Preparation method of HRB400E earthquake-resistant steel bars produced by high-speed single-line rolling

Abstract

The present invention relates to the field of steel smelting technology, and more specifically, to a method for preparing HRB400E earthquake-resistant steel bars by high-speed single-line rolling. The method comprises converter smelting, steel tapping, argon blowing, titanium iron addition, continuous casting, heating, rough rolling, intermediate rolling, pre-finishing rolling, temperature control before finishing rolling, finishing rolling one, temperature control during finishing rolling, finishing rolling two, temperature control after rolling, and cooling bed placement. The temperature control step before finishing rolling includes two stages of temperature control, the temperature control step during finishing rolling includes three stages of temperature control, and the temperature control step after rolling includes two stages of temperature control. The preparation method of the present invention intersperses finishing rolling one and finishing rolling two in the multi-stage temperature control step to realize multi-stage temperature control and rolling technology, and can combine the multi-stage temperature control and rolling technology with Ti microalloying components to improve the strength and toughness of the earthquake-resistant steel bars, reduce manufacturing costs, and improve surface quality.

Description

Technical Field

[0001] The present invention relates to the technical field of steel smelting, and in particular to a method for preparing HRB400E earthquake-resistant steel bars by high-speed single-line rolling. Background Art

[0002] HRB400E earthquake-resistant rebar is an important steel material in the construction industry and other industries. In order to increase the rolling output, the relevant technology usually sets a slitting roller in the finishing rolling unit, and the intermediate billet of the bar is longitudinally cut into 1 to 3 parts. After being guided by a guide, 2 to 4 dividing lines are formed, and each of them enters the rolling mill again along the aqueduct for rolling to form 2 to 4 bars.

[0003] However, the methods provided by related technologies are difficult to ensure the surface quality of steel and also difficult to improve the strength and toughness of steel. Summary of the Invention

[0004] The object of the present invention is to provide a method for preparing HRB400E earthquake-resistant steel bars by high-speed single-line rolling, which can improve the surface quality of the steel and improve the strength and toughness of the steel.

[0005] The present invention is achieved in that:

[0006] The present invention provides a preparation method of high-speed single-line rolled HRB400E earthquake-resistant steel bars. The components of the high-speed single-line rolled HRB400E earthquake-resistant steel bars, calculated by mass percentage, include: C: 0.22-0.25wt%, Si: 0.35-0.5wt%, Mn: 1.15-1.35wt%, P≤0.038wt%, S≤0.038wt%, Ti: 0.006%-0.012wt%, N≤0.012wt%, O≤30ppm, and the balance is Fe and unavoidable impurities;

[0007] The method for preparing HRB400E earthquake-resistant steel bars produced by high-speed single-line rolling includes:

[0008] Converter smelting, steel tapping, argon blowing, titanium iron addition, continuous casting, heating, rough rolling, intermediate rolling, pre-finishing rolling, temperature control before finishing rolling, finishing rolling 1, temperature control between finishing rolling, finishing rolling 2, temperature control after rolling, cooling bed; among them,

[0009] The temperature control step before finishing rolling includes: a first temperature control before finishing rolling and a second temperature control before finishing rolling, wherein the cooling rate of the first temperature control before finishing rolling is 50 < (dT / dt) ≤ 100°C / s, and the cooling rate of the second temperature control before finishing rolling is 25 ≤ (dT / dt) ≤ 50°C / s;

[0010] In the first finishing rolling step, the temperature of the rolled piece is controlled to be 810-830°C;

[0011] The step of temperature control between finishing rolling mills includes: first temperature control between finishing rolling mills, second temperature control between finishing rolling mills, and third temperature control between finishing rolling mills, wherein the cooling rate of the first temperature control between finishing rolling mills is 25<(dT / dt)≤50℃ / s, the cooling rate of the second temperature control between finishing rolling mills is 15<(dT / dt)≤25℃ / s, and the cooling rate of the third temperature control between finishing rolling mills is 10≤(dT / dt)≤15℃ / s;

[0012] In the second finishing rolling step, the temperature of the rolled piece is controlled to be 800-820°C;

[0013] The temperature control step after rolling includes: first cooling after rolling and second cooling after rolling, the rate of the first cooling after rolling is 15<(dT / dt)≤25℃ / s, and the rate of the second cooling after rolling is 10≤(dT / dt)≤15℃ / s.

[0014] In an optional embodiment, before the second cooling after rolling, a first temperature recovery is further included, and the rate of the first temperature recovery is 20<temperature recovery rate≤25°C / s.

[0015] In an optional embodiment, before going onto the cooling bed, a second temperature recovery is further included, and the rate of the second temperature recovery is 15≤temperature recovery rate≤20°C / s.

[0016] In an optional embodiment, the temperature of the upper cooling bed is controlled to be 790-810°C.

[0017] In an optional embodiment, the first temperature control before finish rolling is performed to make the temperature of the rolled piece ≤ 930°C.

[0018] In an optional embodiment, the distance between the finishing mill group of finishing rolling mill 1 and the finishing mill group of finishing rolling mill 2 is greater than 85 m.

[0019] In an optional embodiment, the matrix structure of the high-speed single-line rolled HRB400E earthquake-resistant steel bar is ferrite + pearlite, wherein ferrite accounts for 62% and pearlite accounts for 38%.

