Preparation method of nitrogen-rich microalloy 650MPa high-strength aseismic steel bar with nominal diameter of 12-16mm

Abstract

The invention discloses a preparation method of a nitrogen-rich microalloy 650MPa high-strength aseismic steel bar with the nominal diameter of 12-16mm. According to the nitrogen-rich microalloy 650 MPa high-strength aseismic steel bar with the nominal diameter of 12-16 mm, the yield strength is 665-690 MPa, the tensile strength is 850-900 MPa, the ratio of strength to yield is larger than or equal to 1.28, the percentage elongation after fracture is larger than or equal to 20%, and the maximum force total elongation is larger than or equal to 10.5%. By integrating and innovating chemical component design, converter smelting, deoxidation alloying, argon station treatment, continuous casting, steel rolling heating schedule, process temperature control rolling and controlled cooling after rolling, multiple strengthening effects of precipitation strengthening, fine grain strengthening, structure strengthening and the like are fully exerted; the produced 650MPa anti-seismic steel bar with the nominal diameter of 12-16mm has the advantages of excellent and stable process mechanical properties, fine and uniform microscopic structure, good plasticity and toughness, excellent anti-seismic property and the like. The technology is low in production cost and high in technology applicability and controllability, the application range and the market competitiveness of the product are improved, and remarkable economic and social benefits are achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of steel smelting, and specifically relates to a method for preparing a nitrogen-rich microalloy 650MPa high-strength earthquake-resistant steel bar with a nominal diameter of 12-16mm. 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 one of the important tasks for the steel industry to improve its technical level and adjust its product structure.

[0003] At present, there are relevant research reports on the production technology of 600MPa and 630MPa high-strength steel bars in China, but there are few reports on the production and preparation technology of small-sized 650MPa and above high-strength earthquake-resistant steel bars with a nominal diameter of 12-16mm. Small-sized 600MPa and 630MPa high-strength steel bars with a nominal diameter of 12-16mm mainly adopt vanadium-nitrogen microalloying process, with V content ≥0.150wt% in steel, and the seismic performance index of steel bars, strength-to-yield ratio (R°m / R°eL), is mostly 1.23-1.25, and the maximum force total elongation (Agt) is 7.5-9.0%. The seismic performance matching is not good, which restricts the use of products in building structures and infrastructure structures in high-intensity seismic areas.

[0004] The invention aims to provide a method for preparing a small-size nitrogen-rich microalloy 650MPa high-strength earthquake-resistant steel bar with a nominal diameter of 12-16mm. Summary of the invention

[0005] The object of the present invention is to provide a method for preparing a nitrogen-rich microalloy 650MPa high-strength earthquake-resistant steel bar with a nominal diameter of 12-16mm.

[0006] The object of the present invention is achieved by a method for preparing a nitrogen-rich microalloy 650MPa high-strength earthquake-resistant steel bar with a nominal diameter of 12-16mm, which is achieved by the following steps: A. Molten steel smelting: 200-220kg / t 钢 Cold material charging ratio, adding scrap steel in LD converter; then at 845-855kg / t 钢 The molten iron charging ratio is 20-23kg / t. The molten iron with a temperature of ≥1300℃ is added to the LD converter for conventional top and bottom composite blowing. 钢 、14-16kg / t 钢Lime and light-burned dolomite are added to make slag, and the final carbon content is controlled to be ≥0.07wt%, and the tapping temperature is ≤1620℃; before tapping, 1.0kg / t is added to the bottom of the ladle. 钢 The amount of slag washing material is added for slag washing; the composition of the molten iron is: C 4.2-4.6wt%, Si 0.20-0.40wt%, Mn 0.25-0.40wt%, P 0.075-0.095wt%, S≤0.030wt%, 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 → high-carbon ferrochrome → nitrogen-rich alloy → niobium-phosphorus-iron alloy → vanadium-nitrogen alloy, respectively, at a rate of 2.0 kg / t. 钢 , 3.1~4.5kg / t 钢 , 23.0~24.0kg / t 钢 4.5~5.1kg / t 钢 , 1.20kg / t 钢 , 0.40~0.54kg / t 钢 , 0.50~0.65kg / t 钢 Add silicon calcium barium, ferrosilicon, silicon manganese alloy, high carbon ferrochrome, nitrogen-rich alloy, niobium phosphorus iron 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 3 / 4; C. Argon treatment of molten steel: After the molten steel is tapped in step B, it is hoisted to the argon treatment station and passed through the alloy trough at a pressure of 15.0kg / t 钢 The amount of vanadium-containing pig iron is added and baked for 10 minutes, and the surface temperature of the vanadium-containing pig iron is ≥250°C, and then the molten steel is subjected to nitrogen blowing treatment; the composition of the vanadium-containing pig iron is: 3.3wt%, Si 0.25wt%, Mn 1.24wt%, V 5.05wt%, P 0.85wt%, S0.087wt%, 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. 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 1528-1540°C, the pulling speed is 2.8-3.0 m / min, and the crystallizer cooling water flow rate is 130-145 m 3 / h, and the secondary cooling water volume is 1.6-1.8L / kg, casting the molten steel in step D into a steel billet with a cross-section of 165mm×165mm; F. Billet heating: The billet in step E is sent to a heating furnace with a soaking section temperature of 1120-1160°C for heating for 90 minutes. The billet tapping temperature is 1050-1070°C, and then pushed to a fully continuous bar mill for rolling; G. Controlled rolling and controlled cooling of steel billets: The steel billets in step F are rolled for 6 passes at a rolling speed of 0.8-1.5 m / s by the rough rolling unit, and then rolled for 4 passes at a rolling speed of 2.5-4.5 m / s by the intermediate rolling unit, and then rolled for 6 passes at a rolling speed of 8.0-12.0 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 6 m respectively, and the cooling water volume is 80-100 m 3 / h, then the rolled piece is rolled 1-2 times at a speed of 16.0-27.0m / s through the finishing rolling unit 1, and the temperature of the rolled piece entering the finishing rolling unit 1 is controlled at 820-840℃; before the rolled piece enters the finishing rolling unit 2, it is cooled by two water cooling devices with a length of 8m respectively, and the cooling water volume is 50-60m 3 / h, the temperature of the rolled piece entering the second finishing rolling group is controlled at 810-830℃; then the rolled piece passes through the second finishing rolling group at a rolling speed of 32-38m / 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 930-950℃, and then the steel bar is naturally air-cooled to room temperature on the cooling bed, thus obtaining a 650MPa high-strength earthquake-resistant steel bar with a nominal diameter of 12-16mm.

