A 640mpa grade fine-grained high-strength and high-toughness anti-seismic reinforcing steel bar and a preparation method thereof

Abstract

The application discloses a 640MPa-grade fine-grain high-strength and high-toughness anti-seismic reinforcing steel bar and a preparation method thereof, and belongs to the field of metallurgical technologies. The application provides a 640MPa-grade fine-grain high-strength and high-toughness anti-seismic reinforcing steel bar, the temperature and the cooling speed of the reinforcing steel bar on a cooling bed after rolling are controlled through a niobium-vanadium-nitrogen ratio, more pearlite and a small amount of bainite are formed on the basis of the existing ferrite+pearlite structure of the reinforcing steel bar, the strength and the toughness of the steel are improved through the combination of fine-grain strengthening, precipitation strengthening and phase change strengthening, and the anti-seismic performance of the reinforcing steel bar is improved and stabilized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of metallurgy, in particular to a 640MPa grade fine-grained high-strength and high-toughness anti-seismic steel bar and a preparation method thereof. BACKGROUND

[0002] High-strength anti-seismic steel bars have the advantages of high strength-to-yield ratio and large uniform elongation, and can improve the anti-seismic capability of buildings and reduce personnel casualties and property losses caused by earthquakes. Increasing the strength grade of steel bars is of great significance to resource saving, energy consumption reduction and emission reduction in the steel and construction industries. At present, the methods for increasing the strength and anti-seismic performance of steel bars are mostly achieved by refining the grain size of steel and precipitating second phase particles, but fine-grained high-strength steel bars mainly increase the yield strength of steel bars, and the increase in tensile strength is small, which is not conducive to the stable standardization of the strength-to-yield ratio and affects the anti-seismic performance.

[0003] In view of this, the present application is proposed. SUMMARY

[0004] The purpose of the present application is to provide a 640MPa grade fine-grained high-strength and high-toughness anti-seismic steel bar and a preparation method thereof to overcome the defects of the prior art.

[0005] The technical problem of the present application is solved by using the following technical scheme.

[0006] The present application provides a 640MPa grade fine-grained high-strength and high-toughness anti-seismic steel bar, which comprises the following chemical components in mass percentage: C 0.19%-0.28%, Si 0.55%-0.80%, Mn 1.35%-1.60%, V 0.10%-0.18%, Nb 0.01%-0.025%, P≤0.045%, S≤0.045%, N 0.0132%-0.0337%, T.O≤0.0030%, and the balance being Fe and unavoidable impurities, while the carbon equivalent Ceq≤0.58% and 5.75≤(V+0.55Nb) / N≤8 are also met.

[0007] The present application also provides a preparation method of the above-mentioned 640MPa grade fine-grained high-strength and high-toughness anti-seismic steel bar, and the preparation process route is as follows: converter smelting→argon station bottom blowing gas stirring→LF furnace refining→continuous casting→steel billet heating→rolling and post-rolling cooling.

[0008] The present application has the following beneficial effects:

[0009] The application provides a 640MPa-grade fine-grain high-strength and high-toughness anti-seismic steel bar and a preparation method thereof. The 640MPa-grade fine-grain high-strength and high-toughness anti-seismic steel bar comprises the following components in percentage by mass: C 0.19%-0.28%, Si 0.55%-0.80%, Mn 1.35%-1.60%, V 0.10%-0.18%, Nb 0.01%-0.025%, P≤0.045%, S≤0.045%, N 0.0132%-0.0337%, T.O≤0.0030%, and the balance of Fe and inevitable impurities, and meanwhile, the carbon equivalent Ceq≤0.58% and 5.75≤(V+0.55Nb) / N≤8 are met. Through the component design of adding V and Nb composite micro-alloying, the ratio of V and Nb element to N content is precisely controlled, and the solid solution, precipitation, grain refinement and phase transformation strengthening means of V and Nb are utilized, so that the 640MPa-grade fine-grain high-strength and high-toughness anti-seismic steel bar is prepared, which has a yield strength of≥640MPa, a tensile strength of≥815MPa, a maximum total elongation of≥10%, a ratio of the measured tensile strength to the measured yield strength of≥1.25, a ratio of the measured yield strength to the yield strength characteristic value of≤1.30, and a ferrite grain size of 10.5-12. BRIEF DESCRIPTION OF DRAWINGS

[0010] 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. It should be understood that the following drawings only show some of the embodiments of the application, and therefore should not be regarded as a limitation to the scope. For those skilled in the art, other related drawings can also be obtained without creative labor on the basis of these drawings.

[0011] Figure 1 A 500-fold metallographic structure schematic diagram of the 640MPa-grade fine-grain high-strength and high-toughness anti-seismic steel bar prepared for the embodiment 2 of the application at the center;

[0012] Figure 2 A 500-fold metallographic structure schematic diagram of the 640MPa-grade fine-grain high-strength and high-toughness anti-seismic steel bar prepared for the embodiment 2 of the application at 1 / 4. DETAILED DESCRIPTION

[0013] 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 below. If the specific conditions are not indicated in the embodiments, the conventional conditions or the conditions suggested by the manufacturers are adopted. If the manufacturers of the reagents or instruments are not indicated, they are all the conventional products that can be obtained by market purchase.

[0014] The 640MPa-grade fine-grain high-strength and high-toughness anti-seismic steel bar and the preparation method thereof provided by the embodiments of the application will be specifically described below.

