Large-size 650MPa high-toughness corrosion-resistant aseismic steel bar with nominal diameter of 28-40mm and preparation method thereof

Abstract

The invention discloses a large-size 650MPa high-toughness corrosion-resistant aseismic steel bar with the nominal diameter of 28-40mm and a preparation method thereof. The anti-seismic steel bar comprises the following chemical components in percentage by weight: 0.26 to 0.29 weight percent of C, 0.65 to 0.75 weight percent of Si, 1.52 to 1.60 weight percent of Mn, 0.15 to 0.20 weight percent of Cr, 0.12 to 0.18 weight percent of Ni, 0.136 to 0.150 weight percent of V, 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 0.0040 weight percent of O, 0.0310 to 0.0340 weight percent of N and the balance of Fe and inevitable impurities. According to the invention, chemical component design, converter smelting, deoxidation alloying, continuous casting, steel rolling heating schedule, rolling temperature and controlled cooling process are integrated and innovated, so that multiple strengthening effects such as precipitation strengthening, fine grain strengthening and the like are brought into full play; and the produced large-specification 650MPa reinforcing steel bar has the advantages of excellent and stable process mechanical properties, fine and uniform microscopic structure, good plasticity and toughness, excellent corrosion resistance, excellent anti-seismic property and the like, and the market competitiveness and the application range of the product are improved. In addition, the process disclosed by the invention has the characteristics of low production cost, high process applicability and controllability 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 large-size 650MPa high-strength, tough, corrosion-resistant and earthquake-resistant steel bar with a nominal diameter of 28-40mm and a preparation method thereof. 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, corrosion-resistant, and comprehensive performance earthquake-resistant steel bars with a strength level of 600MPa and above has become one of the important tasks for the steel industry to improve its technical level and adjust its product structure.

[0003] At present, there are related research reports on the production technology of high-strength steel bars above 600MPa in China, which mainly adopt vanadium nitrogen microalloying process, with V content ≥0.160wt% in steel, and the strength-to-yield ratio (R°m / R°eL) of steel bar seismic performance index is mostly 1.23-1.26, and the maximum force total elongation (Agt) is 7.5-9.0%. The seismic performance matching is not good, which restricts the application of the product. The present invention aims to provide a large-size 650MPa high-toughness corrosion-resistant seismic steel bar with a nominal diameter of 28-40mm and a preparation method thereof. Summary of the invention

[0004] The first object of the present invention is to provide a large-size 650MPa high-strength and tough corrosion-resistant and earthquake-resistant steel bar with a nominal diameter of 28-40mm. The second object of the present invention is to provide a preparation method of the large-size 650MPa high-strength and tough corrosion-resistant and earthquake-resistant steel bar with a nominal diameter of 28-40mm.

[0005] The first object of the present invention is achieved in this way. A large-size 650MPa high-strength, toughness, corrosion-resistant and earthquake-resistant steel bar with a nominal diameter of 28-40mm has the following chemical composition in weight percentage: C 0.26~0.29wt%, Si 0.65~0.75wt%, Mn 1.52~1.60wt%, Cr 0.15~0.20wt%, Ni 0.12~0.18wt%, V 0.136~0.150wt%, S≤0.035wt%, P≤0.035wt%, O≤0.0040wt%, N 0.0310~0.0340wt%, and the rest is Fe and inevitable impurities.

[0006] The second object of the present invention is achieved by a method for preparing a large-size 650MPa high-toughness corrosion-resistant and earthquake-resistant steel bar with a nominal diameter of 28-40mm, which is achieved by the following steps: A. Molten steel smelting: 250-260kg / t钢 , 1.0-1.6kg / t 钢 The cold material charging ratio is 800-810kg / t. 钢 The molten iron charging ratio is 15-20kg / t. The molten iron with a temperature of ≥1310℃ is added to the LD converter for conventional top and bottom composite blowing. 钢 , 15-18kg / t 钢 Lime and light-burned dolomite are added in an amount to make slag, and the final carbon content is controlled to be ≥0.08wt%, and the tapping temperature is ≤1650°C; the composition of the molten iron is: C 4.1-4.5wt%, Si 0.15-0.30wt%, Mn 0.25-0.40wt%, P 0.080-0.100wt%, S≤0.035wt%, and the rest is Fe and inevitable impurities; Before tapping, the ladle is 12.0kg / t 钢 The following mass ratios of vanadium-containing pig iron are added: C 3.2wt%, Si0.20wt%, Mn 1.05wt%, V 5.25wt%, P0.60wt%, S 0.155wt%, and the rest are Fe and unavoidable impurities; before tapping, the vanadium content is 1.0kg / t 钢 Adding active lime to the bottom of the ladle for slag washing; baking the vanadium-containing pig iron for 3 minutes after adding it to the ladle; 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 → high carbon ferrochrome → nitrogen-rich alloy → vanadium-nitrogen alloy. The deoxidation and alloying steps are carried out at 1.5 kg / t. 钢 , 3.3~4.5kg / t 钢 23.2~24.5kg / t 钢 , 2.3~3.2kg / t 钢 1.10~1.23kg / t 钢 , 0.95~1.12kg / t 钢 Add silicon calcium barium, ferrosilicon, silicon manganese alloy, high carbon ferrochrome, silicon nitrogen alloy and high vanadium nitrogen 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. LF furnace refining of molten steel: The molten steel in step B 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 3 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; D. Molten steel casting: at 1525-1540℃, the pulling speed is 3.4-3.5m / min, and the crystallizer cooling water flow rate is 150-160m 3 / h, and the secondary cooling water volume is 2.0-2.1L / kg, the molten steel is cast into a steel billet with a cross-section of 165mm×165mm; E. Billet heating: The billet in step D is sent to a heating furnace with a soaking section temperature of 1110-1160°C for heating for 70 minutes. The billet tapping temperature is 1050-1070°C, and then pushed to a fully continuous bar mill for rolling; F. Controlled rolling and controlled cooling of steel billets: The steel billets in step E are rolled for 6 passes at a speed of 0.4-0.6 m / s by the rough rolling unit, and then rolled for 4 passes at a speed of 2.0-2.5 m / s by the intermediate rolling unit, and then rolled for 6 passes at a speed of 5.0-7.0 m / s by the pre-finishing rolling unit; before the rolled pieces enter the finishing rolling, they are cooled by 2 sets of water cooling devices with a length of 4 m respectively, and the cooling water volume is 100-120 m 3 / h, the temperature of the rolled piece entering the finishing rolling unit is controlled at 790-820℃; the rolled piece passes through the finishing rolling unit at a speed of 8.0-9.0m / s for 1-2 passes; before entering the finishing rolling unit 2, the rolled piece passes through 2 sets of water cooling devices with a length of 7m each for controlled cooling, with a cooling water volume of 70-80m 3 / h, the temperature of the rolled piece entering the second finishing rolling group is controlled at 820-840℃; then the rolled piece passes through the second finishing rolling group at a rolling speed of 10-12m / s for 2 passes; after finishing rolling, the rolled piece passes through a group of water cooling devices with a length of 10m for post-finishing cooling, and the cooling water volume is 40-50m 3 / h; after controlled cooling, the temperature of the steel bar on the cooling bed is controlled at 900-930℃, and then the steel bar is naturally air-cooled to room temperature on the cooling bed to obtain large-size 650MPa high-strength and toughness earthquake-resistant steel bars with a nominal diameter of 28-40mm.