[0020] In an optional embodiment, the yield strength R of the high-speed single-line rolled HRB400E seismic steel bar is eL ≥430MPa, tensile strength R m ≥600MPa, elongation A≥26.0%, total elongation at maximum force A gt ≥15.0%, R 0 m / R 0 eL ≥1.35, R 0 eL / R eL ≤1.18.

[0021] In an optional embodiment, the grain size of the high-speed single-line rolled HRB400E earthquake-resistant steel bars is above grade 9.0.

[0022] In an optional embodiment, in the method for preparing HRB400E earthquake-resistant steel bars by high-speed single-line rolling, the single-line rolling speed is up to 45 m / s.

[0023] The present invention includes the following beneficial effects:

[0024] The method for preparing HRB400E earthquake-resistant steel bars by high-speed single-line rolling of the present invention designs the temperature control steps before finishing rolling, the temperature control steps during finishing rolling, and the temperature control steps after rolling as multi-stage temperature control, and intersperses finishing rolling one and finishing rolling two in the multi-stage temperature control steps to realize multi-stage temperature control and rolling technology, and can combine the multi-stage temperature control and rolling technology with Ti microalloying components. Among them, the deformation rolling of the rolled material in the high temperature area can inhibit the growth of austenite and obtain a relatively uniform austenite structure; the precipitation of trace alloying elements in austenite plays an important controlling role in the final microstructure. During the rolling deformation process, the Ti trace alloying element begins to precipitate after low-temperature finish rolling. Fine precipitates such as TiC effectively delay the recovery and recrystallization of the deformed austenite, thereby helping to retain the accumulated strain and deformation structure of the austenite grains. At the same time, it can promote the ferrite to have a higher nucleation rate in the subsequent α phase transformation process, which is beneficial to the refinement of the final steel structure and the improvement of product performance. It can also achieve the partial replacement of the Mn element strengthening effect, so as to avoid the problem of cost increase caused by the need to increase the Mn element to improve the quality of the steel.

[0025] Moreover, the multi-stage cooling of the rolled piece before and after rough rolling and finish rolling, that is, the temperature control step before finish rolling, the temperature control step during finish rolling, and the temperature control step after rolling, accelerates the nucleation rate of ferrite, thereby promoting grain refinement, reducing the finish rolling temperature range (810-830℃), and changing the multi-stage cooling rate from large to small, which helps to promote the increase of the volume fraction of acicular ferrite and the reduction of grain size; further controlling the final rolling of the rolled piece in the non-recrystallization zone at around 800℃ can activate the deformation-induced ferrite transformation (DIFT) mechanism and lead to the appearance of γ phase fiberization. It can be seen that in the multi-stage temperature control steps before and after finish rolling, appropriate control of the cooling rate, so that the multi-stage cooling rate gradually slows down and the temperature of the rolled piece gradually decreases, can effectively optimize the microstructure of the steel. Among them, during the multi-stage cooling process of the rolled piece, TiC interphase precipitation appears on the ferrite, the nano-scale interface phase density is the highest, and the interlayer spacing is the smallest. As the temperature of the rolled piece gradually decreases, the dislocation and grain refinement strengthening become gradually obvious, and the strengthening transitions from interface precipitation strengthening to dislocation and grain refinement strengthening, thereby improving the strength and toughness of the seismic-resistant steel bars and improving the surface quality. DETAILED DESCRIPTION

[0026] To make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer are used. Where the manufacturer of the reagents or instruments is not specified, all are conventional products that can be purchased commercially.

[0027] The composition of the high-speed single-line rolled HRB400E earthquake-resistant steel bar of the present invention includes, by mass percentage: C: 0.22-0.25 wt% (for example: 0.22%, 0.23%, 0.24%, 0.25%, etc.), Si: 0.35-0.5 wt% (for example: 0.35%, 0.38%, 0.42%, 0.45%, 0.48%, 0.50%, etc.), Mn: 1.15-1.35 wt% (for example: 1.15%, 1.20%, 1.25%, 1.30%, 1.35%, etc.), P≤0.038 wt% (for example: 0.038%, %, S≤0.038wt% (for example: 0.038%, 0.036%, 0.034%, 0.033%, etc.), Ti: 0.006%~0.012wt% (for example: 0.006%, 0.008%, 0.010%, 0.012%, etc.), N≤0.012wt% (for example: 0.012%, 0.011%, 0.010%, 0.0008%, etc.), O≤30ppm (for example: 30ppm, 29ppm, 28ppm, etc.), the balance is Fe and unavoidable impurities.

[0028] Among them, carbon is the most effective strengthening element and its cost is relatively low; melting 0.22-0.25wt% carbon (C) into the matrix can play a role of solid solution strengthening and at the same time form more pearlite in the steel, which is beneficial to improve the strength of the steel.

[0029] Silicon (Si) mainly improves the strength of steel bars in the form of solid solution strengthening. It is also a deoxidizing element in steel. Melting 0.35-0.5wt% of silicon into the matrix can not only improve the strength of the steel bars, but also facilitate deoxidation.

[0030] Manganese (Mn) is a weak carbide-forming element. During smelting, 1.15-1.35 wt% of Mn is melted into the matrix to deoxidize and eliminate the effects of sulfur. It can also lower the austenite transformation temperature and refine the ferrite grains, which is beneficial to improving the strength and toughness of the steel bars. It can also strengthen the ferrite through solid solution.