[0007] The present invention adds a nitrogen-rich alloy 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 in the molten steel, reduces the V / N and Nb / N ratios in the steel, promotes the transfer of V and Nb from a solid solution state to a carbonitride precipitation phase during the rolling process, forms and precipitates a large amount of fine dispersed V (C, N) and Nb (C, N) precipitation phases, and significantly improves the precipitation strengthening effect of the steel; after steelmaking is completed, a large amount of vanadium-containing pig iron is added to the molten steel at the argon station to replace the expensive vanadium alloy, thereby increasing the V content in the molten steel and greatly reducing the amount of vanadium alloy added and the cost of microalloying; a certain amount of chromium and a small amount of niobium are added to the steel, which changes the microstructure ratio of the steel, increases the pearlite content and generates a small amount of granular bainite, promotes the optimal matching of the tensile strength and yield strength of the steel, and greatly improves the seismic resistance of the steel. Performance; The rolling start temperature is controlled at a higher level to promote the full solid solution of V and Nb microalloying elements; After pre-finishing rolling, a water cooling device is used to control the lower finishing rolling temperature of the rolled piece; After finishing rolling, the rolled piece is rolled by two groups of finishing mills, and a longer water cooling device is used between the first and second finishing mills to control the lower finishing temperature; After finishing rolling, a longer water cooling device is used for cooling; By adopting multiple graded limited controlled cooling processes such as controlled cooling before finishing rolling, low-temperature temperature controlled rolling of the finishing mill, and controlled cooling after finishing rolling, the original austenite grains are refined, the formation and precipitation of a large number of fine and dispersed V (C, N) and Nb (C, N) precipitation phases are promoted, the nucleation position and nucleation rate of ferrite grains are increased, the ferrite grain size reaches above 12.0, the ultrafine grain strengthening effect is significant, the strength of the steel is greatly improved, and the plasticity and toughness of the steel are improved.

