Ultrahigh-strength steel as well as preparation method and application thereof

Abstract

The invention relates to the technical field of alloy steel, and particularly discloses ultrahigh-strength steel as well as a preparation method and application thereof. The ultrahigh-strength steel provided by the invention is prepared from the following chemical components in percentage by weight: 0.15 to 0.30 percent of C, 1.5 to 3.5 percent of Cr, 11.0 to 13.0 percent of Ni, 7.1 to 7.9 percent of Co, 1.8 to 2.5 percent of Mo, 0.8 to 1.3 percent of Al, 0.01 to 0.10 percent of Nb and the balance of Fe. The invention further provides a preparation method of the ultrahigh-strength steel. The preparation method comprises the following steps of vacuum induction melting, vacuum consumable remelting, forging and heat treatment. The heat treatment comprises solution treatment, subzero treatment and aging treatment. The ultrahigh-strength steel provided by the invention has excellent strength and toughness, and can meet the use requirements of new-generation engines on high-toughness power shaft materials.

Description

Technical Field

[0001] The present application relates to the technical field of alloy steel materials, and in particular to an ultra-high strength steel and a preparation method and application thereof. Background Art

[0002] The material of the power shaft of an aircraft engine is a key component that determines the performance of the engine. When the engine is working, the transmission shaft is subjected to a huge torque load, and the part close to the combustion chamber is also subjected to a certain temperature load. It is subjected to high aerodynamic, high-mass and high-temperature loads, and it is easy to produce stress concentration and high local stress. If the material strength is insufficient or the fatigue resistance is poor, fatigue cracks or even fractures will occur during use, and the consequences are very serious. Therefore, high-performance materials are the basis for ensuring that parts have high comprehensive performance.

[0003] In recent years, with the development of engine power shaft materials and the demand for higher strength of engine transmission shafts, a company has developed a secondary hardened ultra-high strength steel represented by GE1014, whose strength can reach 1950MPa, and has been successfully applied to the low-pressure turbine shaft of GE90 and GENX engines. However, with the needs of engine development, the demand for ultra-high strength and specific strength engine power shaft materials above 2200MPa is becoming increasingly urgent; but research shows that while further improving the strength of steel, the toughness of steel will be significantly reduced, that is, steel cannot meet the needs of strength and toughness at the same time.

[0004] Therefore, it is necessary to develop an ultra-high strength steel with a strength of more than 2200MPa, excellent toughness, high elastic modulus and good medium-temperature strength to meet the engineering application needs of the new generation of engine power shafts. Summary of the invention

[0005] In order to overcome the problem that existing engine power shaft materials cannot have both strength and toughness, the present application provides an ultra-high strength steel and a preparation method and application thereof.

[0006] In a first aspect, the present application provides an ultra-high strength steel, which adopts the following technical solution: An ultra-high strength steel comprises the following chemical components by weight: C 0.15-0.30%, Cr 1.5-3.5%, Ni 11.0-13.0%, Co 7.1-7.9%, Mo 1.8-2.5%, Al 0.8-1.3%, Nb 0.01-0.10%, and the balance is Fe.

[0007] The present application adopts C particles, metal Fe, metal Cr, metal Ni, metal Co, metal Mo, metal Al, metal Nb, etc. to prepare an ultra-high strength steel, and by adjusting the amount of each metal within the above-mentioned range, the obtained ultra-high strength steel has excellent strength and toughness, which can meet the use requirements of the new generation of engines for high-strength and tough power shaft materials.

