Low-cost corrosion-resistant ultra-high strength and toughness steel for laser additive manufacturing and heat treatment method thereof

Abstract

The present application relates to the technical field of laser additive manufacturing and corrosion-resistant super high strength and toughness steel, and particularly relates to a low-cost corrosion-resistant super high strength and toughness steel for laser additive manufacturing and a heat treatment method thereof. The method adopts laser directional energy deposition technology to prepare bulk alloy steel and one-step tempering heat treatment. The chemical composition of the alloy steel is as follows: C 0.1%~0.2%; Cr 13.0%~16.0%; Ni 1.5%~3.5%; Si 0.5%~1.0%; Mn 0.7%~1.2%; Al 0.3%~0.7%; Cu 0.2%~0.8%, and the balance is Fe and inevitable impurities. The present application uses relatively inexpensive alloy elements and abandons the traditional multi-step post-heat treatment process, solving the bottleneck problems of high cost, long process and poor corrosion resistance of the current laser additive manufacturing super high strength and toughness steel.

Description

Technical Field

[0001] This invention relates to the fields of laser additive manufacturing and corrosion-resistant ultra-high strength and toughness steel, specifically to a low-cost corrosion-resistant ultra-high strength and toughness steel for laser additive manufacturing and its heat treatment method. Background Technology

[0002] Ultra-high strength and toughness steel, with its excellent comprehensive mechanical properties, has been applied in important sectors of the national economy such as aerospace, marine engineering, and transportation. However, ultra-high strength and toughness steels currently produced by laser additive manufacturing, such as 300M, Amert100, and 18Ni300, generally suffer from the following two problems: First, insufficient corrosion resistance, failing to meet the stringent requirements for corrosion resistance in service environments such as marine engineering and transportation. Second, complex heat treatment; traditionally laser-prepared ultra-high strength and toughness steel requires multiple post-heat treatment processes, including solution treatment and tempering, to achieve a balance between strength and toughness. However, these complex heat treatment processes result in high energy consumption and long cycles, severely limiting their large-scale industrial application.

[0003] In the prior art, patent CN120400706A discloses a high-strength and tough steel based on laser rapid melting and solidification. The high-strength and tough steel is characterized by its alloy composition consisting of the following elements by mass percentage: C: 0.1~0.3%, Mn: 0.1~2.6%, Ni: 0.1~1.5%, Mo: 0.1~4.0%, W: 1.0~4.5%, Si: 0.1~1.2%, with the balance being Fe and unavoidable impurity elements, where P≤0.01% and S≤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; the high-strength and tough steel requires in-situ infrared ultra-rapid heat treatment (temperature 750~800 ℃, then holding for 3~5 min) to obtain its high strength and toughness properties (yield strength ≥1200 MPa, V-notch impact energy ≥120 MPa). However, it did not focus on corrosion resistance, and its overall performance was far inferior to that of the ultra-high strength, toughness and corrosion resistance steel in this invention.

[0004] Patent CN119859779A discloses a low-cost, ultra-high-strength martensitic aging steel suitable for additive manufacturing. Its chemical composition by mass percentage is: C: ≤0.03%, Ni: 13.0~15.0%, Mo: 2.5~3.5%, Cr: 2.5~3.5%, Mn: 1.3~2.5%, Ti: 0.50~0.80%, Al: 0.05~0.15%, Si≤0.10%, S≤0.010%, P≤0.010%, with the balance being Fe. After being formed into wire or powder and additively manufactured, the resulting parts, after solution treatment at 700~850℃ for 1 hour followed by aging at 400~500℃ for 6 hours, exhibit a tensile strength of not less than 1600 MPa and an elongation after fracture of not less than 8.0%.

[0005] The current invention requires two heat treatment steps to achieve excellent strength and toughness, resulting in high production costs and neglecting corrosion resistance. Therefore, developing a low-cost, short-process ultra-high strength and toughness steel for laser additive manufacturing, possessing ultra-high strength, high elongation, and excellent corrosion resistance, can meet the urgent needs of major national sectors such as aerospace for the complex forming and rapid repair of critical components. Summary of the Invention

[0006] To overcome the shortcomings of existing technologies, the purpose of this invention is to provide a low-cost corrosion-resistant ultra-high strength and toughness steel for laser additive manufacturing and its heat treatment method. Compared with traditional ultra-high strength and toughness steel, this low-cost corrosion-resistant ultra-high strength and toughness steel for laser additive manufacturing reduces the content of the relatively expensive Ni element and does not contain elements such as Co. The Cr element content is controlled at 13.0~16.0%. After a simple one-step heat treatment, nano-scale ε-Cu and NiAl phases are precipitated, increasing the martensite content. The plasticity is improved through the transformation-induced plasticity (TRIP) effect and residual stress release, and the corrosion resistance is improved by using the precipitated phases to suppress Cr-depleted behavior. Ultimately, a comprehensive improvement in strength, toughness, and corrosion resistance is achieved.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A low-cost, corrosion-resistant, ultra-high strength and toughness steel for laser additive manufacturing, wherein the steel has the following chemical composition by weight percentage: C 0.1%~0.2%; Cr 13.0%~16.0%; Ni 1.5%~3.5%; Si 0.5%~1.0%; Mn 0.7%~1.2%; Al 0.3%~0.7%; Cu 0.2%~0.8%, with the balance being Fe and unavoidable impurity elements S≤0.01% and P≤0.01%.

[0009] Preferably, the microstructure of the corrosion-resistant ultra-high strength and toughness steel consists of lath martensite, austenite, carbides, and nano-precipitates.

