Preparation method of 650MPa ultrahigh-strength wire rod anti-seismic reinforcing steel bar with nominal diameter of 8-12mm

Abstract

The invention discloses a preparation method of a 650MPa ultrahigh-strength wire rod anti-seismic reinforcing steel bar with the nominal diameter of 8-12mm. The anti-seismic steel bar comprises the following chemical components in percentage by weight: 0.25 to 0.28 weight percent of C, 0.50 to 0.60 weight percent of Si, 1.10 to 1.25 weight percent of Mn, 0.100 to 0.113 weight percent of V, 0.007 to 0.010 weight percent of Nb, less than or equal to 0.035 weight percent of S, less than or equal to 0.035 weight percent of P, less than or equal to 0.0030 weight percent of O, 0.0230 to 0.0260 weight percent of N and the balance of Fe and inevitable impurities. The yield strength of the aseismic steel bar is 660-690 MPa, the tensile strength is 855-920 MPa, the ratio of strength to yield is larger than or equal to 1.30, the percentage elongation after fracture is larger than or equal to 25.0%, and the maximum force total elongation is larger than or equal to 10.5%. Through integration and innovation of chemical component design, converter smelting, deoxidation alloying, argon station treatment, continuous casting, a steel rolling heating schedule and a controlled rolling and controlled cooling process, multiple strengthening effects of precipitation strengthening, fine grain strengthening and the like are fully exerted. The process disclosed by the invention has the characteristics of low production cost, high process applicability and controllability and the like, and the produced reinforcing steel bar has the advantages of excellent and stable process mechanical properties, fine and uniform microscopic structure, excellent anti-seismic property and the like, and has remarkable economic and social benefits.

Description

Technical Field

[0001] The invention belongs to the technical field of steel smelting, and specifically relates to a method for preparing an ultra-high strength wire rod earthquake-resistant steel bar with a nominal diameter of 8-12 mm and 650 MPa. Background Art

[0002] High-strength earthquake-resistant steel bars are the main reinforcement materials for high-rise and large reinforced concrete building structures, carrying stress and strain of tensile and compressive stress and strain in the structure. With the continuous development of my country's buildings towards high-rise, super-high-rise, and large-span tunnel and bridge earthquake-resistant structures, the development of high-strength and excellent comprehensive performance earthquake-resistant steel bars with a strength level of 600MPa and above has become an important task for the steel industry to improve its technical level and adjust its product structure.

[0003] At present, the production of earthquake-resistant steel bars with a strength level of 600MPa and above in China mainly uses vanadium-nitrogen microalloying technology, with a V content of ≥0.150wt% in the steel, and the strength-to-yield ratio (R°m / R°eL) of the steel bar earthquake-resistant performance index is mostly 1.23-1.26, and the maximum force total elongation (Agt) is 7.5-9.0%. The earthquake-resistant performance matching is not good, which restricts the application of the product in building structures and infrastructure structures in earthquake-resistant high-intensity areas. The present invention aims to provide a method for preparing an ultra-high-strength wire rod earthquake-resistant steel bar with a nominal diameter of 8-12mm and a 650MPa. Summary of the invention

[0004] The object of the present invention is to provide a method for preparing 650MPa ultra-high strength wire rod earthquake-resistant steel bars with a nominal diameter of 8-12mm.