[0008] The present invention integrates and innovates the chemical composition design, converter smelting, deoxidation alloying, argon station treatment, continuous casting, steel rolling heating system, process temperature-controlled rolling and post-rolling controlled cooling process, giving full play to the multiple strengthening effects such as precipitation strengthening, fine grain strengthening and organizational strengthening. The produced 650MPa earthquake-resistant steel bars with a nominal diameter of 12-16mm have the advantages of excellent and stable process mechanical properties, fine and uniform microstructure, good plastic toughness, excellent earthquake resistance, etc. The process of the present invention has low production cost, strong process applicability and controllability, improves the application range and market competitiveness of the product, 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 present invention provides a method for preparing a nitrogen-rich microalloy 650MPa high-strength earthquake-resistant steel bar with a nominal diameter of 12-16mm, which is achieved by the following steps: A. Molten steel smelting: 200-220kg / t 钢Cold material charging ratio, adding scrap steel in LD converter; then at 845-855kg / t 钢 The molten iron charging ratio is 20-23kg / t. The molten iron with a temperature of ≥1300℃ is added to the LD converter for conventional top and bottom composite blowing. 钢 、14-16kg / t 钢 Lime and light-burned dolomite are added to make slag, and the final carbon content is controlled to be ≥0.07wt%, and the tapping temperature is ≤1620℃; before tapping, 1.0kg / t is added to the bottom of the ladle. 钢 The amount of slag washing material is added for slag washing; the composition of the molten iron is: C 4.2-4.6wt%, Si 0.20-0.40wt%, Mn 0.25-0.40wt%, P 0.075-0.095wt%, S≤0.030wt%, 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 → high-carbon ferrochrome → nitrogen-rich alloy → niobium-phosphorus-iron alloy → vanadium-nitrogen alloy, respectively, at a rate of 2.0 kg / t. 钢 、3.1~4.5kg / t 钢 , 23.0~24.0kg / t 钢 4.5~5.1kg / t 钢 , 1.20kg / t 钢 , 0.40~0.54kg / t 钢 , 0.50~0.65kg / t 钢 Add silicon calcium barium, ferrosilicon, silicon manganese alloy, high carbon ferrochrome, nitrogen-rich alloy, niobium phosphorus iron 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 3 / 4; C. Argon treatment of molten steel: After the molten steel is tapped in step B, it is hoisted to the argon treatment station and passed through the alloy trough at a pressure of 15.0kg / t 钢 The amount of vanadium-containing pig iron having the following mass ratio is added: 3.3wt%, Si 0.25wt%, Mn 1.24wt%, V 5.05wt%, P0.85wt%, S 0.087wt%, and the rest is Fe and inevitable impurities; the baking time of the vanadium-containing pig iron is 10 minutes, and the surface temperature of the pig iron is ≥250°C; after the vanadium-containing pig iron is added, the molten steel is subjected to nitrogen blowing treatment; 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. 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 1528-1540°C, the pulling speed is 2.8-3.0 m / min, and the crystallizer cooling water flow rate is 130-145 m 3 / h, and the secondary cooling water volume is 1.6-1.8L / kg, casting the molten steel in step D into a steel billet with a cross-section of 165mm×165mm; F. Billet heating: The billet in step E is sent to a heating furnace with a soaking section temperature of 1120-1160°C for heating for 90 minutes. The billet tapping temperature is 1050-1070°C, and then pushed to a fully continuous bar mill for rolling; G. Controlled rolling and controlled cooling of steel billets: The steel billets in step F are rolled for 6 passes at a rolling speed of 0.8-1.5 m / s by the rough rolling unit, and then rolled for 4 passes at a rolling speed of 2.5-4.5 m / s by the intermediate rolling unit, and then rolled for 6 passes at a rolling speed of 8.0-12.0 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 6 m respectively, and the cooling water volume is 80-100 m 3 / h, then the rolled piece is rolled 1-2 times at a speed of 16.0-27.0m / s through the finishing rolling unit 1, and the temperature of the rolled piece entering the finishing rolling unit 1 is controlled at 820-840℃; before the rolled piece enters the finishing rolling unit 2, it is cooled by two water cooling devices with a length of 8m respectively, and the cooling water volume is 50-60m 3 / h, the temperature of the rolled piece entering the second finishing rolling group is controlled at 810-830℃; then the rolled piece passes through the second finishing rolling group at a rolling speed of 32-38m / 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 930-950℃, and then the steel bar is naturally air-cooled to room temperature on the cooling bed, thus obtaining a 650MPa high-strength earthquake-resistant steel bar with a nominal diameter of 12-16mm.

[0011] In step A, the chemical composition of the scrap steel is: C 0.21-0.25wt%, Si 0.30-0.52wt%, Mn 1.13-1.45wt%, P 0.028-0.045wt%, S 0.025-0.045wt%, and the rest is Fe and inevitable impurities.

[0012] In step A, the chemical composition mass ratio of the slag washing material is: Al2O318.4wt%, SiO27.2wt%, CaO49.5wt%, Al 7.2wt%, MgO6.7wt%, and the rest is Fe and inevitable impurities.

[0013] In step A, the molten steel tapping process adopts the whole bottom blowing nitrogen process, and the nitrogen flow rate is controlled at 20-25NL / 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 65.5wt%, Si17.2wt%, C 1.7wt%, and the rest is Fe and inevitable impurities; the chemical composition of high carbon ferrochrome is: Cr 54.3wt%, C 7.5wt%, P 0.075wt%, S0.068wt%, and the rest is Fe and inevitable impurities; the chemical composition of nitrogen-rich alloy is: Si 57.3wt%, N 40.5wt%, C1.24wt%, P 0.056wt%, S 0.035wt%, the rest are Fe and inevitable impurities; the chemical composition of niobium-phosphorus-iron alloy is: Nb43.5wt%, Si 2.7wt%, C1.25wt%, P 1.85wt%, S 0.065wt%, the rest are Fe and inevitable impurities; the chemical composition of high vanadium-nitrogen alloy is: V 77.8wt%, N 19.5wt%, C3.25wt%, P 0.082wt%, S0.062wt%, the rest are Fe and inevitable impurities.

[0015] In step D, 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 E, R9m straight arc continuous straightening 5-machine 5-strand billet casting machine is used for casting.

