Super high-strength and high-toughness steel and preparation method thereof

Abstract

The invention discloses super high-strength and high-toughness steel and a preparation method thereof. The super high-strength and high-toughness steel comprises the following components in percentage by mass: 0.18 to 0.35 percent of C, 0.05 to 0.12 percent of Si, 0.30 to 0.50 percent of Mn, less than or equal to 0.008 percent of P, less than or equal to 0.008 percent of S, 0.8 to 1.5 percent of Cr, 0.10 to 0.30 percent of Mo, 2.5 to 3.5 percent of Ni, 0.05 to 0.12 percent of V, 0.01 to 0.05 percent of RE and the balance of Fe. When the content of C is not higher than 0.25%, the alloy contains 0.0005-0.003% of B and the balance of Fe and other inevitable impurities; the preparation process comprises the steps of smelting, homogenization treatment and blank opening, intermediate annealing treatment, large-deformation warm rolling, subzero treatment and low-temperature tempering treatment. The medium-carbon martensite super-high-strength and high-toughness steel with a large enough metastable austenite phase region is obtained through component design, conventional equipment and a production process are utilized for tissue regulation and control, the size of a martensite block is refined to about 1 micron, and the comprehensive mechanical property of the medium-carbon martensite steel is remarkably improved. The material prepared by the invention has ultrahigh strength and high toughness, and is easy for industrial large-scale production and lower in cost.

Description

Technical Field

[0001] The present invention relates to the field of metal materials and processing technology, and in particular to super high-strength and high-toughness steel and a preparation method thereof. Background Art

[0002] Due to its unique hierarchical structure and high-density dislocations, martensite has high strength and is an ideal matrix for ultra-high strength steel. The strength of martensite increases with the increase of carbon content. For every 0.1% increase in carbon, the yield strength of steel increases by about 300MP. Therefore, high-carbon martensitic steel usually has high strength, but its poor plasticity and toughness limit its application scenarios. Compared with high-carbon martensite, ultra-high strength medium-carbon martensite has good comprehensive mechanical properties and has a wider application prospect. With the intensification of global resource shortages, the development of low-alloy ultra-high strength medium-carbon martensitic steel with low cost, simple preparation process and excellent comprehensive performance through reasonable regulation of composition has become an important trend in the development of the current steel industry.

[0003] In metal materials, the improvement of strength often comes at the expense of plasticity. How to obtain ultra-high strength while maintaining good plasticity has always been the research and development focus of ultra-high strength steel. Fine grain strengthening is an effective means to simultaneously improve the strength and plasticity of materials, which is mainly achieved through severe plastic deformation (Severe Plastic deformation, SPD), including equal channel angular pressing (Equal Channel Angular Pressing, ECAP), high pressure torsion (High Pressure and torsion, HPT), cumulative roll bonding (Ac-cumulative Roll Bonding, ARB) and other processes. However, these methods are complex and require high equipment, and are not suitable for large-scale industrial production. In contrast, the large deformation warm rolling process is an effective means to prepare ultra-high strength steel. By S , and the time is not enough for other phase transformations to occur) to obtain layered original austenite with high dislocation density, which is transformed into martensite during the subsequent quenching process. The refined original austenite grains and high-density defects provide abundant nucleation sites for the martensitic phase transformation, promoting the refinement of the martensitic structure after the phase transformation. In addition, due to the deformation in the medium temperature range, warm rolling has a higher dislocation density than hot rolling during the rolling process, and these high-density dislocations will be inherited by the lath martensite after the phase transformation. The ability to achieve effective grain refinement and introduce high-density dislocations makes the large deformation warm rolling process show great potential in the production of ultra-high-strength and high-toughness steels.

[0004] Chinese patent CN202311702618.8 discloses a method for producing high-strength maraging steel. The patent regulates the orientation of different types of martensite through multiple high-temperature rotary forging + solid solution + two-stage aging to produce a maraging steel with a yield strength ≥1900MPa and a tensile strength ≥2100MPa. However, the addition of a large amount of alloy elements and the complexity of the process limit its industrial application.

[0005] Chinese patent CN202110316837.7 discloses a high uniform elongation 2000MPa grade ultra-high strength steel and its preparation method, the main steps of which include solution treatment, room temperature rolling, warm rolling treatment, high temperature short-time annealing treatment and medium temperature long-time aging treatment. Ultra-high strength steel with a tensile strength of ≥2000MPa and an elongation of 10% is obtained through deformation heat treatment. Due to the need to use a large amount of precious alloy elements such as Ni, Cr, and Mo, the cost is relatively high.