[0031] Titanium (Ti) is a strong carbide and nitride forming element. When Ti with a content of 0.006% to 0.012wt% is melted into the matrix, the fine and dispersed Ti(C,N) compounds precipitated by Ti at high temperature can inhibit the growth of high-temperature austenite grains, playing a strong role in refining grains. At the same time, recovery and recrystallization occur during high-temperature rolling of steel bars. The formed Ti(C,N) compounds can be strongly pinned to the grain boundaries, hindering grain growth and improving the strength and toughness of the steel bars.

[0032] Nitrogen (N) can participate in the microalloying of Ti as a residual element. N not exceeding 0.012 wt% can meet the aging performance requirements of steel bars, while also reducing the impact of free nitrogen in steel on the elongation and aging of steel.

[0033] In steel, oxygen (O) will preferentially combine with Ti and increase the consumption of Ti iron. When using trace Ti for smelting, the oxygen content in the steel should be controlled as low as possible.

[0034] The present invention's high-speed single-line rolling method for producing HRB400E earthquake-resistant steel bars includes converter smelting, steel tapping, argon blowing, titanium iron addition, continuous casting, heating, rough rolling, intermediate rolling, pre-finishing rolling, temperature control before finishing rolling, finishing rolling (1), temperature control during finishing rolling, finishing rolling (2), temperature control after rolling, and cooling. The single-line rolling speed can reach up to 45 m / s.

[0035] Optionally, for HRB400E seismic-resistant steel bars with specifications of Φ12 to 16 mm, a segmented control design of the rolling mill is adopted to separate the high-speed zone finishing mill group into two mill groups, namely finishing mill group 1 and finishing mill group 2. The distance between the finishing mill group of finishing mill group 1 and the finishing mill group of finishing mill group 2 is greater than 85 m.

[0036] The present invention is an application of HRB400E seismic-resistant steel bar based on critical deformation-induced ferrite transformation (DIFT) in a single-line high-speed bar production line; wherein, after rough rolling, intermediate rolling, and pre-finishing rolling, the rolled piece undergoes a temperature control step before finishing rolling, and the temperature entering the finishing rolling step is controlled at 810-830°C, that is, in the finishing rolling step, the temperature of the rolled piece is controlled at 810-830°C, for example: 810°C, 812°C, 815°C, 817°C, 820°C, 822°C, 825°C, 827°C, 830°C, etc.

[0037] Furthermore, the step of temperature control before finishing rolling includes: a first temperature control before finishing rolling and a second temperature control before finishing rolling, the cooling rate of the first temperature control before finishing rolling is 50<(dT / dt)≤100℃ / s (for example: 51℃ / s, 52℃ / s, 55℃ / s, 60℃ / s, 63℃ / s, 66℃ / s, 70℃ / s, 73℃ / s, 77℃ / s, 80℃ / s, 82℃ / s, 85℃ / s, 90℃ / s, 95℃ / s, 100℃ / s, etc.), so that the temperature of the rolled piece is ≤930℃ (for example: 930℃, 928℃, 925℃, 920℃, etc.). In this way, the temperature after pre-finishing rolling can be controlled. The austenite of the rolled material is completely recrystallized to obtain fine grains, which prevents the austenite grains from growing; the cooling rate of the second temperature control before finish rolling is 25≤(dT / dt)≤50℃ / s (for example: 25℃ / s, 26℃ / s, 30℃ / s, 32℃ / s, 35℃ / s, 37℃ / s, 40℃ / s, 43℃ / s, 46℃ / s, 50℃ / s, etc.), so that the temperature of the rolled piece reaches 810~830℃, which can control the partial recrystallization of austenite, prevent the growth of partially recrystallized grains at the austenite grain boundaries, and prevent the growth of austenite grains caused by excessively high temperature and the precipitation of secondary cementite caused by organizational transformation due to excessively low temperature.

[0038] The temperature control step before finishing rolling is to quickly cool the workpiece from the single austenite region to the two-phase region through strong cooling in the front section and weak cooling in the back section, control the workpiece to be rolled at a lower temperature in the two-phase region, and make full use of the effects of controlled rolling and cooling and the formation of carbonitrides by Ti microalloying elements to promote grain refinement, inhibit austenite recrystallization, and lay the foundation for subsequent cooling to obtain fine ferrite. That is, cooling the workpiece to the austenite non-recrystallization region is beneficial to the finishing rolling module mill to control the forming and improve the performance of the workpiece.

[0039] After the workpiece has been rolled in the first step of finishing rolling, it enters the step of temperature control in the finishing rolling room; the step of temperature control in the finishing rolling room includes: the first temperature control in the finishing rolling room, the second temperature control in the finishing rolling room and the third temperature control in the finishing rolling room; after the workpiece has been rolled in the first step of finishing rolling, deformation and temperature rise occur, and the temperature of the workpiece reaches ≥950℃. In order to control the workpiece to continue rolling at a lower temperature in the two-phase zone, the workpiece needs to be cooled. At the same time, since the workpiece has been fully deformed here, the diameter of the workpiece is small, and the surface cooling heat conduction rate is fast. In order to avoid excessive cooling rate causing too low temperature and prevent the workpiece from undergoing structural transformation and precipitation of secondary cementite, three-stage weak cooling is used to cool the workpiece.

