A fire-resistant and weather-resistant steel for welded structures with a tensile strength of 900 MPa and its production method

Abstract

The present invention relates to a fire-resistant and weather-resistant steel for welded structures with a tensile strength of 900 MPa and a production method thereof. The steel contains chemical components with the following mass percentage contents: C: 0.010 - 0.040%, Si: 0.10 - 0.20%, Mn: 1.71 - 2.23%, P ≤ 0.001%, S ≤ 0.001%, Mo: 0.51 - 0.74%, Cr: 0.42 - 0.65%, Cu: 0.15 - 0.25%, Ni: 0.42 - 0.64%, Nb: 0.061 - 0.082%, V: 0.065 - 0.087%, Ti: 0.007 - 0.021%, Ca: 0.0007 - 0.0020%, Mg: 0.0008 - 0.0023%, Sn: 0.007 - 0.022%, [O]: 0.0013 - 0.0022%, [N] ≤ 0.0018%, As ≤ 0.0005%, and the balance is Fe and inevitable impurities. At the same time, the above chemical components must also satisfy: 17Cu + 4Ni = 5 - 6%, (2Mo + 3Cr) / 3Ni = 1.2 - 2.5, (Ca + Mg + Sn / 9) / [O] = 2 - 3; the production steps include: converter smelting, secondary refining, slab heating, controlled rolling, laminar cooling, and tempering treatment; the manufacturing process of the present invention is simple, the production cycle is short, and it is easy to be implemented on a large scale in each metallurgical enterprise. The finished steel plate has characteristics such as high strength and toughness, fire resistance and weather resistance, resistance to lamellar tearing, a low yield ratio, and excellent welding performance.

Description

Technical Field

[0001] The present invention relates to the technical field of low alloy steel production, in particular to a fire-resistant and weather-resistant steel for welded structures with a tensile strength of 900 MPa and a production method thereof. Background Art

[0002] In recent years, the safety of steel structure projects in fields such as high-rise buildings under fire has received increasing attention. In addition to the conventional properties of steel, special property requirements such as fire resistance, disaster resistance, and corrosion resistance have been put forward to reduce casualties and property losses in the event of a fire. That is, it is required that the steel has excellent high-temperature creep performance and corrosion resistance, which can not only reduce the thickness of fireproof coatings and weather-resistant coatings, but also improve the utilization efficiency of resources and energy. Therefore, in order to achieve sustainable development, alleviate the overcapacity in the steel industry, and practice the supply-side structural reform of the steel industry, it is necessary to develop high-performance structural steel with composite functions of earthquake resistance, corrosion resistance, and fire resistance.

[0003] Before the present invention, the invention products disclosed in Chinese invention patent applications 201310160484.1, 201310033300.52, 201110080774.6, 201110247615.0, 200910045146.7, 201110247615.0, 200910011963.0, 200910272414.9, 200910045146.7, 201110080774.6, 201110247615.0 all have good fire resistance, but do not have corrosion resistance; otherwise, the invention products disclosed in Chinese invention patent applications 201010113848.7, 200910056602.8, 200910180490.7, 200910056602.8 all have good corrosion resistance, but do not have fire resistance.

[0004] Chinese invention patent CN1354273A discloses a high-performance fire-resistant and weather-resistant building steel and a production method thereof. The invention product contains C, Si, Mn, P, S, Cr, Mo, Ti, Als, N, O, Cr, Ni, Cu, Ca, B, and also contains one or more of Nb, V, RE. After smelting, rolling, and heat treatment, the product has excellent fire resistance and weather resistance, but the invention product requires normalizing + tempering treatment and has a low strength level.

[0005] Chinese invention patents CN103695772A and CN103695773A respectively disclose a fire-resistant, weather-resistant and earthquake-resistant building steel with a yield strength of 550 MPa and its production method, and a fire-resistant, weather-resistant and earthquake-resistant building steel with a yield strength of 690 MPa and its production method. The building steels of these two invention patent applications contain C, Si, Mn, P, S, Nb, Ti, Mo, W, Mg, O, and in addition, contain Sb or Zr or a mixture of the two in any proportion. Through processes such as hot metal desulfurization, converter smelting, vacuum treatment, addition of Mg element, conventional continuous casting, heating of the slab, sectional rolling, and cooling after finish rolling, the steel has excellent fire resistance, weather resistance and earthquake resistance performance, and excellent comprehensive performance. However, the disadvantages of these two invention patents are that the corrosion resistance is not very ideal, and only -20°C impact is required.

