1.3 GPa grade bamboo-shaped bionic structure ultrahigh-toughness steel plate and preparation method thereof

Abstract

The invention discloses a 1.3 GPa-grade bamboo-shaped bionic structure ultrahigh-toughness steel plate and a preparation method, and belongs to the field of ultrahigh-toughness steel. The high-strength steel comprises the following chemical components and alloy elements in percentage by mass (wt.%): 0.2-0.80% of C, 2-8% of Mn, 1.10-3.35% of Si, 0.30-4.45% of Al, less than or equal to 0.12% of V + Nb, less than or equal to 0.008% of S, less than or equal to 0.015% of P and the balance of Fe and other inevitable impurities. The preparation method comprises the following steps: smelting in a vacuum furnace, rolling after forging, directly water-cooling to room temperature after rolling, and then treating by a dual deformation and phase change coupling rolling process to obtain the ultrahigh-toughness steel plate. The tensile strength of the steel plate ranges from 1300 MPa to 1380 MPa, the yield strength ranges from 1000 MPa to 1050 MPa, the percentage elongation after fracture ranges from 67.5% to 69.5%, and the product of strength and elongation can reach 93 GPa%. Under reasonable composition and process regulation and control, the product of strength and elongation of the ultrahigh strength and toughness steel plate is far better than that of traditional TWIP steel, the product of strength and elongation ranges from 90 GPa% to 100 GPa%, and the ultrahigh strength and toughness steel plate has a very considerable development prospect in the field of advanced high-strength steel.

Description

Technical Field

[0001] The present invention belongs to the field of ultra-high strength and toughness steel, and specifically relates to a 1.3 GPa-level bamboo-like bionic structure ultra-high strength and toughness steel plate and a preparation method thereof. Background Art

[0002] In metal materials, strength and plasticity have always been considered a pair of mutually balanced existence. How to allocate the strength and plasticity of materials is an important decision in the process of research on the strengthening and toughening of metal materials. The strength-plasticity product, that is, the product of strength and elongation, is the best way to evaluate the strength and plasticity of metal materials. Generally, the product of tensile strength and elongation after fracture is selected.

[0003] At present, in the research of ultra-high strength and toughness steel, medium manganese steel and high manganese steel generally show extremely superior strength-ductility product. As the second-generation automotive steel, high manganese steel is constantly sought after by researchers in this field for its main advantage of a strength-ductility product of up to 60 GPa%. However, its high manganese composition design also brings about problems such as high smelting difficulty and subsequent processing difficulties. In order to solve the many problems of high manganese steel, medium manganese steel with a lower manganese content was developed as the third-generation automotive steel. Although the manganese content is significantly reduced and the metallurgical difficulty is optimized, the strength-ductility product of medium manganese steel is difficult to exceed 60 GPa%. Therefore, low-composition ultra-high strength-ductility material is an important development direction for metal materials.

[0004] Invention patent CN 110408861 B provides a cold-rolled high-strength and high-ductility medium manganese steel with a low manganese content and a preparation method thereof. In the invention, a high-strength and high-ductility medium manganese steel with a low manganese content and a strength-ductility product of 67 GPa% can be obtained through reasonable process control; CN 112410681 A provides a high-strength and high-ductility medium manganese steel and a preparation method thereof. The invention obtains a heterogeneous structure composed of coarse-grained austenite and ultrafine-grained austenite by performing a combined process of cyclic warm rolling + critical annealing on the medium manganese steel, thereby obtaining an ultra-high-strength and high-toughness medium manganese steel, the tensile strength of which can reach 1112 MPa, the elongation after fracture can reach 76.7%, and the strength-ductility product reaches 85 GPa%, but the yield strength is relatively low, generally between 550 and 650 MPa; Patent CN 109666862B invents a high-strength and high-ductility medium manganese steel with a strength-ductility product greater than 60 GPa% high-strength and tough hot-rolled medium manganese steel and its preparation method. The invention obtains a tensile strength of 1039-1183 MPa, an elongation after fracture of 43.5-64.8% through reasonable rolling and heat treatment process regulation, and the strength-plasticity product can reach more than 60 GPa%, and can reach up to 72 GPa%; Patent CN 109930078 B invents a high-strength and high-plasticity hot-rolled medium manganese steel and its preparation method. In the invention, a medium manganese steel with low manganese content, quenching temperature and tempering temperature, reasonable composition design, simple and optimized process, and low production cost is obtained through two quenching + tempering processes. The strength-plasticity product can reach 74 GPa%; Patent CN 111321351 B provides a high-strength and high-plasticity two-stage warm-rolled medium manganese steel and its preparation method. In the invention, a steel plate with a tensile strength of 1300MPa and a strength-plasticity product greater than 60GPa% can be obtained through two-stage warm rolling + annealing. The warm rolling process ensures the product size and accuracy. Although the research on the strength and plasticity of medium manganese steel is relatively rich, there are few reports of breaking through 90GPa%. Although the research of this patent during the same period has reached 90 GPa%, its tensile strength is less than 1200 MPa and the yield strength is around 880 MPa.

