Super-thick steel plate with yield strength of 1000 MPa and production method thereof

Abstract

The invention relates to a super-thick steel plate with yield strength of 1000MPa and a production method thereof, and belongs to the technical field of metal material processing. The steel plate comprises the following chemical components in percentage by weight: 0.40%-0.45% of C, 0.20%-0.40% of Si, 0.95%-1.05% of Mn, less than or equal to 0.012% of P, less than or equal to 0.003% of S, 1.00%-1.10% of Cr, 0.18%-0.25% of Mo, 0.020%-0.040% of Al and the balance of Fe and inevitable residual elements and impurities. The production method comprises the steps of smelting, die casting, heating, rolling, annealing, quenching and tempering. The yield strength of the 100-150mm extra-thick steel plate is greater than or equal to 1000MPa, the tensile strength is greater than or equal to 1100MPa, the ductility is greater than or equal to 10%, the transverse impact energy at 20 DEG C is greater than or equal to 30J, and the matching of strength and toughness is good.

Description

Technical Field

[0001] The invention belongs to the technical field of metal material processing and relates to an extra-thick steel plate with a yield strength of 1000 MPa and a production method thereof. Background Art

[0002] With the rapid development of the manufacturing industry, the requirements for the strength of metal materials are increasing day by day, especially in the fields of engineering equipment, mining machinery, etc., which urgently need steel with higher strength and better performance. When preparing thick 1000MPa-grade high-strength steel, traditional processes often have problems such as poor hardenability, uneven structure, reduced toughness, and poor matching of strength and toughness. In the prior art, although there have been attempts to improve the performance of steel plates through high alloy component design and multiple heat treatments, the process is often complicated and costly, and it is difficult to stably achieve a good match between high yield strength and strength and toughness at the 1000MPa level. Summary of the invention

[0003] In order to solve the above technical problems, the present invention provides an extra-thick steel plate with a yield strength of 1000 MPa and a production method thereof, which has a simple process and controllable costs, and the obtained steel plate has a good match between strength and toughness.

[0004] In order to achieve the above-mentioned invention object, the technical solution adopted by the present invention is: A 1000MPa grade extra-thick steel plate, whose chemical composition and mass percentage are: C: 0.40%-0.45%, Si: 0.20%-0.40%, Mn: 0.95%-1.05%, P≤0.012%, S≤0.003%, Cr: 1.00%-1.10%, Mo: 0.18%-0.25%, Al: 0.020%-0.040%, and the rest are Fe and unavoidable residual elements and impurities.

[0005] Furthermore, the thickness of the steel plate is 100-150 mm.

[0006] Furthermore, the steel plate has a yield strength of ≥1000MPa, a tensile strength of ≥1100MPa, an elongation of ≥10%; a transverse impact energy of ≥30J at 20°C; and a HB hardness of ≥340.

[0007] The present invention also provides a method for producing the above-mentioned extra-thick steel plate with a yield strength of 1000 MPa, which comprises the steps of smelting, die casting, heating, rolling, annealing, quenching and tempering; Mold casting process: Implement inert gas protection throughout the casting process; Heating process: The maximum heating temperature of the steel ingot is 1220±10℃; Rolling process: The starting rolling temperature in stage II is 850℃~860℃, the final rolling temperature is ≤820℃, and the steel plate is air-cooled after rolling without accelerated cooling; Annealing process: The steel plate is kept at 740℃~760℃ for 4h~6h, then cooled with the furnace to ≤300℃ without opening the furnace door, and then air-cooled after being taken out of the furnace; Quenching process: quenching temperature 940℃~960℃; Tempering process: Tempering temperature 500℃~530℃.

[0008] Furthermore, the total heating time of the heating process is 15h to 17h.

[0009] Furthermore, in the annealing process, the steel plate is heated from room temperature to 740°C to 760°C at a rate of ≤50°C / h and then kept warm.

[0010] Furthermore, in the quenching process, the total heating time is 2.5 min / mm to 3.5 min / mm of steel plate thickness.

[0011] Furthermore, in the tempering process, the total heating time is 4 min / mm to 5 min / mm of steel plate thickness, and air cooling is performed after tempering.