[0008] In the ultra-high strength steel provided by the present application, Fe can form a martensitic matrix together with elements such as Ni, Co, Cr, and C, and is the main matrix element. C and Fe form a martensitic matrix, producing solid solution strengthening; C and Mo form M2C type carbides; C and Nb form MC type alloy carbides; the precipitation strengthening of the above carbides can further increase the strengthening effect of solid solution, thereby enabling the steel to obtain higher strength. Cr can produce solid solution strengthening, which has the effect of improving the hardenability of steel, and Cr can also generate (Mo, Cr)2C type alloy carbides with Mo during tempering, forming fine dispersed precipitation, thereby improving the strength of ultra-high strength steel through precipitation strengthening. Ni can produce solid solution strengthening, improve the hardenability of ultra-high strength steel, maintain high dislocation lath martensite, and especially Ni can improve the resistance to cleavage fracture of the martensitic matrix, forming reverse transformation austenite, thereby ensuring that the steel has sufficient toughness. In particular, Ni and Al can form nano-scale NiAl intermetallic compounds, forming a strong secondary hardening effect. The joint strengthening of NiAl intermetallic compounds and M2C carbides is the main strengthening method to obtain ultra-high strength. Co can improve the toughness of steel and promote precipitation strengthening reaction; in addition, Co can also inhibit and delay the recovery of martensite dislocation substructure, maintain the high dislocation density of martensite laths, and provide more nucleation sites for the subsequent precipitation of precipitation phases; at the same time, Co can reduce the solid solubility of Mo, Al, etc. in martensite, increase the nucleation rate of precipitation phases, and promote the formation of fine and dispersed precipitation phases. Mo can form M2C carbides with C, thereby producing strong precipitation strengthening, which is the main reason for the formation of high strength; in addition, Mo also has the effect of increasing hardenability, producing solid solution strengthening, improving the tempering resistance of steel and inhibiting temper brittleness. Al and Ni form nano-scale NiAl precipitation phases, which is one of the important factors for obtaining ultra-high strength. At the same time, Al can also improve the Ms point equilibrium martensite lath structure. Nb is crucial to improving the strength and plastic toughness of ultra-high strength steel. Nb can precipitate NbC carbides with C. While improving the strength of the alloy, the NbC phase has a higher precipitation temperature, which enables the alloy to pin grain boundaries and refine grains under high temperature forging conditions, while improving strength and plastic toughness. In summary, this application regulates the precipitation strengthening of M2C alloy carbides and NiAl intermetallic compounds and 8% reverse transformation austenite toughening through multiple mismatches, thereby preparing an ultra-high strength steel with excellent strength and toughness.

[0009] In the present application, when the C content is low, the strength of the ultra-high strength steel is poor, and when the C content is high, the toughness of the ultra-high strength steel is poor; when the Cr content is low or high, the strength of the ultra-high strength steel is poor; when the Ni content is low, the toughness of the ultra-high strength steel is poor, and when the Ni content is high, the strength of the ultra-high strength steel is poor; when the Mo content is low, the strength of the ultra-high strength steel is poor, and when the Mo content is high, the solution temperature will increase and the M6C carbide will be difficult to dissolve, which will lead to coarsening of the grain size and reduced plastic toughness; when the Nb content is high, the MC carbide will be coarsened, the grain boundary pinning effect will be weakened, and the plastic toughness will be reduced; when Co / Ni is less than 0.5, the above effects will be significantly reduced, resulting in insufficient precipitation strengthening, and when Co / Ni is greater than 0.75, the yield strength ratio will be increased and the toughness will be reduced; when the Al content is low, the strength requirements cannot be met, and when the Al content is high or Ni-2.2Al is less than 10, the plastic toughness is seriously reduced. Therefore, the present application strictly controls the amount of each metal within the above range, so as to obtain ultra-high strength steel with both strength and toughness of tensile strength ≥2200MPa and impact energy ≥60J.

[0010] Optionally, the tensile strength of the ultra-high strength steel is ≥2200MPa, and the impact energy is ≥60J.

[0011] Optionally, the yield strength of the ultra-high strength steel is ≥1800MPa, the elastic modulus E is ≥190Gpa, and the tensile strength at 400°C is ≥1700MPa.

[0012] In a second aspect, the present application provides a method for preparing ultra-high strength steel.

[0013] A method for preparing ultra-high strength steel comprises the following steps: vacuum induction melting, vacuum consumable remelting, forging, and heat treatment; the forging start temperature is 1160-1200°C, and the final forging temperature is 800-900°C.