[0010] Precipitation strengthening is provided by the formation of carbides, while promoting martensitic transformation, which helps to improve strength. However, excessive addition of C will increase the carbon equivalent, which is detrimental in laser rapid melting (cooling rate 10). 3-8 The process (C / s) leads to high internal stress in the formed part, and this tendency to increase internal stress increases with increasing C content. On the other hand, excessive C will form large-sized carbides, deteriorating material properties. Therefore, this invention controls the C content to 0.1~0.2%, which ensures the strengthening effect while avoiding cracking caused by increased internal stress, achieving high-density (99%) high-quality forming.

[0011] Cr is a key element for improving corrosion resistance. It promotes the formation of a dense passivation film on the steel surface, significantly improving the material's corrosion resistance in oxidizing media. Cr also improves the strength and wear resistance of steel and inhibits decarburization during heat treatment. However, Cr significantly lowers the martensitic transformation initiation temperature (Ms), and excessive content will lead to an increase in retained austenite, which is detrimental to strength improvement. Therefore, controlling the Cr content between 13.0% and 16.0% can maintain sufficient martensitic transformation amount while ensuring good corrosion resistance.

[0012] Ni (Ni) exhibits a significant solid solution strengthening effect, maintaining good toughness while improving strength. The synergistic effect of Ni and Cr further enhances the hardenability of steel, facilitating the acquisition of a fully martensitic microstructure during laser rapid solidification. Furthermore, Ni contributes very little to the carbon equivalent, helping to suppress the tendency for hot cracking during rapid solidification. However, as a strong austenite stabilizing element, excessive Ni content significantly lowers the Ms point, thus inhibiting martensitic transformation and resulting in excessive austenite residue in the microstructure, which is detrimental to achieving ultra-high strength. Conversely, excessively low Ni content is insufficient to fully realize its beneficial effects of solid solution strengthening and improved hardenability. Therefore, the Ni content should be controlled within the range of 1.5% to 3.5%, ensuring forming quality while balancing strength and toughness.

[0013] Si has a strong solid solution strengthening effect, which can significantly improve the strength of steel. Si can also inhibit cementite precipitation and improve tempering stability. However, when the Si content exceeds 1.0%, it will strongly increase the tendency of brittle phase precipitation, induce temper brittleness, and reduce impact toughness. Therefore, the Si content is limited to 0.5%~1.0% to achieve a balance between strength and toughness.

[0014] Manganese (Mn) is used as a deoxidizer to improve the mechanical properties of steel. However, as an austenite stabilizing element, excessive Mn addition can significantly lower the Ms temperature, leading to excessive retained austenite and weakening the material's strength. Furthermore, high Mn content promotes the formation of banded MnS inclusions, impairing toughness. Therefore, controlling the Mn content between 0.7% and 1.2% ensures good deoxidation and hardenability while avoiding a decrease in microstructural stability.

[0015] Al primarily functions as a deoxidizer and nitrogen fixator in steel, refining grains and increasing strength. Al also inhibits carbide precipitation, promotes the formation of intermetallic compounds to strengthen the matrix, and improves the steel's oxidation resistance. However, Al is a ferrite stabilizing element; excessive content will promote δ-ferrite formation, impairing material uniformity and machinability. Therefore, the Al content is limited to 0.3%–0.7% to balance its strengthening effect with microstructure control.

[0016] Cu can significantly improve the corrosion resistance of steel (especially in neutral and acidic environments) and further enhance strength through precipitation strengthening by the formation of ε-Cu phase during aging. However, excessive Cu content can easily cause "copper embrittlement" during hot working, reduce thermoplasticity, and may worsen weldability. Therefore, the Cu content should be controlled between 0.2% and 0.8%.

[0017] The balance is Fe and impurity elements that inevitably mix in during manufacturing, S≤0.01% and P≤0.01%.

[0018] To achieve the above objectives, the present invention provides the following technical solution:

[0019] A method for preparing low-cost corrosion-resistant ultra-high strength and toughness steel for laser additive manufacturing, characterized by comprising the following steps:

[0020] Step S1: Obtain corrosion-resistant ultra-high strength and toughness steel powder by non-vacuum nitrogen atomization;

[0021] Step S2: Place the corrosion-resistant ultra-high strength and toughness steel powder prepared in step S1 into a drying oven and dry it at 60°C for 24 hours.

[0022] Step S3: Using corrosion-resistant ultra-high strength and toughness steel powder as raw material and iron-based material as substrate, corrosion-resistant ultra-high strength and toughness steel is prepared by laser-directed energy deposition (LDED) technology. The equipment used in the LED technology includes a laser, a deposition head, and a CNC work platform, with the substrate fixed on the CNC work platform. The process parameters involved in the LED technology are as follows: distance between the deposition head and the substrate is 9-12 mm, laser wavelength is 1064-1080 mm, laser focal length is 180-220 mm, defocusing amount is 23-28 mm, laser spot diameter is 1.2-1.6 mm, laser power is 450-550 W, laser scanning speed is 550-650 mm / min, powder feeding speed is 4-14 g / min, overlap coefficient is 0.45-0.55, protective gas flow rate is 8-18 L / min, and powder feeding gas flow rate is 10-14 L / min. Both the protective gas and the powder feeding gas are high-purity nitrogen.

[0023] Step S4: The corrosion-resistant ultra-high strength and toughness steel prepared in step S3 is subjected to tempering heat treatment.

[0024] Preferably, the parameters for the tempering heat treatment in step S4 are: tempering temperature of 400~500℃ and holding time of 4-8h.

[0025] Preferably, a conventional box-type heat treatment furnace is used for heat treatment.