[0007] The invention adds a large amount of vanadium-containing pig iron to the steelmaking ladle to replace part of the expensive vanadium alloy, thereby increasing the V content of molten steel and reducing the amount of vanadium alloy added; nitrogen-rich alloy is added during the steelmaking deoxidation alloying process, and the molten steel is subjected to LF furnace refining and nitrogen blowing treatment, which significantly increases the nitrogen content of the molten steel, reduces the V / N ratio in the steel, increases the driving force for the precipitation of V(C, N) and VN, promotes the transfer of V from the solid solution state to the carbonitride precipitation phase during the rolling process, and forms and precipitates a large amount of fine and dispersed V(C, N) and VN precipitation phases, so that the precipitation strengthening effect of the steel is significantly improved; a certain amount of chromium and nickel are added to the steel, thereby improving the passivation corrosion resistance of the steel, and the corrosion rate is only 2 / 3 of that of ordinary HRB600 steel bars, while the hardenability and secondary hardening effect are significantly improved, the pearlite content is increased, the tensile strength of the steel is promoted, and the seismic resistance is significantly improved; the high opening of the steel rolling control The rolling temperature is controlled, which promotes the full solid solution of microalloy V; a longer water cooling device is used after pre-finishing rolling to control the lower finishing rolling temperature of the rolled piece; after finishing rolling, two groups of finishing mills are used for rolling, and a water cooling device is used between the first and second groups of finishing rolling to control the lower finishing rolling temperature; a longer water cooling device is used for cooling after finishing rolling; by adopting multiple graded limited controlled cooling processes such as controlled cooling before finishing rolling, temperature-controlled low-temperature rolling of the finishing rolling unit, and controlled cooling after finishing rolling, the original austenite grains are significantly refined, the formation and precipitation of a large number of fine and dispersed V (C, N) and VN precipitation phases are promoted, the nucleation position and nucleation rate of ferrite grains are increased, the ferrite grains are significantly refined, the grain size reaches above 12.0, the fine grain strengthening effect is significant, the strength of the steel is greatly improved, and the plastic toughness of the steel is improved; the C and Mn contents in the steel are controlled at a high level, the pearlite content is increased, the tensile strength of the steel is significantly improved, and the seismic performance is improved.

[0008] The preparation method of the present invention integrates and innovates the chemical composition design, converter smelting, deoxidation alloying, continuous casting, steel rolling heating system, rolling temperature and controlled cooling process, giving full play to the multiple strengthening effects such as precipitation strengthening and fine grain strengthening. The large-scale 650MPa steel bars produced have the advantages of excellent and stable process mechanical properties, fine and uniform microstructure, good plasticity and toughness, excellent corrosion resistance and seismic resistance, etc., which improves the market competitiveness and application scope of the products. In addition, the process of the present invention has the characteristics of low production cost, strong process applicability and controllability, and has significant economic and social benefits. DETAILED DESCRIPTION

[0009] 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.

[0010] The invention discloses a large-size 650MPa high-toughness corrosion-resistant and earthquake-resistant steel bar with a nominal diameter of 28-40mm, which has the following chemical compositions in weight percentage: C 0.26-0.29wt%, Si 0.65-0.75wt%, Mn 1.52-1.60wt%, Cr0.15-0.20wt%, Ni 0.12-0.18wt%, V 0.136-0.150wt%, S≤0.035wt%, P≤0.035wt%, O≤0.0040wt%, N 0.0310-0.0340wt%, and the rest is Fe and inevitable impurities. The process mechanical properties, microstructure, Vickers hardness difference and corrosion resistance of the earthquake-resistant steel bar are shown in Table 1 and Table 2.

