500MPa-grade high-strength aseismic steel bar with nominal diameter of 18-25mm for railway and preparation method of 500MPa-grade high-strength aseismic steel bar

Abstract

The invention discloses a 500MPa-grade high-strength aseismic steel bar with the nominal diameter of 18-25mm for a railway and a preparation method of the 500MPa-grade high-strength aseismic steel bar. The anti-seismic steel bar comprises the following chemical components in percentage by weight: 0.22 to 0.24 weight percent of C, 0.45 to 0.60 weight percent of Si, 0.70 to 0.85 weight percent of Mn, 0.70 to 0.80 weight percent of Cr, 0.17 to 0.21 weight percent of Cu, 0.060 to 0.070 weight percent of V, 0.010 to 0.013 weight percent of Nb, less than or equal to 0.040 weight percent of S, less than or equal to 0.040 weight percent of P, less than or equal to 0.0030 weight percent of O, 0.0160 to 0.0185 weight percent of N and the balance of Fe and inevitable impurities. The yield strength of the anti-seismic steel bar is 530-560 MPa, the tensile strength is 695-750 MPa, the yield-strength ratio is larger than or equal to 1.31, the percentage elongation after fracture is larger than or equal to 23%, and the maximum force total elongation is larger than or equal to 10.5%. The process is low in production cost and high in process applicability and controllability, and the produced reinforcing steel bar has the advantages of being excellent and stable in process mechanical property, fine and uniform in microscopic structure, good in plasticity and toughness, excellent in corrosion resistance and anti-seismic property and the like, and has remarkable economic and social benefits.

Description

Technical Field

[0001] The invention belongs to the technical field of steel smelting, and specifically relates to a 500MPa high-strength earthquake-resistant steel bar with a nominal diameter of 18-25mm for railways and a preparation method thereof. Background Art

[0002] Earthquake-resistant steel bars are the main reinforcement materials for transportation infrastructure structures such as roads and railways, and they bear the stress and strain of tensile and compressive stress and strain in the structure. With the continuous development of my country's high-speed railway infrastructure construction towards high earthquake resistance, high strength and corrosion resistance, the development of high-toughness, excellent corrosion resistance and 500MPa and above strength grade earthquake-resistant steel bars for railways has become an important task for the steel industry to improve its technical level.

[0003] At present, there are reports on the production technology of 400MPa high-strength earthquake-resistant steel bars for railways in China, but there are few reports on the preparation process of 500MPa and above strength earthquake-resistant steel bars for railways with a nominal diameter of 18-25mm. The preparation of 400MPa high-strength earthquake-resistant steel bars for railways mainly adopts the vanadium-nitrogen microalloying process, and the V content in the steel is mostly controlled at 0.020-0.040wt%. By controlling the rolling temperature and rolling passes, 400MPa straight earthquake-resistant steel bars that meet the requirements of high-speed railway GB / T 37439-2019 are obtained. When vanadium microalloy is used to produce 400MPa high-strength earthquake-resistant steel bars for railways, a certain amount of precious vanadium alloy is added to the steel, resulting in a high alloy cost, which is not conducive to improving the competitiveness of the product.

[0004] The invention aims to provide a 500MPa grade high-strength earthquake-resistant steel bar with a nominal diameter of 18-25mm for railways. Summary of the invention

[0005] The first object of the present invention is to provide a 500MPa grade high-strength earthquake-resistant steel bar with a nominal diameter of 18-25mm for railway use. The second object of the present invention is to provide a method for preparing the earthquake-resistant steel bar.

[0006] The first object of the present invention is achieved by providing a 500MPa grade high-strength earthquake-resistant steel bar for railways with a nominal diameter of 18-25mm, wherein the earthquake-resistant steel bar has the following chemical composition in weight percentage: C 0.22-0.24wt%, Si 0.45-0.60wt%, Mn 0.70-0.85wt%, Cr 0.70-0.80wt%, Cu 0.17-0.21wt%, V 0.060-0.070wt%, Nb 0.010-0.013wt%, S≤0.040wt%, P≤0.040wt%, O≤0.0030wt%, N 0.0160-0.0185wt%, and the rest is Fe and inevitable impurities.