[0026] Preferably, the corrosion-resistant ultra-high strength and toughness steel powder is prepared using non-vacuum nitrogen atomization.

[0027] Preferably, the corrosion-resistant ultra-high strength and toughness steel powder has an average particle size of 50~70 μm and must be dried before use.

[0028] Preferably, iron-based materials must be leveled and dried before use.

[0029] Preferably, the corrosion-resistant ultra-high strength and toughness steel contains the following element mass percentages: C 0.1%~0.2%; Cr 13.0%~16.0%; Ni 1.5%~3.5%; Si 0.5%~1.0%; Mn 0.7%~1.2%; Al 0.3%~0.7%; Cu 0.2%~0.8%, with the balance being Fe and unavoidable impurity elements S≤0.01% and P≤0.01%.

[0030] The beneficial effects and advantages of this invention are as follows:

[0031] (1) Compared with the prior art, the low-cost corrosion-resistant ultra-high strength and toughness steel for laser additive manufacturing and its heat treatment method provided by the present invention achieve multi-element synergistic alloying by reasonably matching multiple alloying elements and strictly controlling the content range of each element, especially high-cost elements. It achieves better comprehensive performance at a lower alloy content, and the composition design is more flexible and cost control is more advantageous.

[0032] (2) This invention cleverly combines the advantages of laser directed energy deposition technology with simple one-step heat treatment, thereby avoiding the problems of high energy consumption, long cycle and low parameter fault tolerance caused by traditional multi-step post-heat treatment, so as to adapt to the mass production of multi-size workpieces. The heat-treated steel (YS: 1350~1550 MPa, UTS: 1500~1750 MPa, EL: 10~16%, corrosion rate 0.005~0.010 mm / a) has significantly improved comprehensive performance compared with the deposited state (YS: 950~1150 MPa, UTS: 1150~1400 MPa, EL: 5~8%, corrosion rate 1.0~1.4 mm / a).

[0033] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0034] Figure 1 This diagram illustrates the implementation steps of a low-cost, corrosion-resistant, ultra-high strength and toughness steel for laser additive manufacturing and its heat treatment method.

[0035] Figure 2 The morphology and particle size distribution of Fe-15Cr-3.2Ni-0.8Mn-0.6Cu-0.56Si-0.4Al-0.16C corrosion-resistant ultra-high strength and toughness steel powder produced by non-vacuum nitrogen atomization are shown.

[0036] Figure 3 The X-ray diffraction (XRD) patterns of Fe-15Cr-3.2Ni-0.8Mn-0.6Cu-0.56Si-0.4Al-0.16C corrosion-resistant ultra-high strength and toughness steel in both deposited and heat-treated states are shown.

[0037] Figure 4 Scanning electron microscope (SEM) images of the deposited and heat-treated states of Fe-15Cr-3.2Ni-0.8Mn-0.6Cu-0.56Si-0.4Al-0.16C corrosion-resistant ultra-high strength and toughness steel.

[0038] Figure 5 The image shows the microhardness distribution of Fe-15Cr-3.2Ni-0.8Mn-0.6Cu-0.56Si-0.4Al-0.16C corrosion-resistant ultra-high strength and toughness steel in both deposited and heat-treated states.

[0039] Figure 6 Tensile curves of Fe-15Cr-3.2Ni-0.8Mn-0.6Cu-0.56Si-0.4Al-0.16C corrosion-resistant ultra-high strength and toughness steel in the deposited state and heat-treated state.

[0040] Figure 7 The potentiodynamic polarization curves and electrochemical impedance spectroscopy of the Fe-15Cr-3.2Ni-0.8Mn-0.6Cu-0.56Si-0.4Al-0.16C corrosion-resistant ultra-high strength and toughness steel in both deposited and heat-treated states are presented.

[0041] Figure 8 SEM images of Fe-12.1Cr-2.1Ni-0.75Cu-0.7Mn-0.59Si-0.3Al-0.13C corrosion-resistant ultra-high strength and toughness steel in both deposited and heat-treated states.

[0042] Figure 9 Tensile curves of Fe-12.1Cr-2.1Ni-0.75Cu-0.7Mn-0.59Si-0.3Al-0.13C corrosion-resistant ultra-high strength and toughness steel in the deposited state and heat-treated state.

[0043] Figure 10 SEM images of Fe-13.85Cr-3.12Ni-0.78Si-0.76Mn-0.69Cu-0.64Al-0.15C corrosion-resistant ultra-high strength and toughness steel in both deposited and heat-treated states.

[0044] Figure 11Tensile curves of Fe-13.85Cr-3.12Ni-0.78Si-0.76Mn-0.69Cu-0.64Al-0.15C corrosion-resistant ultra-high strength and toughness steel in the deposited state and heat-treated state.

[0045] Figure 12 SEM images of Fe-14.44Cr-1.81Ni-1.08Mn-0.74Si-0.64Al-0.37Cu-0.11C corrosion-resistant ultra-high strength and toughness steel in both deposited and heat-treated states.

[0046] Figure 13 Tensile curves of Fe-14.44Cr-1.81Ni-1.08Mn-0.74Si-0.64Al-0.37Cu-0.11C corrosion-resistant ultra-high strength and toughness steel in the deposited state and heat-treated state.

[0047] Figure 14 SEM images of Fe-14.44Cr-1.81Ni-1.08Mn-0.74Si-0.64Al-0.37Cu-0.11C corrosion-resistant ultra-high strength and toughness steel in both deposited and heat-treated states.