[0014] The present application provides a method for preparing ultra-high-strength steel. The preparation method first obtains alloy liquid through vacuum induction melting, and obtains electrodes by casting; then improves the uniformity of the melt components through vacuum consumable remelting to obtain a steel ingot with uniform structure; then obtains rods through forging; finally, heat treats the rods through a three-stage heat treatment process, thereby obtaining an ultra-high-strength steel with good structural uniformity, excellent strength and toughness.

[0015] In the present application, "solution treatment" refers to the process of heating the forged rod to the temperature of the solution treatment, keeping it warm, and then cooling the sample. The cooling of the solution treatment is preferably carried out by oil quenching. "Cryogenic treatment" refers to the process of lowering the solution-treated rod to a low temperature state, keeping it warm, and then heating it to room temperature. The cryogenic treatment temperature can be achieved by cooling with a mixture of dry ice + alcohol. "Aging treatment" refers to the process of heating the cryogenic-treated rod to the temperature of the aging treatment, keeping it warm, and then cooling it to room temperature. The cooling of the aging treatment is preferably carried out by air cooling. The present application adopts the three-stage heat treatment process of the above-mentioned solution treatment, cryogenic treatment and aging treatment to obtain a high-toughness martensitic matrix structure, a high-density precipitate phase and the required appropriate amount of reverse transformation austenite, thereby obtaining a new type of power shaft ultra-high strength steel with good strength and toughness.

[0016] Optionally, the heat treatment includes solution treatment, cryogenic treatment and aging treatment; The solution treatment temperature is 950-1000°C and the time is 1-2h; The cryogenic treatment temperature is -73 to -100°C and the time is 1 to 10 hours; The aging treatment temperature is 500-540° C., and the time is 3-10 hours.

[0017] Optionally, the temperature of the vacuum induction melting is 1550-1600° C., the time is 30-180 min, and the vacuum degree is ≤4 Pa.

[0018] Optionally, the vacuum degree of the vacuum consumable remelting is 0.01-2Pa, the melting rate is 4-6kg / min, the voltage is 21-23V, and the current is 11000-13000A.

[0019] In a third aspect, the present application provides an application of ultra-high strength steel as an engine power shaft material.

[0020] In summary, this application has the following beneficial effects: 1. This application adopts the following chemical components: C 0.15~0.30%, Cr 1.5~3.5%, Ni 11.0~13.0%, Co 7.1~7.9%, Mo 1.8~2.5%, Al 0.8~1.3%, Nb 0.01-0.10%, and the balance is Fe; and the dosage relationship of Ni, Co, and Al is controlled to: 0.5≤Co / Ni≤0.75, and 10≤(Ni-2.2Al)≤11, thereby preparing an ultra-high strength steel with excellent strength and toughness, and the ultra-high strength steel can meet the use requirements of the new generation of engines for high-strength and tough power shaft materials.

[0021] 2. The ultra-high strength steel provided in this application has a tensile strength of ≥2200MPa, an impact energy of ≥60J, a yield strength of ≥1800MPa, an elastic modulus E of ≥190Gpa, and a tensile strength at 400°C of ≥1700MPa. DETAILED DESCRIPTION

[0022] The present application provides an ultra-high strength steel, which includes the following chemical components by weight: C 0.15~0.30%, Cr 1.5~3.5%, Ni 11.0~13.0%, Co 7.1~7.9%, Mo 1.8~2.5%, Al 0.8~1.3%, Nb0.01-0.10%, and the balance is Fe; wherein Ni, Co, and Al have the following usage relationship: 0.5≤Co / Ni≤0.75, and 10≤(Ni-2.2Al)≤11.

[0023] The method for preparing the ultra-high strength steel comprises the following steps: (1) Vacuum induction melting: Weigh carbon particles, metal Cr, metal Ni, metal Co, metal Mo, metal Ni, metal Al, metal Nb and pure iron according to their mass content, mix them evenly, and then perform vacuum induction melting and casting on the mixed raw materials in sequence to obtain electrodes; wherein the vacuum induction melting temperature is 1550-1600°C, the time is 30-180 min, and the vacuum degree is ≤4 Pa.

