High-toughness maraging steel and preparation method thereof

Abstract

The invention discloses high-toughness maraging steel which comprises the following components in percentage by weight: less than or equal to 0.005 wt% of C, less than or equal to 0.05 wt% of Si, less than or equal to 0.05 wt% of Mn, less than or equal to 0.005 wt% of P, less than or equal to 0.005 wt% of S, 17.5-19.5 wt% of Ni, 3.5-4.5 wt% of Mo, 2.5-3.5 wt% of Al, 0.01-0.8 wt% of Nb, 0.005-0.015 wt% of B, less than 0.005 wt% of N, less than 0.01 wt% of O and the balance of Fe. Through reasonable alloy component design and optimization of preparation processes such as heat treatment, hot rolling and cold rolling, the high strength and toughness of the maraging steel are achieved, the yield strength of the prepared maraging steel is 1200-1700 MPa, the tensile strength is 1850-2100 MPa, and the ductility is 10.5-13.5%.

Description

Technical Field

[0001] The invention belongs to the technical field of alloy materials and relates to a high-strength and tough martensitic aging steel and a preparation method thereof. Background Art

[0002] Maraging steel has great application potential in transportation, energy extraction and other fields, such as aircraft landing gear, engineering machinery, aerospace, shipbuilding, and offshore platform manufacturing.

[0003] During the aging process of traditional maraging steel, a high-density nano-precipitate phase and a large number of dislocations are formed in the lath martensitic matrix, resulting in high strength. The high strength is achieved due to the strengthening and toughening effect of the Co element on the steel. The addition of high Co elements has become a shortcoming that restricts the development of maraging. Developing low-Co or Co-free maraging steels and reducing costs have become urgent issues to be solved in the process of industrializing maraging steel.

[0004] As researchers continue to study in depth, if a certain amount of Ti is added, the strength is improved by precipitating the Ti-containing intermetallic second phase Ni3Ti through aging treatment, while reducing the C content in maraging steel to prevent the added Ti element from combining with the C element to form titanium carbide non-metallic inclusions, which will reduce the toughness of the steel and consume the Ti element. The maraging steel produced under the above conditions not only obtains good toughness due to the reduced carbon content, but also improves its welding performance. The intermetallic compounds formed after the introduction of Ti elements, such as Ni3Ti, Ni3Mo and Fe2 (Mo, Ti), are usually incoherent or semi-coherent with the matrix. If you want to achieve the best effect of precipitation strengthening of maraging steel, you need to precipitate small-sized, high-density, fully coherent second-phase particles on high-density dislocations based on extremely low lattice mismatch. The uneven distribution of semi-coherent second phase particles will produce large coherent stress, which can significantly hinder dislocation movement to improve strength, but potentially promotes crack initiation near the interface during loading, resulting in high strength and low toughness. Summary of the invention

[0005] (I) Purpose of the invention

[0006] The purpose of the present invention is to provide a high-strength and tough maraging steel and a preparation method thereof. The maraging steel is prepared by replacing Co and Ti with an appropriate content of Al element and strengthening with B2-NiAl nanoparticles by coherent precipitation. Since the interfacial energy required for the precipitation of B2 structured intermetallic compounds is lower and the nucleation work is smaller, the uniform coherent precipitation of high-density B2 nanoparticles on the martensitic matrix can be ensured. The maraging steel designed by this concept has good plasticity and toughness while obtaining ultra-high strength.

[0007] (II) Technical solution

[0008] In order to solve the above technical problems, the present invention provides a high-strength and tough maraging steel, wherein the components and percentages thereof are respectively as follows, by weight percentage: C≤0.005wt%, Si≤0.05wt%, Mn≤0.05wt%, P≤0.005wt%, S≤0.005wt%, Ni: 17.5-19.5wt%, Mo: 3.5-4.5wt%, Al: 2.5-3.5wt%, Nb: 0.01-0.8wt%, B: 0.005-0.015wt%, N<0.005wt%, O<0.01wt%, and the balance is Fe.

