Q345qF bridge plate for extremely cold area and preparation method of Q345qF bridge plate

Abstract

The invention discloses an extremely cold area Q345qF bridge plate and a preparation method thereof, and relates to the technical field of metallurgy. The extremely cold area Q345qF bridge plate comprises the following chemical components in percentage by mass: 0.07-0.11% of C, 1.00-1.60% of Mn, 0.01-0.20% of Cr, less than or equal to 0.010% of P, less than or equal to 0.005% of S, 0.005-0.015% of Nb and the balance of Fe and inevitable impurities. The component design with low C content is adopted, the pearlite and ferrite multi-phase structure steel plate is obtained by adding Nb and Cr for compounding through a special rolling and cooling control mode, and it is guaranteed that the strength, the extremely low yield ratio, low-temperature impact at the temperature of-60 DEG C and aging impact meet the requirements.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of metallurgy, in particular to a Q345qF bridge plate in an extremely cold region and a preparation method thereof. BACKGROUND

[0002] With the increasing application of high-strength bridge steel to national key projects, especially the increasing investment of the motherland in the construction of western regions, which belong to extremely cold regions, high altitudes and complex terrain remote areas, the steel for assembly design projects is complex and has high performance requirements, and large-thickness steel plates are needed to reduce the welding amount of butt welds and reduce construction difficulty. At the same time, the environment in such areas is complex, and the safety of bridge construction should be fully considered during design, so it is necessary to develop cold-resistant bridge plates with large width and high performance requirements to improve the fracture toughness, low-temperature toughness and seismic performance of the steel.

[0003] Patent CN 114262845 B discloses a 500Mpa grade thin specification bridge plate and a production method thereof, which relates to a production method of a 6-16m specification bridge plate with a TMCP state delivery, a strength grade of 500Mpa or more and no tempering, and the thickness range of the produced steel plate is small, which cannot meet the requirements of high-cold, high-altitude and complex terrain remote areas.

[0004] Therefore, it is an urgent technical problem for those skilled in the art to develop an extremely cold region Q345qF bridge plate and a production method thereof that can overcome the above defects. SUMMARY

[0005] The technical problem to be solved by the present application is to overcome the shortcomings of the prior art and provide an extremely cold region Q345qF bridge plate and a preparation method thereof.

[0006] In order to solve the above technical problems, the technical scheme of the present application is as follows: An extremely cold region Q345qF bridge plate, the chemical composition and mass percentage of which are as follows: C: 0.07-0.11%, Mn: 1.00-1.60%, Cr: 0.01-0.20%, P≤0.010%, S≤0.005%, Nb: 0.005-0.015%, and the rest is Fe and unavoidable impurities.

[0007] The present application also provides a preparation method of an extremely cold region Q345qF bridge plate, which comprises the following steps in sequence: converter smelting, refining, continuous casting, casting blank heating, rolling and heat treatment. In the rolling process, the rough rolling temperature is controlled to be 900-980℃, the finish rolling temperature is controlled to be 800-850℃, and the water inlet temperature is controlled to be 700-730℃.

[0008] As a preferred scheme of the preparation method of the Q345qF bridge plate in the extremely cold region according to the application, the rolling process further comprises: controlling the red temperature of the steel plate to be 630-550 DEG C.

[0009] As a preferred scheme of the preparation method of the Q345qF bridge plate in the extremely cold region according to the application, in the heat treatment process, the tempering temperature is controlled to be 480-600 DEG C.

[0010] As a preferred scheme of the preparation method of the Q345qF bridge plate in the extremely cold region according to the application, the refining process comprises: LF+RH refining is adopted, and the content of gas H in the steel plate is controlled to be less than or equal to 0.2 ppm, and the content of N is controlled to be less than or equal to 25 ppm.

[0011] As a preferred scheme of the preparation method of the Q345qF bridge plate in the extremely cold region according to the application, the thickness of the prepared bridge plate is 10-60 mm.

[0012] As a preferred scheme of the preparation method of the Q345qF bridge plate in the extremely cold region according to the application, the yield strength of the prepared bridge plate is greater than or equal to 345 MPa, the tensile strength is 490-610 MPa, the elongation is greater than or equal to 23%, the conventional impact at-60 DEG C is greater than or equal to 250 J, and the yield strength ratio is less than or equal to 0.80.