[0024] (2) Vacuum consumable remelting: The electrode obtained in step (1) is subjected to vacuum consumable remelting to obtain a steel ingot; the vacuum degree of the vacuum consumable remelting is 0.01-2 Pa, the melting rate is 4-6 kg / min, the voltage is 21-23 V, and the current is 11000-13000 A.

[0025] (3) Forging: Forging the steel ingot obtained in step (2) to obtain a forged material; the starting forging temperature of the forging is 1160-1200°C, and the final forging temperature is 800-900°C.

[0026] (4) Heat treatment: The bars obtained by forging are subjected to solution treatment, cryogenic treatment and aging treatment in sequence to obtain ultra-high strength steel; wherein the solution treatment temperature is 950~1000℃ and the time is 1~2h; the cryogenic treatment temperature is -73~-100℃ and the time is 1~10h; the aging treatment temperature is 500~540℃ and the time is 3~10h.

[0027] In the present application, carbon particles, metal Cr, metal Ni, metal Co, metal Mo, metal Ni, metal Al, metal Nb, and pure iron are all blocks of pure metals with a purity of ≥99%. There are no other special requirements. They are all commercially available products well known to those skilled in the art and can be obtained commercially.

[0028] The present application is further described in detail below in conjunction with embodiments and performance testing experiments. Examples 1-6

[0029] Examples 1-6 each provide an ultra-high strength steel.

[0030] The difference between the above-mentioned embodiments 1-6 is that the content of each chemical component in the ultra-high strength steel is specifically shown in Table 1 below.

[0031] The method for preparing the ultra-high strength steel comprises the following steps: (1) Vacuum induction melting: according to the chemical composition mass content in Table 1, carbon particles, metal Cr, metal Ni, metal Co, metal Mo, metal Ni, metal Al, metal Nb and pure iron are weighed respectively, mixed evenly, and then the mixed raw materials are subjected to vacuum induction melting and casting in sequence to obtain electrodes; wherein the vacuum induction melting temperature is 1580°C, the time is 60 min, and the vacuum degree is 0.3 Pa.

[0032] (2) Vacuum consumable remelting: The electrode obtained in step (1) is subjected to vacuum consumable remelting to obtain a steel ingot; the vacuum degree of the vacuum consumable remelting is 1.5 Pa, the melting rate is 4 kg / min, the voltage is 22 V, and the current is 12000 A.

[0033] (3) Forging: Forging the steel ingot obtained in step (2) to obtain a forged material; the starting forging temperature of the forging is 1180°C and the final forging temperature is 850°C.

[0034] (4) Heat treatment: The bars obtained by forging are subjected to solution treatment, cryogenic treatment and aging treatment in sequence to obtain ultra-high strength steel; wherein the solution treatment temperature is 980°C for 1 h; the cryogenic treatment temperature is -73°C for 2 h; and the aging treatment temperature is 520°C for 6 h. Comparative Examples 1-3

[0035] Comparative Examples 1-3 each provide an ultra-high strength steel.

[0036] The difference between the above comparative examples 1-3 and embodiment 1 is that the content of each chemical component in the ultra-high strength steel is specifically shown in Table 1 below.

[0037] Table 1 Chemical composition dosage in ultra-high strength steel provided in Examples 1-6 and Comparative Examples 1-3 Embodiment 7-11

[0038] Examples 7-11 each provide an ultra-high strength steel.

[0039] The difference between the above-mentioned embodiments 7-11 and embodiment 1 is that the process parameters of each step in the preparation method of ultra-high strength steel are specifically shown in Table 2 below.

[0040] Table 2 Process parameters in Example 1, Examples 7-11 Comparative Example 4

[0041] Comparative Example 4 provides an ultra-high strength steel.