[0009] The present invention also provides a method for preparing high-strength and tough maraging steel, which comprises the following steps:

[0010] S1. Prepare component raw materials and smelt to obtain ingots;

[0011] S2, the ingot is subjected to homogenization heat treatment;

[0012] S3, the ingot is subjected to free forging;

[0013] S4, hot rolling the forged billet to obtain a hot rolled plate;

[0014] S5, performing a solution treatment on the hot-rolled plate to obtain a solution hot-rolled plate; heating the hot-rolled plate to 900-950° C. and keeping the temperature for 15-30 minutes, and then quenching and cooling to room temperature to obtain a solution hot-rolled plate;

[0015] S6, cold rolling the solution hot rolled plate to obtain a cold rolled plate; the total cold rolling reduction rate is not less than 60%, and the single pass reduction rate is not less than 5%;

[0016] S7. The cold-rolled sheet is heated to 500-550°C and kept at this temperature for 15-360 minutes for aging treatment. After the aging treatment, the sheet is air-cooled or water-cooled to room temperature to obtain high-strength and tough maraging steel.

[0017] Preferably, in step S1, a vacuum induction furnace is used for smelting to obtain an ingot.

[0018] Preferably, in step S2, the ingot is placed in an argon-protected heating furnace for homogenization heat treatment at a temperature of 1150-1250° C. for 60-300 min. After the insulation is completed, the ingot is furnace-cooled or air-cooled to room temperature. Specifically, the temperature of the homogenization heat treatment may be, for example, but not limited to, any one of 1150°C, 1160°C, 1170°C, 1180°C, 1190°C, 1200°C, 1210°C, 1220°C, 1230°C, 1240°C, 1250°C, or a range between any two thereof; the holding time may be, for example, but not limited to, any one of 60min, 70min, 80min, 90min, 100min, 110min, 120min, 130min, 140min, 150min, 160min, 170min, 180min, 190min, 200min, 210min, 220min, 230min, 240min, 250min, 260min, 270min, 280min, 290min, or 300min, or a range between any two thereof;

[0019] Preferably, in step S3, the billet is heated to 1050-1150°C, kept warm for 45-60 minutes, and then free forging is started, the final forging temperature is ≥900°C, the forging ratio is 4, and after forging, it is slowly cooled while wrapped in heat-insulating cotton to obtain a forged billet. Specifically, the billet heating temperature can be, for example, but not limited to, any one of 1050°C, 1060°C, 1070°C, 1080°C, 1090°C, 1100°C, 1110°C, 1120°C, 1130°C, 1140°C, 1150°C, or a range between any two of them; the holding time can be, for example, but not limited to, any one of 45min, 50min, 55min, 60min, or a range between any two of them;

[0020] Preferably, in step S4, the forging blank is heated to 900-1000°C, kept warm for 25-35 minutes, and then hot rolled, the final rolling temperature is ≥700°C, the total rolling reduction rate is not less than 30%, and the single rolling reduction is not less than 15%. Specifically, the heating temperature of the forging blank can be, for example, but not limited to, any one of 900°C, 910°C, 920°C, 930°C, 940°C, 950°C, 960°C, 970°C, 980°C, 990°C, 1000°C, or any range between two of them; the holding time can be, for example, but not limited to, any one of 25min, 30min, 35min, or any range between two of them;

[0021] Preferably, in step S4, the thickness of the hot-rolled plate is 8 to 24 mm. Specifically, the thickness of the hot-rolled plate can be, for example but not limited to, any one of 8 mm, 12 mm, 18 mm, 24 mm, or a range between any two thereof;

[0022] Preferably, in step S5, the hot-rolled plate is heated to 900-950°C and kept warm for 15-30 minutes, and then quenched and cooled to room temperature to obtain a solution hot-rolled plate. Specifically, the heating temperature of the hot-rolled plate can be, for example, but not limited to, any one of 900°C, 910°C, 920°C, 930°C, 940°C, 950°C, or any range between two thereof; the holding time can be, for example, but not limited to, any one of 15 minutes, 20 minutes, 25 minutes, 30 minutes, or any range between two thereof;

[0023] Preferably, in step S6, the thickness of the cold-rolled sheet is 4-8 mm. Specifically, the thickness of the cold-rolled sheet can be, for example but not limited to, any one of 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, or a range between any two thereof;

[0024] Preferably, in step S6, when the thickness of the hot-rolled plate is ≥18 mm, the total cold-rolling reduction ratio is not less than 70%.

