A 640mpa grade high-strength hot-rolled anti-seismic reinforcing bar and a production method thereof

Abstract

The application discloses a 640MPa-grade high-strength hot-rolled anti-seismic reinforcing steel bar and a production method thereof. The 640MPa-grade high-strength hot-rolled anti-seismic reinforcing steel bar is prepared by adopting a niobium-vanadium-nitrogen micro-alloying and controlled rolling and controlled cooling technology process, through scientific component design and precise control of process parameters of each process of the 640MPa-grade high-strength hot-rolled anti-seismic reinforcing steel bar, full-process precipitation of carbonitride of niobium-vanadium-nitrogen micro-alloying elements is realized, the problems of slab cracks, non-obvious yield platform, low strength-yield ratio and low maximum force total elongation are effectively solved, and the strength-yield ratio and the maximum force total elongation of the 640MPa-grade high-strength hot-rolled anti-seismic reinforcing steel bar are effectively improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of metallurgy, in particular to a 640MPa high-strength hot-rolled anti-seismic steel bar and a production method thereof. BACKGROUND

[0002] Hot-rolled ribbed steel bars are the most widely used steel material, and are developing towards high strength and multi-function. At present, 500MPa steel bars are basically used in the European Union and other countries, and the development of 600MPa or even higher grade steel bars is being carried out. It is very necessary to study higher grade hot-rolled anti-seismic steel bars.

[0003] Anti-seismic steel bars increase the strength-flexibility ratio, the flexibility-flexibility ratio and the maximum force total elongation rate on the basis of ordinary steel bars. The Chinese steel bar standard stipulates that the strength-flexibility ratio of anti-seismic steel bars is greater than or equal to 1.25, the flexibility-flexibility ratio is less than or equal to 1.30, and the maximum force total elongation rate is greater than or equal to 9%. At present, the strength-flexibility ratio performance of 500MPa grade screw steel bars produced by many enterprises under the existing strengthening means is difficult to meet the requirements. With the increase of the strength grade of steel bars, it is more and more difficult to improve the strength-flexibility ratio and the maximum force total elongation rate of 640MPa high-strength hot-rolled anti-seismic steel bars.

[0004] In view of the above problems, it is necessary to provide a 640MPa high-strength hot-rolled anti-seismic steel bar and a production method thereof. SUMMARY

[0005] The purpose of the present application is to overcome the defects of the prior art and provide a 640MPa high-strength hot-rolled anti-seismic steel bar and a production method thereof.

[0006] The technical problem of the present application is solved by adopting the following technical scheme.

[0007] The present application provides a 640MPa high-strength hot-rolled anti-seismic steel bar, the chemical composition and weight percentage of which are as follows: C: 0.24-0.28 Wt%, Si: 0.65-0.80 Wt%, Mn: 1.45-1.60 Wt%, Nb: 0.016-0.023 Wt%, V: 0.15-0.19 Wt%, N: 0.011-0.019 Wt%, O: ≤0.002 Wt%, P: ≤0.035 Wt%, S: ≤0.030 Wt%, [V] / [N]≥8, [V]+[Nb]≥0.17 Wt%, and the balance is Fe and unavoidable impurities.

[0008] The present application also provides a production method of a 640MPa high-strength hot-rolled anti-seismic steel bar, which adopts the following process route: converter tapping→ladle argon blowing→LF refining→continuous casting→heating→rough and medium rolling→pre-precision rolling→pre-precision rolling temperature control cooling→precision rolling→post-precision rolling temperature control cooling→upper cooling bed→collection and storage, wherein:

[0009] The temperature control cooling before finish rolling comprises: the temperature control device used is a water-through device with two sections, each 6 meters long, the water quantity of the first section of the water-through device is controlled to be 80-120 m 3 / h, the pressure is 1.8-2.2 MPa, the water quantity of the second section of the water-through device is controlled to be 40-90 m 3 / h, the pressure is 1.8-2.2 MPa, the rolling speed of the blank is 4-10 m / s, the rolling time is 38-45 s, and the cooling rate is 6-10 ℃ / s, so that the temperature of the blank entering the finish rolling is 960-1000 ℃.

[0010] The application has the following beneficial effects:

[0011] The application provides a 640MPa-grade high-strength hot-rolled anti-seismic steel bar and a production method thereof, and the 640MPa-grade high-strength hot-rolled anti-seismic steel bar is produced through scientific chemical component design, Nb-V-N micro-alloying and controlled rolling and controlled cooling technology, so that the carbonitride of the Nb-V-N micro-alloying element is precipitated in the whole process, the problems of blank crack, non-obvious yield platform, low strength-yield ratio and low maximum force total elongation are effectively solved, and the strength-yield ratio and the maximum force total elongation of the 640MPa-grade high-strength hot-rolled anti-seismic steel bar are improved. BRIEF DESCRIPTION OF DRAWINGS

[0012] In order to more clearly illustrate the technical solutions of the embodiments of the application, the following will briefly introduce the drawings needed to be used in the embodiments, and it should be understood that the following drawings only show some embodiments of the application, and therefore should not be regarded as a limitation to the scope, and for those skilled in the art, other related drawings can also be obtained without creative labor on the basis of the drawings.

[0013] Figure 1 The macroscopic metallographic graph of the 640MPa-grade high-strength hot-rolled anti-seismic steel bar produced by the embodiment of the application;

[0014] Figure 2 The microscopic metallographic graph of the 640MPa-grade high-strength hot-rolled anti-seismic steel bar produced by the embodiment of the application;

[0015] Figure 3 The microscopic scanning electron microscope graph of the 640MPa-grade high-strength hot-rolled anti-seismic steel bar produced by the embodiment 3 of the application (the interlamellar spacing size in the graph is 5 interlamellar spacings). DETAILED DESCRIPTION

[0016] In order to make the purpose, technical solutions and advantages of the embodiments of the application more clear, the technical solutions in the embodiments of the application will be clearly and completely described in the following. The specific conditions not noted in the embodiments are carried out according to the conventional conditions or the conditions suggested by the manufacturers. The reagents or instruments not noted by the manufacturers are all conventional products that can be obtained by market purchase.

[0017] The following is a specific description of a 640MPa high-strength hot-rolled anti-seismic steel bar and a production method thereof provided by the embodiment of the application.