[0007] The second object of the present invention is achieved by the method for preparing the 18-25mm 500MPa grade high-strength earthquake-resistant steel bar for railway, which is specifically implemented by the following steps: A. Molten steel smelting: 260-270kg / t 钢 , 1.3-1.7kg / t 钢 The cold material charging ratio is 785-795kg / t. 钢 The molten iron charging ratio is 15-20kg / t, and the molten iron with a temperature of ≥1310℃ is added to the LD converter for conventional top and bottom composite blowing. The chemical composition of the molten iron is: C 4.1-4.3wt%, Si 0.15-0.30wt%, Mn0.20-0.45wt%, P 0.070-0.080wt%, S≤0.030wt%, and the rest is Fe and unavoidable impurities; then the molten iron is heated to 15-20kg / t 钢 , 15-18kg / t 钢 Add lime and lightly burned dolomite to make slag, control the final carbon content ≥ 0.07wt%, and the tapping temperature ≤ 1600℃; before tapping, press 1.5kg / t 钢 Add active lime to the bottom of the ladle for slag washing; 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. The deoxidation and alloying steps are carried out at 2 kg / t. 钢 , 3.2~5.4kg / t 钢 , 9.7~12.1kg / t 钢 12.6~14.6kg / t 钢 , 0.9~1.0kg / t 钢 , 0.25~0.30kg / 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. Molten steel argon station treatment: The molten steel from step B is hoisted to the argon station treatment station and heated through the alloy trough at 10.0-11.0 kg / t 钢 The vanadium-containing pig iron having a surface temperature of ≥350°C after baking is added in an amount of 25 to 30 NL / min of nitrogen gas to perform nitrogen blowing treatment on the molten steel, and the nitrogen blowing time is 3 minutes; the vanadium-containing pig iron has the following mass ratio composition: C 3.5wt%, Si 0.45wt%, Mn 1.85wt%, V 5.0wt%, P 1.02wt%, S 0.065wt%, and the rest is Fe and inevitable impurities; D. LF furnace refining of molten steel: The molten steel from step C is hoisted to the LF furnace for refining. After refining, the molten steel is subjected to soft nitrogen blowing at a small flow rate of 20-25 NL / min for 2 minutes. After nitrogen blowing, the molten steel is subjected to nitrogen blowing at a rate of 1.0 kg / t 钢 Add the amount of molten steel covering agent, and then lift the molten steel to the casting station; E. Molten steel casting: The tundish temperature is 1525-1535°C, the pulling speed is 3.1-3.3 m / min, and the crystallizer cooling water flow rate is 135-145 m 3 / h, and the secondary cooling water volume is 1.6-1.8L / kg, the molten steel is cast into a billet with a cross section of 165mm×165mm; the straightening temperature of the billet out of the straightening machine is controlled at 1010-1030℃; F. Billet heating: The billet in step E is sent to a heating furnace with a soaking section temperature of 1110-1150°C for heating for 70 minutes. The billet tapping temperature is 1040-1060°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 speed of 0.4-0.8 m / s by the rough rolling unit, and then rolled for 4 passes at a speed of 1.2-2.0 m / s by the intermediate rolling unit; and then rolled for 3-6 passes at a speed of 6.0-8.0 m / s by the pre-finishing rolling unit; before the rolled piece enters the finishing rolling, it is controlled and cooled before finishing rolling by a set of 10m long water cooling devices, and the cooling water volume is 60-80m 3 / h, the temperature of the rolled piece entering the finishing rolling unit is controlled at 880-900℃; the rolled piece passes through the finishing rolling unit at a speed of 9.0-10.0m / s for 1-2 passes; before entering the finishing rolling unit 2, the rolled piece passes through a water cooling device with a length of 8m for controlled cooling, and the cooling water volume is 80-100m 3 / h, the temperature of the rolled piece entering the second finishing rolling group is controlled at 830-850℃; then the rolled piece passes through the second finishing rolling group at a rolling speed of 11.0-13.0m / s for 2 passes; after finishing rolling, the rolled piece passes through a water cooling device with a length of 5m 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 890-920℃, and then the steel bar is naturally air-cooled to room temperature on the cooling bed to obtain 500MPa grade high-strength earthquake-resistant steel bars for railway use with a nominal diameter of 18-25mm.

[0008] The present invention adds a certain amount of vanadium-containing pig iron to the molten steel at the argon station after steelmaking is completed to completely replace the expensive vanadium alloy, thereby increasing the V content of the molten steel and greatly reducing the cost of microalloying; silicon-nitrogen alloy is added during the steelmaking deoxidation alloying process, and the molten steel is refined and nitrogen-blown through an LF furnace, which significantly increases the nitrogen content of the molten steel, promotes the transfer of V and Nb from a solid solution state to a carbonitride precipitation phase during the rolling process, and forms and precipitates a large amount of fine and dispersed V (C, N) and Nb (C, N) precipitation phases, which significantly improves the precipitation strengthening effect of the steel; a certain amount of chromium and copper are added to the steel, which improves the passivation corrosion resistance of the steel, and the corrosion rate is only 1 / 3 of that of 400MPa grade steel bars for railways, while the hardenability and secondary hardening effect of the steel are significantly improved, the pearlite content is increased, and the tensile strength of the steel is promoted, thereby promoting the improvement of the seismic performance of the steel; a small amount of niobium is added to the steel to generate a very small amount of granular bainite, which optimizes The microstructure ratio of the steel is improved, the optimal matching of the tensile strength and yield strength of the steel is promoted, and the seismic resistance of the steel is improved; the high rolling start temperature is controlled during steel rolling, which promotes the full solid solution of V and Nb microalloying elements; a longer water cooling device is used after pre-finishing rolling to control the lower finishing rolling temperature of the rolled piece; two groups of finishing mills are used for rolling after finishing 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 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, controlled cooling low-temperature rolling of the finishing mill, 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 refined, the grain size reaches above 11.0, the fine grain strengthening effect is significant, the strength of the steel is greatly improved, and the plasticity and toughness of the steel are improved at the same time.

[0009] The process of the present invention fully utilizes multiple strengthening effects such as precipitation strengthening and fine grain strengthening through integrated innovation of chemical composition design, converter smelting, deoxidation alloying, argon station treatment, continuous casting, steel rolling heating system, rolling temperature and controlled cooling process. The process of the present invention has low production cost, strong process applicability and controllability, and the produced 500MPa grade earthquake-resistant steel bars for railways with a nominal diameter of 18-25mm have the advantages of excellent and stable process mechanical properties, fine and uniform microstructure, good plasticity and toughness, excellent corrosion resistance and earthquake resistance, etc., and has significant economic and social benefits. DETAILED DESCRIPTION

[0010] 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.