[0015] In order to overcome the above-mentioned deficiencies of the prior art, the embodiments of the present application provide a 640MPa grade fine-grained high-strength and high-toughness anti-seismic steel bar and a preparation method thereof, which combines the production equipment and process of steel enterprises to provide a chemical composition and a production method of the 640MPa grade fine-grained high-strength and high-toughness anti-seismic steel bar with a diameter of 12-40mm.

[0016] In a first aspect, the embodiments of the present application provide a 640MPa grade fine-grained high-strength and high-toughness anti-seismic steel bar, and the chemical composition of the steel bar has a mass percentage of C 0.19%-0.28%, Si 0.55%-0.80%, Mn 1.35%-1.60%, V 0.10%-0.18%, Nb 0.01%-0.025%, P≤0.045%, S≤0.045%, N 0.0132%-0.0337%, T.O≤0.0030%, and the balance is Fe and inevitable impurities, while the carbon equivalent Ceq≤0.58% and 5.75≤(V+0.55Nb) / N≤8 are met.

[0017] The above-mentioned 640MPa grade fine-grained high-strength and high-toughness anti-seismic steel bar has a mass percentage of C 0.26%-0.28%, Si 0.70%-0.80%, Mn 1.45%-1.55%, V 0.10%-0.16%, Nb 0.01%-0.025%, P≤0.045%, S≤0.045%, N 0.0132%-0.0302%, T.O≤0.0030% for the chemical composition of the small size steel bar with a diameter of 12-14mm, and the balance is Fe and inevitable impurities; while the carbon equivalent Ceq≤0.58% and 5.75≤(V+0.55Nb) / N≤8 are met. The chemical composition of the large and medium size steel bar with a diameter of 16-40mm has a mass percentage of C 0.26%-0.28%, Si 0.70%-0.80%, Mn 1.45%-1.55%, V 0.12%-0.18%, Nb 0.01%-0.025%, P≤0.045%, S≤0.045%, N 0.0157%-0.0337%, T.O≤0.0030%, and the balance is Fe and inevitable impurities, while the carbon equivalent Ceq≤0.58% and 5.75≤(V+0.55Nb) / N≤8 are met.

[0018] The 640MPa grade fine-grained high-strength and high-toughness anti-seismic steel bar provided by the embodiments of the present application has the following alloy component effects and principles:

[0019] C, Mn, Si are conventional alloying elements for improving the strength of steel, wherein C is a cost-effective strengthening element, plays a solid solution strengthening role, and combines with V and Nb in the steel to form carbides or carbonitrides to play a precipitation strengthening role, the C content of the application is 0.19%-0.28%, further, preferably C 0.24%-0.28%, more preferably 0.26%-0.28%; Mn plays a solid solution strengthening role and can significantly improve the tensile strength of the steel, and is a beneficial element for improving the strength-yield ratio of the steel bar, the Mn content of the application is 1.35%-1.60%, further, preferably Mn 1.40%-1.55%, more preferably 1.45%-1.55%. Si plays a solid solution strengthening role, its effect on improving the strength of the steel bar is smaller than that of Mn, and it does not improve the strength-yield ratio, the Si content of the application is Si 0.55%-0.80%, further, preferably Si 0.65%-0.80%, more preferably 0.70%-0.80%.

[0020] V: by heating solid solution in the steel rolling process, fine and dispersed V(C, N) compounds are precipitated during deformation and phase change, hindering grain growth, playing a fine-grain strengthening and precipitation strengthening role; V has no special requirements for the preparation process control of the steel bar and will not increase the crack sensitivity of the billet, and is the most important micro-alloying element for high-strength steel bars, and its strengthening characteristics are to simultaneously improve the yield and tensile strength and improve R o m / R o eL The effect is not obvious. The V content of the application is 0.10%-0.18%, because of the specification effect of the strength of the steel bar, the V micro-alloying component is controlled according to the specification group distance, the V of the small specification steel bar with a diameter of 12-14mm is further preferably 0.12%-0.16%, and the V of the large and medium specification steel bar with a diameter of 16-40mm is preferably 0.14%-0.17%.

[0021] Nb: Refine pearlite lamellar structure and ferrite structure, fine grain strengthening effect; In the process of deformation and phase change, precipitate Nb(C, N) compound, fine grain strengthening and precipitation strengthening effect; Inventor found that solid solution of niobium can improve the hardenability of steel, delay the austenite-ferrite phase transition, reduce the proportion of ferrite, increase the proportion of pearlite, promote the formation of low temperature phase change product, produce phase change strengthening effect, significantly improve the tensile strength of steel, improve the high strength steel bar yield ratio anti-seismic performance index; But the Nb-containing steel will precipitate Nb(C, N) compound along the original austenite grain boundary during the cooling process of continuous casting billet, form micropores at the grain boundary, and easily form grain boundary cracks, so that the plasticity of the steel is poor; When the content of Nb is high, the temperature of Nb solid solution into austenite during the heating process of the steel billet is relatively high compared with V, and the solid solution time is relatively long compared with V, which affects the production efficiency and increases the heating energy consumption cost; The inventor found that when Nb is less than or equal to 0.025%, the Nb-V micro-alloyed steel can not only improve the strength and yield ratio, but also avoid the generation of grain boundary cracks in the continuous casting billet, and the heating degree and heating time of the steel billet can be controlled by the conventional process without special control; In the present application, the content of Nb is controlled in the range of 0.01%-0.025%, further, the content of Nb is preferably in the range of 0.012%-0.023%, and more preferably in the range of 0.012%-0.020%.