[0017] In step E, the straightening temperature of the ingot out of the straightening machine is controlled to be 1010-1040°C.

[0018] The present invention also provides a nitrogen-rich microalloy 650MPa high-strength earthquake-resistant steel bar with a nominal diameter of 12-16mm obtained based on the preparation method, which has the following chemical compositions in weight percentage: C 0.25-0.27wt%, Si 0.65-0.75wt%, Mn 1.51-1.59wt%, Cr 0.27-0.30wt%, V 0.120-0.130wt%, Nb 0.020-0.025wt%, S≤0.030wt%, P≤0.030wt%, O≤0.0030wt%, N 0.0290-0.0320wt%, and the rest is Fe and inevitable impurities; its process mechanical properties, microstructure, Vickers hardness difference and timeliness are shown in Tables 1 and 2.

[0019] Table 1 Process mechanical properties of small-size 650MPa high-strength earthquake-resistant steel bars with a nominal diameter of 12-16mm produced by the present invention Table 2 Metallographic structure and Vickers hardness of small-size 650MPa high-strength earthquake-resistant steel bars with a nominal diameter of 12-16mm produced by the present invention Example 1 A. Molten steel smelting: 200kg / t 钢 Cold material charging ratio: add the following scrap steel in the LD converter (chemical composition: C 0.21wt%, Si 0.30wt%, Mn 1.13wt%, P 0.028wt%, S0.025wt%, the rest is Fe and inevitable impurities); then charge 845kg / 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 1300℃, molten iron composition is C 4.2wt%, Si 0.20wt%, Mn 0.25wt%, P 0.075wt%, S 0.016wt%, 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, and the amount of lime added is 20kg / t 钢 , the amount of light-burned dolomite added is 14kg / t 钢 , control the final carbon content to 0.07wt%, the tapping temperature to 1605℃; before tapping, press 1.0kg / t 钢 The amount of slag washing material (chemical composition mass ratio: Al2O318.4wt%, SiO27.2wt%, CaO 49.5wt%, Al 7.2wt%, MgO6.7wt%, the rest are Fe and inevitable impurities) is added for slag washing. The steelmaking process adopts the full bottom blowing nitrogen process, and the nitrogen flow rate is controlled at 20NL / min.

[0020] 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 → niobium phosphorus iron alloy → vanadium nitrogen alloy: 2.0 kg / 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; 3.1kg / t 钢 Add the following mass ratio of ferrosilicon: Si 73.5wt%, the rest is Fe and inevitable impurities; at 23.0kg / t 钢 Add the following mass ratio of silicon-manganese alloy: Mn 65.5wt%, Si 17.2wt%, C1.7wt%, the rest is Fe and unavoidable impurities; at 4.5kg / t 钢 The amount of high carbon ferrochrome in the following mass ratio is added: Cr 54.3wt%, C 7.5wt%, P0.075wt%, S0.068wt%, and the rest is Fe and unavoidable impurities; at 1.20kg / t 钢 The amount of silicon-nitrogen alloy with the following mass ratio is added: Si 57.3wt%, N 40.5wt%, C 1.24wt%, P 0.056wt%, S 0.035wt%, and the rest is Fe and unavoidable impurities; at 0.40kg / t 钢 The following mass ratio of niobium-phosphorus-iron alloy is added: Nb 43.5wt%, Si 2.7wt%, C 1.25wt%, P 1.85wt%, S 0.065wt%, the rest is Fe and unavoidable impurities; 0.50kg / t 钢 The following high nitrogen vanadium alloys are added in the following mass ratios: V 77.8wt%, N 19.5wt%, C 3.25wt%, P 0.082wt%, S0.062wt%, and the rest are Fe and inevitable impurities; the above alloys are added when the amount of molten steel in the ladle reaches 3 / 4; 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.

[0021] 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 15.0kg / t 钢The following vanadium-containing pig iron in mass ratio is added: C 3.3wt%, Si 0.25wt%, Mn 1.24wt%, V 5.05wt%, P0.85wt%, S 0.087wt%, the rest is Fe and inevitable impurities. The baking time of the vanadium-containing pig iron is 10 minutes, and the surface temperature of the pig iron is 250°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 20NL / min for 3 minutes.

[0022] 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 7th to 9th 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 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 10NL / 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.

[0023] E. Molten steel casting: The tundish temperature is 1540℃, the pulling speed is 2.8m / min, and the crystallizer cooling water flow rate is 145m 3 / h, and the secondary cooling water volume is 1.8L / kg, the molten steel in step D 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℃.

[0024] F. Billet heating: The billet in step E is fed into a heating furnace with a temperature of 1120°C in the soaking section and heated for 90 minutes. The billet tapping temperature is 1050°C and then pushed to a fully continuous high-speed bar mill for rolling.