[0011] The present invention provides a 500MPa grade high-strength earthquake-resistant steel bar for railway with a nominal diameter of 18-25mm, wherein the earthquake-resistant steel bar has the following chemical composition in weight percentage: C 0.22-0.24wt%, Si 0.45-0.60wt%, Mn 0.70-0.85wt%, Cr 0.70-0.80wt%, Cu 0.17-0.21wt%, V 0.060-0.070wt%, Nb 0.010-0.013wt%, S≤0.040wt%, P≤0.040wt%, O≤0.0030wt%, N 0.0160-0.0185wt%, and the rest is Fe and inevitable impurities; its process mechanical properties, microstructure, Vickers hardness difference and corrosion resistance are shown in Table 1 and Table 2. Table 1 Processing mechanical properties and corrosion resistance of 500MPa grade high-strength earthquake-resistant steel bars with a nominal diameter of 18-25mm for railways produced by the present invention Table 2 Metallographic structure and Vickers hardness of 500MPa grade high strength earthquake-resistant steel bars for railway use with a nominal diameter of 18-25mm produced by the present invention The present invention also provides a method for preparing the 18-25 mm 500 MPa grade high-strength earthquake-resistant steel bar for railways, which is specifically implemented by the following steps: A. Molten steel smelting: 260-270kg / t 钢 , 1.3-1.7kg / t 钢 The cold material charging ratio is 785-795kg / t. 钢 The molten iron charging ratio is 15-20kg / t, and the molten iron with a temperature of ≥1310℃ is added to the LD converter for conventional top and bottom composite blowing. The chemical composition of the molten iron is: C 4.1-4.3wt%, Si 0.15-0.30wt%, Mn0.20-0.45wt%, P 0.070-0.080wt%, S≤0.030wt%, and the rest is Fe and unavoidable impurities; then the molten iron is heated to 15-20kg / t 钢 , 15-18kg / t 钢 Add lime and lightly burned dolomite to make slag, control the final carbon content ≥ 0.07wt%, and the tapping temperature ≤ 1600℃; before tapping, press 1.5kg / t 钢 Add active lime to the bottom of the ladle for slag washing; 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. The deoxidation and alloying steps are carried out at 2 kg / t.钢 , 3.2~5.4kg / t 钢 , 9.7~12.1kg / t 钢 12.6~14.6kg / t 钢 , 0.9~1.0kg / t 钢 , 0.25~0.30kg / 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. Molten steel argon station treatment: The molten steel from step B is hoisted to the argon station treatment station and heated through the alloy trough at 10.0-11.0 kg / t 钢 The vanadium-containing pig iron having a surface temperature of ≥350°C after baking is added in an amount of 25 to 30 NL / min of nitrogen gas to perform nitrogen blowing treatment on the molten steel, and the nitrogen blowing time is 3 minutes; the vanadium-containing pig iron has the following mass ratio composition: C 3.5wt%, Si 0.45wt%, Mn 1.85wt%, V 5.0wt%, P 1.02wt%, S 0.065wt%, and the rest is Fe and inevitable impurities; D. LF furnace refining of molten steel: The molten steel from step C is hoisted to the LF furnace for refining. After refining, the molten steel is subjected to soft nitrogen blowing at a small flow rate of 20-25 NL / min for 2 minutes. After nitrogen blowing, the molten steel is subjected to nitrogen blowing at a rate of 1.0 kg / t 钢 Add the amount of molten steel covering agent, and then lift the molten steel to the casting station; E. Molten steel casting: The tundish temperature is 1525-1535°C, the pulling speed is 3.1-3.3 m / min, and the crystallizer cooling water flow rate is 135-145 m 3 / h, and the secondary cooling water volume is 1.6-1.8L / kg, the molten steel is cast into a billet with a cross section of 165mm×165mm; the straightening temperature of the billet out of the straightening machine is controlled at 1010-1030℃; F. Billet heating: The billet in step E is sent to a heating furnace with a soaking section temperature of 1110-1150°C for heating for 70 minutes. The billet tapping temperature is 1040-1060°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 speed of 0.4-0.8 m / s by the rough rolling unit, and then rolled for 4 passes at a speed of 1.2-2.0 m / s by the intermediate rolling unit; and then rolled for 3-6 passes at a speed of 6.0-8.0 m / s by the pre-finishing rolling unit; before the rolled piece enters the finishing rolling, it is controlled and cooled before finishing rolling by a set of 10m long water cooling devices, and the cooling water volume is 60-80m 3 / h, the temperature of the rolled piece entering the finishing rolling unit is controlled at 880-900℃; the rolled piece passes through the finishing rolling unit at a speed of 9.0-10.0m / s for 1-2 passes; before entering the finishing rolling unit 2, the rolled piece passes through a water cooling device with a length of 8m for controlled cooling, and the cooling water volume is 80-100m 3 / h, the temperature of the rolled piece entering the second finishing rolling group is controlled at 830-850℃; then the rolled piece passes through the second finishing rolling group at a rolling speed of 11.0-13.0m / s for 2 passes; after finishing rolling, the rolled piece passes through a water cooling device with a length of 5m 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 890-920℃, and then the steel bar is naturally air-cooled to room temperature on the cooling bed to obtain 500MPa grade high-strength earthquake-resistant steel bars for railway use with a nominal diameter of 18-25mm.

[0012] In step A, the chemical composition of the scrap steel is: C 0.19-0.25wt%, Si 0.32-0.55wt%, Mn 1.30-1.52wt%, P 0.024-0.045wt%, S 0.023-0.045wt%, and the rest is Fe and inevitable impurities; the chemical composition of the copper plate is: Cu 99.3wt%, P 0.035wt%, S0.041wt%, and the rest is 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 65.2wt%, Si17.9wt%, C 1.1wt%, and the rest is Fe and inevitable impurities; the chemical composition of high carbon ferrochrome is: Cr 54.2wt%, C 7.4wt%, P 0.072wt%, S0.062wt%, and the rest is Fe and inevitable impurities; the chemical composition of nitrogen-rich alloy is: Si 57.4wt%, N 40.3wt%, C1.75wt%, P 0.075wt%, S 0.038wt%, the rest are Fe and inevitable impurities; the chemical composition of niobium ferrophosphorus alloy is: Nb44.2wt%, Si 3.5wt%, C1.75wt%, P 1.65wt%, S 0.045wt%, the rest are Fe and inevitable impurities.