[0040] Among them, the cooling rate of the temperature control during the first finishing rolling is 25<(dT / dt)≤50℃ / s (for example: 26℃ / s, 27℃ / s, 30℃ / s, 33℃ / s, 36℃ / s, 38℃ / s, 40℃ / s, 42℃ / s, 45℃ / s, 48℃ / s, 50℃ / s, etc.). In this way, the temperature of the rolled piece can be controlled to be about 50℃ above the Ar3 temperature point (specifically about 900℃). After the finished rolling step, the austenite undergoes repeated recrystallization and refinement, which promotes the complete recrystallization of the austenite. It is necessary to prevent the grain growth caused by excessive temperature; the cooling rate of the temperature control during the second finishing rolling is 15<(dT / dt)≤25℃ / s (for example: 16℃ / s, 17℃ / s, 19℃ / s, 21℃ / s, 23℃ / s, 25℃ / s, etc.). In this way, the temperature of the rolled piece can be controlled to be about 50℃ above the Ar3 temperature point (specifically about 900℃). After the rolled piece undergoes a finishing rolling step, the austenite undergoes repeated recrystallization and refinement, which promotes the complete recrystallization of the austenite. It is necessary to prevent the grain growth caused by excessive temperature. The temperature of the rolled piece is around the Ar3 temperature point (specifically around 850°C). Subcrystallization is formed in the austenite grains of the rolled piece after complete recrystallization. The temperature control during the second finishing rolling can promote the formation of fine ferrite grains in the two-phase region phase transformation process of the rolled piece, and at the same time prevent the grain growth caused by excessive temperature; the cooling rate of the temperature control during the third finishing rolling is 10≤(dT / dt)≤15°C / s (for example: 10°C / s, 11°C / s, 13°C / s, 15°C / s, etc.). In this way, the temperature of the rolled piece can be controlled to be around 30°C below the Ar3 temperature point (specifically around 800-820°C) to accelerate the nucleation rate of ferrite in the two-phase region of the rolled piece, thereby promoting grain refinement, and at the same time preventing the grain growth caused by excessive temperature and the precipitation of secondary cementite caused by excessive temperature transformation.

[0041] During the second finishing rolling step, the temperature of the rolled piece is controlled to be 800-820°C, for example, 800°C, 803°C, 806°C, 809°C, 811°C, 813°C, 815°C, 817°C, 820°C, etc. The three-stage weak cooling temperature control of the rolled piece during the finishing rolling process is more precise than the two-stage cooling temperature control before the first finishing rolling process. The narrow temperature range control during the finishing rolling process is beneficial to the refinement of the ferrite grains in the first finishing rolling process. In the second finishing rolling process, new equiaxed ferrite grains are more easily formed during the rolling deformation process in the two-phase region of the second finishing rolling process. These new ferrite grains are formed with the proeutectoid ferrite, thereby further achieving a fine grain strengthening effect. The temperature of the rolled piece is cooled to about 30°C below the ferrite-austenite critical transformation temperature, which is beneficial to the controlled rolling forming in the second finishing rolling process and improves the performance of the rolled piece.

[0042] After the finishing rolling step is completed, the rolled piece can be subjected to post-rolling temperature control; specifically, the post-rolling temperature control includes: the first post-rolling cooling, which is rapid cooling followed by warming, and the second post-rolling cooling, which is weak cooling followed by warming. After the finishing rolling step, the rolled piece undergoes deformation and temperature rise, and the rolled piece temperature is ≥900°C. In order to obtain fine and uniform austenite grains, reduce the precipitation of carbonitrides, retain the dislocations formed during the rolling process, increase the phase transformation undercooling, and provide favorable conditions for obtaining a good structure after the austenite transformation, the rolled piece needs to be cooled. However, since the rolled piece has been rolled, the rolled piece has undergone sufficient deformation, the rolled piece diameter is small, and the surface cooling heat conduction rate is fast. In order to avoid excessive cooling rate causing too low a temperature and prevent the rolled piece from undergoing bainite and martensite transformation, the present invention adopts the first post-rolling cooling (rapid cooling followed by warming) and the coordinated second post-rolling cooling (weak cooling followed by warming) to form a two-stage weak cooling process to cool the rolled piece.

[0043] Furthermore, the first cooling rate after rolling is 15<(dT / dt)≤25℃ / s (for example: 16℃ / s, 17℃ / s, 19℃ / s, 20℃ / s, 21℃ / s, 23℃ / s, 25℃ / s, etc.), and the temperature of the rolled piece is controlled so that the ferrite phase transformation starting point is about 30℃ below the Ar3 temperature point (specifically about 800℃), and a deformed ferrite with a high density of dislocations can be obtained to prepare for the nucleation of ferrite after the phase transformation; at the same time, since the cooling rate of the surface of the rolled piece is greater than the cooling rate of the core, the surface grains of the rolled piece are The temperature of the workpiece should be significantly lower than that of the core. Therefore, in order to prevent the occurrence of mixed crystal structure, it is necessary to ensure that the surface of the rolled piece is warmed up before the second cooling after rolling, and the temperature recovery rate is controlled at 20<(temperature recovery rate)≤25℃ / s (for example: 21℃ / s, 22℃ / s, 23℃ / s, 24℃ / s, 25℃ / s, etc.) to achieve the surface temperature of the rolled piece reaching around the Ar3 temperature point (specifically around 850℃). The heat from the core of the rolled piece is transferred to the outer surface, which can effectively reduce the core temperature of the rolled piece, reduce the grain size grade of the core, and prevent the surface temperature of the rolled piece from further decreasing to cause bainite and martensite transformation.

