A large-size 650mpa high-tenacity corrosion-resistant anti-seismic reinforcing steel with a nominal diameter of 28-40mm and a preparation method thereof

Abstract

The application discloses a kind of nominally diameter 28-40mm large-scale 650MPa high strength and toughness corrosion-resistant anti-seismic reinforcing steel and its preparation method.The anti-seismic reinforcing steel has the following chemical components by weight percentage: C 0.26-0.29wt%, Si 0.65-0.75wt%, Mn 1.52-1.60wt%, Cr 0.15-0.20wt%, Ni 0.12-0.18wt%, V 0.136-0.150wt%, S≤0.035wt%, P≤0.035wt%, O≤0.0040wt%, N 0.0310-0.0340wt%, and the rest is Fe and unavoidable impurities.The application is integrated innovation through chemical composition design, converter smelting, deoxidation alloying, continuous casting, rolling heating system, rolling temperature and controlled cooling process, fully plays the multiple strengthening effects of precipitation strengthening, fine-grain strengthening and the like, and the produced large-scale 650MPa reinforcing steel has the advantages of excellent stable process mechanics performance, fine and uniform microstructure, good plasticity and toughness, excellent corrosion resistance and anti-seismic performance and the like, improves product market competitiveness and application range.In addition, the application process has the characteristics of low production cost, strong process applicability and control, and has significant economic and social benefits.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of steel smelting, and particularly relates to a 28-40 mm large-diameter 650 MPa high-strength and high-toughness corrosion-resistant anti-seismic steel bar and a preparation method thereof. BACKGROUND

[0002] High-strength anti-seismic steel bars are the main reinforcing materials for high-rise and large-scale reinforced concrete building structures, and bear stress and strain such as tensile stress and compressive stress and strain in the structure. With the continuous development of buildings in China towards high-rise, super-high-rise and large-span seismic structure directions, it is an important task for the steel industry to improve the technical level and adjust the product structure to develop high-strength and high-toughness corrosion-resistant anti-seismic steel bars with a strength level of 600 MPa and above.

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

[0004] The first object of the present application is to provide a 28-40 mm large-diameter 650 MPa high-strength and high-toughness corrosion-resistant anti-seismic steel bar. The second object of the present application is to provide a preparation method of the 28-40 mm large-diameter 650 MPa high-strength and high-toughness corrosion-resistant anti-seismic steel bar.

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

[0006] The second object of the present application is achieved by a preparation method of a 28-40 mm large-diameter 650 MPa high-strength and high-toughness corrosion-resistant anti-seismic steel bar, which is achieved by the following steps:

[0007] A, molten steel smelting: according to 250-260kg / t 钢 , 1.0-1.6kg / t 钢 of cold material is loaded into the proportioning, scrap steel and nickel plate are added into the LD converter respectively; then according to 800-810kg / t 钢 of molten iron loading proportion, molten iron with temperature≥1310℃ is added into the LD converter, conventional top and bottom combined blowing is carried out, lime and light-burned dolomite are added in the amount of 15-20kg / t 钢 , 15-18kg / t 钢 , the end point carbon content is controlled to be≥0.08wt%, the tapping temperature is≤1650℃; the composition of the molten iron is: C 4.1-4.5wt%, Si 0.15-0.30wt%, Mn 0.25-0.40wt%, P 0.080-0.100wt%, S≤0.035wt%, the rest is Fe and unavoidable impurities;

[0008] Before tapping, the ladle is added with vanadium-containing pig iron with the following mass ratio in the amount of 12.0kg / t 钢 : composition C 3.2wt%, Si 0.20wt%, Mn 1.05wt%, V 5.25wt%, P 0.60wt%, S 0.155wt%, the rest is Fe and unavoidable impurities; before tapping, active lime is added to the bottom of the ladle in the amount of 1.0kg / t 钢 ; the vanadium-containing pig iron is roasted for 3 minutes after being added into the ladle;

[0009] B, deoxidization and alloying: after the smelting is completed, the molten steel is tapped, when the amount of molten steel in the ladle is greater than 1 / 4, silicon-calcium-barium, silicon-iron, silicon-manganese alloy, high-carbon-chromium-iron, nitrogen-rich alloy, and vanadium-nitrogen alloy are added into the ladle in the order of deoxidization and alloying, in the amount of 1.5kg / t 钢 , 3.3-4.5kg / t 钢 , 23.2-24.5kg / t 钢 , 2.3-3.2kg / t 钢 , 1.10-1.23kg / t 钢 , 0.95-1.12kg / t 钢 , respectively; when the amount of molten steel in the ladle reaches 4 / 5, the above alloys are added;

[0010] C, molten steel LF furnace refining: the steel water in B step is lifted to the LF furnace for refining, after the refining is completed, the molten steel is blown with soft nitrogen at a small flow rate of 10-15NL / min for 3min, after the nitrogen blowing is completed, the molten steel is covered with a covering agent, and then the molten steel is lifted to the casting station;

[0011] D. Steel pouring: at 1525-1540℃, the pulling speed is 3.4-3.5m / min, the crystallizer cooling water flow is 150-160m 3 / h, the secondary cooling specific water flow is 2.0-2.1L / kg, the steel is poured into a billet with a section of 165mmx165mm;

[0012] E. Billet heating: the billet of step D is sent into a heating furnace with a soaking section furnace temperature of 1110-1160℃ for heating for 70 minutes, the billet delivery temperature is 1050-1070℃, and then pushed to a full continuous bar mill for rolling;

[0013] F. Billet controlled rolling and controlled cooling: the billet of step E is rolled by a rough rolling mill group under rolling conditions with a speed of 0.4-0.6m / s for 6 passes, then rolled by a medium rolling mill group under rolling conditions with a speed of 2.0-2.5m / s for 4 passes, and then rolled by a pre-precision rolling mill group under rolling conditions with a speed of 5.0-7.0m / s for 6 passes; the rolled piece is cooled by 2 groups of water cooling devices with a length of 4m respectively before precision rolling for controlled cooling, the cooling water flow is 100-120m 3 / h, the temperature control of the rolled piece entering the first group of precision rolling is 790-820℃; the rolled piece is rolled by the first group of precision rolling mill group under rolling conditions with a speed of 8.0-9.0m / s for 1-2 passes; the rolled piece is cooled by 2 groups of water cooling devices with a length of 7m respectively before entering the second group of precision rolling mill group, the cooling water flow is 70-80m 3 / h, the temperature control of the rolled piece entering the second group of precision rolling is 820-840℃; then the rolled piece is rolled by the second group of precision rolling mill group under rolling conditions with a speed of 10-12m / s for 2 passes; the rolled piece is cooled by 1 group of water cooling devices with a length of 10m after precision rolling for controlled cooling, the cooling water flow is 40-50m 3 / h; the temperature control of the steel bar on the cooling bed after controlled cooling is 900-930℃, then the steel bar is naturally air cooled to room temperature on the cooling bed, and a large-size 650MPa high strength and toughness anti-seismic steel bar with a nominal diameter of 28-40mm is obtained.