[0022] N: As described above, N combines with V and Nb to form fine and dispersed nitrides and carbonitrides, which have fine grain strengthening and precipitation strengthening effects; The solid solution and precipitation of V and Nb and the type of precipitates are complex phase change processes, and the inventor found that the nitrides and carbides of vanadium are completely miscible to form vanadium carbonitride in the form of VC x N 1－x (0.01<x<0.99) form, and the coefficient x is closely related to the content of V, C and N and the precipitation temperature; When the content of N is high, the V precipitates mainly in the form of vanadium carbonitride rich in nitrogen, the coefficient x is small, and the change with temperature is small; When the content of N is low, vanadium carbonitride rich in carbon is formed, and with the decrease of temperature and the decrease of N content, part of N in the vanadium carbonitride rich in nitrogen precipitated by V at high temperature is replaced by C, and the coefficient x increases. The nitrides of V are finer and more dispersed than the carbides, and have smaller tendency to coarsen, so more vanadium carbonitride rich in nitrogen is expected to be precipitated. In the ideal state, V is completely precipitated in the form of vanadium carbonitride, the proportion of VN in the precipitate is in the range of 0.65-0.8, the atomic ratio of V / N is 3.6, and the relationship between the content of N and V is 4.6≤V / N≤5.6; The actual proportion of V precipitated in the form of vanadium carbonitride is 70%-0.80%, and thus the relationship between the content of N and V is 5.75≤V / N≤8, and the combination of niobium with carbon and nitrogen is similar to that of vanadium, in the form of NbC x N 1－xThe precipitates are in the form of (0.01 < x < 0.99), the coefficient of the proportion of NbN in the precipitates is 1-x in the range of 0.65-0.8, the atomic weight ratio of Nb / N is 6.6, the relationship between N and Nb contents is 4.6 ≤ 0.55Nb / N ≤ 5.6, the actual proportion of Nb precipitated carbonitride is 70%-0.80%, thus the relationship between N and Nb contents is 5.75 ≤ 0.55Nb / N ≤ 8, the relationship between N, V and Nb contents is 5.75 ≤ (V+0.55Nb) / N ≤ 8, thus the required N content combined with 0.10%-0.18% V and 0.01%-0.025% Nb is 0.0132%-0.0337%.

[0023] The above 640MPa grade fine-grained high-strength and high-toughness anti-seismic steel bar has a microstructure of ferrite + pearlite + a small amount of bainite, wherein the proportion of pearlite is ≥45%, the proportion of bainite is 2%-5%, and the ferrite grain size is 10.5-12 grade.

[0024] The above 640MPa grade fine-grained high-strength and high-toughness anti-seismic steel bar has a yield strength R eL ≥640MPa, a tensile strength R m ≥815MPa, a maximum force total elongation A gt ≥10% of the anti-seismic performance, a measured tensile strength to measured yield strength ratio R o m / R o eL ≥1.25, a measured yield strength to yield strength characteristic value ratio R o eL / R eL ≤1.30.

[0025] In a second aspect, the embodiments of the present application also provide a preparation method of the above 640MPa grade fine-grained high-strength and high-toughness anti-seismic steel bar, and the preparation process route is as follows: converter smelting, argon station bottom blowing gas stirring, LF furnace refining, continuous casting, billet heating, rolling and post-rolling cooling.

[0026] Converter smelting: the blowing end point P is ≤0.035%, silicon iron and silicon manganese iron are added when the converter tapping is to 1 / 3, vanadium-nitrogen alloy and niobium iron are added when the silicon iron and silicon manganese iron are added by half, appropriate amount of slagging materials are added for slag washing, and the ladle bottom blowing gas stirring is opened for 2-4 min.

[0027] P cannot be removed in the argon station of steelmaking, LF furnace refining and continuous casting process, and the added silicon manganese iron alloy contains P. After adding the alloy, the P content of molten steel increases by 0.002%-0.005%; when half of the silicon iron and silicon manganese iron is added, vanadium-nitrogen alloy and niobium iron are added, mainly because the terminal molten steel has strong oxidizing property, the silicon iron and silicon manganese iron have deoxidizing function, which reduces the oxidizing property of molten steel and improves the recovery rate of vanadium-nitrogen alloy and niobium iron; the purpose of opening the bottom blowing gas stirring of the ladle is to make the added alloy and slagging material quickly melt and homogenize, and prevent the alloy and slagging material from not completely melting at the end of tapping.

[0028] When the terminal C is less than or equal to 0.04%, the dissolved oxygen of molten steel increases exponentially, the molten steel has strong oxidizing property, and the alloy recovery rate is significantly reduced. An appropriate amount of deoxidizer needs to be added during the tapping process to ensure the alloy recovery rate.

[0029] Argon station bottom blowing gas stirring: since V and Nb micro-alloying elements are added to the steel, sufficient N is needed to combine with V and Nb to form carbonitride precipitated phase, which plays a role in fine-grain strengthening and precipitation strengthening. Adding vanadium-nitrogen alloy during the converter tapping process increases the N content in the steel, but N still cannot meet the requirements, and the molten steel still needs to be further increased in N. The cost of increasing N by bottom blowing nitrogen in the argon station is low, and bottom blowing nitrogen is preferred when the conditions for blowing nitrogen are met. The blowing nitrogen time is 7-10 min, and the molten steel can increase N by 20-35 ppm. Alternatively, when the argon station is bottom blowing argon, a nitrogen increasing agent needs to be added during the converter tapping process to increase N. Preferably, the nitrogen increasing agent is one of rare earth nitrogen alloy and silicon nitride.