[0006] Chinese invention patents 202010127534.6 and 202010013530.5 respectively disclose a fire-resistant and weather-resistant steel plate for building structures with a yield strength of 690 MPa and its manufacturing method, and a fire-resistant, earthquake-resistant and corrosion-resistant medium plate steel with a yield strength of 690 MPa and its manufacturing method. These two invention patents contain C, Si, Mn, P, S, Nb, V, Ti, Mo, Cr, Cu, Ni, Al. After rolling, the steel plates need to be subjected to two-phase region tempering treatment. The steel plates have good fire resistance and weather resistance. However, the above patents all contain relatively more Cu and Ni elements, and only require -40°C impact toughness.

[0007] Chinese invention patent 202010804777.9 discloses a fire-resistant steel for welded structures with excellent high-temperature creep fracture performance at 700°C and its production method. The product of this invention has characteristics such as excellent fire resistance, high-temperature creep performance and welding performance. However, this invention does not have corrosion resistance, and the strength level is relatively low. Chinese invention patent 202110945932.3 discloses a high-performance corrosion-resistant and fire-resistant steel with excellent -80°C low-temperature toughness and its production method. The product of this invention has high strength, excellent low-temperature toughness, fire resistance and weather resistance performance, as well as good welding performance and cold working performance. However, the product of this invention contains relatively more precious alloys such as Cu, Cr, Ni, etc., and is not easy to implement on a large scale. Another Chinese invention patent 202210572091.0 discloses a corrosion-resistant and fire-resistant steel with excellent high-temperature creep performance under uniaxial tension and its production method. The finished steel plate of this invention has characteristics such as high strength and toughness, high weather resistance and excellent high-temperature creep performance. However, the product of this invention contains relatively more precious alloys such as Cu, Ni, etc., and does not have requirements for weldability. Summary of the Invention

[0008] The present invention provides a fire-resistant and weather-resistant steel for welded structures with a tensile strength of 900 MPa and a production method thereof, aiming to overcome the current deficiencies in the technical field. The manufacturing process of the present invention is simple and the production cycle is short, and it can be implemented on a large scale in each metallurgical enterprise. The finished steel plate has characteristics such as high strength and toughness, fire resistance and weather resistance, resistance to lamellar tearing, a low yield ratio, and excellent welding performance.

[0009] A fire-resistant and weather-resistant steel for welded structures with a tensile strength of 900 MPa according to the present invention, the steel contains chemical components with the following mass percentage contents: C: 0.010 - 0.040%, Si: 0.10 - 0.20%, Mn: 1.71 - 2.23%, P ≤ 0.001%, S ≤ 0.001%, Mo: 0.51 - 0.74%, Cr: 0.42 - 0.65%, Cu: 0.15 - 0.25%, Ni: 0.42 - 0.64%, Nb: 0.061 - 0.082%, V: 0.065 - 0.087%, Ti: 0.007 - 0.021%, Ca: 0.0007 - 0.0020%, Mg: 0.0008 - 0.0023%, Sn: 0.007 - 0.022%, [O]: 0.0013 - 0.0022%, [N] ≤ 0.0018%, As ≤ 0.0005%, and the balance is Fe and unavoidable impurities. At the same time, the above chemical components must also satisfy the following relationships: (1) 17Cu + 4Ni = 5 - 6%, (2) (2Mo + 3Cr) / 3Ni = 1.2 - 2.5, (3) (Ca + Mg + Sn / 9) / [O] = 2 - 3.

[0010] Preferably, in the above chemical components, Sn: 0.010 - 0.020%, As ≤ 0.0003%.

[0011] The microstructure of the finished steel plate prepared from the above chemical components is lath bainite + a small amount of granular bainite + quasi-polygonal ferrite with a volume percentage > 12 - 15% + M / A island structure with a volume percentage > 10 - 13%. Among them, the width of more than 90% of the lath bainite ≤ 0.87 μm, and the width of the M / A island ≤ 0.32 μm.

[0012] The ReL of the finished steel plate prepared from the above chemical components is 742.3 - 772.1 MPa, the Rm is 948.2 - 964.1 MPa, the ReL / Rm is 0.779 - 0.801, the A is 26.55 - 28.75%, the reduction of area Z in the thickness direction is 55.4 - 64.1%, the -80°C KV2 is 245.2 - 275.5 J, and the high-temperature yield strength R P0.2 at 700°C is 529.3 - 561.4 MPa, R P0.2 / ReL ranges from 0.704 to 0.741, and the corrosion weight loss rate ranges from 0.2253 to 0.2418 g / m 2 ·h. The Charpy V-notch impact energy of the submerged arc welding HAZ at -80°C is 167.5 - 184.6 J.