[0015] In step D, during the refining process, nitrogen gas with a flow rate of 15-20 NL / min is used to blow nitrogen into the molten steel, and then the lower electrode is slag-free at gears 6-8; after 3 minutes of slag-freeing, the electrode is lifted to observe the slag-freeing situation in the furnace; if the slag sample is too thin and the color is too black, lime is added at 4.0-5.0 kg / t 钢 Adjust the slag, otherwise add pre-melted refined slag 1.0~2.0kg / t 钢 Adjustment; then measure temperature and take samples. According to the steel sample and temperature test results, add alloy to adjust the steel liquid composition and lower electrode temperature to ensure that the composition and temperature are qualified.

[0016] In step E, R9m straight arc continuous straightening 5-machine 5-strand billet casting machine is used for casting.

[0017] Example 1 A. Molten steel smelting: 260kg / t 钢 , 1.3kg / t 钢 The cold material charging ratio is as follows: the scrap steel (chemical composition: C 0.19wt%, Si 0.32wt%, Mn 1.30wt%, P 0.024wt%, S0.023wt%, the rest is Fe and inevitable impurities) and copper plate (chemical composition: Cu 99.3wt%, P 0.035wt%, S0.041wt%, the rest is inevitable impurities) in the LD converter in the following mass ratio; then the 785kg / 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 0.20wt%, P0.070wt%, S 0.018wt%, and the rest is Fe and inevitable impurities; after the scrap steel, copper plate 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 , control the final carbon content to 0.07wt%, the tapping temperature to 1580℃; before tapping, press 1.5kg / t to the bottom of the ladle 钢 The amount of activated lime is added for slag washing. The steelmaking process adopts the bottom blowing nitrogen process throughout the process, and the nitrogen flow rate is controlled at 20NL / 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 → niobium phosphorus iron alloy: 2.0 kg / t 钢Add the following mass ratio of silicon, calcium and barium: Si 52.5wt%, Ca 9.85wt%, Ba 12.15wt%, Al 2.45wt%, the rest is Fe and unavoidable impurities; at 3.2kg / t 钢 Add the following mass ratio of ferrosilicon: Si 73.5wt%, the rest is Fe and inevitable impurities; at 9.7kg / t 钢 Add the following mass ratio of silicon-manganese alloy: Mn 65.2wt%, Si 17.9wt%, C1.1wt%, the rest is Fe and inevitable impurities; according to 12.6 kg / t 钢 The amount of high carbon ferrochrome in the following mass ratio is added: Cr 54.2wt%, C 7.4wt%, P 0.072wt%, S0.062wt%, and the rest is Fe and unavoidable impurities; at 0.9kg / t 钢 The amount of silicon-nitrogen alloy is added in the following mass ratio: Si 57.4wt%, N 40.3wt%, C 1.75wt%, P0.075wt%, S 0.038wt%, and the rest is Fe and unavoidable impurities; kg / t 钢 The following mass ratio of niobium-phosphorus-iron alloy is added: Nb 44.2wt%, Si 3.5wt%, C1.75wt%, P1.65wt%, S 0.045wt%, and the rest is Fe and inevitable impurities; the above alloys are added when the amount of molten steel in the ladle reaches 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.

[0019] 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 10.0kg / t 钢 The amount of vanadium-containing pig iron having the following mass ratio is added: components C 3.5wt%, Si 0.45wt%, Mn 1.85wt%, V5.0wt%, P1.02wt%, S 0.065wt%, and the rest are Fe and inevitable impurities. The vanadium-containing pig iron is baked for 8 minutes, and the surface temperature of the pig iron after baking is 350°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.

[0020] D. LF furnace refining of molten steel: Lift the molten steel from step C to the LF furnace refining station and connect the nitrogen belt. Turn on the nitrogen and use nitrogen with a flow rate of 15NL / min to blow nitrogen into the molten steel. Then, use the 6th to 8th gear of the lower electrode to slag. After 3 minutes of slag slag slag, lift the electrode to observe the slag slag situation in the furnace. If the slag sample is too thin and the color is too black, add 4.0kg / t lime. 钢Adjust the slag, otherwise add pre-melted refined slag 1.0kg / t 钢 Adjustment; then measure temperature and take samples, add alloy to adjust the composition of molten steel and raise the temperature of lower electrode according to the steel sample and temperature test results to ensure that the composition and temperature are qualified; after refining, perform soft nitrogen blowing with small flow rate on molten steel, the blowing time is 2 minutes, and the nitrogen flow rate is controlled at 20NL / min; after nitrogen blowing, add molten steel covering agent, the addition amount is 1.0 kg / t 钢 , and then lift the molten steel to the casting station.

[0021] E. Molten steel casting: The tundish temperature is 1535℃, the pulling speed is 3.1m / min, and the crystallizer cooling water flow rate is 135m 3 / h, and the secondary cooling water volume was 1.8L / kg. The molten steel from step C was cast into billets with a cross-section of 165mm×165mm using an R9m straight arc continuous straightening 5-machine 5-strand billet casting machine. The straightening temperature of the billet leaving the straightening machine was controlled at 1010℃.

[0022] F. Billet heating: The billet in step E is fed into a heating furnace with a temperature of 1110°C in the soaking section and heated for 75 minutes. The billet tapping temperature is 1040°C and then pushed to a fully continuous bar mill for rolling.