[0018] The 640MPa high-strength hot-rolled anti-seismic steel bar provided by the embodiment of the application has the following chemical components and weight percentage: C: 0.24-0.28 Wt%, Si: 0.65-0.80 Wt%, Mn: 1.45-1.60 Wt%, Nb: 0.016-0.023 Wt%, V: 0.15-0.19 Wt%, N: 0.011-0.019 Wt%, O: ≤0.002 Wt%, P: ≤0.035 Wt%, S: ≤0.030 Wt%, [V] / [N]≥8, [V]+[Nb]≥0.17 Wt%, and the balance of Fe and inevitable impurities.

[0019] In the above-mentioned 640MPa high-strength hot-rolled anti-seismic steel bar composition, vanadium has strong precipitation strengthening effect but weak fine-grain strengthening effect, but vanadium and nitrogen combine to form vanadium carbon and nitride compounds, the dissolution and precipitation temperature of which is higher than that of vanadium carbide, and the vanadium carbon and nitride compounds in the steel are induced to precipitate during rolling, which prevents the growth of austenite grains and prevents or delays the occurrence of austenite recrystallization, thereby refining the austenite and the ferrite grains. The effect of niobium on inhibiting the growth of austenite grains and the recrystallization of deformed austenite is stronger than that of vanadium. The niobium-vanadium-nitrogen composite strengthening can avoid the defects of excessive niobium content causing the cracking of the casting blank and the excessive bainite affecting the plasticity, and can also avoid the low strength-yield ratio caused by vanadium-nitrogen strengthening, thereby fully utilizing the niobium strengthening to improve the strength-yield ratio of the steel bar, and combining the niobium-vanadium-nitrogen precipitation strengthening and fine-grain strengthening mechanism with the controlled rolling and controlled cooling process to improve the performance indicators of the steel bar.

[0020] Specifically, the roles of the components are as follows:

[0021] C: The carbon content is 0.24-0.28 Wt%, and the carbon can dissolve in the matrix to have a solid solution strengthening effect, and can also form more pearlite in the steel to improve the strength of the steel, and the higher the carbon content, the higher the strength of the steel bar. To reduce the production cost, the C is controlled as high as possible within the standard upper limit.

[0022] Si: The silicon content is 0.65-0.80 Wt%, and the silicon can dissolve in the ferrite and austenite to mainly improve the strength of the steel bar in the form of solid solution strengthening, and the silicon is also a cheap element and a basic element for ensuring the strength of the steel bar, and the higher the silicon content, the higher the strength of the steel bar. To reduce the production cost, the Si is controlled as high as possible within the standard upper limit.

[0023] Mn: Manganese content 1.45-1.60wt%, manganese is the basic element to ensure the strength of steel bar, is one of the main alloying elements of screw steel, and is a weak deoxidizer. The appropriate amount of manganese can significantly improve the cold brittleness of steel and increase its yield strength and tensile strength. At the same time, it does not reduce the plasticity and impact toughness too much. Manganese can reduce the austenite transformation temperature, refine ferrite grains and reduce pearlite interlamellar spacing, which is beneficial to improve the strength and toughness of steel bar. At the same time, it can also solid solution strengthen ferrite. With the increase of Mn content, the strength of steel also increases. In order to reduce the production cost, Mn is controlled at the upper limit of the standard as much as possible.

[0024] Nb: Niobium content 0.016-0.023wt%, niobium cannot be dissolved in austenite. During billet heating and rolling, niobium forms niobium carbonitride with carbon and nitrogen, which is segregated at the austenite grain boundary, effectively inhibits austenite recrystallization, and as a second phase particle prevents austenite grain growth, thereby improving the strength and toughness of steel bar. However, niobium content greater than 0.025% will exacerbate the crack tendency of the casting billet, and the amount of bainite transformation will increase during subsequent controlled rolling and controlled cooling, resulting in no obvious yield platform of steel bar during tension, affecting the plasticity of steel bar. Therefore, the niobium content is controlled at 0.016-0.023wt%.

[0025] V: Vanadium content 0.15-0.19wt%, vanadium nitride and carbide almost completely dissolve in austenite, and vanadium compounds are precipitated during or after the transformation of γ~α, which produces precipitation strengthening. Studies have shown that if 0.01% of vanadium in screw steel is in the form of vanadium nitride particles, it can increase the yield strength of screw steel by more than 25MPa, while if the 0.01% of vanadium in screw steel exists in the form of vanadium carbide or solid solution vanadium, it can only increase the yield strength of screw steel by about 10MPa.

[0026] N: Nitrogen content 0.011-0.019wt%. Studies have shown that: if [V] / [N]>3.64, nitrogen element is completely precipitated in the form of vanadium nitride particles, and the fine-grain strengthening and precipitation strengthening of vanadium nitride are fully utilized to improve the strength of steel bar. However, after hot rolling, the free C and N elements gather at dislocations to form "Cottrell atmosphere", which pins the dislocations, blocks the movement of dislocations, and improves the strength of steel bar, but reduces the toughness and plasticity, resulting in a decrease in elongation. After natural aging, V element combines with N element, reducing the free N element in the matrix and dislocation, which reduces the yield strength, changes the tensile strength little, and improves the strength-to-yield ratio. At the same time, the combination of N element and V element reduces the brittleness of steel bar and improves the elongation. Therefore, too high nitrogen content can easily lead to a decrease in elongation after natural aging. In order to improve the first hit rate of steel bar, the nitrogen content should not exceed 0.020%.

[0027] Meanwhile, the application also provides a production method of the 640MPa high-strength hot-rolled anti-seismic reinforcing steel bar.

[0028] The following process route is adopted: top and bottom combined blowing converter smelting-out, ladle argon blowing, LF furnace refining, 6-machine 6-flow 160mm*160mm square billet continuous casting, step-by-step heating furnace heating, rough rolling, medium rolling, pre-precision rolling, temperature control cooling before precision rolling, precision rolling, post-rolling temperature control cooling, upper cooling bed, and collection and storage.