[0005] The object of the present invention is achieved by a method for preparing a 650MPa ultra-high strength wire rod seismic steel bar with a nominal diameter of 8-12mm, which is achieved by the following steps: A. Molten steel smelting: 240-250kg / t 钢 Cold material charging ratio: add scrap steel into LD converter, and then charge at 800-810kg / t 钢 The molten iron charging ratio is 25-30kg / t. The molten iron with a temperature of ≥1290℃ is added to the LD converter for conventional top and bottom composite blowing. 钢 , 12-15kg / t 钢 Lime and light-burned dolomite are added to make slag, and the final carbon content is controlled to be ≥0.08wt%, and the tapping temperature is ≤1590℃; before tapping, 1.5kg / t 钢Add slag washing material to the bottom of the ladle in an amount for slag washing; the chemical composition of the molten iron is: C 4.2-4.5wt%, Si 0.15-0.38wt%, Mn 0.20-0.40wt%, P 0.070-0.085wt%, S≤0.035wt%, and the rest is Fe and inevitable impurities; B. Deoxidation and alloying: The molten steel after smelting is tapped. When the amount of molten steel in the ladle is greater than 1 / 4, the deoxidation and alloying sequence is silicon-calcium-barium → ferrosilicon → silicon-manganese alloy → nitrogen-rich alloy → niobium-phosphorus-iron alloy. The deoxidation and alloying steps are carried out at 2 kg / t. 钢 , 2.2~3.8kg / t 钢 16.1~18.3kg / t 钢 1.50~1.60kg / t 钢 , 0.15~0.21kg / t 钢 Add silicon calcium barium, ferrosilicon, silicon manganese alloy, nitrogen-rich alloy and niobium phosphorus iron alloy to the ladle in order, and add all the above alloys when the amount of molten steel in the ladle reaches 4 / 5; C. Molten steel argon station treatment: After the steel is tapped in step B, the molten steel is hoisted to the argon station treatment station and heated through the alloy trough at 17.0-18.0 kg / t 钢 The vanadium-containing pig iron having a surface temperature of ≥300°C after baking is added in an amount, and then the molten steel is subjected to nitrogen blowing treatment with nitrogen gas at a flow rate of 25 to 30 NL / min for 3 minutes; the vanadium-containing pig iron has the following components in mass ratio: C3.5wt%, Si 0.45wt%, Mn 1.85wt%, V 6.1wt%, P 1.02wt%, S 0.065wt%, and the rest is Fe and inevitable impurities; D. LF furnace refining of molten steel: The molten steel in step C is hoisted to the LF furnace for refining. After the refining, the molten steel is subjected to soft nitrogen blowing at a small flow rate of 10-15 NL / min for 2 minutes. After the nitrogen blowing is completed, a molten steel covering agent is added, and then the molten steel is hoisted to the casting station; E. Molten steel casting: The tundish temperature is 1525-1538°C, the pulling speed is 3.3-3.5 m / min, and the crystallizer cooling water flow rate is 145-150 m 3 / h, and the secondary cooling water volume is 1.7-1.9L / kg, the molten steel is cast into a steel billet with a cross-section of 165mm×165mm; F. Billet heating: The billet in step D is sent into a heating furnace with a soaking section temperature of 1110-1150°C and heated for 75 minutes. The billet tapping temperature is 1045-1060°C, and then scaled by high-pressure water; G. Controlled rolling and controlled cooling of steel billets: The steel billets in step F are fed into a 30-stand high-speed wire rod mill for rolling. First, the steel billets are roughly rolled for 6 passes in the rough rolling unit at a rolling speed of 0.80 m / s; then, they are intermediately rolled for 5 to 6 passes in the intermediate rolling unit at a rolling speed of 12.0 m / s; then, they are rolled for 5 to 6 passes in the pre-finishing rolling unit at a rolling speed of 50.0 m / s; then, they are rolled for 6 to 8 passes in the finishing rolling unit at a rolling speed of 60 to 70 m / s; then, they are rolled for 3 to 4 passes in the sizing unit at a rolling speed of 70 to 85 m / s; then, they are rolled at a temperature of 800 to 820°C and a speed of 75 to 90 m / s; after spinning, the wire rod enters the Stelmore air cooling line for aerosol cooling and air cooling control, 5 to 7 fans are turned on, and the 10 insulation covers above the fans are fully opened. 3 / h, and the roller speed is 0.65-0.75m / s; after the Stelmor air cooling, the coiling temperature is controlled to be 420-450°C, and then the coil is naturally air-cooled to room temperature to obtain a 650MPa ultra-high strength wire rod earthquake-resistant steel bar with a nominal diameter of 8mm-12mm, which has the following chemical composition in weight percentage: C 0.25-0.28wt%, Si 0.50-0.60wt%, Mn 1.10-1.25wt%, V 0.100-0.113wt%, Nb 0.007-0.010wt%, S≤0.035wt%, P≤0.035wt%, O≤0.0030wt%, N 0.0230-0.0260wt%, and the rest is Fe and inevitable impurities; In the process of the present invention, a large amount of vanadium-containing pig iron is added to the molten steel at the argon station after steelmaking is completed to completely replace the expensive vanadium alloy, thereby increasing the V content of the molten steel and greatly reducing the cost of microalloying; nitrogen-rich alloy is added during the steelmaking deoxidation alloying process, and the molten steel is simultaneously subjected to LF furnace refining and nitrogen blowing treatment, thereby significantly increasing the nitrogen content of the molten steel, controlling the V / N ratio in the steel to be ≤4.4, promoting the transfer of V and Nb from the solid solution state to the carbonitride precipitation phase during the rolling process, and forming and precipitating a large amount of fine dispersed V (C, N) and Nb (C, N) precipitation phases, thereby significantly improving the precipitation strengthening effect of the steel; a small amount of niobium is added to the steel to generate a very small amount of granular bainite, thereby optimizing the microstructure ratio of the steel , which promotes the optimal matching of steel tensile strength and yield strength and improves the seismic performance of steel; the high rolling start temperature is controlled during steel rolling to promote the full solid solution of V and Nb microalloying elements; the low finishing rolling temperature and wire drawing temperature are controlled to inhibit the growth of austenite and ferrite grains, promote the formation and precipitation of a large number of fine and dispersed V(C,N) and Nb(C,N) precipitation phases, and increase the nucleation position and nucleation rate of ferrite grains; after wire drawing, the wire rod is cooled by large air volume on the Stelmor roller table, which reduces the temperature before phase transformation and increases the large amount of nucleation inside the material during the subsequent phase transformation. The wire rod has a fine and uniform microstructure and has excellent seismic resistance and plastic toughness.

[0006] The present invention fully exerts the multiple strengthening effects such as precipitation strengthening and fine grain strengthening through the integrated innovation of chemical composition design, converter smelting, deoxidation alloying, argon station treatment, continuous casting, steel rolling heating system, and controlled rolling and controlled cooling process. The process of the present invention has the characteristics of low production cost, strong process applicability and controllability, and the produced steel bars have the advantages of excellent and stable process mechanical properties, fine and uniform microstructure, and excellent seismic performance, which improves the application scope and market competitiveness of the products and has significant economic and social benefits. DETAILED DESCRIPTION

[0007] The present invention is further described in detail below in conjunction with the embodiments, but the present invention is not limited in any way. Any changes or improvements made based on the teachings of the present invention fall within the protection scope of the present invention.

