site infrared ultra-rapid heat treatment on the high-strength and high-toughness steel formed part to finally obtain high-strength and high-toughness steel. The specific process of the off-site infrared ultra-rapid heat treatment is as follows: rapidly heat the high-strength and high-toughness steel formed part to 800 °C, then hold it for 4 minutes and take it out for air cooling, where the rapid heating rate is 120 °C / s.

[0037] The properties of the high-strength and high-toughness steel prepared in this example are shown in Table 7. Example

[0038] The manufacturing method of the high-strength and high-toughness steel in this example is similar to that in Example 3, the difference lies in the process parameters of in-situ laser ultra-rapid heat treatment in Step 2, as shown in the table: Table 6 Process parameters of in-situ laser ultra-rapid heat treatment corresponding to different laser rapid melting and solidification in Example 5 Number Laser power (W) Scanning speed (mm / s) Scanning spacing (mm) <![CDATA[Surface energy density (J / mm 2 ).]]> Relative density (%) 1 30 1000 0.08 0.375 99.83 2 30 1000 0.09 0.333 99.91 3 30 1000 0.10 0.300 99.87 4 30 1000 0.11 0.273 99.90 5 30 1100 0.08 0.341 99.91 6 30 1100 0.09 0.303 99.88 7 30 1100 0.10 0.273 99.89 8 30 1100 0.11 0.248 99.92 9 30 1200 0.08 0.313 99.89 10 30 1200 0.09 0.278 99.94 11 30 1200 0.10 0.250 99.89 12 30 1200 0.11 0.227 99.93 13 30 1300 0.08 0.288 99.99 14 30 1300 0.09 0.256 99.92 15 30 1300 0.10 0.231 99.90 16 30 1300 0.11 0.210 99.91 It can be seen from Table 6 that the process parameters with the highest relative density are No. 13, and the relative density is 99.99%. The austenite volume fraction and mechanical properties of the high-strength and high-toughness steel prepared with the process parameters of No. 13 in this example are shown in Table 7. Example

[0039] Use an air atomization powder preparation device to prepare the alloy powder of high-strength and high-toughness steel according to the designed target composition, C: 0.1%, Mn: 0.12%, Ni: 1.5%, Mo: 0.1%, W: 4.5%, Si: 0.1%, and the balance is Fe and unavoidable impurity elements. Among the impurity elements, P≤0.01% and S≤0.02%.

[0040] Adopt the additive manufacturing method in Example 2, select No. 5 in Table 4 for the process parameters of laser rapid melting and solidification forming, and select No. 2 in Table 5 for the process parameters of in-situ laser ultra-rapid heat treatment.

[0041] The austenite volume fraction and mechanical properties of the high-strength and high-toughness steel prepared in this example are shown in Table 7. Example

[0042] Use an air atomization powder preparation device to prepare the alloy powder of high-strength and high-toughness steel according to the designed target composition, C: 0.3%, Mn: 2.6%, Ni: 0.1%, Mo: 4%, W: 1%, Si: 1.2%, and the balance is Fe and unavoidable impurity elements. Among the impurity elements, P≤0.01% and S≤0.02%.

[0043] Using the additive manufacturing method in Example 4, the specific process of in-situ infrared ultra-rapid heat treatment is as follows: The high-strength and tough steel formed part is rapidly heated to 750 °C, then held for 5 min and taken out for air cooling, where the heating rate of rapid heating is 130 °C / s.

[0044] The austenite volume fraction and mechanical properties of the high-strength and tough steel prepared in this example are shown in Table 7.

[0045] Table 7 Mechanical properties and austenite volume fraction of high-strength and tough steel prepared in Examples 2-7 Number Yield strength (MPa) Tensile strength (MPa) Elongation at break (%) Volume fraction of austenite (vol.%) CVN (J) Example 2 1318 1431 14 3.5 132 Example 3 1242 1393 16 4.7 137 Example 4 1289 1403 15 4.8 138 Example 5 1267 1398 17 5.6 141 Example 6 1250 1395 15 4.9 139 Example 7 1264 1395 17 5.4 140 By comparing with the properties of steel prepared by other additive manufacturing methods, it can be seen that the high-strength and tough steel in the present invention has extremely excellent strength and toughness. The performance comparison is shown in Figure 6 as follows. Figure 6 In this work, it refers to the high-strength and tough steel prepared in Examples 2-7. The data of other steels prepared by additive manufacturing for comparison come from the data published in existing public literatures, specifically including: H13, H13 + 316, 316L, 30CrMnSiA, 16MND5, HBMDPJ, 18Ni300, ASSI 4140, 2507 Superduplex Steel, SG2, ER110, where Figure 6 WAAM represents wire arc additive manufacturing technology, and LPBF refers to selective laser melting technology.

[0046] The process parameter tests in the embodiments of the present invention are not all the test results in the research process of the present invention. Only part of the test design process is given in the embodiments.

[0047] The above are only the preferred embodiments of the present invention, and do not limit the present invention in any way. Any simple modification, change and equivalent change made to the above embodiments according to the technical essence of the invention still fall within the protection scope of the technical solution of the present invention.