[0013] A production method of a fire-resistant and weather-resistant steel for welded structures with a tensile strength of 900 MPa according to the present invention includes the following steps:

[0014] 1) Converter smelting: Adopt a double slag method for ultra-low phosphorus smelting process, with top and bottom combined blowing throughout the process, lance position of 1.6 - 1.7 m, slag basicity of 2.1 - 2.2, and oxygen supply intensity of 3.6 - 3.7 m 3 / t·min;

[0015] 2) Secondary refining: Adopt an operation mode of pre-adding aluminum ingots, lime, heating, and intermittent circulation desulfurization to reduce nitrogen absorption. The LHF treatment time is 40 - 50 min, CaO / CaF2 = 3.8 - 3.9, slag basicity is 4.2 - 4.4, white slag time ≥ 12 min, and the end point [S] ≤ 10 ppm; the RH vacuum degree ≤ 50 Pa, and the treatment time is 15 - 22 min;

[0016] 3) Slab heating: The heating temperature is 1300 - 1320°C, the holding temperature is 1240 - 1260°C, and the holding time is 55 - 65 min;

[0017] 4) Controlled rolling: In the first stage, the rough rolling starting temperature is 1060 - 1080°C, the final rolling temperature ≤ 1050°C, the number of rolling passes is 7 - 9 times, the reduction per pass is 22 - 28 mm, and the total reduction rate ≥ 55%; in the second stage, the finishing rolling starting temperature ≤ 980°C, the final rolling temperature is (887 - 4h / 5) ± 5°C, where h is the thickness value of the finished steel plate in mm;

[0018] 5) Lamellar cooling: The starting cooling temperature is (743 + 3h / 4) ± 3°C, and the recrystallization temperature is 250 - 350°C, where h is the thickness value of the finished steel plate in mm;

[0019] 6) Tempering treatment: The tempering temperature is 650 - 720°C, and the time in the furnace is [(2.25 - 2.75) × h] min. After the steel plate is taken out of the furnace, it is air-cooled to room temperature, where h is the thickness value of the finished steel plate in mm.

[0020] The reasons for the limited quantitative components in the present invention are described in detail below:

[0021] The C content of the present invention is selected to be 0.010 - 0.040%. C has a significant interstitial solid solution strengthening effect in steel and is one of the essential elements to ensure the strength of the steel plate. However, if its content is too high, it will sharply deteriorate the welding performance, low-temperature toughness and ductility of the steel. In addition, the fine carbonitride particles formed by C with Nb, V, and Ti in the steel have strong grain refinement and precipitation strengthening effects, improving both strength and low-temperature toughness simultaneously. During tempering, C can form high-melting-point and highly corrosion-resistant carbides with Mo and Cr, enhancing the fire and weather resistance. When the C content is lower than 0.010%, the above effects are limited. When the C content is higher than 0.040%, it is not conducive to the performance of the products of the present invention. Therefore, the C content is limited to 0.010 - 0.040%.

[0022] The Si content of the present invention is selected to be 0.10 - 0.20%. Si has a solid solution strengthening and deoxidizing effect, but it is not conducive to low-temperature toughness and ductility. In addition, Ca, Mg, and Sn in the present invention can all play a role in deoxidation. Therefore, considering the performance of the products of the present invention comprehensively, the Si content is limited to 0.10 - 0.20%.

[0023] The Mn content of the present invention is selected to be 1.71 - 2.23%. Mn has the effect of refining grains and is an important element to ensure the strength and low-temperature toughness of the steel. However, if the Mn content is too high, it will significantly increase the sensitivity to welding cracks and is not conducive to the welding performance. Therefore, considering the performance of the products of the present invention comprehensively, the Mn content is limited to 1.71 - 2.23%.

[0024] For the present invention, P ≤ 0.001% and S ≤ 0.001%. P and S are harmful elements. They are both prone to segregate at grain boundaries, reducing the grain boundary strength and increasing the grain boundary brittleness, which is not conducive to the welding performance, low-temperature toughness and high-temperature performance. In addition, S is also prone to form MnS composite inclusions, damaging the performance of the steel. Therefore, considering the performance of the products of the present invention, the contents of P and S should be reduced as much as possible.

