An extra-wide and extra-thick low-alloy high-strength structural steel plate and its production method

Abstract

A kind of ultra-wide and ultra-thick low-alloy high-strength structural steel plate and its production method. The chemical composition of the steel is C = 0.05% - 0.06%, Si = 0.15% - 0.25%, Mn = 1.50% - 1.60%, P ≤ 0.012%, S ≤ 0.005%, Cr = 0.13% - 0.18%, Ni = 0.15% - 0.20%, Nb = 0.030% - 0.035%, Ti = 0.008% - 0.020%, Al = 0.020% - 0.050%, H ≤ 0.0002%, N ≤ 0.0045%, O ≤ 0.0010%, and the rest are Fe and inevitable impurities, CEV ≤ 0.38%, Pcm ≤ 0.18%. The process steps include converter smelting, LF refining, vacuum degassing, continuous casting, heating, rolling, and post-rolling stacking and cooling. The produced steel plate has a yield strength ≥ 390 MPa, a tensile strength of 510 - 650 MPa, an elongation rate ≥ 20%, and an impact Akv2 at -40°C ≥ 80 J.

Description

Technical Field

[0001] The present invention belongs to the technical field of metallurgy and relates to an extra-wide and extra-thick low-alloy high-strength structural steel plate and a production method thereof. Background Art

[0002] With the continuous development of economy and technology, the demand for steel plates with large thickness and large width specifications is increasing continuously. In the prior art, for the production of medium and heavy plates with extreme width and thickness, the production method of ingot + rolling forming + heat treatment is adopted. The ingot is used to ensure that the finished steel plate has a sufficient reduction ratio, so as to press the internal defects of the steel plate and obtain better internal compactness of the steel plate; the rolling process is mainly to meet the order size requirements of the steel plate, and the control of the steel plate structure is of secondary importance; the mechanical properties of the steel plate are ensured through post-rolling heat treatment.

[0003] With the development of medium and heavy plate process technology and equipment, through the reheating of the slab once and the control of the rolling process, not only can the forming of the steel plate be realized, but also the performance of the steel plate can be ensured to meet the target requirements. Summary of the Invention

[0004] The purpose of the present invention is to provide an extra-wide and extra-thick low-alloy high-strength structural steel plate and a production method thereof. The thickness of the produced steel plate is 70 - 100 mm, and the maximum width is 4600 mm. The steel plate is formed by one-time heating and rolling, and does not need to go through heat treatment again. Its yield strength ≥ 390 MPa, tensile strength 510 - 650 MPa, elongation ≥ 20%, and -40 °C impact Akv2 ≥ 80 J.

[0005] The technical solution of the present invention:

[0006] An extra-wide and extra-thick low-alloy high-strength structural steel plate with a thickness specification of 70 - 100 mm and a maximum width specification of 4600 mm, characterized in that: the chemical composition of the steel by weight percentage is C = 0.05% - 0.06%, Si = 0.15% - 0.25%, Mn = 1.50% - 1.60%, P ≤ 0.012%, S ≤ 0.005%, Cr = 0.13% - 0.18%, Ni = 0.15% - 0.20%, Nb = 0.030% - 0.035%, Ti = 0.008% - 0.020%, Al = 0.020% - 0.050%, B ≤ 0.0005, H ≤ 0.0002%, N ≤ 0.0045%, O ≤ 0.0010%, and the rest is Fe and unavoidable impurities, CEV ≤ 0.38%, Pcm ≤ 0.18%; the yield strength of the steel plate ≥ 390 MPa, tensile strength 510 - 650 MPa, elongation ≥ 20%, and -40 °C impact Akv2 ≥ 80 J.

[0007] A production method of an extra-wide and extra-thick low-alloy high-strength structural steel plate, comprising the following process steps:

[0008] (1)Converter: Top and bottom combined blown converter, controlling the tapping temperature at 1560 - 1640 °C. The P content in the tapped steel is ≤0.010%. During the tapping process, deoxidizers and alloys are added for deoxidation and alloying. Among them, low-P alloys are used for alloys to avoid an increase in P content in the molten steel.