[0025] (III) Beneficial effects

[0026] The high-strength and toughness maraging steel and its preparation method provided by the above technical solution utilize Al element to replace Co element and Ti element, introduce Mo element and Nb element, utilize the synergistic effect of NiAl phase intermetallic compound of coherent B2 structure and carbides such as NbC and (Nb, Mo)C to strengthen the steel, realize the high strength and toughness of maraging steel through reasonable alloy composition design and optimization of preparation process such as heat treatment, hot rolling and cold rolling, and the prepared maraging steel has a yield strength of 1200-1700MPa, a tensile strength of 1850-2100MPa and an elongation of 10.5-13.5%. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a SEM image of the maraging steel prepared in Example 1;

[0028] Figure 2 TEM image of the maraging steel prepared in Example 2;

[0029] Figure 3 This is the IPF diagram of the maraging steel prepared in Example 3. DETAILED DESCRIPTION

[0030] In order to make the purpose, content and advantages of the present invention more clear, the specific implementation methods of the present invention are further described in detail below in conjunction with the drawings and examples.

[0031] Example 1

[0032] The high-strength and tough maraging steel of this embodiment has the following composition, by weight percentage: C: 0.003wt%, Si: 0.04wt%, Mn: 0.019wt%, P: 0.005wt%, S: 0.002wt%, Ni: 18.85wt%, Mo: 3.89wt%, Al: 2.64wt%, Nb: 0.58wt%, B: 0.012wt%, N: 0.003wt%, O: 0.002wt%, and the balance is Fe and unavoidable impurity elements.

[0033] The preparation method of the high-strength and tough maraging steel of this embodiment comprises the following steps:

[0034] S1. Prepare the raw materials according to the above ingredients, melt them in a vacuum induction furnace and cast them into ingots;

[0035] S2. The ingot is placed in an argon-protected heating furnace for homogenization heat treatment at a temperature of 1200°C for 180 minutes. After the end of the heat preservation, the ingot is cooled to room temperature with the furnace;

[0036] S3, heating the homogenized ingot to 1100°C for 40 minutes, and then forging along the thickness direction of the ingot cross section, with a forging ratio of 4 and a final forging temperature of 900°C. After forging, slowly cooling is performed under the wrapping of heat preservation cotton to obtain a forging blank with a cross-sectional size of 40*40mm;

[0037] S4, a block sample of 20*20*70 is cut from the forging billet, heated to 950℃ and kept warm for 30min, and then hot rolled along the thickness direction of the forging billet cross section, the total hot rolling reduction rate is 30%, the single pass reduction rate is not less than 15%, the final rolling temperature is 830℃, after the hot rolling is completed, the hot rolled plate is returned to the furnace for heat preservation to obtain a hot rolled plate with a thickness of 14mm;

[0038] S5, subjecting the hot-rolled plate to a solution treatment at a solution temperature of 900° C. and a holding time of 15 min to obtain a solution hot-rolled plate having a thickness of 14 mm;

[0039] S6, cold rolling the solution hot rolled plate, the total cold rolling reduction ratio is 70%, and the single pass reduction ratio is not less than 5%, to obtain a cold rolled plate with a thickness of 4.2 mm;

[0040] S7. The cold-rolled plate is heated to 500°C and kept warm for 180 minutes for aging treatment. After the aging treatment, it is water-cooled to room temperature to obtain high-strength and tough martensitic aging steel. The high-strength and tough martensitic aging steel prepared in this embodiment was subjected to mechanical property tests, and its yield strength was 1719MPa, the tensile strength was 2109MPa, and the elongation at break was 13.45%. A sample was cut from the high-strength and tough martensitic aging steel prepared in this embodiment, and after grinding and polishing, a double A solution prepared with 5g tetramethylammonium chloride + 50ml acetylacetone + 445ml methanol was electrolyzed at 12V, and then observed under a Zeiss Sigma300 field emission scanning electron microscope. The results are as follows Figure 1 As shown. Figure 1 It can be seen that a large number of dispersed second phase particles are precipitated in the steel.