[0025] The Mo content of the present invention is selected to be 0.51 - 0.74%. Mo mainly improves the room-temperature strength and high-temperature performance in the form of solid solution strengthening. In addition, Mo can not only effectively promote the formation of high-density dislocation bainite, but also promote the uniform precipitation of NbC particles, preventing the aggregation and growth of NbC particles at high temperatures. At the same time, high-melting-point Mo carbides can be formed during tempering, enhancing the fire resistance. However, if the Mo content is too high, it will significantly reduce the low-temperature toughness and welding performance, increasing the manufacturing cost and being not conducive to implementation. Therefore, considering the performance of the products of the present invention comprehensively, the Mo content is limited to 0.51 - 0.74%.

[0026] In the present invention, the Cr content is selected to be 0.42 - 0.65%. Cr can also improve the room temperature strength and high temperature performance by solid solution strengthening. Cr and O can form a dense oxide protective film on the steel plate surface to improve the weather resistance. During tempering, Cr can also form high melting point Cr carbides to improve the fire resistance. However, too high Cr content will increase the ductile-brittle transition temperature, which is not conducive to low temperature toughness and welding performance. Therefore, the Cr content is limited to 0.42 - 0.65%.

[0027] In the present invention, the Cu content is selected to be 0.15 - 0.25%. Cu can improve the strength and corrosion resistance, and ε-Cu precipitates during tempering to improve the strength. However, too high Cu content is not conducive to low temperature toughness and welding performance. Therefore, the Cu content is limited to 0.15 - 0.25%.

[0028] In the present invention, the Ni content is selected to be 0.42 - 0.64%. An appropriate amount of Ni is an indispensable element to ensure low temperature toughness. When compounded with an appropriate amount of Cr and Cu, it can significantly improve the corrosion resistance, improve the low temperature toughness, and reduce the slab crack tendency. However, when the Ni content is too high, a large amount of scale that is difficult to remove is easily formed, deteriorating the surface quality and increasing the manufacturing cost. Therefore, considering the product performance of the present invention comprehensively, the Ni content is limited to 0.42 - 0.64%.

[0029] In the present invention, the Nb content is selected to be 0.061 - 0.082%. An appropriate amount of Nb can form fine carbonitride particles with C and N to prevent the growth of austenite grains, thereby refining the grains, playing a role in fine grain strengthening and precipitation strengthening, and improving the strength and low temperature toughness. Especially when added with Mo at the same time, Mo promotes the uniform precipitation of NbC particles and prevents the aggregation and growth of NbC particles at high temperatures, improving the high temperature performance. When Nb is added with V and Ti at the same time, it can also significantly increase the recrystallization temperature, broaden the rolling range of the non-recrystallized zone, facilitate hot rolling, improve the rolling efficiency, and reduce equipment wear. When the Nb content is too high, the Nb carbonitrides are prone to aggregate and grow, and at the same time increase the tendency of Nb-containing complex inclusions, which has an adverse effect on the products of the present invention. Therefore, the Nb content is limited to 0.061 - 0.082%.

[0030] In the present invention, the V content is selected to be 0.065 - 0.087%. Most of V is dissolved in the matrix, and it can form fine carbonitride particles with C and N to prevent the growth of austenite grains, playing a role in fine grain strengthening and precipitation strengthening, and improving the strength and low temperature toughness. In addition, the fine V carbonitride particles have good stability at high temperatures, can prevent the movement of grain boundaries at high temperatures, delay crack propagation, and improve the high temperature performance. However, when the V content is too high, more V is dissolved in the matrix, which is not conducive to low temperature toughness. Therefore, V is limited to 0.065 - 0.087%.

[0031] The Ti content of the present invention is selected to be 0.007-0.021%. When Ti, Nb and V are added simultaneously, the recrystallization temperature can be significantly increased, the rolling range of the non-recrystallization zone can be widened, high-temperature rolling can be facilitated, rolling efficiency can be improved, and equipment wear can be reduced. The fine carbonitride particles formed by Ti, Nb, C and N not only prevent the growth of austenite grains during the heating process of the ingot, but also have significant fine grain strengthening and precipitation strengthening effects to improve strength and low-temperature toughness. In addition, the fine TiN particles can prevent the growth of austenite grains during welding and effectively improve the low-temperature toughness of the welding heat-affected zone. However, when the Ti content is too high, large composite inclusions containing Ti are easily formed, thereby damaging ductility, lamellar tear resistance, low-temperature toughness and welding performance. Therefore, Ti is limited to 0.007-0.021%.