[0029] Converter smelting, ladle argon blowing, and continuous casting include:

[0030] The conventional top and bottom combined blowing oxygen converter is adopted for smelting, and argon blowing is performed throughout the steel tapping process. When more than 1 / 4 of the steel is tapped, silicon manganese, manganese iron, silicon iron, carbon powder, and lime are sequentially added for deoxidization and alloying and slag washing treatment. The temperature of the molten steel is measured and the sample is taken after the molten steel reaches the argon blowing station, and meanwhile, high-flow argon blowing is performed to make the composition and temperature uniform, and the argon blowing time is ensured to be greater than or equal to 5 minutes. After the molten steel enters the LF station, vanadium-nitrogen alloy is added according to the nitrogen lower limit + 30ppm, the vanadium-iron alloy addition amount is calculated according to the vanadium lower limit - 0.002%, and the vanadium-iron alloy is added. According to the slag washing condition, lime and fluorite are added to heat and slag, to ensure good slag flowability, the temperature control heating time is controlled according to the argon station temperature, to ensure that the temperature reaches 1550℃, and then the sample is analyzed, the alloy silicon manganese, silicon iron, niobium iron, carbon powder, vanadium-nitrogen alloy, and vanadium-iron are added again according to the analysis results to make fine adjustment, and then the temperature is continuously increased to the expected target. After the composition is determined to meet the standard by sampling, the seamless calcium wire is fed, and then soft argon blowing is started. The soft blowing process keeps the slag surface peristalsis time greater than or equal to 8 minutes, to ensure uniform composition and sufficient floating of inclusions. The specific water consumption of the continuous casting machine is 1.4-1.7L / t, and the casting speed is 2.6-2.9m / min. Low casting speed is adopted to ensure that no cracks are generated in the continuous casting process and the surface quality of the cast billet is ensured.

[0031] The rolling process includes:

[0032] (1) The 640MPa high-strength hot-rolled anti-seismic reinforcing steel bar covers specifications Φ20-32mm, Φ20-22mm two-cut rolling, and Φ25-32mm single-line rolling.

[0033] (2) Billet heating: first heating temperature: 1000-1100℃, second heating temperature: 1100-1200℃, soaking temperature: 1130-1180℃, and total heating time: 60-90min.

[0034] (3) After the billet leaves the heating furnace, it is subjected to multi-pass rough rolling and intermediate rolling, at which time the temperature of the intermediate billet rises, so temperature control cooling must be performed. The temperature control device is two water sprays, each 6 meters long. The first water spray has a water flow of 80-120 m3 / h and a pressure of 1.8-2.2 MPa, and the second water spray has a water flow of 40-90 m3 / h and a pressure of 1.8-2.2 MPa. The billet rolling speed is 4-10 m / s, and the rolling time is 38-45 s, which ensures a cooling rate of 6-10°C / s, thereby ensuring that the entry temperature into the finishing rolling is 960-1000°C. If the cooling rate is less than 6°C / s, the entry temperature into the finishing rolling will be greater than 1000°C, which will cause the austenite grains to be coarse and the yield strength of the reinforcing bar to decrease. In order to ensure the subsequent temperature on the cooling bed, the cooling rate before the cooling bed must be increased, which will result in a macroscopic metallographic structure having a chilled layer or an increased amount of bainite, and the metallographic structure of the reinforcing bar will be unqualified or will not have a clear yield platform, and the yield strength or plasticity will decrease. If the cooling rate is greater than 10°C / s, the entry temperature into the finishing rolling will be less than 960°C, which will cause the austenite grains to be too fine, and the yield strength and tensile strength of the reinforcing bar will increase, and the strength-yield ratio will be unqualified. In order to ensure the subsequent temperature on the cooling bed, the cooling rate before the cooling bed must be decreased, which will decrease the yield strength of the reinforcing bar.

[0035] (4) After the intermediate billet is subjected to multi-pass finishing rolling, the temperature continues to rise, and the finished product is subjected to temperature control cooling before the cooling bed. The temperature control device is six water sprays, each 1.3 meters long. By opening the first, third and sixth water sprays, the first water spray has a water flow of 110-130 m3 / h and a pressure of 1.8-2.5 MPa, the third water spray has a water flow of 110-120 m3 / h and a pressure of 1.8-2.5 MPa, and the sixth water spray has a water flow of 40-80 m3 / h and a pressure of 1.8-2.5 MPa. The billet rolling speed is 5-15 m / s, and the rolling time is 45-50 s, which ensures a cooling rate of 3-7°C / s, and the cooling bed temperature is 900-950°C. The water sprays must be opened at intervals to ensure that the reinforcing bar has a cooling-reheating process. If the water sprays are opened continuously, the instantaneous cooling rate will be too fast, the macroscopic metallographic structure of the reinforcing bar will easily have a closed chilled layer, the yield strength will be high, and the proportion of unqualified strength-yield ratios will increase. If the cooling rate is less than 3°C / s, the cooling bed temperature will be greater than 950°C, the cooling bed temperature is high, the grains of the reinforcing bar are coarse, the pearlite content decreases, and the yield strength decreases. If the cooling rate is greater than 7°C / s, the cooling bed temperature will be less than 900°C, which will cause the cooling rate to be too large, the macroscopic metallographic structure of the reinforcing bar to have a closed chilled layer, and the metallographic structure to be unqualified. The cooling rate is too large, the grains are too fine, the pearlite content increases, the yield strength and tensile strength of the reinforcing bar increase, and the strength-yield ratio is unqualified.

[0036] (5) After the cooling bed, the reinforcing bar is cooled on the cooling bed at a cooling rate of 1-2°C / s, and the cooling bed is stopped for 420-500 s, after which the reinforcing bar is cut to size and baled.

[0037] Based on the above niobium vanadium nitrogen micro-alloying and controlled rolling and controlled cooling technology process, the 640MPa grade high-strength hot-rolled anti-seismic steel bar of Φ20~32mm specification is realized m ≥835MPa, yield strength R eL ≥660MPa, maximum total elongation A gt ≥10.5%, R 0 eL / R eL ≤1.10, R 0 m / R 0 eL ≥1.26, grain size 9.5~10.0 grade, matrix structure ferrite+pearlite content is greater than 94%, ferrite content 50~58%, pearlite content 37~48%, pearlite interlamellar spacing 90~250nm, bainite and martensite island content is less than 6%, macroscopic metallographic without chilling layer. In the 640MPa grade high-strength hot-rolled anti-seismic steel bar, the higher proportion of pearlite and bainite can ensure the yield strength and tensile strength of the steel bar, but the bainite content should be controlled within 6% to avoid too high strength, low strength yield ratio or no yield platform, thereby affecting the plasticity, and the certain ferrite can ensure the plasticity of the steel bar and ensure the maximum total elongation qualified.