[0025] G. Controlled rolling and controlled cooling of steel billets: The steel billets in step F are rolled 6 times by the rough rolling unit at a rolling speed of 1.5 m / s; then the rolled pieces are rolled 4 times by the intermediate rolling unit at a rolling speed of 4.5 m / s; then the rolled pieces are rolled 6 times by the pre-finishing rolling unit at a rolling speed of 12.0 m / s; then the rolled pieces are controlled and cooled before finishing rolling by two groups of water cooling devices with a length of 6 m respectively, and the cooling water volume is 80 m 3 / h, the temperature of the rolled piece entering the finishing rolling unit is controlled at 840℃; then the rolled piece passes through the finishing rolling unit 1 at a rolling speed of 27.0m / 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 8m respectively, and the cooling water volume is 50m 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 38m / 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 950℃, and then the steel bar is naturally air-cooled to room temperature on the cooling bed, and a small-size 650MPa high-strength earthquake-resistant steel bar with a nominal diameter of 12mm and a chemical composition of the following weight percentage is obtained: C 0.25wt%, Si 0.65wt%, Mn 1.51wt%, Cr 0.27wt%, V0.120wt%, Nb 0.020wt%, S 0.015wt%, P 0.018wt%, O0.0017wt%, N 0.0290wt%, and the rest is Fe and unavoidable impurities. Its process mechanical properties, microstructure, and Vickers hardness difference are shown in Tables 3 and 4.

[0026] Table 3 Processing mechanical properties of 650MPa high-strength earthquake-resistant steel bars with a nominal diameter of 12mm produced in Example 1 Table 4 Metallographic microstructure and Vickers hardness of small-size 650MPa high-strength earthquake-resistant steel bars with a nominal diameter of 12 mm produced in Example 1 Example 2 A. Molten steel smelting: 200kg / t 钢 Cold material charging ratio: add the following scrap steel in the LD converter (chemical composition: C 0.21wt%, Si 0.30wt%, Mn 1.13wt%, P 0.028wt%, S0.025wt%, the rest is Fe and inevitable impurities); then charge 845kg / 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 1300℃, molten iron composition is C 4.2wt%, Si 0.20wt%, Mn 0.25wt%, P 0.075wt%, S 0.016wt%, 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, and the amount of lime added is 20kg / t 钢 , the amount of light-burned dolomite added is 14kg / t 钢, control the final carbon content to 0.07wt%, the tapping temperature to 1605℃; before tapping, press 1.0kg / t 钢 The amount of slag washing material (chemical composition mass ratio: Al2O318.4wt%, SiO27.2wt%, CaO 49.5wt%, Al 7.2wt%, MgO6.7wt%, the rest are Fe and inevitable impurities) is added for slag washing. The steelmaking process adopts the full bottom blowing nitrogen process, and the nitrogen flow rate is controlled at 20NL / min.

[0027] 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 → niobium phosphorus iron alloy → vanadium nitrogen alloy: 2.0 kg / 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; 3.1kg / t 钢 Add the following mass ratio of ferrosilicon: Si 73.5wt%, the rest is Fe and inevitable impurities; at 23.0kg / t 钢 Add the following mass ratio of silicon-manganese alloy: Mn 65.5wt%, Si 17.2wt%, C1.7wt%, the rest is Fe and unavoidable impurities; at 4.5kg / t 钢 The amount of high carbon ferrochrome in the following mass ratio is added: Cr 54.3wt%, C 7.5wt%, P0.075wt%, S0.068wt%, and the rest is Fe and unavoidable impurities; at 1.20kg / t 钢 The amount of silicon-nitrogen alloy with the following mass ratio is added: Si 57.3wt%, N 40.5wt%, C 1.24wt%, P 0.056wt%, S 0.035wt%, and the rest is Fe and unavoidable impurities; at 0.40kg / t 钢 The following mass ratio of niobium-phosphorus-iron alloy is added: Nb 43.5wt%, Si 2.7wt%, C 1.25wt%, P 1.85wt%, S 0.065wt%, the rest is Fe and unavoidable impurities; 0.50kg / t 钢 The following high nitrogen vanadium alloys are added in the following mass ratios: V 77.8wt%, N 19.5wt%, C 3.25wt%, P 0.082wt%, S0.062wt%, and the rest are Fe and inevitable impurities; the above alloys are added when the amount of molten steel in the ladle reaches 3 / 4; 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.

[0028] 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 15.0kg / t 钢 The following vanadium-containing pig iron in mass ratio is added: C 3.3wt%, Si 0.25wt%, Mn 1.24wt%, V 5.05wt%, P0.85wt%, S 0.087wt%, the rest is Fe and inevitable impurities. The baking time of the vanadium-containing pig iron is 10 minutes, and the surface temperature of the pig iron is 250°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 20NL / min for 3 minutes.

[0029] 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 7th to 9th 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 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 10NL / 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.

[0030] E. Molten steel casting: The tundish temperature is 1540℃, the pulling speed is 2.8m / min, and the crystallizer cooling water flow rate is 145m 3 / h, and the secondary cooling water volume is 1.8L / kg, the molten steel in step D 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℃.