[0032] The Ca content of the present invention is selected to be 0.0007-0.0020%. Ca can spheroidize the modified sulfide inclusions and purify the steel. Its oxide material points can serve as the nucleation core of AF, promote the formation of AF, refine the grains, and improve the low-temperature toughness, lamellar tear resistance and low-temperature toughness of the steel heat-affected zone. When the Ca content is too high, large-sized composite inclusions are easily formed, which reduces the purity of the steel and is not conducive to low-temperature toughness, lamellar tear resistance and low-temperature toughness of the heat-affected zone. Therefore, Ca is limited to 0.0007-0.0020%.

[0033] The Mg content of the present invention is selected to be 0.0008-0.0023%. Mg is an important element to ensure the performance of the product of the present invention. It can not only spheroidize the modified sulfide inclusions and purify the steel, but also its nano-scale MgO particles can serve as AF nucleation cores to promote AF formation, refine the AF effective grain size, and improve low-temperature toughness and HAZ toughness. When the Mg content is too high, large-sized composite inclusions are easily formed, which reduces the purity of the steel and is not conducive to low-temperature toughness. Therefore, Mg is limited to 0.0008-0.0023%.

[0034] The Sn content of the present invention is selected to be 0.007-0.022%. Sn is an important element to ensure the weather resistance of the product of the present invention. It forms a dense oxide SnO2 film with O in steel, thereby significantly improving the corrosion resistance. When the Sn content is less than 0.007%, the above effect is limited; but excessive Sn is easy to segregate at the grain boundary, destroy the grain boundary continuity, reduce the grain boundary strength, increase the grain boundary brittleness, and increase the tendency of intergranular fracture, which is not conducive to processing performance, welding performance and low-temperature toughness. At the same time, excessive Sn is also easy to form complex large inclusions with MnS, reduce the purity of steel, and is not conducive to the performance of the product of the present invention. Therefore, considering the performance of the product of the present invention comprehensively, Sn is limited to 0.007-0.022%, preferably 0.008-0.020%.

[0035] The O content of the present invention is selected to be 0.0013 - 0.0022%. Generally, O is a harmful gas. However, to obtain the product performance of the present invention, the functions of Ca, Mg, and Sn in the steel must be fully exerted to obtain the product performance of the present invention. Therefore, O is limited to 0.0013 - 0.0022%.

[0036] The N content of the present invention is selected to be ≤0.0018%. To prevent the increase of dissolved N in the steel and the risk of increasing strain aging sensitivity, N in the present invention is limited to ≤0.0018%.

[0037] As in the present invention is ≤0.0005%. As is prone to segregate at grain boundaries, reducing grain boundary strength and increasing grain boundary brittleness, which is not conducive to low-temperature toughness and welding performance. Therefore, As must be strictly limited to ≤0.0005%, preferably As ≤0.0003%.

[0038] At the same time, the above chemical components must also satisfy the following relationships: (1) 17Cu + 4Ni = 5 - 6%, (2) (2Mo + 3Cr) / 3Ni = 1.2 - 2.5, (3) (Ca + Mg + Sn / 9) / [O] = 2 - 3. When 17Cu + 4Ni < 5%, the weather resistance cannot be guaranteed. When 13Cu + 2Ni > 6%, the slab crack tendency increases and the manufacturing cost increases, which is not conducive to low-temperature toughness. When (2Mo + 3Cr) / 3Ni < 1.2, the room temperature and high temperature performance cannot be guaranteed. When (2Mo + 3Cr) / 3Ni > 2.5, the manufacturing cost increases and the low-temperature toughness and welding performance cannot be guaranteed either. When (Ca + Mg + Sn / 9) / [O] < 2, the functions of Ca, Mg, and Sn cannot be fully exerted, which is not conducive to obtaining the product performance of the present invention. When (Ca + Mg + Sn / 9) / [O] > 3, large composite inclusions are easily formed, reducing the steel purity, which is not conducive to ductility and low-temperature toughness, and deteriorating the resistance to lamellar tearing and welding performance.

[0039] In addition to the above chemical components, the balance of the steel of the present invention is Fe and inevitable inclusions.

[0040] The production process of the steel plate of the present invention and the reasons for setting process parameters are described in detail below:

[0041] 1) Converter smelting: Ultra-low phosphorus double slag method is used for smelting, and top and bottom combined blowing is carried out throughout the process. The lance position is controlled at 1.6 - 1.7 m, the slag basicity is 2.1 - 2.2, and the oxygen supply intensity is 3.6 - 3.7 m 3 / t·min to quickly slag off, ensure the stable progress of the dephosphorization reaction, improve the dephosphorization rate, and ultimately achieve the purpose of deep dephosphorization to reduce the P content as much as possible, which is beneficial to low-temperature toughness and welding performance.