[0008] The present invention provides a method for preparing a 650MPa ultra-high strength wire rod earthquake-resistant steel bar with a nominal diameter of 8-12mm. The preparation method is implemented by the following steps: A. Molten steel smelting: 240-250kg / t 钢 Cold material charging ratio: add scrap steel into LD converter, and then charge at 800-810kg / t 钢 The molten iron charging ratio is 25-30kg / t. The molten iron with a temperature of ≥1290℃ is added to the LD converter for conventional top and bottom composite blowing. 钢 , 12-15kg / t 钢Lime and light-burned dolomite are added to make slag, and the final carbon content is controlled to be ≥0.08wt%, and the tapping temperature is ≤1590℃; before tapping, 1.5kg / t 钢 Add slag washing material to the bottom of the ladle in an amount for slag washing; the chemical composition of the molten iron is: C 4.2-4.5wt%, Si 0.15-0.38wt%, Mn 0.20-0.40wt%, P 0.070-0.085wt%, S≤0.035wt%, and the rest is Fe and inevitable impurities; B. Deoxidation and alloying: The molten steel after smelting is tapped. When the amount of molten steel in the ladle is greater than 1 / 4, the deoxidation and alloying sequence is silicon-calcium-barium → ferrosilicon → silicon-manganese alloy → nitrogen-rich alloy → niobium-phosphorus-iron alloy. The deoxidation and alloying steps are carried out at 2 kg / t. 钢 , 2.2~3.8kg / t 钢 16.1~18.3kg / t 钢 1.50~1.60kg / t 钢 , 0.15~0.21kg / t 钢 Add silicon calcium barium, ferrosilicon, silicon manganese alloy, nitrogen-rich alloy and niobium phosphorus iron alloy to the ladle in order, and add all the above alloys when the amount of molten steel in the ladle reaches 4 / 5; C. Molten steel argon station treatment: After the steel is tapped in step B, the molten steel is hoisted to the argon station treatment station and heated through the alloy trough at 17.0-18.0 kg / t 钢 The vanadium-containing pig iron having a surface temperature of ≥300°C after baking is added in an amount, and then the molten steel is subjected to nitrogen blowing treatment with nitrogen gas at a flow rate of 25 to 30 NL / min for 3 minutes; the vanadium-containing pig iron has the following components in mass ratio: C3.5wt%, Si 0.45wt%, Mn 1.85wt%, V 6.1wt%, P 1.02wt%, S 0.065wt%, and the rest is Fe and inevitable impurities; D. LF furnace refining of molten steel: The molten steel in step C is hoisted to the LF furnace for refining. After the refining, the molten steel is subjected to soft nitrogen blowing at a small flow rate of 10-15 NL / min for 2 minutes. After the nitrogen blowing is completed, a molten steel covering agent is added, and then the molten steel is hoisted to the casting station; E. Molten steel casting: The tundish temperature is 1525-1538°C, the pulling speed is 3.3-3.5 m / min, and the crystallizer cooling water flow rate is 145-150 m 3 / h, and the secondary cooling water volume is 1.7-1.9L / kg, the molten steel is cast into a steel billet with a cross-section of 165mm×165mm; F. Billet heating: The billet in step D is sent into a heating furnace with a soaking section temperature of 1110-1150°C and heated for 75 minutes. The billet tapping temperature is 1045-1060°C, and then scaled by high-pressure water; G. Controlled rolling and controlled cooling of steel billets: The steel billets in step F are fed into a 30-stand high-speed wire rod mill for rolling. First, the steel billets are roughly rolled for 6 passes in the rough rolling unit at a rolling speed of 0.80 m / s; then, they are intermediately rolled for 5 to 6 passes in the intermediate rolling unit at a rolling speed of 12.0 m / s; then, they are rolled for 5 to 6 passes in the pre-finishing rolling unit at a rolling speed of 50.0 m / s; then, they are rolled for 6 to 8 passes in the finishing rolling unit at a rolling speed of 60 to 70 m / s; then, they are rolled for 3 to 4 passes in the sizing unit at a rolling speed of 70 to 85 m / s; then, they are rolled at a temperature of 800 to 820°C and a speed of 75 to 90 m / s; after spinning, the wire rod enters the Stelmore air cooling line for aerosol cooling and air cooling control, 5 to 7 fans are turned on, and the 10 insulation covers above the fans are fully opened. 3 / h, roller speed of 0.65-0.75m / s; after Stelmor air cooling, the coiling temperature is controlled to 420-450℃, and then the coil is naturally air-cooled to room temperature to obtain 650MPa ultra-high strength wire rod seismic steel bars with a nominal diameter of 8mm-12mm, which have the following chemical compositions in weight percentage: C 0.25-0.28wt%, Si 0.50-0.60wt%, Mn 1.10-1.25wt%, V 0.100-0.113wt%, Nb 0.007-0.010wt%, S≤0.035wt%, P≤0.035wt%, O≤0.0030wt%, N 0.0230-0.0260wt%, and the rest are Fe and inevitable impurities; its process mechanical properties, microstructure, Vickers hardness difference and corrosion resistance are shown in Tables 1 and 2.

[0009] Table 1 Mechanical properties of 650MPa ultra-high strength wire rod seismic steel bars with nominal diameter of 8-12mm produced by the process of the present invention Table 2 Metallographic microstructure and Vickers hardness of 650MPa ultra-high strength wire rod seismic steel bars with nominal diameter of 8-12mm produced by the process of the present invention In step A, the chemical composition of the scrap steel is: C 0.22-0.26wt%, Si 0.25-0.50wt%, Mn 1.20-1.50wt%, P0.017-0.045wt%, S 0.018-0.045wt%, and the rest is Fe and inevitable impurities. The chemical composition mass ratio of the slag washing material is: Al2O312.5wt%, SiO26.5wt%, CaO 51.5wt%, Al 6.2wt%, MgO 5.5wt%, and the rest is Fe and inevitable impurities.

[0010] In step A, the whole process of bottom blowing nitrogen is adopted in the process of molten steel tapping, and the nitrogen flow rate is controlled at 15-20NL / min.

[0011] In step B, the chemical composition of silicon calcium barium is: Si 52.5wt%, Ca 9.85wt%, Ba 12.15wt%, Al2.45wt%, and the rest is Fe and inevitable impurities; the chemical composition of ferrosilicon is: Si 73.5wt%, and the rest is Fe and inevitable impurities; the chemical composition of silicon manganese alloy is: Mn 65.2wt%, Si17.9wt%, C1.1wt%, and the rest is Fe and inevitable impurities; the chemical composition of nitrogen-rich alloy is: Si 57.8wt%, N 41.5wt%, C 1.65wt%, P0.085wt%, S0.042wt%, and the rest is Fe and inevitable impurities; the chemical composition of niobium phosphorus iron alloy is: Nb 44.2wt%, Si3.5wt%, C1.75wt%, P1.65wt%, S 0.045wt%, and the rest is Fe and inevitable impurities.

[0012] In step D, during the refining process, nitrogen gas with a flow rate of 15-20 NL / min is used to blow nitrogen into the molten steel, and then the lower electrode is slag-free at gears 6-8; after 3 minutes of slag-freeing, the electrode is lifted to observe the slag-freeing situation in the furnace; if the slag sample is too thin and the color is too black, lime is added at 4.0-5.0 kg / t 钢 Adjust the slag, otherwise add pre-melted refined slag 1.0~2.0kg / t 钢 Adjustment; then measure temperature and take samples. According to the steel sample and temperature test results, add alloy to adjust the steel liquid composition and lower electrode temperature to ensure that the composition and temperature are qualified.

[0013] In step E, R9m straight arc continuous straightening 5-machine 5-strand billet casting machine is used for casting.

[0014] In step E, the straightening temperature of the ingot out of the straightening machine is controlled to be 1010-1025°C.