[0048] Figure 15 Tensile curves of Fe-14.44Cr-1.81Ni-1.08Mn-0.74Si-0.64Al-0.37Cu-0.11C corrosion-resistant ultra-high strength and toughness steel in the deposited state and heat-treated state. Detailed Implementation

[0049] To enable those skilled in the art to better understand the present invention, the invention will be further described below with reference to embodiments and accompanying drawings. Obviously, the described embodiments are merely some embodiments of the present invention, and not all embodiments, and should not be used to limit the scope of protection of the present invention.

[0050] The raw materials used in the embodiments of the present invention are all obtained through conventional commercial channels.

[0051] Example 1: A low-cost, corrosion-resistant, ultra-high strength and toughness steel for laser additive manufacturing, wherein the chemical composition of the steel by weight percentage is: C 0.1%~0.2%; Cr 13.0%~16.0%; Ni 1.5%~3.5%; Si 0.5%~1.0%; Mn 0.7%~1.2%; Al 0.3%~0.7%; Cu 0.2%~0.8%, with the balance being Fe and unavoidable impurity elements S≤0.01% and P≤0.01%.

[0052] Preferably, the microstructure of the corrosion-resistant ultra-high strength and toughness steel consists of lath martensite, austenite, carbides, and nano-precipitates. The balance is Fe and impurity elements inevitably mixed in during manufacturing, S≤0.01%, P≤0.01%.

[0053] Specifically, in Example 2, the chemical composition by weight percentage of the corrosion-resistant ultra-high strength and toughness steel Fe-15Cr-3.2Ni-0.8Mn-0.6Cu-0.56Si-0.4Al-0.16C is as follows: C 0.16%; Cr 15.00%; Ni 3.20%; Si 0.56%; Mn 0.80%; Al 0.40%; Cu 0.60%, with the balance being Fe and impurities inevitably mixed in during manufacturing, S≤0.01% and P≤0.01%.

[0054] Specifically, in Example 3, the chemical composition by weight percentage of the corrosion-resistant ultra-high strength and toughness steel Fe-12.10Cr-2.10Ni-0.75Cu-0.70Mn-0.59Si-0.30Al-0.13C is as follows: C 0.13%; Cr 12.1%; Ni 2.1%; Si 0.59%; Mn 0.7%; Al 0.3%; Cu 0.75%, with the balance being Fe and impurities inevitably introduced during manufacturing, S≤0.01% and P≤0.01%.

[0055] Specifically, in Example 4, the chemical composition by weight percentage of the corrosion-resistant ultra-high strength and toughness steel Fe-13.85Cr-3.12Ni-0.78Si-0.76Mn-0.69Cu-0.64Al-0.15C is as follows: C 0.15%; Cr 13.85%; Ni 3.12%; Si 0.78%; Mn 0.76%; Al 0.64%; Cu 0.69%, with the balance being Fe and impurities inevitably introduced during manufacturing, S≤0.01% and P≤0.01%.

[0056] Specifically, in Example 5, the chemical composition by weight percentage of the corrosion-resistant ultra-high strength and toughness steel Fe-14.44Cr-1.81Ni-1.08Mn-0.74Si-0.64Al-0.37Cu-0.11C is as follows: C 0.11%; Cr 14.44%; Ni 1.81%; Si 0.74%; Mn 0.80%; Al 0.64%; Cu 0.37%, with the balance being Fe and impurities inevitably introduced during manufacturing, S≤0.01% and P≤0.01%.

[0057] Specifically, in Example 6, the chemical composition by weight percentage of the corrosion-resistant ultra-high strength and toughness steel Fe-15.69Cr-2.64Ni-0.89Mn-0.86Si-0.57Al-0.26Cu-0.17C is as follows: C 0.17%; Cr 15.69%; Ni 2.64%; Si 0.86%; Mn 0.89%; Al 0.57%; Cu 0.26%, with the balance being Fe and impurities inevitably introduced during manufacturing, S≤0.01% and P≤0.01%.

[0058] To achieve the above objectives, the present invention provides the following technical solution:

[0059] like Figure 1 As shown in Example 7, a method for preparing a low-cost, corrosion-resistant, ultra-high-strength, and tough steel for laser additive manufacturing includes the following steps:

[0060] Step S1: Obtain corrosion-resistant ultra-high strength and toughness steel powder by non-vacuum nitrogen atomization;

[0061] Step S2: Place the corrosion-resistant ultra-high strength and toughness steel powder prepared in step S1 into a drying oven and dry it at 60°C for 24 hours.

[0062] Step S3: Using corrosion-resistant ultra-high strength and toughness steel powder as raw material and iron-based material as substrate, corrosion-resistant ultra-high strength and toughness steel is prepared by laser-directed energy deposition (LDED) technology. The equipment used in the LED technology includes a laser, a deposition head, and a CNC work platform, with the substrate fixed on the CNC work platform. The process parameters involved in the LED technology are as follows: distance between the deposition head and the substrate is 9-12 mm, laser wavelength is 1064-1080 mm, laser focal length is 180-220 mm, defocusing amount is 23-28 mm, laser spot diameter is 1.2-1.6 mm, laser power is 450-550 W, laser scanning speed is 550-650 mm / min, powder feeding speed is 4-14 g / min, overlap coefficient is 0.45-0.55, protective gas flow rate is 8-18 L / min, and powder feeding gas flow rate is 10-14 L / min. Both the protective gas and the powder feeding gas are high-purity nitrogen.

[0063] Step S4: The corrosion-resistant ultra-high strength and toughness steel prepared in step S3 is subjected to tempering heat treatment.

[0064] Preferably, the parameters for the tempering heat treatment in step S4 are: tempering temperature of 400~500℃ and holding time of 4-8h.