[0005] In order to achieve high strength-ductility product and ultra-high strength at the same time, the present invention mainly targets the current demand for high strength-ductility product of steel materials, and ensures an ultra-high strength of 1300 MPa while having an elongation of nearly 70%. In the present invention, based on the dual deformation phase change coupling rolling process, an ultra-high strength and toughness steel plate with a yield strength greater than 1000 MPa, a tensile strength greater than 1300 MPa, an elongation at the same fracture greater than 68%, and a strength-ductility product of 93 GPa% is invented, which solves the problem of insufficient strength-ductility product of 1.3GPa-level ultra-high strength steel, and fills the gap in the strength-ductility product of ultra-high strength and toughness steel in the range of 90 GPa% to 100 GPa%. Summary of the invention

[0006] The present invention mainly aims at the problem of improving the strength-ductility product of advanced high-strength and tough steel. Through reasonable composition design and the regulation of dual deformation phase change coupled rolling process, an ordered fiber structure composed of martensite / ferrite and austenite is invented, and the strength-ductility product of ultra-high-strength and tough steel and its preparation method can reach 93 GPa%, and the tensile strength of the invention is always higher than 1300MPa. The invention greatly improves the strength-ductility product of ultra-high-strength and tough steel, and fills the gap of the strength-ductility product of traditional steel materials between 90GPa% and 100GPa%.

[0007] A 1.3 GPa-level bamboo-shaped bionic structure ultra-high strength and toughness steel plate, the chemical composition of the high-strength steel and the mass percentage (wt.%) of its alloy elements are C: 0.20-0.80, Mn: 2-8, Si: 1.10-3.35, Al: 2.00-4.45, V+Nb: ≤0.12, S≤0.008, P≤0.015, and the balance is Fe and other inevitable impurities;

[0008] The method for preparing the ultra-high strength and toughness steel plate as described above is characterized in that the ultra-high strength and toughness steel plate is directly water-cooled online to room temperature after rolling, and then the hot-rolled plate is further deformed and phase-changed by a dual deformation and phase-change coupling process. By controlling the deformation and phase-change coupling rolling process within a reasonable range, an ultra-high strength and toughness steel plate with a quasi-ordered fiber structure and a strength-ductility product of 1.3 GPa and 93 GPa% can be obtained.

[0009] Furthermore, the method for preparing the ultra-high strength and toughness medium manganese steel is characterized by comprising the following specific steps:

[0010] (1) Smelting and forging: Smelting in a vacuum induction furnace, accurately controlling the alloy composition and strictly controlling the content of P, S and elements during the process, and then forging into a 70 mm × 70 mm square billet, with a final forging temperature greater than 1050 °C;

[0011] (2) Heating: Use KSL-1200X resistance furnace for heating at 1150-1200 °C, keep warm for 24 h under the protection of anti-oxidation coating, and remove the surface coating after taking out of the furnace;

[0012] (3) Rolling: The heated billet is rolled at a starting temperature of 1150-1100 °C. After multiple passes of rolling, the final rolling temperature is 980-1020 °C.

[0013] (4) Cooling: subjecting the rolled steel plate obtained in step (3) to water quenching treatment;

[0014] (5) Deformation phase change coupling rolling: After cutting the sample in step (4), the sample is rolled twice. After cutting, the sample is heated to 600-1000 °C, kept at this temperature for 20-60 min, and then rapidly rolled. After rolling, it is directly water-cooled to room temperature, and then heated to 600-850 °C and kept at this temperature for 20-60 min, and then water-quenched to room temperature. After quenching, the sample is heated to 600-1000 °C again, kept at this temperature for 20-60 min, and then rapidly rolled. It is then directly water-quenched to room temperature. This is called dual deformation phase change coupling rolling. After dual rolling, an ultra-high strength and toughness steel plate with a strength-ductility product of 93 GPa% at the 1.3 GPa level can be obtained.

