Production method of 635MPa-grade anti-seismic straight deformed steel bar

Abstract

The invention discloses a production method of 635MPa-grade anti-seismic straight deformed steel bar, which comprises the following steps: controlling steelmaking components in percentage by weight: 0.22%-0.28% of C, 0.45%-0.80% of Si, 1.30%-1.50% of Mn, 0.090%-0.150% of V, 0.010%-0.020% of Nb, less than or equal to 0.04% of P and less than or equal to 0.04% of S; molten steel is smelted through an LF furnace, the argon blowing time of CAS refining is longer than 10 min, and the bottom argon blowing pressure is 0.5-1.2 MPa; during continuous casting, the steel casting superheat degree and the pulling speed are controlled so as to control the proportion of casting blank columnar crystals; the casting blank is rolled after being heated by a heating furnace, and the casting blank heating time, the rolling starting temperature and the rolling reduction of the first two passes are controlled. The casting blank quality is improved and the probability of cold bending cracking defects of the deformed steel bar is reduced through continuous casting production of the technological parameters of the superheat degree and the pulling speed of the cast steel.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of steel metallurgy steelmaking and rolling, in particular to a production method of 635MPa-grade anti-seismic straight bar deformed steel bar. BACKGROUND

[0002] The 635MPa-grade deformed steel bar has the characteristics of high strength, good performance and good anti-seismic performance, and is applied to high-rise, large-span and high anti-seismic requirement buildings. Compared with ordinary steel bars, the anti-seismic steel bar additionally has three quality characteristic values of strong yield ratio, yield characteristic ratio and maximum force total elongation, and is required to have high and stable yield strength and good ductility (represented by the maximum force total elongation and the strong yield ratio indexes). The good strength and plasticity of the anti-seismic steel bar make the time interval from deformation to fracture of the steel bar longer, so as to realize the anti-seismic design of "the time interval from deformation to collapse of the building structure is as long as possible".

[0003] The high-strength anti-seismic steel bar is produced by using micro-alloying technology, which can not only stabilize the performance of the steel bar, but also meet the standard requirements. The micro-alloying technology mainly adds trace alloying elements such as niobium and vanadium to the molten steel to form carbides, nitrides or carbonitrides dispersedly distributed in the matrix to produce strengthening. In the production of steel materials, nitrogen can reduce the impact toughness of the steel and is considered to be a harmful element, but nitrogen has a strong affinity with vanadium, and increasing the content of nitrogen can enhance the precipitation strengthening effect of vanadium, thereby improving the strength of the steel bar.

[0004] However, in the prior art, the steel bar of this grade is not mass-produced, the steelmaking composition design lacks verification, and the overheat degree and the withdrawal speed control in the continuous casting process are unreasonable, which can cause excessive growth of columnar crystals and cause center porosity and other defects. The heating temperature and the reduction rate during rolling are not well matched, which can easily lead to insufficient fragmentation of austenite grains, and high cold bending cracking rate. SUMMARY

[0005] In order to overcome the above-mentioned shortcomings of the prior art, the purpose of the present application is to provide a production method of 635MPa-grade anti-seismic straight bar deformed steel bar to solve the problems raised in the background art.

[0006] The technical scheme adopted by the present application to solve its technical problems is: a production method of 635MPa-grade anti-seismic straight bar deformed steel bar, comprising the following steps:

[0007] The steelmaking composition is controlled, and the content of each component is as follows: C: 0.22%-0.28%, Si: 0.45%-0.80%, Mn: 1.30%-1.50%, V: 0.090%-0.150%, Nb: 0.010%-0.020%, P≤0.04%, and S≤0.04%, in percentage by weight.

[0008] The molten steel is smelted by the LF furnace, the argon blowing time of CAS refining is more than 10 minutes, and the bottom argon blowing pressure is 0.5-1.2 MPa.

[0009] The overheat degree and the pulling speed of the molten steel are controlled during continuous casting to control the columnar crystal ratio of the casting blank.

[0010] The casting blank is rolled after being heated by a heating furnace, and the heating time of the casting blank, the starting rolling temperature and the reduction of the first two passes are controlled.

[0011] As a further improvement of the application, the converter tapping adopts vanadium-nitrogen alloy and niobium-phosphorus ferro-alloy micro-alloying, and silicon-calcium-barium deoxidizers, silicon-aluminum-barium deoxidizers, carbon powder, silicon-manganese alloy, silicon-iron alloy, vanadium-nitrogen alloy and niobium-phosphorus ferro-alloy are added to the molten steel at 1 / 4 of the tapping for micro-alloying.