[0031] F. Billet heating: The billet in step E is fed into a heating furnace with a temperature of 1120°C in the soaking section and heated for 90 minutes. The billet tapping temperature is 1050°C and then pushed to a fully continuous high-speed bar mill for rolling.

[0032] G. Controlled rolling and controlled cooling of steel billets: The steel billets in step F are rolled 6 times by the rough rolling unit at a rolling speed of 1.5 m / s; then the rolled pieces are rolled 4 times by the intermediate rolling unit at a rolling speed of 4.5 m / s; then the rolled pieces are rolled 6 times by the pre-finishing rolling unit at a rolling speed of 12.0 m / s; then the rolled pieces are controlled and cooled before finishing rolling by two groups of water cooling devices with a length of 6 m respectively, and the cooling water volume is 80 m 3 / h, the temperature of the rolled piece entering the finishing rolling unit is controlled at 840℃; then the rolled piece passes through the finishing rolling unit 1 at a rolling speed of 27.0m / 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 8m respectively, and the cooling water volume is 50m 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 38m / 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 950℃, and then the steel bar is naturally air-cooled to room temperature on the cooling bed, and a small-size 650MPa high-strength earthquake-resistant steel bar with a nominal diameter of 12mm and a chemical composition of the following weight percentage is obtained: C 0.26wt%, Si 0.70wt%, Mn 1.55wt%, Cr 0.29wt%, V0.126wt%, Nb 0.023wt%, S 0.024wt%, P 0.026wt%, O0.0024wt%, N 0.0305wt%, and the rest is Fe and unavoidable impurities. Its process mechanical properties, microstructure, and Vickers hardness difference are shown in Tables 5 and 6.

[0033] Table 5 Processing mechanical properties of 650MPa high-strength earthquake-resistant steel bars with a nominal diameter of 14mm produced in Example 2 Table 6 Metallographic microstructure and Vickers hardness of small-size 650MPa high-strength earthquake-resistant steel bars with a nominal diameter of 14 mm produced in Example 2 Example 3 A. Molten steel smelting: 220kg / t 钢 Cold material charging ratio: add the following scrap steel in the LD converter (chemical composition: C 0.25wt%, Si 0.52wt%, Mn 1.45wt%, P 0.045wt%, S0.045wt%, the rest is Fe and inevitable impurities); then charge 855kg / 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 1330℃, molten iron composition is C 4.6wt%, Si 0.40wt%, Mn 0.40wt%, P 0.095wt%, S 0.030wt%, 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, and the amount of lime added is 23kg / t 钢 , the amount of light-burned dolomite added is 16kg / t 钢 , control the final carbon content to 0.09wt%, the tapping temperature to 1620℃; before tapping, press 1.0kg / t 钢 The amount of slag washing material (chemical composition mass ratio: Al2O318.4wt%, SiO27.2wt%, CaO 49.5wt%, Al 7.2wt%, MgO6.7wt%, the rest are Fe and inevitable impurities) is added for slag washing. The steelmaking process adopts the full bottom blowing nitrogen process, and the nitrogen flow rate is controlled at 25 / NL / min.

[0034] 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 → niobium phosphorus iron alloy → vanadium nitrogen alloy: 2.0 kg / t 钢 Add the following mass ratio of silicon, calcium and barium: Si52.5wt%, 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 24.0kg / t 钢 Add the following mass ratio of silicon-manganese alloy: Mn 65.5wt%, Si 17.2wt%, C1.7wt%, the rest is Fe and unavoidable impurities; at 5.1kg / t 钢 The amount of high carbon ferrochrome in the following mass ratio is added: Cr 54.3wt%, C 7.5wt%, P0.075wt%, S0.068wt%, and the rest is Fe and unavoidable impurities; at 1.20kg / t 钢 The amount of silicon-nitrogen alloy is added in the following mass ratio: Si 57.3wt%, N 40.5wt%, C 1.24wt%, P 0.056wt%, S 0.035wt%, and the rest is Fe and unavoidable impurities; at 0.54kg / t 钢The following mass ratio of niobium-phosphorus-iron alloy is added: Nb 43.5wt%, Si 2.7wt%, C 1.25wt%, P 1.85wt%, S 0.065wt%, the rest is Fe and unavoidable impurities; 0.65kg / t 钢 The following high nitrogen vanadium alloys are added in the following mass ratios: V 77.8wt%, N 19.5wt%, C 3.25wt%, P 0.082wt%, S0.062wt%, and the rest are Fe and inevitable impurities; the above alloys are added when the amount of molten steel in the ladle reaches 3 / 4; 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.

[0035] 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 15.0kg / t 钢 The following vanadium-containing pig iron in mass ratio is added: C 3.3wt%, Si 0.25wt%, Mn 1.24wt%, V 5.05wt%, P0.85wt%, S 0.087wt%, the rest is Fe and inevitable impurities. The baking time of the vanadium-containing pig iron is 10 minutes, and the surface temperature of the pig iron is 310°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.