[0015] Furthermore, the room temperature structure of the present invention is composed of martensite / ferrite and austenite through reasonable rolling process control, wherein the proportion of retained austenite is 20% to 50%; and its microstructure exhibits ordered fibrous structural characteristics arranged alternately along the rolling direction, and the TD×ND plane is an equiaxed crystal morphology with a grain size of 1 μm.

[0016] Furthermore, the ultra-high strength and toughness steel plate prepared according to the method of the present invention has a tensile strength of 1300 MPa to 1380 MPa, a yield strength of 1000 MPa to 1050 MPa, an elongation after fracture of 67.5% to 69.5%, and a strength-ductility product of up to 93 GPa%.

[0017] The present invention also carried out a simulation experiment on the medium manganese steel in the laboratory. The product of the invention is smelted in a vacuum furnace, and the content of harmful elements such as P and S is strictly controlled. Then, it is forged in the laboratory into a forging billet waiting for rolling. The specific rolling process adopts a method of simulating the on-site TMCP+online quenching process for laboratory rolling. The forging billet is placed in a heating furnace and heated to 1150-1200°C, kept warm for 24 hours, and then taken out and the surface protective coating is removed. The forging billet is rolled on a laboratory rolling mill with a bite temperature of 1100-1050°C. After 6 rolling passes, the steel plate is rolled into a steel plate with a thickness of 10-12 mm. The final rolling temperature is greater than 960°C, and it is directly water quenched to room temperature. Then, the hot-rolled plate is subjected to double deformation phase change coupling rolling to obtain the 1.3 GPa-level ultra-high strength and toughness steel plate with a strength-ductility product of 93 GPa% described in the invention.

[0018] Compared with the existing inventions, the main advantages of the present invention are as follows:

[0019] (1) In terms of production technology, the present invention adopts an online quenching production method to greatly shorten the entire production process and omit the secondary quenching, which not only improves production efficiency but also saves energy consumption;

[0020] (2) The present invention constructs a fiber structure composed of martensite / ferrite and austenite arranged alternately and orderly, which has obvious advantages in mechanical properties.

[0021] (3) The yield strength of the ultra-high strength and toughness steel of the present invention is greater than 1000 MPa, the tensile strength is greater than 1300 MPa, and the elongation after fracture is greater than 68%, and the strength-ductility product can reach 93 GPa%, which is significantly superior to similar products. It mainly shows high yield strength and tensile strength while the strength-ductility product is extremely superior, filling the gap of the strength-ductility product of traditional 1.3 GPa-grade metal materials at this stage of 90 GPa% to 100 GPa%. The comparison data with the current invention patent of ultra-high strength and toughness steel with the best performance is shown in Table 1 and Figure 7 .

[0022] Table 1 Comparison of mechanical properties between the present invention and other inventions

[0023] BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Example 1 SEM morphology;

[0025] Figure 2 Example 2 SEM morphology image;

[0026] Figure 3 Example 3 SEM morphology image;

[0027] Figure 4 Example 1 Engineering stress-strain curve;

[0028] Figure 5 Example 1 Comparison of mechanical properties with other process mechanical properties;

[0029] Figure 6 Comparison chart of mechanical properties of three embodiments and related patents;

[0030] Figure 7 Microscopic morphology of the ordered microstructure described in the invention;

[0031] Figure 8 TD×ND surface effective grain size statistics;

[0032] Fig. 9 The invention measures the elongation after break and compares it with the size of the unstretched sample;

[0033] Table 1 Comparison of mechanical properties between the present invention and other inventions;

[0034] Table 2 Mechanical properties data corresponding to the three embodiments. DETAILED DESCRIPTION

[0035] The technical solution of the present invention is further illustrated by the following examples, but is not limited to the following examples.