[0023] G. Controlled rolling and controlled cooling of steel billets: The steel billets in step F are rolled by the rough rolling unit at a speed of 0.8 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 8.0 m / s for 6 passes; then the rolled pieces are controlled and cooled before finishing rolling by a water cooling device with a length of 10 m before finishing rolling, and the cooling water volume is 60 m 3 / h, the temperature of the rolled piece entering the finishing rolling unit is controlled at 900℃; the rolled piece passes through the finishing rolling unit 1 at a rolling speed of 10.0m / s for 2 passes; before the rolled piece enters the finishing rolling unit 2, it is controlled to cool by a water cooling device with a length of 8m, and the cooling water volume is 80m 3 / h, the temperature of the rolled piece entering the second finishing rolling unit is controlled at 850℃; then the rolled piece passes through the second finishing rolling unit at a rolling speed of 13.0m / s for 2 passes; after finishing rolling, the rolled piece passes through a water cooling device with a length of 5m 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 920℃, and then the steel bar is naturally air-cooled to room temperature on the cooling bed, and a 500MPa grade high-strength earthquake-resistant steel bar with a nominal diameter of 18mm for railway use having the following chemical composition by weight percentage is obtained: C 0.22wt%, Si 0.45wt%, Mn 0.70wt%, Cr0.70wt%, Cu0.17wt%, V 0.060wt%, Nb 0.010wt%, S 0.020wt%, P0.020wt%, O 0.0016wt%, N0.0160wt%, and the rest is Fe and unavoidable impurities. The process mechanical properties, microstructure, Vickers hardness difference and corrosion resistance of the earthquake-resistant steel bar are shown in Tables 3 and 4.

[0024] Table 3 Processing mechanical properties and corrosion resistance of 500MPa grade high strength earthquake-resistant steel bars with a nominal diameter of 18mm for railway use produced in Example 1 Table 4 Metallographic microstructure and Vickers hardness of 500MPa grade high strength earthquake-resistant steel bars for railway use with a nominal diameter of 18mm produced in Example 1 Example 2 A. Molten steel smelting: 265kg / t 钢 、1.5kg / t 钢 The cold material charging ratio is as follows: the scrap steel (chemical composition: C 0.22wt%, Si 0.42wt%, Mn 1.40wt%, P 0.037wt%, S0.033wt%, the rest is Fe and inevitable impurities) and copper plate (chemical composition: Cu 99.3wt%, P 0.035wt%, S0.041wt%, the rest is inevitable impurities) in the LD converter in the following mass ratio; then the 790kg / t 钢 The molten iron charging ratio is as follows: molten iron temperature is 1320℃, molten iron composition is C 4.2wt%, Si 0.22wt%, Mn 0.32wt%, P0.076wt%, S 0.021wt%, and the rest is Fe and inevitable impurities; after the scrap steel, copper plate 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 19kg / t 钢 , the amount of light-burned dolomite added is 17kg / t 钢 , control the final carbon content to 0.08wt%, the tapping temperature to 1595℃; before tapping, press 1.5kg / t to the bottom of the ladle 钢 The amount of activated lime is added for slag washing. The steelmaking process adopts the bottom blowing nitrogen process throughout the process, and the nitrogen flow rate is controlled at 20NL / min.

[0025] 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: 2.0 kg / 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 4.2kg / t 钢 Add the following mass ratio of ferrosilicon: Si 73.5wt%, the rest is Fe and inevitable impurities; at 10.6kg / t 钢 Add the following mass ratio of silicon-manganese alloy: Mn 65.2wt%, Si 17.9wt%, C1.1wt%, the rest is Fe and inevitable impurities; according to 13.7 kg / t 钢 The amount of high carbon ferrochrome in the following mass ratio is added: Cr 54.2wt%, C 7.4wt%, P0.072wt%, S0.062wt%, and the rest is Fe and unavoidable impurities; at 1.0kg / t 钢 The amount of silicon-nitrogen alloy is added in the following mass ratio: Si 57.4wt%, N 40.3wt%, C 1.75wt%, P0.075wt%, S 0.038wt%, and the rest is Fe and unavoidable impurities; kg / t 钢 The following mass ratio of niobium-phosphorus-iron alloy is added: Nb 44.2wt%, Si 3.5wt%, C1.75wt%, P1.65wt%, S 0.045wt%, and the rest is Fe and inevitable impurities; the above alloys are added when the amount of molten steel in the ladle reaches 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.

[0026] 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 10.7kg / t 钢 The amount of vanadium-containing pig iron having the following mass ratio is added: components C 3.5wt%, Si 0.45wt%, Mn 1.85wt%, V5.0wt%, P 1.02wt%, S 0.065wt%, and the rest are Fe and inevitable impurities. The vanadium-containing pig iron is baked for 8 minutes, and the surface temperature of the pig iron after baking is 360°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 30NL / min for 3 minutes.

[0027] D. LF furnace refining of molten steel: Lift the molten steel from step C to the LF furnace refining station and connect the nitrogen belt. Turn on the nitrogen and use nitrogen with a flow rate of 20NL / min to blow nitrogen into the molten steel. Then, use the 6th to 8th gear of the lower electrode to slag. After 3 minutes of slag slag slag, lift the electrode to observe the slag slag situation in the furnace. If the slag sample is too thin and the color is too black, add 5.0kg / t lime. 钢 Adjust the slag, otherwise add 2.0kg / t of pre-melted refined slag 钢 Adjustment; then measure temperature and take samples, add alloy to adjust the composition of molten steel and raise the temperature of lower electrode according to the steel sample and temperature test results to ensure that the composition and temperature are qualified; after refining, perform soft nitrogen blowing with small flow rate on molten steel, the blowing time is 2 minutes, and the nitrogen flow rate is controlled at 25NL / 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.