[0009] (2)Refining: After the molten steel in the tundish is heated up by power supply in the LF furnace, the chemical composition is precisely adjusted, and then it enters the RH furnace or VD furnace for vacuum treatment. When tapping, the measured gas content in the molten steel is H ≤0.00015%, N ≤0.0040%, and O ≤0.0010%.

[0010] (3)Continuous casting: The superheat of the tundish is 8 - 30 °C. Dynamic soft reduction or heavy reduction technology is adopted in continuous casting to improve the internal quality of the continuous casting billet. The thickness of the continuous casting billet is 350 - 450 mm, and the width is 1700 - 2500 mm.

[0011] (4)Heating: The maximum temperature in the furnace chamber does not exceed 1200 °C, the temperature in the preheating section is 650 - 900 °C, the temperature in the heating section is 1050 - 1200 °C, and the temperature in the soaking section is 1130 - 1200 °C.

[0012] (5)Rolling: Three-stage rolling is adopted. The rolling temperature in the first stage is 1000 - 1150 °C, and the thickness of the intermediate billet in the first stage is ≥180 mm or 1.6 times the thickness of the finished product. The rolling temperature in the second stage is 880 - 920 °C, and the thickness of the intermediate billet in the second stage is adjusted according to its length to ensure that the length / width of the billet is ≥1.1. The rolling temperature in the third stage is 780 - 830 °C. After rolling, it is cooled by high-pressure water cooling, and the return red temperature is 350 - 450 °C.

[0013] Principle of the invention: This invention adopts a low-carbon composition system. By adding appropriate elements such as Si, Mn, Cr, Ni, Nb, Ti, and Al, the purpose of solid solution strengthening and microalloying is achieved. In smelting, LF refining and RH / VD vacuum treatment are used to purify the molten steel. In continuous casting, low superheat and dynamic reduction are adopted to improve the internal quality of the slab. The temperature of the heating furnace chamber is strictly controlled to control the austenite grain size. Three-stage rolling is adopted in rolling. Among them, the first stage is rolling in the austenite recrystallization zone, further refining the austenite grain size and realizing the width forming of the steel plate to meet the order requirements. Usually, the length of the intermediate billet in this stage is less than the width. The rolling temperature in the second stage is controlled in the non-recrystallization zone. On the one hand, it realizes the preliminary flattening of the austenite grains, and on the other hand, it reduces the forming difficulty in the third stage of rolling. The rolling temperature in the third stage is slightly higher than the A3 temperature, further flattening the austenite grains and increasing the distortion energy to promote the subsequent phase transformation. After rolling, it is quickly cooled by water, and high-pressure water cooling is adopted to increase the heat transfer efficiency on the surface of the steel plate, so that the steel plate obtains a uniformly refined final structure.

[0014] Advantages of the present invention: The steel plate produced by the above method has a yield strength ≥ 390 MPa, a tensile strength of 510 - 650 MPa, an elongation ≥ 20%, and an impact Akv2 at -40 °C ≥ 80 J. It realizes the one-time hot forming of ultra-wide and ultra-thick steel plates and obtains the required mechanical properties during this process; the production efficiency of ultra-wide and ultra-thick steel plates is greatly improved, and the production cycle is shortened; subsequent heat treatment processes are reduced, achieving energy conservation, emission reduction, and carbon emission reduction. Brief Description of the Drawings

[0015] Figure 1 It is a metallographic structure photo of Example 1 of the present invention. Specific Embodiments

[0016] The following is described in conjunction with embodiments.

[0017] The chemical composition by weight percentage of the steel produced in the embodiment is shown in Table 1, and the test results of the mechanical properties of the steel plate are shown in Table 2. Example 1

[0018] A production method of an ultra-wide and ultra-thick low-alloy high-strength structural steel plate, the process steps are as follows:

[0019] (1) Converter smelting: Top and bottom combined blown converter, controlling the tapping temperature at 1576 °C, P ≤ 0.006% in the converter tapping, adding deoxidizer and alloy during tapping for deoxidation and alloying, and using low-P alloy for the alloy.

