Large-thickness Q500qF bridge plate and production method thereof

Abstract

The invention discloses a large-thickness Q500qF bridge plate and a production method thereof, and belongs to the technical field of metallurgy, the bridge plate comprises the following chemical components in percentage by mass: 0.07-0.11% of C, 1.70-2.00% of Mn, 0.35-0.70% of Cr, less than or equal to 0.015% of P, less than or equal to 0.005% of S, 0.015-0.045% of Nb, 0.15-0.45% of Mo and the balance of Fe and inevitable impurities, the sum of the components is 100%, and the production method comprises the steps of converter smelting, refining, continuous casting, casting blank heating, rolling and heat treatment. According to the method, the component design with the low C content is adopted, the bainite + ferrite + martensite multi-phase structure steel plate is obtained by adding Nb, Cr and Mo for compounding through a special rolling controlled cooling mode, and it is guaranteed that the strength, the extremely low yield ratio, low-temperature impact at the temperature of 60 DEG C below zero, the impact fiber rate and aging impact meet the requirements.

Description

Technical Field

[0001] The invention relates to a bridge plate and a production method thereof, in particular to a thick Q500qF bridge plate and a production method thereof, belonging to the technical field of metallurgy. Background Art

[0002] As high-strength bridge steel is increasingly used in key national projects, especially as the motherland invests more and more in construction in the western region, such areas are remote areas with high altitudes and complex terrain. The assembly design projects require complex steel and high performance indicators. Thick steel plates are needed to reduce the amount of welding at the butt welds and reduce the difficulty of construction.

[0003] At the same time, the environment in such areas is complex, and the safety of bridge construction must be fully considered during the design. To this end, it is necessary to develop large-width, high-performance cold-resistant bridge plates to improve the fracture toughness, low-temperature toughness and seismic resistance of steel.

[0004] Patent application CN112210719A discloses a low-cost, high-performance Q500 bridge steel and production method: the steel plate component system needs to add V and Cu, and the production thickness is 10-60mm. The thickness range of the produced steel plate is small and cannot meet the needs of remote areas with high altitudes and complex terrains; Patent CN 114381663 A discloses a 100mm thick HPS420WZ35 weather-resistant bridge plate and its production method to ensure performance: the steel plate has a strength of 420Mpa, which is low in strength and only 100mm thick. The patent does not cover thicknesses above 100mm. Patent CN 114262845 B discloses a 500Mpa thin-gauge bridge plate and its production method. The patent involves a production method for a bridge plate with a strength level of 500Mpa or more and a size of 6 to 16m delivered in a temper-free TMCP state. The thickness range of the produced steel plate is small and cannot meet the needs of remote areas with high altitudes and complex terrain.

[0005] Therefore, developing a thick Q500qF bridge plate and its production method that can overcome the above defects has become a technical problem that needs to be solved urgently by technical personnel in this field. Summary of the invention

[0006] The technical problem to be solved by the present invention is to propose a large-thickness Q500qF bridge plate and a production method thereof in view of the shortcomings of the above-mentioned prior art. The method adopts a composition design with low C content, and obtains a bainite + ferrite + martensite multiphase structure steel plate by adding Nb, Cr, and Mo in a composite manner through a special rolling controlled cooling mode, thereby ensuring that the strength, extremely low yield strength ratio, -60°C low-temperature impact, impact fiber rate and aging impact meet the requirements.

[0007] The technical solution of the present invention to solve the above technical problems is: A thick Q500qF bridge plate, the chemical composition of which is calculated by mass percentage: C: 0.07-0.11%, Mn: 1.70-2.00%, Cr: 0.35-0.70%, P≤0.015%, S≤0.005%, Nb: 0.015-0.045%, Mo: 0.15-0.45%, and the rest is Fe and unavoidable impurities, and the sum of the above components is 100%.

[0008] Technical effect: The present invention adopts low carbon C: 0.07-0.11% and multi-phase structure design to improve the seismic safety factor.