[0028] E. Molten steel casting: The tundish temperature is 1530℃, the pulling speed is 3.2m / min, and the crystallizer cooling water flow rate is 140m 3 / h, and the secondary cooling water volume was 1.7L / kg. The molten steel from step C was cast into billets with a cross-section of 165mm×165mm using an R9m straight arc continuous straightening 5-machine 5-strand billet casting machine. The straightening temperature of the billet leaving the straightening machine was controlled at 1020℃.

[0029] F. Billet heating: The billet in step E is fed into a heating furnace with a temperature of 1130°C in the soaking section and heated for 75 minutes. The billet tapping temperature is 1050°C and then pushed to a fully continuous bar mill for rolling.

[0030] G. Controlled rolling and controlled cooling of steel billets: The steel billets in step F are rolled for 6 passes at a speed of 0.6 m / s by the rough rolling mill; then the rolled pieces are rolled for 4 passes at a speed of 1.6 m / s by the intermediate rolling mill; then the rolled pieces are rolled for 5 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 a water cooling device with a length of 10 m before finishing rolling, and the cooling water volume is 70 m 3 / h, the temperature of the rolled piece entering the finishing rolling unit is controlled at 890℃; the rolled piece passes through the finishing rolling unit at a speed of 10.0m / s for one pass; before entering the finishing rolling unit 2, the rolled piece is cooled by a water cooling device with a length of 8m, and the cooling water volume is 95m 3 / h, the temperature of the rolled piece entering the second finishing rolling unit is controlled at 845℃; then the rolled piece passes through the second finishing rolling unit at a rolling speed of 12.0m / s for 2 passes; after finishing rolling, the rolled piece passes through a water cooling device with a length of 5m 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 500MPa grade high-strength earthquake-resistant steel bar with a nominal diameter of 22mm for railway use having the following chemical composition by weight percentage is obtained: C 0.23wt%, Si 0.52wt%, Mn 0.78wt%, Cr0.75wt%, Cu0.19wt%, V 0.065wt%, Nb 0.012wt%, S 0.032wt%, P0.031wt%, O 0.0024wt%, N0.0172wt%, and the rest is Fe and unavoidable impurities. The process mechanical properties, microstructure, Vickers hardness difference and corrosion resistance of the earthquake-resistant steel bar are shown in Tables 5 and 6.

[0031] Table 5 Processing mechanical properties and corrosion resistance of 500MPa grade high strength earthquake-resistant steel bars with a nominal diameter of 22mm for railway use produced in Example 2 Table 6 Metallographic microstructure and Vickers hardness of 500MPa grade high strength earthquake-resistant steel bars for railway use with a nominal diameter of 22mm produced in Example 2 Example 3 A. Molten steel smelting: 270kg / t 钢 、1.7kg / t 钢 The cold material charging ratio is as follows: the scrap steel (chemical composition: C 0.25wt%, Si 0.55wt%, Mn 1.52wt%, P 0.045wt%, S0.045wt%, the rest are Fe and inevitable impurities) and copper plate (chemical composition: Cu 99.3wt%, P 0.035wt%, S0.041wt%, the rest are inevitable impurities) in the LD converter are added; then the 795kg / t 钢 The molten iron charging ratio is as follows: molten iron temperature is 1330℃, molten iron composition is C 4.3wt%, Si 0.30wt%, Mn 0.45wt%, P0.080wt%, S 0.030wt%, and the rest is Fe and inevitable impurities; after the scrap steel, copper plate 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 1600℃; before tapping, press 1.5kg / t to the bottom of the ladle 钢The amount of activated lime is added for slag washing. The steelmaking process adopts the bottom blowing nitrogen process throughout the process, and the nitrogen flow rate is controlled at 25NL / min.

[0032] 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: 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; 5.4kg / t 钢 Add the following mass ratio of ferrosilicon: Si 73.5wt%, the rest is Fe and inevitable impurities; at 12.1kg / t 钢 The amount of silicon-manganese alloy with the following mass ratio is added: Mn 65.2wt%, Si 17.9wt%, C1.1wt%, and the rest is Fe and inevitable impurities; according to 14.6 kg / t 钢 The amount of high carbon ferrochrome in the following mass ratio is added: Cr 54.2wt%, C 7.4wt%, P0.072wt%, S0.062wt%, and the rest is Fe and unavoidable impurities; at 1.0kg / t 钢 The amount of silicon-nitrogen alloy is added in the following mass ratio: Si 57.4wt%, N 40.3wt%, C 1.75wt%, P0.075wt%, S 0.038wt%, and the rest is Fe and unavoidable impurities; kg / t 钢 The following mass ratio of niobium-phosphorus-iron alloy is added: Nb 44.2wt%, Si 3.5wt%, C1.75wt%, P1.65wt%, S 0.045wt%, and the rest is Fe and inevitable impurities; the above alloys are added when the amount of molten steel in the ladle reaches 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.

[0033] 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 11.0kg / t 钢The amount of vanadium-containing pig iron having the following mass ratio is added: components C 3.5wt%, Si 0.45wt%, Mn 1.85wt%, V5.0wt%, P1.02wt%, S 0.065wt%, and the rest are Fe and inevitable impurities. The baking time of the vanadium-containing pig iron is 8 minutes, and the surface temperature of the pig iron after baking is 370°C. After the vanadium-containing pig iron is added, nitrogen is turned on and nitrogen is blown to the molten steel with a flow rate of 30NL / min, and the blowing time is 3 minutes.