[0011] Table 1 Mechanical properties and corrosion resistance of the large-size 650MPa high-strength and tough earthquake-resistant steel bars with a nominal diameter of 28-40mm of the present invention Table 2 Metallographic structure and Vickers hardness of the large-size 650MPa high-strength and tough earthquake-resistant steel bars with a nominal diameter of 28-40mm in the present invention The present invention also provides a method for preparing the large-size 650MPa high-toughness corrosion-resistant and earthquake-resistant steel bar with a nominal diameter of 28-40mm, which is achieved by the following steps: A. Molten steel smelting: 250-260kg / t 钢 , 1.0-1.6kg / t 钢 The cold material charging ratio is 800-810kg / t. 钢 The molten iron charging ratio is 15-20kg / t. The molten iron with a temperature of ≥1310℃ is added to the LD converter for conventional top and bottom composite blowing. 钢 , 15-18kg / t 钢 Lime and light-burned dolomite are added in an amount to make slag, and the final carbon content is controlled to be ≥0.08wt%, and the tapping temperature is ≤1650°C; the composition of the molten iron is: C 4.1-4.5wt%, Si 0.15-0.30wt%, Mn 0.25-0.40wt%, P 0.080-0.100wt%, S≤0.035wt%, and the rest is Fe and inevitable impurities; Before tapping, the ladle is 12.0kg / t 钢 The following mass ratios of vanadium-containing pig iron are added: C 3.2wt%, Si0.20wt%, Mn 1.05wt%, V 5.25wt%, P0.60wt%, S 0.155wt%, and the rest are Fe and unavoidable impurities; before tapping, the vanadium content is 1.0kg / t 钢Adding active lime to the bottom of the ladle for slag washing; baking the vanadium-containing pig iron for 3 minutes after adding it to the ladle; 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 → high carbon ferrochrome → nitrogen-rich alloy → vanadium-nitrogen alloy. The deoxidation and alloying steps are carried out at 1.5 kg / t. 钢 , 3.3~4.5kg / t 钢 23.2~24.5kg / t 钢 , 2.3~3.2kg / t 钢 1.10~1.23kg / t 钢 , 0.95~1.12kg / t 钢 Add silicon calcium barium, ferrosilicon, silicon manganese alloy, high carbon ferrochrome, silicon nitrogen alloy and high vanadium nitrogen 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. LF furnace refining of molten steel: The molten steel in step B 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 3 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; D. Molten steel casting: at 1525-1540℃, the pulling speed is 3.4-3.5m / min, and the crystallizer cooling water flow rate is 150-160m 3 / h, and the secondary cooling water volume is 2.0-2.1L / kg, the molten steel is cast into a steel billet with a cross-section of 165mm×165mm; E. Billet heating: The billet in step D is sent to a heating furnace with a soaking section temperature of 1110-1160°C for heating for 70 minutes. The billet tapping temperature is 1050-1070°C, and then pushed to a fully continuous bar mill for rolling; F. Controlled rolling and controlled cooling of steel billets: The steel billets in step E are rolled for 6 passes at a speed of 0.4-0.6 m / s by the rough rolling unit, and then rolled for 4 passes at a speed of 2.0-2.5 m / s by the intermediate rolling unit, and then rolled for 6 passes at a speed of 5.0-7.0 m / s by the pre-finishing rolling unit; before the rolled pieces enter the finishing rolling, they are cooled by 2 sets of water cooling devices with a length of 4 m respectively, and the cooling water volume is 100-120 m 3 / h, the temperature of the rolled piece entering the finishing rolling unit is controlled at 790-820℃; the rolled piece passes through the finishing rolling unit at a speed of 8.0-9.0m / s for 1-2 passes; before entering the finishing rolling unit 2, the rolled piece passes through 2 sets of water cooling devices with a length of 7m each for controlled cooling, with a cooling water volume of 70-80m 3 / h, the temperature of the rolled piece entering the second finishing rolling group is controlled at 820-840℃; then the rolled piece passes through the second finishing rolling group at a rolling speed of 10-12m / s for 2 passes; after finishing rolling, the rolled piece passes through a group of water cooling devices with a length of 10m for post-finishing cooling, and the cooling water volume is 40-50m 3 / h; after controlled cooling, the temperature of the steel bar on the cooling bed is controlled at 900-930℃, and then the steel bar is naturally air-cooled to room temperature on the cooling bed to obtain large-size 650MPa high-strength and toughness earthquake-resistant steel bars with a nominal diameter of 28-40mm.

[0012] In step A, the chemical composition of the scrap steel is: C 0.20-0.26wt%, Si 0.25-0.60wt%, Mn 1.25-1.50wt%, P 0.018-0.042wt%, S 0.015-0.042wt%, and the rest is Fe and inevitable impurities; the chemical composition of the nickel plate is: Ni 99.2wt%, P 0.025wt%, S0.032wt%, and the rest is inevitable impurities.

[0013] 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.

[0014] 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%, Si17.8wt%, C 1.5wt%, and the rest is Fe and inevitable impurities; the chemical composition of high carbon ferrochrome is: Cr 53.8wt%, C 7.2wt%, P 0.061wt%, S0.054wt%, and the rest is Fe and inevitable impurities; the chemical composition of silicon nitrogen alloy is: Si 57.6wt%, N 39.5wt%, C0.95wt%, P 0.045wt%, S 0.024wt%, the rest are Fe and inevitable impurities; the chemical composition of vanadium-nitrogen alloy is: V77.4wt%, N 15.8wt%, C 3.25wt%, P 0.082wt%, S0.062wt%, the rest are Fe and inevitable impurities.

[0015] In step C, during the refining process, nitrogen gas with a flow rate of 20-25 NL / min is used to blow nitrogen into the molten steel, and then the lower electrode is slag-free at gears 7-9; 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 4-5 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.