[0030] LF furnace refining and continuous casting: including power-up temperature adjustment to adjust the temperature of molten steel to meet the requirements of continuous casting, adding alloy to fine-tune the composition according to the composition of the steel, adding lime to make slag, and adding silicon deoxidizer to diffuse and deoxidize, thereby reducing the oxidizing property of the ladle top slag, removing inclusions in the steel, and obtaining molten steel with required chemical composition, temperature meeting the requirements of continuous casting, and high cleanliness.

[0031] Billet heating: including preheating, heating and soaking three stages, billet hot charging or cold charging to the rolling heating furnace, when billet hot charging, the preheating temperature is 600-800℃, the heating temperature is 1170-1210℃, further preferably 1180-1200℃, the soaking temperature is 1160-1200℃, further preferably 1170-1190℃, and the total heating time is ≥70 min; when billet cold charging, the preheating temperature is 500-700℃, the heating temperature is 1180-1220℃, further preferably 1190-1210℃, the soaking temperature is 1170-1210℃, further preferably 1180-1200℃, and the total heating time is ≥80 min.

[0032] The billet heating temperature is relatively high and the heating time is relatively long for the 500 MPa grade steel bar, so as to promote the alloy elements such as Nb and V to be fully solid-solved into austenite, and to play the roles of preventing grain growth, refining grains, precipitation strengthening and phase transformation strengthening during subsequent rolling deformation and phase transformation.

[0033] Rolling: including three stages of rough rolling, intermediate rolling and finish rolling, the rough rolling opening rolling temperature ranges from 1080 to 1130℃, and after the rough rolling and intermediate rolling, the finish rolling inlet temperature is controlled at 900-1000℃ by using a water cooling device.

[0034] Post-rolling cooling: the steel bar temperature on the cooling bed after finish rolling is controlled at 900-980℃ by using a water cooling device, and is further preferably controlled at 920-980℃, and the cooling speed of the steel bar on the cooling bed ranges from 2.5 to 7℃ / s.

[0035] The finish rolling inlet temperature is controlled at 900-1000℃, so as to promote V and Nb to partially precipitate carbonitride to drag the grain boundary movement, to inhibit the recrystallization and recovery of deformed austenite at high temperature, and to refine the original austenite grains. The steel bar temperature on the cooling bed after rolling ranges from 900 to 980℃, and the cooling speed on the cooling bed ranges from 2.5 to 7℃ / s, so as to avoid the formation of harmful martensite when the temperature on the cooling bed is too low and the cooling speed is too fast, to promote the precipitation of fine and dispersed vanadium carbonitride and niobium carbonitride, to inhibit the nucleation and growth of ferrite through the dragging effect of Nb on the phase interface, to delay the γ→α transformation, to promote the formation of more pearlite, and to form a small amount of bainite, and finally to form a fine-grained ferrite, pearlite and a small amount of bainite structure, wherein the ferrite grain size is 10.5-12, the proportion of pearlite structure is ≥45%, and the proportion of bainite structure is 2%-5%, so as to obtain a fine-grained high-strength and high-toughness anti-seismic steel bar.

[0036] Rolling: the split rolling or single-line rolling can be adopted, the split rolling is one of two-split, three-split, four-split or five-split, and the temperature deviation of the steel bar on the cooling bed after the split rolling is not greater than 20℃.

[0037] The fine-grained high-strength and high-toughness anti-seismic steel bar prepared by the method has the mechanical properties of yield strength R eL ≥640MPa, tensile strength R m ≥815MPa, maximum total elongation A gt ≥10%, the ratio of the measured tensile strength to the measured yield strength R o m / R o eL ≥1.25, the ratio of the measured yield strength to the yield strength characteristic value R o eL / R eL ≤1.30.

[0038] It can be seen that the embodiment of the present application provides a 640MPa grade fine-grained high-strength and high-toughness anti-seismic steel bar and a preparation method thereof, through adopting the component design of adding V and Nb composite micro-alloying, precisely controlling the proportion of V, Nb element and N content, using the solid solution, precipitation, grain refinement and phase transformation strengthening means of V and Nb, a 640MPa grade fine-grained high-strength and high-toughness anti-seismic steel bar with yield strength ≥ 640MPa, tensile strength ≥ 815MPa, maximum force total elongation ≥ 10%, the ratio of measured tensile strength to measured yield strength ≥ 1.25, the ratio of measured yield strength to yield strength characteristic value ≤ 1.30, and ferrite grain size of 10.5-12 grade is prepared.