[0013] As a preferred scheme of the preparation method of the Q345qF bridge plate in the extremely cold region according to the application, the aging impact performance of the prepared bridge plate at 5% deformation is greater than or equal to 200 J.

[0014] The application has the following beneficial effects: (1) The application adopts a composition design with low C content, and through the addition of Nb and Cr in a compound manner, a pearlite + ferrite multi-phase structure steel plate is obtained through a special rolling and controlled cooling mode, so that the strength, the extremely low yield strength ratio, the low temperature impact at-60 DEG C and the aging impact meet the requirements.

[0015] (2) The application adopts a low temperature austenitizing technology, reduces the original austenite grain size, ensures the stability of the low temperature impact toughness of the product, controls the second opening temperature, the finish rolling temperature and the relaxation technology, cooperates with the water cooling process, effectively reduces the yield strength of the product, ensures the stability of the tensile strength, and stabilizes the yield strength ratio of the product; the controlled cooling process is controlled to effectively refine the grain size, the second opening temperature and the water inlet temperature are controlled to ensure the organization transformation, a polygonal ferrite and pearlite multi-phase structure is obtained, and the strength and toughness of the steel plate are improved. Compared with the Q345qF steel plate produced by the current ordinary hot rolling, the yield strength ratio is high, the weldability is poor, and the impact toughness is small.

[0016] (3) The rolling process provided by the application is as follows: the rough rolling temperature is 900-980 DEG C, the finish rolling temperature is 800-850 DEG C, and the water entry temperature is 700-730 DEG C. 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 transition zone, so that a batch of dislocations is formed in the steel plate and a large distortion energy is left, and the purpose of repeatedly refining the austenite grains is achieved. Therefore, in the subsequent controlled cooling process, fine ferrite and pearlite grains are generated, thereby ensuring the low yield ratio and low temperature impact toughness of the steel plate. At the same time, by controlling the water entry temperature and using the relaxation technology, the ferrite content is increased, and the yield ratio is more effectively reduced. The controlled cooling process of the application adopts rapid cooling ACC cooling, and the re-red temperature is 630-550 DEG C, so as to ensure the completion of the pearlite phase transition in the full thickness direction and improve the high strength and toughness of the steel plate. At the same time, the high re-red temperature can avoid the secondary buckling of the steel plate due to uneven cooling, ensure the flatness of the steel plate, and reduce the generation of waste plates.

[0017] (4) In the heat treatment process provided by the application, tempering is carried out at a temperature of 480-600 DEG C to eliminate the surface stress of the steel plate and improve the mechanical properties. DETAILED DESCRIPTION

[0018] In order to make the content of the application more easily understood, the application will be further described in detail according to the specific embodiments.

[0019] Example 1: The present embodiment provides an extremely cold area Q345qF bridge plate with a thickness of 10 mm. The partial chemical component composition and mass percentage are shown in Table 1. The rest is Fe and unavoidable impurities. The sum of the above components is 100%.

[0020] The present embodiment also provides a preparation method of an extremely cold area Q345qF bridge plate. The production process includes converter smelting, refining, continuous casting, billet heating, rolling and heat treatment. Among them: (1) In the refining process, the steel plate is refined by LF+RH, so that the content of gas H in the steel plate is 0.1 ppm, and the content of N is 25 ppm; (2) Rolling process: rough rolling temperature 900 DEG C, finish rolling temperature 800 DEG C, water entry temperature 730 DEG C; (3) Controlled cooling process in the rolling process: the re-red temperature of the steel plate is limited to 630 DEG C; (4) Heat treatment process: tempering is carried out at a temperature of 480 DEG C to eliminate the surface stress of the steel plate.

[0021] The mechanical properties of the Q345qF bridge plate obtained in the present embodiment are shown in Table 2.

[0022] Embodiment 2: The embodiment provides an extremely cold area Q345qF bridge plate with a thickness of 18 mm, part of the chemical component composition and mass percentage are shown in Table 1, the rest is Fe and inevitable impurities, and the sum of the above components is 100%.