[0020] (2) Refining: The molten steel in the ladle is heated up by power supply in the LF furnace and then the chemical composition is precisely adjusted, and then enters the VD furnace for vacuum treatment. The measured gas content of the molten steel at the station is H ≤ 0.00012%, N ≤ 0.0030%, O ≤ 0.0006%, and the composition is shown as component ① in Table 1.

[0021] (3) Continuous casting: The superheat of the tundish is 18 - 20 °C, and dynamic soft reduction is used to improve the internal quality of the continuous casting billet. The thickness dimension of the continuous casting billet is 450 mm, and the width dimension is 2300 mm.

[0022] (4) Heating: The billet size is 450 × 2300 × 3800 mm, the preheating section temperature is 800 - 900 °C, the heating section temperature is 1050 - 1200 °C, the soaking section temperature is 1180 - 1200 °C, and the slab tapping temperature is 1180 °C.

[0023] (5) Rolling: Three-stage rolling is adopted. The finished product size is 100×4600×7600 mm. The rolling temperature in the first stage is 1050 - 1120 °C, the thickness of the intermediate billet in the first stage is 200 mm, the width is 4680 mm, and the length is 4200 mm; the rolling temperature in the second stage is 880 - 900 °C, the thickness of the intermediate billet in the second stage is 160 mm, the width is 4680 mm, and the length is 5250 mm; the rolling temperature in the third stage is 790 - 820 °C, and after rolling, it is water-cooled under high pressure, and the return red temperature is 400 - 430 °C. Example 2

[0024] A production method of an ultra-wide and ultra-thick low-alloy high-strength structural steel plate, the technological steps are as follows:

[0025] (1) Converter smelting: Top and bottom combined blown converter, controlling the tapping temperature at 1576 °C, P≤0.006% for converter tapping. During tapping, deoxidizers and alloys are added for deoxidation and alloying, and low-P alloys are used for the alloys.

[0026] (2) Refining: The molten steel in the ladle is heated and the temperature is raised in the LF furnace, and then the chemical composition is precisely adjusted. Subsequently, it enters the VD furnace for vacuum treatment. When leaving the station, the measured gas content of the molten steel is H≤0.00012%, N≤0.0030%, O≤0.0006%, and the composition is shown as component ① in Table 1.

[0027] (3) Continuous casting: The superheat in the tundish is 18 - 20 °C, and dynamic soft reduction is adopted to improve the internal quality of the continuous casting billet. The thickness dimension of the continuous casting billet is 450 mm and the width dimension is 2300 mm.

[0028] (4) Heating: The billet size is 450×2300×3800 mm, the temperature in the preheating section is 800 - 900 °C, the temperature in the heating section is 1050 - 1200 °C, the temperature in the soaking section is 1180 - 1200 °C, and the slab discharging temperature is 1180 °C.

[0029] (5) Rolling: Two-stage rolling is adopted. The finished product size is 100×4600×7600 mm. The rolling temperature in the first stage is 1050 - 1120 °C, the thickness of the intermediate billet in the first stage is 140 mm, the width is 4680 mm, and the length is 6000 mm; the rolling temperature in the second stage is 790 - 820 °C, and after rolling, it is water-cooled under high pressure, and the return red temperature is 400 - 430 °C. Example 3

[0030] A production method of an ultra-wide and ultra-thick low-alloy high-strength structural steel plate, the technological steps are as follows:

[0031] (1) Converter smelting: Top and bottom combined blown converter, controlling the tapping temperature at 1590 °C, P≤0.010% for converter tapping. During tapping, deoxidizers and alloys are added for deoxidation and alloying, and low-P alloys are used for the alloys.