[0039] The preparation method of the above 640MPa grade fine-grained high-strength and high-toughness anti-seismic steel bar adopts the following process route: converter smelting→argon station bottom blowing gas stirring→LF furnace refining→continuous casting→steel billet heating→rolling and post-rolling cooling. The steel billet can be hot charged or cold charged to the steel rolling heating furnace, the heating section temperature when the steel billet is hot charged is 1170-1210℃, the soaking section temperature is 1160-1200℃, and the total heating time is ≥ 70min, the steel billet cold charging heating and soaking temperature is 10℃ higher than that when hot charged, and the heating time is 10min longer, so as to promote the alloy elements such as Nb and V to be fully solid-solved into austenite; the finish rolling inlet temperature is 900-1000℃, so as to promote V and Nb to partially precipitate carbonitride to pin rolling dislocation and drag grain boundary movement, inhibit the recrystallization and recovery of deformed austenite at high temperature, and refine the original austenite grain; the temperature range of the steel bar on the cooling bed after finish rolling is controlled by the water cooling device to be 900-980℃, and the cooling speed of the steel bar on the cooling bed is 2.5-7℃ / s, which is beneficial to promote the precipitation of fine and dispersed vanadium carbonitride and niobium carbonitride, inhibit the ferrite nucleation and growth, delay the γ→α transformation, form more pearlite and a small amount of bainite, the proportion of pearlite structure is ≥ 45%, the proportion of bainite structure is 2%-5%, the strength and toughness of the steel are improved, and the anti-seismic performance of the steel is improved.

[0040] The features and performances of the present application are further described in detail in combination with the embodiments.

[0041] The embodiment of the present application provides a 640MPa grade fine-grained high-strength and high-toughness anti-seismic steel bar, and the mass percentage of the chemical components of the steel is as follows: C 0.19%-0.28%, Si 0.55%-0.80%, Mn 1.35%-1.60%, V 0.10%-0.18%, Nb 0.01%-0.025%, P ≤ 0.045%, S ≤ 0.045%, N 0.0132%-0.0337%, T.O ≤ 0.0030%, the balance is Fe and inevitable impurities, meanwhile, the carbon equivalent Ceq ≤ 0.58% and 5.75 ≤ (V+0.55Nb) / N ≤ 8 need to be met.

[0042] Meanwhile, the application also provides a preparation method of the 640MPa-grade fine-grained high-strength and high-toughness anti-seismic reinforcing steel bar, which comprises the following steps.

[0043] The converter blowing terminal point P is less than or equal to 0.035%, silicon iron and silicon manganese iron are added when the converter is 1 / 3 of the out-steel, vanadium-nitrogen alloy and niobium iron are added when the silicon iron and silicon manganese iron are added by half, and then a proper amount of slagging material is added for slag washing, and the bottom blowing gas stirring of the ladle is started for 2-4 minutes; when the converter terminal point C is less than or equal to 0.04%, a proper amount of aluminum or silicon deoxidizer is added during the out-steel process.

[0044] The bottom blowing gas stirring is carried out at the argon station, the bottom blowing gas is argon or nitrogen, preferably nitrogen, and the bottom blowing nitrogen is 7-10 minutes from the out-steel of the converter; when the argon station is bottom blowing argon, a nitrogen increasing agent is added during the out-steel process of the converter, the nitrogen increasing agent is one of rare earth nitrogen alloy and silicon nitride.

[0045] The LF refining comprises the following steps: the electric heating is used to adjust the temperature of the molten steel to meet the continuous casting pouring requirements, the alloy is added according to the composition of the steel to finely adjust the composition, the lime is added to form slag, the silicon deoxidizer is added to diffuse and deoxidize, the top slag oxidation of the ladle is reduced, the inclusions in the steel are removed, and the molten steel with the required chemical composition, the temperature meeting the continuous casting pouring and the high cleanliness is obtained.

[0046] The billet is hot sent and hot charged or cold charged to the rolling heating furnace, when the billet is hot charged, the preheating temperature is 600-800 DEG C, the heating temperature is 1170-1210 DEG C, the soaking temperature is 1160-1200 DEG C, and the total heating time is greater than or equal to 70 minutes; when the billet is cold charged, the preheating temperature is 500-700 DEG C, the heating temperature is 1180-1220 DEG C, the soaking temperature is 1170-1210 DEG C, and the total heating time is greater than or equal to 80 minutes.

[0047] The rolling rough rolling opening temperature range is 1080-1130 DEG C, after the rough rolling and the medium rolling, the water cooling device is used to control the precision rolling inlet temperature in the range of 900-1000 DEG C, the water cooling device is used to control the temperature range of the reinforcing steel bar on the cooling bed after the precision rolling in the range of 900-980 DEG C, and the temperature range is further preferably 920-980 DEG C, and the cooling speed range of the reinforcing steel bar on the cooling bed is 2.5-7 DEG C / s.

[0048] The rolling can adopt the slitting rolling or the single line rolling, the slitting rolling is one of two slitting, three slitting, four slitting or five slitting, and the temperature deviation of the reinforcing steel bar on the cooling bed after the slitting rolling is not greater than 20 DEG C.

[0049] The following table 1 is the chemical composition and the weight percentage of each embodiment and the comparative example, and the balance is Fe and inevitable impurities.

[0050] Table 1

[0051]

[0052]

[0053] Example 1

[0054] A 640MPa grade fine-grained high-strength and high-toughness anti-seismic steel bar, the chemical composition and the percentage by weight content are shown in Table 1 of Example 1.

[0055] The preparation method of the 640MPa grade fine-grained high-strength and high-toughness anti-seismic steel bar of the present embodiment is as follows: 130t converter smelting→argon station bottom blowing nitrogen→LF furnace refining→billet continuous casting→hot charging of billet hot charging→heating→bar rolling mill rolling→cooling bed cooling→shearing→bundling.