[0016] In step D, R9m straight arc continuous straightening 5-machine 5-strand billet casting machine is used for casting. The straightening temperature of the billet out of the straightening machine is controlled at 960-980°C.

[0017] Example 1 A. Molten steel smelting: 250kg / t 钢 The cold material charging ratio is 1.0kg / t. The following scrap steel (chemical composition: C 0.20wt%, Si 0.25wt%, Mn 1.25wt%, P 0.018wt%, S0.015wt%, the rest is Fe and inevitable impurities) is added to the LD converter; 钢 The charging ratio is as follows: nickel plates (chemical composition: Ni 99.2wt%, P 0.025wt%, S 0.032wt%, the rest are inevitable impurities) are added to the LD converter; then 800kg / t 钢 The molten iron charging ratio is as follows: molten iron temperature is 1310℃, molten iron composition is C 4.1wt%, Si 0.15wt%, Mn 0.25wt%, P 0.080wt%, S 0.016wt%, and the rest is Fe and inevitable impurities; after the scrap steel and molten iron are added into the LD converter, conventional top and bottom composite blowing is carried out, conventional lime and light-burned dolomite are added for slag making, and the amount of lime added is 15kg / t 钢 , the amount of light-burned dolomite added is 15kg / t 钢 , the final carbon content is controlled at 0.08wt%, the tapping temperature is 1626℃; the ladle is pressurized at 12.0kg / t before tapping 钢 The following mass ratio of vanadium-containing pig iron is added: C 3.2wt%, Si 0.20wt%, Mn1.05wt%, V 5.25wt%, P 0.60wt%, S 0.155wt%, the rest is Fe and inevitable impurities. The vanadium-containing pig iron is added to the ladle and baked for 3 minutes; before tapping, active lime is added to the bottom of the ladle for slag washing, and the amount of lime added is 1.0 kg / t 钢 The steel-making process adopts the bottom blowing nitrogen process, and the nitrogen flow rate is controlled at 15NL / min.

[0018] 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 → high carbon ferrochrome → nitrogen-rich alloy → vanadium nitrogen alloy: 1.5kg / t 钢 The following mass ratios of silicon, calcium and barium are added: Si 52.5wt%, Ca 9.85wt%, Ba 12.15wt%, Al 2.45wt%, and the rest is Fe and unavoidable impurities; 3.3kg / t 钢 Add the following mass ratio of ferrosilicon: Si 73.5wt%, the rest is Fe and inevitable impurities; at 23.2kg / t 钢 The amount of silicon-manganese alloy with the following mass ratio is added: Mn 65.2wt%, Si 17.8wt%, C1.5wt%, and the rest is Fe and inevitable impurities; according to 2.3 kg / t 钢 The amount of high carbon ferrochrome in the following mass ratio is added: Cr 53.8wt%, C 7.2wt%, P0.061wt%, S0.054wt%, and the rest is Fe and unavoidable impurities; at 1.10kg / t 钢 The amount of silicon-nitrogen alloy in the following mass ratio is added: Si 57.6wt%, N 39.5wt%, C 0.95wt%, P 0.045wt%, S 0.024wt%, and the rest is Fe and unavoidable impurities; kg / t 钢 The following vanadium-nitrogen alloys are added in the following mass ratios: V 77.4wt%, N 15.8wt%, C 3.25wt%, P 0.082wt%, S 0.062wt%, and the rest are Fe and inevitable impurities; the above alloys are added when the amount of molten steel in the ladle reaches 4 / 5; after tapping, the molten steel is hoisted to the LF furnace for refining treatment.

[0019] C. LF furnace refining of molten steel: Lift the molten steel to the LF furnace refining station and connect the nitrogen belt. Turn on the nitrogen and use a nitrogen flow rate of 20NL / min to blow nitrogen into the molten steel. Then, use the 7th to 9th gear of the lower electrode to slag. After 3 minutes of 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 3 minutes, and the nitrogen flow rate is controlled to 10NL / min; after the nitrogen blowing, add molten steel covering agent, and the addition amount is controlled to 1.0 kg / t钢 , and then lift the molten steel to the casting station.

[0020] D. Molten steel casting: The tundish temperature is 1540℃, the pulling speed is 3.4m / min, and the crystallizer cooling water flow rate is 150m 3 / h, and the secondary cooling water volume was 2.0L / 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 960℃.

[0021] E. Billet heating: The billet in step D is fed into a heating furnace with a temperature of 1110°C in the soaking section and heated for 70 minutes. The billet tapping temperature is 1050°C and then pushed to a fully continuous bar mill for rolling.

[0022] F. Controlled rolling and controlled cooling of steel billets: The steel billets in step E are rolled for 6 passes at a speed of 0.6 m / s by the rough rolling mill; then the rolled pieces are rolled for 4 passes at a speed of 2.5 m / s by the intermediate rolling mill; then the rolled pieces are rolled for 6 passes at a speed of 7.0 m / s by the pre-finishing rolling mill; then the rolled pieces are controlled and cooled before finishing rolling by two groups of water cooling devices with a length of 4 m respectively, and the cooling water volume is 100 m 3 / h, the temperature of the rolled piece entering the finishing rolling unit is controlled at 820℃; then the rolled piece passes through the finishing rolling unit 1 at a rolling speed of 9.0m / s for 2 passes; before entering the finishing rolling unit 2, the rolled piece is cooled by 2 sets of water cooling devices with a length of 7m respectively, and the cooling water volume is 70m 3 / h, the temperature of the rolled piece entering the second finishing rolling unit is controlled at 840℃; then the rolled piece passes through the second finishing rolling unit at a rolling speed of 12m / s for 2 passes; after finishing rolling, the rolled piece passes through a set of water cooling devices with a length of 10m for post-finishing cooling, and the cooling water volume is 40m 3 / h; after controlled cooling, the temperature of the cooling bed on the steel bar is controlled to 930℃, and then the steel bar is naturally air-cooled to room temperature on the cooling bed, and a large-size 650MPa high-strength and tough earthquake-resistant steel bar with a nominal diameter of 28mm and a chemical composition of the following weight percentage is obtained: C 0.26wt%, Si 0.65wt%, Mn 1.52wt%, Cr 0.15wt%, Ni0.12wt%, V 0.136wt%, S 0.017wt%, P 0.016wt%, O 0.0022wt%, N 0.0310wt%, and the rest is Fe and unavoidable impurities. Its process mechanical properties, microstructure, Vickers hardness difference and corrosion resistance are shown in Tables 3 and 4.