[0038] As can be seen, the embodiment of the present application provides a 640MPa grade high-strength hot-rolled anti-seismic steel bar and a production method thereof, the independently developed niobium vanadium nitrogen micro-alloying and controlled rolling and controlled cooling technology process can ensure that the strength yield ratio and the maximum total elongation meet the anti-seismic steel bar index requirements. Specifically:

[0039] (1) The embodiment of the present application adopts the niobium vanadium nitrogen micro-alloying and controlled rolling and controlled cooling technology process, realizes the full-process precipitation of carbonitride of niobium vanadium nitrogen micro-alloying elements by precisely controlling the process parameters of the 640MPa grade high-strength hot-rolled anti-seismic steel bar of Φ20~Φ32mm specification, and effectively solves the problems of casting crack, non-obvious yield platform, low strength yield ratio and low maximum total elongation. The 640MPa grade high-strength hot-rolled anti-seismic steel bar of Φ20~32mm specification realizes m ≥835MPa, yield strength R eL ≥660MPa, maximum total elongation A gt ≥10.5%, R 0 eL / R eL ≤1.10, R 0 m / R 0 eL≥1.26, grain size 9.5-10.0, matrix structure is ferrite + pearlite content greater than 94%, ferrite content 50-58%, pearlite content 37-48%, pearlite interlamellar spacing 90-250nm, bainite and martensite island content less than 6%, no chill layer in macroscopic metallography.

[0040] (2) By adding vanadium-nitrogen alloy, silicon nitride manganese to increase nitrogen, the nitrogen content in the steel is stable, the generated vanadium nitride is precipitated due to deformation induction in the rolling process, and is precipitated during the controlled cooling process after the cooling bed, which can produce precipitation strengthening and fine-grain strengthening to improve the strength and toughness of the steel bar. By adding an appropriate amount of niobium, not only can the grain growth be inhibited during heating, but also the steel strength can be improved.

[0041] The features and properties of the present application are further described in detail below in combination with examples.

[0042] Example 1

[0043] A 640MPa high-strength hot-rolled anti-seismic steel bar, the chemical composition and weight percentage are as follows: C: 0.25Wt%, Si: 0.65Wt%, Mn: 1.51Wt%, Nb: 0.016Wt%, V: 0.16Wt%, N: 0.016Wt%, O: 0.0018Wt%, P: 0.021Wt%, S: 0.009Wt%, [V] / [N]=10, [V]+[Nb]=0.176Wt%, the balance being Fe and unavoidable impurities.

[0044] The production method of the above-mentioned 640MPa high-strength hot-rolled anti-seismic steel bar, comprising the following steps:

[0045] The converter smelting, argon blowing, continuous casting includes:

[0046] The steel is smelted by the conventional top and bottom combined blowing oxygen converter, argon is blown during the whole tapping process, silicon-manganese, ferromanganese, ferrosilicon, carbon powder and lime are sequentially added when more than 1 / 4 of the molten steel is tapped for deoxidation, alloying and slag washing treatment, the temperature and sample are measured after the molten steel reaches the argon blowing station, meanwhile, high flow argon blowing is performed to make the composition and temperature uniform, and the argon blowing time is ensured to be greater than or equal to 5 min. Vanadium-nitrogen alloy and ferrovanadium are pre-added after the molten steel enters the LF station for preliminary addition, nitrogen is taken as the control point, vanadium-nitrogen alloy is added according to the nitrogen lower limit + 30 ppm, the amount of vanadium alloy is calculated according to the addition amount, and the addition amount of ferrovanadium is calculated according to the composition lower limit - 0.002%. According to the slag washing condition, lime and fluorite are added for temperature rising and slag melting, the slag fluidity is ensured to be good, the temperature rising time is controlled according to the argon station temperature, the temperature is ensured to reach 1550℃, then the sample is analyzed, the alloy silicon-manganese, ferrosilicon, ferro-niobium, carbon powder, vanadium-nitrogen alloy and ferrovanadium are added again for fine adjustment according to the analysis results, then the temperature is continuously raised to the expected target, the composition is determined to meet the standard after sampling, then the seamless calcium wire is fed, then soft argon blowing is started, the slag surface peristalsis time is ensured to be greater than or equal to 8 min during the soft blowing process, the composition is ensured to be uniform, and the inclusions are ensured to sufficiently float up. The specific water consumption of the continuous casting machine is 1.4-1.7 L / t, the casting speed is 2.6-2.9 m / min, low casting speed is adopted to ensure that the casting blank does not produce cracks during the continuous casting process, and the surface quality of the casting blank is ensured.

[0047] The rolling process comprises:

[0048] (1) The specification covers Φ20 mm.

[0049] (2) Casting blank heating: first heating temperature: 1010℃, second heating temperature: 1160℃, soaking temperature: 1130℃, total heating time: 63 min.

[0050] (3) After the casting blank leaves the heating furnace, it is subjected to multi-pass rough rolling and intermediate rolling, at this time the intermediate blank temperature rises, therefore temperature control cooling must be performed, the temperature control device is two water penetrators with a length of 6 meters, the water quantity of the first water penetrator is 80 m3 / h, the pressure is 1.8 MPa, the water quantity of the second water penetrator is 40 m3 / h, the pressure is 1.8 MPa, the blank rolling speed is 10 m / s, the rolling time is 38 s, the cooling rate is ensured to be 6℃ / s, thereby ensuring that the entry finish rolling temperature is 995℃.

[0051] (4) After the intermediate blank is subjected to multi-pass finish rolling, the temperature continues to rise, the finished product continues to be subjected to temperature control cooling before the upper cooling bed, the temperature control device is six water penetrators with a length of 1.3 meters, by opening the first, third and sixth water penetrators, the water quantity of the first water penetrator is 110 m3 / h, the pressure is 1.8 MPa, the water quantity of the third water penetrator is 110 m3 / h, the pressure is 1.8 MPa, the water quantity of the sixth water penetrator is 40 m3 / h, the pressure is 1.8 MPa, the blank rolling speed is 15 m / s, the rolling time is 45 s, the cooling rate is ensured to be 3℃ / s, and the upper cooling bed temperature is 935℃.