[0006] Chinese patent CN202011186695.9 discloses an ultra-high strength steel with a yield strength greater than 2000MPa and its preparation method. The patent adopts manganese components in low alloys, and through rotary forging, tempering, pre-deformation and tempering partitioning treatment, a layered structure of martensite and residual austenite is prepared to obtain high strength. However, the process of the patent is relatively complicated and requires pre-deformation treatment, which is not suitable for industrial preparation of large-size block materials. Summary of the invention

[0007] The purpose of the present invention is to provide a super high-strength and high-toughness steel in order to overcome the defects of the above-mentioned prior art. By reasonably adjusting the composition, it has a sufficiently large metastable austenite phase region to meet the industrial warm rolling production needs of large-size block materials. Through large deformation warm rolling, deep cooling and subsequent tempering heat treatment process, an ultrafine martensitic structure is obtained, and its tensile strength is ≥2000MPa, the yield strength is ≥1800MPa, and the elongation at break is not less than 6%.

[0008] The technical solution of the present invention is:

[0009] Super high-strength and high-toughness steel, its chemical composition mass percentage is: C: 0.18-0.35%, Si: 0.05-0.12%, Mn: 0.30-0.50%, P≤0.008%, S≤0.008%, Cr: 0.8-1.5%, Mo: 0.10-0.30%, Ni: 2.5-3.5%, V: 0.05-0.12%, RE: 0.01-0.05%; when the C content is not higher than 0.25%, the alloy contains B: 0.0005-0.003%, and the balance is Fe and other inevitable impurities.

[0010] Preferably, the composition mass percentage of the super high-strength and high-toughness steel is: C: 0.25-0.32%, Si: 0.07%, Mn: 0.38-0.42%, P≤0.008%, S≤0.008%, Cr: 1.0-1.2%, Mo: 0.18-0.22%, Ni: 2.8-3.1%, V: 0.07-0.08%, RE: 0.01-0.05%; the remainder is Fe and other inevitable impurities.

[0011] Further preferably, the composition mass percentage of the super high-strength and high-toughness steel is: C: 0.25-0.32%, Si: 0.07%, Mn: 0.38-0.42%, P≤0.008%, S≤0.008%, Cr: 1.0-1.2%, Mo: 0.18-0.22%, Ni: 2.8-3.1%, V: 0.07-0.08%, RE: 0.01-0.05%; the remainder is Fe and other inevitable impurities.

[0012] In the present invention, each element component has the following characteristics and functions:

[0013] 1) C content: 0.18~0.35%

[0014] Carbon is an important austenite stabilizing element in steel and has an important influence on the strength of martensitic steel. For every 0.1% increase in the mass fraction of carbon dissolved in martensite, the yield strength of the steel increases by about 300MPa. At the same time, carbon will form nano-scale carbides with micro-alloy elements in steel, and improve the strength of steel through precipitation strengthening. Too low carbon content will make the austenite stability lower and the carbides in the steel reduce, resulting in reduced strength and toughness of the steel. In addition, too high carbon content will lead to deterioration of welding performance and affect the subsequent processing of steel. Therefore, the C content of the present invention is 0.18-0.35%, preferably 0.25-0.32%.

[0015] 2) Si content: 0.05~0.12%

[0016] Si is a non-carbide-forming element, which can inhibit the precipitation of carbides, enrich the dissolved carbon atoms in austenite, and improve the stability of metastable austenite during rolling. In addition, Si has a strong retarding effect on the precipitation of cementite, delays the dissolution and decomposition of martensite, and improves the tempering stability of steel. When the Si content is too high, the iron oxide scale formed on the steel in the furnace is difficult to eliminate, which increases the difficulty of dephosphorization; at the same time, SiO2 enriched and formed on the surface during annealing will lead to surface defects such as plating leakage. Therefore, the Si content of the present invention is 0.05-0.12%, preferably 0.07%. 3) Mn content: 0.30-0.50%

[0017] Mn is an austenite stabilizing element. Adding Mn can inhibit martensitic transformation, expand the metastable austenite phase region, expand the warm rolling process window, and significantly improve the hardenability of steel. However, when the Mn content is too high, it will lead to serious segregation, increase costs, and increase the content of retained austenite, which will put higher requirements on the subsequent deep cooling process temperature and holding time. Therefore, the Mn content of the present invention is 0.30-0.50%, preferably 0.38-0.42%.

[0018] 4) P content: P ≤ 0.008%

[0019] P can be dissolved in ferrite to play a role in solid solution strengthening, but it is easy to segregate along the grain boundary during solidification, making the blank brittle and prone to cracking at room temperature and high temperature. In addition, the P element increases the toughness-brittleness transition temperature of the processed steel and increases the sensitivity to hydrogen embrittlement. Therefore, the P content of the present invention is strictly controlled to be less than 0.008%.