[0044] Furthermore, the rate of the second cooling after rolling is 10≤(dT / dt)≤15℃ / s (for example: 10℃ / s, 11℃ / s, 12℃ / s, 13℃ / s, 14℃ / s, 15℃ / s, etc.), and the temperature of the rolled piece at the end of the austenite transformation is controlled to be about 30℃ above AC1 (specifically about 780℃). By controlling the cooling of the rolled piece after final rolling in the austenite non-recrystallization zone, the strengthening mechanisms such as dislocations and substructures in the deformed austenite can be retained in the post-phase transformation structure to improve the strength and toughness of the steel; similarly, after the rolled piece passes through the cooling device, the surface grain size should be significantly smaller than the core grain size to prevent the occurrence of mixed To improve the crystal structure, it is necessary to ensure that the surface of the rolled piece recovers temperature before being put on the cooling bed, and the temperature recovery rate is controlled to be 15≤(temperature recovery rate)≤20℃ / s (for example: 15℃ / s, 16℃ / s, 17℃ / s, 18℃ / s, 19℃ / s, 20℃ / s, etc.), so as to achieve the surface temperature recovery of the rolled piece to about 30-50℃ below the Ar3 temperature point (roughly around 790-810℃), so as to transfer the heat from the core of the rolled piece to the outer surface, effectively reduce the core temperature of the rolled piece, and then reduce the grain size grade of the core, prevent the surface temperature of the rolled piece from further decreasing and causing bainite and martensite transformation, and increase the phase transformation supercooling for the subsequent cooling of the rolled piece on the cooling bed.

[0045] In the present invention, the temperature of the upper cooling bed is controlled at 790-810°C, for example: 790°C, 793°C, 796°C, 800°C, 801°C, 803°C, 805°C, 807°C, 810°C, etc. Specifically, in order to obtain smaller ferrite grains and pearlite with smaller interlamellar spacing, thereby improving the strength and toughness of the steel, and ensuring that the microstructure grain size of the rolled piece after cooling after rolling is consistent with the grain size during the rolling process, and solidifying the strengthening mechanisms such as dislocations and substructures in the deformed austenite during the rolling process, the temperature of the upper cooling bed is optimized to 790-810°C, which can be basically consistent with the temperature of the rolled piece when entering the first finishing rolling step and the temperature when entering the second finishing rolling step; it is worth noting that in order to prevent the occurrence of bainite and martensite transformation, while controlling the temperature of the upper cooling bed to be roughly the same as the temperature of the rolled piece entering the first finishing rolling step and the second finishing rolling step, the temperature of the upper cooling bed can be specifically controlled to be approximately 10°C lower than the temperature of the rolled piece entering the first finishing rolling step and the second finishing rolling step, so as to avoid the formation of coarse polygonal ferrite and pearlite due to excessively high temperature, thereby reducing the strength of the steel, and avoiding the insufficient precipitation of carbides or nitrides dissolved in the ferrite due to excessively low temperature, which cannot achieve the precipitation strengthening effect, and causes the occurrence of bainite and martensite transformation, thereby reducing the plasticity of the steel. Moreover, increasing the degree of supercooling during the transformation of the structure can increase the nucleation rate of the transformation from austenite to ferrite and refine the grains, while inhibiting the growth of ferrite grains after phase transformation, obtaining a fine ferrite + pearlite structure, and avoiding the formation of excessive iron oxide scale.

[0046] It should be noted that in related art, the composition of earthquake-resistant steel bars also includes microalloying elements such as Cr, Nb, and V. These microalloying elements will form precipitates such as carbides and nitrides during the rolling process, which will play a role in precipitation strengthening and fine grain strengthening, increasing the strength and toughness of the steel bars and improving the structural properties of the steel bars. However, Nb, V, and Cr are not only expensive but also have low production, which can easily lead to production stagnation due to lack of availability. Moreover, the extraction of these elements requires a large amount of acid and water, resulting in high energy consumption and serious pollution from waste acid, waste residue, and wastewater. In contrast, Ti has a relatively high and stable production and is relatively low in cost. Therefore, the present invention improves the comprehensive properties of earthquake-resistant steel bars, such as strength and toughness, by combining Ti microalloying technology with multi-stage temperature and rolling control technology without using microalloying elements such as Cr, Nb, and V, and further reducing alloying elements such as Si and Mn. At the same time, it can also reduce the production of Nb, V, and Cr, reduce energy consumption, reduce the discharge of waste acid, waste residue, and wastewater, and reduce the impact on the ecological environment.

[0047] The yield strength R of the high-speed single-line rolled HRB400E earthquake-resistant steel bar of the present invention is eL ≥430MPa, tensile strength R m ≥600MPa, elongation A≥26.0%, total elongation at maximum force A gt ≥15.0%, R 0 m / R 0 eL ≥1.35, R 0 eL / R eL ≤1.18.

[0048] Furthermore, the matrix structure of HRB400E seismic steel bars rolled on a high-speed single-line basis is ferrite + pearlite, of which ferrite accounts for 62% and pearlite accounts for 38%. The deformation of austenite causes recrystallization and non-recrystallization, and the precipitation of deformation-induced microalloying elements (Ti) at the grain boundaries inhibits the recrystallization of austenite, prevents the growth of austenite grains, increases the number of grain boundaries, and causes a large number of dislocations, which provide strong conditions for the nucleation of ferrite. Fine and evenly distributed ferrite pearlite is obtained, in which ferrite accounts for a larger proportion, which can ensure the ductility of the steel. The appropriate pearlite ratio can improve the strength of the steel and achieve a reasonable match of strong plasticity of the steel; the grain size is above level 9.0.