[0042] 2) Secondary refining: The treatment time of LHF is 40 - 50 min, CaO / CaF2 = 3.8 - 3.9, the basicity of the slag is 4.2 - 4.4, the white slag time is ≥ 12 min, and the end point [S] ≤ 10 ppm; the RH vacuum degree ≤ 50 Pa, and the treatment time is 15 - 22 min. The purpose of controlling the above parameters is to ensure the activity of the slag through operations such as pre - adding aluminum ingots and lime at the bottom of the ladle, heating, and the mode of interval operation for circulating desulfurization, quickly and deeply desulfurize to the end point [S] ≤ 10 ppm, reduce the nitrogen increase in the molten steel, so as to facilitate the product performance of the present invention.

[0043] 3) Billet heating: The purpose of restricting the heating and holding temperature and time is to fully austenitize the steel, ensure that Mo, Cr, and Cu in the steel dissolve in austenite, reduce the degree of center segregation as much as possible, and prevent the growth of austenite grains during heating, so as to facilitate the product performance of the present invention.

[0044] 4) Rolling: After the billet is heated and discharged from the furnace and undergoes high - pressure descaling, when the billet temperature is 1060 - 1080 °C, stage I rough rolling is carried out. The reduction per pass is controlled for 7 - 9 rolling passes, the reduction per pass is 22 - 28 mm, the total reduction rate ≥ 55%, and the final rolling temperature ≤ 1050 °C. The purpose is to carry out multi - pass large - reduction rolling in the complete recrystallization zone of austenite, so that the columnar crystal grains are fully broken after multi - pass repeated rolling, thereby fully refining the austenite grains; control the starting rolling temperature of stage II finishing rolling ≤ 980 °C, and the final rolling temperature is (887 - 3h / 2) ± 5 °C. The purpose is to carry out rolling in the non - recrystallization zone of austenite in stage II to avoid the appearance of mixed crystal structure, and rolling and final rolling at a lower temperature to further refine the grains and improve the comprehensive performance.

[0045] 5) Cooling: Control the starting cooling temperature of laminar cooling (743 + h / 2) ± 3 °C, and the recrystallization temperature is 250 - 350 °C, in order to obtain the composite tissue structure required by the present invention, thereby obtaining the product performance level of the present invention.

[0046] 6) Tempering: Carry out critical tempering treatment on the steel plate at 630 - 720 °C and maintain a certain time in the furnace, in order to eliminate the residual stress as much as possible, and make the carbides of Mo and Cr precipitate sufficiently, so as to obtain the composite tissue structure and performance level required by the product of the present invention.

[0047] The microstructure of the finished steel plate obtained by the present invention is lath bainite + a small amount of granular bainite + quasi-polygonal ferrite with a volume percentage > 12 - 15% + M / A island structure with a volume percentage > 10 - 13%. Among them, the width of more than 90% of the lath bainite is ≤ 0.87 μm, the width of the M / A island is ≤ 0.32 μm, ReL is 742.3 - 772.1 MPa, Rm is 948.2 - 964.1 MPa, ReL / Rm is 0.779 - 0.801, A is 26.55 - 28.75%, the reduction of area Z in the thickness direction is 55.4 - 64.1%, -80°C KV2 = 245.2 - 275.5 J, and the high-temperature yield strength R P0.2 = 529.3 - 561.4 MPa, R P0.2 / ReL = 0.704 - 0.741, the corrosion weight loss rate is 0.2253 - 0.2418 g / m 2 ·h, and the submerged arc welding HAZ - 80°C KV2 = 167.5 - 184.6 J.

[0048] Compared with the prior art, the manufacturing process of the present invention is simple, the production cycle is short, and it can be implemented on a large scale in each metallurgical enterprise. The finished steel plate has the characteristics of high strength and toughness, fire and weather resistance, resistance to lamellar tearing, a low yield ratio, and excellent welding performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 is the metallographic structure diagram of the steel produced in Example 4 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0050] In order to better explain the technical solution of the present invention, the technical solution of the present invention will be further described below in conjunction with specific embodiments. The following embodiments are only exemplary descriptions of the technical solution of the present invention and do not limit the present invention in any form. The following serial numbers of each embodiment are only for description and do not represent the advantages or disadvantages of the embodiments.

[0051] Table 1 below is the list of chemical composition values of each embodiment of the present invention;

[0052] Table 2 below is the list of main process parameter values of each embodiment of the present invention;

[0053] Table 3 below is the list of main mechanical property test results of each embodiment of the present invention.