[0020] 5) S content: S ≤ 0.008%

[0021] S is an impurity element, which is easy to form grain boundary segregation and form low-melting-point FeS with Fe, resulting in reduced toughness; in addition, inclusions formed by S, such as MnS, can cause cracking of steel during cold rolling or hot rolling. Therefore, the S content in the present invention is strictly controlled to be less than 0.008%.

[0022] 6) Cr content: 0.8~1.5%

[0023] The addition of Cr can promote the formation of stable carbonitrides, effectively improving the high temperature oxidation resistance and corrosion resistance of steel. In addition, the addition of Cr can delay the pearlite transformation, expand the metastable austenite phase region, and improve the hardenability of steel. Therefore, the Cr content of the present invention is 0.8-1.5%, preferably 1.0-1.2%.

[0024] 7) Mo: 0.10~0.30%

[0025] Mo is a strong carbide element, which can easily promote the formation of secondary hardening carbides during tempering, thereby improving the high temperature performance and tempering resistance stability of the material. Molybdenum is a rare metal with high cost. Too high Mo content will increase the production cost of steel. Therefore, the Mo content of the present invention is 0.10-0.30%, preferably 0.18-0.22%.

[0026] 8) Ni content: 2.5-3.5%

[0027] Ni is one of the most commonly used alloying elements in high-performance alloy steels, and is one of the main alloying elements in the stable austenite region. It shifts the metastable austenite critical transformation curve to the right, expands the metastable austenite phase region, and increases the warm rolling processing window. Adding the Ni element can increase the stacking fault energy and the toughness of the steel. At the same time, the Ni element can also improve the fatigue performance and thermal stability of the steel, making it less likely to fail at high temperatures. However, too high a Ni element can lead to a significant increase in cost. Therefore, the Ni content of the present invention is 2.5-3.5%, preferably 2.8-3.1%.

[0028] 9) V content: 0.05~0.12%

[0029] V easily forms VC with C, which can improve the strength, hardness and thermal stability of steel. Undissolved VC can effectively pin the original austenite grain boundary, hinder the growth of grains, and effectively refine the grains. Therefore, the V content of the present invention is 0.05-0.12%, preferably 0.07-0.08%.

[0030] 10) B content is controlled at 0.0005% to 0.003%

[0031] Boron has the effect of significantly improving the hardenability of austenite and inhibiting the generation of ferrite, but too high a B content will reduce the toughness of the steel and increase the manufacturing cost. Therefore, the B content of the present invention is controlled to be 0.0005% to 0.003%.

[0032] The present invention also provides a method for preparing ultra-high strength and high toughness steel, comprising the following steps:

[0033] Step 1, alloy smelting: after batching according to the ingredients, loading into the furnace, uniformly stirring and smelting in a vacuum induction furnace, and casting into an ingot;

[0034] Step 2: Homogenization and blanking:

[0035] The ingot obtained in step 1 is homogenized at 1200-1350° C. for a holding time of not less than 4.0 hours, and the cooling method is air cooling or furnace cooling to obtain a casting with homogeneous composition, structure and performance; then it is reheated to 1150-1250° C., and hot rolled or hot forged to form a blank, the forming temperature is not less than 1100° C., the final temperature is not less than 900° C., and the thickness of the intermediate blank is not less than 40 mm;

[0036] Step 3, intermediate annealing treatment: perform intermediate annealing treatment on the intermediate billet obtained in step 2, heat the billet to 850-920°C and keep it for 2.0-5.0h, then cool it to 740-800°C and keep it for 2.0-4.0h, cool it to below 500°C, take it out of the furnace and air cool it to room temperature.

[0037] Step 4, austenitization + large deformation medium temperature rolling, heat the billet treated in step 3 to 1100-1200°C, keep it at a temperature for 2.0-4.0h, take it out of the furnace and mist cool it, perform large deformation medium temperature rolling, and water cool it to room temperature after rolling.

[0038] Step 5: Cryogenic treatment: cool the rolled plate treated in step 4 to -60 to -196°C, with a heat preservation time of 4.0h to 10.0h.

[0039] Step 6: Tempering: The rolled plate after deep cooling treatment in step 5 is subjected to low-temperature tempering treatment at a tempering temperature of 150-400°C. After heat preservation, it is water-cooled or air-cooled to room temperature.

[0040] Furthermore, the smelting method in step one is any one of vacuum arc furnace smelting, vacuum induction plus electroslag remelting, vacuum smelting plus vacuum consumables, or a combination of two.

[0041] Furthermore, the homogenization treatment temperature in step 2 is 1250°C and the holding time is 6.0 hours. The starting temperature during blanking is 1150°C and the final temperature is 1050°C, forming an intermediate blank with a thickness of 20 mm.