[0015] Example 1 A. Molten steel smelting: 240kg / t 钢 Cold material charging ratio: add the following scrap steel in the LD converter (chemical composition: C 0.22wt%, Si 0.25wt%, Mn 1.20wt%, P 0.017wt%, S0.018wt%, the rest is Fe and inevitable impurities); then charge 800kg / t 钢 The molten iron charging ratio is as follows: molten iron of the following temperature and mass ratio is added to the LD converter: molten iron temperature is 1290℃, molten iron composition is C 4.2wt%, Si 0.15wt%, Mn 0.20wt%, P 0.070wt%, S 0.015wt%, and the rest is Fe and inevitable impurities; after the scrap steel and molten iron are added to the LD converter, conventional top and bottom composite blowing is carried out, conventional lime and light-burned dolomite are added to make slag, the amount of lime added is 25kg / t steel, the amount of light-burned dolomite added is 12kg / t steel, the terminal carbon content is controlled to be 0.08wt%, and the tapping temperature is 1580℃; before tapping, slag washing material (chemical composition mass ratio: Al2O312.5wt%, SiO26.5wt%, CaO 51.5wt%, Al 6.2wt%, MgO 5.5wt%, the rest is Fe and inevitable impurities) for slag washing, and the steelmaking process adopts the whole bottom blowing nitrogen process, and the nitrogen flow rate is controlled at 15NL / min.

[0016] B. Deoxidation and alloying: After the molten steel smelted in step A is tapped, when the amount of molten steel in the ladle is greater than 1 / 4, add the following materials to the ladle in the following order of deoxidation and alloying: silicon calcium barium → ferrosilicon → silicon manganese alloy → nitrogen-rich alloy → niobium phosphorus iron alloy: 2.0 kg / t 钢 Add the following mass ratio of silicon, calcium and barium: Si 52.5wt%, Ca 9.85wt%, Ba12.15wt%, Al 2.45wt%, the rest is Fe and unavoidable impurities; at 2.2kg / t 钢 Add the following mass ratio of ferrosilicon: Si 73.5wt%, the rest is Fe and inevitable impurities; at 16.1kg / t 钢 Add the following mass ratio of silicon-manganese alloy: Mn 65.2wt%, Si 17.9wt%, C1.1wt%, the rest is Fe and inevitable impurities; at 1.50kg / t 钢 The amount of silicon-nitrogen alloy is added in the following mass ratio: Si 57.8wt%, N 41.5wt%, C 1.65wt%, P0.085wt%, S0.042wt%, and the rest is Fe and unavoidable impurities; at 0.15kg / t 钢The following mass ratio of niobium-phosphorus-iron alloy is added: Nb 44.2wt%, Si 3.5wt%, C1.75wt%, P1.65wt%, S 0.045wt%, and the rest is Fe and inevitable impurities; the above alloys are added when the amount of molten steel in the ladle reaches 4 / 5; after the steel is tapped, the molten steel is hoisted to the argon station for adding vanadium-containing pig iron and nitrogen blowing refining treatment.

[0017] C. Molten steel argon station treatment: The molten steel from step B is hoisted to the argon station treatment station and passed through the alloy trough at a pressure of 17.0kg / t 钢 The amount of vanadium-containing pig iron having the following mass ratio is added: components C 3.5wt%, Si 0.45wt%, Mn 1.85wt%, V6.1wt%, P1.02wt%, S 0.065wt%, and the rest are Fe and inevitable impurities. The vanadium-containing pig iron is baked for 8 minutes, and the surface temperature of the pig iron after baking is 300°C. After the vanadium-containing pig iron is added, nitrogen is turned on and nitrogen is blown to the molten steel at a flow rate of 25NL / min for 3 minutes.

[0018] D. LF furnace refining of molten steel: Lift the molten steel from step C to the LF furnace refining station and connect the nitrogen belt. Turn on the nitrogen and use nitrogen with a flow rate of 15NL / min to blow nitrogen into the molten steel. Then, use the 6th to 8th gear of the lower electrode to slag. After 3 minutes of slag slag slag, lift the electrode to observe the slag slag situation in the furnace. If the slag sample is too thin and the color is too black, add 4.0kg / t lime. 钢 Adjust the slag, otherwise add pre-melted refined slag 1.0kg / t 钢 Adjustment; then measure temperature and take samples, add alloy to adjust the composition of molten steel and raise the temperature of lower electrode according to the steel sample and temperature test results to ensure that the composition and temperature are qualified; after refining, perform soft nitrogen blowing with small flow rate on molten steel, the blowing time is 2 minutes, and the nitrogen flow rate is controlled at 15NL / min; after nitrogen blowing, add molten steel covering agent, the addition amount is 1.0 kg / t 钢 , and then lift the molten steel to the casting station.

[0019] E. Molten steel casting: The tundish temperature is 1538°C, the pulling speed is 3.3m / min, and the crystallizer cooling water flow rate is 145m 3 / h, and the secondary cooling water volume is 1.7L / kg. The molten steel in step C is cast into billets with a cross-section of 165mm×165mm using an R9m straight arc continuous straightening 5-machine 5-strand small square billet casting machine. The straightening temperature of the billet leaving the straightening machine is controlled at 1010℃.

[0020] F. Billet heating: The billet in step E is fed into a heating furnace with a temperature of 1110°C in the soaking section and heated for 75 minutes. The billet tapping temperature is 1045°C. After descaling with high-pressure water, the billet is pushed to a high-speed wire mill for rolling.

[0021] G. Controlled rolling and controlled cooling of steel billets: The steel billets in step F are fed into a 30-stand high-speed wire rod mill for rolling. Under the rolling condition of a speed of 0.80 m / s, the rough rolling unit performs 6 rough rolling passes; then, under the rolling condition of a speed of 12.0 m / s, the intermediate rolling unit performs 6 intermediate rolling passes; then, under the rolling condition of a speed of 50.0 m / s, the pre-finishing rolling unit performs 6 intermediate rolling passes; then, under the rolling condition of a speed of 70 m / s, the finishing rolling unit performs 8 intermediate rolling passes; then, under the rolling condition of a speed of 85 m / s, the sizing unit performs 4 intermediate rolling passes; then, wire is spun at a temperature of 820°C and a speed of 90 m / s; after spinning, the wire rod enters the Stelmor air cooling line for aerosol cooling and air cooling control, 5 fans are turned on, and 10 insulation covers above the fans are fully opened. When the air volume is 200 km 3 / h, roller speed of 0.65-0.75m / s to complete air cooling; after Stelmor air cooling, the coiling temperature is controlled to 450℃, and then the coil is naturally air-cooled to room temperature to obtain a 650MPa ultra-high strength wire rod seismic steel bar with a nominal diameter of 8mm and the following weight percentage chemical composition: C 0.25wt%, Si 0.50wt%, Mn1.10wt%, V 0.100wt%, Nb0.007wt%, S 0.018wt%, P0.021wt%, O 0.0017wt%, N 0.0230wt%, and the rest is Fe and unavoidable impurities. The process mechanical properties, microstructure, Vickers hardness difference and corrosion resistance of the wire rod seismic steel bar are shown in Table 3 and Table 4.