[0009] The present invention also provides a method for producing a thick Q500qF bridge plate, the production process of which includes converter smelting, refining, continuous casting, billet heating, rolling and heat treatment, wherein: (1) Rolling process: In order to obtain multiphase structure and improve the toughness of steel plate, the rough rolling temperature is 900-980℃, the finishing rolling temperature is 700-750℃, and the water entry temperature is 500-630℃; (2) Controlled cooling process during rolling process: the steel plate red-return temperature is limited to 400-500℃; (3) Heat treatment process: Tempering at 480-600℃ is used to eliminate surface stress of the steel plate and improve mechanical properties.

[0010] The technical solution further defined in the present invention is: In the aforementioned production method of the thick Q500qF bridge plate, the steel plate is refined by LF+RH, so that the gas H content of the steel plate is ≤0.5ppm and the N content is ≤35ppm.

[0011] In the aforementioned production method of large-thickness Q500qF bridge plate, the thickness of the produced bridge plate is 100-150mm.

[0012] Technical effect: The bridge plate produced by the present invention has a thickness of 100-150mm, which is much higher than the design thickness of ordinary bridge plates. It is more suitable for remote areas with high altitudes and complex terrains, and thick steel plates to reduce the welding amount of butt welds and reduce construction difficulty.

[0013] In the aforementioned production method of large-thickness Q500qF bridge plates, the produced bridge plates have a yield strength ≥500Mpa, a tensile strength of 630-750Mpa, an elongation ≥18%, a conventional impact at -60°C ≥250J, and a yield strength ratio ≤0.86.

[0014] In the aforementioned production method of the large-thickness Q500qF bridge plate, the fiber rate of the impact section of the produced bridge plate is ≥90%, and the aging impact performance of 5% deformation is ≥150J.

[0015] Technical effect, excellent performance yield strength ≥500Mpa, tensile strength 630-750Mpa, elongation ≥18%, -60℃ conventional impact ≥250J, yield strength ratio ≤0.86 and impact section fiber rate ≥90%, 5% deformation aging impact performance ≥150J. These indicators can greatly improve the characteristics of steel plate welding and assembly to adapt to the high altitude and complex laying environment in the western region.

[0016] The beneficial effects of the present invention are: (1) Low-temperature austenitization technology reduces the original austenite grain size and ensures the stability of the product's low-temperature impact toughness; (2) By controlling the second opening temperature, final rolling temperature and relaxation technology, combined with the water cooling process, the product's yield strength is effectively reduced to ensure the stability of the tensile strength and the stability of the product's yield strength ratio; (3) By controlling the controlled cooling process, the grain size of the organization is effectively refined, and the organization transformation is ensured by the second opening temperature and water entry temperature, and a multi-phase organization of polygonal ferrite, bainite, martensite, etc. is obtained to improve the strength and toughness of the steel plate. Compared with the current ordinary quenching and tempering production of Q500qF steel plate, it has the characteristics of high yield strength ratio, poor weldability, and small impact toughness margin.

[0017] The production method of the present invention adopts a composition design with low C content, and obtains a bainite + ferrite + martensite multiphase structure steel plate by adding Nb, Cr, and Mo in a composite manner through a special rolling controlled cooling mode, thereby ensuring that the strength, extremely low yield ratio, -60°C low-temperature impact, impact fiber rate, and aging impact meet the requirements.

