Low-yield-ratio anti-seismic high-strength Q690GJ steel for building and production method thereof

Abstract

The invention discloses a low-yield-ratio anti-seismic high-strength Q690GJ steel for buildings and a production method thereof. The low-yield-ratio anti-seismic high-strength Q690GJ steel is prepared from the following chemical components in percentage by mass (wt%): 0.08-0.10% of C, 0.01-0.10% of Si, 2.0-2.2% of Mn, less than or equal to 0.010% of P, less than or equal to 0.002% of S, 0.40-0.50% of Cr, 0.05-0.06% of Nb, 0.02-0.03% of V, 0.01-0.02% of Ti and the balance of Fe and inevitable impurities. The steel plate is suitable for production of Q690GJD / Q690GJE steel plates of 80 mm or below, low cost, low yield ratio and high lamellar tearing resistance can be obtained through optimal design of components, strict control of all procedures, no need of heat treatment and short-process production, various requirements of GB / T19879-2023 can be met, and the steel plate is suitable for manufacturing of main structural parts of super high-rise buildings and large public buildings.

Description

Technical Field

[0001] The invention belongs to the technical field of metallurgy, and in particular relates to low-yield ratio earthquake-resistant high-strength Q690GJ steel for construction and a production method thereof. Background Art

[0002] Construction steel refers to steel widely used in steel structures such as super high-rise buildings, stations, airports, and exhibition centers. Construction steel has the characteristics of fast construction speed, good earthquake resistance, and environmental friendliness. Q690GJ grade building structure steel has been widely used in various major projects. It can effectively reduce the deadweight of steel structures and provide higher structural strength.

[0003] 690 grade building structure steel has high strength requirements and strict requirements on yield strength ratio, so multi-phase structure is often used. The ratio between each phase is relatively strict, and the toughness of thick plates is difficult to guarantee. Therefore, thick plates are mostly produced by heat treatment process. However, the existing technical processes are relatively large and more alloys are added, which is not conducive to the promotion and use of this grade of steel.

[0004] The steel plate obtained by using the scheme of “A Q690CF hot-rolled steel plate and its preparation method” with publication number CN105420632A has good low-temperature toughness and welding performance, but the yield strength ratio only meets ≤0.93, and the Z-direction performance of the steel plate cannot meet the requirements of Z35, and cannot meet the requirements of the seismic design code for yield strength ratio ≤0.85.

[0005] The "Low-cost, low-yield ratio tempered Q690E steel plate and production method" with publication number CN106399840A adopts a low-carbon equivalent design and eliminates precious alloys such as Nb and Ni, but the carbon content is relatively high, the production process requires quenching + tempering process, and the obtained steel plate thickness is only 8-40mm.

[0006] The publication number of "A Q690GJ building steel plate and its preparation method" is 108950380A. The steel plate obtained by this scheme has a yield strength ratio of ≤0.85, but the same production process requires quenching + tempering process, and a large amount of alloy needs to be added to the composition, which has high production costs and long delivery cycles.

[0007] In view of this, the present invention is proposed. Summary of the invention

[0008] The object of the present invention is to provide a low yield ratio earthquake-resistant high-strength Q690GJ steel for construction and a production method thereof, by designing the alloy composition, utilizing the cheap Mn element solid solution strengthening and improving the hardenability, utilizing conventional production equipment, optimizing the TMCP production process, and finally obtaining the Q690GJ building structure steel with low cost, high strength, high toughness and low yield ratio.

[0009] Another object of the present invention is to provide a method for producing low yield ratio earthquake-resistant high-strength Q690GJ steel for construction.

[0010] The present invention is realized by the following technical scheme: a low yield ratio earthquake-resistant high-strength Q690GJ steel for construction, using the following chemical composition in mass percentage (wt%): C: 0.08-0.10, Si: 0.01-0.10, Mn: 2.0-2.2, P: ≤0.010, S≤0.002, Cr: 0.40-0.50, Nb: 0.05-0.06, V: 0.02-0.03, Ti: 0.01-0.02, the balance being Fe and unavoidable impurities;

[0011] The production method includes the following process steps:

