Method for preparing 635MPa-grade 14-specification steel bar

Abstract

The invention belongs to the technical field of steel bar production, and particularly discloses a method for preparing 635MPa-grade 14-specification steel bars. According to the method, V and Nb composite microalloying design is adopted, a square billet of 150 mm * 150 mm is formed through converter smelting, LF refining and continuous casting, and then the high-performance hot-rolled ribbed steel bar is produced through controlled rolling and two-section controlled cooling (ultrafast cooling and slow cooling) processes. The yield strength of the steel bar is not less than 635 MPa, the yield-strength ratio is not less than 1.30, the maximum force total elongation Agt is not less than 9.6%, the requirements of the anti-seismic steel bar are completely met, and the steel bar has the advantages of high strength, good ductility, high material saving rate and the like, and is suitable for industrial production of the high-strength anti-seismic steel bar for a building structure.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of steel bar production, in particular to a method for preparing 635MPa grade Ø14 specification steel bar. BACKGROUND

[0002] Hot-rolled ribbed steel bar is a key material in building structure, and its strength and seismic performance are crucial. GB 1499.2 standard has explicit upper limit requirements on the chemical composition of ordinary grade steel bars such as HRB400E (e.g. C≤0.28%, Si≤0.80%, Mn≤1.60%). In order to achieve high yield strength of 635MPa or above, micro-alloy elements such as Nb, V, Ti are usually added to improve the strength through fine-grain strengthening and precipitation strengthening mechanism. However, simply relying on increasing alloy content or using ultra-fast cooling process may easily lead to unqualified strength-yield ratio and decreased elongation after fracture, etc., which cannot meet the comprehensive performance requirements of seismic steel bars. Therefore, there is an urgent need for a steel bar preparation method that can balance high strength, high ductility and good seismic performance. SUMMARY

[0003] The purpose of the present application is to provide a method for preparing 635MPa grade Ø14 specification steel bar, which can produce hot-rolled ribbed steel bar with high strength, high ductility and excellent seismic performance by combining composite micro-alloying with precise controlled rolling and controlled cooling process.

[0004] To achieve the above-mentioned purpose, the basic scheme provided by the present application is as follows: a method for preparing 635MPa grade Ø14 specification steel bar, comprising the following steps: (1) Smelting and refining: after converter smelting, the molten steel is refined in an LF furnace, and the chemical composition of the molten steel is controlled as follows: C: 0.26-0.28%, Si: 0.74-0.78%, Mn: 1.51-1.55%, V: 0.11-0.115%, Nb: 0.015-0.020%, N: 0.016-0.024%, P≤0.03%, S≤0.03%, and carbon equivalent CEQ≤0.58%; (2) Continuous casting: the refined molten steel is cast into a 150mm×150mm square billet; (3) Rolling and cooling: after heating the square billet in the soaking section of the heating furnace at 1080-1130℃, it is rolled at 1040-1070℃, and the wire drawing temperature is controlled at 850-880℃; after rolling, two-stage controlled cooling is adopted: first, ultra-fast cooling at a cooling rate of more than 100℃ / s for 1 second; then, entering the slow cooling stage, the basic speed of the air cooling line is set to 0.9, the speed coefficients of each stage are controlled as 0.50, 0.52, 0.55, 0.57, 0.60, 0.62, 0.64, 0.65, 0.70, 0.7, 0.72, 0.73, respectively, and No.1-4 air fans are opened with an opening degree of 80%.

[0005] Further, the target composition of the molten steel after refining in step (1) is: C: 0.28%, Si: 0.77%, Mn: 1.54%, V 0.113%, Nb: 0.018%, N: 0.02%.

[0006] Further, the wire rod machine in step (3) has a leading coefficient of 1.025, and the product outlet speed is not more than 36 m / s.

[0007] Further, the steel bar produced by the method has a yield strength of ≥635 MPa, a tensile strength of ≥885 MPa, a strength-to-yield ratio of ≥1.30, a maximum force total elongation of Agt ≥9.6%, and a grain size of ≥10.0 grade.

[0008] Further, the steel bar has a microstructure of ferrite + pearlite.

[0009] Compared with the prior art, the advantages of the present application are: 1. The present application adopts vanadium-niobium composite micro-alloying technology, adds V and Nb in the steel, adopts appropriate temperature and control cooling speed during rolling, promotes the precipitation of carbonitride, and improves the strength of the steel bar. The 635MPa high-strength anti-seismic coil steel bar is rolled, and the composition and mechanical properties of the finished product are stable and qualified.

[0010] 2. The present application adopts a more fine controlled rolling and controlled cooling process combination: ultra-fast cooling + subsequent slow cooling control. The first step (ultra-fast cooling: immediately after rolling, ultra-fast cooling (>100℃ / s) is applied to supercool the austenite to the target temperature interval, and the precipitation of ferrite is inhibited. The second step (slow cooling): after 1 second of ultra-fast cooling, the rolled material is allowed to "relax" at the core temperature. During this period, micro-alloyed carbonitride (such as Nb, V compounds) will precipitate, and part of the supercooled austenite will transform into fine bainite. Thus, the strength-to-yield ratio and the maximum force total elongation meet the anti-seismic requirements.