[0065] Preferably, a conventional box-type heat treatment furnace is used for heat treatment.

[0066] Preferably, the corrosion-resistant ultra-high strength and toughness steel powder is prepared using non-vacuum nitrogen atomization.

[0067] Preferably, the corrosion-resistant ultra-high strength and toughness steel powder has an average particle size of 50~70 μm and must be dried before use.

[0068] Preferably, iron-based materials must be leveled and dried before use.

[0069] The following specific example 8 illustrates the use of laser additive manufacturing to produce low-cost corrosion-resistant ultra-high strength and toughness steel and its heat treatment method. The customized powder raw material of corrosion-resistant ultra-high strength and toughness steel, Fe-15Cr-3.2Ni-0.8Mn-0.6Cu-0.56Si-0.4Al-0.16C, obtained by non-vacuum nitrogen atomization, is prepared by laser directional energy deposition technology and then subjected to a simple one-step tempering heat treatment (tempering temperature is 480℃, holding time is 6h).

[0070] The customized powder for corrosion-resistant ultra-high strength and toughness steel, consisting of Fe-15Cr-3.2Ni-0.8Mn-0.6Cu-0.56Si-0.4Al-0.16C, has a particle size range of 20~90μm and exhibits a normal distribution. Before preparation using laser directional energy deposition, the powder is placed in a drying oven and dried at 60℃ for 24h.

[0071] Using Fe-15Cr-3.2Ni-0.8Mn-0.6Cu-0.56Si-0.4Al-0.16C corrosion-resistant ultra-high strength and toughness steel powder as raw material and 45 steel as substrate, Fe-15Cr-3.2Ni-0.8Mn-0.6Cu-0.56Si-0.4Al-0.16C corrosion-resistant ultra-high strength and toughness steel was prepared by laser-directed energy deposition (LDED) technology. The equipment used in the LDED technology included a laser, a deposition head, and a CNC work platform. The substrate was fixed on the CNC work platform. The process parameters involved in the LDED technology were as follows: distance between the deposition head and the substrate was 10 mm, laser wavelength was 1070 mm, laser focal length was 200 mm, defocusing amount was 25 mm, laser spot diameter was 1.4 mm, laser power was 500 W, laser scanning speed was 600 mm / min, powder feeding speed was 4.5 g / min, overlap coefficient was 0.5, protective gas flow rate was 10 L / min, and powder feeding gas flow rate was 10 g / min. L / min, both the protective gas and the powder feeding gas are high-purity nitrogen.

[0072] Detection and Analysis:

[0073] The morphology and particle size distribution of the corrosion-resistant ultra-high strength and toughness steel powder (Fe-15Cr-3.2Ni-0.8Mn-0.6Cu-0.56Si-0.4Al-0.16C) obtained by non-vacuum nitrogen atomization in this embodiment are as follows: Figure 2As shown, the powder exhibits high sphericity, with few satellite spheres and aggregates, high surface smoothness, and a particle size range of 20–90 μm, showing a normal distribution with an average particle size of 58.7 μm. These morphological characteristics are beneficial for improving powder flowability and uniformity of powder spreading, meeting the stringent requirements of laser additive manufacturing processes for powder particle morphology, and contributing to the manufacture of highly dense, defect-free formed parts.

[0074] The XRD patterns of Fe-15Cr-3.2Ni-0.8Mn-0.6Cu-0.56Si-0.4Al-0.16C corrosion-resistant ultra-high strength and toughness steel in both deposited and heat-treated states are shown below. Figure 3 As shown in the figure, the comparison shows that after one-step heat treatment, the content of martensite phase in the steel increases (75.7% in the deposited state and 82.3% in the heat-treated state), accompanied by the precipitation of NiAl and α-Cu.

[0075] The SEM morphology of Fe-15Cr-3.2Ni-0.8Mn-0.6Cu-0.56Si-0.4Al-0.16C corrosion-resistant ultra-high strength and toughness steel in its deposited and heat-treated states is as follows: Figure 4 As shown in the figure. A comparison reveals that the amount of precipitated phase in the sample significantly increases after one heat treatment step. For example... Figure 4 (b) As shown in the illustration, a large number of nano-precipitates appear in the martensitic laths of the heat-treated sample. These finely distributed precipitates can effectively hinder dislocation movement and produce a significant precipitation strengthening effect.

[0076] The microhardness and tensile curves of Fe-15Cr-3.2Ni-0.8Mn-0.6Cu-0.56Si-0.4Al-0.16C corrosion-resistant ultra-high strength and toughness steel in deposited and heat-treated states are shown in the figure. Figure 5 , Figure 6 As shown, the overall mechanical properties of the material are significantly improved after a single tempering treatment. Specifically, the microhardness in the heat-treated state reaches 487 HV. 0.2 Compared to the sedimentary state (424 HV) 0.2 The tensile strength increased by approximately 14.9%; the ultimate tensile strength reached 1712 MPa, an increase of approximately 25% compared to the sedimentary state (1370 MPa); and the elongation increased from 8.7% in the sedimentary state to 15.5%, approximately twice. These performance changes indicate that one-step tempering treatment can effectively promote a good balance between strength and toughness.