[0032] (2)Refining: After the molten steel in the tundish is heated by power supply in the LF furnace, the chemical composition is precisely adjusted, and then it enters the VD furnace for vacuum treatment. When it leaves the station, the gas content in the molten steel is measured as H ≤ 0.00012%, N ≤ 0.0030%, and O ≤ 0.0006%. The composition is shown as Component ② in Table 1.

[0033] (3)Continuous casting: The superheat of the tundish is 12 - 17°C. Dynamic soft reduction is adopted to improve the internal quality of the continuous casting billet. The thickness of the continuous casting billet is 350 mm and the width is 2500 mm.

[0034] (4)Heating: The billet size is 350×2500×3000 mm. The temperature in the preheating section is 800 - 900°C, the temperature in the heating section is 1050 - 1200°C, the temperature in the soaking section is 1180 - 1200°C, and the slab discharging temperature is 1175°C.

[0035] (5)Rolling: Three-stage rolling is adopted. The finished product size is 70×4600×7200 mm. The rolling temperature in the first stage is 1030 - 1100°C. The thickness of the intermediate billet in the first stage is 150 mm, the width is 4680 mm, and the length is 3740 mm. The rolling temperature in the second stage is 880 - 900°C. The thickness of the intermediate billet in the second stage is 105 mm, the width is 4680 mm, and the length is 5340 mm. The rolling temperature in the third stage is 780 - 820°C. After rolling, it is cooled by high-pressure water, and the recrystallization temperature is 380 - 410°C. Example 4

[0036] A production method of an ultra-wide and ultra-thick low-alloy high-strength structural steel plate, the technological steps are as follows:

[0037] (1)Converter smelting: Top-bottom combined blown converter, controlling the tapping temperature at 1590°C. The P content in the converter tapping is ≤ 0.010%. During the tapping process, deoxidizers and alloys are added for deoxidation and alloying, and low-P alloys are used as alloys.

[0038] (2)Refining: After the molten steel in the tundish is heated by power supply in the LF furnace, the chemical composition is precisely adjusted, and then it enters the VD furnace for vacuum treatment. When it leaves the station, the gas content in the molten steel is measured as H ≤ 0.00012%, N ≤ 0.0030%, and O ≤ 0.0006%. The composition is shown as Component ② in Table 1.

[0039] (3)Continuous casting: The superheat of the tundish is 12 - 17°C. Dynamic soft reduction is adopted to improve the internal quality of the continuous casting billet. The thickness of the continuous casting billet is 350 mm and the width is 2500 mm.

[0040] (4)Heating: The billet size is 350×2500×3000 mm. The temperature in the preheating section is 800 - 900°C, the temperature in the heating section is 1050 - 1200°C, the temperature in the soaking section is 1180 - 1200°C, and the slab discharging temperature is 1180°C.

[0041] (5) Rolling: Two-stage rolling is adopted. The finished product size is 70×4600×7200 mm. The rolling temperature in the first stage is 1050 - 1110 °C, the thickness of the intermediate billet in the first stage is 110 mm, the width is 4680 mm, and the length is 5100 mm. The rolling temperature in the second stage is 790 - 820 °C. After rolling, it is water-cooled under high pressure, and the return red temperature is 380 - 410 °C. Example 5

[0042] A production method of an ultra-wide, ultra-thick low-alloy high-strength structural steel plate, the technological steps are as follows:

[0043] (1) Converter smelting: Top and bottom combined blown converter, controlling the tapping temperature at 1590 °C. The P content in the converter tapping is ≤0.010%. During the tapping process, deoxidizers and alloys are added for deoxidation and alloying, and low-P alloys are used as alloys.

[0044] (2) Refining: The molten steel in the tundish is heated and its temperature is raised in the LF furnace, and then the chemical composition is precisely adjusted. Subsequently, it enters the VD furnace for vacuum treatment. When leaving the station, the gas content in the molten steel is measured as H ≤0.00012%, N ≤0.0030%, O ≤0.0006%, and the composition is shown as component ② in Table 1.