[0018] During the controlled rolling process of the present invention, the rough rolling temperature is 900-980℃, the finishing rolling temperature is 700-750℃, and the water entry temperature is 500-630℃. This is to control the rolling of the continuous casting billet in the austenite recrystallization zone, the non-recrystallization zone and the deformation induced phase transformation zone, so that a batch of dislocations are formed inside the steel plate and a large distortion energy is left, so as to achieve the purpose of repeatedly refining the austenite grains, thereby generating fine ferrite and bainite grains in the subsequent controlled cooling process, thereby ensuring the low yield strength ratio and low temperature impact toughness of the steel plate. At the same time, by controlling the water entry temperature of the rolling, the relaxation technology is used to increase the ferrite content and more effectively reduce the yield strength ratio. The controlled cooling process of the present invention adopts rapid cooling ACC cooling, and the red-returning temperature is 400-500℃, which ensures that the bainite phase transformation is completed in the full thickness direction and improves the high strength and toughness of the steel plate; at the same time, the higher red-returning temperature can avoid the secondary buckling of the steel plate due to uneven cooling, ensure the straightness of the steel plate, and reduce the generation of corrugated plates.

[0019] The heat treatment of the present invention adopts 480-600° C. temperature for tempering to eliminate the surface stress of the steel plate and improve the mechanical properties. DETAILED DESCRIPTION

[0020] In order to make the present invention more clear, a thick Q500qF bridge plate and a production method thereof of the present invention are further described below. The specific embodiments described here are only used to explain the present invention and are not used to limit the present invention. Example 1

[0021] This embodiment provides a thick Q500qF bridge plate with a thickness of 100 mm. Some of its chemical components and mass percentages are shown in Table 1. The rest are Fe and unavoidable impurities, and the sum of the above components is 100%.

[0022] The production method of the above-mentioned Q500qF bridge plate has a production process including converter smelting, refining, continuous casting, billet heating, rolling and heat treatment, wherein: (1) During refining, the steel plate is refined by LF+RH, so that the H content of the steel plate gas is 0.5ppm and the N content is 35ppm; (2) Rolling process: rough rolling temperature 900°C, finishing rolling temperature 700°C, water entry temperature 630°C; (3) Controlled cooling process during rolling process: the steel plate return temperature is limited to 400°C; (4) Heat treatment process: Tempering at 480°C to eliminate surface stress of the steel plate.

[0023] The mechanical properties of the thick Q500qF bridge slab obtained in this embodiment are shown in Table 2. Example 2

[0024] This embodiment provides a thick Q500qF bridge plate with a thickness of 110 mm. Some of its chemical components and mass percentages are shown in Table 1. The rest are Fe and unavoidable impurities, and the sum of the above components is 100%.

[0025] The production method of the above-mentioned Q500qF bridge plate has a production process including converter smelting, refining, continuous casting, billet heating, rolling and heat treatment, wherein: (1) During refining, the steel plate is refined by LF+RH, so that the H content of the steel plate gas is 0.4ppm and the N content is 32ppm; (2) Rolling process: rough rolling temperature 970°C, finishing rolling temperature 710°C, water entry temperature 600°C; (3) Controlled cooling process during rolling process: the steel plate red-return temperature is limited to 420°C; (4) Heat treatment process: Tempering at 490°C to eliminate surface stress of the steel plate.

[0026] The mechanical properties of the thick Q500qF bridge slab obtained in this embodiment are shown in Table 2. Example 3

[0027] This embodiment provides a thick Q500qF bridge plate with a thickness of 125 mm. Some of its chemical components and mass percentages are shown in Table 1. The rest are Fe and unavoidable impurities, and the sum of the above components is 100%.

[0028] The production method of the above-mentioned Q500qF bridge plate has a production process including converter smelting, refining, continuous casting, billet heating, rolling and heat treatment, wherein: (1) During refining, the steel plate is refined by LF+RH, so that the H content of the steel plate gas is 0.42ppm and the N content is 31ppm; (2) Rolling process: rough rolling temperature 960°C, finishing rolling temperature 720°C, water entry temperature 610°C; (3) Controlled cooling process during rolling process: the steel plate red-return temperature is limited to 435°C; (4) Heat treatment process: Tempering at 520°C to eliminate surface stress of the steel plate.