[0022] Table 3 Processing mechanical properties of 650MPa ultra-high strength wire rod seismic steel bars with a nominal diameter of 8mm produced in Example 1 Table 4 Metallographic microstructure and Vickers hardness of 650MPa ultra-high strength wire rod seismic steel bars with a nominal diameter of 8mm produced in Example 1 Example 2 A. Molten steel smelting: 247kg / t 钢 Cold material charging ratio: add the following scrap steel in the LD converter (chemical composition: C 0.24wt%, Si 0.37wt%, Mn 1.37wt%, P 0.032wt%, S0.031wt%, the rest is Fe and inevitable impurities); then 810kg / t 钢The molten iron charging ratio is as follows: molten iron of the following temperature and mass ratio is added to the LD converter: molten iron temperature is 1304℃, molten iron composition is C 4.4wt%, Si 0.28wt%, Mn 0.30wt%, P 0.076wt%, S 0.028wt%, and the rest is Fe and inevitable impurities; after the scrap steel and molten iron are added to the LD converter, conventional top and bottom composite blowing is carried out, conventional lime and light-burned dolomite are added to make slag, the amount of lime added is 28kg / t steel, the amount of light-burned dolomite added is 14kg / t steel, the end point carbon content is controlled to be 0.09wt%, and the tapping temperature is 1586℃; before tapping, slag washing material (chemical composition mass ratio: Al2O312.5wt%, SiO26.5wt%, CaO 51.5wt%, Al 6.2wt%, MgO 5.5wt%, the rest is Fe and inevitable impurities) for slag washing, and the steelmaking process adopts the whole bottom blowing nitrogen process, and the nitrogen flow rate is controlled at 20NL / min.

[0023] B. Deoxidation and alloying: After the molten steel smelted in step A is tapped, when the amount of molten steel in the ladle is greater than 1 / 4, add the following materials to the ladle in the following order of deoxidation and alloying: silicon calcium barium → ferrosilicon → silicon manganese alloy → nitrogen-rich alloy → niobium phosphorus iron alloy: 2.0 kg / t 钢 Add the following mass ratio of silicon, calcium and barium: Si 52.5wt%, Ca 9.85wt%, Ba12.15wt%, Al 2.45wt%, the rest is Fe and unavoidable impurities; at 3.0kg / t 钢 Add the following mass ratio of ferrosilicon: Si 73.5wt%, the rest is Fe and inevitable impurities; at 17.1kg / t 钢 The amount of silicon-manganese alloy with the following mass ratio is added: Mn 65.2wt%, Si 17.9wt%, C1.1wt%, and the rest is Fe and inevitable impurities; at 1.56kg / t 钢 The amount of silicon-nitrogen alloy is added in the following mass ratio: Si 57.8wt%, N 41.5wt%, C 1.65wt%, P0.085wt%, S0.042wt%, and the rest is Fe and unavoidable impurities; at 0.18kg / t 钢 The following mass ratio of niobium-phosphorus-iron alloy is added: Nb 44.2wt%, Si 3.5wt%, C1.75wt%, P1.65wt%, S 0.045wt%, and the rest is Fe and inevitable impurities; the above alloys are added when the amount of molten steel in the ladle reaches 4 / 5; after the steel is tapped, the molten steel is hoisted to the argon station for adding vanadium-containing pig iron and nitrogen blowing refining treatment.

[0024] C. Molten steel argon station treatment: The molten steel from step B is hoisted to the argon station treatment station and passed through the alloy trough at a pressure of 17.5kg / t 钢 The amount of vanadium-containing pig iron having the following mass ratio is added: components C 3.5wt%, Si 0.45wt%, Mn 1.85wt%, V6.1wt%, P1.02wt%, S 0.065wt%, and the rest are Fe and inevitable impurities. The baking time of the vanadium-containing pig iron is 8 minutes, and the surface temperature of the pig iron after baking is 320°C; after the vanadium-containing pig iron is added, nitrogen is turned on and nitrogen is blown to the molten steel with a flow rate of 30NL / min, and the blowing time is 3 minutes.

[0025] D. LF furnace refining of molten steel: Lift the molten steel from step C to the LF furnace refining station and connect the nitrogen belt. Turn on the nitrogen and use nitrogen with a flow rate of 20NL / min to blow nitrogen into the molten steel. Then, use the 6th to 8th gear of the lower electrode to slag. After 3 minutes of slag slag slag, lift the electrode to observe the slag slag situation in the furnace. If the slag sample is too thin and the color is too black, add 4.6kg / t lime. 钢 Adjust the slag, otherwise add 1.5kg / t of pre-melted refined slag 钢 Adjustment; then measure temperature and take samples, add alloy to adjust the composition of molten steel and raise the temperature of lower electrode according to the steel sample and temperature test results to ensure that the composition and temperature are qualified; after refining, perform soft nitrogen blowing with small flow rate on molten steel, the blowing time is 2 minutes, and the nitrogen flow rate is controlled at 20NL / min; after nitrogen blowing, add molten steel covering agent, the addition amount is 1.0 kg / t 钢 , and then lift the molten steel to the casting station.

[0026] E. Molten steel casting: The tundish temperature is 1532℃, the pulling speed is 3.4m / min, and the crystallizer cooling water flow rate is 147m 3 / h, and the secondary cooling water volume was 1.8L / kg. The molten steel from step C was cast into billets with a cross-section of 165mm×165mm using an R9m straight arc continuous straightening 5-machine 5-strand billet casting machine. The straightening temperature of the billet leaving the straightening machine was controlled at 1020℃.