[0023] Table 3 Process mechanical properties and corrosion resistance of large-size 650MPa high-strength and tough earthquake-resistant steel bars with a nominal diameter of 28mm produced in Example 1 Table 4 Metallographic microstructure and Vickers hardness of large-size 650MPa high-strength and tough earthquake-resistant steel bars with a nominal diameter of 28 mm produced in Example 1 Example 2 A. Molten steel smelting: 256kg / t 钢 The cold material charging ratio is 1.3kg / t. The following scrap steel (chemical composition: C 0.23wt%, Si 0.42wt%, Mn 1.38wt%, P 0.028wt%, S0.028wt%, the rest is Fe and inevitable impurities) is added to the LD converter; 钢 The charging ratio is as follows: nickel plates (chemical composition: Ni 99.2wt%, P 0.025wt%, S 0.032wt%, the rest are inevitable impurities) are added to the LD converter; then 806kg / t 钢 The molten iron charging ratio is as follows: molten iron temperature is 1320℃, molten iron composition is C 4.3wt%, Si 0.27wt%, Mn 0.32wt%, P 0.090wt%, S 0.028wt%, and the rest is Fe and inevitable impurities; after the scrap steel and molten iron are added into the LD converter, conventional top and bottom composite blowing is carried out, conventional lime and light-burned dolomite are added for slag making, and the amount of lime added is 18kg / t 钢 , the amount of light-burned dolomite added is 17kg / t 钢 , the final carbon content is controlled at 0.09wt%, the tapping temperature is 1640℃; the ladle is pressurized at 12.0kg / t before tapping 钢 The following mass ratio of vanadium-containing pig iron is added: C 3.2wt%, Si 0.20wt%, Mn1.05wt%, V 5.25wt%, P 0.60wt%, S 0.155wt%, the rest is Fe and inevitable impurities. The vanadium-containing pig iron is added to the ladle and baked for 3 minutes; before tapping, active lime is added to the bottom of the ladle for slag washing, and the amount of lime added is 1.0 kg / t 钢 The steel-making process adopts the bottom blowing nitrogen process, and the nitrogen flow rate is controlled at 15-20NL / min.

[0024] 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 → high carbon ferrochrome → nitrogen-rich alloy → vanadium nitrogen alloy: 1.5kg / t 钢The following mass ratios of silicon, calcium and barium are added: Si 52.5wt%, Ca 9.85wt%, Ba 12.15wt%, Al 2.45wt%, and the rest is Fe and unavoidable impurities; 3.8kg / t 钢 Add the following mass ratio of ferrosilicon: Si 73.5wt%, the rest is Fe and inevitable impurities; at 23.9kg / t 钢 The amount of silicon-manganese alloy with the following mass ratio is added: Mn 65.2wt%, Si 17.8wt%, C1.5wt%, and the rest is Fe and inevitable impurities; according to 2.9 kg / t 钢 The amount of high carbon ferrochrome in the following mass ratio is added: Cr 53.8wt%, C 7.2wt%, P0.061wt%, S0.054wt%, and the rest is Fe and unavoidable impurities; at 1.18kg / t 钢 The amount of silicon-nitrogen alloy is added in the following mass ratio: Si 57.6wt%, N 39.5wt%, C 0.95wt%, P0.045wt%, S 0.024wt%, and the rest is Fe and unavoidable impurities; at 0.95~1.12kg / t 钢 The following vanadium-nitrogen alloys are added in the following mass ratios: V 77.4wt%, N 15.8wt%, C3.25wt%, P 0.082wt%, S 0.062wt%, and the rest are 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 LF furnace for refining treatment.

[0025] C. LF furnace refining of molten steel: Lift the molten steel to the LF furnace refining station and connect the nitrogen belt. Turn on the nitrogen and use a nitrogen flow rate of 25NL / min to blow nitrogen into the molten steel. Then, use the 7th to 9th gear of the lower electrode to slag. After 3 minutes of 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 of 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 steel liquid composition and lower electrode temperature according to the steel sample and temperature test results to ensure that the composition and temperature are qualified; after refining, perform small flow soft nitrogen blowing on the molten steel, the blowing time is 3 minutes, and the nitrogen flow rate is controlled to 15NL / min; after the nitrogen blowing is completed, add molten steel covering agent, and the addition amount is controlled to 1.0 kg / t 钢 , and then lift the molten steel to the casting station.

[0026] D. Molten steel casting: The tundish temperature is 1533°C, the pulling speed is 3.5m / min, and the crystallizer cooling water flow rate is 156m 3 / h, and the secondary cooling water volume was 2.1L / 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 970℃.