[0049] The present invention is described in further detail below with reference to the examples.

[0050] Example 1

[0051] The composition of HRB400E seismic-resistant steel bars rolled on a high-speed single wire includes, by mass percentage, C: 0.22wt%, Si: 0.5wt%, Mn: 1.35wt%, P: 0.038wt%, S: 0.038wt%, Ti: 0.012wt%, N: 0.012wt%, O: 30ppm, and the balance is Fe and unavoidable impurities.

[0052] The process includes:

[0053] Converter smelting, steel tapping, argon blowing, titanium iron addition, continuous casting, heating, rough rolling, intermediate rolling, pre-finishing rolling, temperature control before finishing rolling, finishing rolling 1, temperature control between finishing rolling, finishing rolling 2, temperature control after rolling, cooling bed; among them,

[0054] The temperature control steps before finishing rolling include: the first temperature control before finishing rolling and the second temperature control before finishing rolling. The cooling rate of the first temperature control before finishing rolling is 51°C / s, so that the temperature of the rolled piece is 930°C. The cooling rate of the second temperature control before finishing rolling is 25°C / s.

[0055] The temperature of the finishing rolling is 830℃.

[0056] The steps of temperature control between finishing rolling mills include: temperature control between finishing rolling mills for the first time, temperature control between finishing rolling mills for the second time, and temperature control between finishing rolling mills for the third time. The cooling rate of temperature control between finishing rolling mills is 26°C / s, the cooling rate of temperature control between finishing rolling mills for the second time is 16°C / s, and the cooling rate of temperature control between finishing rolling mills for the third time is 10°C / s.

[0057] The temperature of the second finishing rolling is 820°C.

[0058] The temperature control steps after rolling include: the first cooling after rolling, the first warming, the second cooling after rolling and the second warming. The first cooling rate after rolling is 16°C / s, the first warming rate is 21°C / s, the second cooling rate after rolling is 10°C / s, and the second warming rate is 15°C / s.

[0059] The temperature of the upper cooling bed is 810℃.

[0060] Example 2

[0061] The composition of HRB400E seismic-resistant steel bars rolled on a high-speed single wire includes, by mass percentage, C: 0.25wt%, Si: 0.35wt%, Mn: 1.15wt%, P: 0.035wt%, S: 0.036wt%, Ti: 0.006wt%, N: 0.010wt%, O: 28ppm, and the balance is Fe and unavoidable impurities.

[0062] The process includes:

[0063] Converter smelting, steel tapping, argon blowing, titanium iron addition, continuous casting, heating, rough rolling, intermediate rolling, pre-finishing rolling, temperature control before finishing rolling, finishing rolling 1, temperature control between finishing rolling, finishing rolling 2, temperature control after rolling, cooling bed; among them,

[0064] The temperature control steps before finishing rolling include: the first temperature control before finishing rolling and the second temperature control before finishing rolling. The cooling rate of the first temperature control before finishing rolling is 53°C / s, so that the temperature of the rolled piece is 928°C. The cooling rate of the second temperature control before finishing rolling is 26°C / s.

[0065] The temperature of the finishing rolling is 810℃.

[0066] The steps of temperature control between finishing rolling mills include: temperature control between finishing rolling mills for the first time, temperature control between finishing rolling mills for the second time, and temperature control between finishing rolling mills for the third time. The cooling rate of temperature control between finishing rolling mills is 27°C / s, the cooling rate of temperature control between finishing rolling mills for the second time is 18°C / s, and the cooling rate of temperature control between finishing rolling mills for the third time is 11°C / s.

[0067] The temperature of the second finishing rolling is 800°C.

[0068] The temperature control steps after rolling include: the first cooling after rolling, the first warming, the second cooling after rolling and the second warming. The first cooling rate after rolling is 18°C / s, the first warming rate is 22°C / s, the second cooling rate after rolling is 11°C / s, and the second warming rate is 16°C / s.

[0069] The temperature of the upper cooling bed is 790℃.

[0070] Example 3

[0071] The composition of HRB400E seismic-resistant steel bars rolled on a high-speed single wire includes, by mass percentage, C: 0.23wt%, Si: 0.4wt%, Mn: 1.25wt%, P: 0.033wt%, S: 0.037wt%, Ti: 0.010wt%, N: 0.008wt%, O: 30ppm, and the balance is Fe and unavoidable impurities.

[0072] The process includes:

[0073] Converter smelting, steel tapping, argon blowing, titanium iron addition, continuous casting, heating, rough rolling, intermediate rolling, pre-finishing rolling, temperature control before finishing rolling, finishing rolling 1, temperature control between finishing rolling, finishing rolling 2, temperature control after rolling, cooling bed; among them,

[0074] The temperature control steps before finishing rolling include: a first temperature control before finishing rolling and a second temperature control before finishing rolling. The cooling rate of the first temperature control before finishing rolling is 100°C / s, so that the temperature of the rolled piece is 920°C. The cooling rate of the second temperature control before finishing rolling is 50°C / s.