[0014] The present application adds a large amount of vanadium-containing pig iron to replace part of expensive vanadium alloy in the steel ladle, increases the V content of molten steel, and reduces the amount of vanadium alloy; during the steelmaking deoxidation and alloying process, a nitrogen-rich alloy is added, and the molten steel is treated by nitrogen blowing during LF furnace refining, which significantly increases the nitrogen content in the molten steel, reduces the V / N ratio in the steel, increases the driving force for V(C,N) and VN precipitation, promotes the transformation of V from solid solution to carbonitride precipitate phase during rolling, and a large amount of fine dispersed V(C,N) and VN precipitates are formed and precipitated, which significantly improves the precipitation strengthening effect of the steel; a certain amount of chromium and nickel is added to the steel to improve the passivation corrosion resistance of the steel, and the corrosion rate is only 2 / 3 of that of ordinary HRB600 steel, while the hardenability and secondary hardening effect are obviously improved, the pearlite content is increased, the tensile strength of the steel is improved, and the anti-seismic performance is significantly improved; the rolling steel is controlled at a higher opening temperature to promote the full solid solution of micro-alloy V; a longer water cooling device is used after pre-precision rolling to control the lower temperature of the rolled piece; two sets of precision rolling mills are used after the rolled piece enters the precision rolling, and the temperature is controlled by the water cooling device to control the lower precision rolling temperature; a longer water cooling device is used after precision rolling; through the multiple graded limited cooling process of pre-rolling control cooling, precision rolling temperature control low temperature rolling, and post-rolling control cooling, the original austenite grains are significantly refined, the formation and precipitation of fine dispersed V(C,N) and VN precipitates are promoted, the nucleation sites and nucleation rate of ferrite grains are increased, the ferrite grains are significantly refined, the grain size is above 12.0, 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; the C and Mn contents in the steel are controlled to be higher, the pearlite content is increased, the tensile strength of the steel is significantly improved, and the anti-seismic performance is improved.

[0015] The preparation method of the present application integrates innovation of chemical composition design, converter smelting, deoxidation and alloying, continuous casting, rolling heating system, rolling temperature and controlled cooling process, fully plays the multiple strengthening effects of precipitation strengthening, fine grain strengthening and the like, and the large-scale 650MPa steel bar produced has the advantages of excellent and stable process mechanical properties, fine and uniform microstructure, good plasticity and toughness, excellent corrosion resistance and anti-seismic performance, etc., and improves the product market competitiveness and application range. In addition, the process has the characteristics of low production cost, strong process applicability and control, and has significant economic and social benefits. DETAILED DESCRIPTION

[0016] The present application will be further described in detail below in conjunction with the embodiments, but in no way limits the present application, any transformation or improvement based on the teaching of the present application falls within the protection scope of the present application.

[0017] The application discloses a large-size 650MPa high-strength and high-toughness corrosion-resistant anti-seismic reinforcing steel with a nominal diameter of 28-40mm, which has the following chemical components in percentage by weight: C 0.26-0.29wt%, Si 0.65-0.75wt%, Mn 1.52-1.60wt%, Cr 0.15-0.20wt%, Ni 0.12-0.18wt%, V 0.136-0.150wt%, S≤0.035wt%, P≤0.035wt%, O≤0.0040wt%, N 0.0310-0.0340wt%, and the rest is Fe and inevitable impurities. The process mechanical properties, microstructure, Vickers hardness difference and corrosion resistance of the anti-seismic reinforcing steel are shown in Table 1 and Table 2.

[0018] Table 1 mechanical properties and corrosion resistance of the large-size 650MPa high-strength and high-toughness anti-seismic reinforcing steel with a nominal diameter of 28-40mm

[0019]

[0020] Table 2 metallographic structure and Vickers hardness of the large-size 650MPa high-strength and high-toughness anti-seismic reinforcing steel with a nominal diameter of 28-40mm

[0021]

[0022] The application further provides a preparation method of the large-size 650MPa high-strength and high-toughness corrosion-resistant anti-seismic reinforcing steel with a nominal diameter of 28-40mm, which is realized according to the following steps:

[0023] A, smelting of molten steel: according to the proportion of 250-260kg / t 钢 , 1.0-1.6kg / t 钢 of cold charge, scrap steel and nickel plate are added into the LD converter; then according to the proportion of 800-810kg / t 钢 of hot metal, hot metal with a temperature of greater than or equal to 1310 DEG C is added into the LD converter, conventional top and bottom combined blowing is carried out, and lime and light-burned dolomite are added in amounts of 15-20kg / t 钢 , 15-18kg / t 钢 , the end-point carbon content is controlled to be greater than or equal to 0.08wt%, and the tapping temperature is less than or equal to 1650 DEG C; the composition of the hot metal is as follows: C 4.1-4.5wt%, Si 0.15-0.30wt%, Mn 0.25-0.40wt%, P 0.080-0.100wt%, S≤0.035wt%, and the rest is Fe and inevitable impurities;

[0024] Before tapping, the ladle is added with 12.0kg / t 钢, the following mass ratio of vanadium-containing pig iron is added: component C 3.2wt%, Si 0.20wt%, Mn 1.05wt%, V 5.25wt%, P 0.60wt%, S 0.155wt%, and the rest is Fe and inevitable impurities; before tapping, 1.0kg / t 钢 of active lime is added to the bottom of the ladle for slag washing; the vanadium-containing pig iron is roasted for 3 minutes after being added to the ladle;