[0027] E. Billet heating: The billet in step D is fed into a heating furnace with a temperature of 1140°C in the soaking section and heated for 70 minutes. The billet tapping temperature is 1060°C and then pushed to a fully continuous bar mill for rolling.

[0028] F. Controlled rolling and controlled cooling of steel billets: The steel billets in step E are rolled for 6 passes at a speed of 0.5 m / s by the rough rolling mill; then the rolled pieces are rolled for 4 passes at a speed of 2.3 m / s by the intermediate rolling mill; then the rolled pieces are rolled for 6 passes at a speed of 6.0 m / s by the pre-finishing rolling mill; then the rolled pieces are controlled and cooled before finishing rolling by two groups of water cooling devices with a length of 4 m respectively, and the cooling water volume is 110 m 3 / h, the temperature of the rolled piece entering the finishing rolling unit is controlled at 805℃; then the rolled piece passes through the finishing rolling unit at a speed of 8.5m / s for one pass; before entering the finishing rolling unit 2, the rolled piece is cooled by two water cooling devices with a length of 7m each, and the cooling water volume is 75m 3 / h, the temperature of the rolled piece entering the second finishing rolling unit is controlled at 830℃; then the rolled piece passes through the second finishing rolling unit at a rolling speed of 10m / s for 2 passes; after finishing rolling, the rolled piece passes through a set of water cooling devices with a length of 10m for post-finishing cooling, and the cooling water volume is 45m 3 / h; after controlled cooling, the temperature of the cooling bed on the steel bar is controlled to 915℃, and then the steel bar is naturally air-cooled to room temperature on the cooling bed, and a large-size 650MPa high-strength and tough earthquake-resistant steel bar with a nominal diameter of 32mm and a chemical composition of the following weight percentage is obtained: C 0.27wt%, Si 0.70wt%, Mn 1.55wt%, Cr 0.18wt%, Ni0.15wt%, V 0.141wt%, S 0.028wt%, P 0.029wt%, O0.0033wt%, N0.0325wt%, and the rest is Fe and unavoidable impurities. Its process mechanical properties, microstructure, Vickers hardness difference and corrosion resistance are shown in Tables 5 and 6.

[0029] Table 5 Process mechanical properties and corrosion resistance of large-size 650MPa high-strength and tough earthquake-resistant steel bars with a nominal diameter of 32mm produced in Example 2 Table 6 Metallographic microstructure and Vickers hardness of large-size 650MPa high-strength and tough earthquake-resistant steel bars with a nominal diameter of 32 mm produced in Example 2 Example 3 A. Molten steel smelting: 260kg / t 钢 The cold material charging ratio is 1.6kg / t. The following scrap steel (chemical composition: C 0.26wt%, Si 0.60wt%, Mn 1.50wt%, P 0.042wt%, S 0.042wt%, the rest is Fe and inevitable impurities) is added to the LD converter; 钢 The charging ratio is as follows: nickel plates (chemical composition: Ni 99.2wt%, P 0.025wt%, S 0.032wt%, the rest are inevitable impurities) are added to the LD converter; then 810kg / t 钢 The molten iron charging ratio is as follows: molten iron temperature is 1325℃, molten iron composition is C 4.5wt%, Si 0.30wt%, Mn 0.40wt%, P 0.100wt%, S 0.035wt%, and the rest is Fe and inevitable impurities; after the scrap steel and molten iron are added into the LD converter, conventional top and bottom composite blowing is carried out, conventional lime and light-burned dolomite are added for slag making, and the amount of lime added is 20kg / t 钢 , the amount of light-burned dolomite added is 18kg / t 钢 , control the final carbon content to 0.10wt%, the tapping temperature to 1650℃; the ladle before tapping is 12.0kg / t 钢 The following mass ratio of vanadium-containing pig iron is added: C 3.2wt%, Si 0.20wt%, Mn1.05wt%, V 5.25wt%, P 0.60wt%, S 0.155wt%, the rest is Fe and inevitable impurities. The vanadium-containing pig iron is added to the ladle and baked for 3 minutes; before tapping, active lime is added to the bottom of the ladle for slag washing, and the amount of lime added is 1.0 kg / t 钢 The steel-making process adopts the 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 → high carbon ferrochrome → nitrogen-rich alloy → vanadium nitrogen alloy: 1.5kg / t 钢 Add the following mass ratio of silicon, calcium and barium: Si 52.5wt%, Ca 9.85wt%, Ba 12.15wt%, Al 2.45wt%, the rest is Fe and unavoidable impurities; at 4.5kg / t 钢Add the following mass ratio of ferrosilicon: Si 73.5wt%, the rest is Fe and inevitable impurities; at 24.5kg / t 钢 Add the following mass ratio of silicon-manganese alloy: Mn 65.2wt%, Si 17.8wt%, C1.5wt%, the rest is Fe and inevitable impurities; according to 3.2 kg / t 钢 The amount of high carbon ferrochrome in the following mass ratio is added: Cr 53.8wt%, C 7.2wt%, P0.061wt%, S0.054wt%, and the rest is Fe and unavoidable impurities; at 1.23kg / t 钢 The amount of silicon-nitrogen alloy is added in the following mass ratio: Si 57.6wt%, N 39.5wt%, C 0.95wt%, P0.045wt%, S 0.024wt%, and the rest is Fe and unavoidable impurities; according to 1.12 kg / t 钢 The following vanadium-nitrogen alloys are added in the following mass ratios: V 77.4wt%, N 15.8wt%, C 3.25wt%, P 0.082wt%, S 0.062wt%, and the rest are Fe and inevitable impurities; the above alloys are added when the amount of molten steel in the ladle reaches 4 / 5; after tapping, the molten steel is hoisted to the LF furnace for refining treatment.