[0012] As a further improvement of the application, the casting blank heating after the heating furnace includes a heating time of 120 minutes and a starting rolling temperature of 1080-1150 DEG C.

[0013] As a further improvement of the application, the overheat degree of the molten steel for continuous casting is less than or equal to 40 DEG C, and the pulling speed is less than or equal to 3.5 m / min.

[0014] As a further improvement of the application, the reduction of the first two passes is greater than or equal to 28% and greater than or equal to 32% respectively, and the whole process is without water cooling process.

[0015] As a further improvement of the application, the molten steel is subjected to slagging and desulfurization treatment after entering the LF furnace, Si-Ca wire is fed before entering the station, and soft argon blowing treatment is performed.

[0016] As a further improvement of the application, the square billet with a diameter of 155 mm is used during continuous casting, the electromagnetic stirring is started in the crystallizer, the current is 320-350 A, the frequency is 3-5 Hz, and the temperature of the tundish is controlled at 1515-1525 DEG C.

[0017] As a further improvement of the application, the casting blank is heated by a heating furnace after being sent by a hot rail, the preheating temperature is 920-1020 DEG C, the heating temperature is 1120-1200 DEG C, and the soaking temperature is 1150-1200 DEG C.

[0018] As a further improvement of the application, the final rolling speed of the rolling is 15 m / s, and the austenite grain of the casting blank is fully broken by controlling the reduction of the first two passes.

[0019] As a further improvement of the application, the yield ratio of the 635 MPa grade screw steel is greater than or equal to 1.25, the yield characteristic ratio is less than or equal to 1.30, and the maximum force total elongation Agt is greater than or equal to 9%.

[0020] Compared with the prior art, the application has the following beneficial effects:

[0021] The production method of the 635MPa grade threaded steel of the present application avoids cold bending cracking of the threaded steel by optimizing the steelmaking micro alloying, refining process operation, continuous casting process operation, rolling temperature and other processes, the argon blowing operation at the CAS station has a clear argon gas pressure control range, the production operation is strong and is beneficial to improve the cleanliness of the molten steel, by specifying the continuous casting production pouring superheat and the process parameters of the casting speed, the columnar crystal ratio of the casting blank is controlled, the casting blank quality is improved, by specifying the casting blank heating time, the casting blank rolling temperature, the 2-way reduction amount before the casting blank rolling and other process parameters, the probability of cold bending cracking defects of the threaded steel is reduced. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 It is a production flowchart of the 635MPa grade anti-seismic straight threaded steel of the present application.

[0023] Figure 2 It is a metallographic structure diagram of the 25mm specification 635MPa grade anti-seismic threaded steel of the first embodiment of the present application. DETAILED DESCRIPTION

[0024] In order to clearly and completely understand the technical solutions, the present application will be further described in combination with embodiments and drawings. Obviously, the described embodiments are only part of the embodiments of the present application, and all other embodiments obtained by those skilled in the art without creative labor belong to the protection scope of the present application.

[0025] It should be understood that when used in the present specification and the appended claims, the terms "comprise" and "include" indicate the presence of described features, integers, steps, operations, elements, and / or components, but do not exclude one or more other features, integers, steps, operations, elements, components, and / or sets thereof.

[0026] It should also be understood that the terms used in the present application specification are only for the purpose of describing specific embodiments and do not intend to limit the present application. As used in the present application specification and the appended claims, unless the context clearly indicates otherwise, the singular forms "a", "an" and "the" are intended to include the plural forms.

[0027] It should be further understood that the term "and / or" used in the present application specification and the appended claims means any combination of one or more of the associated listed items and all possible combinations, and includes these combinations.

[0028] The embodiment of the present application provides a 635MPa grade anti-seismic straight bar thread steel production method, comprising the following steps: steelmaking component control, according to the percentage by weight, C: 0.22%-0.28%, Si: 0.45%-0.80%, Mn: 1.30%-1.50%, V: 0.090%-0.150%, Nb: 0.010%-0.020%, P≤0.04%, S≤0.04%;

[0029] The molten steel is smelted by the LF furnace, the argon blowing time of the CAS refining is greater than 10 minutes, and the bottom argon blowing pressure is 0.5-1.2 MPa;

[0030] The pouring superheat degree and the pulling speed are controlled during continuous casting to control the columnar crystal ratio of the casting blank.

[0031] The casting blank is rolled after heating by the heating furnace, and the casting blank heating time, the opening rolling temperature and the first two pass reduction are controlled.