[0036] This embodiment is the composition design and production process of the ultra-high-strength steel with a strength-ductility product of 93 GPa% at 1.3 GPa level. The finished plate thickness is 1.2 mm. The chemical composition of the high-strength steel and the mass percentage (wt.%) of its alloy elements are C: 0.20-0.80, Mn: 2-8, Si: 1.10-3.35, Al: 2.00-4.45, V+Nb: ≤0.12, S≤0.008, P≤0.015, and the balance is Fe and other unavoidable impurities; at the same time, in order to ensure data reliability, Figure 6 The mechanical properties data of samples under different processes, where HR represents hot-rolled samples; HR-IA represents samples subjected to intercritical annealing directly after hot rolling; HR-WR represents samples subjected to warm rolling directly after hot rolling; HR-WR-IA represents samples subjected to warm rolling directly after hot rolling and then intercritical annealing. Figure 7 A microscopic morphology diagram of the ordered microstructure described in the invention is given; Figure 8 The effective grain size of the ND×TD surface of the invention was statistically analyzed; Fig. 9 An original sample and a sample of the present invention after being stretched and broken were selected, and the elongation after fracture was measured. In this experiment, a 15 mm extensometer was used for stretching, and it can be seen that the gauge length after fracture is 25.25 mm, that is, the elongation after fracture is 68.33%. The final mechanical properties of the three embodiments are shown in Table 2.

[0037] Example 1

[0038] The present embodiment is a bamboo-like bionic structure ultra-high strength and toughness steel plate with a strength and plasticity product of 1.3 GPa and a product of 93 GPa%. The finished product thickness is 1.21 mm. The specific production method is as follows: the product is smelted in a vacuum furnace, the content of harmful elements such as P and S is strictly controlled, and then it is forged in the laboratory into a forging billet waiting for rolling. The specific rolling process adopts a method of simulating the on-site TMCP+online quenching process for laboratory rolling. The forging billet is placed in a heating furnace and heated to 1200°C, kept warm for 24 hours, and then the surface protective coating is removed after being taken out. The steel plate is rolled on a laboratory rolling mill with a bite temperature of 1100°C. After 6 rolling passes, the steel plate is rolled into a plate thickness of 10 mm. The final rolling temperature is 970°C, and it is directly water quenched to room temperature. Then, the hot-rolled plate is subjected to double deformation phase change coupling rolling to obtain the ultra-high strength and toughness steel plate with a strength and plasticity product of 93 GPa% of 1.3 GPa described in the invention. Its tensile strength is 1366.5 MPa, yield strength is 1020.2 MPa, austenite accounts for 41.7%, and the strength-ductility product is 94.95 GPa%. The final mechanical properties curve is shown in Figure 4 , microstructure and morphology such as Figure 1 EBSD reconstruction of its ordered fiber structure arrangement Figure 5 At the same time, the statistics of the grain size of the TD×ND surface are shown in Figure 6 .

[0039] Example 2

[0040] The present embodiment is a bamboo-like bionic structure ultra-high strength and toughness steel plate with a strength and plasticity product of 1.3 GPa and a product of 93 GPa%. The finished product has a thickness of 1.25 mm. The specific production method is as follows: the product is smelted in a vacuum furnace, the content of harmful elements such as P and S is strictly controlled, and then it is forged in a laboratory into a forging billet waiting for rolling. The specific rolling process adopts a method of simulating the on-site TMCP+online quenching process for laboratory rolling. The forging billet is placed in a heating furnace and heated to 1200°C, kept warm for 24 hours, and then the surface protective coating is removed after being taken out. The steel plate is rolled on a laboratory rolling mill with a bite temperature of 1100°C. After 6 rolling passes, the steel plate is rolled into a plate with a thickness of 10 mm. The final rolling temperature is 970°C, and the steel plate is directly water quenched to room temperature. The hot-rolled plate is then subjected to double deformation phase change coupling rolling to obtain the ultra-high strength and toughness steel plate with a strength and plasticity product of 93 GPa% of 1.3 GPa described in the invention. Its tensile strength is 1352.8 MPa, yield strength is 1020.8 MPa, austenite accounts for 37.8%, and the strength-ductility product is 92.94 GPa%. The microstructure and morphology are as follows: Figure 2