[0031] C. LF furnace refining of molten steel: Lift the molten steel to the LF furnace refining station and connect the nitrogen belt. Turn on the nitrogen and use a nitrogen flow rate of 25NL / min to blow nitrogen into the molten steel. Then, use the 7th to 9th gear of the lower electrode to slag. After 3 minutes of 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 of 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 steel liquid composition and lower electrode temperature according to the steel sample and temperature test results to ensure that the composition and temperature are qualified; after refining, perform small flow soft nitrogen blowing on the molten steel, the blowing time is 3 minutes, and the nitrogen flow rate is controlled to 15NL / min; after the nitrogen blowing is completed, add molten steel covering agent, and the addition amount is controlled to 1.0 kg / t 钢 , and then lift the molten steel to the casting station.

[0032] D. Molten steel casting: The tundish temperature is 1525℃, the pulling speed is 3.5m / min, and the crystallizer cooling water flow rate is 160m 3 / h, and the secondary cooling water volume was 2.1L / 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 980℃.

[0033] E. Billet heating: The billet in step D is fed into a heating furnace with a temperature of 1160°C in the soaking section and heated for 70 minutes. The billet tapping temperature is 1070°C and then pushed to a fully continuous bar mill for rolling.

[0034] F. Controlled rolling and controlled cooling of steel billets: The steel billets in step E are rolled by the rough rolling unit at a speed of 0.4 m / s for 6 passes; then the rolled pieces are rolled by the intermediate rolling unit at a speed of 2.0 m / s for 4 passes; then the rolled pieces are rolled by the pre-finishing rolling unit at a speed of 5.0 m / s for 6 passes; then the rolled pieces are controlled and cooled before finishing rolling by two groups of water cooling devices with a length of 4 m respectively, and the cooling water volume is 120 m 3 / h, the temperature of the rolled piece entering the finishing rolling unit is controlled at 790℃; then the rolled piece passes through the finishing rolling unit 1 at a rolling speed of 8.0m / s for one pass; before entering the finishing rolling unit 2, the rolled piece is controlled to cool by two water cooling devices with a length of 7m each, and the cooling water volume is 80m 3 / h, the temperature of the rolled piece entering the second finishing rolling unit is controlled at 820℃; then the rolled piece passes through the second finishing rolling unit at a rolling speed of 10m / s for 2 passes; after finishing rolling, the rolled piece passes through a set of water cooling devices with a length of 10m for post-finishing cooling, and the cooling water volume is 50m 3 / h; after controlled cooling, the temperature of the cooling bed on the steel bar is controlled to 900℃, and then the steel bar is naturally air-cooled to room temperature on the cooling bed, and a large-size 650MPa high-strength and tough earthquake-resistant steel bar with a nominal diameter of 40mm and a chemical composition of the following weight percentage is obtained: C 0.29wt%, Si 0.75wt%, Mn 1.60wt%, Cr 0.20wt%, Ni0.18wt%, V 0.150wt%, S 0.035wt%, P 0.035wt%, O0.0040wt%, N0.0340wt%, and the rest is Fe and unavoidable impurities. Its process mechanical properties, microstructure, Vickers hardness difference and corrosion resistance are shown in Tables 7 and 8.

[0035] Table 7 Process mechanical properties and corrosion resistance of large-size 650MPa high-strength and tough earthquake-resistant steel bars with a nominal diameter of 40 mm produced in Example 3 Table 8 Metallographic microstructure and Vickers hardness of large-size 650MPa high-strength and tough earthquake-resistant steel bars with a nominal diameter of 40 mm produced in Example 3 .

Claims

1. A large-size 650MPa high-strength, tough, corrosion-resistant and earthquake-resistant steel bar with a nominal diameter of 28-40mm. It is characterized in that The earthquake-resistant steel bar has the following chemical composition in weight percentage: C 0.26-0.29wt%, Si 0.65-0.75wt%, Mn 1.52-1.60wt%, Cr 0.15-0.20wt%, Ni 0.12-0.18wt%, V 0.136-0.150wt%, S≤0.035wt%, P≤0.035wt%, O≤0.0040wt%, N 0.0310-0.0340wt%, and the rest is Fe and inevitable impurities.

2. According to claim 1, the large-size 650MPa high-toughness corrosion-resistant and earthquake-resistant steel bar with a nominal diameter of 28-40mm, It is characterized in that The seismic steel bar has a yield strength of 670-700 MPa, a tensile strength of 860-910 MPa, a strength-to-yield ratio of ≥1.28, an elongation after fracture of ≥18%, and a total elongation at maximum force of ≥10.5%.