[0077] Potentiodynamic polarization curves and electrochemical impedance spectroscopy of corrosion-resistant ultra-high strength and toughness steel in deposited state, heat-treated state, and laser-prepared AISI 420 stainless steel are shown in the following figures: Figure 7 As shown, the corrosion resistance of the three, from highest to lowest, is as follows: heat-treated state > AISI 420 > deposited state. From... Figure 7The polarization curve of a shows the corrosion potential of the heat-treated sample. E corr The positive shift was 168.8 mV compared to the deposited state, and 85 mV higher than AISI 420; its corrosion current density ( J corr Compared to the sedimentary state and AISI 420, it decreased by 2.5 × 10⁻⁶. -5 A / cm 2 and 1.2×10 -5 A / cm 2 This indicates that the anodic dissolution process of the heat-treated sample was significantly suppressed. Electrochemical impedance spectroscopy (EIS) Figure 7 (c~d) further confirms that the heat-treated sample has the best corrosion resistance, and its charge transfer resistance (R) is... t ) reaching 17253 Ω·cm 2 The values ​​are respectively sedimentary state (3704 Ω·cm). 2 ) and AISI 420 (6236 Ω·cm) 2 The capacitance was 4.7 times and 2.8 times that of the deposited state and AISI 420, respectively. Furthermore, the capacitive arc radius of the heat-treated sample was significantly larger than that of the deposited state and AISI 420, reflecting the superior barrier ability of its surface protective film. These results indicate that one-step tempering followed by heat treatment (480℃×6h) can significantly improve the corrosion resistance of Fe-15Cr-3.2Ni-0.8Mn-0.6Cu-0.56Si-0.4Al-0.16C corrosion-resistant ultra-high strength and toughness steel, and is superior to AISI 420 stainless steel produced by laser additive manufacturing.

[0078] The following specific example 9 illustrates the use of laser additive manufacturing to produce low-cost corrosion-resistant ultra-high strength and toughness steel and its heat treatment method. The customized powder raw material of corrosion-resistant ultra-high strength and toughness steel, Fe-12.1Cr-2.1Ni-0.75Cu-0.7Mn-0.59Si-0.3Al-0.13C, obtained by non-vacuum nitrogen atomization, is prepared by laser directional energy deposition technology and then subjected to a simple one-step tempering heat treatment (tempering temperature is 480℃, holding time is 4h).

[0079] Using Fe-12.1Cr-2.1Ni-0.75Cu-0.7Mn-0.59Si-0.3Al-0.13C corrosion-resistant ultra-high strength and toughness steel powder as raw material and 45 steel as substrate, Fe-12.1Cr-2.1Ni-0.75Cu-0.7Mn-0.59Si-0.3Al-0.13C corrosion-resistant ultra-high strength and toughness steel was prepared by laser-directed energy deposition (LDED) technology. The equipment used in the LDED technology included a laser, a deposition head, and a CNC work platform. The substrate was fixed on the CNC work platform. The process parameters involved in the LDED technology were as follows: distance between the deposition head and the substrate was 10 mm, laser wavelength was 1070 mm, laser focal length was 200 mm, defocusing amount was 25 mm, laser spot diameter was 1.4 mm, laser power was 480 W, laser scanning speed was 600 mm / min, powder feeding speed was 4.5 g / min, overlap coefficient was 0.5, and protective gas flow rate was 10 g / min. The flow rate of the powder feeding gas is 10 L / min, and both the protective gas and the powder feeding gas are high-purity nitrogen.

[0080] The SEM morphology of corrosion-resistant ultra-high strength and toughness steel in its deposited and heat-treated states is shown in the following figures. Figure 8 As shown in the figure, the density and quantity of precipitated phase in the sample significantly increased after one heat treatment step. Figure 8 (b) As shown in the illustration, a large number of nano-precipitates appear in the martensitic laths of the heat-treated sample. These finely distributed precipitates act as effective barriers to dislocation movement, resulting in significant precipitation strengthening.

[0081] The tensile curves of Fe-12.1Cr-2.1Ni-0.75Cu-0.7Mn-0.59Si-0.3Al-0.13C corrosion-resistant ultra-high strength and toughness steel in the deposited and heat-treated states are shown below. Figure 9 As shown, the comprehensive mechanical properties of the material are significantly improved after one-step tempering, exhibiting an excellent synergistic effect of strength and toughness. Specifically, the ultimate tensile strength reaches 1682 MPa, an increase of approximately 21% compared to the deposited state (1387 MPa); the elongation increases from 8.6% in the deposited state to 14.5%, approximately 1.7 times. These performance changes indicate that one-step tempering can effectively promote a good balance between strength and toughness.

[0082] The following specific example 10 illustrates the use of laser additive manufacturing to produce low-cost corrosion-resistant ultra-high strength and toughness steel and its heat treatment method. The customized powder raw material of corrosion-resistant ultra-high strength and toughness steel, Fe-13.85Cr-3.12Ni-0.78Si-0.76Mn-0.69Cu-0.64Al-0.15C, obtained by non-vacuum nitrogen atomization, is prepared by laser directional energy deposition technology and then subjected to a simple one-step tempering heat treatment (tempering temperature is 430℃, holding time is 6h).

[0083] Using Fe-13.85Cr-3.12Ni-0.78Si-0.76Mn-0.69Cu-0.64Al-0.15C corrosion-resistant ultra-high strength and toughness steel powder as raw material and 45 steel as substrate, Fe-13.85Cr-3.12Ni-0.78Si-0.76Mn-0.69Cu-0.64Al-0.15C corrosion-resistant ultra-high strength and toughness steel was prepared by laser-directed energy deposition (LDED) technology. The equipment used in the LDED technology included a laser, a deposition head, and a CNC work platform. The substrate was fixed on the CNC work platform. The process parameters involved in the LDED technology were as follows: distance between the deposition head and the substrate was 11 mm, laser wavelength was 1070 mm, laser focal length was 200 mm, defocusing amount was 25 mm, laser spot diameter was 1.4 mm, laser power was 480 W, laser scanning speed was 600 mm / min, and powder feeding speed was 4.8 ppm. g / min, overlap coefficient 0.5, protective gas flow rate 12 L / min, powder feeding gas flow rate 10 L / min, both protective gas and powder feeding gas are high-purity nitrogen.