[0025] B, deoxidation and alloying: after the molten steel is smelted, when the amount of molten steel in the ladle is greater than 1 / 4, the deoxidation and alloying sequence of silicon-calcium-barium→silicon-iron→silicon-manganese alloy→high-carbon chromium iron→nitrogen-rich alloy→vanadium-nitrogen alloy is followed, and the following amounts of silicon-calcium-barium, silicon-iron, silicon-manganese alloy, high-carbon chromium iron, silicon-nitrogen alloy and high-vanadium-nitrogen alloy are added to the ladle in sequence: 1.5kg / t 钢 , 3.3-4.5kg / t 钢 , 23.2-24.5kg / t 钢 , 2.3-3.2kg / t 钢 , 1.10-1.23kg / t 钢 , 0.95-1.12kg / t 钢 , 0.95-1.12kg / t 3 The above alloys are added when the amount of molten steel in the ladle reaches 4 / 5;

[0026] C, LF furnace refining of molten steel: the molten steel in step B is lifted to the LF furnace for refining, after the refining is completed, the molten steel is subjected to soft nitrogen blowing at a small flow rate of 10-15NL / min for 3min, after the nitrogen blowing is completed, the molten steel is covered with a covering agent, and then the molten steel is lifted to the casting station;

[0027] D, molten steel casting: under the conditions of 1525-1540℃, a drawing speed of 3.4-3.5m / min, a crystallizer cooling water flow rate of 150-160m 3 / h, and a secondary cooling water amount of 2.0-2.1L / kg, the molten steel is cast into a billet with a cross section of 165mm×165mm;

[0028] E, billet heating: the billet in step D is sent to a heating furnace with a furnace temperature of 1110-1160℃ for heating for 70 minutes, the billet tapping temperature is 1050-1070℃, and then the billet is pushed to a full continuous bar mill for rolling;

[0029] F, billet controlled rolling and controlled cooling: the billet of step E is rolled by 6 passes through a rough rolling mill set at a rolling speed of 0.4-0.6 m / s, then rolled by 4 passes through a medium rolling mill set at a rolling speed of 2.0-2.5 m / s, and then rolled by 6 passes through a pre-precision rolling mill set at a rolling speed of 5.0-7.0 m / s; the rolled piece is cooled by 2 groups of water cooling devices with a length of 4 m before entering the precision rolling mill, the cooling water flow is 100-120 m 3 / h, the temperature of the rolled piece entering the first group of the precision rolling mill is controlled at 790-820℃; the rolled piece is rolled by 1-2 passes through the first group of the precision rolling mill at a rolling speed of 8.0-9.0 m / s; the rolled piece is cooled by 2 groups of water cooling devices with a length of 7 m before entering the second group of the precision rolling mill, the cooling water flow is 70-80 m 3 / h, the temperature of the rolled piece entering the second group of the precision rolling mill is controlled at 820-840℃; then the rolled piece is rolled by 2 passes through the second group of the precision rolling mill at a rolling speed of 10-12 m / s; the rolled piece is cooled by 1 group of water cooling devices with a length of 10 m after the precision rolling, the cooling water flow is 40-50 m 3 / h; the temperature of the rebar on the cooling bed after the controlled cooling is controlled at 900-930℃, then the rebar is naturally air-cooled to room temperature on the cooling bed, and a large-size 650MPa high-strength and high-toughness anti-seismic rebar with a nominal diameter of 28-40 mm is obtained.

[0030] In step A, the chemical composition of the scrap steel is: C 0.20-0.26wt%, Si 0.25-0.60wt%, Mn 1.25-1.50wt%, P 0.018-0.042wt%, S 0.015-0.042wt%, and the rest is Fe and inevitable impurities; the chemical composition of the nickel plate is: Ni 99.2wt%, P 0.025wt%, S 0.032wt%, and the rest is inevitable impurities.

[0031] In step A, the full-process bottom blowing nitrogen process is adopted during the tapping of the molten steel, and the nitrogen flow is controlled at 15-20 NL / min.

[0032] In Step B, the chemical composition of the silicon-calcium-barium is: Si 52.5wt%, Ca 9.85wt%, Ba 12.15wt%, Al 2.45wt%, and the rest is Fe and inevitable impurities; the chemical composition of the silicon-iron is: Si 73.5wt%, and the rest is Fe and inevitable impurities; the chemical composition of the silicon-manganese alloy is: Mn 65.2wt%, Si 17.8wt%, C 1.5wt%, and the rest is Fe and inevitable impurities; the chemical composition of the high-carbon chromium iron is: Cr 53.8wt%, C 7.2wt%, P 0.061wt%, S 0.054wt%, and the rest is Fe and inevitable impurities; the chemical composition of the silicon-nitrogen alloy is: Si 57.6wt%, N 39.5wt%, C 0.95wt%, P 0.045wt%, S 0.024wt%, and the rest is Fe and inevitable impurities; the chemical composition of the vanadium-nitrogen alloy is: V 77.4wt%, N 15.8wt%, C 3.25wt%, P 0.082wt%, S 0.062wt%, and the rest is Fe and inevitable impurities.

[0033] In Step C, during the refining process, nitrogen gas with a flow rate of 20-25 NL / min is used to treat the molten steel, and then the electrode is lowered with gear 7-9 to slag; after 3 minutes of power-on slagging, the electrode is lifted to observe the slag in the furnace; if the slag sample is too thin and the color is too black, add 4-5 kg / t of lime 钢 If not, add 1.0-2.0 kg / t of premelted refining slag 钢 Adjust; then measure the temperature and take samples, and according to the steel sample and temperature test results, add alloys to adjust the composition of the molten steel and lower the electrode to increase the temperature, to ensure that the composition and temperature are qualified.

[0034] In Step D, R9m straight arc continuous straightening 5-machine 5-flow billet casting machine is used for casting. The casting billet straightening temperature out of the straightening machine is controlled at 960-980°C.

[0035] Example 1

[0036] A, molten steel smelting: according to 250 kg / t 钢 of cold charge ratio, the following mass ratio of scrap steel (chemical composition: C 0.20wt%, Si 0.25wt%, Mn 1.25wt%, P 0.018wt%, S 0.015wt%, and the rest is Fe and inevitable impurities) is added in the LD converter; according to 1.0 kg / t 钢 of charging ratio, the following mass ratio of nickel plate (chemical composition: Ni 99.2wt%, P 0.025wt%, S 0.032wt%, and the rest is inevitable impurities) is added in the LD converter; then according to 800 kg / t 钢molten iron charging ratio, the following temperature and mass ratio of molten iron is added into the LD converter: molten iron temperature 1310℃, molten iron composition C 4.1wt%, Si 0.15wt%, Mn 0.25wt%, P 0.080wt%, S 0.016wt%, and the rest is Fe and inevitable impurities; after the scrap and molten iron are charged into the LD converter, the conventional top and bottom combined blowing is carried out, the conventional lime and light-burned dolomite are added, the lime addition amount is 15kg / t 钢 , the light-burned dolomite addition amount is 15kg / t 钢 , the end point carbon content is controlled to be 0.08wt%, and the tapping temperature is 1626℃; before tapping, the ladle is added with the following mass ratio of vanadium-containing pig iron in an amount of 12.0kg / t 钢 : composition C 3.2wt%, Si 0.20wt%, Mn 1.05wt%, V 5.25wt%, P 0.60wt%, S 0.155wt%, and the rest is Fe and inevitable impurities, and the vanadium-containing pig iron is baked for 3 minutes after being added into the ladle; before tapping, the active lime is added to the bottom of the ladle for slag washing, and the lime addition amount is 1.0

[0037] kg / t 钢 ; the nitrogen blowing process is adopted during the whole tapping process, and the nitrogen flow rate is controlled to be 15NL / min.