[0054] Among them, the product thicknesses of Examples 1 - 8 are 15 mm, 20 mm, 30 mm, 40 mm, 50 mm, 60 mm, 70 mm, and 80 mm respectively.

[0055] A production method of a fire and weather-resistant steel for welded structures with a tensile strength of 900 MPa according to each embodiment of the present invention includes the following steps:

[0056] 1) Converter smelting: The double slag method for ultra-low phosphorus smelting process is adopted, with top and bottom combined blowing throughout the process. The lance position is 1.6 - 1.7 m, the slag basicity is 2.1 - 2.2, and the oxygen supply intensity is 3.6 - 3.7 m 3 / t·min;

[0057] 2) Secondary refining: The operation mode of pre-adding aluminum ingots, lime, heating, and intermittent circulation desulfurization is adopted to reduce nitrogen absorption. The LHF treatment time is 40 - 50 min, CaO / CaF2 = 3.8 - 3.9, the slag basicity is 4.2 - 4.4, the white slag time is ≥12 min, and the end point [S] ≤ 10 ppm; The RH vacuum degree ≤ 50 Pa, and the treatment time is 15 - 22 min;

[0058] 3) Slab heating: The heating temperature is 1300 - 1320 °C, the holding temperature is 1240 - 1260 °C, and the holding time is 55 - 65 min;

[0059] 4) Controlled rolling: In the first stage, the rough rolling starting temperature is 1060 - 1080 °C, the finishing rolling temperature ≤ 1050 °C, the number of rolling passes is 7 - 9 times, the reduction per pass is 22 - 28 mm, and the total reduction ratio ≥ 55%; In the second stage, the finishing rolling starting temperature ≤ 980 °C, the finishing rolling temperature is (887 - 4h / 5) ± 5 °C, where h is the thickness value of the finished steel plate in mm;

[0060] 5) Lamellar cooling: The starting cooling temperature is (743 + 3h / 4) ± 3 °C, and the recrystallization temperature is 250 - 350 °C, where h is the thickness value of the finished steel plate in mm;

[0061] 6) Tempering treatment: The tempering temperature is 650 - 720 °C, and the time in the furnace is [(2.25 - 2.75) × h] min. After the steel plate is taken out of the furnace, it is air-cooled to room temperature, where h is the thickness value of the finished steel plate in mm.

[0062] Table 1 Chemical composition value list of each embodiment of the present invention (wt, %)

[0063]

[0064] Table 2 Main process parameter value list of each embodiment of the present invention

[0065]

[0066] Table 3 Mechanical property test result list of each embodiment of the present invention

[0067]

[0068] Samples were taken at 1 / 4 of the thickness of the steel plates in the examples and comparative examples of the present invention for room temperature tensile properties, -80°C longitudinal impact energy, and 700°C high temperature tensile properties tests. The test results are shown in Table 3 above. The finished steel plates produced by the method of the present invention have ReL of 742.3 - 772.1 MPa, Rm of 948.2 - 964.1 MPa, ReL / Rm of 0.779 - 0.801, A of 26.55 - 28.75%, thickness direction reduction of area Z of 55.4 - 64.1%, -80°C KV2 of 245.2 - 275.5 J, and 700°C high temperature yield strength R P0.2 of 529.3 - 561.4 MPa, R P0.2 / ReL of 0.704 - 0.741, corrosion weight loss rate of 0.2253 - 0.2418 g / m 2 ·h, submerged arc welding HAZ - 80°C KV2 = 167.5 - 184.6 J, and has characteristics such as high strength and toughness, fire and weather resistance, resistance to lamellar tearing, lower yield ratio, and excellent welding performance.

[0069] Figure 1 is the microstructural photograph of the finished steel plate obtained in Example 4 of the present invention. It can be seen from the figure that the microscopic structure characteristics of the steel of the present invention are lath bainite + a small amount of granular bainite + quasi-polygonal ferrite with a volume percentage > 12 - 15% + M / A island structure with a volume percentage > 10 - 13%. Among them, the width of more than 90% of the lath bainite is ≤ 0.87 μm, and the width of the M / A island is ≤ 0.32 μm. It is this uniform and fine multi-phase structure that ensures the performance of the products of the present invention.

[0070] The above embodiments are only specific examples cited to explain the present invention and do not limit the present invention in any form. Any non-substantive changes made by anyone based on the above content and form without departing from the protection scope of the claims of the present invention shall be considered to fall within the protection scope of the claims of the present invention. The present invention is not limited to the above specific embodiments.