[0041] Example 2

[0042] The high-strength and tough maraging steel of this embodiment has the following composition, by weight percentage: C: 0.005wt%, Si: 0.019wt%, Mn: 0.015wt%, P: 0.004wt%, S: 0.002wt%, Ni: 19.06wt%, Mo: 4.00wt%, Al: 2.68wt%, Nb: 0.0.097wt%, B: 0.013wt%, N: 0.002wt%, O: 0.009wt%, and the balance is Fe and unavoidable impurity elements.

[0043] The preparation method of the high-strength and tough maraging steel of this embodiment comprises the following steps:

[0044] S1. Prepare the raw materials according to the above ingredients, melt them in a vacuum induction furnace and cast them into ingots;

[0045] S2. The ingot is placed in an argon-protected heating furnace for homogenization heat treatment at a temperature of 1200°C for 180 minutes. After the end of the heat preservation, the ingot is cooled to room temperature with the furnace;

[0046] S3, heating the homogenized ingot to 1100°C for 40 minutes, and then forging along the thickness direction of the ingot cross section, with a forging ratio of 4 and a final forging temperature of 900°C. After forging, slowly cooling is performed under the wrapping of heat preservation cotton to obtain a forging blank with a cross-sectional size of 40*40mm;

[0047] S4, a block sample of 20*20*70 is cut from the forging billet, heated to 950℃ and kept warm for 30min, and then hot rolled along the thickness direction of the forging billet cross section, the total hot rolling reduction rate is 30%, the single pass reduction rate is not less than 15%, the final rolling temperature is 830℃, after the hot rolling is completed, the hot rolled plate is returned to the furnace for heat preservation to obtain a hot rolled plate with a thickness of 14mm;

[0048] S5, subjecting the hot-rolled plate to a solution treatment at a solution temperature of 900° C. and a holding time of 15 min to obtain a solution hot-rolled plate having a thickness of 14 mm;

[0049] S6, cold rolling the solution hot rolled plate, the total cold rolling reduction ratio is 70%, and the single pass reduction ratio is not less than 5%, to obtain a cold rolled plate with a thickness of 4.2 mm;

[0050] S7. Heat the cold-rolled sheet to 500°C and keep it warm for 60 minutes for aging treatment. After the aging treatment, water cool it to room temperature to obtain high-strength and tough martensitic aging steel. The high-strength and tough martensitic aging steel prepared in this embodiment was tested for mechanical properties. Its yield strength was 1708MPa, its tensile strength was 2042MPa, and its elongation at break was 11.7%. A sample was cut from the high-strength and tough martensitic aging steel prepared in this embodiment, finely ground to a thickness of 50μm, and double-sprayed thinned at -25°C using a 10% perchloric acid alcohol solution. The fine structure of the sample was characterized using a JEOL JEM-2100F field emission transmission electron microscope. The results are as follows: Figure 2 As shown. Figure 2 It can be seen that the fine structure of the second phase particles in the steel.

[0051] Example 3

[0052] The high-strength and tough maraging steel of this embodiment has the following compositions, by weight percentage: C: 0.004wt%, Si: 0.026wt%, Mn: 0.007wt%, P: 0.005wt%, S: 0.002wt%, Ni: 18.94wt%, Mo: 3.97wt%, Al: 2.64wt%, Nb: 0.32wt%, B: 0.012wt%, N: 0.007wt%, O: 0.004wt%, and the remainder is Fe and unavoidable impurity elements.