[0038] B, deoxidation and alloying: the molten steel of the A step is tapped, when the molten steel amount in the ladle is greater than 1 / 4, the following deoxidation and alloying sequence is adopted: silicon calcium barium→silicon iron→silicon manganese alloy→high-carbon chromium iron→nitrogen-rich alloy→vanadium-nitrogen alloy, and the following substances are sequentially added into the ladle: the following mass ratio of silicon calcium barium is added in an amount of 1.5kg / t 钢 : Si 52.5wt%, Ca 9.85wt%, Ba 12.15wt%, Al 2.45wt%, and the rest is Fe and inevitable impurities; the following mass ratio of silicon iron is added in an amount of 3.3kg / t 钢 : Si 73.5wt%, and the rest is Fe and inevitable impurities; the following mass ratio of silicon manganese alloy is added in an amount of 23.2kg / t 钢 : Mn 65.2wt%, Si 17.8wt%, C 1.5wt%, and the rest is Fe and inevitable impurities; the following mass ratio of high-carbon chromium iron is added in an amount of 2.3

[0039] kg / t 钢 : Cr 53.8wt%, C 7.2wt%, P 0.061wt%, S 0.054wt%, and the rest is Fe and inevitable impurities; the following mass ratio of nitrogen-rich alloy is added in an amount of 1.10kg / t 钢kg / t, the following mass ratio of silicon-nitrogen alloy is added: Si 57.6wt%, N 39.5wt%, C 0.95wt%, P 0.045wt%, S 0.024wt%, the rest being Fe and inevitable impurities; 0.95

[0040] kg / t 钢 kg / t, the following mass ratio of vanadium-nitrogen alloy is added: V 77.4wt%, N 15.8wt%, C 3.25wt%, P 0.082wt%, S 0.062wt%, the rest being Fe and inevitable impurities; the above alloy is added when the ladle steel reaches 4 / 5; after the steel is discharged, the molten steel is lifted to the LF furnace for refining treatment.

[0041] C, LF furnace refining of molten steel: the molten steel is lifted to the LF furnace refining station and connected to the nitrogen gas belt, the nitrogen gas with a flow rate of 20 NL / min is turned on to treat the molten steel by nitrogen blowing, then the electrode is lowered to use gear 7-9 to slag; after 3 minutes of power-on slagging, the electrode is lifted to observe the slagging in the furnace; if the slag sample is too thin and the color is too black, add 4.0 kg / t 钢 of lime to adjust the slag, otherwise add 1.0 kg / t of premelted refining slag 钢 ; then measure the temperature and take samples, according to the steel sample and temperature test results, add alloy to adjust the composition of the molten steel and lower the electrode to increase the temperature, to ensure that the composition and temperature are qualified; after the refining is completed, the molten steel is treated by soft blowing nitrogen with a small flow rate, the nitrogen blowing time is 3 minutes, and the nitrogen flow rate is controlled at 10 NL / min; after the nitrogen blowing is completed, the molten steel is added with a covering agent, the addition amount is controlled at 1.0 kg / t 钢 , and then the molten steel is lifted to the casting station.

[0042] D, molten steel casting: under the conditions of a tundish temperature of 1540℃, a withdrawal speed of 3.4m / min, a crystallizer cooling water flow rate of 150m 3 / h, and a secondary cooling water amount of 2.0L / kg, the molten steel of step C is cast into a billet with a cross section of 165mm x 165mm by using a R9m straight-arc continuous straightening 5-machine 5-stream small billet caster; the casting billet is straightened at a temperature of 960℃ out of the straightening machine.

[0043] E, billet heating: the billet of step D is sent into a heating furnace with a furnace temperature of 1110℃, and heated for 70 minutes, the billet discharge temperature is 1050℃, and then pushed to a full continuous bar mill for rolling.

[0044] F, billet controlled rolling and controlled cooling: the billet of step E is rolled by 6 passes through the rough rolling mill set under the rolling condition of a speed of 0.6 m / s; then the rolled piece is rolled by 4 passes through the intermediate rolling mill set under the rolling condition of a speed of 2.5 m / s; then the rolled piece is rolled by 6 passes through the pre-precision rolling mill set under the rolling condition of a speed of 7.0 m / s; then the rolled piece enters the pre-precision rolling controlled cooling through 2 groups of water cooling devices with a length of 4 m respectively, and the cooling water amount is 100 m 3 / h, and the temperature control of the rolled piece entering the first group of precision rolling is 820℃; then the rolled piece is rolled by 2 passes through the first group of precision rolling mill set under the rolling condition of a speed of 9.0 m / s; the rolled piece enters the second group of precision rolling mill set before being controlled cooling through 2 groups of water cooling devices with a length of 7 m respectively, and the cooling water amount is 70 m 3 / h, and the temperature control of the rolled piece entering the second group of precision rolling is 840℃; then the rolled piece is rolled by 2 passes through the second group of precision rolling mill set under the rolling condition of a speed of 12 m / s; the rolled material is controlled cooling after precision rolling through 1 group of water cooling devices with a length of 10 m respectively, and the cooling water amount is 40 m 3 / h; the temperature control of the reinforcing bar on the cooling bed after controlled cooling is 930℃, and then the reinforcing bar is naturally air-cooled to room temperature on the cooling bed, thereby obtaining the large-size 650MPa high-strength and high-toughness anti-seismic reinforcing bar with a nominal diameter of 28 mm and having the following weight percentage chemical components: C 0.26wt%, Si 0.65wt%, Mn 1.52wt%, Cr 0.15wt%, Ni 0.12wt%, V 0.136wt%, S 0.017wt%, P 0.016wt%, O 0.0022wt%, N 0.0310wt%, and the rest is Fe and inevitable impurities. The process mechanical properties, microstructure, Vickers hardness difference and corrosion resistance of the reinforcing bar are shown in Tables 3 and 4.