[0032] The 635MPa grade thread steel production method of the present application avoids the cold bending cracking of the thread steel by optimizing the steelmaking micro-alloying, the refining process operation, the continuous casting process operation and the rolling temperature, the argon blowing operation at the CAS station has a clear argon blowing gas pressure control range, the production operability is strong and is beneficial to improving the molten steel cleanliness, the pouring superheat degree and the pulling speed process parameters are determined during the continuous casting production, the columnar crystal ratio of the casting blank is controlled, the casting blank quality is improved, the casting blank heating time, the casting blank opening rolling temperature and the first two pass reduction of the casting blank are determined, and the probability of the cold bending cracking defect of the thread steel is reduced; the production is smelted by the LF furnace, the argon blowing time of the molten steel in the CAS refining is greater than 10 minutes, the inclusions in the molten steel have a longer floating time during the refining process at the CAS station, the bottom argon blowing gas pressure range of the molten steel tank is 0.5-1.2 MPa, the effect of the refining blowing gas on the inclusion removal is ensured, and the secondary oxidation of the molten steel due to the violent stirring is avoided.

[0033] In one embodiment of the present application, when the converter is tapped, vanadium-nitrogen alloy and niobium-phosphorus ferroalloy are used for micro-alloying, silicon-calcium-barium deoxidizer, silicon-aluminum-barium deoxidizer, carbon powder, silicon-manganese alloy, silicon-iron alloy, vanadium-nitrogen alloy and niobium-phosphorus ferroalloy are added to the molten steel at 1 / 4 of the tapping to perform micro-alloying. By adding vanadium-nitrogen alloy and niobium-phosphorus ferroalloy at 1 / 4 of the tapping, VN precipitated phases are formed by using the strong affinity of vanadium and nitrogen, the strength of the reinforcing bar is improved by precipitation strengthening, the addition of silicon-calcium-barium deoxidizer and silicon-aluminum-barium deoxidizer can reduce the oxygen content of the molten steel and reduce brittle inclusions such as Al2O3 and SiO2, and the argon blowing process at the CAS station is used to improve the inclusion floating rate to more than 90%, improve the purity of the molten steel, and avoid cold bending cracking caused by the aggregation of inclusions.

[0034] In one embodiment of the present application, the slab is heated in a heating furnace and then rolled, including a slab heating time of 120 min and a rolling start temperature of 1080-1150℃. The slab is heated for 120 min to ensure that the slab is fully austenitized at a heating section temperature of 1120-1200℃ and a soaking section temperature of 1150-1200℃, and to dissolve carbides and micro-alloyed carbonitrides. Long-time holding reduces the temperature difference between the core and the surface of the slab, eliminates residual stress generated during casting, and avoids edge cracks caused by stress concentration during rolling.

[0035] In one embodiment of the present application, the reduction rates of the first two passes are ≥28% and ≥32%, respectively, and the whole process is free of water cooling. When the rolling start temperature is controlled at 1080-1150℃, the austenite is in the active recrystallization zone, and the large reduction rates of the first two passes can break the initial austenite grains. The temperature range of 1080-1150℃ avoids abnormal grain growth caused by a temperature >1150℃ and ensures that dynamic recrystallization is fully carried out during rolling. The final product has a uniform ferrite + pearlite microstructure, and no tempered martensite is present in the base circle.

[0036] In one embodiment of the present application, the overheat degree of the molten steel for continuous casting is ≤40℃, and the withdrawal speed is ≤3.5 m / min. By controlling the overheat degree of the molten steel for continuous casting to be ≤40℃, the undercooling degree of the molten steel is reduced, and the solidification time is extended by controlling the withdrawal speed to be ≤3.5 m / min. The overheat degree of the molten steel for continuous casting is ≤40℃, and the molten steel tank is covered for insulation. The withdrawal speed is controlled to be ≤3.5 m / min to avoid the development of columnar grains in the slab.

[0037] In one embodiment of the present application, the molten steel is subjected to a reduction slag operation and desulfurization treatment after entering the LF furnace, Si-Ca wire is fed before entering the station, and soft argon blowing treatment is performed. CaO in the reduction slag reacts with [O] in the molten steel to form CaO·Al2O3 low-melting-point inclusions, promotes the aggregation of inclusions, and creates conditions for subsequent soft argon blowing removal. The calcium element in the Si-Ca wire reacts with Al2O3 in the steel to form 12CaO·7Al2O3 plastic inclusions before entering the station, reducing the size of the inclusions and avoiding cracking during rolling. Soft argon blowing treatment removes inclusions by driving the migration of inclusions through bubble floating,

[0038] In one embodiment of the present application, a 155 mm square billet is used for continuous casting, electromagnetic stirring is started in the mold, the current is 320A-350A, the frequency is 3-5 Hz, and the tundish temperature is controlled at 1515-1525℃. The forced convection generated by electromagnetic stirring promotes the migration of inclusions, and the tundish temperature is controlled at 1515-1525℃ to increase the floating speed of the inclusions.