[0056] The converter end point C=0.08%, P=0.021%, silicon iron, silicon manganese, vanadium-nitrogen alloy and niobium iron are added at 1 / 3 tapping, 500Kg of lime and 400Kg of bauxite are used for slagging, and the ladle is bottom blown with nitrogen during tapping.

[0057] The molten steel is bottom blown with nitrogen for 8min in the argon station.

[0058] The molten steel is deoxidized by adding silicon deoxidizer during LF refining.

[0059] The billet is hot charged to the rolling heating furnace after continuous casting, and single-line rolling is adopted to roll the 32mm diameter steel bar, the temperature before the billet enters the furnace is measured to be 565-630℃, the billet heating temperature is 1195℃, the soaking temperature is 1190℃, and the heating time is 72min.

[0060] The opening rolling temperature is 1105℃, the precision rolling inlet temperature is controlled at 930℃, the steel bar is rapidly cooled after rolling, and the temperature when it is on the cooling bed is 940℃, and the cooling speed of the steel bar on the cooling bed is 2.5-3℃ / s.

[0061] The mechanical property test results of the steel bar prepared in Example 1 are shown in Table 2.

[0062] Table 2

[0063] [R eL / MPa]]> [R m / MPa]]> A / ％ A gt / %]]> [R o m / R o eL ]]> [R o eL / R eL ]]> 650 825 22 14.0 1.27 1.02 650 820 22 14.5 1.26 1.02 655 830 22 12.5 1.27 1.02

[0064] The microstructure of the steel is ferrite+pearlite+small amount of bainite, wherein the proportion of pearlite is 48.5%, the proportion of bainite is 3.5%, and the ferrite grain size is 10.5.

[0065] Example 2

[0066] A 640MPa grade fine-grained high-strength and high-toughness anti-seismic steel bar, the chemical composition and the percentage by weight content are shown in Table 1 of Example 2.

[0067] The preparation method of the 640MPa grade fine-grained high-strength and high-toughness anti-seismic steel bar of the embodiment is as follows: 130t converter smelting→argon station bottom blowing nitrogen→LF furnace refining→square billet continuous casting→hot charging of billet after hot charging→heating→bar rolling mill rolling→cooling bed cooling→shearing→bundling.

[0068] Converter end point C=0.06%, P=0.019%, silicon iron, silicon manganese, vanadium-nitrogen alloy and niobium iron alloying are added when tapping to 1 / 3, 500Kg lime, 400Kg bauxite are used for slagging, and nitrogen gas is blown at the bottom of the ladle during tapping.

[0069] The molten steel is bottom blown with nitrogen for 7 minutes in the argon station.

[0070] The molten steel is deoxidized by adding silicon deoxidizer during LF refining.

[0071] The billet is hot charged to the rolling heating furnace after being continuously cast, and a two-line rolling mode is used to roll the 20mm diameter steel bar, the temperature of the billet before entering the furnace is 550-610℃, the heating temperature of the billet is 1205℃, the soaking temperature is 1200℃, and the heating time is 75 minutes.

[0072] The opening rolling temperature is 1110℃, the entry temperature of the finishing rolling is 960℃, the steel bar is rapidly cooled after rolling, and the temperature when the steel bar is on the cooling bed is 940-960℃, and the cooling speed of the steel bar on the cooling bed is 3-4.5℃ / s.

[0073] The mechanical property test results of the steel bar prepared in Example 2 are shown in Table 3.

[0074] Table 3

[0075] [R eL / MPa]]> [R m / MPa]]> A / ％ A gt / %]]> [R o m / R o eL ]]> [R o eL / R eL ]]> 660 835 21 11.8 1.27 1.03 670 850 22 12.6 1.27 1.05 660 830 21 11.3 1.26 1.03

[0076] The microstructure of the steel is ferrite+pearlite+small amount of bainite, wherein the proportion of pearlite is 47%, the proportion of bainite is 3.5%, and the ferrite grain size is 11-11.5 grade.

[0077] Figure 1 The 500 times metallographic structure schematic diagram of the center of the 640MPa grade fine-grained high-strength and high-toughness anti-seismic steel bar prepared in the embodiment is shown, wherein the white blocky structure is ferrite, the gray structure is pearlite, and the white fine strip-shaped structure is bainite, and the grain size is 11 grade.

[0078] Figure 2 The 500 times metallographic structure schematic diagram of the quarter of the 640MPa grade fine-grained high-strength and high-toughness anti-seismic steel bar prepared in the embodiment is shown, wherein the white blocky structure is ferrite, the gray structure is pearlite, and the white fine strip-shaped structure is bainite, and the grain size is 11.5 grade.

[0079] Example 3

[0080] A 640MPa grade fine-grained high-strength and high-toughness anti-seismic reinforcing steel bar, the chemical composition and the percentage by weight content are shown in Table 1 of Example 3.

[0081] The preparation method of the 640MPa grade fine-grained high-strength and high-toughness anti-seismic reinforcing steel bar of the embodiment has the following preparation process flow: 130t converter smelting→argon station bottom blowing nitrogen→LF furnace refining→square billet continuous casting→hot charging of billets→heating→bar rolling mill rolling→cooling bed cooling→shearing→bundling.

[0082] The converter end point C=0.08%, P=0.022%, silicon iron, silicon manganese, vanadium-nitrogen alloy and niobium iron are added for alloying when tapping to 1 / 3, 500Kg of lime and 400Kg of bauxite are used for slagging, and the ladle is bottom blown with nitrogen for stirring during tapping.