[0012] (1) Smelting: The converter-LF-RH smelting process is adopted, and the converter smelting endpoint is controlled to be C≤0.10%, O≤0.10%. The refining LF furnace uses high basicity slag and stirring desulfurization; the process Al is controlled to be ≤0.035%, and calcium treatment is performed before leaving the station; the RH furnace production adopts a deep degassing process, and the total vacuum treatment time is ≥15min;

[0013] (2) Continuous casting: superheat is controlled at 10℃~20℃, constant casting speed, weak cooling is used for secondary cooling, 5~7mm large reduction is used for final light reduction, and macrosegregation is controlled at 0.5 or below of national standard C class;

[0014] (3) Heating: hot charging and hot delivery are adopted, the billet is charged into the furnace at 500-600℃, the temperature of the holding section is 1180℃-1220℃, and the heating time of the holding section is controlled at 2-2.5h;

[0015] (4) Rolling: Two-stage rolling is adopted, the starting rolling temperature of rough rolling is ≥1000°C, the cumulative reduction rate of the last three passes is ≥50%, and the thickness is rolled to more than 1.5 times the target thickness, the starting rolling temperature of the second stage is 760°C to 800°C, and the final rolling temperature is 760°C to 780°C;

[0016] (5) Rapid cooling: After the steel plate is rolled, laminar cooling is directly adopted, and the cooling rate is controlled at 8℃ / s~12℃ / s. The red-return temperature is controlled at 380℃~450℃. The steel plate is straightened and slowly cooled after being stacked. After slowly cooling to room temperature, it enters the finishing process.

[0017] The Q690GJ construction steel plate produced by the above method has a yield strength between 725 and 750 MPa, a tensile strength between 860 and 890 MPa, an elongation of more than 15%, a yield strength ratio of ≤0.85, a Z-direction tensile shrinkage of ≥35%, and a -20°C impact of more than 200 J.

[0018] The present invention adopts low temperature rolling, and the ferrite structure first formed on the surface of the steel plate divides the original austenite grains into many small areas, thereby limiting the subsequent phase transformation in these small areas, and finally obtaining a fully refined composite structure. With the continuous addition of deformation dislocations, the angle between subgrains increases. On the boundaries of these cellular structures composed of dislocations, trace elements such as Nb and Cr undergo non-equilibrium segregation and precipitation deformation induction precipitation. After rolling to a short relaxation control process of more than 20 seconds in water, the steel plate is accelerated to cool. During the cooling process, since there are a large number of substructures and precipitates in the deformed grains (especially those precipitates with larger sizes that lose the coherence relationship with the matrix), their interfaces with the matrix become favorable positions for phase transformation. In the further rapid cooling process, phase transformation occurs in each substructure, and the width of its lath is hindered by the subgrain boundary and the needle-shaped ferrite or bainite formed early, making the bainite structure thinner and shorter, and realizing the ultra-fine structure; short relaxation can make the yield strength ratio ≤0.85, and not make the yield strength ratio too small.

[0019] The present invention is suitable for the production of Q690GJD / Q690GJE steel plates of 80 mm and below. Through the optimized design of components and strict control of each process, no heat treatment is required and a short process production is adopted to obtain low cost, low yield strength ratio and strong anti-laminar tearing performance. The present invention can meet the requirements of GB / T19879-2023 and is suitable for the production of main structural parts of super high-rise buildings and large public buildings. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is the metallographic structure diagram of 1 / 2 thickness of 80mm thick Q690GJ steel plate. DETAILED DESCRIPTION

[0021] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0022] The features and performance of the present invention are further described in detail below in conjunction with the embodiments.

[0023] Example 1:

[0024] 1) Smelting: The converter smelting was a hit, the end point control C: 0.08%, the end point O content 670ppm, LF used high basicity slag desulfurization, the maximum aluminum content of the process was 0.026%, and Al alloying was performed before leaving the station. The RH furnace vacuum treatment time was 15min, and the residual H was measured to be 1.5ppm.

[0025] 2) Continuous casting: 300mm thick section production, superheat 12 ~ 18 ℃, the whole process of pulling speed 0.75m / min, the final stage of light pressure down 6mm.

[0026] 3) Heating: Hot charging and hot delivery are adopted, the steel billet is loaded into the furnace within 8 hours, the hot charging temperature is 570℃, the temperature of the insulation section of the heating furnace is 1200℃, and the heating time of the insulation section is controlled at 2 to 2.5 hours.