[0023] The embodiment also provides a preparation method of the extremely cold area Q345qF bridge plate, and the production process comprises converter smelting, refining, continuous casting, casting blank heating, rolling and heat treatment. (1) In the refining process, the LF+RH refining is used for the steel plate, so that the content of gas H in the steel plate is 0.17 ppm, and the content of N is 22 ppm; (2) The rolling process: the rough rolling temperature is 970 DEG C, the finish rolling temperature is 810 DEG C, and the water inlet temperature is 715 DEG C; (3) In the rolling process, the controlled cooling process: the red return temperature of the steel plate is limited to 600 DEG C; (4) The heat treatment process: tempering is carried out at a temperature of 490 DEG C, and the surface stress of the steel plate is eliminated.

[0024] The mechanical properties of the Q345qF bridge plate obtained in the embodiment are shown in Table 2.

[0025] Embodiment 3: The embodiment provides an extremely cold area Q345qF bridge plate with a thickness of 28 mm, part of the chemical component composition and mass percentage are shown in Table 1, the rest is Fe and inevitable impurities, and the sum of the above components is 100%.

[0026] The embodiment also provides a preparation method of the extremely cold area Q345qF bridge plate, and the production process comprises converter smelting, refining, continuous casting, casting blank heating, rolling and heat treatment. (1) In the refining process, the LF+RH refining is used for the steel plate, so that the content of gas H in the steel plate is 0.12 ppm, and the content of N is 21 ppm; (2) The rolling process: the rough rolling temperature is 960 DEG C, the finish rolling temperature is 820 DEG C, and the water inlet temperature is 710 DEG C; (3) In the rolling process, the controlled cooling process: the red return temperature of the steel plate is limited to 600 DEG C; (4) The heat treatment process: tempering is carried out at a temperature of 520 DEG C, and the surface stress of the steel plate is eliminated.

[0027] The mechanical properties of the Q345qF bridge plate obtained in the embodiment are shown in Table 2.

[0028] Embodiment 4: The embodiment provides an extremely cold area Q345qF bridge plate with a thickness of 38 mm, part of the chemical component composition and mass percentage are shown in Table 1, the rest is Fe and inevitable impurities, and the sum of the above components is 100%.

[0029] The embodiment also provides a preparation method of the Q345qF bridge plate in an extremely cold region, and the production process comprises converter smelting, refining, continuous casting, casting blank heating, rolling and heat treatment. (1) The LF+RH refining is used for the steel plate in the refining, so that the content of gas H in the steel plate is 0.05 ppm, and the content of N is 20 ppm; (2) Rolling process: the rough rolling temperature is 930 DEG C, the finish rolling temperature is 830 DEG C, and the water inlet temperature is 700 DEG C; (3) The controlled cooling process in the rolling process: the red return temperature of the steel plate is limited to 570 DEG C; (4) Heat treatment process: tempering is carried out at 540 DEG C, and the surface stress of the steel plate is eliminated.

[0030] The mechanical properties of the Q345qF bridge plate obtained in the embodiment are shown in Table 2.

[0031] In the embodiment, a Q345qF bridge plate in an extremely cold region is provided, and the thickness of the Q345qF bridge plate is 45 mm, the partial chemical component composition and the mass percentage content are shown in Table 1, the rest is Fe and inevitable impurities, and the sum of the above components is 100%.

[0032] The embodiment also provides a preparation method of the Q345qF bridge plate in an extremely cold region, and the production process comprises converter smelting, refining, continuous casting, casting blank heating, rolling and heat treatment. (1) The LF+RH refining is used for the steel plate in the refining, so that the content of gas H in the steel plate is 0.05 ppm, and the content of N is 20 ppm; (2) Rolling process: the rough rolling temperature is 930 DEG C, the finish rolling temperature is 830 DEG C, and the water inlet temperature is 700 DEG C; (3) The controlled cooling process in the rolling process: the red return temperature of the steel plate is limited to 570 DEG C; (4) Heat treatment process: tempering is carried out at 540 DEG C, and the surface stress of the steel plate is eliminated.

[0033] The mechanical properties of the Q345qF bridge plate obtained in the embodiment are shown in Table 2.

[0034] In the embodiment, a Q345qF bridge plate in an extremely cold region is provided, and the thickness of the Q345qF bridge plate is 45 mm, the partial chemical component composition and the mass percentage content are shown in Table 1, the rest is Fe and inevitable impurities, and the sum of the above components is 100%.