[0052] (5) After the upper cooling bed, the cooling rate is 1.6℃ / s on the cooling bed, the residence time on the cooling bed is 420s, and then sizing and baling are performed.

[0053] Example 2

[0054] A 640MPa high-strength hot-rolled anti-seismic reinforcing steel bar, the chemical composition and the percentage by weight are as follows: C: 0.26wt%, Si: 0.68wt%, Mn: 1.59wt%, Nb: 0.017wt%, V: 0.16wt%, N: 0.013wt%, O: 0.0015wt%, P: 0.025wt%, S: 0.012wt%, [V] / [N]=12.3, [V]+[Nb]=0.177wt%, and the balance is Fe and inevitable impurities.

[0055] The production method of the above-mentioned 640MPa high-strength hot-rolled anti-seismic reinforcing steel bar, comprising the following steps:

[0056] The converter smelting, argon blowing, and continuous casting include:

[0057] The conventional top and bottom combined blowing oxygen converter is used for smelting, and argon is blown throughout the tapping process. When more than 1 / 4 of the tapping is completed, silicon manganese, manganese iron, silicon iron, carbon powder, and lime are sequentially added for deoxidization and alloying and slag washing treatment. The temperature and sample of the molten steel are measured after the molten steel reaches the argon blowing station, and the composition and temperature are uniformized by large-flow argon blowing, and the argon blowing time is ensured to be ≥5 min. After the molten steel enters the LF station, vanadium-nitrogen alloy and vanadium iron are pre-added for preliminary addition. Nitrogen is used as the control point, vanadium-nitrogen alloy is added according to the nitrogen lower limit + 30 ppm, the alloy amount of vanadium is calculated according to the addition amount, and the addition amount of vanadium iron is calculated according to the composition lower limit - 0.002%. According to the slag washing condition, lime and fluorite are added to heat and slag, to ensure good slag flowability. The temperature control is used to control the heating time according to the argon station temperature, to ensure that the temperature reaches 1550℃, and then the sample is analyzed. The alloy silicon manganese, silicon iron, niobium iron, carbon powder, vanadium-nitrogen alloy, and vanadium iron are added again according to the analysis results to fine-tune, and then the temperature is continuously increased to the expected target. After the composition meets the standard through sampling, the seamless calcium wire is fed, and then soft argon blowing is started. The soft blowing process maintains the slag surface peristalsis time ≥8 min, to ensure that the composition is uniform and the inclusions are fully floated. The specific water consumption of the continuous casting machine is 1.4-1.7 L / t, and the withdrawal speed is 2.6-2.9 m / min. Low withdrawal speed is used to ensure that no cracks occur in the casting billet during continuous casting, and to ensure the surface quality of the casting billet.

[0058] The rolling process includes:

[0059] (1) The specification covers Φ22mm.

[0060] (2) Billet heating: first heating temperature: 1070℃, second heating temperature: 1165℃, soaking temperature: 1170℃, total heating time: 70min.

[0061] (3) After the billet leaves the heating furnace, it is subjected to multi-pass rough rolling and intermediate rolling, at which time the temperature of the intermediate billet rises, so temperature control cooling must be performed. The temperature control device is two water sprayers, each 6 meters long. The first water sprayer has a water flow of 100 m3 / h and a pressure of 2.0 MPa, and the second water sprayer has a water flow of 60 m3 / h and a pressure of 1.9 MPa. The billet rolling speed is 8 m / s, and the rolling time is 40 s, which ensures a cooling rate of 7°C / s, thereby ensuring that the entry temperature for finish rolling is 980°C.

[0062] (4) After the intermediate billet is subjected to multi-pass finish rolling, the temperature continues to rise, so temperature control cooling is continued before the product reaches the upper cooling bed. The temperature control device is six water sprayers, each 1.3 meters long. By opening the first, third, and sixth water sprayers, the first water sprayer has a water flow of 115 m3 / h and a pressure of 2.1 MPa, the third water sprayer has a water flow of 110 m3 / h and a pressure of 2.0 MPa, and the sixth water sprayer has a water flow of 60 m3 / h and a pressure of 2.0 MPa. The billet rolling speed is 12 m / s, and the rolling time is 46 s, which ensures a cooling rate of 5°C / s, and the upper cooling bed temperature is 920°C.

[0063] (5) After the upper cooling bed, cooling is performed on the cooling bed at a cooling rate of 1.5°C / s, and the billet stays on the cooling bed for 460 s, after which it is cut to size and baled.

[0064] Example 3

[0065] A 640 MPa grade high-strength hot-rolled anti-seismic reinforcing bar, the chemical composition and weight percentage contents are as follows: C: 0.27 Wt%, Si: 0.75 Wt%, Mn: 1.48 Wt%, Nb: 0.019 Wt%, V: 0.18 Wt%, N: 0.017 Wt%, O: 0.002 Wt%, P: 0.028 Wt%, S: 0.010 Wt%, [V] / [N]=10.5, [V]+[Nb]=0.197 Wt%, the balance being Fe and unavoidable impurities.

[0066] The production method of the above-mentioned 640 MPa grade high-strength hot-rolled anti-seismic reinforcing bar, comprising the following steps:

[0067] Converter smelting, argon blowing, and continuous casting include:

[0068] The steel is smelted by the conventional top and bottom combined blowing oxygen converter, argon is blown during tapping, silicon-manganese, ferromanganese, ferrosilicon, carbon powder and lime are added in sequence when more than 1 / 4 of the molten steel is tapped for deoxidation, alloying and slag washing treatment, the temperature and sample are measured after the molten steel reaches the argon blowing station, meanwhile, high flow argon blowing is carried out to make the composition and temperature uniform, and the argon blowing time is ensured to be greater than or equal to 5 min. Vanadium-nitrogen alloy and ferrovanadium are added in advance after the molten steel enters the LF station for preliminary addition, nitrogen is taken as the control point, vanadium-nitrogen alloy is added according to the nitrogen lower limit + 30 ppm, the amount of vanadium alloy is calculated according to the addition amount, and the addition amount of ferrovanadium is calculated according to the composition lower limit - 0.002%. According to the slag washing condition, lime and fluorite are added for temperature rising and slag melting, the slag fluidity is ensured to be good, the temperature rising time is controlled according to the argon station temperature, the temperature is ensured to reach 1550 ℃, then the sample is analyzed, the alloy silicon-manganese, ferrosilicon, ferro-niobium, carbon powder, vanadium-nitrogen alloy and ferrovanadium are added again for fine adjustment according to the analysis results, then the temperature continues to rise to the expected target, the composition is determined to be up to the standard after sampling, then the seamless calcium wire is fed, then soft argon blowing is started, the slag surface peristalsis time is ensured to be greater than or equal to 8 min during the soft blowing process, the composition is ensured to be uniform, and the inclusions are ensured to float up sufficiently. The specific water consumption of the continuous casting machine is 1.4-1.7 L / t, the casting speed is 2.6-2.9 m / min, low casting speed is adopted to ensure that the casting blank does not produce cracks during the continuous casting process, and the surface quality of the casting blank is ensured.