[0042] Furthermore, the reheating temperature described in step three is 900°C, which is kept at this temperature for 2.0 hours and then furnace-cooled to 750°C and kept at this temperature for 3.0 hours, and then furnace-cooled to below 480°C and air-cooled out of the furnace.

[0043] Furthermore, the austenitizing temperature in step 4 is 1100°C, and after keeping warm for 2.0 hours, the steel is spray-cooled to 700°C for large deformation medium-temperature rolling, and the final rolling temperature is 500°C; the rolling process adopts 5 rolling passes, and the cumulative deformation is not less than 80%.

[0044] Furthermore, the cryogenic treatment temperature in step five is -60 to -120°C, and the insulation time is 6.0h to 8.0h.

[0045] Furthermore, the post-rolling low-temperature tempering treatment in step six is ​​to heat the rolled steel plate to 150-250° C., keep it warm for 1.0 h, and water-cool it to room temperature.

[0046] The present invention uses medium carbon martensitic steel as raw material, and uses methods such as hot working treatment, intermediate annealing treatment, large deformation warm rolling, deep cooling and medium and low temperature tempering heat treatment to utilize the shearing effect of the warm rolling process to transform the equiaxed original austenite structure into layered metastable austenite, and then transform it into a parallel lath martensite structure in the subsequent quenching process, and effectively improves the strength of the material by fine grain strengthening. A small amount of residual austenite after the rolled plate is quenched is transformed into martensite through a deep cooling process. The internal structure of the material is restored through tempering heat treatment, the internal stress is reduced, and carbides are precipitated in the martensite matrix, increasing its toughness and plasticity. Due to the anisotropy of mechanical behavior, the parallel lath martensite has a longer dislocation mean free path, which enhances the ability of work hardening, thereby delaying the arrival of necking and improving the plasticity of the material. Therefore, the super high-strength and high-toughness steel exhibits good comprehensive mechanical properties.

[0047] Compared with the prior art, the present invention has the following advantages:

[0048] 1. The grain size of the super high-strength and high-toughness steel produced by the present invention is about 1 μm, and the structure is composed of ultrafine lamellar martensite arranged parallel to the original Austenite boundary at 40° to 50°. Excellent comprehensive mechanical properties are achieved through the synergistic strengthening of fine grain strengthening and ultrafine lamellar structure. The yield strength of the material is not less than 1500MPa, the tensile strength is not less than 1800MPa, and the elongation at break is not less than 6%.

[0049] 2. Compared with the ultrafine-grained or nanocrystalline materials prepared by traditional SPD technology, the large deformation warm rolling process adopted in the present invention only requires conventional industrial production equipment, such as rolling mills and heat treatment furnaces, and has no special requirements for product size and processing equipment. The production process is simple and easy to operate, and can realize the preparation of large-size bulk metal materials.

[0050] 3. The large deformation warm rolling process adopted by the preparation method of the present invention rolls the metastable austenite below the A1 temperature, which is easier to process and has a larger deformation amount than cold-rolled martensitic steel, reducing the load on the rolling mill. Compared with high-temperature rolling, warm rolling in the metastable austenite phase region is difficult to recrystallize, and the reduction in processing temperature can effectively inhibit the growth of austenite grains. The refined austenite grains form a finer martensitic structure in the subsequent quenching process, ultimately achieving effective refinement of the super high-strength and high-toughness steel structure, significantly improving the strength of the material.

[0051] 4. The ultra-high-strength and high-toughness steel prepared by the method of the present invention has significantly lower alloy elements than common high-strength steels above 2000MPa by optimizing the ratio of alloy elements without sacrificing material properties. At the same time, it has a larger metastable austenite phase region, providing sufficient time and temperature windows for the industrial application of multi-pass warm rolling process. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 A schematic diagram of the process for preparing super high-strength and high-toughness steel according to the present invention;

[0053] Figure 2 The CCT curve of the super high strength and high toughness steel prepared by the present invention;

[0054] Figure 3 This is a typical scanning electron microscope microstructure photograph of the steel prepared in the present invention before large deformation warm rolling;

[0055] Figure 4 This is a typical scanning electron microscope microstructure photo of the super high strength and high toughness steel prepared by the present invention after large deformation warm rolling;

[0056] Figure 5 This is a partial tensile mechanical property curve of the super high-strength and high-toughness steel prepared in the present invention. DETAILED DESCRIPTION

[0057] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments. It should be pointed out that, for ordinary technicians in this field, several improvements and adjustments can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. The chemical composition and mass percentage of the super high strength and high toughness steel of Examples 1-11 are shown in Table 1.