[0042] The difference between the comparative example and Example 1 is that the alloy composition of the ultra-high strength steel is GE1014; the alloy composition of GE1014 is: C 0.2%, Cr 2.5%, Ni 14%, Co 10%, Mo 1.4%, Al 0.85%, and the balance is Fe. Comparative Example 5

[0043] Comparative Example 5 provides an ultra-high strength steel.

[0044] The difference between the comparative example and Example 1 is that the alloy composition of the ultra-high strength steel is C250; the alloy composition of C250 is: C 0.007%, Ni 18%, Co 8.0%, Mo 5.0%, Al 0.03%, Ti0.4%, and the balance is Fe. Comparative Example 6

[0045] Comparative Example 6 provides an ultra-high strength steel.

[0046] The difference between the comparative example and Example 1 is that the alloy composition of the ultra-high strength steel is 4340; the alloy composition of 4340 is: C 0.40%, Cr 1.0%, Ni 1.8%, Mo 0.3%, and the balance is Fe. Comparative Example 7

[0047] Comparative Example 7 provides an ultra-high strength steel.

[0048] The difference between the comparative example and Example 1 is that in the forging step, the start forging temperature is 1110°C and the final forging temperature is 750°C. Performance testing

[0049] The mechanical properties of the ultra-high strength steels obtained in Examples 1-11 and Comparative Examples 1-7 were tested, and the results are shown in Table 3 below.

[0050] (1) Conduct tensile tests on ultra-high strength steel in accordance with GB / T228.1-2021, including room temperature tensile strength Rm, 400℃ tensile strength Rm, yield strength Rp 0.2 , elastic modulus E.

[0051] (2) Impact energy A of ultra-high strength steel according to GB / T229-2020 ku Conduct testing.

[0052] Table 3 Mechanical properties test results of ultra-high strength steel obtained in Examples 1-11 and Comparative Examples 1-7

[0053] According to the test results in Table 3, the room temperature tensile strength of the ultra-high strength steel obtained in Examples 1-11 of the present application is 2213-2267 MPa, the impact energy is 61-67 J, the yield strength is 1830-1902 MPa, the elastic modulus is 195-198 Gpa, and the tensile strength at 400°C is 1724-1783 MPa. Therefore, it is explained that the present application adopts the following chemical components: C 0.15~0.30%, Cr 1.5~3.5%, Ni 11.0~13.0%, Co 7.1~7.9%, Mo 1.8~2.5%, Al 0.8~1.3%, Nb 0.01-0.10%, and the balance is Fe; and the dosage relationship of Ni, Co, and Al is controlled to: 0.5≤Co / Ni≤0.75, and 10≤(Ni-2.2Al)≤11, so that an ultra-high strength steel with high strength, good toughness and excellent plasticity can be prepared, which is used to prepare engine shaft materials, and can meet the high strength and high toughness requirements of the engine power shaft.

[0054] In Comparative Example 1, when the C content is controlled to 0.12% and the Ni content is controlled to 14.0%, the room temperature tensile strength of the obtained ultra-high strength steel is only 1628 MPa, the 400°C tensile strength is 1328 MPa, and the yield strength is only 1667 MPa; this indicates that the strength of the ultra-high strength steel obtained by the composition ratio of Comparative Example 1 is poor, and therefore cannot meet the use requirements of engine power shaft materials.

[0055] In Comparative Example 2, the Ni content is controlled to 10.5%, and the Co content is controlled to 8.4%, that is, Co / Ni=0.8. The room temperature tensile strength of the obtained ultra-high strength steel is only 2143 MPa, the tensile strength at 400°C is 1685 MPa, the yield strength is only 1796 MPa, the elastic modulus is 190 GPa, and the impact energy is only 52 J. This indicates that the ultra-high strength steel obtained by the component ratio of Comparative Example 2 has poor plasticity and toughness, and therefore cannot meet the use requirements of engine power shaft materials.