[0045] Table 3 Process mechanical properties and corrosion resistance of the large-size 650MPa high-strength and high-toughness anti-seismic reinforcing bar with a nominal diameter of 28 mm produced in Example 1

[0046]

[0047] Table 4 Metallographic microstructure and Vickers hardness of the large-size 650MPa high-strength and high-toughness anti-seismic reinforcing bar with a nominal diameter of 28 mm produced in Example 1

[0048]

[0049] Example 2

[0050] A, molten steel smelting: according to 256 kg / t 钢The cold charge ratio is as follows: In the LD converter, scrap steel is added in the following mass ratio (chemical composition: C 0.23wt%, Si 0.42wt%, Mn 1.38wt%, P 0.028wt%, S 0.028wt%, the remainder being Fe and unavoidable impurities); at a rate of 1.3 kg / t. 钢 The following mass ratio of nickel plates (chemical composition: Ni 99.2wt%, P 0.025wt%, S 0.032wt%, the remainder being unavoidable impurities) was added to the LD converter; then, it was added at a rate of 806 kg / t. 钢 The molten iron was added to the LD converter at the following temperature and mass ratio: molten iron temperature 1320℃, molten iron composition C 4.3wt%, Si 0.27wt%, Mn 0.32wt%, P 0.090wt%, S 0.028wt%, with the remainder being Fe and unavoidable impurities; after the scrap steel and molten iron were added to the LD converter, conventional top and bottom combined blowing was carried out, with conventional lime and lightly calcined dolomite added for slag formation, the lime addition amount being 18kg / t. 钢 The amount of lightly calcined dolomite added is 17 kg / t. 钢 The final carbon content was controlled at 0.09 wt%, and the tapping temperature was 1640℃; before tapping, the ladle was filled with 12.0 kg / t of steel. 钢 The following vanadium-containing pig iron was added in the specified mass ratio: C 3.2wt%, Si 0.20wt%, Mn 1.05wt%, V 5.25wt%, P 0.60wt%, S 0.155wt%, with the remainder being Fe and unavoidable impurities. The vanadium-containing pig iron was baked for 3 minutes after being added to the ladle. Before tapping, 1.0 tonnes of quicklime were added to the bottom of the ladle for slag washing.

[0051] kg / t 钢 The tapping process adopts a full bottom-blowing nitrogen process, with the nitrogen flow rate controlled at 15-20 NL / min.

[0052] B. Deoxidation and Alloying: After tapping the molten steel from step A, when the ladle contains more than 1 / 4 tonnes of molten steel, add the following substances to the ladle in the following deoxidation and alloying sequence: silicon-calcium-barium → ferrosilicon → silicon-manganese alloy → high-carbon ferrochrome → nitrogen-rich alloy → vanadium-nitrogen alloy, at a rate of 1.5 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%, with the remainder being Fe and unavoidable impurities; at a rate of 3.8 kg / t. 钢 Add the following mass ratio of ferrosilicon: Si 73.5wt%, the remainder being Fe and unavoidable impurities; at a rate of 23.9 kg / t. 钢The following silicon-manganese alloy was added in the specified mass ratio: Mn 65.2wt%, Si 17.8wt%, C 1.5wt%, with the remainder being Fe and unavoidable impurities; according to 2.9...

[0053] kg / t 钢 Add the following high-carbon ferrochrome in the specified mass ratio: Cr 53.8wt%, C 7.2wt%, P 0.061wt%, S 0.054wt%, with the remainder being Fe and unavoidable impurities; at a concentration of 1.18 kg / t. 钢 The following silicon-nitrogen alloy was added in the specified mass ratio: Si 57.6wt%, N 39.5wt%, C 0.95wt%, P 0.045wt%, S 0.024wt%, with the remainder being Fe and unavoidable impurities; at a concentration of 0.95–1.12 kg / t. 钢 The following vanadium-nitrogen alloy was added in the specified mass ratio: V 77.4wt%, N 15.8wt%, C 3.25wt%, P 0.082wt%, S 0.062wt%, with the remainder being Fe and unavoidable impurities. The alloy was added when the ladle was 4 / 5 full. After tapping, the molten steel was hoisted to the LF furnace for refining.

[0054] C. Steel Refining in the LF Furnace: The molten steel is hoisted to the LF furnace refining station and connected to the nitrogen supply. Nitrogen is then applied at a flow rate of 25 NL / min to purge the molten steel. The lower electrode is then used at setting 7-9 for slag formation. After slag formation for 3 minutes, the electrode is raised to observe the slag formation within the furnace. If the slag sample is too thin or too dark, 5.0 kg / t of lime is added. 钢 Adjust the slag; otherwise, add 2.0 kg / t of pre-melted refining slag. 钢 Adjustments were made; subsequently, temperature was measured and samples were taken. Based on the steel sample and temperature test results, alloys were added to adjust the composition of the molten steel and the lower electrode temperature was increased to ensure that the composition and temperature were within acceptable limits. After refining, the molten steel was subjected to soft nitrogen blowing at a low flow rate for 3 minutes, with the nitrogen flow rate controlled at 15 NL / min. After nitrogen blowing, a covering agent was added to the molten steel at a controlled amount of 1.0 kg / t. 钢 Then the molten steel is hoisted to the casting station.

[0055] D. Steel casting: The tundish temperature is 1533℃, the casting speed is 3.5m / min, and the coolant flow rate in the crystallizer is 156m³ / min. 3 Under the conditions of 2.1 L / kg for secondary cooling water, the molten steel from step C is cast into steel billets with a cross section of 165 mm × 165 mm using a 5-strand small square billet casting machine with an R9m straight arc continuous straightening machine; the straightening temperature of the billet exiting the straightening machine is controlled at 970℃.

[0056] E, billet heating: the billet of step D is sent into a heating furnace with a furnace temperature of 1140℃ in the soaking section, heated for 70 minutes, and the billet is discharged at a temperature of 1060℃, and then pushed to the full continuous bar mill for rolling.