[0027] F. Billet heating: The billet in step E is fed into a heating furnace with a temperature of 1130°C in the soaking section and heated for 75 minutes. The billet tapping temperature is 1055°C. After descaling with high-pressure water, the billet is pushed to a high-speed wire mill for rolling.

[0028] G. Controlled rolling and controlled cooling of billets: The billets in step F are fed into a 30-stand high-speed wire rod mill for rolling. Under the rolling condition of a speed of 0.80 m / s, the billets are roughly rolled for 6 passes in the rough rolling unit; then, under the rolling condition of a speed of 12.0 m / s, the billets are intermediately rolled for 6 passes in the intermediate rolling unit; then, under the rolling condition of a speed of 50.0 m / s, the billets are rolled for 6 passes in the pre-finishing rolling unit; then, under the rolling condition of a speed of 65 m / s, the billets are rolled for 7 passes in the finishing rolling unit; then, under the rolling condition of a speed of 80 m / s, the billets are rolled for 3 passes in the sizing unit; then, wire is spun at a temperature of 810°C and a speed of 85 m / s; after spinning, the wire rods enter the Stelmor air cooling line for aerosol cooling and air cooling control, with 6 fans turned on and 10 insulation covers above the fans fully opened. At an air volume of 200 km 3 / h, roller speed of 0.65-0.75m / s to complete air cooling; after Stelmor air cooling, the coiling temperature is controlled to 440℃, and then the coil is naturally air-cooled to room temperature to obtain a 650MPa ultra-high strength wire rod seismic steel bar with a nominal diameter of 10mm and the following weight percentage chemical composition: C 0.27wt%, Si 0.56wt%, Mn1.18wt%, V 0.107wt%, Nb0.009wt%, S 0.028wt%, P0.026wt%, O 0.0026wt%, N 0.0245wt%, and the rest is Fe and unavoidable impurities. The process mechanical properties, microstructure, Vickers hardness difference and corrosion resistance of the seismic steel bar are shown in Tables 5 and 6.

[0029] Table 5 Processing mechanical properties of 650MPa ultra-high strength wire rod seismic steel bars with a nominal diameter of 10mm produced in Example 2 Table 6 Metallographic microstructure and Vickers hardness of 650MPa ultra-high strength wire rod seismic steel bars with a nominal diameter of 10mm produced in Example 2 Example 3 A. Molten steel smelting: 250kg / t 钢 Cold material charging ratio: add the following scrap steel in the LD converter (chemical composition: C 0.26wt%, Si 0.50wt%, Mn 1.50wt%, P 0.045wt%, S0.045wt%, the rest is Fe and inevitable impurities); then charge 815kg / t 钢The molten iron charging ratio is as follows: molten iron of the following temperature and mass ratio is added to the LD converter: molten iron temperature is 1310℃, molten iron composition is C 4.5wt%, Si 0.38wt%, Mn 0.40wt%, P 0.085wt%, S 0.035wt%, and the rest is Fe and inevitable impurities; after the scrap steel and molten iron are added to the LD converter, conventional top and bottom composite blowing is carried out, conventional lime and light-burned dolomite are added to make slag, the amount of lime added is 30kg / t steel, the amount of light-burned dolomite added is 15kg / t steel, the terminal carbon content is controlled to be 0.10wt%, and the steel tapping temperature is 1590℃; before steel tapping, slag washing material (chemical composition mass ratio: Al2O312.5wt%, SiO26.5wt%, CaO 51.5wt%, Al 6.2wt%, MgO 5.5wt%, the rest is Fe and inevitable impurities) for slag washing, and the steelmaking process adopts the whole bottom blowing nitrogen process, and the nitrogen flow rate is controlled at 20NL / min.

[0030] B. Deoxidation and alloying: After the molten steel smelted in step A is tapped, when the amount of molten steel in the ladle is greater than 1 / 4, add the following materials to the ladle in the following order of deoxidation and alloying: silicon calcium barium → ferrosilicon → silicon manganese alloy → nitrogen-rich alloy → niobium phosphorus iron alloy: 2.0 kg / t 钢 Add the following mass ratio of silicon, calcium and barium: Si 52.5wt%, Ca 9.85wt%, Ba12.15wt%, Al 2.45wt%, the rest is Fe and unavoidable impurities; at 3.8kg / t 钢 Add the following mass ratio of ferrosilicon: Si 73.5wt%, the rest is Fe and inevitable impurities; at 18.3kg / t 钢 Add the following mass ratio of silicon-manganese alloy: Mn 65.2wt%, Si 17.9wt%, C1.1wt%, the rest is Fe and inevitable impurities; according to 1.60kg / t 钢 The amount of silicon-nitrogen alloy is added in the following mass ratio: Si 57.8wt%, N 41.5wt%, C 1.65wt%, P0.085wt%, S0.042wt%, and the rest is Fe and unavoidable impurities; at 0.21kg / t 钢 The following mass ratio of niobium-phosphorus-iron alloy is added: Nb 44.2wt%, Si 3.5wt%, C1.75wt%, P1.65wt%, S 0.045wt%, and the rest is Fe and inevitable impurities; the above alloys are added when the amount of molten steel in the ladle reaches 4 / 5; after the steel is tapped, the molten steel is hoisted to the argon station for adding vanadium-containing pig iron and nitrogen blowing refining treatment.

[0031] C. Molten steel argon station treatment: The molten steel from step B is hoisted to the argon station treatment station and passed through the alloy trough at a pressure of 18.0kg / t 钢 The amount of vanadium-containing pig iron having the following mass ratio is added: C 3.5wt%, Si 0.45wt%, Mn 1.85wt%, V6.1wt%, P1.02wt%, S 0.065wt%, and the rest is Fe and inevitable impurities. The vanadium-containing pig iron is baked for 8 minutes, and the surface temperature of the pig iron after baking is 332°C. After the vanadium-containing pig iron is added, nitrogen is turned on and nitrogen is blown to the molten steel at a flow rate of 25-30NL / min for 3 minutes.