[0056] In Comparative Example 3, the Ni content is controlled to 10.0%, and the Al content is controlled to 1.1%, that is, Ni-2.2Al=7.58. The room temperature tensile strength of the obtained ultra-high strength steel is only 2126 MPa, the tensile strength at 400°C is 1706 MPa, the yield strength is only 1843 MPa, the elastic modulus is 190 GPa, and the impact energy is only 49 J. This indicates that the strength, plasticity and toughness of the ultra-high strength steel obtained by the composition ratio of Comparative Example 3 are poor, so it cannot meet the use requirements of engine power shaft materials.

[0057] Comparative Examples 4-6 are GE1014, C250, and 4340 steels in the prior art, whose room temperature tensile strength is only 1801-1981 MPa, and whose impact energy is only 38-46 J; this indicates that the strength and toughness of the power shaft materials provided by the prior art are relatively poor, and cannot meet the use requirements of the new generation of engines for high-strength and tough power shaft materials.

[0058] In Comparative Example 7, the start forging temperature of the forging step is controlled at 1110°C and the final forging temperature is controlled at 750°C. The elastic modulus of the obtained ultra-high strength steel is 190 GPa and the impact energy is only 54 J, indicating that the above forging temperature will lead to poor plasticity and toughness of the ultra-high strength steel.

[0059] To summarize, the present application provides an ultra-high strength steel prepared by using C particles, metal Fe, metal Cr, metal Ni, metal Co, metal Mo, metal Al, metal Nb, etc. The ultra-high strength steel has excellent strength and toughness, with a tensile strength ≥2200MPa and an impact energy ≥60J, which can meet the use requirements of the new generation of engines for high-strength and tough power shaft materials.

[0060] Although the present invention has been described in detail above with general descriptions and specific embodiments, it is obvious to those skilled in the art that some modifications or improvements may be made thereto based on the present invention. Therefore, these modifications or improvements made without departing from the spirit of the present invention all fall within the scope of protection claimed by the present invention.

Claims

1. An ultra-high strength steel, characterized in that: The chemical composition includes the following by weight: C 0.15-0.30%, Cr 1.5-3.5%, Ni 11.0-13.0%, Co 7.1-7.9%, Mo 1.8-2.5%, Al 0.8-1.3%, Nb 0.01-0.10%, and the balance is Fe; Among them, Ni, Co and Al have the following usage relationship: 0.5≤Co / Ni≤0.75, and 10≤(Ni-2.2Al)≤11.

2. The ultra-high strength steel according to claim 1, characterized in that: The tensile strength of the ultra-high strength steel is ≥2200MPa, and the impact energy is ≥60J.

3. The ultra-high strength steel according to claim 1, characterized in that: The yield strength of the ultra-high strength steel is ≥1800MPa, the elastic modulus is ≥190Gpa, and the tensile strength at 400°C is ≥1700MPa.

4. A method for preparing ultra-high strength steel according to any one of claims 1 to 3, characterized in that: The following steps are involved: Vacuum induction melting, vacuum consumable remelting, forging, and heat treatment; the starting forging temperature of the forging is 1160-1200°C, and the final forging temperature is 800-900°C.

5. The method for preparing ultra-high strength steel according to claim 1, characterized in that: The heat treatment includes solution treatment, cryogenic treatment and aging treatment; The solution treatment temperature is 950-1000°C and the time is 1-2h; The cryogenic treatment temperature is -73 to -100°C and the time is 1 to 10 hours; The aging treatment temperature is 500-540° C., and the time is 3-10 hours.

6. The method for preparing ultra-high strength steel according to claim 1, characterized in that: The vacuum induction melting temperature is 1550-1600° C., the time is 30-180 min, and the vacuum degree is ≤4 Pa.

7. The method for preparing ultra-high strength steel according to claim 1, characterized in that: The vacuum degree of the vacuum consumable remelting is 0.01-2Pa, the melting speed is 4-6kg / min, the voltage is 21-23V, and the current is 11000-13000A.

8. Use of the ultra-high strength steel according to any one of claims 1 to 3 or the ultra-high strength steel obtained by the method for preparing the ultra-high strength steel according to any one of claims 4 to 7 as a material for an engine power shaft.

Images