[0039] In one embodiment of the present application, the casting blank is hot sent to a steel heating furnace after hot sending by a hot sending track, the preheating section temperature is 920-1020℃, the heating section temperature is 1120-1200℃, and the soaking section temperature is 1150-1200℃. Slowly increasing the temperature of the preheating section 920-1020℃ can make the temperature difference between the surface and the core of the casting blank ≤50℃, eliminate thermal stress, avoid surface cracks, the heating section temperature 1120-1200℃ can improve the solid solubility of micro-alloy carbonitride, and the vanadium and niobium elements are fully dissolved into austenite, so that the rolling process is rolled and precipitated, and when the soaking section temperature is 1150-1200℃, the temperature uniformity of the casting blank is controlled within ±30℃, the austenitization is sufficient, and the finished product after rolling is uniform ferrite + pearlite, and the base circle is free of tempered martensite.

[0040] In one embodiment of the present application, the final rolling speed of the rolling is 15 m / s, and the austenite grains of the casting blank are fully broken by controlling the reduction rate of the first two passes. When the reduction rate of the first two passes is ≥28% and ≥32%, the austenite grains undergo strong plastic deformation, and the final rolling speed is 15 m / s. The metallographic detection shows that the base circle structure of the finished product is uniform ferrite + pearlite, and the base circle is free of tempered martensite.

[0041] In one embodiment of the present application, the yield ratio of the produced 635MPa grade threaded steel is ≥1.25, the yield characteristic ratio is ≤1.30, and the maximum total elongation Agt is ≥9%.

[0042] Case 1:

[0043] Taking the production of 25mm specification 635MPa grade anti-seismic threaded steel as an example:

[0044] The composition standard of 25mm specification 635MPa anti-seismic steel is as follows: C: 0.22%-0.28%; Si: 0.45%-0.80%; Mn: 1.30%-1.50%; P≤0.04%; S≤0.04%; V: 0.090%-0.150%; Nb: 0.010%-0.020%.

[0045] 100 tons of molten iron and 22 tons of scrap steel are added, and the composition of the molten iron is: C: 0.42%; Si: 0.34%; Mn: 0.38%; P: 0.14%; S: 0.020%; and the temperature of the molten iron is 1299℃.

[0046] The converter smelting adopts high-ladle-repairing blowing process, and the composition of the molten steel at the end of smelting is: C: 0.08%; Si: 0.0036%; Mn: 0.15%; P: 0.015%; S: 0.021%; and the end temperature is 1639℃.

[0047] Converter tapping with vanadium-nitrogen alloy plus niobium-phosphorus ferro-alloy micro-alloying, at 1 / 4 tapping time, into the molten steel, add: silicon-calcium-barium deoxidizer 20 kg, silicon-aluminum-barium deoxidizer 20 kg, carbon powder 180 kg, silicon-manganese alloy 2235 kg, silicon-ferro-alloy 420 kg, vanadium-nitrogen alloy 140 kg, niobium-phosphorus ferro-alloy 42 kg.

[0048] Converter tapping 115.3 tons, into the refining station composition: C: 0.24%; Si: 0.48%; Mn: 1.30%; P: 0.020%; S: 0.021%; V: 0.093%; Nb: 0.013%, into the refining station molten steel temperature 1583℃, in the station add carbon additive 30 kg, silicon-manganese alloy 100 kg: refining argon blowing time 12 minutes, molten steel ladle argon pressure range 0.5-1.2 MPa, out of station temperature 1558℃.

[0049] Molten steel into the LF furnace temperature sampling, then the reduction slag operation, desulfurization treatment. Before entering the station, feeding Si-Ca wire and soft argon blowing treatment, to achieve the purpose of degassing, inclusion removal, then again temperature sampling, after adding covering agent out of station on the platform.

[0050] Continuous casting machine 5 machine 5 flow, cross-section size 155 mm square billet, mold opening electromagnetic stirring, current 320A-350A, frequency 3-5 Hz, HRB635 liquidus temperature 1505℃, tundish temperature range 1515-1525℃; drawing speed 3.3-3.4 m / min; drawing cycle 32 min. Tundish sampling results: C: 0.26%; Si: 0.48%; Mn: 1.36%; P: 0.021%; S: 0.011%; V: 0.093%; Nb: 0.013%.