[0069] The rolling process comprises:

[0070] (1) The specification covers Φ25 mm.

[0071] (2) Casting blank heating: first heating temperature: 1035 ℃, second heating temperature: 1170 ℃, soaking temperature: 1165 ℃, total heating time: 72 min.

[0072] (3) After the casting blank leaves the heating furnace, it is subjected to multi-pass rough rolling and intermediate rolling, at this time the intermediate blank temperature rises, therefore temperature control cooling must be carried out, the temperature control device is two water-through devices with a length of 6 meters, the water flow of the first water-through device is 110 m3 / h, the pressure is 2.1 MPa, the water flow of the second water-through device is 80 m3 / h, the pressure is 2.1 MPa, the blank rolling speed is 6 m / s, the rolling time is 43 s, the cooling rate is ensured to be 9 ℃ / s, thereby ensuring that the entry finish rolling temperature is 970 ℃.

[0073] (4) After the intermediate blank is subjected to multi-pass finish rolling, the temperature continues to rise, the finished product continues to be subjected to temperature control cooling before the upper cooling bed, the temperature control device is six water-through devices with a length of 1.3 meters, by opening the first, third and sixth water-through devices, the water flow of the first water-through device is 120 m3 / h, the pressure is 2.3 MPa, the water flow of the third water-through device is 120 m3 / h, the pressure is 2.2 MPa, the water flow of the sixth water-through device is 70 m3 / h, the pressure is 2.3 MPa, the blank rolling speed is 10 m / s, the rolling time is 48 s, the cooling rate is ensured to be 6 ℃ / s, and the upper cooling bed temperature is 910 ℃.

[0074] (5) After the upper cooling bed, the cooling rate is 1.4℃ / s on the cooling bed, the residence time on the cooling bed is 465s, and then sizing and baling are performed.

[0075] Example 4

[0076] A 640MPa high-strength hot-rolled anti-seismic reinforcing steel bar, the chemical composition and the percentage by weight are as follows: C: 0.28wt%, Si: 0.77wt%, Mn: 1.45wt%, Nb: 0.022wt%, V: 0.19wt%, N: 0.019wt%, O: 0.0017wt%, P: 0.026wt%, S: 0.008wt%, [V] / [N]=10, [V]+[Nb]=0.212wt%, the balance being Fe and unavoidable impurities.

[0077] The production method of the above-mentioned 640MPa high-strength hot-rolled anti-seismic reinforcing steel bar, comprising the following steps:

[0078] The converter smelting, argon blowing, and continuous casting include:

[0079] The conventional top and bottom combined blowing oxygen converter is used for smelting, and argon is blown throughout the tapping process. When more than 1 / 4 of the steel is tapped, silicon manganese, manganese iron, silicon iron, carbon powder, and lime are sequentially added for deoxidization and alloying and slag washing treatment. The temperature and sample are measured after the molten steel reaches the argon blowing station, and the composition and temperature are uniformed by large flow argon blowing, and the argon blowing time is ensured to be ≥5 min. After the molten steel enters the LF station, vanadium-nitrogen alloy and vanadium iron are pre-added for preliminary addition. According to the nitrogen control point, vanadium-nitrogen alloy is added according to the nitrogen lower limit + 30ppm, the alloy amount of vanadium is calculated according to the addition amount, and the addition amount of vanadium iron is calculated according to the composition lower limit-0.002%. According to the slag washing condition, lime and fluorite are added to heat and slag, to ensure good slag flowability. The temperature control is used to control the heating time according to the argon station temperature, to ensure that the temperature reaches 1550℃ and then the sample is analyzed. Through the analysis results, the alloy silicon manganese, silicon iron, niobium iron, carbon powder, vanadium-nitrogen alloy, and vanadium iron are added again for fine adjustment, and then the temperature continues to rise to the expected target. After the sample is taken and the composition is determined to meet the standard, the seamless calcium line is fed, and then soft argon blowing starts. The soft blowing process maintains the slag surface peristalsis time ≥8 min, to ensure that the composition is uniform and the inclusions are fully floated. The specific water consumption of the continuous casting machine is 1.4-1.7L / t, and the withdrawal speed is 2.6-2.9m / min. Low withdrawal speed is adopted to ensure that no cracks occur in the casting billet during continuous casting, and the surface quality of the casting billet is ensured.

[0080] The rolling process includes:

[0081] (1) The specification covers Φ32mm.

[0082] (2) Billet heating: first heating temperature: 1090℃, second heating temperature: 1190℃, soaking temperature: 1180℃, total heating time: 85min.

[0083] (3) After the billet leaves the heating furnace, it is subjected to multi-pass rough rolling and intermediate rolling, at which time the temperature of the intermediate billet rises, so temperature control cooling must be performed. The temperature control device is two water sprayers, each 6 meters long. The first water sprayer has a water flow of 120 m3 / h and a pressure of 2.2 MPa, and the second water sprayer has a water flow of 90 m3 / h and a pressure of 2.2 MPa. The rolling speed of the billet is 4 m / s, and the rolling time is 45 s, so as to ensure that the cooling rate is 10°C / s, thereby ensuring that the temperature of the billet entering the finishing rolling is 960°C.