[0058] Table 1 Chemical composition and mass percentage of super high strength and high toughness steel in the embodiment

[0059] Group C Si Mn P S Cr Mo Ni V RE Embodiment 1-2 0.30 0.07 0.40 0.008 0.006 1.0 0.20 2.9 0.07 0.05 Example 3 0.22 0.05 0.50 0.006 0.007 1.2 0.25 2.5 0.12 0.05 Example 4 0.18 0.10 0.36 0.004 0.008 1.4 0.30 2.5 0.12 0.03 Example 5 0.35 0.12 0.44 0.008 0.005 0.8 0.32 3.2 0.08 0.03 Example 6 0.30 0.08 0.30 0.008 0.006 0.9 0.14 3.1 0.05 0.04 Example 7 0.25 0.10 0.40 0.006 0.005 1.2 0.14 3.5 0.11 0.01 Embodiments 8 to 10 0.34 0.07 0.32 0.005 0.006 1.5 0.10 2.6 0.10 0.03

[0060] Example 1

[0061] The mass percentage of each component in the super high strength and high toughness steel provided in this embodiment is shown in Table 1. The continuous cooling curve calculated for the sample of this composition is shown in Attachment Figure 2 , A1 temperature and M s The temperatures are 712°C and 297°C respectively, with a processing temperature window of about 400°C. At the same time, the critical transformation curve is on the right, and there is sufficient processing time. The preparation method of the super high-strength and high-toughness steel with the above composition includes smelting, homogenization treatment + blanking, austenitization + large deformation warm rolling. The specific steps are as follows:

[0062] (1) Melting: The raw materials are mixed according to the above ingredients and evenly stirred and melted in a vacuum arc furnace. Each ingot is melted repeatedly for 5 times. Combined with electromagnetic stirring in the chamber, the components in the ingot are evenly distributed. The ingredients are tested and adjusted to the requirements before casting into ingots.

[0063] (2) Homogenization treatment + hot forging: The ingot is heated to 1200°C, kept at this temperature for 6.0 h, and cooled by air to obtain a billet with homogeneous structure and properties; then it is reheated to 1200°C, taken out of the furnace for hot forging, with the starting forging temperature not less than 1150°C and the final forging temperature being 1050°C, and finally forged into an intermediate billet with a thickness of 20 mm;

[0064] (3) Intermediate annealing: heat the billet to 900℃ and keep it for 2 hours, then furnace cool it to 750℃ and keep it for 3 hours, furnace cool it to below 480℃ and air cool it to room temperature.

[0065] (4) Austenitization + large deformation warm rolling: The annealed billet is heated to 1100℃, kept at this temperature for 2.0h, then taken out and spray-cooled to 700℃ for rolling. The final rolling temperature is 500℃, and the billet is water-quenched after rolling. The rolling process adopts 5 passes, the cumulative deformation is not less than 85%, and the final thickness is 2.7mm. The scanning electron microscope photos of the samples directly quenched without deformation after austenitization are attached. Figure 3 The obtained structure is a uniform equiaxed crystal, the component segregation is eliminated, and no second phase particles such as carbides are produced.

[0066] Typical scanning microstructure of large deformation warm rolled ultra-high strength and high toughness steel sample Figure 4 As shown in the figure, the structure of the prepared steel is mainly composed of martensite transformed from ultra-fine lamellar original Austrian structure, with a lamellar width of ≤2 microns and parallel martensite laths inside. The tensile strength of the prepared super high-strength and high-toughness steel is 2580MPa, the yield strength is 1930MPa, and the elongation at break is 6.7%.

[0067] Example 2

[0068] Preparation method of super high strength and high toughness steel, such as Figure 1 The process comprises the following steps:

[0069] (1) Alloy smelting treatment is the same as step (1) of Example 1;

[0070] (2) Homogenization treatment + blanking treatment is the same as step (2) of Example 1;

[0071] (3) Intermediate annealing treatment is the same as step (3) of Example 1

[0072] (4) Large deformation warm rolling treatment is the same as step (4) of Example 1;

[0073] (5) Cryogenic treatment: the temperature of the rolled plate obtained in step 4 is reduced to -80°C, kept at this temperature for 6 hours, and then taken out and placed at room temperature.

[0074] (6) Tempering after rolling: The plate subjected to deep cryogenic treatment in step (5) is tempered at 150°C for 1.0 h; and quenched to room temperature. Low temperature tempering is used to eliminate internal stress, while forming carbon clusters and nano-precipitations, thereby improving the yield strength and ductility of the material at a slightly lower strength.