[0084] The SEM morphology of corrosion-resistant ultra-high strength and toughness steel in its deposited and heat-treated states is shown in the following figures: Fe-13.85Cr-3.12Ni-0.78Si-0.76Mn-0.69Cu-0.64Al-0.15C. Figure 10 As shown in the figure, the comparison clearly shows that a single heat treatment induced a large amount of precipitation of the second phase. For example... Figure 10 (b) As shown in the inset, a large number of nano-precipitates were generated inside the martensitic laths of the heat-treated sample. These finely distributed precipitates effectively hinder dislocation movement and produce a significant precipitation strengthening effect.

[0085] The tensile curves of Fe-13.85Cr-3.12Ni-0.78Si-0.76Mn-0.69Cu-0.64Al-0.15C corrosion-resistant ultra-high strength and toughness steel in the deposited and heat-treated states are shown below. Figure 11As shown in the comparison, the one-step tempering treatment synergistically enhances the overall mechanical properties. Specifically, the ultimate tensile strength increases from 1289 MPa in the deposited state to 1585 MPa, an increase of approximately 23%; simultaneously, the elongation also increases from 8.9% to 15.2%, approximately 1.7 times. This result confirms that the one-step tempering treatment achieves simultaneous optimization of the material's strength and toughness.

[0086] The following specific example 11 illustrates the use of laser additive manufacturing to produce low-cost corrosion-resistant ultra-high strength and toughness steel and its heat treatment method. The customized powder raw material of corrosion-resistant ultra-high strength and toughness steel, Fe-14.44Cr-1.81Ni-1.08Mn-0.74Si-0.64Al-0.37Cu-0.11C, obtained by non-vacuum nitrogen atomization, is prepared by laser directional energy deposition technology and then subjected to a simple one-step tempering heat treatment (tempering temperature is 450℃, holding time is 6h).

[0087] Using Fe-14.44Cr-1.81Ni-1.08Mn-0.74Si-0.64Al-0.37Cu-0.11C corrosion-resistant ultra-high strength and toughness steel powder as raw material and 45 steel as substrate, Fe-14.44Cr-1.81Ni-1.08Mn-0.74Si-0.64Al-0.37Cu-0.11C corrosion-resistant ultra-high strength and toughness steel was prepared by laser-directed energy deposition (LDED) technology. The equipment used in the LDED technology included a laser, a deposition head, and a CNC work platform. The substrate was fixed on the CNC work platform. The process parameters involved in the LDED technology were as follows: distance between the deposition head and the substrate was 11 mm, laser wavelength was 1070 mm, laser focal length was 200 mm, defocusing amount was 25 mm, laser spot diameter was 1.4 mm, laser power was 530 W, laser scanning speed was 600 mm / min, and powder feeding speed was 4.5 mm / min. g / min, overlap coefficient 0.5, protective gas flow rate 8 L / min, powder feeding gas flow rate 10 L / min, both protective gas and powder feeding gas are high-purity nitrogen.

[0088] The SEM morphology of corrosion-resistant ultra-high strength and toughness steel in its deposited and heat-treated states is shown in the following figures: Fe-14.44Cr-1.81Ni-1.08Mn-0.74Si-0.64Al-0.37Cu-0.11C. Figure 12 As shown in the figure. Comparative analysis indicates that the one-step heat treatment process significantly increased the density of precipitated phases in the samples. Figure 12 (b) As shown in the inset, a large number of nano-precipitates formed within the martensitic laths of the heat-treated sample. The significant hindrance to dislocation movement can be attributed to these densely distributed precipitates, resulting in a strong precipitation strengthening effect.

[0089] The tensile curves of corrosion-resistant ultra-high strength and toughness steel in the deposited and heat-treated states are shown in the figure. (Fe-14.44Cr-1.81Ni-1.08Mn-0.74Si-0.64Al-0.37Cu-0.11C) Figure 13 As shown, the comprehensive mechanical properties of the material are significantly improved after one-step tempering. Specifically, the ultimate tensile strength reaches 1585 MPa, an increase of approximately 23% compared to the deposited state (1289 MPa); the elongation increases from 8.9% in the deposited state to 15.2%, approximately 1.7 times. These performance changes indicate that one-step tempering can effectively promote a good balance between strength and toughness.

[0090] The following specific example 12 illustrates the use of laser additive manufacturing to produce low-cost corrosion-resistant ultra-high strength and toughness steel and its heat treatment method. The customized powder raw material of corrosion-resistant ultra-high strength and toughness steel, Fe-15.69Cr-2.64Ni-0.89Mn-0.86Si-0.57Al-0.26Cu-0.17C, obtained by non-vacuum nitrogen atomization, is prepared by laser directional energy deposition technology and then subjected to a simple one-step tempering heat treatment (tempering temperature is 430℃, holding time is 6h).