[0084] (4) After the intermediate billet is subjected to multi-pass finishing rolling, the temperature continues to rise, so the finished product is subjected to temperature control cooling before it reaches the upper cooling bed. The temperature control device is six water sprayers, each 1.3 meters long. By opening the first, third and sixth water sprayers, the first water sprayer has a water flow of 120 m3 / h and a pressure of 2.5 MPa, the third water sprayer has a water flow of 120 m3 / h and a pressure of 2.5 MPa, and the sixth water sprayer has a water flow of 80 m3 / h and a pressure of 2.5 MPa. The rolling speed of the billet is 5 m / s, and the rolling time is 50 s, so as to ensure that the cooling rate is 7°C / s, and the temperature of the upper cooling bed is 900°C.

[0085] (5) After the upper cooling bed, the billet is cooled on the cooling bed at a cooling rate of 1.3°C / s, and the billet stays on the cooling bed for 490 s, at which time the pearlite transformation is completed, and then the billet is cut to size and baled.

[0086] Comparative Example 1

[0087] Comparative Example 1 is similar to Example 1, except that the 640 MPa high-strength hot-rolled anti-seismic reinforcing bar has a chemical composition in which [V] / [N] = 7.5.

[0088] Comparative Example 2

[0089] Comparative Example 2 is similar to Example 1, except that the 640 MPa high-strength hot-rolled anti-seismic reinforcing bar has a chemical composition in which [V] + [Nb] = 0.16 Wt%.

[0090] Comparative Example 3

[0091] Comparative Example 3 is similar to Example 1, except that the 640 MPa high-strength hot-rolled anti-seismic reinforcing bar has a chemical composition in which the N content is 0.010 Wt%.

[0092] Comparative Example 4

[0093] Comparative Example 4 is similar to Example 1, except that in the temperature control step before the finishing rolling, the first water sprayer has a water flow of 75 m3 / h and a pressure of 1.7 MPa, the second water sprayer has a water flow of 35 m3 / h and a pressure of 1.7 MPa, the cooling rate is 5°C / s, and the temperature of the billet entering the finishing rolling is 1010°C.

[0094] Comparative Example 5

[0095] Comparative Example 5 is similar to Example 1, except that in the temperature control step before the finish rolling, the water quantity of the first water passage is 125 m3 / h, the pressure is 2.3 MPa, the water quantity of the second water passage is 95 m3 / h, the pressure is 2.3 MPa, the cooling rate is 11 ℃ / s, and the temperature of the finish rolling is 950 ℃.

[0096] Comparative Example 6

[0097] Comparative Example 6 is similar to Example 1, except that in the temperature control step before the finish rolling, the water quantity of the first water passage is 125 m3 / h, the pressure is 2.3 MPa, the water quantity of the second water passage is 95 m3 / h, the pressure is 2.3 MPa, the cooling rate is 11 ℃ / s, and the temperature of the finish rolling is 950 ℃.

[0098] Comparative Example 7

[0099] Comparative Example 7 is similar to Example 1, except that in the temperature control step before the finish rolling, the water quantity of the first water passage is 125 m3 / h, the pressure is 2.3 MPa, the water quantity of the second water passage is 95 m3 / h, the pressure is 2.3 MPa, the cooling rate is 11 ℃ / s, and the temperature of the finish rolling is 950 ℃.

[0100] Test results

[0101] The macroscopic metallographic graph of the 640 MPa high-strength hot-rolled anti-seismic steel bar produced in the example of the present application is shown in Figure 1 , and the microstructure of the 640 MPa high-strength hot-rolled anti-seismic steel bar produced in the example of the present application is shown in Figure 1 It can be seen that the macroscopic metallographic graph has no chilling layer, and the microstructure of the 640 MPa high-strength hot-rolled anti-seismic steel bar is shown in Figure 2 , and the microstructure of the 640 MPa high-strength hot-rolled anti-seismic steel bar produced in the example of the present application is shown in Figure 2 It can be seen that the microstructure is composed of ferrite and pearlite. From the macroscopic metallographic graph and the microstructure, it can be seen that the internal structure of the 640 MPa high-strength hot-rolled anti-seismic steel bar prepared in the example of the present application completely meets the requirements of the standard anti-seismic steel bar. The microstructure of the 640 MPa high-strength hot-rolled anti-seismic steel bar produced in Example 3 is shown in Figure 3 , and the pearlite interlamellar spacing of the 640 MPa high-strength hot-rolled anti-seismic steel bar produced in Example 3 is 96-242 nm.

[0102] The test results of the steel bars obtained in Examples 1-4 and Comparative Examples 1-7 are shown in the following table:

[0103]

[0104] As can be seen from the above table, the mechanical properties and the metallographic structure of the 640MPa high-strength hot-rolled anti-seismic reinforcing steel bars prepared in the embodiment of the present application fully meet the requirements of the anti-seismic reinforcing steel bar standard. When the chemical composition is different or the process parameters are changed, the macrostructure or the mechanical properties of the obtained reinforcing steel bars cannot meet the requirements of the anti-seismic reinforcing steel bars.

[0105] In conclusion, the embodiment of the present application provides a 640MPa high-strength hot-rolled anti-seismic reinforcing steel bar and a production method thereof, the chemical composition and the weight percentage of which are as follows: C: 0.24-0.28 Wt%, Si: 0.65-0.80 Wt%, Mn: 1.45-1.60 Wt%, Nb: 0.016-0.023 Wt%, V: 0.15-0.19 Wt%, N: 0.011-0.019 Wt%, O: ≤0.002 Wt%, P: ≤0.035 Wt%, S: ≤0.030 Wt%, [V] / [N]≥8, [V]+[Nb]≥0.17 Wt%, and the balance is Fe and inevitable impurities. The following process route is adopted: "top and bottom combined blowing converter smelting→ tapping→ ladle argon blowing→ LF refining→ 6-machine 6-flow 160mm×160mm square billet continuous casting→ step-by-step heating furnace heating→ rough and medium rolling→ pre-precision rolling→ pre-precision rolling temperature control cooling→ precision rolling→ post-precision rolling temperature control cooling→ upper cooling bed→ collection and storage". The 640MPa high-strength hot-rolled anti-seismic reinforcing steel bar and the production method thereof provided by the embodiment of the present application have the following advantages:

[0106] The 640MPa high-strength hot-rolled anti-seismic reinforcing steel bar and the production method thereof provided by the embodiment of the present application adopt niobium-vanadium-nitrogen micro-alloying and controlled rolling and controlled cooling technology, realize the role of niobium-vanadium-nitrogen micro-alloying elements in refining grains and precipitation strengthening by precisely controlling the process parameters in the production process of the Φ20-Φ32mm specification 640MPa high-strength hot-rolled anti-seismic reinforcing steel bar, effectively solve the problems of the 640MPa high-strength hot-rolled anti-seismic reinforcing steel bar, such as billet crack, non-obvious yield platform, low strength-to-yield ratio and low maximum total elongation, and improve the strength-to-yield ratio and the maximum total elongation of the 640MPa high-strength hot-rolled anti-seismic reinforcing steel bar.