[0027] 4) Rolling: Two-stage rolling is adopted, the starting temperature of rough rolling is 1050℃, the cumulative reduction rate of the last three passes is 60%, the thickness of the intermediate billet is 135mm, the starting temperature of rough rolling is 785℃, the rolling is 80mm thick, and the final rolling temperature is 776℃.

[0028] 5) Rapid cooling: After rolling, the steel plate directly enters ultra-fast laminar cooling, with a return temperature of 410°C and a cooling rate of about 10°C / s. After hot straightening, it is slowly cooled in the stack and then enters the finishing process after slowly cooling to room temperature.

[0029] Example 2:

[0030] 1) Smelting: The converter smelting was a hit, the end point control C: 0.09%, the end point O content 870ppm, LF used high basicity slag desulfurization, the maximum Al content of the process was 0.022%, and Al alloying was performed before leaving the station. The RH furnace vacuum treatment time was 16min, and the residual H was measured to be 1.4ppm.

[0031] 2) Continuous casting: 300mm thick section production, superheat 13 ~ 18 ℃, the whole process of pulling speed 0.8m / min, the final stage of light pressure down 6mm.

[0032] 3) Heating: Hot charging and hot delivery are adopted, and the billet is loaded into the furnace within 8 hours. The hot charging temperature is 575℃, the temperature of the insulation section of the heating furnace is 1211℃, and the heating time of the insulation section is controlled at 2 to 2.5 hours.

[0033] 4) Rolling: Two-stage rolling is adopted, the starting temperature of rough rolling is 1050℃, the cumulative reduction rate of the last three passes is 62%, the thickness of the intermediate billet is 135mm, the starting temperature of rough rolling is 765℃, the rolling is 80mm thick, and the final rolling temperature is 768℃.

[0034] 5) Rapid cooling: After rolling, the steel plate directly enters ultra-fast laminar cooling, with a return temperature of 420°C and a cooling rate of 11°C / s. After hot straightening, it is slowly cooled in the stack and then enters the finishing process after slowly cooling to room temperature.

[0035] Example 3:

[0036] 1) Smelting: The converter smelting was a hit, the end point control C: 0.10%, the end point O content was 740ppm, LF used high basicity slag desulfurization, the maximum Al content in the process was 0.022%, and Al alloying was performed before leaving the station. The RH furnace vacuum treatment time was 18min, and the residual H was measured to be 1.3ppm.

[0037] 2) Continuous casting: 300mm thick section production, superheat 14℃~20℃, full pulling speed 0.8m / min, and light pressure reduction of 6mm at the end.

[0038] 3) Heating: Hot charging and hot delivery are adopted, the billet is loaded into the furnace within 8 hours, the hot charging temperature is 580℃, the temperature of the insulation section of the heating furnace is 1200℃, and the heating time of the insulation section is controlled at 2 to 2.5 hours.

[0039] 4) Rolling: Two-stage rolling is adopted, the starting temperature of rough rolling is 1030℃, the cumulative reduction rate of the last three passes is 60%, the thickness of the intermediate billet is 135mm, the starting temperature of rough rolling is 775℃, the thickness is rolled to 80mm, and the final rolling temperature is 768℃.

[0040] 5) Rapid cooling: After rolling, the steel plate directly enters ultra-fast laminar cooling, with a return temperature of 435°C and a cooling rate of about 8°C / s. After hot straightening, it is slowly cooled in the stack and then enters the finishing process after slowly cooling to room temperature.

[0041] Example 4:

[0042] 1) Smelting: The converter smelting was successful in one shot, the endpoint control C: 0.08%, the endpoint O content 890ppm, LF used high basicity slag for desulfurization, the maximum Al content of the process was 0.026%, Al alloying was performed before leaving the station, the RH furnace vacuum treatment time was 17min, and the residual H was measured to be 1.3ppm.

[0043] 2) Continuous casting: 300mm thick section production, superheat 15℃~19℃, full casting speed 0.8m / min, and light pressure reduction of 6mm at the end.