[0012] The beneficial effects of adopting the above technical solution are: (1) The functions of the various components in the steel plate are as follows: C: Carbon can effectively improve the hardenability and can significantly increase the yield strength and tensile strength of the steel plate through interstitial solid solution.

[0013] Si: It acts as a reducing agent and deoxidizer in the steelmaking process. At the same time, Si can play a role in solid solution strengthening, which can significantly improve the elastic limit, yield point and tensile strength of steel.

[0014] Mn: It can increase the toughness, strength and hardness of steel, improve the hardenability of steel, improve the hot processing performance of steel, and it is low in price, which can reduce the production cost of steel plates.

[0015] P and S: In general, they are harmful elements in steel and will increase the brittleness of steel. P will deteriorate the welding performance of steel, reduce plasticity, and deteriorate the cold bending performance; S will reduce the ductility and toughness of steel and cause cracks during forging and rolling. Therefore, the content of P and S in steel should be reduced as much as possible.

[0016] Cr: Its content has a great influence on the strength, plasticity and low-temperature impact toughness of the steel plate. This is because Cr can be dissolved in ferrite and austenite, and can form various carbides with C in the steel; when Cr is dissolved in austenite, it can improve the hardenability of the steel. When Cr forms complex carbides with C and disperses and precipitates in the steel, it can play a role of dispersion strengthening.

[0017] Mo: It can greatly improve the strength, plasticity and low-temperature impact toughness of steel plates. This is because when Mo is dissolved in ferrite and austenite, the C curve of steel can be shifted to the right, thereby significantly improving the hardenability of steel. Mo can also significantly increase the recrystallization temperature of steel and improve the tempering stability. After quenching and tempering, fine-grained sorbite can be obtained, which improves the strength and toughness. When Mo carbides are formed, they can play a role of dispersion strengthening. Therefore, as the Mo content increases, the strength and toughness are improved.

[0018] Al: A commonly used deoxidizer in steel. Adding a small amount of Al can refine the grains and improve impact toughness.

[0019] (2) The purpose of the mold casting process in the production method of the present invention is to prevent the introduction of harmful gas elements such as nitrogen, hydrogen and oxygen into the casting process and to ensure the purity of the steel.

[0020] (3) The maximum heating temperature of the heating process in the production method of the present invention is 1220±10°C, which can effectively prevent the grain coarsening of the rolled structure of the steel plate and ensure the strength and toughness of the final steel plate.

[0021] (4) In the production method of the present invention, the starting rolling temperature of stage II is 850°C to 860°C, and the final rolling temperature is ≤820°C. The purpose is to effectively refine the grain structure of the steel plate by rolling in the non-recrystallization zone and improve its strength and toughness. The steel plate is air-cooled after rolling without accelerated cooling in order to avoid the thermal stress problem caused by rapid cooling and ensure the uniform release of internal stress of the steel plate.

[0022] (5) In the annealing process of the production method of the present invention, the steel plate is kept at 740°C to 760°C. The purpose is to obtain a balanced organizational structure through two-phase zone annealing, and at the same time form a fine layered "dual-phase" structure with two different components. This structure can be transformed into martensite at different temperatures during the subsequent quenching process, produce non-oriented lath boundaries, form an effective grain size of submicron level, and significantly improve the strength and toughness of the steel plate.

[0023] (6) The quenching process of the production method of the present invention has a heating temperature of 940°C to 960°C. The purpose is to increase the austenitizing temperature so that the carbides and other alloying elements in the steel can be more evenly distributed in the matrix, thereby reducing the possibility of forming lamellar or twin martensite in local high-carbon areas, and at the same time increasing the total amount of residual austenite film around the martensite laths, thereby effectively improving the toughness of the steel plate.

[0024] The tempering temperature of the production method of the present invention is 500°C to 530°C. Tempering within this temperature range can release the residual stress in the steel and improve the toughness. At the same time, it can also optimize the microstructure of the steel plate, such as reducing twin martensite and improving the comprehensive mechanical properties of the steel plate.