Claims

1. A high-strength and tough steel based on laser rapid melting and solidification, characterized in that, The alloy composition of the high-strength and high-toughness steel consists of the following elements by mass percentage: C: 0.1 - 0.3%, Mn: 0.1 - 2.6%, Ni: 0.1 - 1.5%, Mo: 0.1 - 4%, W: 1 - 4.5%, Si: 0.1 - 1.2%, the balance being Fe and inevitable impurity elements, and in the impurity elements, P ≤ 0.01% and S ≤ 0.02%; among them, the ratio of the sum of the mass percentages of Ni and Mn to the mass percentage of Si is not less than 1.572; the yield strength of the high-strength and high-toughness steel ≥ 1200 MPa, and the V-notch impact energy ≥ 120 J.

2. The high-strength and tough steel based on laser rapid melting and solidification according to claim 1, wherein There is no macroscopic segregation in the microstructure of the high-strength and high-toughness steel, and it is composed of lath martensite and nano-level austenite, among which the content of thin-film austenite is 3 - 7% by volume percentage.

3. The high-strength and tough steel based on laser rapid melting and solidification according to claim 1, characterized in that, The alloy composition of the high-strength and high-toughness steel consists of the following elements by mass percentage: C: 0.19%, Mn: 1.2%, Ni: 1.4%, Mo: 3.28%, W: 3.53%, Si: 0.5%, the balance being Fe and inevitable impurity elements, and in the impurity elements, P ≤ 0.01% and S ≤ 0.02%.

4. An additive manufacturing method for high-strength and tough steel based on laser rapid melting and solidification as described in any one of claims 1-3, characterized in that, This manufacturing method includes the following steps: Step 1: Take alloy powder of high-strength and high-toughness steel and spread it on a substrate to obtain the first layer of metal powder. Then, perform laser rapid melting and solidification forming, and then conduct in-situ laser ultra-rapid heat treatment to obtain the first layer of high-strength and high-toughness steel. During the laser rapid melting and solidification forming process, the laser power is 260 - 320 W, the scanning speed is 600 - 900 mm / s, the scanning spacing is 0.08 - 0.11 mm, and the surface energy density is 2.63 - 6.67 J / mm 2 , the powder spreading layer thickness is 0.03 - 0.06 mm, and the substrate is preheated to a temperature not exceeding 80°C. During the in-situ laser rapid heat treatment, the laser power is 10 - 30 W, the scanning speed is 1000 - 1300 mm / s, the scanning spacing is 0.08 - 0.11 mm, and the surface energy density is 0.07 - 0.375 J / mm 2 ; Step 2: Powder is laid on the first layer of high-strength and high-toughness steel obtained in Step 1, and then in-situ laser ultra-rapid heat treatment and in-situ laser ultra-rapid heat treatment are carried out in sequence to obtain the second layer of high-strength and high-toughness steel; the above powder laying, in-situ laser ultra-rapid heat treatment and in-situ laser ultra-rapid heat treatment are repeated until high-strength and high-toughness steel with the required height is obtained.

5. The additive manufacturing method according to claim 4, characterized in that, During the laser rapid melting and solidification forming process, the laser power is 260 W, the scanning speed is 600 mm / s, the scanning spacing is 0.091 mm, and the surface energy density is 4.815 J / mm 2 , the powder spreading layer thickness is 0.04 mm, and the substrate is preheated to 70 °C in advance; for the in-situ laser rapid heat treatment, the laser power is 10 W, the scanning speed is 1000 mm / s, the scanning spacing is 0.09 mm, and the surface energy density is 0.111 J / mm 2 , or for the in-situ laser rapid heat treatment, the laser power is 30 W, the scanning speed is 1300 mm / s, the scanning spacing is 0.08 mm, and the surface energy density is 0.288 J / mm 2 .

6. An additive manufacturing method for high-strength and tough steel based on laser rapid melting and solidification as described in any one of claims 1-3, characterized in that, This manufacturing method includes the following steps: Step 1: Take the alloy powder of high-strength and tough steel and spread it on the substrate, and then obtain a high-strength and tough steel formed part through the method of laser rapid melting and solidification layer by layer; during the laser rapid melting and solidification forming process, the laser power is 260 - 320 W, the scanning speed is 600 - 900 mm / s, the scanning spacing is 0.08 - 0.11 mm, and the surface energy density is 2.63 - 6.67 J / mm 2 , the powder spreading layer thickness is 0.03 - 0.06 mm, and the substrate is preheated to a temperature not exceeding 80 °C; Step 2: The high-strength and high-toughness steel formed part obtained in Step 1 is taken for off-site infrared ultra-rapid heat treatment to finally obtain high-strength and high-toughness steel; the process of the off-site infrared ultra-rapid heat treatment is: the high-strength and high-toughness steel formed part is rapidly heated to 750 - 800 °C at a rate not lower than 100 °C / s, then held for 3 - 5 min and taken out for air cooling to obtain high-strength and high-toughness steel.

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