[0057] F, controlled rolling and controlled cooling of the billet: the billet of step E is rolled by the rough rolling mill group under rolling conditions with a speed of 0.5 m / s for 6 passes; then the rolled piece is rolled by the intermediate rolling mill group under rolling conditions with a speed of 2.3 m / s for 4 passes; then the rolled piece is rolled by the pre-precision rolling mill group under rolling conditions with a speed of 6.0 m / s for 6 passes; then the rolled piece enters the pre-precision rolling control cooling by 2 groups of water cooling devices with lengths of 4 m respectively, and the cooling water flow is 110 m 3 / h, and the temperature control of the rolled piece entering the first group of precision rolling is 805℃; then the rolled piece is rolled by the first group of precision rolling mill group under rolling conditions with a speed of 8.5 m / s for 1 pass; before the rolled piece enters the second group of precision rolling mill group, it is controlled by 2 groups of water cooling devices with lengths of 7 m respectively, and the cooling water flow is 75 m 3 / h, and the temperature control of the rolled piece entering the second group of precision rolling is 830℃; then the rolled piece is rolled by the second group of precision rolling mill group under rolling conditions with a speed of 10 m / s for 2 passes; after precision rolling, the rolled piece is controlled by 1 group of water cooling device with a length of 10 m for post-precision rolling control cooling, and the cooling water flow is 45 m 3 / h; after the controlled cooling, the temperature control of the rebar on the cooling bed is 915℃, and then the rebar is naturally air-cooled to room temperature on the cooling bed, thereby obtaining a nominal diameter 32 mm large-scale 650 MPa high strength and toughness anti-seismic rebar with the following weight percentage chemical composition: C 0.27wt%, Si 0.70wt%, Mn 1.55wt%, Cr 0.18wt%, Ni 0.15wt%, V 0.141wt%, S 0.028wt%, P 0.029wt%, O 0.0033wt%, N 0.0325wt%, and the rest is Fe and unavoidable impurities. The process mechanical properties, microstructure, Vickers hardness difference and corrosion resistance of the rebar are shown in Tables 5 and 6.

[0058] Table 5 Process mechanical properties and corrosion resistance of the nominal diameter 32 mm large-scale 650 MPa high strength and toughness anti-seismic rebar produced in Example 2

[0059]

[0060] Table 6 Metallographic microstructure and Vickers hardness of the nominal diameter 32 mm large-scale 650 MPa high strength and toughness anti-seismic rebar produced in Example 2

[0061]

[0062] Example 3

[0063] A, molten steel smelting: according to 260 kg / t钢 of the cold charge, the following mass ratio of scrap (chemical composition: C 0.26wt%, Si 0.60wt%, Mn 1.50wt%, P 0.042wt%, S 0.042wt%, the rest being Fe and inevitable impurities) was added in the LD converter; 1.6kg / t 钢 of the charge, the following mass ratio of nickel plate (chemical composition: Ni 99.2wt%, P 0.025wt%, S 0.032wt%, the rest being inevitable impurities) was added in the LD converter; then 810kg / t 钢 of the hot metal charge, the following hot metal with temperature and mass ratio was added in the LD converter: hot metal temperature 1325℃, hot metal composition C 4.5wt%, Si 0.30wt%, Mn 0.40wt%, P 0.100wt%, S 0.035wt%, the rest being Fe and inevitable impurities; after the scrap and hot metal were mixed in the LD converter, the conventional combined blowing was carried out, the conventional lime and light-burned dolomite were added, the lime addition amount was 20kg / t 钢 , the light-burned dolomite addition amount was 18kg / t 钢 , the end-point carbon content was controlled to be 0.10wt%, and the tapping temperature was 1650℃; before tapping, the following mass ratio of vanadium-containing pig iron was added in the ladle in an amount of 12.0kg / t 钢 : composition C 3.2wt%, Si 0.20wt%, Mn 1.05wt%, V 5.25wt%, P 0.60wt%, S 0.155wt%, the rest being Fe and inevitable impurities, and the vanadium-containing pig iron was baked for 3 minutes after being added in the ladle; before tapping, the active lime was added to the bottom of the ladle for slag washing, and the lime addition amount was 1.0

[0064] kg / t 钢 ; the whole-process bottom blowing nitrogen process was adopted during tapping, and the nitrogen flow rate was controlled to be 20NL / min.

[0065] B, deoxidation and alloying: the molten steel of the A step was tapped, and when the amount of the molten steel in the ladle was greater than 1 / 4, the following deoxidation and alloying sequence was carried out: silicon-calcium-barium→ silicon-iron→ silicon-manganese alloy→ high-carbon chromium iron→ nitrogen-rich alloy→ vanadium-nitrogen alloy, and the following substances were sequentially added in the ladle: 1.5kg / t 钢 of the amount, the following mass ratio of silicon-calcium-barium was added: Si 52.5wt%, Ca 9.85wt%, Ba 12.15wt%, Al 2.45wt%, the rest being Fe and inevitable impurities; 4.5kg / t 钢 of the amount, the following mass ratio of silicon-iron was added: Si 73.5wt%, the rest being Fe and inevitable impurities; 24.5kg / t 钢The following mass ratio of silicon-manganese alloy was added: Mn 65.2wt%, Si 17.8wt%, C 1.5wt%, with the remainder being Fe and unavoidable impurities; according to 3.2

[0066] kg / t 钢 Add the following high-carbon ferrochrome in the specified mass ratio: Cr 53.8wt%, C 7.2wt%, P 0.061wt%, S 0.054wt%, with the remainder being Fe and unavoidable impurities; at a concentration of 1.23 kg / t. 钢 The following silicon-nitrogen alloy was added in the specified mass ratio: Si 57.6 wt%, N 39.5 wt%, C 0.95 wt%, P 0.045 wt%, S 0.024 wt%, with the remainder being Fe and unavoidable impurities; according to 1.12...

[0067] kg / t 钢 The following vanadium-nitrogen alloy was added in the specified mass ratio: V 77.4wt%, N 15.8wt%, C 3.25wt%, P 0.082wt%, S 0.062wt%, with the remainder being Fe and unavoidable impurities. The alloy was added when the ladle was 4 / 5 full. After tapping, the molten steel was hoisted to the LF furnace for refining.