[0025] The 100-150 mm thick steel plate provided by the present invention has the following mechanical properties: yield strength ≥1000 MPa, tensile strength ≥1100 MPa, elongation ≥10%, 20°C transverse impact energy ≥30 J, and HB hardness ≥340. The steel plate has high strength and hardness, stable impact toughness, good matching of strength and toughness, simple production method, and controllable cost. DETAILED DESCRIPTION Example 1

[0026] The chemical composition and mass percentage of the 1000MPa grade extra thick steel plate of this embodiment are: C: 0.40%, Si: 0.20%, Mn: 0.95%, P: 0.008%, S: 0.003%, Cr: 1.02%, Mo: 0.20%, Al: 0.025%, and the rest are Fe and inevitable residual elements and impurities. Its production process includes smelting, die casting, heating, rolling, annealing, quenching, and tempering processes, which are as follows: (1) Smelting: Smelting is done in an electric furnace, followed by refining in an LF refining furnace and adjusting the composition. The total refining time is 55 minutes. Then the smelting is done in a vacuum degassing furnace, and the vacuum is maintained for 20 minutes.

[0027] (2) Mold casting: The molten steel after smelting is mold cast under the protection of inert gas throughout the process. The liquidus temperature Tll = 1492℃, the superheat is controlled at 40℃±5℃, and a 22.5-ton steel ingot is obtained.

[0028] (3) Heating: The steel ingot is heated in a single-type soaking furnace with a maximum heating temperature of 1220°C and a total heating (holding) time of 16 hours.

[0029] (4) Rolling: The rolling temperature at the beginning of stage I is 1100°C, the rolling temperature at the beginning of stage II is 850°C, the final rolling temperature is 810°C, and the cumulative reduction rate is 85%; after rolling, a 100 mm thick semi-finished steel plate is obtained; after rolling, the steel plate is air-cooled without accelerated cooling.

[0030] (5) Annealing: The steel plate is heated from room temperature to 740°C at a rate of 45°C / h, kept at this temperature for 6 hours, then cooled to 290°C in the furnace without opening the furnace door, and then air-cooled out of the furnace.

[0031] (6) Quenching: Quenching temperature 940°C, total heating time 2.5 min / mm steel plate thickness, water quenching to room temperature, water temperature ≤30°C.

[0032] (7) Tempering: Tempering temperature 530°C, total heating time 4.0 min / mm steel plate thickness, air cooling after tempering.

[0033] The thickness of the steel plate obtained in this embodiment is 100 mm, and the mechanical properties are: yield strength 1027 MPa, tensile strength 1130 MPa, elongation 12%; 20°C transverse impact energy: 36.1 J, 45.3 J, 37.0 J; HB hardness 345. Example 2

[0034] The chemical composition and mass percentage of the 1000MPa grade extra-thick steel plate of this embodiment are: C: 0.41%, Si: 0.22%, Mn: 0.98%, P: 0.007%, S: 0.003%, Cr: 1.04%, Mo: 0.21%, Al: 0.032%, and the rest are Fe and inevitable residual elements and impurities. Its production process includes smelting, die casting, heating, rolling, annealing, quenching, and tempering processes, which are as follows: (1) Smelting: Smelting is done in an electric furnace, followed by refining in an LF refining furnace and adjusting the composition. The total refining time is 50 minutes. Then the smelting is done in a vacuum degassing furnace, and the vacuum is maintained for 21 minutes.

[0035] (2) Mold casting: The molten steel after smelting is mold cast under the protection of inert gas throughout the process. The liquidus temperature Tll = 1492℃, the superheat is controlled at 38℃ ± 5℃, and a 25-ton steel ingot is obtained.

[0036] (3) Heating: The steel ingot is heated in a single-type soaking furnace with a maximum heating temperature of 1210°C and a total heating (holding) time of 16.5 h.

[0037] (4) Rolling: The rolling temperature at the beginning of stage I is 1050°C, the rolling temperature at the beginning of stage II is 850°C, the final rolling temperature is 815°C, and the cumulative reduction rate is 83%; after rolling, a 110 mm thick semi-finished steel plate is obtained; after rolling, the steel plate is air-cooled without accelerated cooling.

[0038] (5) Annealing: The steel plate is heated from room temperature to 745°C at a rate of 46°C / h, kept at this temperature for 5 hours, then cooled to 295°C in the furnace without opening the furnace door, and then air-cooled out of the furnace.