[0032] D. LF furnace refining of molten steel: Lift the molten steel from step C to the LF furnace refining station and connect the nitrogen belt. Turn on the nitrogen and use nitrogen with a flow rate of 20NL / min to blow nitrogen into the molten steel. Then, use the 6th to 8th gear of the lower electrode to slag. After 3 minutes of slag slag slag, lift the electrode to observe the slag slag situation in the furnace. If the slag sample is too thin and the color is too black, add 5.0kg / t lime. 钢 Adjust the slag, otherwise add 2.0kg / t of pre-melted refined slag 钢 Adjustment; then measure temperature and take samples, add alloy to adjust the composition of molten steel and raise the temperature of lower electrode according to the steel sample and temperature test results to ensure that the composition and temperature are qualified; after refining, perform soft nitrogen blowing with small flow rate on molten steel, the blowing time is 2 minutes, and the nitrogen flow rate is controlled at 20NL / min; after nitrogen blowing, add molten steel covering agent, the addition amount is 1.0 kg / t 钢 , and then lift the molten steel to the casting station.

[0033] E. Molten steel casting: The tundish temperature is 1525℃, the pulling speed is 3.5m / min, and the crystallizer cooling water flow rate is 150m 3 / h, and the secondary cooling water volume was 1.9L / kg. The molten steel from step C was cast into billets with a cross-section of 165mm×165mm using an R9m straight arc continuous straightening 5-machine 5-strand billet casting machine. The straightening temperature of the billet leaving the straightening machine was controlled at 1025℃.

[0034] F. Billet heating: The billet in step E is fed into a heating furnace with a temperature of 1150°C in the soaking section and heated for 75 minutes. The billet tapping temperature is 1060°C. After descaling with high-pressure water, it is pushed to a high-speed wire mill for rolling.

[0035] G. Controlled rolling and controlled cooling of steel billets: The steel billets in step F are fed into a 30-stand high-speed wire rod mill for rolling. Under the rolling condition of a speed of 0.80 m / s, the rough rolling unit performs 6 rough rolling passes; then, under the rolling condition of a speed of 12.0 m / s, the intermediate rolling unit performs 5 intermediate rolling passes; then, under the rolling condition of a speed of 50.0 m / s, the pre-finishing rolling unit performs 5 rolling passes; then, under the rolling condition of a speed of 60 m / s, the finishing rolling unit performs 6 rolling passes; then, under the rolling condition of a speed of 70 m / s, the sizing unit performs 3 rolling passes; then, wire is spun at a temperature of 800°C and a speed of 75 m / s; after spinning, the wire rod enters the Stelmor air cooling line for aerosol cooling and air cooling control, 7 fans are turned on, and 10 insulation covers above the fans are fully opened. At an air volume of 200 km 3 / h, roller speed of 0.65-0.75m / s; after Stelmor air cooling, the coiling temperature is controlled to 450℃, and then the coil is naturally air-cooled to room temperature to obtain a 650MPa ultra-high strength wire rod seismic steel bar with a nominal diameter of 12mm and the following weight percentage chemical composition: C 0.28wt%, Si 0.60wt%, Mn1.25wt%, V 0.113wt%, Nb0.010wt%, S 0.035wt%, P 0.035wt%, O 0.0030wt%, N 0.0260wt%, and the rest is Fe and unavoidable impurities. The process mechanical properties, microstructure, Vickers hardness difference and corrosion resistance of the 650MPa ultra-high strength wire rod seismic steel bar are shown in Table 7 and Table 8.

[0036] Table 7 Process mechanical properties of 650MPa ultra-high strength wire rod seismic steel bars with a nominal diameter of 12mm produced in Example 3 Table 8 Metallographic microstructure and Vickers hardness of 650MPa ultra-high strength wire rod seismic steel bars with a nominal diameter of 12mm produced in Example 3 .

Claims

1. A method for preparing 650MPa ultra-high strength wire rod seismic steel bars with a nominal diameter of 8-12mm, characterized in that: To do this, follow these steps: A. Molten steel smelting: 240-250kg / t 钢 Cold material charging ratio: add scrap steel into LD converter, and then charge at 800-810kg / t 钢 The molten iron charging ratio is 25-30kg / t. The molten iron with a temperature of ≥1290℃ is added to the LD converter for conventional top and bottom composite blowing. 钢 , 12-15kg / t 钢 Lime and light-burned dolomite are added to make slag, and the final carbon content is controlled to be ≥0.08wt%, and the tapping temperature is ≤1590℃; before tapping, 1.5kg / t 钢 Add slag washing material to the bottom of the ladle in an amount for slag washing; the chemical composition of the molten iron is: C 4.2-4.5wt%, Si 0.15-0.38wt%, Mn 0.20-0.40wt%, P 0.070-0.085wt%, S≤0.035wt%, and the rest is Fe and inevitable impurities; B. Deoxidation and alloying: The molten steel after smelting is tapped. When the amount of molten steel in the ladle is greater than 1 / 4, the deoxidation and alloying sequence is silicon-calcium-barium → ferrosilicon → silicon-manganese alloy → nitrogen-rich alloy → niobium-phosphorus-iron alloy. The deoxidation and alloying steps are carried out at 2 kg / t. 钢 , 2.2~3.8kg / t 钢 16.1~18.3kg / t 钢 1.50~1.60kg / t 钢 , 0.15~0.21kg / t 钢 Add silicon calcium barium, ferrosilicon, silicon manganese alloy, nitrogen-rich alloy and niobium phosphorus iron alloy to the ladle in order, and add all the above alloys when the amount of molten steel in the ladle reaches 4 / 5; C. Molten steel argon station treatment: After the steel is tapped in step B, the molten steel is hoisted to the argon station treatment station and heated through the alloy trough at 17.0-18.0 kg / t 钢 The vanadium-containing pig iron having a surface temperature of ≥300°C after baking is added in an amount, and then the molten steel is subjected to nitrogen blowing treatment with nitrogen gas at a flow rate of 25 to 30 NL / min for 3 minutes; the vanadium-containing pig iron has the following components in mass ratio: C3.5wt%, Si 0.45wt%, Mn 1.85wt%, V 6.1wt%, P 1.02wt%, S 0.065wt%, and the rest is Fe and inevitable impurities; D. LF furnace refining of molten steel: The molten steel in step C is hoisted to the LF furnace for refining. After the refining, the molten steel is subjected to soft nitrogen blowing at a small flow rate of 10-15 NL / min for 2 minutes. After the nitrogen blowing is completed, a molten steel covering agent is added, and then the molten steel is hoisted to the casting station; E. Molten steel casting: The tundish temperature is 1525-1538°C, the pulling speed is 3.3-3.5 m / min, and the crystallizer cooling water flow rate is 145-150 m 3 / h, and the secondary cooling water volume is 1.7-1.9L / kg, the molten steel is cast into a steel billet with a cross-section of 165mm×165mm; F. Billet heating: The billet in step D is sent into a heating furnace with a soaking section temperature of 1110-1150°C and heated for 75 minutes. The billet tapping temperature is 1045-1060°C, and then scaled by high-pressure water; G. Controlled rolling and controlled cooling of steel billets: The steel billets in step F are fed into a 30-stand high-speed wire rod mill for rolling. First, the steel billets are roughly rolled for 6 passes in the rough rolling unit at a rolling speed of 0.80 m / s; then, they are intermediately rolled for 5 to 6 passes in the intermediate rolling unit at a rolling speed of 12.0 m / s; then, they are rolled for 5 to 6 passes in the pre-finishing rolling unit at a rolling speed of 50.0 m / s; then, they are rolled for 6 to 8 passes in the finishing rolling unit at a rolling speed of 60 to 70 m / s; then, they are rolled for 3 to 4 passes in the sizing unit at a rolling speed of 70 to 85 m / s; then, they are rolled at a temperature of 800 to 820°C and a speed of 75 to 90 m / s; after spinning, the wire rod enters the Stelmore air cooling line for aerosol cooling and air cooling control, 5 to 7 fans are turned on, and the 10 insulation covers above the fans are fully opened. 3 / h, roller speed of 0.65-0.75m / s; after Stelmor air cooling, the coiling temperature is controlled at 420-450℃, and then the coil is naturally air-cooled to room temperature to obtain 650MPa ultra-high strength wire rod earthquake-resistant steel bars with a nominal diameter of 8mm-12mm.