Claims

1. A fire-resistant and weather-resistant steel for welded structures with a tensile strength of 900 MPa, characterized in that The steel contains chemical components with the following mass percentage contents: C: 0.010 - 0.040%, Si: 0.10 - 0.20%, Mn: 1.71 - 2.23%, P ≤ 0.001%, S ≤ 0.001%, Mo: 0.51 - 0.74%, Cr: 0.42 - 0.65%, Cu: 0.15 - 0.25%, Ni: 0.42 - 0.64%, Nb: 0.061 - 0.082%, V: 0.065 - 0.087%, Ti: 0.007 - 0.021%, Ca: 0.0007 - 0.0020%, Mg: 0.0008 - 0.0023%, Sn: 0.007 - 0.022%, [O]: 0.0013 - 0.0022%, [N] ≤ 0.0018%, As ≤ 0.0005%, and the balance is Fe and inevitable impurities. At the same time, the above chemical components must also satisfy the following relationships: (1) 17Cu + 4Ni = 5 - 6%, (2) (2Mo + 3Cr) / 3Ni = 1.2 - 2.5, (3) (Ca + Mg + Sn / 9) / [O] = 2 - 3.

2. The fire-resistant and weather-resistant steel for welded structures with a tensile strength of 900 MPa according to claim 1, characterized in that: Sn: 0.010 - 0.020%, As ≤ 0.0003%.

3. The fire-resistant and weather-resistant steel for welded structures with a tensile strength of 900 MPa according to claim 1, characterized in that: The microstructure of the obtained finished steel plate is lath bainite + a small amount of granular bainite + quasi-polygonal ferrite with a volume percentage of 12 - 15% + M / A island structure with a volume percentage of 10 - 13%. Among them, the width of more than 90% of the lath bainite ≤ 0.87 μm, and the width of the M / A island ≤ 0.32 μm.

4. The fire-resistant and weather-resistant steel for welded structures with a tensile strength of 900 MPa according to claim 1, characterized in that: The obtained finished steel plate has ReL of 742.3 - 772.1 MPa, Rm of 948.2 - 964.1 MPa, ReL / Rm of 0.779 - 0.801, A of 26.55 - 28.75%, thickness direction reduction of area Z of 55.4 - 64.1%, -80 °C KV2 of 245.2 - 275.5 J, and high temperature yield strength R P0.2 at 700 °C of 529.3 - 561.4 MPa, R P0.2 / ReL of 0.704 - 0.741, corrosion weight loss rate of 0.2253 - 0.2418 g / m 2 ·h, submerged arc welding HAZ - 80 °C KV2 = 167.5 - 184.6 J.

5. A production method of the fire-resistant and weather-resistant steel for welded structures with a tensile strength of 900 MPa according to claim 1, characterized in that It includes the following steps: 1) Converter smelting: The double slag method for ultra-low phosphorus smelting process is adopted, with top and bottom combined blowing throughout the process. The lance position is 1.6 - 1.7 m, the slag basicity is 2.1 - 2.2, and the oxygen supply intensity is 3.6 - 3.7 m 3 / t·min; 2) Secondary refining: Adopt the operation mode of pre-adding aluminum ingots, lime, heating, and circulating desulfurization at intervals to reduce nitrogen pickup. The LHF treatment time is 40 - 50 min, CaO / CaF2 = 3.8 - 3.9, the slag basicity is 4.2 - 4.4, the white slag time ≥ 12 min, and the end point [S] ≤ 10 ppm; the RH vacuum degree ≤ 50 Pa, and the treatment time is 15 - 22 min; 3) Slab heating: The heating temperature is 1300 - 1320 °C, the holding temperature is 1240 - 1260 °C, and the holding time is 55 - 65 min; 4) Controlled rolling: In the first stage of rough rolling, the starting rolling temperature is 1060 - 1080 °C, the finishing rolling temperature ≤ 1050 °C, the number of rolling passes is 7 - 9 times, the reduction per pass is 22 - 28 mm, and the total reduction rate ≥ 55%; in the second stage of finish rolling, the starting rolling temperature ≤ 980 °C, and the finishing rolling temperature is (887 - 4h / 5) ± 5 °C, where h is the thickness value of the finished steel plate in mm; 5) Lamellar cooling: The starting cooling temperature is (743 + 3h / 4) ± 3 °C, and the recrystallization temperature is 250 - 350 °C, where h is the thickness value of the finished steel plate in mm; 6) Tempering treatment: The tempering temperature is 650 - 720 °C, and the time in the furnace is [(2.25 - 2.75)×h] min. After the steel plate is taken out of the furnace, it is air-cooled to room temperature, where h is the thickness value of the finished steel plate in mm.

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