[0039] (6) Quenching: Quenching temperature 945°C, total heating time 2.7 min / mm steel plate thickness, water quenching to room temperature, water temperature ≤30°C.

[0040] (7) Tempering: Tempering temperature 525℃, total heating time 4.2min / mm steel plate thickness, air cooling after tempering.

[0041] The thickness of the steel plate obtained in this embodiment is 110 mm, and the mechanical properties are: yield strength 1023 MPa, tensile strength 1120 MPa, elongation 13.5%; 20°C transverse impact energy: 40.1 J, 53.7 J, 38.3 J; HB hardness 352. Example 3

[0042] The chemical composition and mass percentage of the 1000MPa grade extra-thick steel plate of this embodiment are: C: 0.43%, Si: 0.28%, Mn: 0.99%, P: 0.009%, S: 0.002%, Cr: 1.08%, Mo: 0.18%, Al: 0.035%, and the rest are Fe and inevitable residual elements and impurities. Its production process includes smelting, die casting, heating, rolling, annealing, quenching, and tempering processes, which are as follows: (1) Smelting: Smelting is done in an electric furnace, followed by refining in an LF refining furnace and adjusting the composition. The total refining time is 60 minutes. Then the smelting is done in a vacuum degassing furnace, and the vacuum is maintained for 22 minutes.

[0043] (2) Mold casting: The molten steel after smelting is mold cast under the protection of inert gas throughout the process. The liquidus temperature Tll = 1489 ° C, the superheat is controlled at 36 ° C ± 5 ° C, and a 25-ton steel ingot is obtained.

[0044] (3) Heating: The steel ingot is heated in a single-type soaking furnace with a maximum heating temperature of 1215°C and a total heating (holding) time of 17 hours.

[0045] (4) Rolling: The rolling temperature at the beginning of stage I is 1000°C, the rolling temperature at the beginning of stage II is 855°C, the final rolling temperature is 815°C, and the cumulative reduction rate is 82%; after rolling, a 120 mm thick semi-finished steel plate is obtained; after rolling, the steel plate is air-cooled without accelerated cooling.

[0046] (5) Annealing: The steel plate is heated from room temperature to 748°C at a rate of 47°C / h, kept at this temperature for 5 hours, then cooled to 290°C in the furnace without opening the furnace door, and then air-cooled out of the furnace.

[0047] (6) Quenching: Quenching temperature 945°C, total heating time 2.9 min / mm steel plate thickness, water quenching to room temperature, water temperature ≤30°C.

[0048] (7) Tempering: Tempering temperature 525℃, total heating time 4.4min / mm steel plate thickness, air cooling after tempering.

[0049] The thickness of the steel plate obtained in this embodiment is 120 mm, and the mechanical properties are: yield strength 1060 MPa, tensile strength 1160 MPa, elongation 12%; 20°C transverse impact energy: 51.7 J, 68.7 J, 51.2 J; HB hardness 355. Example 4

[0050] The chemical composition and mass percentage of the 1000MPa grade extra-thick steel plate of this embodiment are: C: 0.42%, Si: 0.30%, Mn: 1.00%, P: 0.007%, S: 0.001%, Cr: 1.06%, Mo: 0.22%, Al: 0.030%, and the rest are Fe and unavoidable residual elements and impurities. Its production process includes smelting, die casting, heating, rolling, annealing, quenching, and tempering processes, which are as follows: (1) Smelting: Smelting is done in an electric furnace, followed by refining in an LF refining furnace and adjusting the composition. The total refining time is 55 minutes. Then the smelting is done in a vacuum degassing furnace, and the vacuum is maintained for 20 minutes.

[0051] (2) Mold casting: The molten steel after smelting is mold cast under the protection of inert gas throughout the process. The liquidus temperature Tll = 1490℃, the superheat is controlled at 40℃±5℃, and a 22.5-ton steel ingot is obtained.

[0052] (3) Heating: The steel ingot is heated in a single-type soaking furnace with a maximum heating temperature of 1210°C and a total heating (holding) time of 15 hours.