[0011] 3. The steel bar produced by the method of the present application has a performance fluctuation of ≤5 MPa, a uniform microstructure (ferrite + pearlite, grain size 10 grade), a yield strength of ≥635 MPa, a strength-to-yield ratio of ≥1.3, and a maximum force total elongation of ≥9%; the material saving rate is 33%, the CO2 emission is reduced by about 2 tons / ton of steel, and the concrete vibration compactness is improved. DETAILED DESCRIPTION

[0012] The present application will be further described in detail through specific embodiments: A method for preparing a 635MPa grade Ø14 specification steel bar, comprising the following steps: (1) Smelting and refining: after converter smelting, the molten steel is refined in the LF furnace, and the weight percentage of the molten steel chemical composition is controlled as follows: C: 0.26-0.28%, Si: 0.74-0.78%, Mn: 1.51-1.55%, V: 0.11-0.115%, Nb: 0.015-0.020%, N: 0.016-0.024%, P≤0.03%, S≤0.03%, and carbon equivalent CEQ≤0.58%; after refining, the target composition of the molten steel is as follows: C: 0.28%, Si: 0.77%, Mn: 1.54%, V 0.113%, Nb: 0.018%, and N: 0.02%; (2) Continuous casting: the refined molten steel is cast into 150mm×150mm square billets; (3) Rolling and cooling: after the square billets are heated in the heating furnace at 1080-1130℃, the rolling is started at 1040-1070℃, and the wire drawing temperature is controlled at 850-880℃; after rolling, two-stage controlled cooling is adopted: first, ultra-fast cooling is performed at a cooling rate of more than 100℃ / s for 1 second; then, the billets enter the slow cooling stage, the basic speed of the air cooling line is set to 0.9, the speed coefficients of the stages are controlled as 0.50, 0.52, 0.55, 0.57, 0.60, 0.62, 0.64, 0.65, 0.70, 0.7, 0.72, 0.73 in sequence, and the No.1-4 air fans are opened with an opening degree of 80%; the wire drawing machine has a leading coefficient of 1.025, and the product outlet speed is not more than 36m / s.

[0013] The steel bar produced by the method has the following performances: yield strength≥635MPa, tensile strength≥885MPa, strength-yield ratio≥1.30, maximum total elongation rate Agt≥9.6%, and grain size≥10.0 grade; the microstructure of the steel bar is ferrite+pearlite.

[0014] The above is only an embodiment of the present application, and the specific structure and characteristics of the scheme are not described in detail. It should be pointed out that for those skilled in the art, without departing from the structure of the present application, a number of modifications and improvements can be made, which should also be considered as the protection scope of the present application, and these will not affect the effect and practicality of the present application. The protection scope claimed in the present application should be subject to the content of its claims, and the specific implementation mode and the like recorded in the specification can be used to explain the content of the claims.

Claims

1. A method of producing a 635 MPa grade of steel bar of the Ø 14 gauge, characterized in that, The method comprises the following steps: (1) smelting and refining: after converter smelting, the molten steel is refined in a LF furnace, and the chemical composition of the molten steel is controlled to be: C: 0.26-0.28%, Si: 0.74-0.78%, Mn: 1.51-1.55%, V: 0.11-0.115%, Nb: 0.015-0.020%, N: 0.016-0.024%, P≤0.03%, S≤0.03%, and carbon equivalent CEQ≤0.58%; (2) continuous casting: the refined molten steel is cast into 150mm*150mm square billets; (3) rolling and cooling: after the square billets are heated in a heating furnace at a soaking section of 1080-1130℃, the rolling is started at 1040-1070℃, and the wire drawing temperature is controlled at 850-880℃; after rolling, two-stage controlled cooling is adopted: first, ultra-fast cooling is performed at a cooling rate of more than 100℃ / s for 1 second; then, the billets enter a slow cooling stage, the basic speed of the air cooling line is set to 0.9, the speed coefficients of the stages are controlled to be 0.50, 0.52, 0.55, 0.57, 0.60, 0.62, 0.64, 0.65, 0.70, 0.7, 0.72, 0.73 in sequence, and the No.1-4 air fans are opened with an opening degree of 80%.

2. A method of producing 635 MPa grade of ø 14 size reinforcement as claimed in claim 1, wherein, In the step (1), the target composition of the molten steel after refining is: C: 0.28%, Si: 0.77%, Mn: 1.54%, V: 0.113%, Nb: 0.018%, and N: 0.02%.

3. A method of producing 635 MPa grade of ø 14 size reinforcement as claimed in claim 1, wherein, In the step (3), the wire drawing machine has an advance coefficient of 1.025, and the product outlet speed is not more than 36m / s.

4. A method of producing 635 MPa grade of ø 14 size reinforcement as claimed in claim 1, wherein, The steel bars produced by the method have a yield strength of ≥635MPa, a tensile strength of ≥885MPa, a strength-to-yield ratio of ≥1.30, a maximum force total elongation Agt of ≥9.6%, and a grain size of ≥10.0 grade.

5. The method of producing 635 MPa grade of ø 14 size reinforcement as claimed in claim 1 wherein, The microstructure of the steel bars is ferrite+pearlite.