[0041] Example 3

[0042] The present embodiment is a bamboo-like bionic structure ultra-high strength and toughness steel plate with a strength and plasticity product of 1.3 GPa and a product of 93 GPa%. The finished product thickness is 1.30 mm. The specific production method is as follows: the product is smelted in a vacuum furnace, the content of harmful elements such as P and S is strictly controlled, and then it is forged in the laboratory into a forging billet waiting for rolling. The specific rolling process adopts a method of simulating the on-site TMCP+online quenching process for laboratory rolling. The forging billet is placed in a heating furnace and heated to 1200°C, kept warm for 24 hours, and then the surface protective coating is removed after being taken out. The steel plate is rolled on a laboratory rolling mill with a bite temperature of 1100°C. After 6 rolling passes, the steel plate is rolled into a plate thickness of 10 mm. The final rolling temperature is 970°C, and it is directly water quenched to room temperature. Then, the hot-rolled plate is subjected to double deformation phase change coupling rolling to obtain the ultra-high strength and toughness steel plate with a strength and plasticity product of 93 GPa% of the invention. Its tensile strength is 1360.7 MPa, yield strength is 100.5 MPa, austenite accounts for 37.5%, and the strength-ductility product is 93.89 GPa%. The microstructure and morphology are as follows: Figure 3

[0043] Table 2 Mechanical properties data corresponding to the three embodiments

[0044]

Claims

1. A 1.3GPa-level bamboo-like bionic structure ultra-high strength steel plate, characterized in that: The chemical composition of the high-strength steel and the mass percentage (wt.%) of its alloy elements are: C: 0.20-0.80, Mn: 2-8, Si: 1.10-3.35, Al: 2.00-4.45, V+Nb: ≤0.12, S≤0.008, P≤0.015, and the remainder is Fe and other inevitable impurities.

2. The method for preparing the 1.3 GPa-level bamboo-like bionic structure ultra-high strength steel plate according to claim 1, characterized in that: The ultra-high strength and toughness steel plate adopts a rolling process in which the steel plate is directly water-cooled online to room temperature after rolling, and then double-rolled by a deformation and phase change coupled rolling process, and then quickly water-cooled to room temperature after rolling, so as to obtain an ultra-high strength and toughness steel with an ordered fiber structure having a strength-ductility product greater than 93 GPa%.

3. The method for preparing the 1.3 GPa-level bamboo-like bionic structure ultra-high strength steel plate according to claim 2, characterized in that: The specific steps are as follows: (1) Smelting and forging: Smelting in a vacuum induction furnace, accurately controlling the alloy composition and strictly controlling the content of P, S and elements during the process, and then forging into a 70 mm × 70 mm square billet, with a final forging temperature greater than 1050 °C; (2) Heating: Use KSL-1200X resistance furnace for heating at 1150-1200 °C, keep warm for 24 h under the protection of anti-oxidation coating, and remove the surface coating after taking out of the furnace; (3) Rolling: The heated billet is rolled at a starting temperature of 1150-1100 °C. After multiple passes of rolling, the final rolling temperature is 980-1020 °C. (4) Cooling: subjecting the rolled steel plate obtained in step (3) to water quenching treatment; (5) Deformation phase change coupled rolling: The sample in step (4) is cut and then rolled twice. After cutting, the sample is heated to 600-1000 °C, kept at this temperature for 20-60 min, and then rapidly rolled. After rolling, it is directly water-cooled to room temperature, and then heated to 600-850 °C and kept at this temperature for 20-60 min, and then water-quenched to room temperature. After quenching, the sample is heated to 600-1000 °C again, kept at this temperature for 20-60 min, and then rapidly rolled and then directly water-quenched to room temperature. This is called dual deformation phase change coupled rolling. After dual rolling, an ultra-high strength and toughness steel plate with a strength-ductility product of 1.3 GPa and 93 GPa% can be obtained.

4. The method for preparing the 1.3 GPa-level bamboo-like bionic structure ultra-high strength steel plate according to claim 2, characterized in that: Through reasonable rolling process control, its room temperature structure is composed of martensite / ferrite and austenite, in which the proportion of retained austenite is between 20% and 50%; and its microstructure exhibits ordered fibrous structural characteristics arranged alternately along the rolling direction, and the TD×ND plane is an equiaxed crystal morphology with a grain size of 1 μm.

5. The method for preparing the 1.3 GPa-level bamboo-like bionic structure ultra-high strength steel plate according to claim 2, characterized in that: The tensile strength is between 1300 MPa and 1380 MPa, the yield strength is between 1000 MPa and 1050 MPa, the elongation at break is between 67.5% and 69.5%, and the strength-ductility product can reach 93 GPa%.

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