[0034] D. LF furnace refining of molten steel: Lift the molten steel from step C to the LF furnace refining station and connect the nitrogen belt. Turn on the nitrogen and use nitrogen with a flow rate of 20NL / min to blow nitrogen into the molten steel. Then, use the 6th to 8th gear of the lower electrode to slag. After 3 minutes of slag slag slag, lift the electrode to observe the slag slag situation in the furnace. If the slag sample is too thin and the color is too black, add 5.0kg / t lime. 钢 Adjust the slag, otherwise add 2.0kg / t of pre-melted refined slag 钢 Adjustment; then measure temperature and take samples, add alloy to adjust the composition of molten steel and 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 small flow soft nitrogen blowing on molten steel, the blowing time is 2 minutes, and the nitrogen flow rate is controlled at 25NL / min; after nitrogen blowing, add molten steel covering agent, the addition amount is 1.0kg / t 钢 , and then lift the molten steel to the casting station.

[0035] E. Molten steel casting: The tundish temperature is 1525℃, the casting speed is 3.3m / min, and the crystallizer cooling water flow rate is 145m 3 / h, and the secondary cooling water volume was 1.6L / 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 small square billet casting machine. The straightening temperature of the billet leaving the straightening machine was controlled at 1030℃.

[0036] F. Billet heating: The billet in step E is fed into a heating furnace with a temperature of 1150°C in the soaking section and heated for 75 minutes. The billet tapping temperature is 1060°C and then pushed to a fully continuous bar mill for rolling.

[0037] G. Controlled rolling and controlled cooling of steel billets: The steel billets in step F are rolled for 6 passes at a speed of 0.4 m / s by the rough rolling mill; then the rolled pieces are rolled for 4 passes at a speed of 1.2 m / s by the intermediate rolling mill; then the rolled pieces are rolled for 3 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 a water cooling device with a length of 10 m before finishing rolling, and the cooling water volume is 80 m 3 / h, the temperature of the rolled piece entering the finishing rolling unit is controlled at 880℃; the rolled piece passes through the finishing rolling unit at a speed of 9.0m / s for one pass; before entering the finishing rolling unit 2, the rolled piece is cooled by a water cooling device with a length of 8m, and the cooling water volume is 100m 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 11.0m / s for 2 passes; after finishing rolling, the rolled piece passes through a water cooling device with a length of 5m 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 890°C, and then the steel bar is naturally air-cooled to room temperature on the cooling bed, and a 500MPa grade high-strength earthquake-resistant steel bar with a nominal diameter of 25mm for railway use having the following chemical composition by weight percentage is obtained: C 0.24wt%, Si 0.60wt%, Mn 0.85wt%, Cr 0.80wt%, Cu0.21wt%, V 0.070wt%, Nb 0.013wt%, S 0.040wt%, P0.040wt%, O 0.0030wt%, N 0.0185wt%, and the rest is Fe and unavoidable impurities. The process mechanical properties, microstructure, Vickers hardness difference and corrosion resistance of the two earthquake-resistant steel bars are shown in Tables 7 and 8.

[0038] Table 7 Processing mechanical properties and corrosion resistance of 500MPa grade high strength earthquake-resistant steel bars with a nominal diameter of 25mm for railways produced in Example 3 Table 8 Metallographic microstructure and Vickers hardness of 500MPa grade high strength earthquake-resistant steel bars for railway with a nominal diameter of 25mm produced in Example 3 .

Claims

1. A 500MPa grade high strength earthquake resistant steel bar for railway use with a nominal diameter of 18-25mm, characterized in that: The earthquake-resistant steel bar has the following chemical composition in weight percentage: C 0.22-0.24wt%, Si 0.45-0.60wt%, Mn 0.70-0.85wt%, Cr 0.70-0.80wt%, Cu 0.17-0.21wt%, V 0.060-0.070wt%, Nb 0.010-0.013wt%, S≤0.040wt%, P≤0.040wt%, O≤0.0030wt%, N 0.0160-0.0185wt%, and the rest is Fe and inevitable impurities.

2. The 500MPa grade high-strength earthquake-resistant steel bar for railway use with a nominal diameter of 18-25mm according to claim 1, characterized in that: The seismic steel bar has a yield strength of 530-560 MPa, a tensile strength of 695-750 MPa, a strength-to-yield ratio of ≥1.31, an elongation after fracture of ≥23%, and a total elongation at maximum force of ≥10.5%.