[0068] C. Steel Refining in the LF Furnace: The molten steel is hoisted to the LF furnace refining station and connected to the nitrogen supply. Nitrogen is then applied at a flow rate of 25 NL / min to purge the molten steel. The lower electrode is then used at setting 7-9 for slag formation. After slag formation for 3 minutes, the electrode is raised to observe the slag formation within the furnace. If the slag sample is too thin or too dark, 5.0 kg / t of lime is added. 钢 Adjust the slag; otherwise, add 2.0 kg / t of pre-melted refining slag. 钢 Adjustments were made; subsequently, temperature was measured and samples were taken. Based on the steel sample and temperature test results, alloys were added to adjust the composition of the molten steel and the lower electrode temperature was increased to ensure that the composition and temperature were within acceptable limits. After refining, the molten steel was subjected to soft nitrogen blowing at a low flow rate for 3 minutes, with the nitrogen flow rate controlled at 15 NL / min. After nitrogen blowing, a covering agent was added to the molten steel at a controlled amount of 1.0 kg / t. 钢 Then the molten steel is hoisted to the casting station.

[0069] D. Steel casting: The tundish temperature is 1525℃, the casting speed is 3.5m / min, and the coolant flow rate in the crystallizer is 160m³ / min. 3 Under the conditions of 2.1 L / kg for secondary cooling water, the molten steel from step C is cast into billets with a cross section of 165 mm × 165 mm using a 5-strand small square billet casting machine with an R9m straight arc continuous straightening machine; the straightening temperature of the billet exiting the straightening machine is controlled at 980℃.

[0070] E, billet heating: the billet of step D is sent into a heating furnace with a soaking section furnace temperature of 1160℃, and heated for 70 minutes, and the billet is discharged at a temperature of 1070℃, and then pushed to a full continuous bar mill for rolling.

[0071] F, controlled rolling and controlled cooling of the billet: the billet of step E is rolled by a rough rolling mill group under rolling conditions of a speed of 0.4 m / s for 6 passes; then the rolled piece is rolled by a medium rolling mill group under rolling conditions of a speed of 2.0 m / s for 4 passes; then the rolled piece is rolled by a pre-precision rolling mill group under rolling conditions of a speed of 5.0 m / s for 6 passes; then the rolled piece enters a pre-precision rolling control cooling through 2 groups of water cooling devices with lengths of 4 m respectively, and the cooling water flow is 120 m 3 / h, and the temperature control of the rolled piece entering the first group of precision rolling is 790℃; then the rolled piece is rolled by the first group of precision rolling mill group under rolling conditions of a speed of 8.0 m / s for 1 pass; the rolled piece enters the second group of precision rolling mill group through 2 groups of water cooling devices with lengths of 7 m respectively for control cooling, and the cooling water flow is 80 m 3 / h, and the temperature control of the rolled piece entering the second group of precision rolling is 820℃; then the rolled piece is rolled by the second group of precision rolling mill group under rolling conditions of a speed of 10 m / s for 2 passes; the rolled piece is cooled by 1 group of water cooling devices with a length of 10 m after precision rolling for control cooling, and the cooling water flow is 50 m 3 / h; the temperature control of the rebar on the cooling bed after control cooling is 900℃, and then the rebar is naturally air-cooled to room temperature on the cooling bed, thereby obtaining a nominal diameter 40 mm large-scale 650 MPa high-strength and tough anti-seismic rebar with the following weight percentage chemical composition: C 0.29wt%, Si 0.75wt%, Mn 1.60wt%, Cr 0.20wt%, Ni 0.18wt%, V 0.150wt%, S 0.035wt%, P 0.035wt%, O 0.0040wt%, N 0.0340wt%, and the rest is Fe and unavoidable impurities. The process mechanical properties, microstructure, Vickers hardness difference, and corrosion resistance of the rebar are shown in Tables 7 and 8.

[0072] Table 7 Process mechanical properties and corrosion resistance of the nominal diameter 40 mm large-scale 650 MPa high-strength and tough anti-seismic rebar produced in Example 3

[0073]

[0074] Table 8 Metallographic microstructure and Vickers hardness of the nominal diameter 40 mm large-scale 650 MPa high-strength and tough anti-seismic rebar produced in Example 3

[0075] .