[0107] The above merely describes preferred embodiments of the present application but is not intended to limit the present application. The present application can be variously changed and modified by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for producing a 640 MPa grade high-strength hot-rolled anti-seismic reinforcing bar, characterized by, The chemical composition and weight percentage of the 640MPa high-strength hot-rolled anti-seismic reinforcing steel bar are as follows: C: 0.24-0.28wt%, Si: 0.65-0.80wt%, Mn: 1.45-1.60wt%, Nb: 0.016-0.023wt%, V: 0.15-0.19wt%, N: 0.011-0.019wt%, O: ≤0.002wt%, P: ≤0.035wt%, S: ≤0.030wt%, [V] / [N]≥8, [V]+[Nb]≥0.17wt%, and the balance being Fe and inevitable impurities; The production method of the 640MPa high-strength hot-rolled anti-seismic reinforcing steel bar adopts the following process route: converter tapping→ladle argon blowing→LF refining→continuous casting→heating→rough and intermediate rolling→pre-precision rolling→pre-precision rolling temperature control cooling→precision rolling→post-precision rolling temperature control cooling→cooling bed→collection and storage, wherein: The LF refining process comprises the following steps: after the molten steel enters the LF station, vanadium-nitrogen alloy is added according to the nitrogen lower limit+30ppm, vanadium-iron alloy is added according to the vanadium lower limit-0.002%, and lime and fluorite are added for temperature rising and slag melting according to the slag washing condition to obtain good fluidity of the slag, the temperature rising time is controlled according to the argon station temperature, the molten steel temperature reaches 1550℃, then sampling analysis is performed, the alloying silicon manganese, silicon iron, niobium iron, carbon powder, vanadium-nitrogen alloy and vanadium iron are added again according to the analysis results, the temperature is continuously raised to the expected target, sampling is performed to determine that the composition meets the standard, then the seamless calcium wire is fed, and then soft argon blowing is started, the soft blowing process keeps the slag surface peristalsis time≥8min to ensure that the composition is uniform and the inclusions are fully floated; In the rolling process, the 640MPa high-strength hot-rolled anti-seismic reinforcing steel bar has a specification of Φ20-32mm, wherein Φ20-22mm is rolled by two-cutting, and Φ25-32mm is rolled by single-line rolling; the pre-precision rolling temperature control cooling process comprises the following steps: the used temperature control device is a water cooler with two sections, each with a length of 6 meters, the water flow of the first section is controlled to be 80-120m³ / h, the pressure is controlled to be 1.8-2.2MPa, the water flow of the second section is controlled to be 40-90m³ / h, the pressure is controlled to be 1.8-2.2MPa, the rolling speed of the blank is controlled to be 4-10m / s, the rolling time is controlled to be 38-45s, the cooling rate is controlled to be 6-10℃ / s, so that the temperature of the blank entering the precision rolling is 960-1000℃; the post-precision rolling temperature control cooling process comprises the following steps: the used temperature control device is a water cooler with six sections, each with a length of 1.3 meters, the first, third and sixth sections are opened, and the second, fourth and fifth sections are closed, the water flow of the first section is controlled to be 110-130m³ / h, the pressure is controlled to be 1.8-2.5MPa, the water flow of the third section is controlled to be 110-120m³ / h, the pressure is controlled to be 1.8-2.5MPa, the water flow of the sixth section is controlled to be 40-80m³ / h, the pressure is controlled to be 1.8-2.5MPa, the rolling speed of the blank is controlled to be 5-15m / s, the rolling time is controlled to be 45-50s, and the cooling rate is controlled to be 3-7℃ / s, so that the temperature of the blank on the cooling bed is 900-950℃. The tensile strength Rm of said 640 MPa grade high-strength hot-rolled anti-seismic reinforcing bar m ≥ 835 MPa, yield strength R eL ≥ 660 MPa, maximum total elongation A gt ≥ 10.5%, R 0 eL / R eL ≤ 1.10, R 0 m / R 0 eL ≥ 1.26, grain size of 9.5-10.0 grade; The base structure of the 640 MPa high-strength hot-rolled anti-seismic reinforcing steel bar is: ferrite + pearlite content is greater than 94%, ferrite content is 50-58%, pearlite content is 37-48%, pearlite interlamellar spacing is 90-250 nm, bainite and martensite island content is less than 6%, and there is no chill layer in macroscopic metallography.

2. The production method according to claim 1, characterized by, The converter tapping and ladle argon blowing include: adopting a conventional top and bottom combined blowing oxygen converter for smelting, blowing argon throughout tapping, adding silicon manganese, manganese iron, silicon iron, carbon powder and lime in sequence for deoxidation and alloying and slag washing treatment when more than 1 / 4 of the tapping, measuring temperature and sampling after the molten steel reaches the argon blowing station, and blowing argon at a large flow rate to make the composition and temperature uniform, and the argon blowing time is ensured to be greater than or equal to 5 min.

3. The production method according to claim 1, characterized by, The continuous casting process includes: controlling the specific water consumption of the continuous casting machine to be 1.4-1.7 L / t, and the pulling speed to be 2.6-2.9 m / min.

4. The production method according to claim 1, characterized by, The heating process includes: controlling the first heating temperature to be 1000-1100℃, the second heating temperature to be 1100-1200℃, the soaking temperature to be 1130-1180℃, and the total heating time to be 60-90 min.

5. The production method according to claim 1, characterized by, The upper cooling bed process includes: after the billet is placed on the cooling bed, cooling at a cooling rate of 1℃ / s-2℃ / s on the cooling bed, the residence time on the cooling bed is 420-500 s, and then sizing and bundling are performed.

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