[0053] (4) Rolling: The rolling temperature at the beginning of stage I is 1100°C, the rolling temperature at the beginning of stage II is 855°C, the final rolling temperature is 815°C, and the cumulative reduction rate is 80%; after rolling, a 130 mm thick semi-finished steel plate is obtained; after rolling, the steel plate is air-cooled without accelerated cooling.

[0054] (5) Annealing: The steel plate is heated from room temperature to 750°C at a rate of 48°C / h, kept at this temperature for 5 hours, then cooled to 295°C in the furnace without opening the furnace door, and then air-cooled out of the furnace.

[0055] (6) Quenching: Quenching temperature 950°C, total heating time 3.0 min / mm steel plate thickness, water quenching to room temperature, water temperature ≤30°C.

[0056] (7) Tempering: Tempering temperature 520℃, total heating time 4.5min / mm steel plate thickness, air cooling after tempering.

[0057] The thickness of the steel plate obtained in this embodiment is 130 mm, and the mechanical properties are: yield strength 1066 MPa, tensile strength 1170 MPa, elongation 10%; 20°C transverse impact energy: 53.0 J, 50.3 J, 50.5 J; HB hardness 356. Example 5

[0058] The chemical composition and mass percentage of the 1000MPa grade extra-thick steel plate of this embodiment are: C: 0.44%, Si: 0.35%, Mn: 1.03%, P: 0.008%, S: 0.002%, Cr: 1.10%, Mo: 0.25%, Al: 0.038%, and the rest are Fe and inevitable residual elements and impurities. Its production process includes smelting, die casting, heating, rolling, annealing, quenching, and tempering processes, which are as follows: (1) Smelting: Smelting is done in an electric furnace, followed by refining in an LF refining furnace and adjusting the composition. The total refining time is 55 minutes. Then the smelting is done in a vacuum degassing furnace, and the vacuum is maintained for 20 minutes.

[0059] (2) Mold casting: The molten steel after smelting is mold cast under the protection of inert gas throughout the process. The liquidus temperature Tll = 1488℃, the superheat is controlled at 38℃ ± 5℃, and a 25-ton steel ingot is obtained.

[0060] (3) Heating: The steel ingot is heated in a single-type soaking furnace with a maximum heating temperature of 1225°C and a total heating (holding) time of 16 hours.

[0061] (4) Rolling: The rolling temperature at the beginning of stage I is 1050°C, the rolling temperature at the beginning of stage II is 860°C, the final rolling temperature is 820°C, and the cumulative reduction rate is 78%; after rolling, a 140 mm thick semi-finished steel plate is obtained; after rolling, the steel plate is air-cooled without accelerated cooling.

[0062] (5) Annealing: The steel plate is heated from room temperature to 755°C at a rate of 49°C / h, kept at this temperature for 4 hours, then cooled to 280°C in the furnace without opening the furnace door, and then air-cooled out of the furnace.

[0063] (6) Quenching: Quenching temperature 955°C, total heating time 3.5 min / mm steel plate thickness, water quenching to room temperature, water temperature ≤30°C.

[0064] (7) Tempering: Tempering temperature 510℃, total heating time 4.8min / mm steel plate thickness, air cooling after tempering.

[0065] The thickness of the steel plate obtained in this embodiment is 140 mm, and the mechanical properties are: yield strength 1066 MPa, tensile strength 1200 MPa, elongation 12%; 20°C transverse impact energy: 35.2 J, 32.4 J, 36.7 J; HB hardness 362. Example 6

[0066] The chemical composition and mass percentage of the 1000MPa grade extra thick steel plate of this embodiment are: C: 0.45%, Si: 0.40%, Mn: 1.05%, P: 0.006%, S: 0.002%, Cr: 1.09%, Mo: 0.24%, Al: 0.040%, and the rest are Fe and inevitable residual elements and impurities. Its production process includes smelting, die casting, heating, rolling, annealing, quenching, and tempering processes, which are as follows: (1) Smelting: Smelting is done in an electric furnace, followed by refining in an LF refining furnace and adjusting the composition. The total refining time is 55 minutes. Then the smelting is done in a vacuum degassing furnace, and the vacuum is maintained for 20 minutes.