[0029] The mechanical properties of the thick Q500qF bridge slab obtained in this embodiment are shown in Table 2. Example 4

[0030] This embodiment provides a thick Q500qF bridge plate with a thickness of 130 mm. Some of its chemical components and mass percentages are shown in Table 1. The rest are Fe and unavoidable impurities, and the sum of the above components is 100%.

[0031] The production method of the above-mentioned Q500qF bridge plate has a production process including converter smelting, refining, continuous casting, billet heating, rolling and heat treatment, wherein: (1) During refining, the steel plate is refined by LF+RH, so that the H content of the steel plate gas is 0.35ppm and the N content is 30ppm; (2) Rolling process: rough rolling temperature 930°C, finishing rolling temperature 720°C, water entry temperature 600°C; (3) Controlled cooling process during rolling process: the steel plate red-return temperature is limited to 470°C; (4) Heat treatment process: Tempering at 540°C to eliminate surface stress of the steel plate.

[0032] The mechanical properties of the thick Q500qF bridge slab obtained in this embodiment are shown in Table 2. Example 5

[0033] This embodiment provides a thick Q500qF bridge plate with a thickness of 140 mm. Some of its chemical components and mass percentages are shown in Table 1. The rest are Fe and unavoidable impurities, and the sum of the above components is 100%.

[0034] The production method of the above-mentioned Q500qF bridge plate has a production process including converter smelting, refining, continuous casting, billet heating, rolling and heat treatment, wherein: (1) During refining, the steel plate is refined by LF+RH, so that the H content of the steel plate gas is 0.38ppm and the N content is 30ppm; (2) Rolling process: rough rolling temperature 920°C, finishing rolling temperature 700°C, water entry temperature 540°C; (3) Controlled cooling process during rolling process: the steel plate red-return temperature is limited to 480°C; (4) Heat treatment process: Tempering at 580°C to eliminate surface stress of the steel plate.

[0035] The mechanical properties of the thick Q500qF bridge slab obtained in this embodiment are shown in Table 2. Example 6

[0036] This embodiment provides a thick Q500qF bridge plate with a thickness of 145 mm. Some of its chemical components and mass percentages are shown in Table 1. The rest are Fe and unavoidable impurities, and the sum of the above components is 100%.

[0037] The production method of the above-mentioned Q500qF bridge plate has a production process including converter smelting, refining, continuous casting, billet heating, rolling and heat treatment, wherein: (1) During refining, the steel plate is refined by LF+RH, so that the H content of the steel plate gas is 0.45ppm and the N content is 25ppm; (2) Rolling process: rough rolling temperature 910°C, finishing rolling temperature 710°C, water entry temperature 510°C; (3) Controlled cooling process during rolling process: the steel plate red-return temperature is limited to 480°C; (4) Heat treatment process: Tempering at 590°C to eliminate surface stress of the steel plate.

[0038] The mechanical properties of the thick Q500qF bridge slab obtained in this embodiment are shown in Table 2. Example 7

[0039] This embodiment provides a thick Q500qF bridge plate with a thickness of 150 mm. Some of its chemical components and mass percentages are shown in Table 1. The rest are Fe and unavoidable impurities, and the sum of the above components is 100%.

[0040] The production method of the above-mentioned Q500qF bridge plate has a production process including converter smelting, refining, continuous casting, billet heating, rolling and heat treatment, wherein: (1) During refining, the steel plate is refined by LF+RH, so that the H content of the steel plate gas is 0.36ppm and the N content is 30ppm; (2) Rolling process: rough rolling temperature 900°C, finishing rolling temperature 700°C, water entry temperature 500°C; (3) Controlled cooling process during rolling process: the steel plate red-return temperature is limited to 490°C; (4) Heat treatment process: Tempering at 600°C to eliminate surface stress of the steel plate.

[0041] The mechanical properties of the thick Q500qF bridge slab obtained in this embodiment are shown in Table 2.