[0044] 3) Heating: Hot charging and hot delivery are adopted, the billet is loaded into the furnace within 8 hours, the hot charging temperature is 555℃, the temperature of the insulation section of the heating furnace is 1190℃, and the heating time of the insulation section is controlled at 2 to 2.5 hours.

[0045] 4) Rolling: Two-stage rolling is adopted, the starting temperature of rough rolling is 1030℃, the cumulative reduction rate of the last three passes is 59%, the thickness of the intermediate billet is 140mm, the starting temperature of rough rolling is 785℃, the rolling is 80mm thick, and the final rolling temperature is 776℃.

[0046] 5) Rapid cooling: After rolling, the steel plate directly enters ultra-fast laminar cooling, with a return temperature of 390°C and a cooling rate of about 11°C / s. After hot straightening, it is slowly cooled in the stack and then enters the finishing process after slowly cooling to room temperature.

[0047] The ingredients of Examples 1-4 are controlled as shown in Table 1: (wt%)

[0048] Table 1 Example ingredients

[0049]

[0050] The steel plate performance test results obtained in Examples 1-4 are shown in Table 2.

[0051] Table 2 Performance of Examples (Shock Temperature -20°C)

[0052]

[0053] As can be seen from Table 2, all indicators of the material of the present invention meet the requirements of GB / T19879-2023 for construction steel, and the strength and yield strength ratio are relatively stable, indicating that the steel plate has excellent seismic resistance, especially the -20°C impact is relatively high, basically stable at more than 200J, so the steel plate of the present invention has excellent comprehensive mechanical properties. It can be applied to super high-rise buildings, factories and mines, towers, large spans and large structural projects, and can be used in buildings with low ambient temperatures or high requirements for low-temperature impact toughness.

[0054] Metallographic examination of the steel plate structure obtained in Example 2 showed that it was composed of granular bainite + a small amount of ferrite. The overall structure was relatively uniform and fine, which was an ideal structure for this grade of steel.

Claims

1. A low yield ratio earthquake-resistant high-strength Q690GJ steel for construction and its production method, characterized in that: The following chemical composition by mass percentage (wt%) is adopted: C: 0.08-0.10, Si: 0.01-0.10, Mn: 2.0-2.2, P: ≤0.010, S≤0.002, Cr: 0.40-0.50, Nb: 0.05-0.06, V: 0.02-0.03, Ti: 0.01-0.02, and the balance is Fe and unavoidable impurities; The steel plate has a yield strength of 725-750 MPa, a tensile strength of 860-890 MPa, an elongation of more than 15%, a yield strength ratio of ≤0.85, a Z-direction tensile shrinkage of ≥35%, and an impact of more than 200 J at -20°C; 2. The method for producing low yield ratio earthquake-resistant high-strength Q690GJ steel for construction according to claim 1, characterized in that The process steps include: 1) Smelting: The converter-LF-RH smelting process is adopted, and the converter smelting endpoint is controlled to be C≤0.10%, O≤0.10%. The refining LF furnace uses high basicity slag and stirring desulfurization; the process Al is controlled to be ≤0.035%, and calcium treatment is performed before leaving the station; the RH furnace production adopts a deep degassing process, and the total vacuum treatment time is ≥15min; 2) Continuous casting: superheat is controlled at 10℃~20℃, constant casting speed, weak cooling is used for secondary cooling, 5~7mm large reduction is used for final light reduction, and macrosegregation is controlled at 0.5 or below of national standard C class; 3) Heating: hot charging and hot delivery are adopted, the steel billet is charged into the furnace at 500-600℃, the temperature of the holding section is 1180℃-1220℃, and the heating time of the holding section is controlled at 2-2.5h; 4) Rolling: adopt two-stage rolling, the starting rolling temperature of rough rolling is ≥1000℃, the cumulative reduction rate of the last three passes is ≥50%, and the rolling is more than 1.5 times the target thickness. The starting rolling temperature of the second stage is 760℃~800℃, and the final rolling temperature is 760℃~780℃; 5) Rapid cooling: After the steel plate is rolled, laminar cooling is directly adopted, and the cooling rate is controlled at 8℃ / s~12℃ / s. The red-return temperature is controlled at 380℃~450℃. The steel plate is straightened and slowly cooled in the stack. After slowly cooling to room temperature, it enters the finishing process.

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