[0045] (3) Continuous casting: The superheat degree of the tundish is 12 - 17 °C. Dynamic soft reduction is adopted to improve the internal quality of the continuous casting billet. The thickness size of the continuous casting billet is 350 mm and the width size is 2500 mm.

[0046] (4) Heating: The billet size is 350×2500×3000 mm. The temperature in the preheating section is 800 - 900 °C, the temperature in the heating section is 1050 - 1200 °C, the temperature in the soaking section is 1180 - 1200 °C, and the slab discharging temperature is 1185 °C.

[0047] (5) Rolling: Two-stage rolling is adopted. The finished product size is 70×4600×7200 mm. The rolling temperature in the first stage is 1060 - 1130 °C, the thickness of the intermediate billet in the first stage is 140 mm, the width is 4680 mm, and the length is 4000 mm. The starting rolling temperature in the second stage is 830 °C. The head of the steel plate warped severely during the 3rd rolling pass, and the rolling was abandoned.

[0048] Table 1 Melting chemical composition of the steel in the example (%)

[0049] 。

[0050] Table 2 Detection results of the tensile, bending and impact properties of the steel plate in the example

[0051] 。

Claims

1. A super-wide and super-thick low-alloy high-strength structural steel plate with a thickness specification of 70 - 100 mm, characterized in that: The width specification is 4600mm, and the chemical composition of the steel in weight percentage is C = 0.05% - 0.06%, Si = 0.15% - 0.25%, Mn = 1.50% - 1.60%, P ≤ 0.012%, S ≤ 0.005%, Cr = 0.13% - 0.18%, Ni = 0.15% - 0.20%, Nb = 0.030% - 0.035%, Ti = 0.008% - 0.020%, Al = 0.020% - 0.050%, B ≤ 0.0005, H ≤ 0.0002%, N ≤ 0.0045%, O ≤ 0.0010%, and the rest is Fe and inevitable impurities, CEV ≤ 0.38%, Pcm ≤ 0.18%; the yield strength of the steel plate is ≥390MPa, the tensile strength is 510 - 650MPa, the elongation is ≥20%, and the impact Akv2 at -40°C is ≥80J; It includes the following technological steps: (1) Converter: Top-bottom combined blown converter, controlling the tapping temperature at 1560 - 1640°C, P in the converter tapping ≤ 0.010%, adding deoxidizer and alloy during the tapping process for deoxidation and alloying, and using low-P alloy for the alloy to avoid the increase of P in the molten steel; (2) Refining: After the molten steel in the tundish is heated and raised in temperature in the LF furnace, the chemical composition is precisely adjusted, and then it enters the RH furnace or VD furnace for vacuum treatment. When leaving the station, the gas in the molten steel is measured as H ≤ 0.00015%, N ≤ 0.0040%, O ≤ 0.0010%; (3) Continuous casting: The superheat of the tundish is 8 - 30°C. Dynamic soft reduction or heavy reduction technology is adopted in continuous casting to improve the internal quality of the continuous casting billet. The thickness of the continuous casting billet is 350 - 450mm, and the width is 1700 - 2500mm; (4) Heating: The maximum temperature in the furnace does not exceed 1200°C, the temperature in the preheating section is 650 - 900°C, the temperature in the heating section is 1050 - 1200°C, and the temperature in the soaking section is 1130 - 1200°C; (5) Rolling: Three-stage rolling is adopted. The rolling temperature in the first stage is 1000 - 1150°C, and the thickness of the intermediate billet in the first stage is ≥1.6 times the thickness of the finished product; the rolling temperature in the second stage is 880 - 920°C, and the thickness of the intermediate billet in the second stage is adjusted according to its length to ensure that the length / width of the billet ≥ 1.1; the rolling temperature in the third stage is 780 - 830°C, and after rolling, it is cooled by high-pressure water, and the return red temperature is 350 - 450°C; The thickness of the intermediate billet in the first stage is ≥1.6 times the thickness of the finished product.

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