3. The method for preparing the large-size 650MPa high-toughness corrosion-resistant and earthquake-resistant steel bar with a nominal diameter of 28-40mm as claimed in claim 1, It is characterized in that To do this, follow these steps: A. Molten steel smelting: 250-260kg / t 钢 , 1.0-1.6kg / t 钢 The cold material charging ratio is 800-810kg / t. 钢 The molten iron charging ratio is 15-20kg / t. The molten iron with a temperature of ≥1310℃ is added to the LD converter for conventional top and bottom composite blowing. 钢 , 15-18kg / t 钢 Lime and light-burned dolomite are added in an amount to make slag, and the final carbon content is controlled to be ≥0.08wt%, and the tapping temperature is ≤1650°C; the composition of the molten iron is: C 4.1-4.5wt%, Si 0.15-0.30wt%, Mn 0.25-0.40wt%, P 0.080-0.100wt%, S≤0.035wt%, and the rest is Fe and inevitable impurities; Before tapping, the ladle is 12.0kg / t 钢 The amount of vanadium-containing pig iron is added in the following mass ratio: C 3.2wt%, Si0.20wt%, Mn 1.05wt%, V 5.25wt%, P 0.60wt%, S 0.155wt%, and the rest is Fe and inevitable impurities; before tapping, the vanadium content is 1.0kg / t 钢 Adding active lime to the bottom of the ladle for slag washing; baking the vanadium-containing pig iron for 3 minutes after adding it to the ladle; 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 → high carbon ferrochrome → nitrogen-rich alloy → vanadium-nitrogen alloy. The deoxidation and alloying steps are carried out at 1.5 kg / t. 钢 , 3.3~4.5kg / t 钢 , 23.2~24.5kg / t 钢 , 2.3~3.2kg / t 钢 1.10~1.23kg / t 钢 , 0.95~1.12kg / t 钢 Add silicon calcium barium, ferrosilicon, silicon manganese alloy, high carbon ferrochrome, silicon nitrogen alloy and high vanadium nitrogen 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. LF furnace refining of molten steel: The molten steel in step B 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 3 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; D. Molten steel casting: at 1525-1540℃, the pulling speed is 3.4-3.5m / min, and the crystallizer cooling water flow rate is 150-160m 3 / h, and the secondary cooling water volume is 2.0-2.1L / kg, the molten steel is cast into a steel billet with a cross-section of 165mm×165mm; E. Billet heating: The billet in step D is sent to a heating furnace with a soaking section temperature of 1110-1160°C for heating for 70 minutes. The billet tapping temperature is 1050-1070°C, and then pushed to a fully continuous bar mill for rolling; F. Controlled rolling and controlled cooling of steel billets: The steel billets in step E are rolled for 6 passes at a speed of 0.4-0.6 m / s by the rough rolling unit, and then rolled for 4 passes at a speed of 2.0-2.5 m / s by the intermediate rolling unit, and then rolled for 6 passes at a speed of 5.0-7.0 m / s by the pre-finishing rolling unit; before the rolled pieces enter the finishing rolling, they are cooled by 2 sets of water cooling devices with a length of 4 m respectively, and the cooling water volume is 100-120 m 3 / h, the temperature of the rolled piece entering the finishing rolling unit is controlled at 790-820℃; the rolled piece passes through the finishing rolling unit at a speed of 8.0-9.0m / s for 1-2 passes; before entering the finishing rolling unit 2, the rolled piece passes through 2 sets of water cooling devices with a length of 7m each for controlled cooling, with a cooling water volume of 70-80m 3 / h, the temperature of the rolled piece entering the second finishing rolling group is controlled at 820-840℃; then the rolled piece passes through the second finishing rolling group at a rolling speed of 10-12m / s for 2 passes; after finishing rolling, the rolled piece passes through a group of water cooling devices with a length of 10m for post-finishing cooling, and the cooling water volume is 40-50m 3 / h; after controlled cooling, the temperature of the steel bar on the cooling bed is controlled at 900-930℃, and then the steel bar is naturally air-cooled to room temperature on the cooling bed to obtain large-size 650MPa high-strength and toughness earthquake-resistant steel bars with a nominal diameter of 28-40mm.

4. The method for preparing the large-size 650MPa high-strength and tough earthquake-resistant steel bar with a nominal diameter of 28-40mm according to claim 3, It is characterized in that In step A, the chemical composition of the scrap steel is: C 0.20-0.26wt%, Si 0.25-0.60wt%, Mn1.25-1.50wt%, P 0.018-0.042wt%, S 0.015-0.042wt%, and the rest is Fe and inevitable impurities; the chemical composition of the nickel plate is: Ni 99.2wt%, P 0.025wt%, S 0.032wt%, and the rest is inevitable impurities.

5. The method for preparing the large-size 650MPa high-strength and tough earthquake-resistant steel bar with a nominal diameter of 28-40mm according to claim 3, It is 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.

6. The method for preparing the large-size 650MPa high-strength and tough earthquake-resistant steel bar with a nominal diameter of 28-40mm according to claim 3, It is 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 17.8wt%, C 1.5wt%, and the rest is Fe and inevitable impurities; the chemical composition of high carbon ferrochrome is: Cr 53.8wt%, C 7.2wt%, P 0.061wt%, S0.054wt%, and the rest is Fe and inevitable impurities; the chemical composition of silicon nitrogen alloy is: Si 57.6wt%, N39.5wt%, C 0.95wt%, P 0.045wt%, S 0.024wt%, and the rest is Fe and inevitable impurities; the chemical composition of vanadium nitrogen alloy is: V 77.4wt%, N 15.8wt%, C 3.25wt%, P 0.082wt%, S 0.062wt%, and the rest are Fe and inevitable impurities.

7. The method for preparing the large-size 650MPa high-strength and tough earthquake-resistant steel bar with a nominal diameter of 28-40mm according to claim 3, It is characterized in that In step C, during the refining process, nitrogen gas with a flow rate of 20-25 NL / min is used to blow nitrogen into the molten steel, and then the lower electrode is slag-free at gears 7-9; 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 4-5 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.

8. The method for preparing the large-size 650MPa high-strength and tough earthquake-resistant steel bar with a nominal diameter of 28-40mm according to claim 3, It is characterized in that In step D, R9m straight arc continuous straightening 5-machine 5-strand billet casting machine is used for casting.

9. The method for preparing the large-size 650MPa high-strength and tough earthquake-resistant steel bar with a nominal diameter of 28-40mm according to claim 3, It is characterized in that In step D, the straightening temperature of the ingot out of the straightening machine is controlled at 960-980°C.

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