2. The method for preparing the 650MPa ultra-high strength wire rod seismic steel bar with a nominal diameter of 8-12mm according to claim 1, characterized in that: In step A, the chemical composition of the scrap steel is: C 0.22-0.26wt%, Si 0.25-0.50wt%, Mn 1.20-1.50wt%, P 0.017-0.045wt%, S 0.018-0.045wt%, and the rest is Fe and inevitable impurities.

3. The method for preparing the 650MPa ultra-high strength wire rod seismic steel bar with a nominal diameter of 8-12mm according to claim 1, characterized in that: In step A, the chemical composition mass ratio of the slag washing material is: Al2O3 12.5wt%, SiO2 6.5wt%, CaO 51.5wt%, Al 6.2wt%, MgO 5.5wt%, and the rest is Fe and unavoidable impurities.

4. The method for preparing the 650MPa ultra-high strength wire rod seismic steel bar with a nominal diameter of 8-12mm according to claim 1, characterized in that: In step A, the whole process of bottom blowing nitrogen is adopted in the process of molten steel tapping, and the nitrogen flow rate is controlled at 15-20NL / min.

5. The method for preparing the 650MPa ultra-high strength wire rod earthquake-resistant steel bar with a nominal diameter of 8-12mm according to claim 1, characterized in that: In step B, the chemical composition of silicon-calcium-barium is: Si 52.5wt%, Ca 9.85wt%, Ba 12.15wt%, Al2.45wt%, and the rest is Fe and inevitable impurities; the chemical composition of ferrosilicon is: Si 73.5wt%, and the rest is Fe and inevitable impurities; the chemical composition of silicon-manganese alloy is: Mn 65.2wt%, Si 17.9wt%, C1.1wt%, and the rest is Fe and inevitable impurities; the chemical composition of nitrogen-rich alloy is: Si 57.8wt%, N 41.5wt%, C 1.65wt%, P0.085wt%, S 0.042wt%, and the rest is Fe and inevitable impurities; the chemical composition of niobium-phosphorus-iron alloy is: Nb44.2wt%, Si 3.5wt%, C1.75wt%, P 1.65wt%, S 0.045wt%, and the rest is Fe and inevitable impurities.

6. The method for preparing the 650MPa ultra-high strength wire rod seismic steel bar with a nominal diameter of 8-12mm according to claim 1, characterized in that: In step D, during the refining process, nitrogen gas with a flow rate of 15-20 NL / min is used to blow nitrogen into the molten steel, and then the lower electrode is slag-free at gears 6-8; after 3 minutes of slag-freeing, the electrode is lifted to observe the slag-freeing situation in the furnace; if the slag sample is too thin and the color is too black, lime is added at 4.0-5.0 kg / t 钢 Adjust the slag, otherwise add pre-melted refined slag 1.0~2.0kg / t 钢 Adjustment; then measure temperature and take samples. According to the steel sample and temperature test results, add alloy to adjust the steel liquid composition and lower electrode temperature to ensure that the composition and temperature are qualified.

7. The method for preparing the 650MPa ultra-high strength wire rod seismic steel bar with a nominal diameter of 8-12mm according to claim 1, characterized in that: In step E, R9m straight arc continuous straightening 5-machine 5-strand billet casting machine is used for casting.

8. The method for preparing the 650MPa ultra-high strength wire rod earthquake-resistant steel bar with a nominal diameter of 8-12mm according to claim 1, characterized in that: In step E, the straightening temperature of the ingot out of the straightening machine is controlled to be 1010-1025°C.

9. 650MPa ultra-high strength wire rod earthquake-resistant steel bar with a nominal diameter of 8-12mm obtained by the preparation method according to any one of claims 1 to 8, characterized in that: The seismic steel bar has the following chemical composition in weight percentage: C 0.25-0.28wt%, Si 0.50-0.60wt%, Mn 1.10-1.25wt%, V 0.100-0.113wt%, Nb 0.007-0.010wt%, S≤0.035wt%, P≤0.035wt%, O≤0.0030wt%, N 0.0230-0.0260wt%, and the rest is Fe and inevitable impurities; the seismic steel bar has a yield strength of 660-690MPa, a tensile strength of 855-920MPa, a strength-to-yield ratio of ≥1.30, an elongation after fracture of ≥25.0%, and a total elongation at maximum force of ≥10.5%.

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