3. The method for preparing the 500MPa grade high-strength earthquake-resistant steel bar for railway use with a nominal diameter of 18-25mm as claimed in claim 1, characterized in that: To do this, follow these steps: A. Molten steel smelting: 260-270kg / t 钢 , 1.3-1.7kg / t 钢 The cold material charging ratio is 785-795kg / t. 钢 The molten iron charging ratio is 1310℃ molten iron is added to the LD converter for conventional top and bottom composite blowing. The chemical composition of the molten iron is: C 4.1-4.3wt%, Si 0.15-0.30wt%, Mn 0.20-0.45wt%, P 0.070-0.080wt%, S≤0.030wt%, and the rest is Fe and unavoidable impurities; then the molten iron is heated to 15-20kg / t 钢 , 15-18kg / t 钢 Add lime and lightly burned dolomite to make slag, control the final carbon content ≥ 0.07wt%, and the tapping temperature ≤ 1600℃; before tapping, press 1.5kg / t 钢 Add active lime to the bottom of the ladle for slag washing; 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. The deoxidation and alloying steps are carried out at 2 kg / t. 钢 , 3.2~5.4kg / t 钢 , 9.7~12.1kg / t 钢 12.6~14.6kg / t 钢 , 0.9~1.0kg / t 钢 , 0.25~0.30kg / 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. Molten steel argon station treatment: The molten steel from step B is hoisted to the argon station treatment station and heated through the alloy trough at 10.0-11.0 kg / t 钢 The vanadium-containing pig iron having a surface temperature of ≥350°C after baking is added in an amount of 1000 wt %. After the vanadium-containing pig iron is added, nitrogen is blown to the molten steel at a flow rate of 25 to 30 NL / min for 3 minutes. The vanadium-containing pig iron has the following mass ratio composition: C 3.5wt%, Si 0.45wt%, Mn 1.85wt%, V 5.0wt%, P 1.02wt%, S 0.065wt%, and the rest is Fe and unavoidable impurities. D. LF furnace refining of molten steel: The molten steel from step C is hoisted to the LF furnace for refining. After refining, the molten steel is subjected to soft nitrogen blowing at a small flow rate of 20-25 NL / min for 2 minutes. After nitrogen blowing, the molten steel is subjected to nitrogen blowing at a rate of 1.0 kg / t 钢 Add the amount of molten steel covering agent, and then lift the molten steel to the casting station; E. Molten steel casting: The tundish temperature is 1525-1535°C, the pulling speed is 3.1-3.3 m / min, and the crystallizer cooling water flow rate is 135-145 m 3 / h, and the secondary cooling water volume is 1.6-1.8L / kg, the molten steel is cast into a billet with a cross section of 165mm×165mm; the straightening temperature of the billet out of the straightening machine is controlled at 1010-1030℃; F. Billet heating: The billet in step E is sent to a heating furnace with a soaking section temperature of 1110-1150°C for heating for 70 minutes. The billet tapping temperature is 1040-1060°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 speed of 0.4-0.8 m / s by the rough rolling unit, and then rolled for 4 passes at a speed of 1.2-2.0 m / s by the intermediate rolling unit; and then rolled for 3-6 passes at a speed of 6.0-8.0 m / s by the pre-finishing rolling unit; before the rolled piece enters the finishing rolling, it is controlled and cooled before finishing rolling by a set of 10m long water cooling devices, and the cooling water volume is 60-80m 3 / h, the temperature of the rolled piece entering the finishing rolling unit is controlled at 880-900℃; the rolled piece passes through the finishing rolling unit at a speed of 9.0-10.0m / s for 1-2 passes; before entering the finishing rolling unit 2, the rolled piece passes through a water cooling device with a length of 8m for controlled cooling, and the cooling water volume is 80-100m 3 / h, the temperature of the rolled piece entering the second finishing rolling group is controlled at 830-850℃; then the rolled piece passes through the second finishing rolling group at a rolling speed of 11.0-13.0m / s for 2 passes; after finishing rolling, the rolled piece passes through a water cooling device with a length of 5m 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 890-920℃, and then the steel bar is naturally air-cooled to room temperature on the cooling bed to obtain 500MPa grade high-strength earthquake-resistant steel bars for railway use with a nominal diameter of 18-25mm.

4. The method for preparing the 500MPa grade high-strength earthquake-resistant steel bar for railway with a nominal diameter of 18-25mm according to claim 3, characterized in that: In step A, the chemical composition of the scrap steel is: C 0.19-0.25wt%, Si 0.32-0.55wt%, Mn1.30-1.52wt%, P 0.024-0.045wt%, S 0.023-0.045wt%, and the rest is Fe and inevitable impurities; the chemical composition of the copper plate is: Cu 99.3wt%, P 0.035wt%, S 0.041wt%, and the rest is inevitable impurities.

5. The method for preparing the 500MPa grade high-strength earthquake-resistant steel bar for railway with a nominal diameter of 18-25mm according to claim 3, 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.

6. The method for preparing the 500MPa grade high-strength earthquake-resistant steel bar for railway with a nominal diameter of 18-25mm according to claim 3, characterized in that: In step B, the chemical composition of silicon calcium barium is: Si 52.5wt%, Ca 9.85wt%, Ba 12.15wt%, Al2.45wt%, and the rest is Fe and inevitable impurities; the chemical composition of ferrosilicon is: Si 73.5wt%, and the rest is Fe and inevitable impurities; the chemical composition of silicon manganese alloy is: Mn 65.2wt%, Si 17.9wt%, C 1.1wt%, and the rest is Fe and inevitable impurities; the chemical composition of high carbon ferrochrome is: Cr 54.2wt%, C 7.4wt%, P 0.072wt%, S0.062wt%, and the rest is Fe and inevitable impurities; the chemical composition of nitrogen-rich alloy is: Si 57.4wt%, N40.3wt%, C 1.75wt%, P 0.075wt%, S 0.038wt%, the rest is Fe and inevitable impurities; the chemical composition of niobium ferrophosphide alloy is: Nb 44.2wt%, Si 3.5wt%, C1.75wt%, P 1.65wt%, S 0.045wt%, the rest is Fe and inevitable impurities.

7. The method for preparing the 500MPa grade high-strength earthquake-resistant steel bar for railway with a nominal diameter of 18-25mm according to claim 3, characterized in that: In step D, during the refining process, nitrogen gas with a flow rate of 15-20 NL / min is used to blow nitrogen into the molten steel, and then the lower electrode is slag-free at gears 6-8; after 3 minutes of slag-freeing, the electrode is lifted to observe the slag-freeing situation in the furnace; if the slag sample is too thin and the color is too black, lime is added at 4.0-5.0 kg / t 钢 Adjust the slag, otherwise add pre-melted refined slag 1.0~2.0kg / t 钢 Adjustment; then measure temperature and take samples. According to the steel sample and temperature test results, add alloy to adjust the steel liquid composition and lower electrode temperature to ensure that the composition and temperature are qualified.

8. The method for preparing the 500MPa grade high-strength earthquake-resistant steel bar for railway with a nominal diameter of 18-25mm according to claim 3, characterized in that: In step E, R9m straight arc continuous straightening 5-machine 5-strand billet casting machine is used for casting.

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