[0036] 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 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 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 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 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.

[0037] E. Molten steel casting: The tundish temperature is 1528℃, the pulling speed is 3.0m / min, and the crystallizer cooling water flow rate is 130m 3 / h, and the secondary cooling water volume was 1.6L / kg. The molten steel in step D 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 1040℃.

[0038] F. Billet heating: The billet in step E is fed into a heating furnace with a temperature of 1160°C in the soaking section and heated for 90 minutes. The billet tapping temperature is 1070°C and then pushed to a fully continuous high-speed bar mill for rolling.

[0039] G. Controlled rolling and controlled cooling of steel billets: The steel billets in step F are rolled for 6 passes at a speed of 0.8 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 8.0 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 6 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 16.0m / 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 8m and a cooling water volume of 60m 3 / h, the temperature of the rolled piece entering the second finishing rolling unit is controlled at 810℃; then the rolled piece passes through the second finishing rolling unit at a rolling speed of 32m / 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 930℃, and then the steel bar is naturally air-cooled to room temperature on the cooling bed, and a small-size 650MPa high-strength earthquake-resistant steel bar with a nominal diameter of 16mm and a chemical composition of the following weight percentage is obtained: C 0.27wt%, Si 0.75wt%, Mn 1.59wt%, Cr 0.30wt%, V0.130wt%, Nb 0.025wt%, S 0.030wt%, P 0.030wt%, O0.0030wt%, N 0.0320wt%, and the rest is Fe and unavoidable impurities. Its process mechanical properties, microstructure, and Vickers hardness difference are shown in Tables 7 and 8.

[0040] Table 7 Process mechanical properties of 650MPa high-strength earthquake-resistant steel bars with a nominal diameter of 16mm produced in Example 3 Table 8 Metallographic microstructure and Vickers hardness of small-size 650MPa high-strength earthquake-resistant steel bars with a nominal diameter of 16 mm produced in Example 3 .

Claims

1. A method for preparing a nitrogen-rich microalloy 650MPa high-strength earthquake-resistant steel bar with a nominal diameter of 12-16mm. It is characterized in that To do this, follow these steps: A. Molten steel smelting: 200-220kg / t 钢 Cold material charging ratio, adding scrap steel in LD converter; then at 845-855kg / t 钢 The molten iron charging ratio is 20-23kg / t. The molten iron with a temperature of ≥1300℃ is added to the LD converter for conventional top and bottom composite blowing. 钢 、14-16kg / t 钢 Lime and light-burned dolomite are added to make slag, and the final carbon content is controlled to be ≥0.07wt%, and the tapping temperature is ≤1620℃; before tapping, 1.0kg / t is added to the bottom of the ladle. 钢 The slag washing material is added in an amount for slag washing; the composition of the molten iron is: C4.2-4.6wt%, Si 0.20-0.40wt%, Mn 0.25-0.40wt%, P 0.075-0.095wt%, S≤0.030wt%, 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 → high-carbon ferrochrome → nitrogen-rich alloy → niobium-phosphorus-iron alloy → vanadium-nitrogen alloy, respectively, at a rate of 2.0 kg / t. 钢 、3.1~4.5kg / t 钢 , 23.0~24.0kg / t 钢 4.5~5.1kg / t 钢 , 1.20kg / t 钢 , 0.40~0.54kg / t 钢 , 0.50~0.65kg / t 钢 Add silicon calcium barium, ferrosilicon, silicon manganese alloy, high carbon ferrochrome, nitrogen-rich alloy, niobium phosphorus iron 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 3 / 4; C. Argon treatment of molten steel: After the molten steel is tapped in step B, it is hoisted to the argon treatment station and passed through the alloy trough at a pressure of 15.0kg / t 钢 The amount of vanadium-containing pig iron is added and baked for 10 minutes, and the surface temperature of the vanadium-containing pig iron is ≥250°C, and then the molten steel is subjected to nitrogen blowing treatment; the composition of the vanadium-containing pig iron is: 3.3wt%, Si 0.25wt%, Mn 1.24wt%, V 5.05wt%, P 0.85wt%, S 0.087wt%, 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. 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 1528-1540°C, the pulling speed is 2.8-3.0 m / min, and the crystallizer cooling water flow rate is 130-145 m 3 / h, and the secondary cooling water volume is 1.6-1.8L / kg, casting the molten steel in step D into a steel billet with a cross-section of 165mm×165mm; F. Billet heating: The billet in step E is sent to a heating furnace with a soaking section temperature of 1120-1160°C for heating for 90 minutes. The billet tapping temperature is 1050-1070°C, and then pushed to a fully continuous bar mill for rolling; G. Controlled rolling and controlled cooling of steel billets: The steel billets in step F are rolled for 6 passes at a rolling speed of 0.8-1.5 m / s by the rough rolling unit, and then rolled for 4 passes at a rolling speed of 2.5-4.5 m / s by the intermediate rolling unit, and then rolled for 6 passes at a rolling speed of 8.0-12.0 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 6 m respectively, and the cooling water volume is 80-100 m 3 / h, the temperature of the rolled piece entering the finishing rolling unit is controlled at 820-840℃; the rolled piece passes through the finishing rolling unit at a speed of 16.0-27.0m / s for 1-2 passes; before entering the finishing rolling unit 2, the rolled piece passes through two water cooling devices with a length of 8m each for controlled cooling, with a cooling water volume of 50-60m 3 / h, the temperature of the rolled piece entering the second finishing rolling group is controlled at 810-830℃; then the rolled piece passes through the second finishing rolling group at a rolling speed of 32-38m / 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 930-950℃, and then the steel bar is naturally air-cooled to room temperature on the cooling bed, thus obtaining a 650MPa high-strength earthquake-resistant steel bar with a nominal diameter of 12-16mm.