[0075] The yield strength of the prepared super high-strength and high-toughness steel is 2138MPa, the yield strength is 2413MPa, and the elongation at break is 10.3%

[0076] Example 3

[0077] A method for preparing super high-strength and high-toughness steel, the steps of which are as follows:

[0078] (1) Alloy smelting treatment is the same as step (1) of Example 1;

[0079] (2) Homogenization treatment + blanking treatment is the same as step (2) of Example 1;

[0080] (3) Intermediate annealing treatment is the same as step (3) of Example 1

[0081] (4) Large deformation warm rolling treatment is the same as step (4) of Example 1;

[0082] (5) Cryogenic treatment is the same as step (5) of Example 2;

[0083] (6) Tempering after rolling: The deep-cold treated plate is tempered at 200 °C, kept at this temperature for 1.0 h, and then quenched to room temperature.

[0084] The yield strength of the prepared super high-strength and high-toughness steel is 2153 MPa, the tensile strength is 2383 MPa, and the elongation at break is 9.1%.

[0085] Example 4

[0086] A method for preparing super high-strength and high-toughness steel, the steps of which are as follows:

[0087] (1) Alloy smelting treatment is the same as step (1) of Example 1;

[0088] (2) Homogenization treatment + blanking treatment is the same as step (2) of Example 1;

[0089] (3) Intermediate annealing treatment is the same as step (3) of Example 1

[0090] (4) Large deformation warm rolling treatment is the same as step (4) of Example 1;

[0091] (5) Cryogenic treatment is the same as step (5) of Example 2;

[0092] (6) Tempering after rolling: The deep-cold treated plate is tempered at 250°C for 1.0 h; quenched to room temperature.

[0093] The yield strength of the prepared super high-strength and high-toughness steel is 1839MPa, the tensile strength is 2026MPa, and the elongation at break is 8.7%.

[0094] Example 5

[0095] A method for preparing super high-strength and high-toughness steel, the steps of which are as follows:

[0096] (1) Alloy smelting treatment is the same as step (1) of Example 1;

[0097] (2) Homogenization treatment + blanking treatment is the same as step (2) of Example 1;

[0098] (3) Intermediate annealing treatment is the same as step (3) of Example 1

[0099] (4) Large deformation warm rolling treatment is the same as step (4) of Example 1;

[0100] (5) Cryogenic treatment is the same as step (5) of Example 2;

[0101] (6) Tempering after rolling: The deep-cold treated plate is tempered at 300°C for 1.0 h; quenched to room temperature.

[0102] The yield strength of the prepared super high-strength and high-toughness steel is 1813MPa, the tensile strength is 2004MPa, and the elongation at break is 6.5%.

[0103] Example 6

[0104] A method for preparing super high-strength and high-toughness steel, the steps of which are as follows:

[0105] (1) Alloy smelting treatment is the same as step (1) of Example 1;

[0106] (2) Homogenization treatment + blanking treatment is the same as step (2) of Example 1;

[0107] (3) Intermediate annealing treatment is the same as step (3) of Example 1

[0108] (4) Large deformation warm rolling treatment is the same as step (4) of Example 1;

[0109] (5) Cryogenic treatment is the same as step (5) of Example 2;

[0110] (6) Tempering after rolling: The deep-cold treated plate is tempered at 200°C for 1.0 h; then air-cooled to room temperature.

[0111] The yield strength of the prepared super high-strength and high-toughness steel is 2113MPa, the tensile strength is 2350MPa, and the elongation at break is 10.2%.

[0112] Example 7

[0113] A method for preparing super high-strength and high-toughness steel, the steps of which are as follows:

[0114] (1) Alloy smelting treatment is the same as step (1) of Example 1;

[0115] (2) Homogenization treatment + blanking treatment is the same as step (2) of Example 1;

[0116] (3) Intermediate annealing treatment is the same as step (3) of Example 1

[0117] (4) Large deformation warm rolling treatment is the same as step (4) of Example 1;

[0118] (5) Post-rolling tempering treatment: The plate obtained by warm rolling is directly subjected to low-temperature tempering treatment at a temperature of 150°C for 1.0 h; and water-cooled to room temperature.

[0119] The yield strength of the prepared super high-strength and high-toughness steel is 2091MPa, the tensile strength is 2382MPa, and the elongation at break is 10.7%.

[0120] Example 8

[0121] A method for preparing super high-strength and high-toughness steel, the steps of which are as follows:

[0122] (1) Alloy smelting treatment is the same as step (1) of Example 1;

[0123] (2) Homogenization treatment + blanking treatment is the same as step (2) of Example 1;

[0124] (3) Intermediate annealing treatment is the same as step (3) of Example 1

[0125] (4) The large deformation warm rolling treatment is the same as step (4) of Example 1; the difference is that the starting rolling temperature is 670°C, the final rolling temperature is 480°C, and the final thickness is 2.3 mm;

[0126] (5) Cryogenic treatment is the same as step (5) of Example 2;

[0127] (6) Post-rolling annealing treatment is the same as step (6) of Example 2.