Claims

1. A large-size 650 MPa high-strength and tough corrosion-resistant anti-seismic reinforcing bar with a nominal diameter of 28-40 mm, characterized in that, The anti-seismic steel has the following weight percentage chemical components: C 0.26-0.29wt%, Si 0.65-0.75wt%, Mn 1.52-1.60wt%, Cr 0.15-0.20wt%, Ni 0.12-0.18wt%, V 0.136-0.150wt%, S≤0.035wt%, P≤0.035wt%, O≤0.0040wt%, N 0.0310-0.0340wt%, and the rest is Fe and inevitable impurities; The high-strength and high-toughness corrosion-resistant anti-seismic steel is realized by the following steps: A, molten steel smelting: according to 250-260 kg / t 钢 , 1.0-1.6 kg / t 钢 The cold material is loaded into the ratio, and the scrap steel and nickel plate are added into the LD converter; then according to 800-810 kg / t 钢 The molten iron with a temperature of ≥1310℃ is added into the LD converter, the conventional top and bottom combined blowing is carried out, the lime and light-burned dolomite are added in an amount of 15-20 kg / t 钢 , 15-18 kg / t 钢 The end point carbon content is controlled to be ≥0.08wt%, and the tapping temperature is ≤1650℃; the composition of the molten iron is: C 4.1-4.5wt%, Si 0.15-0.30wt%, Mn 0.25-0.40wt%, P 0.080-0.100wt%, S≤0.035wt%, and the rest is Fe and inevitable impurities; Before tapping, the ladle should be charged at 12.0 kg / t. 钢 Add the following vanadium-containing pig iron in the specified mass ratio: C 3.2wt%, Si 0.20wt%, Mn 1.05wt%, V 5.25wt%, P 0.60wt%, S 0.155wt%, with the remainder being Fe and unavoidable impurities; before tapping, add 1.0 kg / t 钢 Add active lime to the bottom of the ladle for slag washing; the vanadium-containing pig iron is added to the ladle and then baked for 3 minutes; B, deoxidation alloying: the molten steel is tapped after smelting, when the amount of molten steel in the ladle is greater than 1 / 4, silicon calcium barium→ silicon iron→ silicon manganese alloy→ high carbon chromium iron→ rich nitrogen alloy→ vanadium nitrogen alloy is added into the ladle in the order of deoxidation alloying, respectively 1.5kg / t 钢 , 3.3-4.5kg / t 钢 , 23.2-24.5kg / t 钢 , 2.3-3.2kg / t 钢 , 1.10-1.23kg / t 钢 , 0.95-1.12kg / t 钢 The amount of silicon calcium barium, silicon iron, silicon manganese alloy, high carbon chromium iron, silicon nitrogen alloy and high vanadium nitrogen alloy is added into the ladle in turn, and the above alloy is added when the amount of molten steel in the ladle reaches 4 / 5. C. LF furnace refining of the molten steel: the molten steel of step B is hoisted to the LF furnace for refining, after the refining is completed, the molten steel is subjected to soft nitrogen blowing at a small flow rate of 10-15 NL / min for 3 min, after the nitrogen blowing is completed, the molten steel is hoisted to the casting station after adding a molten steel covering agent; D. Casting of molten steel: The molten steel was cast into a billet having a cross section of 165 mm x 165 mm under conditions that the temperature of the molten steel was 1525 to 1540 °C, the casting speed was 3.4 to 3.5 m / min, the flow rate of the crystallizer cooling water was 150 to 160 m 3 / h, the specific secondary cooling water amount was 2.0 to 2.1 L / kg. E. billet heating: the billet of step D is sent to a heating furnace with a furnace temperature of 1110-1160℃ for heating for 70 min, the billet out-of-furnace temperature is 1050-1070℃, and then it is pushed to a full continuous bar mill for rolling; F, billet controlled rolling and controlled cooling: the billet of step E is rolled by 6 passes through a rough rolling mill group at a rolling speed of 0.4-0.6 m / s, then rolled by 4 passes through a medium rolling mill group at a rolling speed of 2.0-2.5 m / s, and then rolled by 6 passes through a pre-precision rolling mill group at a rolling speed of 5.0-7.0 m / s; before entering the precision rolling, the rolling piece is cooled by 2 groups of water cooling devices with a length of 4 m for pre-precision rolling control cooling, the cooling water amount is 100-120 m 3 / h, the temperature of the rolling piece entering the first group of precision rolling is controlled to be 790-820 ℃; the rolling piece is rolled by 1-2 passes through the first group of precision rolling mill group at a rolling speed of 8.0-9.0 m / s; before entering the second group of precision rolling mill group, the rolling piece is cooled by 2 groups of water cooling devices with a length of 7 m for control cooling, the cooling water amount is 70-80 m 3 / h, the temperature of the rolling piece entering the second group of precision rolling is controlled to be 820-840 ℃; then the rolling piece is rolled by 2 passes through the second group of precision rolling mill group at a rolling speed of 10-12 m / s; after the precision rolling, the rolling piece is cooled by 1 group of water cooling device with a length of 10 m for post-precision rolling control cooling, the cooling water amount is 40-50 m 3 / h; after the control cooling, the temperature of the reinforcing bar on the cooling bed is controlled to be 900-930 ℃, then the reinforcing bar is naturally air-cooled to room temperature on the cooling bed, and a large-size 650 MPa high-strength and high-toughness anti-seismic reinforcing bar with a nominal diameter of 28-40 mm is obtained.

2. The public designation diameter 28-40 mm large size 650 MPa high strength and toughness corrosion resistant anti-seismic reinforcing bar according to claim 1, characterized in that, The anti-seismic steel has a yield strength of 670-700 MPa, a tensile strength of 860-910 MPa, a strength-to-yield ratio of ≥1.28, an elongation after fracture of ≥18%, and a maximum force total elongation of ≥10.5%.

3. The high-strength high-ductility earthquake resistant reinforcement bar of nominal diameter 28-40 mm according to claim 1, characterized in that, In step A, the chemical components of the scrap steel are: C 0.20-0.26wt%, Si 0.25-0.60wt%, Mn 1.25-1.50wt%, P 0.018-0.042wt%, S 0.015-0.042wt%, and the rest is Fe and inevitable impurities; the chemical components of the nickel plate are: Ni 99.2wt%, P 0.025wt%, S 0.032wt%, and the rest is inevitable impurities.

4. The high-strength high-ductility earthquake resistant reinforcement bar of nominal diameter 28-40 mm according to claim 1, characterized in that, In step A, the whole-process bottom nitrogen blowing process is adopted during the molten steel tapping process, and the nitrogen flow rate is controlled to be 15-20 NL / min.

5. The high-strength high-ductility earthquake resistant reinforcement bar of nominal diameter 28-40 mm according to claim 1, characterized in that, In step B, the chemical composition of the silico-calcio-barium is: Si 52.5wt%, Ca 9.85wt%, Ba 12.15wt%, Al 2.45wt%, and the rest is Fe and inevitable impurities; the chemical composition of the ferro-silicon is: Si 73.5wt%, and the rest is Fe and inevitable impurities; the chemical composition of the ferro-silicon-manganese alloy is: Mn 65.2wt%, Si 17.8wt%, C 1.5wt%, and the rest is Fe and inevitable impurities; the chemical composition of the high-carbon ferro-chromium is: Cr 53.8wt%, C 7.2wt%, P 0.061wt%, S 0.054wt%, and the rest is Fe and inevitable impurities; the chemical composition of the ferro-silicon-nitrogen alloy is: Si 57.6wt%, N 39.5wt%, C 0.95wt%, P 0.045wt%, S 0.024wt%, and the rest is Fe and inevitable impurities; the chemical composition of the ferro-vanadium-nitrogen alloy is: V 77.4wt%, N 15.8wt%, C 3.25wt%, P 0.082wt%, S 0.062wt%, and the rest is Fe and inevitable impurities.

6. The high-strength high-ductility earthquake resistant reinforcement bar of nominal diameter 28-40 mm according to claim 1, characterized in that, In Step C, during the refining process, nitrogen is blown into the molten steel at a flow rate of 20-25 NL / min, and then the electrode is lowered at a gear of 7-9 to slag; after 3 minutes of power-on slagging, the electrode is lifted to observe the slag in the furnace; if the slag sample is too thin and the color is too black, 4-5 kg / t of lime is added 钢 Slagging, otherwise 1.0-2.0 kg / t of pre-melted refining slag is added 钢 Adjustment; then temperature measurement and sampling, according to the steel sample and temperature test results, add alloy to adjust the composition of the molten steel and lower the electrode to increase the temperature, to ensure that the composition and temperature are qualified.

7. The high-strength high-ductility earthquake resistant reinforcement bar of nominal diameter 28-40 mm according to claim 1, characterized in that, In step D, the R9m straight arc continuous straightening 5-machine 5-flow billet casting machine is used.

8. The high-strength high-ductility earthquake resistant reinforcement bar of nominal diameter 28-40 mm according to claim 1, characterized in that, In step D, the temperature of the straightening of the billet out of the straightening machine is controlled at 960-980℃.

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