[0067] (2) Mold casting: The molten steel after smelting is mold cast under the protection of inert gas throughout the process. The liquidus temperature Tll = 1486℃, the superheat is controlled at 40℃ ± 5℃, and a 22.5-ton steel ingot is obtained.

[0068] (3) Heating: The steel ingot is heated in a single-type soaking furnace with a maximum heating temperature of 1230°C and a total heating (holding) time of 17 hours.

[0069] (4) Rolling: The rolling temperature at the beginning of stage I is 1100°C, the rolling temperature at the beginning of stage II is 860°C, the final rolling temperature is 820°C, and the cumulative reduction rate is 77%; after rolling, a 150 mm thick semi-finished steel plate is obtained; after rolling, the steel plate is air-cooled without accelerated cooling.

[0070] (5) Annealing: The steel plate is heated from room temperature to 760°C at a rate of 50°C / h, kept at this temperature for 4 hours, then cooled to 300°C in the furnace without opening the furnace door, and then air-cooled out of the furnace.

[0071] (6) Quenching: Quenching temperature 960°C, total heating time 3.2 min / mm steel plate thickness, water quenching to room temperature, water temperature ≤30°C.

[0072] (7) Tempering: Tempering temperature 500°C, total heating time 5.0 min / mm steel plate thickness, air cooling after tempering.

[0073] The thickness of the steel plate obtained in this embodiment is 150 mm, and the mechanical properties are: yield strength 1069 MPa, tensile strength 1200 MPa, elongation 13%; 20°C transverse impact energy: 34.4 J, 34.7 J, 30.6 J; HB hardness 366.

Claims

1. A 1000MPa grade extra thick steel plate, characterized in that: The chemical composition of the steel plate and its mass percentage are: C: 0.40% ~ 0.45%, Si: 0.20% ~ 0.40%, Mn: 0.95% ~ 1.05%, P ≤ 0.012%, S ≤ 0.003%, Cr: 1.00% ~ 1.10%, Mo: 0.18% ~ 0.25%, Al: 0.020% ~ 0.040%, and the rest are Fe and unavoidable residual elements and impurities.

2. The extra-thick steel plate with a yield strength of 1000 MPa according to claim 1, characterized in that: The thickness of the steel plate is 100-150 mm.

3. The extra-thick steel plate with a yield strength of 1000 MPa according to claim 2, characterized in that: The steel plate has a yield strength of ≥1000MPa, a tensile strength of ≥1100MPa, an elongation of ≥10%, a transverse impact energy of ≥30J at 20°C, and a HB hardness of ≥340.

4. The method for producing a 1000 MPa grade extra thick steel plate according to any one of claims 1 to 3, characterized in that: Including smelting, die casting, heating, rolling, annealing, quenching and tempering processes; Mold casting process: Implement inert gas protection throughout the casting process; Heating process: The maximum heating temperature of the steel ingot is 1220±10℃; Rolling process: The starting rolling temperature in stage II is 850℃~860℃, the final rolling temperature is ≤820℃, and the steel plate is air-cooled after rolling without accelerated cooling; Annealing process: The steel plate is kept at 740℃~760℃ for 4h~6h, then cooled with the furnace to ≤300℃ without opening the furnace door, and then air-cooled after being taken out of the furnace; Quenching process: quenching temperature 940℃~960℃; Tempering process: Tempering temperature 500℃~530℃.

5. The method for producing a 1000 MPa grade extra thick steel plate according to claim 4, characterized in that: The total heating time of the heating process is 15h to 17h.

6. The method for producing a 1000 MPa grade extra thick steel plate according to claim 5, characterized in that: In the annealing process, the steel plate is heated from room temperature to 740°C to 760°C at a rate of ≤50°C / h and then kept warm.

7. The method for producing a 1000 MPa grade extra thick steel plate according to claim 6, characterized in that: The total heating time of the quenching process is 2.5 min / mm to 3.5 min / mm of steel plate thickness.

8. The method for producing a 1000 MPa grade extra thick steel plate according to claim 7, characterized in that: In the tempering process, the total heating time is 4 min / mm to 5 min / mm steel plate thickness, and air cooling is performed after tempering.