[0075] The temperature of the finishing rolling is 820℃.

[0076] The steps of temperature control between finishing rolling mills include: temperature control between finishing rolling mills for the first time, temperature control between finishing rolling mills for the second time and temperature control between finishing rolling mills for the third time. The cooling rate of temperature control between finishing rolling mills is 50°C / s, the cooling rate of temperature control between finishing rolling mills for the second time is 25°C / s, and the cooling rate of temperature control between finishing rolling mills for the third time is 15°C / s.

[0077] The temperature of the second finishing rolling is 810°C.

[0078] The temperature control steps after rolling include: the first cooling after rolling, the first warming, the second cooling after rolling and the second warming. The first cooling rate after rolling is 25°C / s, the first warming rate is 25°C / s, the second cooling rate after rolling is 15°C / s, and the second warming rate is 20°C / s.

[0079] The temperature of the upper cooling bed is 800℃.

[0080] Comparative Example 1

[0081] Comparative Example 1 is similar to Example 1, except that: in the temperature control step before finishing rolling, the temperature is lowered once at a cooling rate of 51°C / s, and the temperature before finishing rolling is set to 830°C; other process parameters refer to Example 1.

[0082] Comparative Example 2

[0083] Comparative Example 2 is similar to Example 1, except that: in the temperature control step before finishing rolling, the temperature is lowered once at a cooling rate of 25°C / s, and the temperature before finishing rolling is set to 830°C; other process parameters refer to Example 1.

[0084] Comparative Example 3

[0085] Comparative Example 3 is similar to Example 1, except that: in the temperature control step between finishing rolling, the temperature is lowered once at a cooling rate of 25°C / s, and the temperature before finishing rolling 2 is set to 820°C; other process parameters refer to Example 1.

[0086] Comparative Example 4

[0087] Comparative Example 4 is similar to Example 1, except that: in the temperature control step between finishing rolling, the temperature is lowered once at a cooling rate of 10°C / s, and the temperature before finishing rolling 2 is set to 820°C; other process parameters refer to Example 1.

[0088] Comparative Example 5

[0089] Comparative Example 5 is similar to Example 1, except that: in the temperature control step after rolling, the temperature is lowered once at a cooling rate of 15°C / s and then the temperature is placed on a cooling bed; other process parameters refer to Example 1.

[0090] Comparative Example 6

[0091] Comparative Example 6 is similar to Example 1, except that: in the temperature control step after rolling, the temperature is lowered once at a cooling rate of 10°C / s and then the temperature is placed on a cooling bed; other process parameters refer to Example 1.

[0092] Comparative Example 7

[0093] Comparative Example 7 is similar to Example 1, except that: in the temperature control step between finishing rolling, the first cooling is performed at a cooling rate of 25°C / s, and then the second cooling is performed at a cooling rate of 10°C / s, so that the temperature entering the second finishing rolling is 820°C; other process parameters refer to Example 1.

[0094] Comparative Example 8

[0095] Comparative Example 8 is similar to Example 1, except that: in the temperature control step before finishing rolling, the temperature is lowered once at a cooling rate of 51°C / s, and the temperature entering finishing rolling one is 830°C; in the temperature control step between finishing rolling, the temperature is lowered once at a cooling rate of 25°C / s, and the temperature entering finishing rolling two is 820°C; other process parameters refer to Example 1.

[0096] Comparative Example 9

[0097] Comparative Example 9 is similar to Example 1, except that: in the temperature control step before finishing rolling, the temperature is lowered once at a cooling rate of 51°C / s, and the temperature before finishing rolling is set to 830°C; in the temperature control step after rolling, the temperature is lowered once at a cooling rate of 15°C / s, and then the cooling bed is placed; other process parameters refer to Example 1.

[0098] Comparative Example 10

[0099] Comparative Example 10 is similar to Example 1, except that: in the temperature control step between finishing rolling, the temperature is lowered once at a cooling rate of 25°C / s, and then the temperature before finishing rolling 2 is 820°C; in the temperature control step after rolling, the temperature is lowered once at a cooling rate of 15°C / s, and then the cooling bed is placed; other process parameters refer to Example 1.

[0100] Comparative Example 11

[0101] Comparative Example 11 is similar to Example 1, except that: in the temperature control step before finishing rolling, the temperature is lowered once at a cooling rate of 51°C / s, and the temperature entering finishing rolling one is set to 830°C; in the temperature control step between finishing rolling, the temperature is lowered once at a cooling rate of 25°C / s, and the temperature entering finishing rolling two is set to 820°C; in the temperature control step after rolling, the temperature is lowered once at a cooling rate of 15°C / s, and then the cooling bed is placed; other processes refer to Example 1.

[0102] Comparative Example 12

[0103] Comparative Example 12 is similar to Example 1, except that:

[0104] In the step of temperature control before finishing rolling, the cooling rate of the first temperature control before finishing rolling is 45°C / s, and the cooling rate of the second temperature control before finishing rolling is 20°C / s.

[0105] In the step of temperature control between finishing rolling, the cooling rate of the first temperature control between finishing rolling is 20°C / s, the cooling rate of the second temperature control between finishing rolling is 10°C / s, and the cooling rate of the third temperature control between finishing rolling is 5°C / s.

[0106] In the temperature control step after rolling, the first cooling rate after rolling is 10℃ / s, the first warming rate is 15℃ / s, the second cooling rate after rolling is 5℃ / s, and the second warming rate is 10℃ / s.