[0083] The molten steel is bottom blown with nitrogen for 4min in the argon station, and the total bottom blowing time is 8min.

[0084] The molten steel is deoxidized by adding silicon deoxidizer during the LF refining process.

[0085] The billets are cold charged to the steel rolling heating furnace, and the steel bars with a diameter of 14mm are rolled by three-cut rolling, the billet heating temperature is 1200℃, the soaking temperature is 1190℃, and the heating time is 85min.

[0086] The opening rolling temperature is 1100℃, the finish rolling inlet temperature is 980℃, the steel bars are rapidly cooled after rolling, and the temperature when the steel bars are on the cooling bed is 930-950℃, and the cooling speed of the steel bars on the cooling bed is 4-5℃ / s.

[0087] The mechanical property test results of the steel bars prepared in Example 3 are shown in Table 4.

[0088] Table 4

[0089] [R eL / MPa]]> [R m / MPa]]> A / ％ A gt / %]]> [R o m / R o eL ]]> [R o eL / R eL ]]> 665 840 20 11.7 1.26 1.04 675 850 20 11.6 1.26 1.05 680 855 22 11.4 1.25 1.06

[0090] The microstructure of the steel is ferrite+pearlite+small amount of bainite, wherein the proportion of pearlite is 47.5%, the proportion of bainite is 4.8%, and the ferrite grain size is 11.5 grade.

[0091] Comparative Example 1

[0092] The chemical composition and the percentage by weight content of the steel are shown in Table 1 of Comparative Example 1, the preparation method is similar to that of Example 1, and the only difference is that the N in the steel is 0.0186%, and (V+0.55Nb) / N is 8.58. The mechanical property test results of the prepared steel bars are shown in Table 5, the microstructure of the steel is ferrite+pearlite+small amount of bainite, wherein the proportion of pearlite is 43%, the proportion of bainite is 2.6%, and the ferrite grain size is 11 grade, wherein the yield strength is 630-635MPa, and the tensile strength is 800-805MPa, which is lower than the specified requirement of the strength of the present application.

[0093] Table 5

[0094]

[0095] Comparative Example 2

[0096] The chemical composition of the steel and the content of the steel in percentage by weight is shown in Table 1 for Comparative Example 2. The method of preparation is similar to that of Example 1 except that the N in the steel is 0.0336% and (V + 0.55Nb) / N is 4.72. The mechanical properties of the steel bars prepared are shown in Table 6 below and the microstructure of the steel is ferrite + pearlite + small amount of bainite, wherein the proportion of pearlite is 48.5% and the proportion of bainite is 3.2% and the ferrite grain size is 9.5 grade. The yield ratio of the steel bars is 1.22-1.23 which is lower than the specified requirement of the yield ratio of the present application.

[0097] Table 6

[0098]

[0099] Comparative Example 3

[0100] The chemical composition of the steel and the content of the steel in percentage by weight is shown in Table 1 for Comparative Example 3. The method of preparation is similar to that of Example 3 except that the Nb in the steel is 0.007%. The mechanical properties of the steel bars prepared are shown in Table 7 below and the microstructure of the steel is ferrite + pearlite + small amount of bainite, wherein the proportion of pearlite is 42% and the proportion of bainite is 3.8% and the ferrite grain size is 10.5 grade. The yield ratio of the steel bars is 1.24-1.25 which is lower than the specified requirement of the yield ratio of the present application.

[0101] Table 7

[0102]

[0103] Comparative Example 4

[0104] The chemical composition of the steel and the content of the steel in percentage by weight is shown in Table 1 for Comparative Example 4. The method of preparation is similar to that of Example 3 except that the billet heating temperature is 1165°C and the soaking temperature is 1170°C. The mechanical properties of the steel bars prepared are shown in Table 8 below and the microstructure of the steel is ferrite + pearlite + small amount of bainite, wherein the proportion of pearlite is 43% and the proportion of bainite is 1.8% and the ferrite grain size is 11 grade. The yield ratio of the steel bars is 1.24-1.25 which is lower than the specified requirement of the yield ratio of the present application.

[0105] Table 8

[0106]

[0107] Comparative Example 5

[0108] The chemical composition and weight percentage content of the steel of Comparative Example 5 are shown in Table 1 as in Example 2. The preparation method is similar to that of Example 2, except that the temperature of the rolled steel on the upper cooling bed is 1010°C. The mechanical property test results of the prepared steel are shown in Table 9, and the microstructure of the steel is ferrite + pearlite + a small amount of bainite, wherein the proportion of pearlite is 51%, the proportion of bainite is 3.6%, and the ferrite grain size is 10 grade. The yield strength of the steel bar is 630-645, which is lower than the specified requirement of the present application.

[0109] Table 9

[0110]

[0111] Comparative Example 6

[0112] The chemical composition and weight percentage content of the steel of Comparative Example 5 are shown in Table 1 as in Example 2. The preparation method is similar to that of Example 2, except that the temperature of the rolled steel on the upper cooling bed is 1010°C. The mechanical property test results of the prepared steel are shown in Table 9, and the microstructure of the steel is ferrite + pearlite + a small amount of bainite, wherein the proportion of pearlite is 51%, the proportion of bainite is 3.6%, and the ferrite grain size is 10 grade. The yield strength of the steel bar is 630-645, which is lower than the specified requirement of the present application.