[0128] The yield strength of the prepared super high-strength and high-toughness steel is 2067MPa, the tensile strength is 2380MPa, and the elongation at break is 6.3%.

[0129] Example 9

[0130] A method for preparing super high-strength and high-toughness steel, the steps of which are as follows:

[0131] (1) Alloy smelting treatment is the same as step (1) of Example 1;

[0132] (2) Homogenization treatment + blanking treatment is the same as step (2) of Example 1;

[0133] (3) Intermediate annealing treatment is the same as step (3) of Example 1

[0134] (4) The large deformation warm rolling treatment is the same as step (4) of Example 1, except that the starting rolling temperature is 650°C, the final rolling temperature is 460°C, and the final thickness is 2.7 mm;

[0135] (5) Cryogenic treatment is the same as step (5) of Example 2;

[0136] (6) Post-rolling annealing treatment is the same as step (6) of Example 2.

[0137] The yield strength of the prepared super high-strength and high-toughness steel is 1997MPa, the tensile strength is 2350MPa, and the elongation at break is 6.1%.

[0138] Example 10

[0139] A method for preparing super high-strength and high-toughness steel, the steps of which are as follows:

[0140] (1) Alloy smelting treatment is the same as step (1) of Example 1;

[0141] (2) Homogenization treatment + blanking treatment is the same as step (2) of Example 1;

[0142] (3) Intermediate annealing treatment is the same as step (3) of Example 1

[0143] (4) The large deformation warm rolling treatment is the same as step (4) of Example 1, except that the starting rolling temperature is 630°C, the final rolling temperature is 450°C, and the final thickness is 3.1 mm;

[0144] (5) Cryogenic treatment is the same as step (5) of Example 2;

[0145] (6) Post-rolling annealing treatment is the same as step (6) of Example 2.

[0146] The yield strength of the prepared super high-strength and high-toughness steel is 1921 MPa, the tensile strength is 2312 MPa, and the elongation at break is 6.2%.

[0147] Embodiment 11

[0148] A method for preparing super high-strength and high-toughness steel, the steps of which are as follows:

[0149] (1) Alloy smelting treatment is the same as step (1) of Example 1;

[0150] (2) Homogenization treatment + blanking treatment is the same as step (2) of Example 1;

[0151] (3) Intermediate annealing treatment is the same as step (3) of Example 1

[0152] (4) The large deformation warm rolling process is the same as step (4) of Example 1; the difference is that the warm rolling is kept at a temperature of 10 seconds between warm rolling passes and the final rolling temperature is 430°C.

[0153] (5) Cryogenic treatment is the same as step (5) of Example 2;

[0154] (6) Post-rolling annealing treatment is the same as step (6) of Example 2.

[0155] The yield strength of the prepared super high-strength and high-toughness steel is 1981 MPa, the tensile strength is 2375 MPa, and the elongation at break is 7.1%.

[0156] The present invention provides a detailed description of the production of super high-strength and high-toughness steel and its preparation method, with the aim of facilitating the technical personnel in this research field to quickly understand and grasp the content of the invention. At the same time, researchers familiar with the field can also make certain modifications based on the examples of the present invention to facilitate their own use. Therefore, the examples of the present invention are not limited to the contents mentioned above, and the modifications made by those skilled in the art based on the basic ideas and content framework of the present invention should be within the scope of protection of the present invention.

Claims

1. Super high-strength and high-toughness steel and its preparation method, characterized in that: The chemical composition mass percentage is: C: 0.18-0.35%, Si: 0.05-0.12%, Mn: 0.30-0.50%, P≤0.008%, S≤0.008%, Cr: 0.8-1.5%, Mo: 0.10-0.30%, Ni: 2.5-3.5%, V: 0.05-0.12%, RE: 0.01-0.05%; when the C content is not higher than 0.25%, the alloy contains B: 0.0005-0.003%, and the balance is Fe and other inevitable impurities.

2. The super high strength and high toughness steel and the preparation method thereof according to claim 1, characterized in that: The mass percentage of each component is: C: 0.22-0.33%, Si: 0.06-0.10%, Mn: 0.35-0.45%, P≤0.008%, S≤0.008%, Cr: 0.8-1.4%, Mo: 0.15-0.25%, Ni: 2.6-3.3%, V: 0.05-0.10%, RE: 0.01-0.05%; when the C content is not higher than 0.25%, the alloy contains B: 0.0005-0.003%, and the balance is Fe and other inevitable impurities.

3. The super high strength and high toughness steel according to claim 2, characterized in that: The mass percentages of the components in the alloy steel are: C: 0.25-0.32%, Si: 0.07%, Mn: 0.38-0.42%, P≤0.008%, S≤0.008%, Cr: 1.0-1.2%, Mo: 0.18-0.22%, Ni: 2.8-3.1%, V: 0.07-0.08%, RE: 0.01-0.05%; the remainder is Fe and other inevitable impurities.