[0107] Other processes refer to Example 1.

[0108] The strength and toughness of the steel materials of each embodiment and each comparative example, as well as the surface crack conditions, were tested, and the results are shown in the following table.

[0109]

[0110] The preparation method of the present invention performs multi-stage temperature control before, during and after finishing rolling, thereby improving the problem of difficult uniform and accurate temperature control of high-speed rolled pieces during multi-pass deformation, improving the precise control of the rolled piece temperature, refining the grains, ensuring the strength and toughness of the steel, and improving the surface quality.

[0111] In summary, the method for preparing HRB400E earthquake-resistant steel bars by high-speed single-line rolling of the present invention effectively improves the contradiction between the microstructure and properties of low-Mn and low-Si steel bars under Ti microalloying conditions through three-stage temperature control before, during, and after finishing rolling, refines the structure and grains, and improves the microstructure and properties of the steel.

[0112] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for preparing HRB400E earthquake-resistant steel bars by high-speed single-line rolling, characterized in that: The composition of the high-speed single-line rolled HRB400E earthquake-resistant steel bar includes, by mass percentage, C: 0.22-0.25 wt%, Si: 0.35-0.5 wt%, Mn: 1.15-1.35 wt%, P≤0.038 wt%, S≤0.038 wt%, Ti: 0.006%-0.012 wt%, N≤0.012 wt%, O≤30 ppm, and the balance is Fe and unavoidable impurities; The method for preparing the high-speed single-line rolled HRB400E earthquake-resistant steel bar comprises: Converter smelting, steel tapping, argon blowing, titanium iron addition, continuous casting, heating, rough rolling, intermediate rolling, pre-finishing rolling, temperature control before finishing rolling, finishing rolling 1, temperature control between finishing rolling, finishing rolling 2, temperature control after rolling, cooling bed; among them, The temperature control step before finishing rolling includes: a first temperature control before finishing rolling and a second temperature control before finishing rolling, wherein the cooling rate of the first temperature control before finishing rolling is 50<(dT / dt)≤100°C / s, and the cooling rate of the second temperature control before finishing rolling is 25≤(dT / dt)≤50°C / s; In the first finishing rolling step, the temperature of the rolled piece is controlled to be 810-830° C. The temperature control step between the finishing rolling mills includes: a first temperature control between the finishing rolling mills, a second temperature control between the finishing rolling mills, and a third temperature control between the finishing rolling mills. The cooling rate of the first temperature control between the finishing rolling mills is 25 < (dT / dt) ≤ 50 ° C / s, the cooling rate of the second temperature control between the finishing rolling mills is 15 < (dT / dt) ≤ 25 ° C / s, and the cooling rate of the third temperature control between the finishing rolling mills is 10 ≤ (dT / dt) ≤ 15 ° C / s. In the second finishing rolling step, the temperature of the rolled piece is controlled to be 800-820°C; The temperature control step after rolling includes: a first cooling after rolling and a second cooling after rolling, wherein the first cooling rate after rolling is 15 < (dT / dt) ≤ 25 ° C / s, and the second cooling rate after rolling is 10 ≤ (dT / dt) ≤ 15 ° C / s; Before the second cooling after rolling, it also includes a first temperature return, the first temperature return rate 20 < temperature return rate ≤ 25 ℃ / s; Before the upper cooling bed, a second temperature recovery is also included, and the rate of the second temperature recovery is 15≤temperature recovery rate≤20°C / s.

2. The method for preparing HRB400E earthquake-resistant steel bars by high-speed single-line rolling according to claim 1, characterized in that: The temperature of the upper cooling bed is controlled to be 790-810°C.

3. The method for preparing HRB400E earthquake-resistant steel bars by high-speed single-line rolling according to claim 1, characterized in that: The first temperature control before the finish rolling is to make the temperature of the rolled piece ≤ 930°C.

4. The method for preparing HRB400E earthquake-resistant steel bars by high-speed single-line rolling according to claim 1, characterized in that: The distance between the finishing mill group of the finishing rolling mill 1 and the finishing mill group of the finishing rolling mill 2 is greater than 85m.

5. The method for preparing HRB400E earthquake-resistant steel bars by high-speed single-line rolling according to claim 1, characterized in that: The matrix structure of the high-speed single-line rolled HRB400E earthquake-resistant steel bar is ferrite + pearlite, wherein ferrite accounts for 62% and pearlite accounts for 38%.

6. The method for preparing HRB400E earthquake-resistant steel bars by high-speed single-line rolling according to claim 1, characterized in that: The yield strength R of the high-speed single-line rolled HRB400E earthquake-resistant steel bar eL ≥430MPa, tensile strength R m ≥600MPa, elongation A≥26.0%, total elongation at maximum force A gt ≥15.0%, R 0 m / R 0 eL ≥1.35, R 0 eL / R eL ≤1.

18.

7. The method for preparing HRB400E earthquake-resistant steel bars by high-speed single-line rolling according to claim 1, characterized in that: The grain size of the high-speed single-line rolled HRB400E earthquake-resistant steel bar is above grade 9.

0.

8. The method for preparing HRB400E earthquake-resistant steel bars by high-speed single-line rolling according to claim 1, characterized in that: In the method for preparing HRB400E earthquake-resistant steel bars by high-speed single-line rolling, the single-line rolling speed is up to 45 m / s.

Images