[0053] The preparation method of the high-strength and tough maraging steel of this embodiment comprises the following steps:

[0054] S1. Prepare the raw materials according to the above ingredients, melt them in a vacuum induction furnace and cast them into ingots;

[0055] S2. The ingot is placed in an argon-protected heating furnace for homogenization heat treatment at a temperature of 1200°C for 180 minutes. After the end of the heat preservation, the ingot is cooled to room temperature with the furnace;

[0056] S3, heating the homogenized ingot to 1100°C for 40 minutes, and then forging along the thickness direction of the ingot cross section, with a forging ratio of 4 and a final forging temperature of 900°C. After forging, slowly cooling is performed under the wrapping of heat preservation cotton to obtain a forging blank with a cross-sectional size of 40*40mm;

[0057] S4, a block sample of 20*20*70 is cut from the forging billet, heated to 950℃ and kept warm for 30min, and then hot rolled along the thickness direction of the forging billet cross section, the total hot rolling reduction rate is 30%, the single pass reduction rate is not less than 15%, the final rolling temperature is 830℃, after the hot rolling is completed, the hot rolled plate is returned to the furnace for heat preservation to obtain a hot rolled plate with a thickness of 14mm;

[0058] S5, subjecting the hot-rolled plate to a solution treatment at a solution temperature of 900° C. and a holding time of 15 min to obtain a solution hot-rolled plate having a thickness of 14 mm;

[0059] S6, cold rolling the solution hot rolled plate, the total cold rolling reduction ratio is 70%, and the single pass reduction ratio is not less than 5%, to obtain a cold rolled plate with a thickness of 4.2 mm;

[0060] S7. Heat the cold-rolled plate to 500°C and keep it warm for 60 minutes for aging treatment. After the aging treatment, water-cool it to room temperature to obtain high-strength and tough martensitic aging steel. The high-strength and tough martensitic aging steel prepared in this embodiment was tested for mechanical properties. The yield strength was 1544MPa, the tensile strength was 2011MPa, and the elongation at break was 11.5%. A sample was cut from the high-strength and tough martensitic aging steel prepared in this embodiment. After grinding and polishing, it was electrolyzed at 18V using a 10% mass fraction perchloric acid alcohol solution. The sample was characterized by EBSD using a Zeiss Sigma 300 field emission scanning electron microscope equipped with an OXFORD-EBSD imaging system. The scanning step length was 0.8μm. The results are as follows: Figure 3 As shown. Figure 3 It can be seen that there are martensite laths with various orientations in the steel.

[0061] Example 4

[0062] The high-strength and tough maraging steel of this embodiment has the following composition, by weight percentage: C: 0.003wt%, Si: 0.04wt%, Mn: 0.019wt%, P: 0.005wt%, S: 0.002wt%, Ni: 18.85wt%, Mo: 3.89wt%, Al: 2.64wt%, Nb: 0.58wt%, B: 0.012wt%, N: 0.003wt%, O: 0.002wt%, and the balance is Fe and unavoidable impurity elements.

[0063] The preparation method of the high-strength and tough maraging steel of this embodiment comprises the following steps:

[0064] S1. Prepare the raw materials according to the above ingredients, melt them in a vacuum induction furnace and cast them into ingots;

[0065] S2. The ingot is placed in an argon-protected heating furnace for homogenization heat treatment at a temperature of 1200°C for 180 minutes. After the end of the heat preservation, the ingot is cooled to room temperature with the furnace;

[0066] S3, heating the homogenized ingot to 1100°C for 40 minutes, and then forging along the thickness direction of the ingot cross section, with a forging ratio of 4 and a final forging temperature of 900°C. After forging, slowly cooling is performed under the wrapping of heat preservation cotton to obtain a forging blank with a cross-sectional size of 40*40mm;

[0067] S4, a block sample of 20*20*70 is cut from the forging billet, heated to 950℃ and kept warm for 15min, and then hot rolled along the thickness direction of the forging billet cross section, the total hot rolling reduction rate is 30%, the single pass reduction rate is not less than 15%, the final rolling temperature is 850℃, and after the hot rolling is completed, the hot rolled plate is returned to the furnace for heat preservation to obtain a hot rolled plate with a thickness of 14mm;

[0068] S5, subjecting the hot-rolled plate to a solution treatment at a solution temperature of 900° C. and a holding time of 30 min to obtain a solution hot-rolled plate having a thickness of 14 mm;