[0035] The embodiment also provides a preparation method of the Q345qF bridge plate in an extremely cold region, and the production process comprises converter smelting, refining, continuous casting, casting blank heating, rolling and heat treatment. (1) The LF+RH refining is used for the steel plate in the refining, so that the content of gas H in the steel plate is 0.05 ppm, and the content of N is 20 ppm; (2) Rolling process: roughing temperature 910℃, finishing temperature 810℃, water immersion temperature 710℃; (3) Controlled cooling process in rolling: The temperature of the steel plate when it turns red is limited to 560℃; (4) Heat treatment process: Tempering is carried out at a temperature of 590℃ to eliminate surface stress of the steel plate.

[0036] The mechanical properties of the Q345qF bridge deck obtained in this implementation are shown in Table 2.

[0037] Example 7: This example provides a Q345qF bridge plate for extremely cold regions with a thickness of 60mm. Its chemical composition and mass percentage are shown in Table 1. The remainder is Fe and unavoidable impurities. The sum of the above components is 100%.

[0038] This embodiment also provides a method for preparing Q345qF bridge plates for extremely cold regions. The production process includes converter smelting, refining, continuous casting, billet heating, rolling, and heat treatment. Wherein: (1) During refining, the steel plate is refined using LF+RH, resulting in a gas H content of 0.12ppm and a N content of 20ppm. (2) Rolling process: roughing temperature 900℃, finishing temperature 850℃, water immersion temperature 700℃; (3) Controlled cooling process in rolling: The temperature of the steel plate when it turns red is limited to 550℃; (4) Heat treatment process: Tempering is carried out at 600℃ to eliminate surface stress of steel plate.

[0039] The mechanical properties of the Q345qF bridge deck obtained in this implementation are shown in Table 2.

[0040] Table 1. Chemical composition of bridge plates in Examples 1-7

[0041] Table 2. Mechanical performance data of bridge decks in Examples 1-7

[0042] As can be seen from Tables 1 and 2, the preparation method provided in this application adopts a low C content composition design, and obtains a pearlite + ferrite multiphase steel plate by adding Nb, Cr and Mo composite and through a special rolling controlled cooling mode. This ensures that the strength, extremely low yield strength ratio, -60℃ low temperature impact and aging impact meet the requirements. These performance indicators can greatly improve the welding and assembly characteristics of the steel plate to adapt to the characteristics of high altitude and complex laying environment in western regions.

[0043] In addition to the above embodiments, the present invention may have other implementation methods; all technical solutions formed by equivalent substitution or equivalent transformation fall within the protection scope claimed by the present invention.

Claims

1. A Q345qF bridge slab for extremely cold regions, characterized in that: Its chemical composition and mass percentage are as follows: C: 0.07-0.11%, Mn: 1.00-1.60%, Cr: 0.01-0.20%, P≤0.010%, S≤0.005%, Nb: 0.005-0.015%, with the remainder being Fe and unavoidable impurities.

2. A method for preparing a Q345qF bridge plate for extremely cold regions as described in claim 1, characterized in that: The process includes the following steps in sequence: converter smelting, refining, continuous casting, billet heating, rolling and heat treatment; In the rolling process, the roughing temperature is controlled at 900-980℃, the finishing temperature at 800-850℃, and the water immersion temperature at 700-730℃.

3. The method for preparing Q345qF bridge deck for extremely cold regions according to claim 2, characterized in that: The rolling process also includes controlling the reddening temperature of the steel plate to 630-550℃.

4. The method for preparing Q345qF bridge deck for extremely cold regions according to claim 2, characterized in that: In the heat treatment process, the tempering temperature is controlled at 480-600℃.

5. The method for preparing Q345qF bridge deck for extremely cold regions according to claim 2, characterized in that: The refining process includes: LF+RH refining, and controlling the H content of the steel plate gas to be ≤0.2ppm and the N content to be ≤25ppm.

6. The method for preparing Q345qF bridge deck for extremely cold regions according to claim 2, characterized in that: The thickness of the bridge slab produced is 10~60mm.

7. The method for preparing Q345qF bridge deck for extremely cold regions according to claim 2, characterized in that: The resulting bridge deck has a yield strength ≥345 MPa, tensile strength 490-610 MPa, elongation ≥23%, conventional impact strength at -60℃ ≥250 J, and yield strength ratio ≤0.

80.

8. The method for preparing Q345qF bridge deck for extremely cold regions according to claim 2, characterized in that: The bridge slab with 5% deformation has an aging impact performance of ≥200J.

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