[0051] Molten steel ladle opening tundish temperature and flow speed as follows:

[0052]

[0053] Continuous casting billet respectively in the early and middle and late stage of the furnace pouring each flow each take a low, the low-grade rating results as follows:

[0054]

[0055] Steel product composition test results: C: 0.27%; Si: 0.49%; Mn: 1.35%; P: 0.021%; S: 0.012%; V: 0.093%; Nb: 0.013%.

[0056] The casting blank is directly sent into the rolling steel heating furnace after being sent by the hot sending track, the preheating section temperature is 920-1020℃, the heating section temperature is 1120-1200℃, the soaking section temperature is 1150-1200℃, the furnace time is 120min, the rolling starting temperature is 1100℃, the final rolling speed is 15m / s, the first pass reduction is 29%, and the second pass reduction is 32%.

[0057] The mechanical property detection result of the steel material is as follows:

[0058]

[0059] The finished product metallographic structure is ferrite+pearlite, and there is no tempered martensite on the base circle, and the metallographic picture is as Figure 2 .

[0060] According to the technical scheme and technical concept of the present application, the person skilled in the art can make other corresponding transformation schemes without creative mental labor, which all belong to the protection scope of the present application.

Claims

1. A method for producing 635MPa grade seismic resistant straight threaded steel bar, characterized in that: The following steps are involved: Steelmaking composition control, by weight percentage, C: 0.22%-0.28%, Si: 0.45%-0.80%, Mn: 1.30%-1.50%, V: 0.090%-0.150%, Nb: 0.010%-0.020%, P≤0.04%, S≤0.04%; The molten steel is smelted in LF furnace, and the CAS refining argon blowing time is greater than 10 minutes and the bottom blowing argon pressure is 0.5-1.2MPa; During continuous casting, control the superheat of the steel and the casting speed to control the proportion of columnar crystals in the ingot; The ingot is heated in a heating furnace and then rolled, and the heating time of the ingot, the starting rolling temperature and the reduction in the first two passes are controlled.

2. The method for producing 635MPa grade seismic resistant straight threaded steel bars according to claim 1, characterized in that: When the converter is tapping steel, microalloying of vanadium-nitrogen alloy and niobium-phosphorus-iron block alloy is adopted. Silicon-calcium-barium deoxidizer, silicon-aluminum-barium deoxidizer, carbon powder, silicon-manganese alloy, silicon-iron alloy, vanadium-nitrogen alloy and niobium-phosphorus-iron block alloy are added to the molten steel for microalloying when 1 / 4 of the steel is tapped.

3. The method for producing 635MPa grade seismic resistant straight threaded steel bars according to claim 2, characterized in that: The casting blank is heated in a heating furnace and then rolled, including a casting blank heating time of 120 minutes and a rolling start temperature of 1080-1150°C.

4. The method for producing 635MPa grade seismic resistant straight threaded steel bars according to claim 3, characterized in that: The superheat of molten steel in continuous casting is ≤40℃, and the casting speed is ≤3.5m / min.

5. The method for producing 635MPa grade seismic resistant straight threaded steel bars according to claim 4, characterized in that: The reduction rates of the first two passes are ≥28% and ≥32% respectively, and there is no water cooling process throughout the process.

6. The method for producing 635MPa grade seismic resistant straight threaded steel bars according to claim 1, characterized in that: After the molten steel enters the LF furnace, it undergoes a reducing slag making operation and a desulfurization treatment, and before entering the station, it is fed into the Si-Ca line and undergoes a soft argon blowing treatment.

7. The method for producing 635MPa grade seismic resistant straight threaded steel bars according to claim 1, characterized in that: During continuous casting, 155mm square billets are used, electromagnetic stirring is turned on in the crystallizer, the current is 320A-350A, the frequency is 3-5Hz, and the tundish temperature is controlled at 1515-1525℃.

8. The method for producing 635MPa grade seismic resistant straight threaded steel bars according to claim 1, characterized in that: The ingot is hot-transported by a hot-transport track and then enters a steel rolling heating furnace, with a preheating section temperature of 920-1020°C, a heating section temperature of 1120-1200°C, and a soaking section temperature of 1150-1200°C.

9. The method for producing 635MPa grade seismic resistant straight threaded steel bars according to claim 5, characterized in that: The final rolling speed is 15 m / s, and the austenite grains of the ingot are fully broken by controlling the reduction rates of the first two passes.

10. The method for producing 635MPa grade seismic resistant straight threaded steel bars according to claim 1, characterized in that: The strength-to-yield ratio of the produced 635MPa grade threaded steel is ≥1.25, the yield characteristic ratio is ≤1.30, and the maximum force total elongation Agt is ≥9%.

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