[0113] Table 10

[0114]

[0115] The above is only the preferred embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing a 640 MPa grade fine-grained high-strength and high-ductility anti-seismic reinforcing steel, characterized in that, The 640MPa grade fine-grained high-strength and high-toughness anti-seismic steel bar contains the following components in mass percentage: C 0.19%-0.28%, Si 0.55%-0.80%, Mn 1.35%-1.60%, V 0.10%-0.18%, Nb 0.01%-0.025%, P≤0.045%, S≤0.045%, N 0.0132%-0.0337%, T.O≤0.0030%, the balance being Fe and unavoidable impurities, while meeting the requirements of carbon equivalent Ceq≤0.58% and 5.75≤(V+0.55Nb) / N≤8; The microstructure of the 640MPa grade fine-grained high-strength and high-toughness anti-seismic steel bar is ferrite + pearlite + a small amount of bainite, wherein the proportion of pearlite is≥45%, the proportion of bainite is 2%-5%, and the ferrite grain size is 10.5-12 grade; The preparation process route is as follows: converter smelting→argon station bottom blowing gas stirring→LF furnace refining→continuous casting→steel billet heating→rolling and post-rolling cooling, wherein: The converter smelting process includes: controlling the converter end point P≤0.035%, starting to add ferrosilicon and silicomanganese at 1 / 3 of the converter tapping, adding vanadium-nitrogen alloy and niobium ferroalloy at half of the ferrosilicon and silicomanganese addition, then adding an appropriate amount of lime and bauxite for slag washing, and starting the bottom blowing gas stirring of the ladle for 2-4min; When the converter end point C≤0.04%, an appropriate amount of aluminum or silicon deoxidizer needs to be added during the tapping process; Nitrogen is added to the molten steel by bottom blowing nitrogen gas or adding nitrogen increasing agent, the bottom blowing nitrogen gas is calculated from the converter tapping, and the bottom blowing gas time is 7-10min, the nitrogen increasing agent includes one or more of rare earth nitrogen alloy and silicon nitride; The LF refining process includes: adjusting the molten steel temperature by electric heating to meet the continuous casting pouring requirements, adding alloy to fine-tune the composition according to the composition of the steel, adding lime to form slag, adding silicon deoxidizer for diffusion deoxidization, reducing the oxidizing property of the ladle top slag, removing inclusions in the steel, obtaining molten steel with required chemical composition, temperature meeting continuous casting pouring and high cleanliness; The steel billet heating process includes three stages of preheating, heating and soaking: when the steel billet is hot sent and hot charged to the rolling heating furnace, the preheating temperature is 600-800℃, the heating temperature is 1170-1210℃, and the soaking temperature is 1160-1200℃, and the total heating time is≥70min; when the steel billet is cold charged to the rolling heating furnace, the preheating temperature is 500-700℃, the heating temperature is 1180-1220℃, and the soaking temperature is 1170-1210℃, and the total heating time is≥80min; The rolling process includes three stages of rough rolling, intermediate rolling and finish rolling; the rough rolling opening temperature is 1080-1130 DEG C, after rough rolling and intermediate rolling, the finish rolling inlet temperature is controlled at 900-1000 DEG C by using a water cooling device; after finish rolling, the temperature of the reinforcing bar on the cooling bed is controlled at 900-980 DEG C by using a water cooling device, and the cooling speed of the reinforcing bar on the cooling bed is 2.5-7 DEG C / s; the rolling adopts slitting rolling or single line rolling, and the slitting rolling is any one of two slitting, three slitting, four slitting or five slitting, and the temperature deviation of the reinforcing bar on the cooling bed after slitting rolling is not more than 20 DEG C.

2. The method of producing a 640 MPa grade fine-grained high-strength high-ductility seismic reinforcing bar according to claim 1, characterized by, The chemical composition of the small-diameter reinforcing bar with a diameter of 12-14 mm is as follows: C 0.26%-0.28%, Si 0.70%-0.80%, Mn 1.45%-1.55%, V 0.10%-0.16%, Nb 0.01%-0.025%, P≤0.045%, S≤0.045%, N 0.0132%-0.0302%, T.O≤0.0030%, and the balance is Fe and inevitable impurities; meanwhile, the carbon equivalent Ceq≤0.58%, and 5.75≤(V+0.55Nb) / N≤8.

3. The method of producing 640 MPa grade fine-grained high-strength high-ductility seismic reinforcing steel according to claim 1, characterized in that, The chemical composition of the large and medium-diameter reinforcing bar with a diameter of 16-40 mm is as follows: C 0.26%-0.28%, Si 0.70%-0.80%, Mn 1.45%-1.55%, V 0.12%-0.18%, Nb 0.01%-0.025%, P≤0.045%, S≤0.045%, N 0.0157%-0.0337%, T.O≤0.0030%, and the balance is Fe and inevitable impurities; meanwhile, the carbon equivalent Ceq≤0.58%, and 5.75≤(V+0.55Nb) / N≤8.

4. The method of manufacturing a 640 MPa grade fine-grained high strength and toughness anti-seismic reinforcing bar according to any one of claims 1-3, characterized in that, The yield strength R eL ≥ 640 MPa, tensile strength R m ≥ 815 MPa, maximum force total elongation A gt ≥ 10%, measured tensile strength to measured yield strength ratio R o m / R o eL ≥ 1.25, measured yield strength to yield strength characteristic value ratio R o eL / R eL ≤ 1.30.

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