4. The method for preparing super high strength and high toughness steel according to claim 1, characterized in that: The following steps are involved: Step 1: Alloy smelting: C: 0.18-0.35%, Si: 0.05-0.12%, Mn: 0.30-0.50%, P≤0.008%, S≤0.008%, Cr: 0.8-1.5%, Mo: 0.10-0.30%, Ni: 2.5-3.5%, V: 0.05-0.12%, RE: 0.01-0.05%; when the C content is not higher than 0.25%, the alloy contains B: 0.0005-0.003%, and the balance is Fe and other inevitable impurities; according to the above claims, the above ingredients are mixed and loaded into the furnace, and the mixture is uniformly stirred and melted in a vacuum induction furnace and cast into an ingot; Step 2: Homogenization and blanking: The ingot obtained in step 1 is homogenized at 1200-1350° C. for a holding time of not less than 4.0 hours, and the cooling method is air cooling or furnace cooling to obtain a casting with homogeneous composition, structure and performance; then it is reheated to 1150-1250° C., and hot rolled or hot forged to form a blank, the forming temperature is not less than 1100° C., the final temperature is not less than 900° C., and the thickness of the intermediate blank is not less than 40 mm; Step 3, intermediate annealing treatment: intermediate annealing treatment is performed on the intermediate billet obtained in step 2, the billet is heated to 850-920°C and kept at this temperature for 2.0-5.0h, then furnace cooled to 740-800°C and kept at this temperature for 2.0-4.0h, furnace cooled to below 500°C, and then air cooled to room temperature after being taken out of the furnace; Step 4: austenitization + large deformation medium temperature rolling, heating the billet treated in step 3 to 1100-1200°C, keeping the temperature for 2.0-4.0h, taking it out of the furnace, mist cooling, large deformation medium temperature rolling, and water cooling to room temperature after rolling; Step 5: cryogenic treatment, cooling the rolled plate after the treatment in step 4 to -60 to -196°C, with a holding time of 4.0h to 10.0h; Step 6: Tempering: The rolled plate after deep cooling treatment in step 5 is subjected to low-temperature tempering treatment at a tempering temperature of 150-400°C. After heat preservation, it is water-cooled or air-cooled to room temperature.

5. The method for preparing super high strength and high toughness steel according to claim 4, characterized in that: The smelting method in step 1 is any one of vacuum arc furnace smelting, vacuum induction plus electroslag remelting, vacuum smelting plus vacuum consumable, or a combination of the two; The homogenization treatment temperature in step 2 is 1250°C, and the holding time is 6.0h. The blanking temperature is 1150°C, and the final temperature is 1050°C, forming an intermediate blank with a thickness of 20mm; The reheating temperature in step 3 is 900°C, which is kept for 2.0 hours and then cooled to 750°C for 3.0 hours, then cooled to below 480°C and air-cooled; The austenitizing temperature in step 4 is 1100°C, and after keeping the temperature for 2.0h, the steel is spray-cooled to 700°C for large deformation medium-temperature rolling, and the final rolling temperature is 500°C; the rolling process adopts 5 rolling passes, and the cumulative deformation is not less than 80%; The cryogenic treatment temperature in step 5 is -60 to -120°C, and the holding time is 6.0h to 8.0h; The post-rolling low-temperature tempering treatment in step 6 is to heat the rolled steel plate to 150-250° C., keep the temperature for 1.0 h, and quench to room temperature.

6. The method for preparing super high strength and high toughness steel according to claim 5, characterized in that: The quenching medium in step six can be water, oil or a water-soluble quenching liquid.

7. The method for preparing super high strength and high toughness steel according to claim 4, characterized in that: Step 5: After deep cryogenic treatment, the rolled plate is a fully martensitic structure.

8. The method for preparing super high strength and high toughness steel according to claim 5, characterized in that: The microstructure of the prepared super high-strength and high-toughness steel is mainly composed of ultrafine-grained martensite transformed from layered metastable austenite structure, wherein the lamellar width is ≤2.0μm, the inside of the lamellar is parallel-arranged lath martensite, and the thickness of the martensite lath is ≤0.5μm.

9. The method for preparing super high strength and high toughness steel according to claim 5, characterized in that: Its yield strength is ≥1500MPa, tensile strength is ≥1800MPa, and elongation at break is not less than 12.0%.

10. The method for preparing super high strength and high toughness steel according to claim 5, characterized in that: The yield strength of the prepared mold steel is ≥2000MPa, the tensile strength is ≥2600MPa, and the elongation at break is not less than 6.0%.

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