[0069] S6, cold rolling the solution hot rolled plate, the total cold rolling reduction ratio is 70%, and the single pass reduction ratio is not less than 5%, to obtain a cold rolled plate with a thickness of 4.2 mm;

[0070] S7, heating the cold-rolled sheet to 500°C and keeping it for 180 minutes for aging treatment, and cooling it to room temperature after the aging treatment to obtain high-strength and tough martensitic aging steel. The high-strength and tough martensitic aging steel prepared in this embodiment was tested for mechanical properties, and its yield strength was 1196MPa, tensile strength was 1861MPa, and elongation at break was 12.65%.

[0071] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A high-strength and tough maraging steel, characterized in that: In terms of weight percentage, its components and percentages are: C≤0.005wt%, Si≤0.05wt%, Mn≤0.05wt%, P≤0.005wt%, S≤0.005wt%, Ni: 17.5~19.5wt%, Mo: 3.5~4.5wt%, Al: 2.5~3.5wt%, Nb: 0.01~0.8wt%, B: 0.005~0.015wt%, N<0.005wt%, O<0.01wt%, and the balance is Fe.

2. A method for preparing high-strength and tough maraging steel, characterized in that: The steps include: S1. Prepare component raw materials and smelt to obtain ingots; S2, the ingot is subjected to homogenization heat treatment; S3, the ingot is subjected to free forging; S4, hot rolling the forged billet to obtain a hot rolled plate; S5, performing a solution treatment on the hot-rolled plate to obtain a solution hot-rolled plate; heating the hot-rolled plate to 900-950° C. and keeping the temperature for 15-30 minutes, and then quenching and cooling to room temperature to obtain a solution hot-rolled plate; S6, cold rolling the solution hot rolled plate to obtain a cold rolled plate; the total cold rolling reduction rate is not less than 60%, and the single pass reduction rate is not less than 5%; S7. The cold-rolled sheet is heated to 500-550°C and kept at this temperature for 15-360 minutes for aging treatment. After the aging treatment, the sheet is air-cooled or water-cooled to room temperature to obtain high-strength and tough maraging steel.

3. The method for preparing high-strength and tough maraging steel according to claim 2, characterized in that: In step S1, a vacuum induction furnace is used for smelting to obtain an ingot.

4. The method for preparing high-strength and tough maraging steel according to claim 3, characterized in that: In step S2, the ingot is placed in an argon-protected heating furnace for homogenization heat treatment at a temperature of 1150-1250° C. for 60-300 minutes. After the end of the heat preservation, the ingot is cooled to room temperature in the furnace or in air.

5. The method for preparing high-strength and tough maraging steel according to claim 4, characterized in that: In step S3, the ingot is heated to 1050-1150°C, kept warm for 45-60 minutes, and then free forging is started, the final forging temperature is ≥900°C, the forging ratio is 4, and after forging, it is slowly cooled while wrapped in heat-insulating cotton to obtain a forged ingot.

6. The method for preparing high-strength and tough maraging steel according to claim 5, characterized in that: In step S4, the forging blank is heated to 900-1000°C, kept warm for 25-35 minutes, and then hot rolled. The final rolling temperature is ≥700°C, the total rolling reduction rate is not less than 30%, and the single rolling reduction is not less than 15%.

7. The method for preparing high-strength and tough maraging steel according to claim 6, characterized in that: In step S4, the thickness of the hot-rolled plate is 8 to 24 mm.

8. The method for preparing high-strength and tough maraging steel according to claim 7, characterized in that: In step S5, the hot-rolled plate is heated to 900-950° C. and kept at this temperature for 15-30 min, and then quenched and cooled to room temperature to obtain a solution hot-rolled plate.

9. The method for preparing high-strength and tough maraging steel according to claim 8, characterized in that: In step S6, the thickness of the cold-rolled sheet is 4 to 8 mm.

10. The method for preparing high-strength and tough maraging steel according to claim 9, characterized in that: In step S6, when the thickness of the hot-rolled plate is ≥18 mm, the total cold-rolling reduction ratio is not less than 70%.

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