2. The method for preparing the nitrogen-rich microalloy 650MPa high-strength earthquake-resistant steel bar with a nominal diameter of 12-16mm according to claim 1, It is characterized in that In step A, the chemical composition of the scrap steel is: C 0.21-0.25wt%, Si 0.30-0.52wt%, Mn1.13-1.45wt%, P 0.028-0.045wt%, S 0.025-0.045wt%, and the rest is Fe and inevitable impurities.

3. The method for preparing the nitrogen-rich microalloy 650MPa high-strength earthquake-resistant steel bar with a nominal diameter of 12-16mm according to claim 1, It is characterized in that In step A, the chemical composition mass ratio of the slag washing material is: Al 2 O 3 18.4wt%,SiO 2 7.2wt%, CaO49.5wt%, Al 7.2wt%, MgO6.7wt%, and the rest are Fe and inevitable impurities.

4. The method for preparing the nitrogen-rich microalloy 650MPa high-strength earthquake-resistant steel bar with a nominal diameter of 12-16mm according to claim 1, It is characterized in that In step A, the molten steel tapping process adopts the whole bottom blowing nitrogen process, and the nitrogen flow rate is controlled at 20-25NL / min.

5. The method for preparing the nitrogen-rich microalloy 650MPa high-strength earthquake-resistant steel bar with a nominal diameter of 12-16mm according to claim 1, 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 65.5wt%, Si 17.2wt%, C 1.7wt%, and the rest is Fe and inevitable impurities; the chemical composition of high carbon ferrochrome is: Cr 54.3wt%, C 7.5wt%, P 0.075wt%, S0.068wt%, and the rest is Fe and inevitable impurities; the chemical composition of nitrogen-rich alloy is: Si 57.3wt%, N40.5wt%, C 1.24wt%, P 0.056wt%, S 0.035wt%, the rest are Fe and inevitable impurities; the chemical composition of niobium-phosphorus-iron alloy is: Nb 43.5wt%, Si 2.7wt%, C1.25wt%, P 1.85wt%, S 0.065wt%, the rest are Fe and inevitable impurities; the chemical composition of high vanadium-nitrogen alloy is: V 77.8wt%, N 19.5wt%, C 3.25wt%, P0.082wt%, S 0.062wt%, the rest are Fe and inevitable impurities.

6. The method for preparing the nitrogen-rich microalloy 650MPa high-strength earthquake-resistant steel bar with a nominal diameter of 12-16mm according to claim 1, It is characterized in that In step D, 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.

7. The method for preparing the nitrogen-rich microalloy 650MPa high-strength earthquake-resistant steel bar with a nominal diameter of 12-16mm according to claim 1, It is 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 nitrogen-rich microalloy 650MPa high-strength earthquake-resistant steel bar with a nominal diameter of 12-16mm according to claim 1, It is characterized in that In step E, the straightening temperature of the ingot out of the straightening machine is controlled to be 1010-1040°C.

9. A nitrogen-rich microalloy 650MPa high-strength earthquake-resistant steel bar with a nominal diameter of 12-16mm obtained by the preparation method according to any one of claims 1-8, It is characterized in that The nitrogen-rich microalloy 650MPa high-strength earthquake-resistant steel bar with a nominal diameter of 12-16mm has the following chemical compositions in weight percentage: C 0.25-0.27wt%, Si 0.65-0.75wt%, Mn 1.51-1.59wt%, Cr 0.27-0.30wt%, V 0.120-0.130wt%, Nb 0.020-0.025wt%, S≤0.030wt%, P≤0.030wt%, O≤0.0030wt%, N 0.0290-0.0320wt%, and the rest are Fe and inevitable impurities; its yield strength is 665-690MPa, the tensile strength is 850-900MPa, the strength-to-yield ratio is ≥1.28, the elongation after fracture is ≥20%, and the total elongation at maximum force is ≥10.5%.

Images