[0091] Using Fe-15.69Cr-2.64Ni-0.89Mn-0.86Si-0.57Al-0.26Cu-0.17C corrosion-resistant ultra-high strength and toughness steel powder as raw material and 45 steel as substrate, Fe-15.69Cr-2.64Ni-0.89Mn-0.86Si-0.57Al-0.26Cu-0.17C corrosion-resistant ultra-high strength and toughness steel was prepared by laser-directed energy deposition (LDED) technology. The equipment used in the LDED technology included a laser, a deposition head, and a CNC work platform. The substrate was fixed on the CNC work platform. The process parameters involved in the LDED technology were as follows: distance between the deposition head and the substrate was 11 mm, laser wavelength was 1070 mm, laser focal length was 200 mm, defocusing amount was 25 mm, laser spot diameter was 1.4 mm, laser power was 500 W, laser scanning speed was 600 mm / min, and powder feeding speed was 5.0 mm / min. g / min, overlap coefficient 0.5, protective gas flow rate 10 L / min, powder feeding gas flow rate 10 L / min, both protective gas and powder feeding gas are high-purity nitrogen.

[0092] The SEM morphology of corrosion-resistant ultra-high strength and toughness steel in its deposited and heat-treated states is shown in the following figures: Fe-15.69Cr-2.64Ni-0.89Mn-0.86Si-0.57Al-0.26Cu-0.17C. Figure 14 As shown in the figure. Comparative analysis indicates that the one-step heat treatment process significantly increased the density of precipitated phases in the samples. Figure 14(b) As shown in the illustration, a large number of nano-precipitates were generated inside the martensitic laths of the heat-treated sample. These finely distributed precipitates can effectively hinder dislocation movement and produce a significant precipitation strengthening effect.

[0093] The tensile curves of corrosion-resistant ultra-high strength and toughness steel in the deposited and heat-treated states are shown in the figure. (Fe-15.69Cr-2.64Ni-0.89Mn-0.86Si-0.57Al-0.26Cu-0.17C) Figure 15 As shown, the comprehensive mechanical properties of the material are significantly improved after one-step tempering. Specifically, the ultimate tensile strength reaches 1602 MPa, an increase of approximately 22% compared to the deposited state (1312 MPa); the elongation increases from 7.6% in the deposited state to 13.8%, approximately 1.8 times. These performance changes indicate that one-step tempering can effectively promote a good balance between strength and toughness.

[0094] The low-cost corrosion-resistant ultra-high strength and toughness steel for laser additive manufacturing and its heat treatment method in this embodiment achieve synergistic control of the mechanical and corrosion resistance properties of additive manufacturing steel.

[0095] Although embodiments of the present invention have been described above, any modifications and substitutions made by those skilled in the art without departing from the principles and spirit of the present invention are within the scope of protection claimed by the present invention.

Claims

1. A low-cost, corrosion-resistant, ultra-high strength and toughness steel for laser additive manufacturing, characterized in that, The corrosion-resistant ultra-high strength and toughness steel contains the following elemental mass percentages: C 0.1%~0.2%; Cr 13.0%~16.0%; Ni 1.81%~3.5%; Si 0.5%~1.0%; Mn 0.7%~1.2%; Al 0.3%~0.7%; Cu 0.2%~0.8%, with the balance being Fe and unavoidable impurity elements S≤0.01% and P≤0.01%.

2. The low-cost, corrosion-resistant, ultra-high strength and toughness steel for laser additive manufacturing according to claim 1, characterized in that, The microstructure of the corrosion-resistant ultra-high strength and toughness steel consists of lath martensite, austenite, carbides, and nano-precipitates.

3. The method for preparing a low-cost corrosion-resistant ultra-high strength and toughness steel for laser additive manufacturing according to claim 1, characterized in that, Includes the following steps: Step S1: Prepare corrosion-resistant ultra-high strength and toughness steel powder; the mass percentage of elements contained in the corrosion-resistant ultra-high strength and toughness steel powder is C 0.1%~0.2%; Cr 13.0%~16.0%; Ni 1.81%~3.5%; Si 0.5%~1.0%; Mn 0.7%~1.2%; Al 0.3%~0.7%; Cu 0.2%~0.8%, with the balance being Fe and unavoidable impurity elements S≤0.01% and P≤0.01%; Step S2: Place the corrosion-resistant ultra-high strength and toughness steel powder prepared in step S1 into a drying oven and dry it at 60°C for 24 hours. Step S3: Using corrosion-resistant ultra-high strength and toughness steel powder as raw material and iron-based material as substrate, corrosion-resistant ultra-high strength and toughness steel is prepared by laser-directed energy deposition (LDED). The equipment used in the LED includes a laser, a deposition head, and a CNC work platform, with the substrate fixed on the CNC work platform. The process parameters involved in the LED are as follows: distance between the deposition head and the substrate is 9-12 mm, laser wavelength is 1064-1080 mm, laser focal length is 180-220 mm, defocusing amount is 23-28 mm, laser spot diameter is 1.2-1.6 mm, laser power is 450-550 W, laser scanning speed is 550-650 mm / min, powder feeding speed is 4-14 g / min, overlap coefficient is 0.45-0.55, protective gas flow rate is 8-18 L / min, and powder feeding gas flow rate is 10-14 L / min. Both the protective gas and the powder feeding gas are high-purity nitrogen. Step S4: The corrosion-resistant ultra-high strength and toughness steel prepared in step S3 is subjected to tempering heat treatment. The parameters of the tempering heat treatment are: tempering temperature of 400~500℃ and holding time of 4~8h.

4. The method according to claim 3, characterized in that, Heat treatment is performed using a standard box-type heat treatment furnace.

5. The method according to claim 3, characterized in that, The corrosion-resistant ultra-high strength and toughness steel powder is prepared using non-vacuum nitrogen atomization.

6. The method according to claim 3, characterized in that, The average particle size of the corrosion-resistant ultra-high strength and toughness steel powder is 50~70 μm, and it must be dried before use.

7. The method according to claim 3, characterized in that, Iron-based materials must be leveled and dried before use.

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