[0042] Table 1 Chemical composition of bridge plates of Examples 1-7 Example No. C（%） Mn (%) P（%） S（%） Cr（%） Nb(%) Mo (%) 1 0.07 1.70 0.012 0.003 0.35 0.015 0.15 2 0.08 1.75 0.010 0.002 0.42 0.035 0.25 3 0.08 1.83 0.008 0.003 0.51 0.040 0.28 4 0.07 1.91 0.008 0.002 0.57 0.041 0.35 5 0.09 1.95 0.006 0.002 0.65 0.039 0.40 6 0.11 1.97 0.010 0.002 0.68 0.042 0.41 7 0.10 2.00 0.010 0.003 0.70 0.045 0.45 Table 2 Mechanical properties data of bridge slabs of Examples 1-7 Example No. Yield StrengthMpa Tensile strengthMpa Elongation% Yield-to-strength ratio -60℃ impact energy J -60℃ impact section fiber rate% -60℃ aging impact energy (5% deformation) J 1 512 677 21 0.76 275，289，295 95，100，100 170，200，212 2 522 685 22 0.76 300，310，299 100，100，100 199，201，220 3 531 690 22 0.77 282，301，288 100，100，100 198，187，175 4 527 688 22.5 0.77 372，299，298 100，100，100 190，200，183 5 530 678 21 0.78 299，310，297 100，97，100 177，168，197 6 525 685 22 0.77 269，256，270 100，90，98 166，187，179 7 530 690 23 0.77 255，279，262 100，95，100 189，173，162 As can be seen from Tables 1 and 2, the production method of the present invention adopts a composition design with low C content, and obtains a bainite + ferrite + martensite multiphase structure steel plate by adding Nb, Cr, and Mo in a composite manner through a special rolling controlled cooling mode, ensuring that the strength, extremely low yield ratio, -60°C low-temperature impact, impact fiber rate and aging impact meet the requirements. These performance indicators can well improve the characteristics of steel plate welding and assembly to adapt to the characteristics of high altitude and complex laying environment in the western region.

[0043] In addition to the above embodiments, the present invention may also have other implementation modes. Any technical solution formed by equivalent replacement or equivalent transformation falls within the protection scope required by the present invention.

Claims

1. A thick Q500qF bridge plate, characterized in that: The chemical composition of the bridge plate is calculated by mass percentage as follows: C: 0.07-0.11%, Mn: 1.70-2.00%, Cr: 0.35-0.70%, P≤0.015%, S≤0.005%, Nb: 0.015-0.045%, Mo: 0.15-0.45%, and the rest are Fe and unavoidable impurities. The sum of the above components is 100%.

2. A method for producing a thick Q500qF bridge plate according to claim 1, characterized in that: The production process includes converter smelting, refining, continuous casting, billet heating, rolling and heat treatment, among which: (1) Rolling process: rough rolling temperature 900-980℃, finishing rolling temperature 700-750℃, water entry temperature 500-630℃; (2) Controlled cooling process during rolling process: the steel plate red-return temperature is limited to 400-500℃; (3) Heat treatment process: Tempering at 480-600℃ to eliminate surface stress of the steel plate.

3. The method for producing a thick Q500qF bridge plate according to claim 2, characterized in that: During the refining, the steel plate is refined by LF+RH, so that the H content of the steel plate gas is ≤0.5ppm and the N content is ≤35ppm.

4. The method for producing a thick Q500qF bridge plate according to claim 2, characterized in that: The thickness of the produced bridge slabs is 100-150mm.

5. The method for producing a thick Q500qF bridge plate according to claim 2, characterized in that: The yield strength of the produced bridge panels is ≥500Mpa, the tensile strength is 630-750Mpa, the elongation is ≥18%, the conventional impact at -60℃ is ≥250J, and the yield strength ratio is ≤0.

86.

6. The method for producing a thick Q500qF bridge plate according to claim 2, characterized in that: The fiber ratio of the impact section of the produced bridge plate is ≥90%, and the aging impact performance of 5% deformation is ≥150J.